Patent Application
20150150973
The present invention relates to magnesium phosphate gels. More specifically, the present invention is concerned with magnesium phosphate gels, dehydrated magnesium phosphate gels and xerogels produced from these gels.
In the search for alternative drug delivery methods to enhance compliance and improve safety, researchers have discovered that the permeability of mucous membranes provides a convenient route for the systemic delivery of new and existing drugs. Transmucosal delivery offers the potential for once daily dosage, avoids the effects of first pass metabolism, and can provide as much as four times the absorption rate of drugs delivered transdermally. The improved bioavailability allows more accurate and lower dosing and fewer side effects. There are a number of transmucosal formulation platforms currently in existence. Most focus on one specific type of administration such as BEMA polymer film (BioDelivery Sciences International), RapidMist™ aerosol (Generex Biotechnology), OraDisc™ film (Uluru), OraVescent™ tablet (Cima Labs), Transmucosal Film (Auxilium Pharmaceuticals) for oral drug delivery, ChiSys™ (West Pharmaceutical Services) and Intravail™ (Aegis Therapeutics) for nasal delivery. These formulations are generally washed out or they dissolve after a certain length of exposure. Transmucosal delivery has been mainly used to administer hormones such as insulin, calcitonin and estrogens or nitroglycerin, and opiates such as fentanyl or morphine for pain management.
On the other hand, topical mucosal delivery is a route of choice to administer a drug destined to treat a mucosa.
In adhesive pharmaceutical drugs, such as muco-adhesive drugs, topical mucosal or transmucosal drug delivery agents should ideally be biocompatible, bioadhesive, thixotropic and bioresorbable.
Most mucoadhesive polymers, such as carbopol and hydroxypropyl methyl cellulose, do not possess both thixotropy and bioresorption properties. This limits their usefulness as drug delivery additives. Currently, very few synthetic mucoadhesive-thixotropic polymers are FDA approved as drug additives. These include hydroxy-ethylcellulose (HEC), polycarbophil (PC), poly(vinylpyrrolidone) (PVP), poloxamer 407 (P407), carbopol 934P (C934P), and propolis extract (PE). None of these polymers is resorbable in vivo. On the other hand, resorbable mucoadhesive polymers such as chitosan lack thixotropic properties. Currently, there are no FDA approved materials combining all the above properties.
Water-based gels (hydrogels) have a wide range of biomedical applications such as drug delivery, food additives and cell therapy. While numerous organic hydrogels have been developed, only a limited number of inorganic systems exhibit hydrogel-like properties; well-known examples being silica gel, aluminum based gels and the V2O5— based hydro- and aerogels. Most inorganic hydrogels cannot be used for biomedical applications due to toxicity, impurities, extreme pH levels, instability under physiological conditions, and/or their lack of bioresorption.
In particular, the use of silicate based thixotropic clays (such as Laponite Clay) in the food and drug industry is indeed very limited due to their lack of resorption in the body. These materials are rather used to improve the performance and properties of a wide range of industrial and consumer products. More specifically, layered silicates are used as film formers and rheology modifiers. They are thus added to waterborne products, such as surface coatings, household cleaners and personal care products, to impart thixotropic properties, shear sensitive viscosity and improved stability and syneresis control.
In accordance with the invention, there is provided:
In the appended drawings:
In accordance with the present invention, there is provided a magnesium phosphate gel. This gel comprises water as its dispersing phase. Further, this gel comprises phosphate (PO43−) ions; a divalent cation (i.e. magnesium (Mg2+) ions optionally with some calcium (Ca2+) ions); and sodium (Na+) ions.
The phosphate ions are typically provided by a solution of phosphoric acid (H3PO4) or monomagnesium phosphate (Mg(H2PO4)2) in water used to make the gel. The magnesium ions are typically provided by magnesium hydroxide (Mg(OH)2—a solid) or trimagnesium phosphate (Mg3(PO4)2—another solid) that is added to the abovementioned solution. The calcium is typically provided by calcium hydroxide or calcium chloride that is also added to that solution. The sodium ions are typically provided by a solution of sodium hydroxide (NaOH) that is mixed with the magnesium-containing solution.
