Patent Application
20120052234
The present invention relates to polymer-based structures having shapes and mechanical properties that optimize adhesion to a specific target, e.g., a tissue or organ target.
There is an ongoing need for adhesive structures having improved adhesion obtained through physical attractive forces. Such structures can be suited to use in various applications, such as medical applications, e.g., as an adjunct or replacement to sutures and staples used to close surgical incisions. For the adhered to substrate, e.g., living tissue, providing an adhesive structure that provides adhesive forces by non-chemical interactions between adhesive structure and substrate would be highly desirable.
Intermolecular forces are exerted by molecules on each other and affect the macroscopic properties of the material of which the molecules are a part. Such forces may be either attractive or repulsive in nature. They are conveniently divided into two classes: short-range forces, which operate when the centers of the molecules are separated by 3 angstroms or less, and long-range forces, which operate over greater distances.
Generally, if molecules do not interact chemically, the short-range forces between them are repulsive. These forces arise from interactions of the electrons associated with the molecules and are also known as exchange forces. Molecules that interact chemically have attractive exchange forces, also known as valence forces. Mechanical rigidity of molecules and effects such as limited compressibility of matter arise from repulsive exchange forces.
For present purposes, physical attractive forces are considered to be attractive forces that are not chemical in nature, e.g., not dependent on or associated with ionic bonding, covalent bonding, or hydrogen bonding. Physical attractive forces can include long-range forces or van der Waals forces as they are also called. These forces account for a wide range of physical phenomena, such as friction, surface tension (capillary actions), adhesion and cohesion of liquids and solids, viscosity and the discrepancies between the actual behavior of gases and that predicted by the ideal gas law. Typical bond energies from van der Waals forces are about 1 kcal/mol compared to about 6 kcal/mol for hydrogen bonds and about 80 kcal/mol for carbon-to-carbon bonds. Van der Waals forces arise in a number of ways, one being the tendency of electrically polarized molecules to become aligned. Quantum theory indicates also that in some cases the electrostatic fields associated with electrons in neighboring molecules constrain the electrons to move more or less in phase.
The London dispersion force otherwise known as quantum induced instantaneous polarization (one of the three types of van der Waals forces) is caused by instantaneous changes in the dipole of atoms, resulting from the location of the electrons in the atoms' orbitals. When an electron is on one side of the nucleus, this side becomes slightly negative (indicated by δ−); this in turn repels electrons in neighboring atoms, making these regions slightly positive (δ+). This induced dipole causes a brief electrostatic attraction between the two molecules. The electron immediately moves to another point and the electrostatic attraction is broken. London dispersion forces are typically very weak because the attractions are so quickly broken, and the charges involved are so small.
Despite the weakness of van der Waals forces, it has been recognized that such forces can contribute to adhesion by a structure formed in nature. For example, it has been observed that the adhesive force of a gecko's foot is attributable to the van der Waals forces generated by hundreds of thousands of fibrillar, hair-like microstructures known as setae, which terminate in even smaller structures (200 to 400 nanometers in diameter) known as spatulae. Such structure permits a gecko to climb even smooth surfaces such as vertical planes of glass, achieving adhesion without any requirement that the target substrate itself provide adhesive characteristics. Structures mimicking a gecko's foot have been attempted by various methods including nano-molding using a template, polymer self-assembly, lithography, and etching. However, such structures are inherently delicate and can suffer from durability problems in practical applications. Accordingly, structures offering adhesion attributable to van der Waals forces but with simpler shapes and construction are desirable.
U.S. Pat. No. 6,872,439 proposes a fabricated microstructure comprising at least one protrusion capable of providing an adhesive force at a surface of between about 60 and 2,000 nano-Newtons. A stalk supports the protrusion at an oblique angle relative to a supporting surface, and the microstructure can adhere to different surfaces.
U.S. Pat. No. 7,479,318 relates to a fibrillar microstructure and processes for its manufacture. These processes involve micromachining and molding, and can be used to prepare sub-micron dimensioned fibrillar microstructures of any shape from polymeric as well as other materials.
WO 2008076390 teaches dry adhesives and a method for forming a dry adhesive structure on a substrate by forming a template backing layer of energy sensitive material on the substrate, forming a template layer of energy sensitive material on the template backing layer, exposing the template layer to a predetermined pattern of energy, removing a portion of the template layer exposed to the predetermined pattern of energy, and leaving a template structure formed from energy sensitive material and connected to the substrate through the template backing layer.
WO 2009067482 proposes an adhesive article that includes a biocompatible and at least partially biodegradable substrate having a surface; and a plurality of protrusions extending from the surface. The protrusions include a biocompatible and at least partially biodegradable material, and have an average height of less than approximately 1,000 micrometers.
A review of the prior art shows use of micro-nano structures on polymer substrates for adhesion to tissue (WO 2009067482), but the materials used to fabricate these structures comprise “softer” polymers, i.e., polymers or polymer mixtures having a Young's modulus ≦17 MPa. Moreover, they do not provide a solution for adhesion to specific types of tissue.
It would be desirable to provide an adhesive structure without relying solely on surface chemical groups to provide acceptable conformal contact and adhesion with its intended target surface.
It would also be desirable to provide an adhesive structure that has a stiffness (Young's modulus) greater than 17 MPa that provides a means by which a fluid such as the tissue's own fluid or a chemical group such as a fibrin sealant can wick into the structure to enhance adhesion with its intended target surface.
The present invention relates to polymer-based, adhesive micro-nano structures with formed surface features and mechanical properties that optimize adhesion to a specific target. The present invention relates to structures containing pillar-like projections which can be of a specific diameter, length, and aspect ratio (length/diameter) or spacing and can be fabricated with stiff polymers. The shape of the structure can be formed to enhance adhesion to specific substrates, e.g., certain tissue types. Suitable polymers for use in the present invention include stiff polymers having Young's modulus >17 MPa that can be hydrophilic or hydrophobic, or bio-absorbable or non bio-absorbable, depending on their intended use and target substrate.
