Patent Application
20090110738
Small particles, including microspheres and nanospheres, have many medical uses in diagnostic and therapeutic procedures. In selected clinical applications, it may be advantageous to provide such microspheres and nanospheres to selectively augment defects in tissues for improved cosmesis and/or functional restoration.
Most prior art particles used in medical applications are characterized by numerous disadvantages including irritation of the tissues with which they come in contact and initiation of adverse immune reactions. Additionally, many of the materials used to prepare the prior art particles may degrade relatively rapidly within the mammalian body, thereby detracting from their utility in certain procedures where long term presence of intact particles may be necessary. Moreover, the degradation of the prior art materials may release toxic or irritating compounds causing adverse reactions in the patients.
It is also a problem in the art for certain types of prior art particles that it is difficult to achieve desirable suspension properties when the particles are incorporated into a delivery suspension for injection into a site in the body to be treated. Many times, the particles settle out or tend to “float” in the solution such that they are not uniformly suspended for even delivery. Furthermore, particles may tend to aggregate within the delivery solution and/or adhere to some part of the delivery device, making it necessary to compensate for these adhesive/attractive forces.
In order to achieve a stable dispersion, it is known to add suitable dispersing agents that may include surfactants directed at breaking down attractive particle interaction. Depending on the nature of the particle interaction, the following materials may be used: cationic, anionic or nonionic surfactants such as Tween™ 20, Tween™ 40, Tween™ 80, polyethylene glycols, sodium dodecyl sulfate, various naturally occurring proteins such as serum albumin, or any other macromolecular surfactants in the delivery formulation. Furthermore thickening agents can be used help prevent particles from settling by sedimentation and to increase solution viscosity, for example, polyvinyl alcohols, polyvinyl pyrrolidones, sugars or dextrins. Density additives may also be used to achieve buoyancy.
It can also be difficult to visualize microparticles in solution to determine their degree of suspension when using clear, transparent polymeric acrylate hydrogel beads in aqueous suspension. Attempts to use the inert precipitate, barium sulfate, in particle form is known as an additive for bone cement, for silicones for rendering items visible during X-ray examination and for providing radiopacity to polymeric acrylate particles. See Jayakrishnan et al., Bull. Mat. Sci., Vol. 12, No. 1, pp. 17-25 (1989). The barium sulfate also is known for improving fluidization, and is often used as an inorganic filler to impart anti-stick behavior to moist, aggregated particles. Other prior art attempts to increase visualization of microparticles include use of gold, for example, Embosphere Gold™ provides a magenta color to acrylate microparticles using small amounts of gold.
In certain medical applications, it may further be of value to provide microparticles such as microspheres in one or more sizes. Furthermore, it may also be of value to a user to provide each of such sizes of microspheres incorporated with color-coded associated dyes to indicate the microsphere size to the user. In yet other applications of use, it may further be of value to provide sized and color-coded microspheres to a user in similarly color-coded syringes or other containers for transport and delivery to further aid a user in identifying the size of microspheres being used.
There thus exists in the art a need for small particles that can be formed to have a preferential generally spherical configuration for certain applications such as various therapeutic and diagnostic procedures which are not degraded by the natural systems of the mammalian system, are biocompatible, are easy to visualize in suspension while in use and/or demonstrate acceptable physical and suspension properties.
At the same time, in other medical applications, the need exists for small particles that can be formed to have a preferred generally spherical configuration for certain applications such as various therapeutic and diagnostic procedures. In certain applications, the particles of the present invention may be provided in a bioabsorbable form which may be degraded by the natural systems of the mammalian system. Particles of the present invention are biocompatible, easy to visualize in suspension while in use, and demonstrate acceptable physical and suspension properties.
The invention includes a particle for use in a therapeutic and/or diagnostic procedure. The particle comprises poly[bis(trifluoroethoxy)phosphazene] and/or a derivative thereof.
The present invention further includes particles comprising poly[bis(trifluoroethoxy)phosphazene and/or a derivative thereof provided as microspheres provided in one or more specified sizes.
The present invention further includes particles comprising poly[bis(trifluoroethoxy)phosphazene and/or a derivative thereof provided as sized microspheres and further comprising a color-coded dye incorporated into or attached to the exterior of the microspheres to visually aid a user in identifying the size of microspheres in use.
Microspheres of the present invention may further be provided as sized microspheres further comprising a color-coded dye incorporated into or attached to the exterior of the microspheres and contained or delivered in a similarly color-coded syringe or other transport or delivery container to further visually aid a user in providing a visual confirmation of the specific size of microspheres in use.
Microspheres of the present invention may further be provided as sized microspheres further comprising a colored dye incorporated into or attached to the exterior of the microspheres and contained or delivered in a similarly color-coded syringe or other transport or delivery container to functionally serve to impart a desired color to mammalian tissues in use.
Further described herein is a method of delivering an active agent to a localized area within a body of a mammal comprising contacting the localized area with at least one of a particle comprising poly[bis(trifluoroethoxy)phosphazene] and/or a derivative thereof and an active agent, such that an effective amount of the active agent is exposed to the localized area.
The invention also includes a method of delivering an active agent to a localized area within the body of a mammal comprising contacting the localized area with at least one of a particle comprising poly[bis(trifluoroethoxy)phosphazene] and/or a derivative thereof and an active agent, such that an effective amount of the active agent is exposed to the localized area, wherein the particle comprises an agent to increase density.
Further, a method for minimizing agglomeration of particles formed from acrylic-based polymers is described in which the method comprises providing barium sulfate to the core and/or surface of the particles.
The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments that are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
In the drawings:
Described herein are particles that may be manufactured using poly[bis(trifluoroethoxy)phosphazene] and/or derivatives thereof, as well as methods of preparing such particles. Additionally, described herein are therapeutic and/or diagnostic methods and procedures which use the particles as described herein, including methods of delivery of an active agent using the particle (either orally or locally).
Also included are sustained release drug delivery formulations including the particles for localized delivery of an active agent to the integument and/or systemic delivery of an active agent as well as a sustained release drug delivery formulation that can be injected for localized delivery of an active agent.
All of the methods, compositions and formulations of the invention utilize at least one particle as described herein. “Particle” and “particles” as used herein mean a substantially spherical or ellipsoid article(s), hollow or solid, that may have any diameter suitable for use in the specific methods and applications described below, including a microsphere(s) and a nanosphere(s), beads and other bodies of a similar nature known in the art.
The preferred particles of the invention according to one embodiment described herein are composed, in whole or in part, the specific polyphosphazene polymer known as poly[bis(trifluoroethoxy)phosphazene] or a derivative of poly[bis(trifluoroethoxy)phosphazene]. Use of this specific polymer provides particles that are at least in part inorganic in that they include an inorganic polymer backbone and which are also biocompatible in that when introduced into a mammal (including humans and animals), they do not significantly induce a response of the specific or non-specific immune systems. The scope of the invention also includes the use(s) of such particles as controlled drug delivery vehicles or tracer particles for targeted tissues and other organs.
The particles are useful in a variety of therapeutic and/or diagnostic procedures in part because they can be prepared in a variety of sizes and colors for various purposes. Additionally, owing to the biocompatible nature of the polymer, the particles facilitate avoidance or elimination of immunogenic reactions generally encountered when foreign bodies are introduced into a mammalian body, such as “implant rejection” or “allergic shock,” and other adverse reactions of the immune system. Moreover, it has been found that the particles of the invention may be provided in a form to exhibit reduced biodegradation in vivo, thereby increasing the long-term stability of the particle in the biological environment. Moreover, in those situations where some degradation is undergone by the polymer in the particle, the products released from the degradation include only non-toxic concentrations of phosphorous, ammonia, and trifluoroethanol, which, advantageously, is known to promote anti-inflammatory responses when in contact with mammalian tissue.
Reduction and/or elimination of immunogenic reactions is particularly important in cosmetic and restorative surgical applications, where scarring and tissue edema are particularly undesirable, especially in thin skin or other tissues where secondary tissue reactions may distort or defeat the purpose of an augmentation implant or injection.
Each of the particles in the invention is formed at least in part of the polymer, poly[bis(2,2,2-trifluoroethoxy)phosphazene] or a derivative thereof (referred to further herein as “poly[bis(trifluoroethoxy)phosphazene]”. As described herein, the polymer poly[bis(2,2,2-trifluoroethoxy)phosphazene] or derivatives thereof have chemical and biological qualities that distinguish this polymer from other know polymers in general, and from other know polyphosphazenes in particular. In one aspect of this invention, the polyphosphazene is poly[bis(2,2,2-trifluoroethoxy)phosphazene] or derivatives thereof, such as other alkoxide, halogenated alkoxide, or fluorinated alkoxide substituted analogs thereof. The preferred poly[bis(trifluoroethoxy)phosphazene] polymer is made up of repeating monomers represented by the formula (I) show below:
wherein R1 to R6 are all trifluoroethoxy (OCH2CF3) groups, and wherein n may vary from at least about 40 to about 100,000, as disclosed herein. Alternatively, one may use derivatives of this polymer in the present invention. The term “derivatives” is meant to refer to polymers made up of monomers having the structure of formula I but where one or more of the R1 to R6 functional group(s) is replaced by a different functional group(s), such as an unsubstituted alkoxide, a halogenated alkoxide, a fluorinated alkoxide, or any combination thereof, or where one or more of the R1 to R6 is replaced by any of the other functional group(s) disclosed herein, but where the biological inertness of the polymer is not substantially altered.