More specifically, the gel comprises phosphate, the divalent cation, and sodium at mole fractions of about 0.33 to about 0.44, about 0.03 to about 0.09, and about 0.48 to about 0.63, respectively. For example, the gel can comprise phosphate, the divalent cation, and sodium at mole fractions of about 0.36 to about 0.42, about 0.05 to about 0.08, and about 0.50 to about 0.57, respectively. Further examples of such gels include gels comprising the phosphate ions, the divalent cation and sodium ions at mole fractions of:
0.36, 0.07, and 0.57, respectively,
0.39, 0.08, and 0.53, respectively,
0.41, 0.05, and 0.54, respectively, and
0.42, 0.08, and 0.50, respectively.
It will be readily apparent to the skilled person that, as the above amounts of phosphate, divalent cation and sodium are given as mole fractions, the sum of these three mole fractions should be 1 (give or take the rounding errors). This is indeed the standard definition of mole fraction in the art: “In chemistry, the mole fraction is defined as the amount of a constituent divided by the total amount of all constituents in a mixture. The sum of all the mole fractions is equal to 1”. Herein, the mole fractions take only the divalent cation, phosphate and sodium into account. Water and optional additives that can be added to the gel are not considered.
In embodiments, the divalent cation is magnesium (Mg2+) only. In other embodiments, it is a mixture of magnesium and calcium, the mixture comprising up to 30% by weight of calcium based on the total weight of the mixture. In embodiments, the mixture comprises about 10% to about 30% by weight of calcium based on the total weight of the mixture.
In embodiments, the gel comprises phosphate, magnesium, and sodium ions at mole fractions of about 0.39, about 0.08, and about 0.53, respectively (that corresponds to the gel identified as 0.75 0.15 1 in the Examples below).
The amount of water (as a dispersing phase) in the gel is typically about 50% or more, for example 70% or more by weight based on the total weight of the gel. In embodiments, the gel may comprise more than about 90% of water, for example between about 92 and 98% or between about 92 and 96% of water as the dispersing phase.
When observed by transmission electron microscopy (TEM), in embodiments, the gel appears to comprise thin nano-plates or nanosheets. More specifically, these nanosheets can be about 200 nm wide, very thin (e.g. about 10 nm thick) and up to 1 μm long. As seen by TEM, these nanosheets agglomerate, and form interconnected planes (see
The nanosheets are made of magnesium phosphate (with some sodium). This magnesium phosphate contains magnesium bi- and tri-phosphate. This magnesium phosphate contains hydration water. For example, it may contain between about 10 and about 20% of hydration water by weight.
A distinction should be drawn between water as a dispersing phase and hydration water. Water as a dispersing phase is the medium in which the nanosheets are dispersed. This water can be removed by drying the gel at a relatively low temperature, for example a temperature below the boiling temperature of water, such as 80° C. (See the section entitled “Water Content” in Example 1). This process will produce a product that looks and feels dry, but that still contain hydration water. Hydration water consists in molecules of water that are bonded or somehow associated with a solid (for example entrapped within it). These molecules are typically only removed from the solid by heating the solid above the boiling temperature of water, often well above this temperature, for example between 100 and 250° C. (See the section entitled “Thermogravimetry” in Example 2).
When there is no calcium in the gel, the gel may further comprise up to 200% by weight of pyrophosphate (P2O74−), based on the weight of the phosphate. In embodiments, the gel may comprise between about 10% and about 20% by weight of pyrophosphate based on the weight of the phosphate. The presence of pyrophosphate makes the gel more acidic and thereby tends to improve its resistance to acidic media.
The gel may also comprise chloride (Cl−) ions. These may be provided by one of the compounds used for making the gel, for example calcium chloride, when it is present.
Additives can also be added to the gel. For example, these additives can aim at improving the resistance of the gel to dissolution in acidic media. Such additives include:
The gel of the invention can be loaded with a variety of substances, including bioactive substances, depending of the desired properties and its end use. Substances that can be loaded in the gel will be discussed below when some of the end uses of the gel will be discussed.
Further, the gel can be dehydrated in an organic liquid, for example ethanol or glycerol, to partly or completely replace the water therein by these substances.
The gel of the invention can also be dried to form a xerogel. This xerogel is in embodiments, in the form of a membrane, such as a translucent membrane. Herein, “xerogels” are solids formed from the gel by drying with unhindered shrinkage. In embodiment, the drying is carried out at room temperature.