In one aspect, the present invention relates to an adhesive structure comprising a substrate with a surface from which extend protrusions, e.g., substantially cylindrical protrusions, comprising a resin having a Young's modulus of greater than 17 MPa, as measured by ASTM standard D412-98a, which protrusions are of sufficiently low average diameter to promote adhesion by increasing physical attractive forces, e.g., van der Waals attractive forces, between the adhesive structure and a target surface to which the adhesive structure is to be adhered, as measured by shear adhesion. For present purposes, a resin can be defined as any of a class of solid or semisolid viscous substances obtained either as exudations from certain plants or prepared by polymerization of simpler molecules. Resins can include single polymer compounds or mixtures of polymer compounds.
For purposes of the present invention, a target surface can include biological tissue, or non-tissue, e.g., a surface associated with a medical device. In certain embodiments, the target surface can be associated with the adhesive structure itself, e.g., in the case of a substrate or film comprising protrusions on either side, which can be utilized as a double-sided adhesive tape. Such double-sided embodiments can even be wrapped around itself or a similar adhesive structure, to provide adhesion at least partially promoted by physical attractive forces.
In still another aspect, the present invention relates to an adhesive structure comprising a two-sided substrate from each side of which extend protrusions comprising one or more resins having a Young's modulus of greater than 17 MPa, which protrusions are of sufficiently low diameter to promote adhesion by increasing physical attractive forces, as measured by shear adhesion between the adhesive structure and a target surface.
In another aspect, the present invention relates to an adhesive structure comprising a substrate with a surface from which extend protrusions, e.g., substantially cylindrical protrusions, comprising a resin having a Young's modulus of greater than 17 MPa, as measured by ASTM standard D412-98a, which protrusions are of sufficiently low average diameter to promote adhesion by increasing physical attractive forces between the adhesive structure and a target surface to which the adhesive structure is to be adhered, as measured by shear adhesion, wherein the substrate surface contains reactive chemical groups that interact with the target surface.
In another aspect, the present invention relates to a method for providing an adhesive structure adherable to a target surface which comprises: a) measuring surface roughness of the target surface to determine average dimensions of microstructures associated with the surface; and b) forming a polymer-containing adhesive structure comprising a substrate having an adhesive surface which includes protrusions, e.g., pillar-like protrusions, of sufficient height, diameter, and aspect ratio for the surface to interact with the microstructures on the target surface to promote adhesion by van der Waals attractive forces between the adhesive structure and the target surface, as measured by shear adhesion. For present purposes, microstructures include micron-dimensioned and sub-micron-dimensioned structures, e.g., nano-dimensioned structures, of any shape, e.g., fibrillar microstructures or pillar-like microstructures, whose lengths (or heights) typically exceed their diameters.
In still another aspect, the present invention relates to a method of providing an adhesive structure adherable to a target surface which comprises: a) measuring surface roughness of the target surface to determine the average longest dimension of microstructures associated with the surface roughness; b) forming a polymer-containing adhesive structure comprising an adhesive surface which includes protrusions of a sufficiently low average diameter to interact with target microstructures on the target surface to promote adhesion by physical attractive forces, e.g., Van der Waals attractive forces, between the adhesive structure and the target surface, as measured by shear adhesion.
In yet another aspect, the present invention relates to a method for preparing an adhesive structure which comprises: a) providing a specific solvent-dissolvable mold including indentations; b) introducing a stiff polymer having a Young's modulus of greater than 17 MPa or a precursor to the stiff polymer, to the mold under conditions, e.g., temperatures and pressures, sufficient to permit filling the indentations of the mold by the polymer, said polymer being substantially non-dissolvable by the specific solvent; c) cooling the mold and polymer of step b) to an extent sufficient to substantially solidify the polymer; d) releasing pressure on the mold and polymer of step c); and e) exposing the mold and polymer to the specific solvent under mold-dissolving conditions to provide a molded polymer substrate material having a Young's modulus of greater than 17 MPa comprising protrusions conforming to the indentations of the mold. In certain embodiments of the invention, the stiff polymer can be provided as a meltable polymer. In some embodiments the stiff polymer can be provided as a soluble polymer, i.e., a polymer which can be provided dissolved in a “non-specific solvent,” hereinafter defined. In some embodiments, introducing a stiff polymer having a Young's modulus of greater than 17 MPa to the mold can be carried out by providing monomer precursors which can be polymerized within the mold. In other embodiments of the invention, introducing a stiff polymer having a Young's modulus of greater than 17 MPa to the mold can be carried out by providing a precursor polymer mixture comprising soluble polymer and non-specific solvent, or comprising soluble polymer precursors and non-specific solvent, into the mold and evaporating off the non-specific solvent. By “non-specific solvent” is meant a solvent which will dissolve the ultimate stiff polymer product or its precursors, without substantially dissolving the “specific solvent dissolvable mold.”
In another aspect, the present invention relates to a method for preparing an adhesive structure which comprises: a) providing a specific solvent-dissolvable mold including indentations; b) providing to the mold a polymer in a mold-conformable condition having a Young's modulus of greater than 17 MPa under conditions sufficient to permit filling the indentations of the mold by the polymer, said polymer being substantially non-dissolvable by the specific solvent; c) treating the mold and polymer of step b) to an extent sufficient to substantially solidify the polymer; and d) exposing the mold and polymer to the specific solvent under mold-dissolving conditions to provide a molded polymer substrate material having a Young's modulus of greater than 17 MPa comprising protrusions conforming to the indentations of the mold.
In still another aspect, the present invention relates to a combination of an adhesive structure and a target to which the adhesive structure is adherable, wherein the adhesive structure comprises a surface from which extend substantially cylindrical protrusions comprising a resin having a Young's modulus of greater than 17 MPa, which protrusions are of sufficiently low average diameter and sufficient average length to promote adhesion by Van der Waals attractive forces between the adhesive structure and target, as measured by shear adhesion.