In one aspect of the polyphosphazene of formula (I) illustrated above, for example, at least one of the substituents R1 to R6 can be an unsubstituted alkoxy substituent, such as methoxy (OCH3), ethoxy (OCH2CH3) or n-propoxy (OCH2CH2CH3). In another aspect, for example, at least one of the substituents R1 to R6 is an alkoxy group substituted with at least one fluorine atom. Examples of useful fluorine-substituted alkoxy groups R1 to R6 include, but are not limited to OCF3, OCH2CF3, OCH2CH2CF3, OCH2CF2CF3, OCH(CF3)2, OCCH3(CF3)2, OCH2CF2CF2CF3, OCH2(CF2)3CF3, OCH2(CF2)4CF3, OCH2(CF2)5CF3, OCH2(CF2)6CF3, OCH2(CF2)7CF3, OCH2CF2CHF2, OCH2CF2CF2CHF2, OCH2(CF2)3CHF2, OCH2(CF2)4CHF2, OCH2(CF2)5CHF2, OCH2(CF2)6CHF2, OCH2(CF2)7CHF2, and the like. Thus, while trifluoroethoxy (OCH2CF3) groups are preferred, these further exemplary functional groups also may be used alone, in combination with trifluoroethoxy, or in combination with each other. In one aspect, examples of especially useful fluorinated alkoxide functional groups that may be used include, but are not limited to, 2,2,3,3,3-pentafluoropropyloxy (OCH2CF2CF3), 2,2,2,2′,2′,2′-hexafluoroisopropyloxy (OCH(CF3)2), 2,2,3,3,4,4,4-heptafluorobutyloxy (OCH2CF2CF2CF3), 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyloxy (OCH2(CF2)7CF3), 2,2,3,3,-tetrafluoropropyloxy (OCH2CF2CHF2), 2,2,3,3,4,4-hexafluorobutyloxy (OCH2CF2CF2CHF2), 3,3,4,4,5,5,6,6,7,7,8,8-dodecafluorooctyloxy (OCH2(CF2)7CHF2) and the like, including combinations thereof.
Further, in some embodiments, 1% or less of the R1 to R6 groups may be alkenoxy groups, a feature that may assist in crosslinking to provide a more elastomeric phosphazene polymer. In this aspect, alkenoxy groups include, but are not limited to, OCH2CH═CH2, OCH2CH2CH═CH2, allylphenoxy groups, and the like, including combinations thereof. Also in formula (I) illustrated herein, the residues R1 to R6 are each independently variable and therefore can be the same or different.
By indicating that n can be as large as ∞ in formula I, it is intended to specify values of n that encompass polyphosphazene polymers that can have an average molecular weight of up to about 75 million Daltons. For example, in one aspect, n can vary from at least about 40 to about 100,000. In another aspect, by indicating that n can be as large as ∞ in formula I, it is intended to specify values of n from about 4,000 to about 50,000, more preferably, n is about 7,000 to about 40,000 and most preferably n is about 13,000 to about 30,000.
In another aspect of this invention, the polymer used to prepare the polymers disclosed herein has a molecular weight based on the above formula, which can be a molecular weight of at least about 70,000 g/mol, more preferably at least about 1,000,000 g/mol, and still more preferably a molecular weight of at least about 3×106 g/mol to about 20×106 g/mol. Most preferred are polymers having molecular weights of at least about 10,000,000 g/mol.
In a further aspect of the polyphosphazene formula (I) illustrated herein, n is 2 to ∞, and R1 to R6 are groups which are each selected independently from alkyl, aminoalkyl, haloalkyl, thioalkyl, thioaryl, alkoxy, haloalkoxy, aryloxy, haloaryloxy, alkylthiolate, arylthiolate, alkylsulphonyl, alkylamino, dialkylamino, heterocycloalkyl comprising one or more heteroatoms selected from nitrogen, oxygen, sulfur, phosphorus, or a combination thereof, or heteroaryl comprising one or more heteroatoms selected from nitrogen, oxygen, sulfur, phosphorus, or a combination thereof. In this aspect of formula (I), the pendant side groups or moieties (also termed “residues”) R1 to R6 are each independently variable and therefore can be the same or different. Further, R1 to R6 can be substituted or unsubstituted. The alkyl groups or moieties within the alkoxy, alkylsulphonyl, dialkylamino, and other alkyl-containing groups can be, for example, straight or branched chain alkyl groups having from 1 to 20 carbon atoms, typically from 1 to 12 carbon atoms, it being possible for the alkyl groups to be further substituted, for example, by at least one halogen atom, such as a fluorine atom or other functional group such as those noted for the R1 to R6 groups above. By specifying alkyl groups such as propyl or butyl, it is intended to encompass any isomer of the particular alkyl group.
In one aspect, examples of alkoxy groups include, but are not limited to, methoxy, ethoxy, propoxy, and butoxy groups, and the like, which can also be further substituted. For example the alkoxy group can be substituted by at least one fluorine atom, with 2,2,2-trifluoroethoxy constituting a useful alkoxy group. In another aspect, one or more of the alkoxy groups contains at least one fluorine atom. Further, the alkoxy group can contain at least two fluorine atoms or the alkoxy group can contain three fluorine atoms. For example, the polyphosphazene that is combined with the silicone can be poly[bis(2,2,2-trifluoroethoxy)phosphazene]. Alkoxy groups of the polymer can also be combinations of the aforementioned embodiments wherein one or more fluorine atoms are present on the polyphosphazene in combination with other groups or atoms.
Examples of alkylsulphonyl substituents include, but are not limited to, methylsulphonyl, ethylsulphonyl, propylsulphonyl, and butylsulphonyl groups. Examples of dialkylamino substituents include, but are not limited to, dimethyl-, diethyl-, dipropyl-, and dibutylamino groups. Again, by specifying alkyl groups such as propyl or butyl, it is intended to encompass any isomer of the particular alkyl group.
Exemplary aryloxy groups include, for example, compounds having one or more aromatic ring systems having at least one oxygen atom, non-oxygenated atom, and/or rings having alkoxy substituents, it being possible for the aryl group to be substituted for example by at least one alkyl or alkoxy substituent defined above. Examples of aryloxy groups include, but are not limited to, phenoxy and naphthoxy groups, and derivatives thereof including, for example, substituted phenoxy and naphthoxy groups.
The heterocycloalkyl group can be, for example, a ring system which contains from 3 to 10 atoms, at least one ring atom being a nitrogen, oxygen, sulfur, phosphorus, or any combination of these heteroatoms. The hetereocycloalkyl group can be substituted, for example, by at least one alkyl or alkoxy substituent as defined above. Examples of heterocycloalkyl groups include, but are not limited to, piperidinyl, piperazinyl, pyrrolidinyl, and morpholinyl groups, and substituted analogs thereof.
The heteroaryl group can be, for example, a compound having one or more aromatic ring systems, at least one ring atom being a nitrogen, an oxygen, a sulfur, a phosphorus, or any combination of these heteroatoms. The heteroaryl group can be substituted for example by at least one alkyl or alkoxy substituent defined above. Examples of heteroaryl groups include, but are not limited to, imidazolyl, thiophene, furane, oxazolyl, pyrrolyl, pyridinyl, pyridinolyl, isoquinolinyl, and quinolinyl groups, and derivatives thereof, such as substituted groups.
The diameter of a particle formed according to the invention will necessarily vary depending on the end application in which the particle is to be used. The diameter of such particles is preferably about 0.1 to about 5,000 μm, with a diameter of about 0.1 to about 1,000 μm being most preferred. Other preferred sizes include diameters of about 0.1 to about 10 μm, 100 to about 500 μm, about 1 to about 200 μm and greater than about 500 μm. In methods using the particle where more than one particle is preferred it is not necessary that all particles be of the same diameter or shape.
The particles may also include other compounds which function to enhance, alter or otherwise modify the behavior of the polymer or particle either during its preparation or in its therapeutic and/or diagnostic use. For example, active agents such as peptides, proteins, hormones, carbohydrates, polysaccharides, nucleic acids, lipids, vitamins, steroids and organic or inorganic drugs may be incorporated into the particle. Excipients such as dextran, other sugars, polyethylene glycol, glucose, and various salts, including, for example, chitosan glutamate, may be included in the particle.
Additionally, if desired, polymers other than the poly[bis(trifluoroethoxy)phosphazene] and/or its derivative may be included with in the particle. Examples of polymers may include poly(lactic acid), poly(lactic-co-glycolic acid), poly(caprolactone), polycarbonates, polyamides, polyanhydrides, polyamino acids, polyorthoesters, polyacetals, polycyanoacrylates, and polyurethanes. Other polymers include polyacrylates, ethylene-vinyl acetate co-polymers, acyl substituted cellulose acetates and derivatives thereof, degradable or non-degradable polyurethanes, polystyrenes, polyvinylchloride, polyvinyl fluoride, poly(vinyl imidazole), chlorosulphonated polyolefins, and polyethylene oxide. Examples of polyacrylates include, but are not limited to, acrylic acid, butyl acrylate, ethylhexyl acrylate, methyl acrylate, ethyl acrylate, acrylonitrile, methyl methacrylate, TMPTA (trimethylolpropane triacrylate), and the like. One may incorporate the selected compounds by any means known in the art, including diffusing, inserting or entrapping the additional compounds in the matrix of an already formed particle or by adding the additional compound to a polymer melt or to a polymer solvent in the preparation of the particle such as described herein.
The loaded or unloaded particle may be coated with an additional polymer layer or layers, including polymers such as those mentioned hereinabove. Further, poly bis(trifluoroethoxy)phosphazene or its derivatives may be used to form such a coating on a particle formed of other suitable polymers or copolymers known or to be developed in the art that are used to form particles as described herein. Preferably, when coating a particle such as a microparticle, poly[bis(trifluoroethoxy)phosphazene is applied as a coating on a microparticle(s) formed of an acrylic-based polymer as set forth in further detail below.
Coatings are beneficial, for example, if the particle(s) are to be used in a sustained release, orally administered, drug delivery formulation (enteric coating) or if the particles are to be loaded with a potentially toxic contrast agent (non-biodegradable coating).
The microspheres may be prepared by any means known in the art that is suitable for the preparation of particles containing poly[bis(trifluoroethoxy)phosphazene]. In a procedure according to an embodiment herein a “polymer solution” is prepared by mixing one or more polymer solvent(s) and the poly[bis(trifluoroethoxy)phosphazene and/or a derivative thereof until the polymer is dissolved.
Suitable solvents for use in the preparation of the polymer solution include any in which the polymer poly[bis(trifluoroethoxy)phosphazene and/or its derivatives are soluble. Exemplary solvents include, without limitation, ethyl-, propyl-, butyl-, pentyl-, octylacetate, acetone, methylethylketone, methylpropylketone, methylisobutylketone, tetrahydrofurane, cyclohexanone, dimethylacetamide, acetonitrile, dimethyl ether, hexafluorobenzene or combinations thereof.
The polymer solution contains the poly[bis(trifluoroethoxy)phosphazene and/or its derivative polymer in a concentration of about 1% by weight of polymer to 20% by weight of polymer, preferably about 5% to 10% by weight of polymer. Other polymers, as discussed above, may be present in the solution, or may be added to the vessel in the form of a second solution powder or other form, if one wishes to include such polymers in the final particle.
