WO2008030939A2 - Porous polymeric material particularly suited for medical implant applications - Google Patents

Abstract

Porous, biocompatible materials are described for a wide variety of applications. The material is a porous polymer comprising polyisobutylene with pores that are formed by the elution of a sacrificial polymer component out of the polymer by a liquid solvent. This porous polymeric material is suitable for medical implant applications as it is biocompatible, permeable, atraumatic, and does not damage adjacent tissue structures. It can also be made compliant such that it stretches as adjacent tissue structures, which increases durability of the polymer. The porous polymeric material is also suitable for other non-medical applications.

Description

POROUS POLYMERIC MATERIAL PARTICULARLY SUITED

FOR MEDICAL IMPLANT APPLICATIONS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application Serial Nos. 60/824,632 filed September 6, 2006 and 60/825,595 field September 14, 2006, both of which are herein incorporated by reference in their entireties.

BACKGROUND QF THE INVENTION

1. Field of the Invention

[0002] This invention relates broadly to materials suitable for medical implant applications. More particularly, this invention relates to a porous, biocompatible polymeric material.

2. State of the Art

[0003] Biological and synthetic porous materials have been used for selected medical implant applications. Synthetic materials such as expanded polytetrafluoroethylene (ePTFE), porous polyethylene, porous polypropylene, porous polyethylene terephthalate (PET), and the like, have been used to close various surgical incisions. For example, PET and ePTFE are often used in arterial patches to close arterial incisions in the carotids following endarterectomy. Hernias are often patched using fabrics made of PET and composites of PET or polypropylene used in combination with ePTFE. In addition, materials such as ePTFE ribbons or patches are also used in plastic surgery to provide fillers for deep facial defects, and the like.

[0004] In many medical implant applications (e.g., fixing an implant to tissue), the medical implant generally must be porous having pores sizes between 0.01 μm and 100 μm. It is also important that the pores are interconnected and that the structure surrounding each pore is rounded as opposed to sharp and ragged. Additionally, medical implant materials must be sufficiently soft because hard materials are biologically incompatible and cause inflammation at the site of implantation.

[0005] The porosity of the implanted material is important to promote tissue ingrowth and allow oxygen and metabolite permeation. Non-porous materials that prevent metabolite transport may cause the surrounding tissue to necrose. Further, the porosity serves to "soften" the feel or drapiness of the material to enable conformation to various geometries, as otherwise the sharp stiff edges of the otherwise stiff material might erode through tissue. Rounded pores are thus important in medical material applications because they are atraumatic to tissue. Interconnected pores are important for metabolite transfer and tissue in-growth.

[0006] It is known that sharp and ragged pores may be created by the elution of crystalline materials such as salt through polymeric materials (see U.S. Patent 4,657,544 to Pinchuk). It is also known that pores can be created in polymer materials by phase inversion processes whereby the polymer is dissolved in a first solvent then precipitated out onto a porous structure. The precipitation occurs due to the addition of a second solvent that forms a solution with the first solvent but is incapable of retaining the polymer in solution. See U.S. Patent Publication 2005/0055075 to Pinchuk.

[0007] Polymers that have been commonly tried for medical implant devices include polyethylene, polypropylene, polyethylene terephthalate. However, these materials when made porous are known to embrittle with time and fail too often to be desirable for medical implants. Porous polyurethane has also been used but fails due to degradation at high porosity and the increase in surface area of the exposed polymer.

[0008] Biological porous materials are used in homograft patches comprised of cadaver sclera, pericardium, cornea, amniotic membrane, fascia lata, and the like. Biological porous materials are often used to patch holes in the eye. These holes in the eye frequently result from erosion of drainage tubes through the conjunctiva or as a result of disintegration of the conjunctiva by drugs such as mitomycin C or 5- fluorouracil. It is also a common prophylactic practice to prevent erosion of the conjunctiva by protecting drainage tubes with cadaver patches during filtering surgery. These biocompatible cadaver patches are also microporous.

[0009] In addition to porosity and as previously discussed, hardness is another characteristic that must be considered in the selection of medical implant materials. Referring back to synthetics, non-porous slabs of polytetrafluoroethylene, polyethylene terephthalate, polyethylene, and polypropylene are relatively hard materials of Shore 5OD and harder. In addition, none of these synthetic materials are elastomeric. For the purposes of this application, an elastomeric material is capable of deformation under stress and returning to its original shape.