Young's modulus (E) is a measure of the stiffness of an isotropic elastic material. It is also known as the Young modulus, modulus of elasticity, elastic modulus (though Young's modulus is actually one of several elastic moduli such as the bulk modulus and the shear modulus) or tensile modulus. It is defined as the ratio of the uniaxial stress over the uniaxial strain in the range of stress in which Hooke's Law holds. This can be experimentally determined from the slope of a stress-strain curve created during tensile tests conducted on a sample of the material. Young's modulus quantifies the elasticity of the polymer. It is defined, for small strains, as the ratio of rate of change of stress to strain. Like tensile strength, this is highly relevant in polymer applications involving the physical properties of polymers, such as rubber bands. The modulus is strongly dependent on temperature.
Young's modulus, E, can be calculated by dividing the tensile stress by the tensile strain:
where
E is the Young's modulus (modulus of elasticity)
F is the force applied to the object;
A0 is the original cross-sectional area through which the force is applied;
ΔL is the amount by which the length of the object changes;
L0 is the original length of the object.
For present purposes, Young's modulus can be measured in accordance with ASTM standard D412-98a.
For present purposes, target surface roughness can be defined as the average longest dimension of the particles or microstructures that provide roughness to a surface of the target. For a spherical or roughly spherical shape, the diameter can be considered the longest dimension. Standard surface roughness analysis can be carried out by microscopy techniques such as scanning electron microscopy (SEM), atomic force microscopy (AFM) and optical interferometric profiling. Another method of determining roughness is by comparison of a surface with silicon carbide grinding papers of different FEPA (Federation of European Producers Association) surface roughnesses—P#4000 (3 microns size grains), P#2400 (8 microns size grains) and P#500 (30 microns size grains). These grains are roughly spherical and their size determined by their largest dimension.
For purposes of the present invention, a target surface can include biological tissue, or non-tissue, e.g., a surface associated with a medical device or prosthetic. In certain embodiments, the target surface can be associated with the adhesive structure itself, e.g., in the case of a substrate or film comprising protrusions on either side, which can be utilized as a double-sided adhesive tape. Such a double-sided embodiment can even be wrapped around itself or a similar adhesive structure, to provide adhesion at least partially promoted by physical attractive forces.
The polymer substrates of which the structures are made are typically stiff, with a Young's modulus greater than 17 MPa, and can be hydrophilic or hydrophobic. The dimensions of the nanostructures are engineered for adhesion to specific targets with a diameter from 0.1-5 microns and height greater than 1 micron. The dimensions are tailored to match the dimensions of the substrate so that maximum adhesion can be had. Polymers used may be biodurable such as polypropylene (PP) or bioabsorbable such as poly(lactic-co-glycolic acid) (PLGA) and polydioxanone (PDO).
As earlier noted, in one aspect the present invention relates to an adhesive structure comprising a surface from which extend protrusions comprising a resin having a Young's modulus of greater than 17 MPa, which protrusions are of sufficiently low diameter to promote adhesion by increasing physical attractive forces, e.g., Van der Waals attractive forces between the adhesive structure and a target surface, as measured by shear adhesion.
In one embodiment, the protrusions have an average diameter ranging from 0.2 to 5 microns, an average length greater than 1 micron and an aspect ratio (length/diameter) of 1 to 33
In another embodiment, the protrusions have an average diameter ranging from 0.2 to 2 microns, an average length greater than 3 microns and an aspect ratio (length/diameter) of 2 to 30.
In still another embodiment, the structure is integrally molded from a resin selected from at least one of thermoplastic resin, thermosetting resin, and curable resin. By integrally molded is meant that the structure is formed in one piece, including its protrusions, from a mold. For present purposes, thermoplastic resin is a resin that softens when heated and hardens again when cooled. Thermosetting resin is a resin that hardens when heated, cannot be remolded and is deformable from a solid to a liquid. Curable resins are resins that are toughened or hardened by cross-linking of their polymer chains, brought about by chemical additives, ultraviolet radiation, electron beam, and/or heat.
In yet another embodiment, the resin comprises at least one polymer having a Young's modulus of greater than 17 MPa.
In still yet another embodiment, the resin comprises at least one polymer having a Young's modulus ranging from 20 MPa to 5 GPa.
In yet still another embodiment, the polymer is selected from at least one of a thermoplastic polymer. For present purposes, thermoplastic polymer is a polymer that softens when heated and hardens again when cooled.
In another embodiment, the polymer is selected from at least one of poly(lactic-co-glycolic acid) (PLGA), polylactic acid (PLA), polydioxanone (PDO), poly(trimethylene carbonate), poly(caprolactone-co-glycolide) and polypropylene (PP).
In still another embodiment, the resin is hydrophobic. For present purposes, a hydrophobic resin is a resin that does not substantially absorb, or be wetted by, water.
In yet another embodiment, the resin is hydrophobic and comprises a polymer selected from aliphatic polyesters, and polypropylenes.
In still yet another embodiment, the resin is hydrophilic. For present purposes, hydrophilic resins are resins that have a Young's modulus greater than 17 MPa and can be generally classified by their interaction with water into roughly two types, water-soluble resins and water-absorbent resins. Water-soluble resins are hydrophilic resins of the type which dissolve in water and are used, for example, as water treatment grade flocculants, oil drilling additives, food additives, and viscosity enhancers. Absorbent resins are water-insoluble hydrophilic resins of the type which absorb water and consequently undergo gelation and are widely used in the fields of agriculture and forestry and in the field of civil engineering as well as in the field of hygienic materials such as disposable diapers and sanitary napkins. In yet still another embodiment, the hydrophilic resin comprises a polymer selected from polyoxaesters, hyaluronic acids, and polyvinyl alcohols.
In another embodiment, the polymer is a biodegradable polymer. For present purposes, a biodegradable polymer is a polymer capable of being decomposed by the action of biological agents, e.g., bacteria, enzymes or water.