In carrying out the process, the polymer solution is next dispensed, preferably in the form of drops or an aerosol, into a vessel containing a non-solvent. By “non-solvent” it is meant any organic or inorganic solvents that do not substantially dissolve the poly[bis(trifluoroethoxy)phosphazene polymer and which have a melting point that is lower relative to the melting point of the solvent in which the polymer is dissolved (“polymer solvent”), so that the non-solvent thaws before the solvent thaws in the course of the incubation step. Preferably, this difference between the melting point of the non-solvent and the polymer solvent is about 10° C., more preferably about 15° C., and most preferably, greater than about 20° C. Under certain conditions it has been found that the structural integrity of the resultant particle may be enhanced if the difference of the melting points of the polymer solvent and of the non-solvent is greater than 15° C. However, it is sufficient that the non-solvent point is merely slightly lower than that of the polymer solvent.
The non-solvent/polymer solvent combination is incubated for approximately 1 to 5 days or until the polymer solvent has been completely removed from the particles. While not wishing to be bound by theory, it is hypothesized that during the incubation, the non-solvent functions to extract the polymer solvent from the microscopic polymer solution droplets from the particles such that the polymer is at least gelled. As the incubation period passes, the droplets will shrink and the solvent becomes further extracted, leading to a hardened outer polymeric shell containing a gelled polymer core, and finally, after completion of the incubation, a complete removal of the residual solvent. To ensure that the polymeric droplets retain a substantially spherical shape during the incubation period, they are maintained in a frozen or substantially gelled state during most if not all of the incubation period. Therefore, the non-solvent temperature may stay below the melting point of the solvent during the cryoextraction process.
As shown in
In one embodiment of a method of preparing a poly[bis(trifluoroethoxy)phosphazene-containing particle(s) according to the invention, such particles can be formed using any way known or to be developed in the art. Two exemplary preferred methods of accomplishing this include wherein (i) the non-solvent residing in the vessel in the method embodiment described above is cooled to close to its freezing point or to its freezing point prior to the addition of the polymer solution such that the polymer droplets freeze upon contact with the pre-cooled non-solvent; or (ii) the polymer droplets are frozen by contacting them with a liquefied gas such as nitrogen, which is placed over a bed of pre-frozen non-solvent (see,
By modifying this general process, one may prepare particles that are hollow or substantially hollow or porous. For example, if the removal of the solvent from the bead is carried out quickly, e.g., by applying a vacuum during the final stage of incubation, porous beads will result.
The particles of the invention can be prepared in any size desired, “Microspheres” may be obtained by nebulizing the polymer solution into a polymer aerosol using either pneumatic or ultrasonic nozzles, such as, for example a Sonotek 8700-60 ms or a Lechler US50 ultrasonic nozzle, each available from Sono[.tek] Corporation, Milton, N.Y., U.S.A. and Lechler GmbH, Metzingen, Germany. Larger particles may be obtained by dispensing the droplets into the non-solvent solution using a syringe or other drop-forming device. Moreover, as will be known to a person of skill in the art, the size of the particle may also be altered or modified by an increase or decrease of the initial concentration of the polymer in the polymer solution, as a higher concentration will lead to an increased sphere diameter.
In an alternative embodiment of the particles described herein, the particles can include a standard and/or a preferred core based on an acrylic polymer or copolymer with a shell of poly[bis(trifluoroethoxy)phosphazene. The acrylic polymer based polymers with poly[bis(trifluoroethoxy)phosphazene shell described herein provide a substantially spherical shape, mechanical flexibility and compressibility, improved specific gravity properties. The core polymers may be formed using any acceptable technique known in the art, such as that described in B. Thanoo et al., “Preparation of Hydrogel Beads from Crosslinked Poly(Methyl Methacrylate) Microspheres by Alkaline Hydrolysis,” J. Appl. P. Sci., Vol. 38, 1153-1161 (1990), incorporated herein by reference with respect thereto. Such acrylic-based polymers are preferably formed by polymerizing unhydrolyzed precursors, including, without limitation, methyl acrylate (MA), methyl methacrylate (MMA), ethylmethacrylate (EMA), hexamethyl (HMMA) or hydroxyethyl methacrylate (HEMA), and derivatives, variants or copolymers of such acrylic acid derivatives. Most preferred is MMA. The polymer should be present in the core in a hydrated or partially hydrated (hydrogel) form. Such polymers are preferably cross-linked in order to provide suitable hydrogel properties and structure, such as enhanced non-biodegradability, and to help retain the mechanical stability of the polymer structure by resisting dissolution by water.
Preferably, the core prepolymers are formed by dispersion polymerization that may be of the suspension or emulsion polymerization type. Emulsion polymerization results in substantially spherical particles of about 10 nm to about 10 microns. Suspension polymerization results in similar particles but of larger sizes of about 50 to about 1200 microns.
Suspension polymerization may be initiated with a thermal initiator, which may be solubilized in the aqueous or, more preferably, monomer phase. Suitable initiators for use in the monomer phase composition include benzoyl peroxide, lauroyl peroxide or other similar peroxide-based initiators known or to be developed in the art, with the most preferred initiator being lauroyl peroxide. The initiator is preferably present in an amount of about 0.1 to about 5 percent by weight based on the weight of the monomer, more preferably about 0.3 to about 1 percent by weight based on the weight of the monomer. As noted above, a cross-linking co-monomer is preferred for use in forming the hydrated polymer. Suitable cross-linking co-monomers for use with the acrylic-based principle monomer(s) used in preparing a polymerized particle core, include various glycol-based materials such as ethylene glycol dimethacrylate (EGDMA), diethylene glycol dimethacrylate (DEGDMA) or most preferably, triethylene glycol dimethacrylate (TEGMDA). A chain transfer agent may also be provided if desired. Any suitable MA polymerization chain transfer agent may be used. In the preferred embodiment herein, dodecylmercaptane may be used as a chain transfer agent in amounts acceptable for the particular polymerization reaction.
The aqueous phase composition preferably includes a surfactant/dispersant as well as a complexing agent, and an optional buffer is necessary. Surfactants/dispersants should be compatible with the monomers used herein, including Cyanamer® 370M, polyacrylic acid and partially hydrolyzed polyvinyl alcohol surfactants such as 4/88, 26/88, 40/88. A dispersant should be present in an amount of about 0.1 to about 5 percent by weight based on the amount of water in the dispersion, more preferably about 0.2 to about 1 percent by weight based on the amount of water in the dispersion. An optional buffer solution may be used if needed to maintain adequate pH. A preferred buffer solution includes sodium phosphates (Na2HPO4/NaH2PO4). A suitable complexing agent is ethylene diamine tetraacetic acid (EDTA), which may be added to the aqueous phase in a concentration of from about 10 to about 40 ppm EDTA, and more preferably about 20 to about 30 ppm. It is preferred that in the aqueous phase composition, the monomer to water ratio is about 1:4 to about 1:6.
The polymerization should take place at about ambient conditions, preferably from about 60° C. to about 80° C. with a time to gelation of about one to two hours. Stirring at rates of 100 to 500 rpm is preferred for particle formation, with lower rates applying to larger sized particles and higher rates applying to smaller sized particles.
Once PMMA particles, such as microparticles, are formed, they are preferably subjected to hydrolysis conditions typical of those in the art, including use of about 1-10 molar excess of potassium hydroxide per mol of PMMA. Such potassium hydroxide is provided in a concentration of about 1-15% potassium hydroxide in ethylene glycol. The solution is then heated preferably at temperatures of about 150-185° C. for several hours. Alternatively, to minimize reactant amounts and cost, it is preferred that lesser amounts of potassium hydroxide be used which are less than about 5 molar excess of potassium hydroxide per mole of PMMA, more preferably about 3 molar excess or less. For such hydrolytic reactions, a concentration of about 10-15% potassium hydroxide in ethylene glycol is also preferably used, and more preferably about 14% to about 15%. It will be understood by one skilled in the art, that heating conditions at higher temperatures may be used to decrease overall reaction times. Reaction times may be varied depending on the overall diameter of the resultant particles. For example, the following conditions are able to provide particles having about 35% compressibility and desired stability: for diameters of about 200-300 μm, the solution should be heated for about 7.5 to about 8.5 hours; for diameters of about 300-355 μm, about 9.5 to about 10.5 hours; for diameters of about 355-400 μm, about 11.5 to about 12.5 hours; and for about 400-455 μm, about 13.5 to about 14.5 hours, etc. The particle size can be adjusted using variations in the polymerization process, for example, by varying the stirring speed and the ratio of the monomer to the aqueous phase. Further, smaller sizes can be achieved by increasing surfactant/dispersant ratio.
Following hydrolysis, particles are separated from the reaction mixture and their pH may be adjusted to any range as suited for further processing steps or intended uses. The pH of the particle core may be adjusted in from about 1.0 to about 9.4, preferably about 7.4 if intended for a physiological application. Since size, swelling ratio and elasticity of the hydrogel core material are dependent on pH value, the lower pH values may be used to have beneficial effects during drying to prevent particle agglomeration and/or structural damage. Particles are preferably sieved into different size fractions according to intended use. Drying of particles preferably occurs using any standard drying process, including use of an oven at a temperature of about 40°-80° C. for several hours up to about a day.
To provide desired surface properties to the hydrophilic hydrogel particles, in order to provide adhesion for receiving a poly[bis(trifluoroethoxy)phosphazene coating, the surface of the hydrogel may be subjected to treatment with any suitable ionic or non-ionic surfactant, such as tetraalkylammonium salts, polyalcohols and similar materials. A more permanent change in adhesion properties is brought about by rendering the surface of the particles hydrophobic by reaction of its polymethacrylic acid groups with a suitable reactant. Suitable reactants include, but are not limited to, hydrophobic alcohols, amides and carboxylic acid derivatives, more preferably they include halogenated alcohols such as trifluoroethanol. Such surface treatment also prevents delamination of the coating from the core once the coating is applied. Preferred surface treatments may include, without limitation, an initial treatment with thionyl chloride followed by reaction with trifluoroethanol. Alternatively, the surface may be treated by suspending the particles in a mixture of sulfuric acid and a hydrophobic alcohol, such as trifluoroethanol. Such treatments are preferred if the particles are to be coated in that they minimize any delamination of a coating.