The above gel represents a new phase of phosphate minerals.
Sodium, magnesium and phosphate are all naturally found in the body. In embodiments, where they are the sole components of the gel, this indicates that the gel should be non-toxic. This would be also true of embodiments, where non-toxic substances are added to the gel.
In embodiments, this gel has a unique combination of four desirable properties: bioadhesion, thixotropy, bioresorption, and biocompatibility.
First, the inorganic gel can be thixotropic and even, in embodiments, highly thixotropic. This means that it does not flow at rest, but can reversibly liquefy with shear stress. This makes it very useful for applications requiring coating and injection. For example, in an embodiment, it can be injected through an insulin needle (φ260 μm) and solidify after injection (see Example 2—Rheology). In embodiments, the gel has a liquefaction stress of about 50 Pa or less, for example a liquefaction stress between about 30 and about 40 Pa. In embodiments, the gel has a recovery time of 10 seconds or less, for example about 6 seconds. Moreover, the gel can be injected into water without mixing or disintegrating (see Example 2—Stability in Water). In fact, in embodiments, the gel has properties similar to those of layered silicate clays.
Further, tests demonstrated that, in embodiments, this gel was bioadhesive, biocompatible and could modulate drug release (see Examples 3, 4 and 6 below). As shown in the Examples below, rheological analysis indeed revealed that the gel is thixotropic, which makes it useful for applications requiring coating and injection. The gel was tested for bioadhesion and proved adhesive to mucosa over prolonged periods of agitation. The gel also showed good biocompatibility as well as resorption. Accordingly, in embodiments, the gel makes a useful additive for minimally invasive controlled drug release applications, administered by injection.
The gel was also tested as a drug delivery system. This suggested that the gel could function as a controlled release system where control over the release rate can be obtained by modifying the degree of gel hydration.
Finally, upon drying, the gel can in embodiments form homogeneous xerogels and coatings with high specific surface area. Such xerogels, with such high surface area, are widely used as drug delivery systems for oral drug administration due to their high adsorption capacity. Such xerogels and coatings can be used for adsorbing bioactive molecules. The xerogel obtained with the gel of the invention appeared as a translucent membrane (See Example 5 below).
In addition to the previously mentioned properties, the solubility of the gel was found to be pH sensitive, and could be adjusted by modifying its ionic structure (see the addition of pyrophosphate discussed above). This property makes it an interesting material for site-specific drug delivery in inflamed tissues (low pH).
In summary, the gel of the invention is a unique inorganic gel that, in embodiments, combines several interesting properties such as stability, biocompatibility, bioresorption, bioadhesion, thixotropy, and injectability. To the best of the inventors' knowledge, these properties have never been observed in a single material before. These properties open a wide range of industrial and biomedical applications, in particular in topical, mucosal, transmucosal and injectable drug delivery applications.
The gel could be used in drug delivery systems. In particular, the gel can be used in the following areas:
In particular, the gel could be used as a mucoadhesive for use in localized drug delivery to mucosal surfaces, more specifically to the oral mucosa. More specific examples of mucosal topical delivery include oral and dental applications (oral ulcerations, oral inflammation, periodontal diseases, etc), topical treatment of clinical manifestations on the mucosal layer of other organs such as bladder (for topical delivery of chemotherapy for bladder cancer, infections, inflammations, etc), vaginal ephitelium, ocular topical applications (keratitis, etc).
For example, the gel could be loaded with a drug, such as an antibiotic, and used as a localized drug delivery system, for example to a mucosa, in particular to the oral mucosa. This system could be used in particular for the treatment of peri-implantitis, which is a chronic infection of the bone surrounding osseointegrated dental implants. In such an application, the gel would be deposited, using a syringe or the like, in the periodontal (or peri-implant) pocket as illustrated in
Another use in topical delivery would be in wound healing where hydrogels are known as being useful. Hydrogel dressings are seen as an essential component of wound care. They are designed to hold moisture in the surface of the wound, providing the ideal environment for cleaning the wound and also help to prevent bacteria and oxygen from reaching the wound, providing a barrier for infections. Hydrogels can be used on their own for their water absorbing and donating capacity to either absorb exudate or to hydrate the wound to promote healing. They can also incorporate drugs, in particular antimicrobials to better control wound infection and promote faster healing.