In still another embodiment, the polymer is a biodegradable polymer selected from aliphatic polyesters, poly (amino acids), copoly (ether-esters), polyalkylenes oxalates, tyrosine-derived polycarbonates, poly (iminocarbonates), polyorthoesters, polyoxaesters, polyamidoesters, polyoxaesters containing amine groups, poly (anhydrides), polyphosphazenes, collagen, elastin, hyaluronic acid, laminin, gelatin, keratin, chondroitin sulfate, polyglycolide (PGA), poly(propylenefumarate), poly(cyanoacrylate), polycaprolactone (PCL), poly(trimethylene carbonate), poly(lactide), poly(dioxanone), poly(glycerol sebacate) (PGS), poly(glycerol sebacate acrylate) (PGSA), and biodegradable polyurethanes.
In yet another embodiment, the polymer is a non-biodegradable polymer. For present purposes, a non-biodegradable polymer is a polymer that is not capable of being decomposed by the action of biological agents, e.g., bacteria, enzymes, or water.
In still yet another embodiment, the polymer is a non-biodegradable polymer selected from acrylics, polyamide-imide (PAI), polyetherketones (PEEK), polycarbonate, polyethylenes (PE), polybutylene terephthalates (PBT), polyethylene terephthalates (PET), polypropylene, polyamide (PA), polyvinylidene fluoride (PVDF), and polyvinylidene fluoride-co-hexafluoropropylene (PVDF/HFP), polymethylmethacrylate (PMMA), polyvinylalcohol (PVA), polyhydroxyethylmethacrylate, polyvinylalcohol (PVA), polyhydroxyethylmethacrylate (PHEMA), poly(N-isopropylacrylamide) (PNIPAAm), and polyolefins.
In yet still another embodiment, the adhesive structure surface is substantially planar and the protrusions are within ±45 degrees of normal to the planar surface.
In still yet another embodiment, the adhesive structure surface is substantially planar and the protrusions are within ±30 degrees of normal to the planar surface
In another embodiment, the adhesive structure has a protrusion density of from 1×105 to 6×108 protrusions/cm2. For present purposes, “protrusion density” can be described as the number of protrusions or pillars present per square centimeter of adhesive structure surface.
In still another embodiment, the adhesive structure has a density of protrusions on its surface ranging from about 10×106 to about 50×106 protrusions per cm2.
In yet another embodiment, at least a portion of the adhesive structure has a dry adhesive strength of at least 3 N/cm2 of projected area when measured according to ASTM standard D4501.
In still yet another embodiment, at least a portion of the adhesive structure has a wet adhesive strength of at least 0.5 N/cm2 of projected area when measured according to ASTM standard D4501.
In yet still another embodiment, the polymer is selected from at least one of poly(lactic-co-glycolic acid) (PLGA), polylactic acid (PLA), polydioxanone (PDO), poly(glycolide), poly(trimethylene carbonate), poly(glycolide) and polypropylene (PP) and adhesion is measured by adhesive force measurements and ranges from 0.1 to 0.5 N/cm2 on a target surface having a roughness of 0.1 to 8 microns.
In another embodiment, the adhesive structure is at least partially formed by a process selected from nanomolding using a template, polymer self-assembly, lithography, and etching.
As earlier noted, in another aspect the present invention relates to an adhesive structure comprising a two-sided substrate from each side of which extend protrusions comprising one or more resins having a Young's modulus of greater than 17 MPa, which protrusions are of sufficiently low diameter to promote adhesion by increasing physical attractive forces between the adhesive structure and a target surface, as measured by shear adhesion.
In one embodiment of this aspect, the protrusions have an average diameter ranging from 0.2 to 5 microns, an average length greater than 1 micron and an aspect ratio (length/diameter) of 1 to 33.
In another embodiment, the protrusions have an average diameter ranging from 0.2 to 2 microns, an average length greater than 3 microns and an aspect ratio (length/diameter) of 2 to 30.
In still another embodiment, the structure is integrally molded from a resin selected from at least one of thermoplastic resin, thermosetting resin, and curable resin.
In yet another embodiment, the resin comprises at least one polymer having a Young's modulus of greater than 17 MPa.
In still yet another embodiment, the resin comprises at least one polymer having a Young's modulus ranging from 20 MPa to 5 GPa.
In yet still another embodiment, the polymer is selected from at least one of a thermoplastic polymer.
In another embodiment, the polymer is selected from at least one of poly(lactic-co-glycolic acid) (PLGA), polylactic acid (PLA), polydioxanone (PDO), poly(trimethylene carbonate), poly(caprolactone-co-glycolide) and polypropylene (PP).
In still another embodiment, the resin is hydrophobic.
In yet another embodiment, the resin is hydrophobic and comprises a polymer selected from aliphatic polyesters, and polypropylenes.
In still yet another embodiment, the resin is hydrophilic.
In yet still another embodiment, the hydrophilic resin comprises a polymer selected from polyoxaesters, hyaluronic acids, and polyvinyl alcohols.
In another embodiment, the polymer is a biodegradable polymer.
In still another embodiment, the polymer is a biodegradable polymer selected from aliphatic polyesters, poly (amino acids), copoly (ether-esters), polyalkylenes oxalates, tyrosine-derived polycarbonates, poly (iminocarbonates), polyorthoesters, polyoxaesters, polyamidoesters, polyoxaesters containing amine groups, poly (anhydrides), polyphosphazenes, collagen, elastin, hyaluronic acid, laminin, gelatin, keratin, chondroitin sulfate, polyglycolide (PGA), poly(propylenefumarate), poly(cyanoacrylate), polycaprolactone (PCL), poly(trimethylene carbonate), poly(lactide), poly(dioxanone), poly(glycerol sebacate) (PGS), poly(glycerol sebacate acrylate) (PGSA), and biodegradable polyurethanes.
In yet another embodiment, the polymer is a non-biodegradable polymer.