[0010] Processes used to make synthetic materials often make them undesirable for medical implant applications due to the resulting hardness, abrasiveness, or lack of compliance. For example, ePTFE is rendered porous by a technique of sintering microbeads of PTFE together under controlled temperature and pressure and then expanding the sintered construct to form ePTFE. EPTFE is non-compliant and therefore will not stretch with tissue when the tissue becomes elongated. Polyethylene terephthalate, polyethylene, polypropylene, and the like are knitted, woven, or electrostatically spun (non-woven) into textiles or mats to form porous structures. These porous textiles can bend, as they are relatively "open" structures, however, when knitted, woven, or non-woven into tight constructs, they lose their ability to bend easily. In addition, when porosity results in these materials from these processes, they demonstrate undesirable hardness characteristics and become abrasive which limits their usage in superficial areas of the body. For example, if ePTFE were used just below the skin to elevate superficial wrinkles, this synthetic would tend to irritate the implanted area of the skin because the elongation and hardness properties of ePTFE differ significantly from skin. Further, the recipient of the ePTFE would feel an abnormal and undesirable hard and abrasive area under the skin.

[0011] Durability of medically implanted materials is also a concern, particularly in the area of occular implants. For example, erosion of ePTFE or PET fabric occurs when these materials are used in long-term applications such as scleral patches to fix a hole in the conjunctiva or sclera. To address the issue of durability, several other materials have been tried unsuccessfully including polyurethane, silicone rubber, and combinations and copolymers of these materials. Although porous polyurethane has a very high surface area, it is unstable in the body and leads to biodegradation and inflammation. Silicone rubber is a more biostable elastomer, but tends to produce thick hard capsules which render them inappropriate for many superficial applications.

[0012] Biological materials appear to be better suited for use in superficial environments such as the eye because they are less traumatic (more biocompatible) and therefore less likely to erode through the conjunctiva. The drawback of using biological materials is that they are expensive and unavailable in many parts of the world. In addition, biological materials present concerns about the transmission of viruses such as hepatitis, HIV, and the like because they are derived from human tissue.

[0013] Thus, implantable medical materials have numerous requirements to make them suitable for implantation into the human body. The ideal medical material is a non-biodegradable, biocompatible elastomer having a Shore hardness less than 9OA. Additionally, the material should be porous to allow for the in-growth of tissue.

[0014] Therefore, there is a need for a biocompatible, porous material that can be used in places where biological tissue and/or synthetic materials are being used. A suitable substitute material would ideally be inexpensive, soft (i.e., having a Shore hardness of 9OA or less), non-traumatic, non-inflammatory, and would promote tissue in-growth with time. The ideal substitute should also be useable in superficial environments such as under the conjunctiva in the eye. The material must be able to withstand the rigors of implantation into the body without degrading and instigating an inflammatory reaction.

SUMMARY OF THE INVENTION

[0015] It is therefore an object of the invention to provide a biocompatible material suitable for implantation into the human body that is atraumatic (non-inflammatory and non-destructive of surrounding tissues).

[0016] It is another object of the invention to provide an implantable, biocompatible material for use in the human body that is soft having a shore hardness of 9OA or less and/or is compliant such that it stretches with tissue as the tissue is elongated.

[0017] It is still another object of the invention to provide an implantable, biocompatible material for use in the human body that has rounded pores.

[0018] In accord with these objectives, which will be discussed in detail below, a polymeric structure realized from polyisobutylene (and preferably polystyrene) is made porous by compounding a thermoformable polymer component (hereinafter referred to as a "sacrificial polymer component") with a polymer component including polyisobutylene (and preferably polystyrene) in a melt phase to form a melt phase composite polymer blend. The melt phase polymer composite blend is then formed to a desired shape in a solid phase. This formation may occur by a number of mechanical processing steps including compression molding, injection-molding, extrusion, or spin-casting to attain the final desired shape in the solid phase. The formed solid phase composite polymer structure is then rinsed in a solvent bath that dissolves the sacrificial polymer component without substantially altering the polyisobutylene-based polymer component therein, thereby leaving pores that result from the elution of the sacrificial polymer component. Alternatively, the formed solid phase composite polymer structure can be Soxhlet extracted to remove the sacrificial polymer component when it is water soluble (e.g., PEO), thereby leaving pores where the water soluble sacrificial polymer component previously resided.