Therefore, it is to be understood that the gel can be loaded with all sorts of bioactive substances. As used herein, a bioactive substance includes any of one or more substances that produces or promotes a beneficial therapeutic, physiological, homeopathic, allopathic and/or pharmacological effect on the body. Such beneficial effects may be brought upon any animal or human patient, and various systems associated therewith, including the immune system, respiratory system, circulatory system, nervous system, digestive system, urinary system, endocrine system, muscular system, skeletal system, and the like, as well as any organs, tissues, membranes, cells, and subcellular components associated therewith. As will be appreciated by those skilled in the art, beneficial effects include assisting the more efficient functioning of the abovementioned systems, such as, for example, helping the body fight sickness and disease, helping the body to heal, etc. Exemplary bioactive substances include any element, composition or material producing a beneficial effect, including vitamins, minerals, nucleic acids, amino acids, peptides, polypeptides, proteins, genes, mutagens, antiviral agents, antibacterial agents, anti-inflammatory agents, decongestants, histamines, anti-histamines, anti-allergens, allergy-relief substances, homeopathic substances, pharmaceutical substances (i.e. a drug), such as antibiotics and other drugs, and the like.
The gel may also comprise additives like those usually found in other compositions with the same end use. For example, for composition for oral mucosal delivery, the gel can comprise flavoring, oral-hygiene agents, colorants and/or opacifying agents.
There is also provided a method of producing a magnesium phosphate gel. The method comprise the step of providing (A) a aqueous solution comprising sodium hydroxide (NaOH) and (B) a aqueous solution comprising phosphoric acid (H3PO4) or monomagnesium phosphate (Mg(H2PO4)2). Then, magnesium hydroxide (Mg(OH)2) or trimagnesium phosphate (Mg3(PO4)2), and optionally calcium chloride or calcium hydroxide, is dissolved in the phosphoric acid or monomagnesium phosphate containing solution. Finally, this last solution is mixed with the solution comprising sodium hydroxide (NaOH). The gel forms within seconds of mixing both solutions. For better results, the time between the addition of the magnesium hydroxide or trimagnesium phosphate and the addition of the sodium hydroxide solution should be no more than several minutes, for example 10 minutes.
The concentration and quantity of solutions and solutes used to make the gel will be chosen so that the quantity of phosphate, magnesium (and optional calcium), and sodium in the gel respects the mole fractions and the water content discussed in the previous section.
In embodiments, the solution of phosphoric acid (H3PO4) or monomagnesium phosphate (Mg(H2PO4)2) in water comprises phosphoric acid. In embodiments, magnesium hydroxide is dissolved into this dissolution.
All the above steps can advantageously be carried out at room temperature.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context.
The terms “comprising”, “having”, “including”, and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to”) unless otherwise noted.
Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All subsets of values within the ranges are also incorporated into the specification as if they were individually recited herein.
All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.
The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed.
No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Herein, the term “about” has its ordinary meaning. For example, it may means plus or minus 10% of the numerical value thus qualified.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
Other objects, advantages and features of the present invention will become more apparent upon reading of the following non-restrictive description of specific embodiments thereof, given by way of example only with reference to the accompanying drawings.
The present invention is illustrated in further details by the following non-limiting examples.
Gels were made by dissolving magnesium hydroxide (Mg(OH)2) in a phosphoric acid (H3PO4) aqueous solution, reacting the obtained mixture with sodium hydroxide (NaOH) in solution, and filtering the product. A whole range of concentration of these reactants was tested. Gels were only obtained in a specific window of concentrations. Not all concentration combinations allow forming gels; some formulations precipitated crystals, some precipitated nothing, and some formulations were not acidic enough to dissolve the magnesium hydroxide in the first place.
Table 1 shows the different products obtained for an array of reactant concentrations. In these experiments, 25 mL of phosphoric acid (1M-0.5M) was used. Magnesium hydroxide was then dissolved in the acid to a concentration of 0.2M-0.1M. Then, 25 mL of sodium hydroxide at 1.0M-0.2M was added to the mixture.