In still yet another embodiment, the polymer is a non-biodegradable polymer selected from acrylics, polyamide-imide (PAI), polyetherketones (PEEK), polycarbonate, polyethylenes (PE), polybutylene terephthalates (PBT), polyethylene terephthalates (PET), polypropylene, polyamide (PA), polyvinylidene fluoride (PVDF), and polyvinylidene fluoride-co-hexafluoropropylene (PVDF/HFP), polymethylmethacrylate (PMMA), polyvinylalcohol (PVA), polyhydroxyethylmethacrylate, polyvinylalcohol (PVA), polyhydroxyethylmethacrylate (PHEMA), poly(N-isopropylacrylamide) (PNIPAAm), and polyolefins.
In yet still another embodiment, the adhesive structure surface is substantially planar and the protrusions are within ±45 degrees of normal to the planar surface.
In another embodiment, the adhesive structure has a protrusion density of from 1×105 to 6×108 protrusions/cm2.
In yet another embodiment, at least a portion of the adhesive structure has a dry adhesive strength of at least 3 N/cm2 of projected area when measured according to ASTM standard D4501.
In still yet another embodiment, at least a portion of the adhesive structure has a wet adhesive strength of at least 0.5 N/cm2 of projected area when measured according to ASTM standard D4501.
In yet still another embodiment, the polymer is selected from at least one of poly(Iactic-co-glycolic acid) (PLGA), polylactic acid (PLA), polydioxanone (PDO), poly(glycolide), poly(trimethylene carbonate), poly(glycolide) and polypropylene (PP) and adhesion is measured by adhesive force measurements and ranges from 0.1 to 0.5 N/cm2 on a target surface having a roughness of 0.1 to 8 microns.
In another embodiment, the adhesive structure is at least partially formed by a process selected from nanomolding using a template, polymer self-assembly, lithography, and etching.
In yet another embodiment, the two-sided substrate comprises one or more extruded resin layers.
In still another embodiment, the adhesive structure two-sided substrate comprises two or more co-extruded resin layers, each of which resin layer can be the same as or different from another resin layer of the substrate.
In still yet another embodiment, the two-sided substrate is derived from a film co-extruded from more than one resin.
In yet still another embodiment, the two-sided substrate is selected from a single layer substrate comprising a core layer, a double layer substrate comprising two skin layers, and a triple layer substrate having a core layer and two skin layers.
As earlier noted, in another aspect, the present invention relates to an adhesive structure comprising a surface from which extend protrusions comprising a resin having a Young's modulus of greater than 17 MPa, which protrusions are of sufficiently low diameter to promote adhesion by increasing physical attractive forces, as measured by shear adhesion, between the adhesive structure and a target surface, said adhesive structure further comprising chemical groups on at least a portion of the adhesive structure surface, capable of interacting with the target surface.
In an embodiment of this aspect of the invention, the chemical groups are provided by cyanoacrylates, fibrin sealants, hydroxysuccinimides, acrylates, and aldehydes.
In another embodiment of this aspect of the invention, the chemical groups are provided by fibrin sealants.
In another embodiment, the protrusions have an average diameter ranging from 0.2 to 2 microns, an average length greater than 3 microns and an aspect ratio (length/diameter) of 2 to 30.
In still another embodiment, the structure is integrally molded from a resin selected from at least one of thermoplastic resin, thermosetting resin, and curable resin.
In yet another embodiment, the resin comprises at least one polymer having a Young's modulus of greater than 17 MPa.
In still yet another embodiment, the resin comprises at least one polymer having a Young's modulus ranging from 20 MPa to 5 GPa.
In yet still another embodiment, the polymer is selected from at least one of a thermoplastic polymer.
In another embodiment, the polymer is selected from at least one of poly(lactic-co-glycolic acid) (PLGA), polylactic acid (PLA), polydioxanone (PDO), poly(trimethylene carbonate), poly(caprolactone-co-glycolide) and polypropylene (PP).
In still another embodiment, the resin is hydrophobic.
In yet another embodiment, the resin is hydrophobic and comprises a polymer selected from aliphatic polyesters, and polypropylenes.
In still yet another embodiment, the resin is hydrophilic.
In yet still another embodiment, the hydrophilic resin comprises a polymer selected from polyoxaesters, hyaluronic acids, and polyvinyl alcohols.
In still another embodiment, the polymer is a biodegradable polymer selected from aliphatic polyesters, poly (amino acids), copoly(ether-esters), polyalkylenes oxalates, tyrosine-derived polycarbonates, poly (iminocarbonates), polyorthoesters, polyoxaesters, polyamidoesters, polyoxaesters containing amine groups, poly (anhydrides), polyphosphazenes, collagen, elastin, hyaluronic acid, laminin, gelatin, keratin, chondroitin sulfate, polyglycolide (PGA), poly(propylenefumarate), poly(cyanoacrylate), polycaprolactone (PCL), poly(trimethylene carbonate), poly(lactide), poly(dioxanone), poly(glycerol sebacate) (PGS), poly(glycerol sebacate acrylate) (PGSA), and biodegradable polyurethanes.
In still yet another embodiment, the polymer is a non-biodegradable polymer selected from acrylics, polyamide-imide (PAI), polyetherketones (PEEK), polycarbonate, polyethylenes (PE), polybutylene terephthalates (PBT), polyethylene terephthalates (PET), polypropylene, polyamide (PA), polyvinylidene fluoride (PVDF), and polyvinylidene fluoride-co-hexafluoropropylene (PVDF/HFP), polymethylmethacrylate (PMMA), polyvinylalcohol (PVA), polyhydroxyethylmethacrylate, polyvinylalcohol (PVA), polyhydroxyethylmethacrylate (PHEMA), poly(N-isopropylacrylamide) (PNIPAAm), and polyolefins.
In yet still another embodiment, the adhesive structure surface is substantially planar and the protrusions are within ±45 degrees of normal to the planar surface.
