AU2004242432B2 - Bioabsorbable, biocompatible polymers for tissue engineering - Google Patents

Description

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AUSTRALIA

Patents Act 1990 TEPHA, INC.

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Bioabsorbable, biocompatible polymers for tissue engineering The following statement is a full description of this invention including the best method of performing it known to us:- BIOABSORBABLE, BIOCOMPATIBLE

POLYMERS

O FOR TISSUE ENGINEERING SField of the Invention (C The present invention generally relates to bioabsorbable, biocompatible polymers and methods for making devices for tissue on engineering and tissue regeneration from these materials.

C- Background to the Invention Durig the last20 to 30 years, several bioabsorbable, biocompatible polymers have been developed for use in medical devices, and approved for

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use by the U.S. Food and Drug Administration (FDA). These FDA approved materials include polyglycolic acid (PGA), polylactic acid (PLA), Polyglactin 910 (comprising a 9:1 ratio of glycolide per lactide unit, and known also as VICRYLM), polyglyconate (comprising a 9: ratio of glycolide per trimethylene carbonate unit, and known also as MAXON

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m), and polydioxanone (PDS). In general, these materials biodegrade in vivo in a Imatter of months, although certain more crystalline forms biodegrade more slowly. These materials have been used in orthopedic applications, wound healing applications, and extensively in sutures after processing into fibers.

More recently, some of these polymers also have been used in tissue engineering applications.

Tissue engineering has emerged as a multi-disciplinary field combining biology, materials science, and surgical reconstruction, to provide living tissue products that restore, maintain, or improve tissue function. The need for this approach has arisen primarily out of a lack of donor organs and tissues, but also because it offers the promise of being able to dramatically expand the ability to repair tissues and develop improved surgical procedures.

In general, three distinct approaches currently are used to engineer new tissue. These are infusion of isolated cells or cell substitutes, use of tissue inducing materials and/or tissue regeneration scaffolds (sometimes referred to as guided tissue repair), and implantation of cells seeded in 0 scaffolds (either prior to or subsequent to implantation). In the third case, the 0 scaffolds may be configured either in a closed manner to protect the implanted cells from the body's immune system, or in an open manner so C, that the new cells can be incorporated into the body.

In open scaffold systems and guided tissue repair, tissue engineering S ~devices have normally been fabricated from natural protein polymers such as c- collagen, or from the synthetic polymers listed above, which in both cases degrade over time and are replaced by. new tissue. While some of these materials have proven to be good substrates for cell and tissue growth, and provide good scaffolding to guide and organize the regeneration of certain tissues, they often do not have the specific mechanical requirements that the scaffold needs to provide until the new tissue is developed and able to take over these functions. These materials may also be difficult to process and fabricate into the desired form, handle poorly in the operating room, be difficult to suture, and sometimes fall apart prematurely. For example, it has been reported that tissue engineered heart valve leaflet scaffolds derived from polyglactin and PGA are too stiff and cause severe pulmonary stenosis when implanted in sheep (Shinoka, et al., "New frontiers in tissue engineering: tissue engineered heart valves" in Synthetic Bioabsorbable Polymer Scaffolds (Atala Mooney, eds.) pp.187-98 (Birkhduser, Boston, 1997)).

Figure 1, which plots the tensile strength and elongation to break values for representative FDA approved (compression molded).

bioabsorbable biocompatible polymers against these valtes for different tissue structures, reveals a significant mismatch between the mechanical properties of these polymers and the different tissue structures. In particular, it is apparent that the existing bioabsorbable biocompatible polymers are stiff, inelastic materials, with elongations to break of around 25%, yet many tissues are much more flexible, elastic, and have longer elongation to break values. Accordingly, the biomaterial products currently used in temporary scaffolds for regenerating human tissues do not exhibit the same multi-axial physical and mechanical properties as native tissues, which are hierarchical, 0three-dimensional structures (see abstract of an award by the Advanced 0 Technology Program to Johnson and Johnson Corporate Biomaterials Center, October 1997).- Attempts have been made to develop new bioabsorbable biocompatible polymers with more flexible, elastomeric properties. One approach has been to incorporate lactide orglycolide and caprolactone joined C by a lysine-based diisocyante into a polyurethane (Lamba, et al., <1 "Degradation of polyurethanes" in Polvurethanes in Biomedical O Applications, pp.199-200 (CRC Press LLC, Boca Raton, Florida, 1998).