Alternatively, in some preferred embodiments of the present invention, the PMA core particles may be coated with a surface layer of and/or infused with barium sulfate. The barium sulfate is radiopaque and aids in visualization of the finished particles when in use. It also provides enhanced fluidization properties to the particles such that it reduces agglomeration especially during drying and allows for fluid bed coating of the PMA particles with an outer coating of poly[bis(trifluoroethoxy)phosphazene, thereby providing improved adhesion between a poly[bis(trifluoroethoxy)phosphazene outer core and a polymeric acrylate core particles. By allowing fluidization even when the core particles are swollen, barium sulfate also improves the overall coating and adhesion properties. By enabling the coating of the core particles even in a swollen state with poly[bis(trifluoroethoxy)phosphazene, barium sulfate also reduces the potential tendency of the poly[bis(trifluoroethoxy)phosphazene shells to crack or rupture in comparison with coating the particles in a dry state and then later exposing the particles to a suspension in which the core particles swell and exert force on the shell of poly[bis(trifluoroethoxy)phosphazene. A coating of barium sulfate on the core particles is preferably applied by adhesion of the barium sulfate in the form of an opaque coating on the hydrogel surface of the PMA beads. Barium sulfate can further assist in reducing electrostatic effects that limit particle size. By allowing for absorption of additional humidity, the barium sulfate tends to counteract the electrostatic effects.
Barium sulfate crystals adhering only loosely to the PMA particles may be covalently crosslinked or chemically grafted to the particle surface by spraycoating a sufficient amount of an aminosilane adhesion promoter onto the PMA particle. This will help to effectively reduce barium sulfate particulate matter in solution after hydration of the particles. Exemplary particles include 3-aminopropyl-trimethoxysilane and similar silane-based adhesion promoters.
A further alternative for improving visualization of and potential functionality of microparticles made as noted herein include the absorption of a chromophoric agent such as a non-water soluble organic dye or dye combination inside the hydrogel core particles. Chromophoric agents of the present invention may also include, but are not limited to, organic and inorganic dyes, pigments, colorants, fillers, and additives that may reactively bind to the hydrogel core of the microparticles, Exemplary dyes are preferably those FDA dyes approved for human use and which are known or to be developed for safe, non-toxic use in the body and which are capable of providing acceptable contrast. Organic dyes may include dyes such as D&C Violet no. 2 and others preferably approved for medical device uses, such as for contact lenses and resorbable sutures Whereas barium sulfate operates as an inorganic filler and finely dispersed pigment that makes the particles visible by light diffraction due to small crystal size, the dyes when impregnated in the particles absorb the complementary part of the visible color spectrum.
Chromophoric agents in various embodiments of the present invention may be provided in colors that approximate various shades of human flesh or other tissue tones for improved cosmesis.
Yet another alternative embodiment of the present invention relates to the use of custom color dyes for inclusion in the microspheres for patient-specific applications. These applications include, but are not limited to situations in which such microspheres are to be introduced and left within thin or superficial tissues, including the epidermis, dermis, and subcuticular tissues, where the presence of the microspheres might otherwise be visible to an observer. In such embodiments, a user would first provide a quantitative analysis of a desired tissue using a hand-held spectrophotometer or other device to records data from a desired area of a mammalian patient's skin or other organs is used in conjunction with a computerized color formulation system. Based on this color measurement, a color formula will be calculated by the computer, and appropriate dyes will be mixed to produce pigmented microspheres to match the color of the desired target skin or other organs.
Particles, including microparticles made in accordance with the foregoing process for forming a core hydrogel polymer are then coated with poly[bis(trifluoroethoxy)phosphazene and/or its derivatives. Any suitable coating process may be used, including solvent fluidized bed and/or spraying techniques. However, preferred results may be achieved using fluidized bed techniques in which the particles pass through an air stream and are coated through spraying while they spin within the air stream. The poly[bis(trifluoroethoxy)phosphazene or derivative polymer is provided in dilute solution for spraying to avoid clogging of the nozzle.
Exemplary solvents for use in such solutions include ethyl acetate, acetone, hexafluorbenzene, methyl ethyl ketone and similar solvents and mixtures and combinations thereof, most preferred is ethyl acetate alone or in combination with isoamyl acetate. Typical preferred concentrations include about 0.01 to about 0.3 weight percent poly[bis(trifluoroethoxy)phosphazene or its derivative in solution, more preferably about 0.02 to 0.2 weight percent poly[bis(trifluoroethoxy)phosphazene, and most preferably about 0.075 to about 0.2 weight percent. It should be understood based on this disclosure that the type of hydrogel core can be varied as can the technique for coating a particle, however it is preferred that a core which is useful in the treatment techniques and applications described herein is formed and subsequently coated with poly[bis(trifluoroethoxy)phosphazene and/or its derivatives as described herein.
One method for increasing the density of the particles is by use of heavy water or deuterium oxide (D2O). When heavy water is used to swell the particles, D2O displaces H2O, thereby increasing the weight of the particles for better dispersion and buoyancy levels. Typically this leads to the ability to add higher amounts of contrast agent of at least about 5% using such a technique. However some equilibrating effect can occur over time when the particles are contacted with an aqueous solution of contrasting agent. Thus, it is preferred that when using D2O for this purpose, either that suspension times are kept to a minimum or, more preferably, that the contrast agent be provided in a solution which also uses D2O.
Alternatively, particles of pH 1 can be neutralized with cesium hydroxide and/or the final neutralized particles can be equilibrated with cesium chloride. Such compounds diffuse cesium into the particles, such that either the cesium salt of polymethacrylic acid is formed or polymethacrylic acid is diffused and thereby enriched with cesium chloride.
The cesium increases the density of the particles, thereby increasing the ability to add higher amounts of contrast agent. Typical buoyancy levels can be adjusted using the cesium technique such that about 45 to about 50% contrast agent may be added to the delivery medium as is desired for embolization. Cesium salts are non-toxic and render the particles visible using fluoroscopy. Cesium's atomic weight of 132.9 g/mol is slightly higher than that of iodine providing beneficial effects including increase in overall density and enhancement of X-ray contrast visibility even without a contrast agent. For certain cancer treatments where a radioactive isotope of cesium is desired, such active agent can be used as an alternative cesium source rendering the particles buoyant in an embolic solution as well as able to be used as an active treatment source.
The above-noted techniques for improving density of particles, such as microparticles for embolization or other applications where density and/or buoyancy in solution are applicable properties may be applied in to the preferred particles described herein and/or may be applied for other similar particles. It should be understood that the disclosure is not limited to cesium and/or D2O treatment of the preferred particles herein and that such techniques may have broader implications in other particles such as other acrylic-based hydrogels and other polymeric particles.
As noted above, barium sulfate may be used between the core particles and the preferred poly[bis(trifluoroethoxy)phosphazene coating or introduced into the interior of the core particles using any technique known or to be developed in the art. Also, organic dyes may similarly be included in the particle core. These materials, particularly the barium sulfate, also contribute to an increase in density as well as providing radiopacity. In addition to a general density increase as provided by the above-noted D2O or cesium compounds, the barium sulfate allows this benefit even upon substantial and/or full hydration, allowing particles in suspension to remain isotonic. Thus, a barium sulfate powder coating can provide an inert precipitate having no effect on physiological osmolarity.
It should be understood, based on this disclosure, that the various buoyancy additives noted above can be used independently or in combination to provide the most beneficial effects for a given core particle and coating combination.
The invention also includes methods of delivering an active agent to a localized area within the body of a mammal. The method includes contacting the localized area with at least one of the particles of the invention as described above, such that an effective amount of the active agent is released locally to the area. Diseases or pathologies that may be treated by this method include any wherein the localized or topical application of the active agent achieves some benefit in contrast to the systemic absorption of the drug. Suitable active agents include NSAIDS, steroids, hormones, and nucleic acids,
If the particle formulated for delivery of an active agent to a localized area is about 1 to about 1,000 μm in diameter, the drug loaded microspheres can be applied to localized areas within the mammalian body using syringes and/or catheters as a delivery device, without causing inadvertent occlusions. For example, using a contrast agent, a catheter can be inserted into the groin artery and its movement monitored until it has reached the area where the localized administration is desired. A dispersion of the particles in a suitable injection medium can be injected through the catheter, guaranteeing only a specific area of the body will be subjected to treatment with drug loaded beads (particles). As will be understood to a person of skill in the art, injection mediums include any pharmaceutically acceptable mediums that are known or to be developed in the art, such as, e.g., saline, PBS or any other suitable physiological medium. In accordance with a further embodiment described herein, the invention may include an injectable dispersion including particles and a contrasting agent which particles are substantially dispersed in the solution. In a preferred embodiment, the particles are also detectible through fluoroscopy or other imaging modalities.
The polymeric particles of the invention may be used to prepare a sustained release formulation of an active agent for local administration. The formulation comprises a particle, as described above, loaded with an active agent. The polymeric particle utilized may be hollow, substantially hollow or solid. The particle can be loaded with the active agent either by dispersion or solvation of the active agent in the polymer solution prior to the production of micro-sized particles through spray droplets, pastillation of a polymer melt or carrying out of a cryoextraction process. Alternatively, an unloaded polymer particle can be prepared and subsequently immersed in solutions containing active agents. The particles are then incubated in these solutions for a sufficient amount of time for the active agent to diffuse into the matrix of the polymer. After drying the particles, the active agent will be retained in the polymer particle. If this loading mechanism is utilized, drug loading can be controlled by adjusting drug concentrations of the incubation medium and removing the particles from the incubation medium when an equilibrium condition has been attained.
In yet other preferred embodiments of the present invention, it may be desirable to amalgamate or otherwise fix the polymeric particles of the present invention once they have been delivered in satisfactory quantity and configuration to the desired targeted tissue. This is particularly desirable in cosmetic applications, where post-implantation migration of particles might distort or compromise the initial result of tissue augmentation. In such settings, tissue adhesives or sealants such as fibrin, cyanoacrylate tissue adhesives, fibrinogen sealants, or other tissue adhesives including any tissue-compatible matrix within which the active component is retained, suitable for topical or other application to the locus of treatment. It may therefore be a gel-like substance comprising pores within which the agent is held. It may be proteinaceous, and it may be biodegradable. Tissue adhesives or sealants of the present invention may also include crosslinkable macromolecular compounds of natural or synthetic origin such as such as oxidized starch or a polyaldehyde. An albumin-glutaraldehyde tissue adhesive may be employed in other exemplary embodiments of the present invention.