In another embodiment, the adhesive structure has a protrusion density of from 1×105 to 6×108 protrusions/cm2.
In yet another embodiment, at least a portion of the adhesive structure has a dry adhesive strength of at least 3 N/cm2 of projected area when measured according to ASTM standard D4501.
In still yet another embodiment, at least a portion of the adhesive structure has a wet adhesive strength of at least 0.5 N/cm2 of projected area when measured according to ASTM standard D4501.
In yet still another embodiment, the polymer is selected from at least one of poly(lactic-co-glycolic acid) (PLGA), polylactic acid (PLA), polydioxanone (PDO), poly(glycolide), poly(trimethylene carbonate), poly(glycolide) and polypropylene (PP) and adhesion is measured by adhesive force measurements and ranges from 0.1 to 0.5 N/cm2 on a target surface having a roughness of 0.1 to 8 microns.
In another embodiment, the adhesive structure is at least partially formed by a process selected from nanomolding using a template, polymer self-assembly, lithography, and etching.
In still another embodiment, the adhesive structure comprises a two-sided substrate from each side of which extend the protrusions.
In yet another embodiment, the two-sided substrate comprises one or more extruded resin layers.
In still another embodiment, the two-sided substrate comprises two or more co-extruded resin layers, each of which resin layer can be the same as or different from another resin layer of the substrate.
In still yet another embodiment, the two-sided substrate is derived from a film co-extruded from more than one resin.
In yet still another embodiment, the two-sided substrate is selected from a single layer substrate comprising a core layer, a double layer substrate comprising two skin layers, and a triple layer substrate having a core layer and two skin layers.
In another embodiment of this aspect, the chemical groups are selected from pressure sensitive adhesives such as acrylates, adhesives applied in the molten state (hot melt adhesives), solvent based adhesives such as poly(vinyl acetate), multi-part adhesives that can be cured by radiation, heat or moisture such as cyanoacrylates, and urethanes, natural sealants such as fibrin sealants and starches, hydroxysuccinimides, and aldehydes.
As earlier noted, another aspect of the invention is directed to a method of providing an adhesive structure adherable to a target surface which comprises: a) measuring surface roughness of the target surface to determine the average longest dimension of microstructures associated with the surface roughness; and b) forming a polymer-containing adhesive structure comprising an adhesive surface which includes protrusions of a sufficiently low average diameter to interact with target microstructures on the target surface to promote adhesion by increasing physical attractive forces between the adhesive structure and the target surface, as measured by shear adhesion.
In one embodiment, the polymer has a Young's modulus above 17 MPa.
In another embodiment, the target surface comprises biological tissue.
In still another embodiment, the target surface is selected from at least one of bladder tissue and intestinal tissue.
As earlier noted, yet another aspect of the invention relates to a method for preparing an adhesive structure which comprises: a) providing a specific solvent-dissolvable mold including indentations; b) providing a meltable polymer having a Young's modulus of greater than 17 MPa to the mold under conditions sufficient to permit filling the indentations of the mold by the polymer, said polymer being substantially non-dissolvable by the specific solvent; c) treating the mold and polymer of step b) to an extent sufficient to substantially solidify the polymer; and d) exposing the mold and polymer to the specific solvent under mold-dissolving conditions to provide a molded polymer substrate material having a Young's modulus of greater than 17 MPa comprising protrusions conforming to the indentations of the mold. Optionally, this aspect further comprises at least one of the following conditions:
For present purposes, a meltable polymer can include a single polymer or a mixture of polymers.
In one embodiment, the first stage is carried out at a temperature ranging from 90 to 110° C., pressure ranging from about 0 to about 20 kPa (about 0 to about 20 Bar), for a duration of 7 to 12 minutes, and the second stage is carried out at a temperature ranging from 90 to 110° C., pressure ranging from about 6 to about 20 kPa (about 6 to about 20 Bar), for a duration of 15 to 25 minutes.
In another embodiment of this aspect, step b) provides a solvent-dissolvable mold to both surfaces of the meltable polymer film, yielding a molded polymer substrate material comprising substantially cylindrical protrusions extending from both sides of the film.
In another embodiment of this aspect of the invention, step b) provides a solvent-dissolvable mold to both surfaces of the polymer film, yielding a molded polymer substrate material comprising protrusions extending from both sides of the film.
In yet another embodiment, step b)'s conditions are sufficient to permit filling the indentations of the mold by the polymer and include pressures provided by upper and lower horizontal opposing surfaces, between which surfaces is positioned a space-filling shim surrounding an opening in which are placed from the bottom 1) a first solvent-dissolvable mold layer, 2) a meltable polymer layer, and 3) a second solvent-dissolvable mold layer, and further wherein, 4) an optional protective layer is provided between the lower horizontal opposing surface and the first solvent-dissolvable mold layer and 5) an optional protective layer is provided between the upper horizontal opposing surface and the second solvent-dissolvable mold layer.
The invention is further explained in the description that follows with reference to the drawings illustrating, by way of non-limiting examples, various embodiments of the invention.
The aim of this example was to fabricate polypropylene films with pillar like protrusions. A commercial track etched polycarbonate membrane was obtained from Millipore Corporation of Billerica, Mass., USA having pores of 0.6 microns diameter and a circular diameter of 2.5 cm, with a thickness of 20 microns. The membrane was used as a template to imprint a solvent-resistant polypropylene (PP) polymer film of 300 microns thickness, obtained from Ethicon, Inc. of Somerville, N.J., USA. The polypropylene film was pressed into the polycarbonate membrane template under controlled temperature and pressures (180° C., 600 kPa (6 bar)) for 20 minutes, melting the polypropylene and forming an overfilling of polypropylene to the top side of the membrane. The polypropylene polymer and the membrane are cooled to 175° C. before removal of pressure, after which the polymer structures are de-molded and released by dissolving the membrane in dichloromethane. The overfilling of polypropylene holds the resulting pillar-like structures in place in the subsequent removal of the membrane by dissolving with dicholoromethane. After the membrane was completely dissolved and dried, the substrate was exposed to oxygen plasma to etch the overfilled layer of polymer on top, thereby releasing the pillar-like structures.