SHowever, these crosslinked polyurethane networks cannot be processed by standard techniques such as solution casting or melt processing,I limiting their usefulness. There is also no evidence that the polyurethane segments are completely biodegraded in vivo. A commercial material, known as TONET, has also been evaluated as an elastomeric implant material. However, this material degrades in vivo very slowly; and therefore has limited application (Perrin, et al., "Polycaprolactone" in Handbook of Bioabsorbable Polymers (Domb, et al., eds.) pp.63-76 (Harwood, Amsterdam,1997)). Another approach has been to synthesize protein-based polymers, particularly polymers containing elastomeric polypeptide sequences (Wong, et al., "Synthesis and properties of bioabsorbable polymers used as synthetic matrices for tissue engineering" in Synthetic Bioabsorbable Polymer Scaffolds (Atala Mooney, eds.) pp.51-82 (Birkhauser, Boston, 1997).

However, these materials are not reported to biodegrade in vivo, although cells can invade matrices derived from these materials. They also lack the advantages of thermoplastic polymers in fabrication of devices.

U.S. Patents No. 5,468,253 and No. 5,713,920, both to Bezwada et al,, disclose bioabsorbable elastomeric materials which are used to form devices that, based on in vitro data, are alleged to completely bioabsorb within one year or six months. However, deGroot et al., Biomaterials, 18:613-22 (1997) provides in vivo data for these materials and reports that

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the implanted material fragmented after 56 weeks into white crystalline-like u fragments. It is suspected that these fragments are crystalline poly-L-lactide, which is very slow to degrade. Nonetheless, whatever the composition of the c fragments, the material is not completely bioabsorbed after one year in vivo.

These materials also typically are difficult to process and may have poor shelf C- stability.

Thus, while the current bioabsorbable biocompatible polymers offer a range of useful properties for certain medical applications, it is desirable to develop methods to prepare bioabsorbable biocompatible polymers that significantly extend the range of properties available. It would thus be desirable Nc to develop methods for preparing bioabsorbable biocompatible polymers with mechanical properties closer to those of tissue, particularly soft tissues. It would also be desirable to develop methods for making bioabsorbable biocompatible materials which can be readily processed, and fabricated into tissue engineering devices that can be easily implanted.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia before the priority date of each claim of this application.

SUMMARY OF THE INVENTION Bioabsorbable biocompatible polymers are selected based on their physical and/or mechanical properties to correspond to the physical properties of tissues to be regenerated or constructed. Physical properties include elasticity, strength, flexibility, and processibility. These properties can be measured by determining factors such as tensile strength, elongation or extension to break, and Youngs modulus.

Accordingly, the present invention provides a composition or device for use in tissue engineering comprising a bioabsorbable biocompatible polymer comprising polyhydroxyalkanoate, wherein the composition or device has one or more mechanical properties selected from the group consisting of stress, strain, stress-strain, stress-strain hysteresis, stress-strain relaxation, viscoelasticity, contraction stress, resting stress, Young's modulus, tensile strength, durability, yield point, failure strength, toughness, ductility, softness, hardness, creep, elastic deformation, wear resistance, shear failure, roughness, compressive strength, load capacity, modulus of elasticity, ultimate compressive strength, yield strength, stress-strain relationship, scratch resistance, abrasion resistance,. flexural modulus, shear modulus, contact angle, surface tension, adhesive strength, surface free energy, bending strength, shear strength, bonding strength, bending strength, bending stiffness, compressive modulus, bending modulus, fracture toughness, elongation, fiber strength, fiber modulus, fiber elongationi thermal expansion coefficient, fracture 0 10 toughness, static and dynamic elasticity, longitudinal stretch, stress, and strain, c radial stretch, stress and strain, circumferential stretch, stress and strain, ultimate elongation, viscosity, expansion, static and kinetic coefficients of friction, plasticity, axial tension, shock absorbance, bearing strength, formability, rigidity, stress rupture, bend radius, impact strength, and fatigue strength, equivalent to the same properties of a differentiated tissue or tissue structure to be regenerated or constructed.

Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a.

stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

In a preferred embodiment, the polymers have an extension to break over 25%, tensile strength less than 10,000 psi, Youngs modulus less than 100,000 psi, glass transition temperature less than 20 and melting temperature less than 190 In one embodiment, the bioabsorbable biocompatible polymers can be prepared with tensile strengths equivalent to the tensile strengths of the tissues of the cardiovascular, gastrointestinal, kidney and genitourinary, musculoskeletal, and nervous systems, as well as those of the oral, dental, periodontal, and skin tissues. In another embodiment, the bioabsorbable biocompatible polymers can be prepared with elongations to break equivalent to the elongations to break of the same tissues. In still another embodiment, the bioabsorbable biocompatible polymers can be prepared with tensile modulus (Young's modulus) values equivalent to these tissues.