Tissue adhesives or sealants in other preferred embodiments of the present invention may also include use of biocompatible compounds or compositions, which are not used as an adhesive towards the tissue, but instead act as an adhesive for the microparticles of the present invention. Compounds or compositions able to achieve such microparticle to microparticle adhesion/interaction are generally compounds that will lead to a physical, chemical or ionic crosslinking of the microparticles' hydrogel core material, such as all polymeric compounds of synthetic or natural origin exhibiting a positive net charge such as polyethyleneimines, polyallylamines, polydiallyldimethylammonium chloride (DADMAC), poly[di(carboxylatophenoxy)phosphazene] (PCPP), poly-N-vinyl pyrrolidinone (PVP), and other suitable compounds which may be co-injected during and/or after the microparticle application in the present invention. Such crosslinking compounds or compositions may be provided in a gel type form in some embodiments of the present invention, interacting via net charge by means of electrostatic interaction/affinity towards the negatively charged hydrogel core of the microparticles.
Other tissue adhesives or sealants in other preferred embodiments of the present invention may also include of calcium alginates, chitosanes, hyaluronates, or any other ionically crosslinkable gels, which can transfer some of their multivalent ion content onto their surrounding environment, including the microparticle hydrogel core, which then may be crosslinked via the multivalent cation's presence and thereby attached to the injected gel in-situ. Such compounds and compositions may be injected in liquid form in some embodiments of the present invention and then crosslinked (gelled) post-injection through addition of multivalent ions such as calcium.
Preferred methods to create cross-linking of polymeric microspheres after their delivery to a target tissue as described herein include incorporating a thermal initiator or a photoinitiator agent in the absence of an exogenous protein to the shell of the microspheres and activating the agent, for example, photoactivating the photoinitiator agent with electromagnetic radiation after the microspheres have been suitable placed in the desired site and configuration.
As used herein, photoactivation is the process by which energy in the form of electromagnetic radiation (e.g., light) is absorbed by a compound, e.g., a photoinitiator, thus “exciting” the compound, which then becomes capable of converting the energy to another form of energy, preferably chemical energy. The electromagnetic radiation can include energy, e.g., light, having a wavelength in the visible range or portion of the electromagnetic spectrum, or the ultraviolet and infrared regions of the spectrum. The chemical energy can be in the form of a reactive species, e.g., a reactive oxygen species, e.g., a singlet oxygen, superoxide anion, hydroxyl radical, the excited state of the photoinitiator, photoinitiator free radical or substrate free radical species. The photoactivation process described herein preferably involves insubstantial transfer of the absorbed energy into heat energy. Preferably, photoactivation occurs with a rise in temperature of less than 3 degrees Celsius (C.), more preferably a rise of less than 2 degrees C. and even more preferably, a rise in temperature of less than 1 degree C. as measured, e.g., by an imaging thermal camera that looks at the tissue during irradiation.
As used herein, a “photoinitiator” is a biocompatible chemical compound that produces a biological effect upon photoactivation or a biological precursor of a compound that produces a biological effect upon photoactivation. Preferred photoinitiators are those that absorb electromagnetic energy, such as light. While not wishing to be bound by theory, the photoinitiator may act by producing an excited photoinitiator or derived species that interacts with the polymeric shell of the microspheres of the present invention to form a bond, e.g., a covalent bond or crosslink. Photoinitiators typically have chemical structures that include multiple conjugated rings that allow for light absorption and photoactivation. Examples of photosensitive compounds include various light-sensitive dyes and biological molecules such as, for example, xanthenes, e.g., rose bengal and erythrosin; flavins, e.g., riboflavin; thiazines, e.g., methylene blue; porphyrins and expanded porphyrins, e.g., protoporphyrin I through protoporphyrin IX, coproporphyrins, uroporphyrins, mesoporphyrins, hematoporphyrins and sapphyrins; chlorophylis, e.g., bacteriochlorophyll A, and photosensitive derivatives thereof. Preferred photoinitiators for use in the methods described herein are compounds capable of causing a photochemical reaction capable of producing a reactive intermediate when exposed to light and which do not release a substantial amount of heat energy. Preferred photoinitiators are also water soluble. Preferred photoinitiators include commercially available, synthetic biocompatible photoinitiators such as Irgacure D2959. Other preferred photoinitiators of the present invention include, but are not limited to, Rose Bengal (RB); riboflavin-5-phosphate (R-5-P); other riboflavins; methylene blue (MB); and N-hydroxypyridine-2-(1H)-thione (N-HTP).
Without being bound by theory, it is believed that the chemical energy, e.g., a reactive oxygen species, produced by photoactivation of the photoinitiator agent with which adjacent microspheres are contacted, binds and causes structural changes in the amino acids of the proteins of the tissue, resulting in the formation of covalent bonds, polymerization, or cross-links between amino acids of the tissue, thus creating a proteinaceous framework that serves to amalgamate or interconnect the plurality of microspheres delivered to the targeted tissue site.
The photoinitiator agent, e.g., RB, R-5-P, MB, or N-HTP, can be dissolved in a biocompatible buffer or solution, e.g., saline solution, and used at a concentration of from about 0.1 mM to 10 mM, preferably from about 0.5 mM to 5 mM, more preferably from about 1 mM to 3 mM.
As described above, the photoinitiator may be incorporated into the surface coating or shell of the microspheres prior to their delivery to the targeted tissue site. Alternately, the photoinitiator agent may be administered to the targeted tissue site after microsphere delivery, e.g., by post-implantation injection into the site. An amount of photoinitiator sufficient to stain, e.g., to cover the surfaces of the microspheres implanted, may be applied. For example, at least 10 μl of photoinitiator solution, preferably 50 μl, 100 μl, 250 μl, 500 μl or 1 ml, or more, of photoinitiator solution may be applied to the accumulated microspheres.
The electromagnetic radiation, e.g., light, is applied to the tissue at an appropriate wavelength, energy, and duration, to cause the photoinitiator to undergo a reaction to affect the structure of the polymeric shell of the microspheres to cause cross-linking and thereby cause amalgamation of the accumulated microspheres. The wavelength of light may be chosen so that it corresponds to or encompasses the absorption of the photoinitiator, and reaches the area of the tissue that has been contacted with the photoinitiator, e.g., penetrates into the region where the photoinitiator is injected. The electromagnetic radiation, e.g., light, necessary to achieve photoactivation of the photoinitiator agent can have a wavelength from about 350 nm to about 800 nm, preferably from about 400 to 700 nm and can be within the visible, infra red or near ultra violet spectra. The energy can be delivered at an irradiance of about between 0.5 and 5 W/cm2, preferably between about 1 and 3 W/cm2. The duration of irradiation may be sufficient to allow cross linking of the polymeric shells of one or more microspheres. For example, in an exemplary embodiment, the duration of irradiation can be from about 30 seconds to 30 minutes, preferably from about 1 to 5 minutes. The duration of irradiation can be substantially longer in a tissue where the light has to penetrate a scattering layer to reach the wound, e.g., skin. For example, the duration of irradiation to deliver the required dose to a subcutaneous or intradermal site through the skin can be at least between one minute and two hours, preferably between 30 minutes to one hour.
Suitable sources of electromagnetic energy include commercially available lasers, lamps, light emitting diodes, or other sources of electromagnetic radiation. Light radiation can be supplied in the form of a monochromatic laser beam, e.g., an argon laser beam or diode-pumped solid state laser beam. Light can also be supplied to a non-external surface tissue through an optical fiber device, e.g., the light can be delivered by optical fibers threaded through a small gauge hypodermic needle (such as the needle used for microsphere injection) or an endoscope. Light can also be transmitted by percutaneous instrumentation using optical fibers or cannulated waveguides.
The choice of energy source will generally be made in conjunction with the choice of photoinitiator employed in the method. For example, an argon laser is a preferred energy source suitable for use with RB or R-5-P because these dyes are optimally excited at wavelengths corresponding to the wavelength of the radiation emitted by the argon laser. Tunable dye lasers can also be used with the methods described herein. Other suitable combinations of lasers and photoinitiators will be known to those of skill in the art. In addition, post-implantation cross-linking of polymer coating of microspheres may be induced by heat, radio frequency radiation, applied radiation, altered pH, enzymes, or other factors to cause the amalgamation of microspheres in situ after implantation for physical stabilization of the implant as desired in the targeted tissue site.
In various preferred embodiments of the present invention, contrast agents may be provided within particles of the invention as described herein. In other preferred embodiments of the present invention, contrast agents may be delivered along with particles of the invention as a suspension or delivery medium. In yet other preferred embodiments of the present invention, contrast agents may be delivered in a separate injection or instillation than the particles of the invention.
If the particles are loaded with a contrast agent, their movement can be visualized with X-ray machines, or any other imaging modality, depending on the contrast agent utilized. However, if the particles do not contain a contrast agent, the flow of the particles may be visualized using 19F-NMR based computer tomography.
Further, it is to be understood that this invention is not limited to specific materials, agents, polyphosphazenes, or other compounds used and disclosed in the invention described herein, including in the following examples, as each of these can vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects or embodiments and is not intended to be limiting. Should the usage or terminology used in any reference that is incorporated by reference conflict with the usage or terminology used in this disclosure, the usage aid terminology of this disclosure controls.
Unless indicated otherwise, temperature is reported in degrees Centigrade and pressure is at or near atmospheric. An example of the preparation of a polyphosphazene of this invention is provided with the synthesis of poly[bis(trifluoroethoxy)phosphazene] (PzF) polymer, which may be prepared according to U.S. Patent Application Publication No. 2003/0157142, the entirety of which is hereby incorporated by reference.