In the above table, the mention “GEL” indicates a gel that is grey, translucent, fairly soft, and thixotropic. In contrast, the mention “GEL(thick)” means gels that are very white, opaque and thick. The present invention is concerned with the products marked “GEL” only.
In some cases, the formation of the gel was sensitive to the time taken to mix the reactants. Once the magnesium hydroxide was dissolved in the phosphoric acid, it could not be left out for more than several minutes. Sodium hydroxide had to be mixed in and the gel formed. Otherwise, the gel might crystallize. The different formulations were not equally sensitive to this factor, some were more affected, others less so.
Some of the tests below were carried on a gel formed using 0.75M phosphoric acid in which magnesium hydroxide is dissolved to 0.15M and to which a 1M solution of sodium hydroxide is added in equal proportions. This gel formulation will be referred hereinafter as “0.75 0.15 1”. A similar nomenclature will be adopted for the other gel formulations.
The 0.75 0.15 1 is not very sensitive to the time taken to prepare it, produces a large amount of thixotropic gel with an interesting texture.
Even after filtering, the gels obtained were composed largely of water. Heated at 80° C. for 24 hours, they lost over 90% of their mass. Although the exact mass fraction of water differed slightly between different gel formulations, it was always between 0.92-0.96.
Once a gel was filtered, it still acted like a gel even if it was then diluted with water. If the gel was diluted up to a fraction, i.e. (gel+water)/(gel), of 1.3, it was still a gel. At a fraction of around 1.35-1.4, the gel became very thin, but was still thixotropic. For example, if it was left standing for 30 seconds, the container in which it resided could be turned upside down without the gel flowing, however with one shake of the container, the gel turned into a runny liquid. At a dilution fraction of about 1.5-1.6 or more, the gel lost its thixotropic properties and behaved like a liquid.
The pH of the gels was affected by the concentration of the reactants. This was expected as phosphoric acid is an acid and sodium hydroxide is a base.
For example, gel 0.5 0.1 1 is basic because the initial concentration of acid is only 0.5M while the concentration of the base is 1M. Likewise, 1 0.2 1 is neutral because 1M acid is mixed with 1M base.
Gel 0.75 0.15 1 is a basic gel with a final pH of approximately 10.75.
Most of the above gels were made in small volume batches of 50 mL. However, no difficulties were encountered when making ×10 scale batches. Gel formulations 1 0.2 1; 0.75 0.15 1; 0.5 0.1 0.8; and 0.25 0.05 0.8 were made at 500 mL.
Some of the reactants used for making the gels were replaced by similar chemicals.
Gels 1 0.2 1; 0.75 0.15 1; and 0.5 0.1 1 were made by replacing 10% (by weight) of the magnesium hydroxide by calcium hydroxide (Ca(OH)2). Although, calcium hydroxide was somewhat more difficult to dissolve than the magnesium hydroxide, gels formed normally. These gels were slightly more alkaline than the pure-magnesium gels.
In gel 0.75 0.15 1, 10 to 100% (in increments of 10%) of the magnesium hydroxide was replaced by calcium chloride (CaCl2). Calcium chloride dissolved very well. Formulations with 10-70% of the magnesium hydroxide replaced produced gels. In particular, formulations with 10-30% produced good quality gels. Replacing more magnesium hydroxide (80-100%) yielded crystals.
When sodium hydroxide was replaced completely with potassium hydroxide (KOH), the products were crystalline.
Pyrophosphoric acid as a solid was added to the phosphoric acid. Pyrophosphoric acid dissolved readily. 1% (by weight) additions of pyrophosphoric acid to gels 1 0.2 1; 0.75 0.15 1; and 0.5 0.1 1 did not affect normal formation of the gels. However, this changed when the addition was increased to 10% weight. TABLE 2 shows the products of an array of gel formulations with 10% pyrophosphoric acid as an additive. In these experiments, 25 mL of phosphoric acid at 1M-0.5M was used. Solid pyrophosphoric acid was added to the phosphoric acid at 10% weight, which represented 2.5 g. Magnesium hydroxide was then dissolved in the acid at a concentration of 0.4M-0.2M. Then, 25 mL of sodium hydroxide at 1.0M was added to the mixture.