In a second aspect the invention provides a device comprising a bioabsorbable biocompatible polyhydroxyalkanoate polymer wherein the device 4a a, has one or more mechanical properties equivalent to the same properties of a Sspecific tissue or tissue structure to be regenerated or constructed wherein the device is selected from the group consisting of a tissue engineering scaffold, guided tissue repair material, wound dressing, drug delivery vehicle, anti- Sadhesion material, cell encapsulation material, coating, implant, stent, Sorthopaedic device, prosthetic, adhesive, diagnostic, sutures, surgical meshes, Sstaples, meniscus repair and regeneration devices, screws (interference 1screws and meniscal screws), bone plates and plating systems, cardiovascular 0 10 patches, pericardial patches, slings, pins, anti-adhesion barriers, articular cartilage repair devices, nerve guides, tendon and ligament repair devices, atrial septal defect patches, bulking and filling agents, vein valves, bone marrow scaffolds, bone graft scaffolds, skin substitutes, dural substitutes, ocular implants, spinal fusion cages, and muscular implants (cardiac and.

skeletal), wherein the mechanical properties are selected from the group consisting of stress, strain, stress-strain, stress-strain hysteresis, stress-strain relaxation, viscoelasticity, contractionstress, resting stress, Young's modulus, tensile strength, durability, yield point, failure strength, toughness, ductility, softness, hardness, creep, elastic deformation, wear resistance, shear failure, roughness, compressive strength, load capacity, modulus of elasticity, ultimate compressive strength, yield strength, stress-strain relationship, scratch resistance, abrasion resistance, flexural modulus, shear modulus, contact angle, surface tension, adhesive strength, surface free energy, bending strength, shear strength, bonding strength, bending strength, bending stiffness, compressive modulus, bending modulus, fracture toughness, elongation, fiber strength, fiber modulus, fiber elongation, thermal expansion coefficient, fracture toughness, static and dynamic elasticity, longitudinal stretch, stress, and strain, radial stretch, stress and strain, circumferential stretch, stress and strain, ultimate elongation, viscosity, expansion, static and kinetic coefficients of friction, plasticity, axial tension, shock absorbance, bearing strength, formability, rigidity, stress rupture, bend radius, impact strength, and fatigue strength, equivalent to the same properties of a differentiated tissue or tissue structure to be regenerated or constructed.

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SIn a third aspect the invention provides a method for producing a C) bioabsorbable biocompatible, polyhydroxyalkanoate polymer composition comprising: selecting a tissue structure and measuring one or more mechanical properties selected from the group consisting of stress, strain, stress-strain, stress-strain hysteresis, stress-strain relaxation, viscoelasticity, contraction stress, resting stress, Young's modulus, tensile strength, durability, yield point, failure strength, toughness, ductility, softness, hardness, creep, elastic deformation, wear resistance, shear failure, roughness, compressive strength, load capacity, modulus of elasticity, ultimate compressive strength, yield strength, stressstrain relationship, scratch resistance, abrasion resistance, flexural modulus, shear modulus, shear modulus, contact angle, surface tension, adhesive strength, surface free energy, bending strength, shear strength, bonding strength, bending strength, bending stiffness, compressive modulus, bending modulus, fracture toughness, elongation, fiber strength, fiber modulus, fiber elongation, thermal expansion coefficient, fracture toughness, static and dynamic elasticity, longitudinal stretch, stress, and strain, radial stretch, stress and strain, circumferential stretch, stress and strain, ultimate elongation, viscosity, expansion, static and kinetic coefficients of friction, plasticity, axial tension, shock absorbance, bearing strength, formability rigidity, stress rupture, bend radius, impact strength, and fatigue strength, equivalent to the same properties of a differentiated tissue or tissue structure to be regenerated or constructed, and selecting from a combination of monomers that can be polymerised to make a polymer, one or more monomers which when linked in a polymeric form, have the mechanical property or properties of the tissue or tissue structure.

BRIEF DESCRIPTION OF THE DRAWINGS Figure I is a graph comparing the mechanical properties of PGA, PLA, polyglactin, polyglyconate, and polydioxanone with those of different tissue structures..

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C Figure 2 is a graph comparing the mechanical properties of au bioabsorbable polymers described herein with the mechanical properties of different tissues or tissue structures.