[0019] In the preferred embodiment, the polyisobutylene-based polymer component of the structure is realized from a block copolymer of poly(styrene-ιb/oc/c- isobutylene-Woc/c-styrene), which is hereinafter referred to as "SIBS" or "SIBS" material. In this preferred embodiment, the SIBS material is made porous by compounding polyethylene oxide (PEO) as the sacrificial polymer component with the SIBS material in a melt phase to form a melt phase polymer blend. The melt phase polymer composite blend is then formed to a desired shape in a solid phase. The formed solid phase composite polymer structure is then rinsed in an aqueous bath that dissolves the PEO component without substantially altering the SIBS component therein, thereby leaving pores that result from the elution of the PEO. Alternatively, the formed solid phase composite polymer structure can be Soxhlet extracted to remove the PEO, thereby leaving pores where the PEO previously resided.

[0020] The pores of the resulting porous structure are preferably round. Such round pores are atraumatic (non-inflammatory and non-destructive of surrounding tissues) to surrounding tissue and are interconnected to allow for tissue ingrowth. The resulting porous structure is implantable and biocompatible material for use in the human body for many applications as described herein. It is also atraumatic for such applications because it is soft with a Shore hardness of 9OA or less and because it is compliant such that it stretches with tissue as the tissue is elongated.

BRIEF DESCRIPTION OF THE EMBODIMENTS

[0021] Figure 1 is a perspective view of the porous membrane realized from porous polymeric material in accordance with the present invention.

[0022] Figure 2 is a perspective view of the porous membrane heat bonded to fabric.

[0023] Figures 3A is a scanning electron microscope (SEM) image of SIBS having a porosity of 30% eluting polyethylene oxide (PEO).

[0024] Figure 3B is an SEM image of SIBS having a porosity of 30%.

[0025] Figure 3C is an SEM image of porous SIBS having a porosity of 30%.

[0026] Figures 4A is an SEM image of SIBS having a porosity of 50% eluting PEO.

[0027] Figure 4B is an SEM image of SIBS having a porosity of 50%.

[0028] Figure 4C is an SEM image of SIBS having a porosity of 50%.

[0029] Figures 5A is an SEM image of SIBS having a porosity of 70% eluting PEO.

[0030] Figure 5B is an SEM image of SIBS having a porosity of 70%.

[0031] Figure 5C is an SEM image of SIBS having a porosity of 70%.

[0032] Figure 6 is a schematic diagram of a vascular graft formed from a porous polymeric material in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] As used herein, the term "porous" refers to a material or structure that has a plurality of holes, perforations, openings, or void spaces (collectively, "pores"). For purposes of this application, pore size shall mean the largest dimension of the pore, and "round pores" are pores that do not have sharp edges and are generally curved about their respective perimeters.

[0034] As used herein, the term "porosity" refers to the ratio of non-solid volume to the total volume of a porous material.

[0035] In accordance with the present invention, a polymeric structure realized from polyisobutylene (and preferably polystyrene) is made porous by compounding a thermoformable polymer component (herein after referred to as a "sacrificial polymer component") with a polymer component including polyisobutylene (and preferably polystyrene) in a melt phase to form a melt phase composite polymer blend. The melt phase polymer composite blend is then formed to a desired shape in a solid phase. This formation may occur by a number of mechanical processing steps including compression molding, injection-molding, extrusion, or spin-casting to attain the final desired shape in the solid phase. The formed solid phase composite polymer structure is then rinsed in a solvent bath that dissolves the sacrificial polymer component without substantially altering the polyisobutylene-based component therein, thereby leaving pores that result from the elution of the sacrificial polymer component. Alternatively, the formed solid phase composite polymer structure can be Soxhlet extracted to remove the sacrificial polymer component when it is water soluble (e.g., PEO), thereby leaving pores where the water soluble sacrificial polymer component previously resided.