Pyrophosphoric acid is a very strong acid. It thus made the solution of phosphoric acid and magnesium hydroxide much more acidic than it would otherwise be. This meant that more magnesium hydroxide could be dissolved. In fact, the maximum concentration of magnesium hydroxide was 0.4M with pyrophosphoric acid compared to 0.2M without it. The increased initial acidity also meant that the gels formed were less alkaline. These gels indeed had pHs between 3.5 and 4.25.
Pyrophosphoric acid was added by mass as high as 50% at which point a hard white gel formed at high concentrations of magnesium hydroxide.
When pyrophosphoric acid replaced phosphoric acid in a typical gel such as 0.75 0.15 1, no product formed. However when the amount of magnesium hydroxide was increased to 0.3M, the pyrophosphoric acid gel 0.75 0.15 1 was a thick white gel.
10% pyrophosphoric acid was also added when making gels with 10-30% calcium chloride replacing the magnesium hydroxide. The products were thick white gels.
X-ray diffractograms of gels 1 0.2 1 and 0.5 0.1 1 and of the crystal products resulting of formulations 0.75 0.15 0.2; 0.5 0.1 0.8, and 0.25 0.05 0.4 were recorded.
The crystal products were identified as forms of magnesium phosphates. More specifically, the crystal product of 0.75 0.15 0.2 appear to contain Newberyite (MgHPO4:3H2O) as shown in
The gels did not dissolve or disintegrate when submerged in water.
When placed in an acidic solution, the gels dissolved over 24 hours. Many additives were tested to deter the gels from dissolving in an acidic solution. Table 3 shows how gels dissolved over 24 hours with different additives.
The acidic solutions used were sodium citrate/citric acid buffers. All experiments were done with 0.2 mL of gel. The corn oil, sodium metaphosphate, sodium pyrophosphate, sodium citrate, xanthan gum, sodium alginate, and chitosan solutions were prepared by taking a 0.5-0.125% (by weight) solution of the additive, mixing it with an equal volume of gel, and filtering the solution. The calcium chloride gels were made by replacing 10-30% of the magnesium hydroxide with calcium chloride in the actual production of the gel. The pyrophosphoric acid gels were prepared by adding 10% (weight) pyrophosphoric acid to the phosphoric acid before adding the magnesium hydroxide when producing the gels. And the ethanol and glycerol gels were made by dehydrating the gel in a solution of ethanol or glycerol.
The gels are over 90% water.
Dehydration of the gel involved removing that water and replacing it with ethanol and glycerol. Two pieces of gel (2 mL each) were placed in 20% ethanol and 20% glycerol solution. Every hour each beaker was drained of the solution and replaced with a 10% stronger solution. After 9 hours, the gels were finally placed in a 100% ethanol and 100% glycerol solution. At the end of this process, each gel had been drained of water and had absorbed its respective solution.
The following reagents were purchased from Sigma-Aldrich and used without further purification: magnesium hydroxide (MO), sodium hydroxide (SH) and phosphoric acid (PA).
The precipitation of magnesium phosphates in the presence of sodium ions was studied by dissolving magnesium hydroxide (300-0 mg) into to a 10 ml solution of phosphoric acid (1.0-0.0 M) and sodium hydroxide (1.0-0.0 M).
The magnesium hydroxide powder was first added to the phosphoric acid solution and mixed until it was dissolved. Then, sodium hydroxide (as a solution) was added to the mixture. Several batches representing different MO:PA:SH ratios were prepared.
The pH of the resulting solutions was measured, and the precipitates were washed and dried for analysis with EDX, transmission electron microscopy (TEM) and BET surface area analysis.
Phase composition of the precipitates was characterized with X-ray diffraction (XRD).
A vertical-goniometer X-ray diffractometer (Philips model PW1710, Bedrijven b. v. S&I, The Netherlands), equipped with a Cu Kα radiation source, was used for the powder diffraction pattern collection. Data was collected from 20° to 40° with a step size of 0.02° and a normalized count time of 1 s per step. The phase composition was examined by means of the International Centre for Diffraction Data (ICDD) reference patterns.
The gel sample was tested for rheological properties with a rheometer Rheostress I (Haake, Thermo) with two 20.0 mm parallel plates with a gap of 0.2 mm at 37° C.