DETAILED DESCRIPTION OF THE INVENTION c Polymers are provided which are bioabsorbable, biocompatible, and have mechanical properties similar to the physical and/or mechanical properties of tissue structures, including stress, strain, stress, strain, stress strain hysteresis, stress-strain relaxation, viscoelasticity, contraction stress, 0 10 resting stress, Young's modulus, tensile strength, durability, yield point, failure C strength, toughness, ductility, softness, hardness, creep, elastic deformation, wear resistance, shear failure, roughness, compressive strength, load capacity, modulus of elasticity, ultimate compressive strength, yield strength, stressstrain relationship, scratch resistance, abrasion resistance, flexural modulus, shear modulus, contact angle, surface tension, adhesive

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strength, surface free energy, bending strength, shear strength, bonding Sstrength, bending strength; bending stiffness, compressive modulus, bending U modulus, fracture toughness, elongation, fiber strength, fiber modulus, fiber elongation, thermal expansion coefficient, fracture toughness, static and C dynamic elasticity, longitudinal stretch, stress, and strain, radial stretch, stress and strain, circumferential stretch, stress and strain, ultimate m elongation, viscosity, expansion, static and kinetic coefficients of friction, C. plasticity, axial tension, shock absorbance, bearing strength, formability, Srigidity, stress rupture, bend radius, impact strength, and fatigue strength.. In Sa preferred embodiment, the polymers have elongations to break of more than 25%, and/or tensile modulus values less than 500,000 psi. In another preferred embodiment, the polymers are fabricated into medical devices using standard polymer processing techniques, and used as tissue engineering devices to provide living tissue products that restore, maintain, or improve tissue function, for example, in the cardiovascular, gastrointestinal, kidney and genitourinary, musculoskeletal, and nervous systems, as well as those of the oral, dental, periodontal, and skin tissues.

I. Polymers The polymers described herein may be prepared by synthetic or natural methods. However, the method must provide the desired polymer in a form sufficiently pure for use as an implantable material. The polymer should not contain any undesirable residues or impurities which could elicit an undesirable response either in vitro in the case of a cell-seeded construct or in vivo.

The polymers may be prepared from any combination of monomeric units. These units must, however, be capable of biodegrading in vivo to nontoxic compounds, which can optionally be excreted or further metabolized.

The combination of units in the polymer must also be biocompatible, and not elicit an undesirable biological response upon implantation. The polymer may be biodegraded in vivo by any means, including hydrolysis, enzymatic attack,: a cell-mediated process, or by any other biologically mediated

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process. It is considered desirable for tissue engineering applications that the polymer scaffold serve as a transitional construct, and thus be fully degraded once the new tissue is able to take over the function of the scaffold. Since the rates at which different new tissues are likely to be able to assume their new function will vary, it is desirable to have polymers with a range of degradation rates as well as a range of different properties. Generally, however, preferred polymers will degrade in a matter of weeks to months, preferably less than one year, rather than several years.

The mechanical properties of thepolymer are designed to meet the needs of the particular tissue engineering application. Thus, according to the method described herein for preparing bioabsorbable biocompatible polymers, the monomeric units can be selected to provide upon combination of the correct ratios of these monomeric units the desired property or property set. If necessary, the monomeric units may be combined in a specific order as in, for example, a block copolymer, or alternatively they can be assembled in a random manner. They may also be prepared with different molecular weights to achieve the correct performance.

In a preferred method as described herein, the monomeric units are hydroxy acids, and the polymers are polyesters. The distance between the hydroxy group and the acid group can be small or large, however, monomers are preferably or 6-hydroxy acids. The hydroxy acids may optionally contain other functional groups and be substituted at any position, including heteroatoms between the hydroxy and acid groups. These hydroxy acids may be polymerized eitherusing synthetic methods or preferably using biological methods. In the latter case, the hydroxy acids may be derived in vivo from a non-hydroxy acid source.

Suitable methods for preparing the polyesters are described in Williams, S.F. and Peoples, O.P. CHEMTECH, 26:38-44 (1996), Williams, S.F. and Peoples, Chem. Br., 33:29-32 (1997), U.S. Patent No.

4,910,145 to Holmes, P.A. and Lim, Byrom, "Miscellaneous Biomaterials," in D. Byrom, Ed., "Biomaterials" MacMillan Publishers, London, 1991, pp. 333-59; Hocking, P.J. and Marchessault, R.H.