[0036] The polyisobutylene-based component of the initial polymeric structure includes polyisobutylene and preferably polystyrene. In the preferred embodiment, the polyisobutylene-based component of the initial polymeric structure is realized from a block copolymer of poly(styrene-ιb/oc/c-isobutylene-ιb/oc/c-styrene), which is referred to herein as "SIBS" or "SIBS" material. SIBS is realized from polyisobutylene and polystyrene. Polyisobutylene (PIB) is a soft elastomeric material with a Shore hardness of approximately 1OA to 3OA. When copolymerized with polystyrene, it can be made at hardnesses ranging up that of polystyrene having a Shore hardness of 100D. Thus, depending on the relative amounts of polystyrene and polyisobutylene, the SIBS material can have a range of hardnesses from as soft as Shore 10A to as hard as Shore 100D. In this manner, the SIBS material can be adapted to have elastomeric and hardness qualities desirable for human implant applications. In the preferred embodiment as a porous material, the SIBS material has a hardness less than Shore 9OA. Details of the SIBS material is set forth in U.S. Patent Nos. 5,741 ,331 ; 6,102,939; 6,197,240; 6,545,097, which are hereby incorporated by reference in their entireties. The SIBS material may be polymerized in a controlled manner using carbocationic polymerization techniques such as those described in U.S. Patent Nos. 4,276,394; 4,316,973; 4,342,849; 4,910,321 ; 4,929,683; 4,946,899; 5,066,730; 5,122,572; and Re 34,640, each herein incorporated by reference in their entireties. The amount of styrene in the copolymer material is preferably between 2 mole % and 50 mole % and most preferably between 5 mole % and 25 mole %. The polystyrene and polyisobutylene copolymer materials are preferably copolymerized in solvents. The preferred SIBS material provides superb biocompatibility and biostability characteristics. Moreover, animal tests have shown an unexpected result in that it will not significantly encapsulate in the eye nor activate platelets in the cardiovascular system resulting in unwanted inflammation.

[0037] Alternative polymeric materials can be used for the polyisobutylene-based component of the initial polymeric structure. Such alternative polymeric materials preferably include polyisobutylene-based material capped with a glassy segment. The glassy segment provides a hardener component for the elastomeric polyisobutylene. The glassy segment preferably does not contain any cleavable group which will release in the presence of body fluid inside the human eye and cause toxic side effects and cell encapsulation. The glassy segment can be a vinyl aromatic polymer (such as styrene, α-methylstyrene, or a mixture thereof), or a methacrylate polymer (such as methylmethacrylate, ethylmethacrylate, hydroxymethalcrylate, or a mixture thereof). Such materials preferably have a general block structure with a central elastomeric polyolefinic block and thermoplastic end blocks. Even more preferably, such materials have a general structure:

BAB or ABA (linear triblock),

B(AB)_n or a(BA)_n (linear alternating block), or

X-(AB)_n or X-(BA)_n (includes diblock, triblock and other radial block copolymers), where A is an elastomeric polyolefinic block, B is a thermoplastic block, n is a positive whole number and X is a starting seed molecule.

Such materials may be star-shaped block copolymers (where n=3 or more) or multi- dendrite-shaped block copolymers. These materials collectively belong to the polymeric material referred to herein as SIBS material.

[0038] As described above, the formed solid phase composite polymer structure can be rinsed in a solvent bath that dissolves the sacrificial polymer component without substantially altering the polyisobutylene-based component therein, thereby leaving pores that result from the elution of the sacrificial polymer component. This rinsing step can be performed at any temperature; however, extraction of the thermoformable polymer occurs more quickly at higher temperatures. When a water soluble, thermoformable polymer is used as the sacrificial polymer component, the temperature for extraction is preferably on the order of 100⁰C. Alternatively, the formed solid phase composite polymer structure can be Soxhlet extracted to remove the sacrificial polymer component when it is water soluble (e.g., PEO), thereby leaving pores where the water soluble sacrificial polymer component previously resided. In either case, swelling agents can be added to the solvent to facilitate elution of the water soluble sacrificial polymer component. Exemplary swelling agents include acetone, isopropyl alcohol, ethanol, methanol, chlorosolvents, and the like.

[0039] In an alternate embodiment, a porous polymeric material can be realized by elution of a sacrificial polymeric component from a polyisobutylene-based thermoset polymer. In an illustrative embodiment, linear or branched prepolymers of polyisobutylene are end-terminated with vinyl groups and polymerized into a thermoset polymer. The end group formation is known by those of ordinary skill in the art of polymer chemistry and can include cyanoacrylate groups, acrylate groups, methacrylate groups and the like. In this embodiment, the sacrificial polymer component is mixed with the polyisobutylene prepolymer prior to polymerizing the prepolymer. The thermoset polymer is processed to form a solid phase polymeric structure. A liquid solution is applied to the solid phase polymeric structure to elute the sacrificial polymeric component therefrom without substantially altering the polyisobutylene-based component therein, thereby leaving pores that result from the elution of the sacrificial polymer component.