The aim of this example was to develop an accurate and reproducible test method to measure shear adhesion. Modifications were made to the mechanical testing instrument sold under the tradename INSTRON by Instron Industrial Products, Grove City, Pa. The mechanical testing set up was modified to improve the precision and reproducibility of the shear adhesion measurements of the films having pillar-like structures. The modifications were made to decrease the source of noise from the hardware components and control the preload or initial contact force between the adhesive surfaces. The standard clamp operated with compressed air to grip the glass slide was replaced by a fixed rigid clamp and the length of the glass slide was shortened to reduce noise due to cantilever bending effect. Similarly, the length of the lower glass slide was shortened to reduce noise. A solid block of aluminum was used as a backing for the glass slide. A control of preload was added consisting of: a spring gauge to the preload force between the surfaces. The spring gauge consisted of a spring that is translated to distance when a force is applied. The spring constant was measured and 20 mN of load translated to 10 units on the dial. As the spring constant was linear, the amount of preload was varied by reading the displacement of the dial in the gauge. During testing, the spring gauge was first brought in light contact with the upper glass slide. Using the XY stage, the lower glass slide was brought in contact with the upper glass slide and a displacement shown on the dial. For all the tests, 30 mN of preload was set (literature values vary from 20-40 mN). After the preload was set, the spring gauge was removed to prevent noise from the spring when the tester was in motion. With the rigid upper clamp, preload was constant throughout the duration of the tests, maintaining a constant preload value from sample to sample to compare adhesion values.
The polypropylene pillared substrate prepared as described in Example 1 as well as its corresponding flat surface film (unpillared) were tested for shear adhesion against substrates (sandpaper) with varying surface roughness values under wet conditions i.e. the substrates and the structures were immersed in DI water and the mechanical testing was then conducted by the method described in Example 2. This was done to mimic the wet conditions that exist in-vivo. The surface roughness value represents the average feature dimensions expected for different surfaces. These tests were performed using a mechanical tester sold under the tradename INSTRON (lnstron Industrial Products, Grove City, Pa.) and the results are summarized in
From this data we have shown that the dimensions of the pillar-like protrusions need to be tailored to match the substrate roughness for maximum adhesion.
The polypropylene pillared substrate prepared as described in Example 1 as well as its corresponding flat surface film (unpillared) were tested against, two tissue types, porcine intestine and porcine bladder for tissue adhesion using the methods described in Example 5. Adhesive force was measured with a 1.8 kg (four pound) preload for two minutes. These tissues differ in characteristics such as elasticity, thickness, and surface roughness. The shear adhesion data is shown in
The aim of this example was to develop an accurate and reproducible test method to measure shear adhesion to tissue samples. Shear adhesion values of polypropylene samples of the present invention against freshly harvested tissue were measured on a mechanical testing instrument sold under the tradename INSTRON by Instron Industrial Products, Grove City, Pa. The polymer sample was made on a polymer substrate and the fresh tissue was soft and flexible. The tissue was mounted in the apparatus shown in
After the appropriate amount of time, the preload force was removed by pulling back on the lever arm. The load as read by the mechanical tester was zeroed and test was then commenced. For the test method, the glass slide was pulled upwards at the rate of 8 mm/min and the force was recorded. The maximum force was then recorded as a measure of the shear adhesive force.
The polypropylene samples prepared as described in Example 1 were tested for tissue adhesion against three tissue types i.e. intestine, bladder and epithelium, using the methods described in Example 5. The results are shown in
In order to determine the effect of pillar dimensions, polypropylene samples with different pillar dimensions (about 0.6 micron diameter×about 20 microns length and about 5 microns diameter×about 15 microns length) prepared as in Example 1 were tested against two tissue types, i.e., intestine and epithelium, as described in Example 5. As mentioned earlier, the intestine tissue was smoother than the epithelial tissue. From the results shown in
An experiment was conducted to prepare a polypropylene film with pillar-like structures on both sides and test its effectiveness for adhesion to tissue. The polypropylene film with pillar-like structures on both sides were prepared as follows: A 25 microns thick polypropylene film was compressed under heat and pressure between two 20 microns thick sheets of polycarbonate filter material, which polycarbonate filter material thickness corresponds to the desired length (or height) of the pillar-like structures to be formed. The filter material possessed microscopic (0.8 micron) holes, which correspond to the eventual diameter of the pillar-like structures to be formed. The polypropylene film melted and flowed into the holes. After processing, the sheet was annealed. The polycarbonate membrane filter was then dissolved in a bath of dichloromethane. The membrane filters (0.8 micron ATTP, Cat No. ATTP14250, Lot No. R9SN70958, available from Millipore Corporation of Billerica, Mass., USA) possessed two distinct sides, one having a shiny appearance while the other side was duller. A laminate for compression molding was constructed as follows:
Any thermoformable material as previously described can be substituted for polypropylene as the substrate or core material. The porous solvent-dissolvable polycarbonate material which acts as a template for the pillar-like protrusions of the product can be substituted by another solvent-dissolvable porous polymeric material. Alternately, a strippable mold such as anodized aluminum oxide can be substituted to provide the pillar-like cylindrical protrusions of the final product, without the need for exposure to a chemical solvent. Polyimide film was used as a capping means or shield to protect polymer surfaces from directly contacting surfaces such as metal. Other suitable substantially chemically inert materials which can also be provided as a film or other layer for this purpose include polytetrafluoroethylene (sold under the tradename TEFLON by DuPont, Wilmington, Del.). Advantageously, these materials are not reactive with the polycarbonate solvent-dissolvable mold or template material and can be readily removed or peeled therefrom once compression is completed.