"Biopolyesters", GJ.L.Griffn, Ed. "Chemistry andTechnology of Bioabsorbable Polymers," Chapmanand Hall, London, 1994, pp.48-96; Q Holmes, "Biologically Produced (e)-3-hydroxyalkanoate Polymers and N Copolymers," in D.C. Bassett Ed., "Developments in Crystalline Polymers," Elsevier, London, Vol. 2, 1988, pp. 1-65; Lafferty et al., "Microbial SProduction of Poly-p-hydroxybutyric acid," H.J. Rehm and G. Reed, Eds., "Biotechnology", Verlagsgesellschaft, Weinheim, Vol. 66, 1988, pp. 135-76; Mller and Seebach, Angew. Chem. Int.Ed. Engl 32:477-502 (1993); SSteinbiichel, A. "Polyhydroxyalkanoic Acids," in D. Byrom Ed., "Biomaterials", MacMillan Publishers, London, 1991, pp. 123-213; Steinbtichel and Wiese, Appl. Microbiol. Biotechnol., 37:691-697 (1992); U.S. Patent Nos. 5,245,023; 5,250,430; 5,480,794; 5,512,669; 5,534,432; Agostini, D.E. et al., Polym, Sci., Part A-i, 9:2775-87 (1971); Gross, R.A. et al., Macromolecules, 21:2657-68 (1988); Dubois, P.I. et al., Macromolecules, 26:4407-12 (1993); Le Borgne, A. and Spassky, N., Polymer, 30:2312-19 (1989); Tanahashi, N. and Doi, Macromolecules, 24:5732-33 (1991); Hori, Y.M. et al., Macromolecules, 26:4388-90 (1993); Kemnitzer, J.E. et al., Macromolecules, 26:1221-1229 (1993); Hori, Y.M. et al., Macromolecules, 26:5533-34 (1993); Hocking, P.J. and Marchessault, Polym. Bull., 30:163-70 (1993); Xie, W. et al., Macromolecules, 30:6997-98 (1997), U.S. Pat. No. 5,563,239 to Hubbs, J.C. and Harrison, and Braunegg, G. et al., J.Biotechnol. 65:127-61 (1998), and Madison Huisman, Microb. Mol. Biol. Rev. 63:21-53 (1999).

In another preferred method described herein, the bioabsorbable biocompatible polymers are polyesters including one or more linkages in the main polymer chain which are not ester linkages. These linkages should be susceptible to cleavage in vivo. Suitable non-ester linkages may include amides, urethanes, carbonates, iminocarbonates, oxalates, oxamates, orthoesters, anhydrides, phosphazenes, glycosides, and ethers. Incorporation of such chemistries can be used to alter biodegradation rates, tailor

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mechanical, surface, or other properties of the polymer, improve processibility and handling of the materials, and/or to provide methods for attachment of other compounds to the polymers.

The bioabsorbable biocompatible polymers described herein may optionally be further modified either prior to or subsequent to fabrication.

Representative modifications include derivatization, surface treatments, coatings, coupling of other compounds particularly biologically active agents.

II .Mechanical Properties and Polymer Compositions The bioabsorbable biocompatible polymers described herein may be prepared with mechanical properties that resemble those of tissue. These properties are achieved by preparing the polymers with different compositions and ratios of monomeric constituents. For example, polymers with tensile strengths near or equal to that of tendon and dentin can be prepared by polymerizing 4-hydroxybutyric acid. By incorporating R-3hydroxybutyric acid with 4-hydroxybutyric acid into the same polymer as a random copolymer, it is possible to prepare a material with a tensile strength near or equal to that of cortical bone. Using combinations of R-3hydroxyoctanoate and R-3-hydroxyhexanoate, it is possible to prepare a copolymer with a tensile strength near or equal to that of skin and enamel.

Other monomers may be incorporated to increase or decrease the tensile strengths of the bioabsorbable biocompatible polymers.

The elongation to break of the bioabsorbable biocompatible polymers may also be controlled and tailored to those of tissue in a similar manner.

For example, the homopolymer of R-3-hydroxybutyric acid has an elongation to break of around close to tendon. This elongation to break may be progressively increased to values for cartilage, cardiac muscle, cardiovascular tissues, skin, aorta, urological tissue, in fact virtually any tissue, by incorporating a co-monomer, 4-hydroxybutyric acid, with R-3hydroxybutyric acid into a copolymer. A copolymer comprising 3-8% 4hydroxybutyric acid polymerized with 3-hydroxybutyric acid has an

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extension to break of 45% to over 1 00 which are similar values to those of 0 cardiac muscle, skin, urological and cardiovascular tissues including blood Svessels and heart valves: Q In the same manner, it is also possible to prepare bioabsorbable biocompatible polymers described herein with a range of tensile modulus values (Youngs modulus) that match those of tissue structures. For example, n depending upon the age of;the person, skin has a tensile modulus value 1 -ranging from about 2,000 psi for young children to around 18,000 psi for c older people. According to the method described herein, it is possible to produce a copolymerof R-3-hydroxyoctanoic acid and R-3-hydroxyhexanoic c acid with a Youngs modulus value of around 1,000-2,000 psi, and a copolymer of R-3-hydroxybutyric acid and 4-hydroxybutyric acid with a Youngs modulus ranging:from 3,000 psi to 22,000 psi as the percentage of 4hydroxybutyric acid is increased from 78% to 100%. Other compositions can be used for applications requiring higher Youngs modulus values. For example, the homopolymer of R-3-hydroxybutyric acid has a Youngs modulus value of around 500,000 psi. Thus, by using combinations of different hydroxy acid monomers, it is possible to prepare bioabsorbable biocompatible polymers with a:wide range of Youngs modulus values that encompass different tissue structures.