[0040] The pores of the resulting porous structure as described herein are round, are generally tortuous in path, and are interconnect to one another. Such pores preferably have a size in a range between 0.01 μm and 100 μm. The round pores are atraumatic to tissue. The interconnection of the pores allows for tissue ingrowth. The resulting porous structure is usually opaque white in color due to the diffraction of light by the porous structure.

[0041] The resulting porous structure is implantable and biocompatible material for use in the human body for many applications. It is also atraumatic (non-inflammatory and non-destructive of surrounding tissues) for such applications because it is soft with a Shore hardness of 9OA or less and because it is compliant such that it stretches with tissue as the tissue is elongated.

[0042] The sacrificial polymer component can be a thermoformable polymer such as polyethylene oxide (PEO), non-crosslinked polyvinylpyrrolidone, non-crosslinked poly(2-hydroxyethylmethacrylate), or non-crosslinked polysaccharides e.g., pectin, gellan, alginate, sulfonated polystyrene, gelatin, etc. The molecular weight of the sacrificial polymer is not of importance as long as it melts at the temperature that the polymer melts without appreciable boiling. In the preferred embodiment, polyethylene oxide (PEO) elution is used as the sacrificial polymer component to create the porosity of the end product.

[0043] The porous polymeric material of the present invention is illustrated in the following example. Porous SIBS was made by melt-phase compounding a mixture of 60% PEO and 40% SIBS material, and compression molding the compounded mixture it into a flat sheet 1 mm thick. The sheet was soaked in deionized water for 24 hours to dissolves the PEO component without substantially altering the SIBS material therein and rendering the sheet porous. A section of the porous sheet was placed over a 10mm diameter orifice connected to a pressure head of 10mmHg. Deionized water was flowed through the orifice and sheet and collected in a beaker. The flow rate measured through this 10mm diameter and 1 mm thick disk was 2.3ml_/min. The permeability of this first sample is on the order of 3.66 x 10^"9 cm². This can be derived according to Darcy's law, which equates the permeability (K) of the material to the flow rate (Q), the viscosity (μ) of the deionized water, the thickness (T) of the sample, the area (A) of the sample, and the pressure drop (P) across the sample as follows:

K = (Q * μ * T) / (P * A)

where Q = 2.3/60 cm³/s = 0.0383 cm³/s

μ = 10^"3 Pa s

T = 0.1 cm

A = 0.7854 cm²

P = 10 mmHg = 1333.2 Pa

K = ( 0.0383 cm³/s^* 10^"3 Pa s^* 0.1 cm) / ( 0.7854 cm^{2 *} 1333.2 Pa)

K = 3.66 x 10^"9 cm²

A similar disk was made using the phase inversion technique as described in U.S. Patent Publication 2005/0055075 to Pinchuk. SIBS material at 10% concentration in THF was pipetted onto a petri dish and the remainder of the petri disk filled with deionized water. The SIBS material is dissolved in the THF and then precipitated out as a porous film. A section of the porous film thus formed was subject to the same flow rate measurement test as above. The flow rate through the disk was less than 0.001 mL/min. The permeability of this second sample is on the order of 1.59 x 10^~12 cm², which can be derived according to Darcy's law in the manner described above. This example clearly shows that the porous polymeric material of the present invention realized by melt-phase compounding a liquid-dissolvable sacrificial component (e.g. PEO) with a polyisobutylene-based component (e.g., SIBS material) yields significantly higher permeability than that achieved by the phase inversion method.

[0044] Exemplary applications of the porous end product as described herein are included in the Table below. Included in the Table are embodiments using porous polymers that do not require long-term biostability. Exemplary polymers for these applications include polyurethane, co-polymers of polyamide, copolymers of polyester, polyolefin, and the like.