Also unless indicated otherwise, when a range of any type is disclosed or claimed, for example a range of molecular weights, layer thicknesses, concentrations, temperatures, and the like, it is intended to disclose or claim individually each possible number that such a range could reasonably encompass, including any sub-ranges encompassed therein. For example, when the Applicants disclose or claim a chemical moiety having a certain number of atoms, for example carbon atoms, Applicants' intent is to disclose or claim individually every possible number that such a range could encompass, consistent with the disclosure herein. Thus, by the disclosure that an alkyl substituent or group can have from 1 to 20 carbon atoms, Applicants intent is to recite that the alkyl group have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 carbon atoms. In another example, by the disclosure that microspheres have a diameter of approximately 500 to 600 μm, Applicants include within this disclosure the recitation that the microspheres have a diameter of approximately 500 μm, approximately 510 μm, approximately 520 μm, approximately 530 μm, approximately 540 μm, approximately 550 μm, approximately 560 μm, approximately 570 μm, approximately 580 μm, approximately 590 μm, and/or approximately 600 μm, including any range or sub-range encompassed therein. Accordingly, Applicants reserve the right to proviso out or exclude any individual members of such a group, including any sub-ranges or combinations of sub-ranges within the group, that can be claimed according to a range or in any similar manner, if for any reason Applicants choose to claim less than the full measure of the disclosure, for example, to account for a reference that Applicants are unaware of at the time of the filing of the application.
Microspheres having a diameter of approximately 500 to 600 μm were prepared. First, a polymer solution was prepared by dissolving poly[bis(trifluoroethoxy)phosphazene polymer of a molecular weight 3×106 g/mol in the polymer solvent ethyl acetate to obtain a 2% (wt/v) polymer solution. Four milliliters of this polymer solution was manually dripped into liquid nitrogen using a 5 ml syringe. This dispersion was dispensed onto a frozen layer of 150 milliliters of pentane. (See
Microspheres having a diameter of approximately 350 to 450 μm were prepared. First, a polymer solution was prepared by dissolving poly[bis(trifluoroethoxy)phosphazene polymer of a molecular weight 3×106 g/mol in ethyl acetate to obtain a 1% (wt/v) polymer solution. Four milliliters of this polymer solution was manually dripped into liquid nitrogen using a 5 ml syringe. This dispersion was dispensed onto a frozen layer of 150 milliliters of pentane. (See
Microspheres having a diameter of approximately 500 to 600 μm were prepared. First, a polymer solution was prepared by dissolving poly[bis(trifluoroethoxy)phosphazene polymer of a molecular weight 12×106 g/mol in methylisobutylketone to obtain a 2% (wt/v) polymer solution. Four milliliters of this polymer solution was manually dripped into liquid nitrogen using a 5 ml syringe. This dispersion was dispensed onto a frozen layer of 150 milliliters of a 1.9 (v/v) ethanol/pentane mixture (See
Microspheres having a diameter of approximately 500 to 600 μm were prepared. First, a polymer solution was prepared by dissolving poly[bis(trifluoroethoxy)phosphazene polymer of a molecular weight 9×106 g/mol in isoamylketone to obtain a 2% (wt/v) polymer solution. Four milliliters of this polymer solution was manually dripped into liquid nitrogen using a 5 ml syringe. This dispersion was dispensed onto a frozen layer of 150 milliliters of pentane. (See
Microspheres having a diameter of approximately 500 to 600 μm were prepared. First, a polymer solution was prepared by dissolving poly[bis(trifluoroethoxy)phosphazene polymer of a molecular weight 16×106 g/mol in cyclohexanone to obtain a 2% (wt/v) polymer solution. Four milliliters of this polymer solution was manually dropped into liquid nitrogen using a 5 ml syringe. This dispersion was dispensed onto a frozen layer of 150 milliliters of a 1:1 (v/v) ethanol/diethyl ether mixture. (See
Microspheres having a diameter of approximately 500 to 600 μm were prepared. First, a polymer solution was prepared by dissolving poly[bis(trifluoroethoxy)phosphazene polymer of a molecular weight 3×106 g/mol in ethyl acetate to obtain a 2% (wt/v) polymer solution. Four milliliters of this polymer solution was manually dripped into liquid nitrogen using a 5 ml syringe. This dispersion was dispensed onto a frozen layer of 150 milliliters of hexane. (See
Microspheres having a diameter of approximately 500 to 600 μm were prepared. First, a polymer solution was prepared by dissolving poly[bis(trifluoroethoxy)phosphazene polymer of a molecular weight 3×106 g/mol in ethyl acetate to obtain a 2% (wt/v) polymer solution. Four milliliters of this polymer solution was manually dripped into liquid nitrogen using a 5 ml syringe. This dispersion was dispensed onto a frozen layer of 150 milliliters of ethanol. (See
Microspheres having a diameter of approximately 500 to 600 μm were prepared. First, a polymer solution was prepared by dissolving poly[bis(trifluoroethoxy)phosphazene polymer of a molecular weight 3×106 g/mol in ethyl acetate to obtain a 2% (wt/v) polymer solution. Four milliliters of this polymer solution was manually dripped into liquid nitrogen using a 5 ml syringe. This dispersion was dispensed onto a frozen layer of 150 milliliters of diethylether. (See
A two liter cryovessel as shown in
The syringe pump as shown in
In carrying out this process, it is noted that it is preferable that the needle tips used for dispensing are small, such as the G33 size. Additionally, the dropping distance should be more than 5 cm, so that the droplets aided by gravity immediately sink into the liquid nitrogen upon hitting the surface.
The liquid nitrogen in the vessel was slowly allowed to evaporate, taking approximately one day. The non-solvent slowly began to melt, and the polymer solution droplets, still frozen, sank into the cold non-solvent. After another day of incubation, the now gelled polymer beads (particles) were retrieved from the vessel by simple filtration. They were allowed to dry at room temperature for approximately 30 minutes and then were ready for use in any of the applications described herein.
The microspheres prepared by the process of Example 1 were examined for shape and surface morphology by optical microscope, scanning electron microscope (SEM) and atomic force microscopy. The results of these analyses are shown in
It can be seen that surface morphology of the unloaded spheres is typical for semi-crystalline polymers above glass transition temperature. Amorphous as well crystalline regions are prevalent throughout the sample surface. The surface is microporous in nature, with pore sizes ranging from nanometers to few micrometers in diameter.
Particles loaded with bovine insulin were also analyzed using scanning electron microscopy (100× magnification). The result of these analyses can be seen in
Several polymerizations were carried out using varying combinations of PMMA and three different crosslinking monomers (EDGMA, DEGDMA and TEGDMA), different radical initiators (benzoyl peroxide (BPO) and lauroyl peroxide (LPO), EDTA as a complexing agent and varying dispersants (Cyanamer 370M, polyacrylic acid (PAA) and varying types of polyvinyl alcohol (PVA) to achieve the preferred core particles. In some polymerizations, sodium phosphate buffer solution (Na2HPO4/NaH2PO4) was used. It was observed that some of the reaction procedures went unsuccessful due to the type of dispersant and concentration chosen. Failure of the dispersant was demonstrated in the form of early onset of an exothermic reaction, coalescing aqueous and organic phases and premature onset of the vitrification phase. Only the successful examples are shown. The successful runs are shown below in Table 1, which includes the components, concentrations and reaction conditions for such samples (1-6).
Hydrogel microparticles formed in accordance with the procedures described herein were evaluated for buoyancy and suspension properties for use in embolization applications. The microparticles included a sample using unmodified polymethacrylic acid potassium salt hydrogel particles (Sample A); a sample using trifluoroethyl esterified polymethacrylic acid potassium salt hydrogels (Sample B); and a sample using the same hydrogel as Sample B, but wherein the particles were coated with poly[bis(trifluoroethoxy)phosphazene (Sample C). An isotonic phosphate buffered saline solution of pH 7.4 having 0.05 volume % Tween™ 20 was prepared by dissolving 5 phosphate buffered saline tablets (Fluka®) in 999.5 ml of milliQ ultrapure water. 0.5 ml of Tween 20™ surfactant was added to the solution. Solutions having between 20 and 50 percent by volume of Imeron300® contrast agent in the isotonic buffered saline solution were then prepared for evaluation.
The contrast agent solutions which were prepared were then placed in 4 ml vials in aliquots of 2 ml each. To the vials, 50-80 mg of the hydrated hydrogel Samples A-C were added. Each Sample was first hydrated by adding to 100 mg of dry hydrogel microparticles either 900 mg of isotonic phosphate buffered saline solution or D2O to obtain 1 ml swollen hydrogel. Buoyancy properties were measured immediately and every 10 minutes thereafter until buoyancy equilibrium was achieved and/or surpassed.
All of the particles reached equilibrium density in the contrast agent solution having 30-40% contrasting agent within 5 min. Particles which were swollen with D2O were heavier within the first 10 minutes, but the D2O did diffuse out of the particles over time within 15-20 min. of immersion. If additional water which could displace the D2O were not added, microparticles hydrated with D2O would be able to increase the contrast agent percentage achievable with adequate buoyancy by as much as 5%. Particles began to float to the top over time when the contrast agent was added in percentages of 40%-50%.
The equilibrium buoyancy (matching densities) was achieved for Sample C in 31±1 volume percent of contrast agent in solution. With regard to Samples A and B, swelling behavior and subsequent density are typically dependent on crosslinking content, pH, ionic strength and valence of cations used. However, it was assumed herein that the swelling does not influence buoyancy due to the sponge-like nature of the polymethacrylic acid hydrogel material. After such material was coated with the poly[bis(trifluoroethoxy)phosphazene as in Sample C, a time lag of swelling was observed and buoyancy equilibrium was slower to achieve.
In order to take account of the time lag and to achieve a more preferred density, as well as to enhance the fluoroscopic visibility of the particles, cesium treatment was then effected for the types of microparticles used in Samples B and C of Example 12.
100 mg of Sample C and of Sample B were hydrated each for 10 min. in a 30 weight percent solution of sodium chloride. The supernatant liquid was decanted after equilibrium and the microparticles were washed thoroughly with deionized water. They were then equilibrated for another 10 min., decanted and suspended in 3 ml of surfactant-free isotonic phosphate buffer solution at a pH 7.4. The effect on buoyancy was then evaluated using contrast agent solutions varying from 20 to 50% by volume of Imeron® 300. In this Example, 0.1 g of the microparticles of Samples B and C were used. 3.5 ml of Imeron 300 contrast agent were provided to the initial buffer solution which included 4.0 ml isotonic phosphate buffer/Tween™ 20 solution.