y using a similar approach of combining appropriate monomer units, bioabsorbable biocompatible polymers can be produced that have other desirable mechanical properties and even desirable barrier properties that provide a good compliance match with tissue. Examples pf other mechanical properties which can be prepared according to the method described herein include, but are not limited to, compressive strength, hardness, burst strength, impact strength, toughness, as well as other viscoelastic elastic properties.

Examples of desirable barrier properties include water and fluid barrier properties, moisture vapor barrier properties, and gas barrier properties.

In some embodiments, it may be desirable to produce a bioabsorbable biocompatible polymer with two or more mechanical properties providing a

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good compliance match with a specific tissue structure. For example, tendon Shas a tensile strength ofaround 6,000 psi and an elongation to break of SAccording to the method described herein,a bioabsorbable biocompatible Q polymer can be produced comprising 10% R-3-hydroxypentanoic acid and C-i R-3-hydroxybutyric acid, with approximately the same tensile strength of about 6,000 psi and an extension to break of 10% as tendon. Similarly, other cn combinations of one, two, or more monomeric units can be used to provide C bioabsorbable biocompatible polymers with two or more of the desired mechanical properties of a particular tissue structure.

0 III. Fabrication of Bioabsorbable Biocompatible Devices The bioabsorbable biocompatible polymer compositions are useful for preparing a variety of medical devices. Examples of applications of such devices include tissue engineering scaffold, guided tissue repair material, wound dressing, drug delivery vehicle, anti-adhesion material, cell encapsulation material, coating, implant, stent, orthopaedic device, prosthetic, adhesives, diagnostics, sutures, surgical meshes, staples, meniscus repair and regeneration devices, screws (interference screws and meniscal screws), bone plates and plating systems, cardiovascular patches, pericardial patches, slings, pins, anti-adhesion barriers, articular cartilage repair devices, nerve guides, tendon and ligament repair devices, atrial septal defect pathces, bulking and filling agents, vein valves, bone marrow scaffolds, bone graft scaffolds, skin substitutes, dural substitutes, ocular implants, spinal fusion cages, and muscular implants (cardiac and skelatal). These materials may be used alone, with additives or in combinations with themselves or other materials. Additives and other materials may include those components added for the purpose of further modification of a particular property or properties, and/or those components which are biologically active such as cell attachment factors, growth factors, peptides, antibodies and their fragments.

In general, a key advantage described herein is that the bioabsorbable biocompatible polymers can be processed using conventional polymer

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processing techniques. Many of the materials are thermoplastics, and are thus amenable to.standard methods for processing.such materials. Such methods are well known to those skilled in the art, and include such methods as melt processing, solvent processing, leaching, foaming, extrusion, CI injection molding, compression molding, blow molding, spray drying, extrusion coating, spinning of fibers and subsequent processing into woven C or non-woven constructs.

A preferred fabricated form of the compositions is a porous (fibrous) construct, particularly ones which can be used as tissue engineering 0 scaffolds, and guided tissue repair meshes and matrices. This construct or matrix may be derived by any suitable method, including salt leaching, sublimation, solvent evaporation, spray drying, foaming, processing of the materials into fibers and subsequent processing into woven or non-woven devices. Such constructs can be used in tissue engineering applications of the tissues of the cardiovascular, gastrointestinal, kidney and genitourinary, musculoskeletal, and nervous systems, as well as those of the oral, dental, .periodontal, and skintissues. Examples of such constructs can be used to prepare tissue engineering scaffolds for both hard and soft tissues.

Representative tissue types include, but are not limited to, cardiovascular (including blood vessel, artery, and heart valve), cornea and other ocular tissues,,pancreas, alimentary tract esophagus and intestine), ureter, bladder, skin, cartilage, dental, gingival tissue, bone, liver, kidney, genital organs (including penis, urethra, vagina, uterus, clitoris, and testis), nerve, spinal cord, meniscus, pericardium, muscle skeletal), tendon, ligament, trachea, phalanges and small joints, fetal, and breast.