The solutions where any one of magnesium, sodium, or phosphate was absent did not form gels. The solutions with more than 0.75 M of phosphoric acids did not form precipitates either. Solutions with magnesium hydroxide (0.25 M), phosphoric acid (0.4-0.5M), and sodium hydroxide (0.5-0.6 M) formed an amorphous gel. The remaining solutions precipitated to form crystals (see
Despite their high water content, the magnesium sodium phosphate gels obtained were stable in water, and could be injected into distilled water to form pellets.
Using X-ray diffraction analysis, the gel 0.75 0.15 1 appeared to be amorphous. Other precipitates obtained were Newberyite, Cattiite, Brucite (magnesium hydroxide), and mixtures of Cattiite with Brucite (see
To characterize the elemental composition of the solid and liquid phases of the gel, EDX analysis was performed on the gel 0.75 0.15 1 either (A) filtered-washed and dried (in vacuum at 40° C.) or (B) dried without filter-washing. The elemental composition of the washed and un-washed gels (as atomic percentage values) is presented in Table 4.
The un-washed gel had a high concentration of sodium phosphate, whereas the washed gel was composed of sodium magnesium phosphate. The ratio between magnesium and phosphate ions in the washed samples is 2.62, which indicates the presence of both di-magnesium and tri-magnesium phosphate species in the structure.
Thermogravimetry analysis (TGA) and differentials scanning calorimetric (DSC) analysis of washed and un-washed dried-gel samples were performed (see
Infrared spectroscopy was performed to characterize the chemical composition of the gels.
Very strong peaks at 980 cm−1 and 1062 cm−1 indicating PO stretching could be observed in all the samples. In addition, bands characteristic of di-phosphate groups (P—O(H)) were also detected in the dried-unwashed gel and in the washed-dried gel samples at 858 cm−1 and 1900-2100 cm−1. Also, bands characteristic of hydration water were observed at 1648 cm−1 and 2900-3400 cm−1. A band characteristic of Na2HPO4 was observed in the unwashed-dried samples at 1402 cm−1.
Rheological analysis revealed that the gel 0.75 0.15 1 had an extreme thixotropic behavior.
Upon TEM analysis, the gel 0.75 0.15 1 appeared to be formed of nanosheets that are about 200 nm wide, very thin and up 1 μm long. These nanosheets appeared crystalline when observed by TEM, although the gel itself appeared amorphous when studied by X-ray diffraction. The nanosheets in the original hydrated gel however appeared amorphous when studied by electron diffraction.
The dried gel had a BET specific surface area of BET 59.2087 m2/g and a density of 0.1527±0.0078 g/ml.
The above characterization of the sodium magnesium phosphate gel indicates that this material is composed of flat layered nano-crystals that are hydrated, and are composed of a mixture of di- and tri-phosphate ions combined with magnesium, and small amounts of sodium.
Gel 0.75 0.15 1 was tested for bioadhesion on explanted gastric mucosae. It proved highly adhesive to fresh gastric mucosa from a sacrificed rabbit over prolonged periods of agitation.
Gel 0.75 0.15 1 was also tested for cellular biocompatibility by cultivating human bone marrow stem cells into it, and tested for cytotoxicity. The test revealed over 50% cell survival within 24 hours, indicating good biocompatibility (see
Gel 0.75 0.15 1 was injected intramuscularly and subcutaneously in mice without causing any ill effects. Five days after injection, the animals were sacrificed. Histopathological examination revealed the gel had partially resorbed without causing any major inflammation at the injection site.
Gel 0.75 0.15 1 was dried into a xerogel forming translucent membranes that have a specific surface area of ˜60 m2/g and a density of 0.15 g/cm3.
Gel 0.75 0.15 1 was tested as a drug delivery system in two forms: totally hydrated (crude), and partially hydrated (dried by filtration).
The scope of the claims should not be limited by the preferred embodiments set forth in the above examples, but should rather be given the broadest possible interpretation consistent with the description as a whole.
The present description refers, above and below, to a number of documents, the content of which is herein incorporated by reference in their entirety.
This application claims benefit, under 35 U.S.C. §119(e), of U.S. provisional application Ser. No. 61/618,059, filed on Mar. 30, 2012.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CA2013/050250 | 3/28/2013 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61618059 | Mar 2012 | US |