The equilibration procedure using cesium chloride yielded particles of increased density. Both microparticle samples showed a final buoyancy in the Imeron® 300 contrast agent solutions at concentrations of 45-50% contrast agent, regardless of the presence or absence of Tween™ 20 surfactant. The conditions for saturation appeared to be dependent upon the initial pH of the particles, the pH used during the procedure and the corresponding saturation with methacrylic acid groups in the particle. At pH below 3.6, constant exchange between protons and cations was observed. As a result, more beneficial results were shown at pH above about 3.6 and below about 6.6 to temper the amount of cesium. Within the preferred range, buoyancy can be varied. At reasonably neutral levels, based on test at pH of 7.4, the microparticles did not lose their buoyancy after storage in the contrast agent buffered solution over night.
Further compressibility and mechanical property testing were done on microspheres in accordance of Samples B and/or C of Example 12. A pressure test stand which was used for further evaluation is shown in
In order to make certain calculations, the following information was applied as based on typical use of microspheres for embolization. Typically such microspheres have a water content of about 90% such that a vial for embolization would therefore contain 0.2 mg of embolization particles in 9.8 ml of injection liquid (2 ml of hydrated microparticles in 8 ml supernatant liquid). Standard preparation procedures include adding 8 ml of Imeron® 300 contrast agent to the contents of a single vial. This would provide an equilibrium concentration of contrast agent of 8 ml/(9.8 ml+8 ml)=44.9 volume percent within an injection solution. The solution is typically drawn up in 1 ml syringes for final delivery. The injection density thus equals:
ρVEmb/VTot=2 ml/18 ml=0.111 Embolization agent per volume fraction.
The Sample C spheres demonstrated approximately the same equilibrium water content as typical embolization spheres. To achieve the same injection density desired for typical surgical procedures, 56 mg of Sample C microspheres were added to 5 ml of a 31 volume percent contrast agent solution in isotonic phosphate buffer and surfactant as noted above.
The Sample B and C microspheres were evaluated in different microcatheters of equal lumen diameter at a pH of 7.4. Injections in both the horizontal and vertical direction were made under different buoyancy levels and using different swelling levels (based on pH of 6.0 in contrast to pH 7.4). The results demonstrated that as long as the diameter of the microspheres was below the internal diameter of the microcatheter, the microparticles passed through the catheter without additional frictional force in the same manner as the reference solution. An increase to about 1.0 to 1.4 kg gravitation force was measured when the microparticle diameter reached the same dimension as the lumen diameter. At roughly 20% compression, forces of about 1.5-2.3 kg were needed to overcome frictional forces within the catheter. Forces greater than 5 kg were taken as a guideline for moderate to high injection pressures. When particles are heavier than the injection medium, clogging was observed when injecting in the vertical position. When injecting the microparticles in the horizontal position, it was observed that serious clogging was alleviated and that larger volumes were injectible over time.
Injection pressure was further minimized when a lower pH (reduced swelling) was used in combination with horizontal injection such that the injection pressures were comparable to the injection media itself. In addition, injection of Sample C microparticles also exhibited a good injection pressure pattern at a physiological pH. The catheter entrance did not clog and each peak in the curve corresponded to either a single microparticle or number of particles passing through the catheter.
The results of the various catheter simulation tests shows that the invention can be used to form injectible microparticles having a density which substantially matches the density of the injection medium for embolization use. The particles' compressibility can further be such that it can be injected without forces over more than about 5 kg on the syringe plunger. The pH of the injection medium can be taken down to about 6 or injections can be done horizontally to increase the ease of passage of Sample B and C microparticles through the catheter. Once within the blood stream, the particles can expand to their original size in the pH 7.4 environment.
Additional swelling tests were conducted on the microparticles of Sample C and it was observed that when ion concentrations were low, swelling increased. In higher concentrated solutions, swelling decreased. Continued dilution of the microparticles of Sample C in a buffer solution led to an increase from 17% to 20% in size of the microparticles. When mixed into an isotonic phosphate buffer solution, the microparticles initially increase in size between 83.8 and 97%, wherein in deionized water, size increases are from about 116.2 to about 136.6%, referring to the dry particles.
In further testing to evaluate the compressibility of the microparticles of Sample C, the syringe pressure test stand of
Sample C microparticles were further subjected to mechanical and thermal stress stability testing. Microparticles, after passing through a Terumo Progreat Tracker catheter were washed with deionized water to remove residual buffer solution along with contrast agent. They were dehydrated for 12 h at 60° C. and then transferred to an SEM for surface analysis. They were compared with particles from the original batch of microparticles which had undergone the same hydration/dehydration cycle in milliQ ultrapure water, but which had not been passed through the catheter.
A sterilizer was filled with 2 l of deionized water and 10 vials each having 56 mg of Sample C microparticles in 3.3 g of solution of isotonic phosphate buffer/surfactant (Tween™ 20) and turned on. The water boiling point was reached about 15 min. after the start of the sterilizer, and temperature was held at that point for 3 min. to remove air by water vapor. The vessel was then sealed shut to raise pressure and temperature to 125° C. and 1.2 bar pressure. This took approximately 10 min. The temperature was then maintained for 15 min, and then the vessel was shut down for a cooling phase. A temperature of 60° C. was reached about 30 min later, after which the vessel was vented, the samples withdrawn and the vessel shut tightly. A sample vial was opened, and the supernatant liquid decanted. The microparticles were washed with deionized water. After dehydration, they were subjected to measurement using an SEM. The results demonstrated only a small number of delaminated coatings on the microparticles under such thermal stress (see
Microparticles were formed in accordance with a preferred embodiment herein. A deionized water solution of polyvinyl alcohol (PVA) was prepared using about 23 g of PVA of weight average molecular weight of about 85,000-124,000, which PVA was about 87-89% hydrolyzed and 1000 g water. A phosphate buffer solution was prepared using 900 g deionized water, 4.53 g disodium hydrogen phosphate, 0.26 g sodium dihydrogen phosphate and 0.056 g ethylenediamine tetraacetic acid (EDTA). Methyl methacrylate (MMA) monomer was vacuum distilled prior to use.
Polymerization was carried out in a three-necked, round-bottomed, 2000-ml flask with a KPG mechanical stirring apparatus attached. The flask was also equipped with a thermometer, reflux condenser and a pressure release valve with a nitrogen inlet. The polymerization process further utilized 100 ml of the PVA solution prepared above, 900 ml of the phosphate buffer solution, 0.65 g of dilauroyl peroxide, 200.2 g methacrylic acid methyl ester and 2.86 g triethylene glycol dimethacrylate.
The PVA and buffer solutions were provided to the reactor flask. The distilled MMA and triethylene glycol dimethacrylate were introduced, dilauroyl peroxide then added to the same flask and the components were agitated to ensure dissolved solids. The reaction flask was flushed with argon and the stirrer speed set to at 150 rpm to produce particle sizes of a majority in the range of 300-355 μm. Stirring continued for approximate 5 minutes. The stirrer was then set to 100 rpm and argon flushing was discontinued. The reaction flask was then subjected to a water bath which was heated to 70° C. and held at approximately that temperature for about 2 hours. The temperature of the bath was then increased to 73° C. and held for an hour, then the water bath temperature was raised again to 85° C. and held for another hour. The stirring and heat were discontinued. The solution was filtered and the resulting polymethylacrylate microparticles were dried in an oven at 70° C. for about 12 hours. The microparticles were subjected to sieving and collected in size fractions of from 100-150; 150-200; 200-250; 250-300; 300-355; 355-400; and 400-450 μm with a maximum yield at 300-355 μm.
The PMMA microparticles thus formed were then hydrolyzed. A portion of 100 g 250-300 μm sized microparticles, 150 g potassium hydroxide and 1400 g of ethylene glycol were added to a 2000 ml flask, reflux condenser with drying tube connected, and the mixture was heated at 165° C. for 8 hours for full hydrolysis. The mixture was allowed to cool to room temperature, solution decanted and the microparticles were washed with deionized water. The procedure was repeated for other calibrated sizes of microparticles (the following reaction times applied: 300-355 micron particles: 10 hours; 355-400 micron particles: 12 hours and 400-455 micron particles: 14 hours).
The microparticles were finally acidified with hydrochloric acid to a pH of 7.4, and dried in an oven at approximately 70° C.
Microparticles formed in accordance with Example 15 were then esterified in this Example. For esterification surface treatment, 800 g of dried microparticles from Example 15 were weighed in a 2 L reaction vessel with a reflux condenser. 250 g thionyl chloride in 1.5 L diethyl ether were added under stirring. Stirring was continued at room temperature for 20 hours. The solvent and volatile reactants were removed by filtration and subsequent vacuum drying. Then 500 g trifluoroethanol in 1.5 L ether were introduced and the suspension stirred for another 20 hours at room temperature. The particles were finally dried under vacuum.
In an alternative surface treatment to Example 16, 800 g dried microparticles from Example 15 were reacted with 1140 g trifluoroethanol and 44 g sulfuric acid added as a catalyst. The mixture was stirred for 20 hours at room temperature, filtered and dried under vacuum.
800 g of dry PMMA potassium salt microparticles which were partially esterified with trifluoroethanol as described above in Examples 15-16 were spray coated with poly[bis(trifluoroethoxy)phosphazene in an MP-1 Precision Coater™ fluidized bed coating apparatus (available from Aeromatic-Fielder AG, Bubendor, Switzerland). The particles were picked up by an air stream (40-60 m3/h, 55° C. incoming temperature) and spray coated with poly[bis(trifluoroethoxy)phosphazene solution microdroplets from an air-fluid coaxial nozzle. The solution composition was 0.835 g poly[bis(trifluoroethoxy)phosphazene, 550 g ethyl acetate and 450 g isopentyl acetate. It was fed through the nozzle's 1.3 mm wide inner bore at a rate of 10-30 g/min. At the nozzle head, it was atomized with pressurized air (2.5 bar). The total amount of spray solution (3 kg) was calculated to coat the particle with a 150 nm thick poly[bis(trifluoroethoxy)phosphazene film.