A further advantage of some of the compositions described herein is their ability to be sterilized by radiation sources, in addition to ethylene oxide. Moreover, certain compositions described herein have the additional advantage of good shelf stability, resistance to hydrolysis by water and moisture, and thus less restrictive packaging needs to exclude moisture after preparation, fabrication, and during storage.

SAnother advantage to using the compositions described herein is the ability to create three dimensional polymer scaffold systems with properties Sin different regions. This can be achieved by combining the compositions described herein either in different forms, or combining different N compositions to make one or more forms. For example, a specific composition may be processed into a fibrous form, and then subsequently Sprocessed and combined with another different fibrous or non-fibrous c o p s t o c composition. Such combinations may be achieved by weaving, melt processink, solvent processing, coating, and other methods known to those skilled in the art.

Those skilled in the art will recognize,. or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein.

Claims (16)

1. A composition or device for use in tissue engineering comprising a bioabsorbable biocompatible polymer comprising polyhydroxyalkanoate, wherein the composition or device has one or more mechanical properties selected from the group consisting of stress, strain, stress-strain, stress-strain hysteresis, stress-strain relaxation, viscoelasticity, contraction stress, resting stress, Young's modulus, tensile strength, Sdurability, yield point, failure strength, toughness, ductility, softness, hardness, creep, elastic deformation, wear resistance, shear failure, roughness, compressive strength, load capacity, modulus of elasticity, ultimate compressive strength, yield strength, stress-strain relationship, scratch resistance, abrasion resistance, flexural modulus, shear modulus, contact angle, surface tension, adhesive strength, surface free energy, bending strength, shear strength, bonding strength, bending strength, bending stiffness, compressive modulus, bending modulus, fracture toughness, elongation, fiber strength, fiber modulus, fiber elongation, thermal expansion coefficient, fracture toughness, static and dynamic elasticity, longitudinal stretch, stress, and strain, radial stretch, stress and strain, circumferential stretch, ultimate elongation, viscosity, expansion, static and kinetic coefficients of friction, plasticity, axial tension, shock absorbance, bearing strength, and fatigue strength, equivalent to the same properties of a differentiated tissue or tissue structure to be regenerated or constructed.

2. The composition of claim 1 wherein the polymer degrades in vivo in less than one year.

3. The composition of claim 1 or claim 2 wherein the polymer has an extension break of over 25%, such as over

4. The composition of any one of claims 1 to 3 wherein the polymer has a tensile strength less than 50,000 psi, such as less than 10,000 psi. The composition of any one of claims 1 to 4 wherein the polymer has a Young's modulus of less than 200,000 psi, such as less than 100,000 psi.

6. The polymer of any one of claims I to 5 wherein the polymer is in the form of a fiber.

7. The composition of any one of claims 1 to 5 wherein the polymer has a melting temperature less than 190"C.

8. The composition of any one of claims I to 5 and 7 wherein the polymer has a glass transition temperature less than

9. The composition of claim 1 wherein the tissue is selected from the group consisting of cardiovascular, gastrointestinal, kidney, genitourinary, musculoskeletal, nervous, oral, breast, periodontal, and skin. c:\n rportbl\syddocs\lfj\49452_1 .doc The composition of claim 1 wherein the mechanical property is selected from the group consisting of tensile strength, Young's modulus, elongation to break, hardness, compressive strength, burst strength, toughness, and impact strength.

11. The composition of claim 1 wherein: the tissue is cartilage and the polymer has a tensile strength of 435 psi the tissue is skin and the polymer has a tensile strength of 1,100 psi the tissue is tendon and the polymer has a tensile strength of 7,700 psi the tissue is aorta and the polymer has a tensile strength of 160 psi the tissue is cardiac muscle and the polymer has a tensile strength of 16 psi the tissue is bone and a polymer has a tensile strength of 10,000 psi the tissue is enamel and the polymer has a tensile strength of 1,600 psi the tissue is skin and the polymer has an ultimate elongation of the tissue is tendon and the polymer has an ultimate elongation of 10%±25%; the tissue is cartilage and polymer has an ultimate elongation of 30%±25%; or the tissue is heart and the polymer has an ultimate elongation of 10-15%±25%.

12. The composition of claim 1 wherein the tissue is aorta and the polymer has an ultimate elongation in the transverse and longitudinal directions of 77-81%±25%.