The resulting sample was loaded into a heated press with vacuum (less than 150 microns mercury) capability and was processed as follows:
The sample was annealed in the constrained condition (between two steel plates) in an oven purged with nitrogen gas at 130° C. immediately for two hours. Temperature was reduced to 100° C. and the sample was annealed at this temperature for an additional 12.5 hours. Finally, the temperature was slowly reduced to 25° C. over a period of five hours. The annealing of the sample was then complete.
The polycarbonate membrane had been fused to the surface of the polypropylene film. The membrane was removed by chemical etching. The membrane was removed from the surface of the polypropylene film by immersing the sample in a bath of dichloromethane at room temperature for five minutes. The resulting sample was allowed to air dry prior to handling. Scanning electron microscope (SEM) images confirmed the presence of pillar-like structures which were about 20 microns high and 0.8 microns in diameter.
In order to assess the capacity of the modified film to promote tissue adhesion, a study was conducted. A 2.5 cm by 10.1 cm (1 inch by 4 inch) section of polypropylene film with pillar structures was cut from the sheet prepared as described above. Another 2.5 cm by 10.1 cm (1 inch by 4 inch) sample of 25 microns thick polypropylene film without pillar structures was used as a control. Fresh porcine small intestine was cleaned with Phosphate Buffered Saline (PBS) at room temperature. A section of the intestine approximately 10.1 cm (4 inches) long was mounted in a fixture that allowed it to be inflated with air and at the same time monitored the air pressure within the intestine. A one centimeter long incision was made in the center of the intestine segment its length. Fibrin sealant (Human), sold under the tradename EVICEL by Johnson & Johnson Wound Management, a division of Ethicon Inc. of Somerville, N.J., USA was prepared in accordance with the manufacturer's directions. The 5 mL application device for the sealant was used to aspirate a coating of fibrin sealant onto the surfaces of both films. The films were then wrapped around the circumference of the intestine covering the 1 cm long incision. The films were then clamped in place with a spring-loaded clamp while the fibrin sealant was allowed to stabilize for 5 minutes. The sample was then immersed in a PBS bath maintained at 37° C. and slowly inflated with air (approximately 5 mm Hg/sec). The air pressure increased until a maximum value was reached at which point air bubbles were observed in the PBS bath. The maximum value achieved by the control film under these conditions was 8.1 mm Hg. The maximum value achieved by the film with the pillar structures under these conditions was 41.6 mm Hg. The film with the pillar structures was thus able to attain a burst pressure greater than five times that of the control in this experiment.
A 100 microns thick polydioxanone film with pillar-like structures on both sides was prepared. A polydioxanone film was compressed under heat and pressure between two 20 microns thick sheets of polycarbonate filter material. The filter material possesses microscopic (0.8 micron) holes. The polydioxanone film melted and flowed into the holes. After processing the sheet was annealed. The polycarbonate membrane filter was then dissolved in a bath of dichloromethane. The membrane filters used (0.8 micron ATTP, Cat No. ATTP14250, Lot No. R9SN70958 available from Millipore Corporation of Billerica, Mass., USA) possessed two distinct sides. One side had a shiny appearance while the other was duller. A laminate for compression molding was constructed as follows:
h. A segment of polyimide film was placed on the top membrane;
i. A 15.2 cm (6 inch) polished square metal plate (thickness 0.8 mm) (shiny side down) was placed on the polyimide film; and
j. Another segment of polyimide film was placed on the steel plate.
The resulting sample was loaded into a heated press with vacuum (less than 150 microns mercury) capability and was processed as follows:
The sample was annealed in the constrained condition (between two steel plates) in an inert environment (nitrogen gas) for a minimum of six hours at 70° C.
The polycarbonate membrane had been fused to the surface of the polydioxanone film. The membrane was removed by chemical etching. The membrane was removed from the surface of the polydioxanone film by immersing the sample in a bath of dichloromethane at room temperature for five minutes and was allowed to air dry prior to handling. Scanning electron microscope (SEM) images of the sample confirmed the presence of pillar-like structures which were about 20 microns high and 0.8 micron in diameter.
An anodized aluminum oxide (AAO) mold was prepared for imprinting of poly(lactic acid) (DL-PLA) polymer into pillar-like structures. The mold was prepared by forming an AAO film by electropolishing and etching, and silane-treating the mold by silane vapor deposition. The resulting mold contains randomly distributed recesses which provide pillar-like projections in the demolded product of 200 nanometers by 2 microns. DL-PLA film obtained from PURAC America of Lincolnshire, Ill., USA and having a thickness of 100-300 microns is pressed into the AAO mold under high temperature and pressure in two steps at 100° C. The first step is carried out at a pressure of 0 kPa (0 bar) for 5 minutes and the second step at 6000 kPa (60 bar) for 20 minutes. The polymer and mold are cooled to 35° C. before removal of pressure. Then, the polymer structures are demolded and released by mechanically peeling them from the mold.
The resulting demolded DL-PLA polymer structure comprises pillar-like projections of about 200 nm diameter and about 2 microns length having an aspect ratio (length/diameter) of about 10.
The pillared D,L-PLA substrate prepared by the methods of Example 10 as well as its corresponding flat surface film (unpillared) were tested for shear adhesion using the methods of Example 2 against substrates (sandpaper) with varying surface roughness values. The surface roughness value represents the average feature dimensions expected for different surfaces. These tests were performed using a mechanical testing instrument sold under the tradename INSTRON by Instron Industrial Products, Grove City, Pa. The results are summarized in
All patents, test procedures, and other documents cited herein, including priority documents, are fully incorporated by reference to the extent such disclosure is not inconsistent and for all jurisdictions in which such incorporation is permitted.
When numerical lower limits and numerical upper limits are listed herein, ranges from any lower limit to any upper limit are contemplated.
Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent.
While the present invention has been described and illustrated by reference to particular embodiments and examples, those of ordinary skill in the art will appreciate that the invention lends itself to variations not necessarily illustrated herein. For this reason, then, reference should be made solely to the appended claims for purposes of determining the true scope of the invention.