The dry potassium salt microparticles of Examples 15-16, which were partially esterified with trifluoroethanol as described above, were spray-coated with diluted poly[bis(trifluoroethoxy)phosphazene solution in ethyl acetate in a commercially available fluidized bed coating device (see Example 16). 100 mg of such coated, dried microparticles as well as 100 mg of uncoated, dried PMA potassium salt microparticles which were partially esterified with trifluoroethanol, were immersed in about 30% aqueous cesium chloride solution, prepared by dissolving 30.0 g cesium chloride in 100 ml deionized water. The supernatant liquid was decanted after 10 min. equilibrium time and the microparticles were washed thoroughly with deionized water, equilibrated for another 10 min., decanted and suspended in 3 ml surfactant free phosphate buffer solution at a pH of 7.4. Density of the particles in solution was measured for matching density in a contrast agent solution. To each type of microparticle was added a contrast agent solution which included a ratio of 3.5 ml of Imeron® 300 contrast agent (density 1.335 g/ml) and 4 ml phosphate buffered saline (density 1.009 g/ml). Both hydrogel types reached buoyancy at levels of 45-50% contrast agent in solution. This corresponds to an increased density of the microparticles of 1.16 g/ml.
Microparticles were formed in accordance with the procedure of Example 15 with the exception that an exterior barium sulfate coating was prepared on the microparticles after neutralization of the particles and the microparticles were not dried after neutralization prior to the barium sulfate coating step. To prepare the barium sulfate coating, 2500 ml hydrated particles were subjected to 2000 ml of 0.5 M sodium sulfate (Na2SO4) solution and saturated for 4-12 hours. To the particle suspension was then slowly added 1950 ml of 0.5 M barium chloride (BaCl2) solution under stirring at room temperature. After washing with excess deionized water, the resulting particles in a swollen state included a barium sulfate powder coated surface. The particles were then dried and esterified in the manner noted above in Example 16. The particles were then coated using the fluidized bed process of Example 21 below. The resulting microparticles were externally coated with a non-adhesive barium sulfate powder. Barium sulfate coatings prepared in accordance with this invention and procedure are capable of preventing particle agglomeration during drying and also increase density. The concentration and ratios of barium sulfate may be varied to provide different results and a use of an excess of sodium sulfate can minimize residual barium chloride. The particles formed in accordance with this example were effectively washed with hot water to minimize excess barium sulfate powder that may contaminate vials, etc. The barium sulfate works effectively to prevent adhesion of particles prior to drying to assist in fluidization of the hydrated microparticles.
Fluidized bed coating of barium sulfate powdered beads was performed using polymethacrylate beads with a surface layer of barium sulfate formed in accordance with Example 20 but an excess of barium chloride was used such that barium ions diffused inside the core and formed a precipitate inside the hydrogel core.
In preparing the particles, the same procedure for barium sulfate coated particles set forth in Example 20 was repeated with the exception that the order of addition was reversed. Thus, 2500 ml hydrated microparticles were suspended in 2500 ml deionized water and slowly, 5 mol % (200 ml) of a 0.5 M (BaCl2) were added slowly under stirring. The addition was performed within a time period of three minutes to prevent irreversible barium acrylate formation taking place. The suspension was then immediately quenched with the double amount (400 ml) of 0.5 M sodium sulfate (Na2SO4) solution under stirring at room temperature. Afterwards, the particles were washed three times with 2 L of deionized water each. This procedure precipitated barium sulfate inside the particles.
The resulting precipitate was precipitated within the pores of the hydrogel core and could not be removed by multiple washings with water. The particles thus formed were found to have a permanent increased density in contrast to unmodified particles. The density increase was controllable by the molar amount of barium chloride used. Amounts ranging from 0-15 mol % of barium chloride were used reproducibly with this procedure. It was observed during evaluations of this procedure that, if the time period of addition exceeded 5 minutes, based upon the diffusion speed of barium chloride within the particles, the outer pores of the hydrogel core became irreversibly crosslinked, thereby preventing the barium sulfate precipitate inside from leaching out. This effect was visible by optical microscopy as the “diffusion front” of the barium sulfate was clearly visible as a white band inside the particle, whereas the surface remained clear.
Both Examples 20 and 21 provided particles having anti-adhesive properties that tend not to agglomerate during drying processes; therefore avoiding surface damage. Generally, such an advantage helps minimize the amount of particles needed for a fluidized bed procedure as the particles can be fluidized without being completely dried. The residual water content may be increased up to 1:1 based on dry weight without agglomeration. The Examples also produce particles with increased density properties wherein the density change appears to be permanent.
It should also be understood according to this disclosure that generally when applying the procedures noted herein, barium sulfate may be introduced in accordance with the invention in a range of from 0 to about 100 mol %, and preferably 0 to about 15 mol % to provide particles that have preferred elasticity, density and mechanical stability properties.
The particles formed according to this Example having a barium sulfate load inside the core were then esterified according to Example 16 and vacuum-dried. 300 g of the dry beads were suspended in 300 g water which was completely absorbed by the polymethacrylate cores within less than 1 min while the barium sulfate powdered particle surface appeared dry and the particles showed no tendency to agglomerate.
The particles (now 600 g) with 50 weight percent (wt %) water inside were spray coated with APTMS/poly[bis(trifluoroethoxy)phosphazene in an MP-1 Precision Coater™ fluidized bed coating apparatus according to Example 18 with the exception that an additional aminosilane adhesion promoter was used. The process equipment used was the same as that of Example 18, but the coating provided included three different layers. A bottom coating of 3-aminopropyltrimethoxysilane (APTMS) adhesion promoter was provided upon which was a second coating layer of a mixture of APTMS and poly[bis(trifluoroethoxy)phosphazene and a third, top coating layer of poly[bis(trifluoroethoxy)phosphazene. All three spray solutions were prepared by dissolving the coating material in isopentyl acetate and ethyl acetate in a 1:1 weight percentage ratio mixture. The first solution included 35 μl APTMS dissolved in 200 g acetate mixture. The second solution included 25 μl APTMS and 125 mg poly[bis(trifluoroethoxy)phosphazene in 150 mg of the acetate mixture and the third included 50 mg poly[bis(trifluoroethoxy)phosphazene in 60 g of the acetate mixture. The spray solution quantities and concentrations refer to the coating of a 300 g batch with 350 μm particles. The absorbed water evaporated at a rate of 5-10 g/min. The process was stopped after 30 min when the coating thickness reached 100 nm and the residual water content was 18.4 wt %.
The absorption of organic dyes was tested on microparticles formed according to Example 15. To 2 ml of phosphate buffered saline solution containing 1 ml of hydrated beads was provided an amount of 5-10 μl of the respective dye as a 10 millimolar solution in ethanol. The samples were incubated for 30-60 minutes at room temperature under gentle shaking of the vial. Supernatant liquid was discarded and particles were washed three times with 2 ml of deionized water, saline or PBS buffer solution prior to visualization with optical and fluorescence microscopy. The dyes tested included triphenylmethane derived dyes such as Fluoescein diacetate and Rhodamin 6G which were evaluated along with carbocyanine based dyes such as DiI. The triphenylmethane based Fluorecein and Rhoamine dyes exhibited a specific affinity for the hydrophilic PMMA hydrogel core through ionic interactions. They were able to easily withstand the rigorous conditions of repeated washing and steam sterilization without substantial leaching.
The carbocyanine dye DiI on the other hand exhibited a high selectivity for the hydrophobic poly[bis(trifluoroethoxy)phosphazene shell, without penetrating the hydrophilic PMAA core material. Thus with the subsequent staining employing the combination of DiI and Fluorescein diacetate both core and shell could be simultaneously visualized employing a fluorescence optical microscope. As a result, this procedure provides a fast, sensitive fluorescence-staining assay for the PMAA particles that makes core and shell simultaneously visible under conditions encountered in actual application. This procedure further enables assessment of the mechanical-elastic stress or damage to the poly[bis(trifluoroethoxy)phosphazene shell. It further shows the affinity of certain classes of dyes for the various components of the particle.
Use of these and other dyes may be used to visually identify selected microspheres, which may be provided and dyed for identification to indicate certain sizes of microspheres for use in selected clinical or diagnostic applications. Color-coding may also be used to identify selected microspheres on the basis of other properties, such as content of certain therapeutic or diagnostic agents. Applications according to the present invention may also improve the imaging visualization by enhancing the particles' buoyancy behavior.
In various embodiments according to the present invention, microspheres may be produced in calibrated sizes ranging from about 1 to about 10,000 nanometers in diameter. In one embodiment of the present invention, microspheres of the present invention may be provided in sizes of about 40, about 100, about 250, about 400, about 500, about 700, and about 900 nanometers in diameter, with a visually distinctive color imparted to each size of microsphere. Other sizes, size ranges, and calibrated sized microspheres lacking color dye are also included in the present invention. Not only may the microspheres or particles be provided in different size ranges, but their elasticity may be controlled according to the present invention to specifically provide for proximal or distal embolization behavior, due to potentially differing ranges of compressibility which may alter the traveling distance of the particles or microspheres upon their release within a selected blood vessel. Microspheres of the present invention may also be provided in customized sizes and/or with customized colors as specified by a user for specific clinical diagnostic or therapeutic applications.
As provided in previous examples of the present invention, different-sized microspheres of the present invention may further be provided with color-coding to allow user identification and visual confirmation of the sized microspheres in use at any given stage of the clinical procedure.
The delivery of microspheres of different sizes or other inherent qualities may further be facilitated by the use of transport packaging and/or delivery devices which are color-coded to allow user identification and visual confirmation of the sized microspheres in use at any given stage of the clinical procedure in exemplary applications according to the present invention. In various exemplary applications of the present invention, such color-coded devices may be used in combination with color-coding of the microspheres themselves, with corresponding microsphere and packaging/delivery device color-coding.
In yet other exemplary embodiments of the present invention, a hand-held spectrophotometer that records data from a desired area of a mammalian patient's skin or other organs is used in conjunction with a computerized color formulation system. Based on this color measurement, a color formula will be calculated by the computer, and appropriate dyes will be mixed to produce pigmented microspheres to match the color of the target skin or other organs.
For exemplary microspheres 140 whose polymeric coating incorporates one or more suitable photoinitiator agents, a fiberoptic light carrier (not shown) can be introduced through the needle 130 and appropriate electromagnetic energy can be applied therethrough for sufficient time to cause amalgamation of the mass of microspheres injected into the tissue location. This amalgamation has the effect of stabilizing the position of the microspheres in their desired location, to prevent inadvertent and undesired displacement of the microspheres following their placement.
It will be appreciated by those possessing ordinary skill in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.