13. The composition of claim 1 wherein the tissue is skin and the polymer has a Young's modulus of 2,000-18,000 psi

14. A device comprising a bioabsorbable biocompatible polyhydroxyalkanoate polymer, wherein the device has one or more mechanical properties equivalent to the same properties of a specific tissue or tissue structure to be regenerated or constructed, wherein the device is selected from the group consisting of a tissue engineering scaffold, guided tissue repair material, wound dressing, drug delivery vehicle, anti- adhesion material, cell encapsulation material, coating, implant, stent, orthopaedic device, prosthetic, adhesive, diagnostic, sutures, surgical meshes, staples, meniscus repair and regeneration devices, screws, (interference screws and meniscal screws), bone plates and plating systems, cardiovascular patches, pericardial patches, slings, pins, anti-adhesion barriers, articular cartilage, repair devices, nerve guides, tendon and ligament repair devices, atrial septal defect patches, bulking and filling agents, vein valves, bone marrow scaffolds, bone graft scaffolds, skin substitutes, dural substitutes, ocular implants, spinal fusion cages, and muscular implants (cardiac and skeletal), wherein the mechanical properties are selected from the group consisting of stress, strain, stress-strain, stress-strain hysteresis, stress-strain relaxation, c:\nrportbl\syddocs\lfj\49452_1 .doc viscoelasticity, contraction stress, resting stress, Young's modulus, tensile strength, durability, yield point, failure strength, toughness, ductility, softness, hardness, creep, elastic deformation, wear resistance, shear failure, roughness, compressive strength, load capacity, modulus of elasticity, ultimate compressive strength, yield strength, stress-strain relationship, scratch resistance, abrasion resistance, flexural modulus, shear modulus, contact angle, surface tension, adhesive strength, surface free energy, bending strength, shear strength, bonding strength, bending strength, bending stiffness, compressive modulus, bending modulus, fracture toughness, elongation, fiber strength, fiber modulus, fiber elongation, thermal expansion coefficient, fracture toughness, static and dynamic elasticity, longitudinal stretch, stress, and strain, radial stretch, stress and strain, circumferential stretch, ultimate elongation, viscosity, expansion, static and kinetic coefficients of friction, plasticity, axial tension, shock absorbance, bearing strength, and fatigue strength. The device of claim 14 wherein the device is a tissue engineering scaffold or matrix, optionally having different properties in different regions and optionally seeded with cells for implantation.

16. The device of claim 15 wherein the polymer degrades in vivo in less than two years.

17. The device of any one of claims 15 or 16 wherein the tissue is selected from heart valve, blood vessel, cartilage, tendon, ligament, and bone.

18. A method for producing a bioabsorbable biocompatible polyhydroxyalkanoate polymer composition comprising: selecting a tissue structure and measuring one or more mechanical properties selected from the group consisting of stress, strain, stress-strain, stress-strain hysteresis, stress-strain relaxation, viscoelasticity, contraction stress, resting stress, Young's modulus, tensile strength, durability, yield point, failure strength, toughness, ductility, softness, hardness, creep, elastic deformation, wear resistance, shear failure, roughness, compressive strength, load capacity, modulus of elasticity, ultimate compressive strength, yield strength, stress-strain relationship, scratch resistance, abrasion resistance, flexural modulus, shear modulus, contact angle, surface tension, adhesive strength, surface free energy, bending strength, shear strength, bonding strength, bending strength, bending stiffness, compressive modulus, bending modulus, fracture toughness, elongation, fiber strength, fiber modulus, fiber elongation, thermal expansion coefficient, fracture toughness, static and dynamic elasticity, longitudinal stretch, stress, and strain, radial stretch, stress and strain, circumferential stretch, ultimate elongation, viscosity, expansion, static and kinetic coefficients of friction, c:\nrportbl\syddocs\lf\49452_1 .doc 017 plasticity, axial tension, shock absorbance, bearing strength, and fatigue strength, equivalent to the same properties of a differentiated tissue or tissue structure to be regenerated or constructed and selecting from a combination of monomers that can be polymerized to make a polymer, one or more monomers which when linked in a polymeric form, have the I mechanical property or properties of the tissue or tissue structure. r r

19. The method of claim 18 wherein the monomers are selected from hydroxy acids. The method of claim 18 wherein: the polymer is selected from the group consisting of polyester, poly (orthoester)m, polyanhydride, polyphosphazene, polyesteramide, polypeptide, polyamide, polydihydropyran, and polycyanoacrylate; and/or wherein the polymer contain one or more linkages selected from the group consisting of ester amide, urethane, carbonate, iminocarbonate, oxalate, oxamate, orthoeste, anyhydride, phosphazene, glycoside, and ether linkages. Dated this thirtieth day of April 2007 Tepha, Inc. Patent Attorneys for the Applicant: F B RICE CO c:\nrportbl\syddocs\lfj\49452_1.doc