[0045] The porosity of the end product can be managed by controlling the relative weights of the sacrificial polymeric component to the insoluble polyisobutylene-based component in the solid-phase composite polymer structure. For example, consider the preferred embodiment where the solid phase composite polymer structure includes SIBS material and PEO. In order to obtain an end product having a porosity of 70%, one would mix 70 grams (g) of PEO with 30 g of SIBS material in the melt phase, form the solid phase composite polymeric structure, and then rinse out the PEO from the solid phase composite polymeric structure with water. The PEO acts as a sacrificial polymer component and is eluted out to form the pores of the end product. Using this technique, a porosity of the end product in a range from 30% to 70% can be accurately controlled and managed. A useful porosity range for the ocular drainage devices listed above would be 30% to 70%. The preferred range of the porosity of the end product is about 40% to about 60%. Figures 3A-C, 4A-C, and 5A-C are scanning electron micrographs of the porous structure thus formed by eluting PEO from SIBS with different PEO contents. Figures 3A-C show the porous SIBS material having a porosity of 30%, with Figure 3A being an edge shot at 50Ox magnification, Figure 3B a top view at 50Ox and Figure 3C a top view at 1000x. Figures 4A-C is the porous SIBS material having a porosity of 50% with Figure 4A being an edge shot at 500 magnification, Figure 4B a top view at 50Ox and Figure 4C a top view at 1000x. Figures 5A-C has a porosity of 70% with Figure 5A being an edge shot at 500 magnification, Figure 5B a top view at 50Ox, and Figure 5C a top view at 1000x. As the porosity increases, the relative pore size increases and the tensile strength of the porous structure decreases.

[0046] The porosity of the end product can also be managed by controlling the molecular weight of the sacrificial polymeric component. For example lower molecular weight elutable polymers generally produce smaller pore sizes due to its ability to disperse in the melt rather than form clumps which would be typical of high molecular weight elutable polymers.

[0047] The pore size of the porous end product as described herein can be varied dependent upon the application and preferably falls within the range between 0.1 μm to 100 μm. For porous end products suitable for vascular graft applications (e.g., self- sealable AV access grafts, coronary grafts, peripheral grafts, stent-graft liners) and vascular patches, it is preferable that the pore size of the porous end product be in the range between 10 μm and 30 μm to allow tissue ingrowth. FIG. 6 illustrates an exemplary embodiment of a vascular graft 110 in accordance with the present invention, which includes an elongate tubular structure 112 formed of a porous polymeric structure as described herein. A central lumen 114 extends through the graft 110. The central lumen 114 is defined by the inner wall surface 116 of the tubular structure 112. The central lumen 114 permits the passage of blood through the graft 110 once the graft 110 is properly implanted in the vascular system. A coating can be applied to the tubular structure 112 in order to render the tubular structure 112 impermeable to blood flowing through the central lumen 114.

[0048] Certain applications such as hernia repair require that the porous material be supported by a load bearing material such as PET fabric. Composites of porous SIBS with PET fabric can be made by laminating one or more films of SIBS/PEO with PET fabric under temperature and pressure. The composite thus formed is then immersed in water to remove the PEO. The result is a fabric reinforced porous matrix (see Figure 2). Materials of this nature can be used for hernia repair, apparel, AV access grafts, vascular grafts, stent-grafts and the like.

[0049] Alternatively, the porous end products as described herein can be realized from other soft elastomeric polymeric material. Preferably, the soft elastomeric polymeric material is biocompatible and biostable. Moreover, it is preferable that the soft elastomeric polymeric material not naturally attract leukocytes and/or myofibroblasts, which protects against encapsulation of the material in the body. An example of an alternate material that may function in this capacity is silicone rubber that has been cleansed of cyclic impurities. Also suitable is the family of methacrylate polymers such as non-crosslinked poly(2-phenylethyl methacrylate), non-crosslinked poly(2-hydroxyethyl methacrylate), and others of this genus.

[0050] Although this invention has been described in multiple embodiments for use in medical implant applications and non-medical applications, it will be appreciated that still other synthetic materials may be used as well. It will therefore be appreciated by those skilled in the art that yet other modifications could be made to the provided invention without deviating from its spirit and scope as claimed.

Claims

WHAT IS CLAIMED IS:

1. A composition of matter, comprising: a porous polymeric material comprising polyisobutylene with pores formed by the dissolution of a sacrificial polymeric component by a liquid solvent.

2. The composition of claim 1 , wherein: said pores are round pores.

3. The composition of claim 1 , wherein: said pores have a pore size not greater than one micrometer.

4. The composition of claim 1 , wherein: the porous polymeric material has a permeability of at least 3.66 x 10^~9 cm².

5. The composition of claim 1 , wherein: said porous polymeric material is biocompatible, compliant, and has a hardness between about Shore 1OA and Shore 9OA.

6. The composition of claim 1 , wherein: said porous polymeric material is formed by compounding a block polymer component comprising polyisobutylene and the sacrificial polymer component in a melt phase to thereby form a melt phase composite polymeric structure, processing the melt phase composite structure to form a solid phase composite polymeric structure, the liquid solution applied to the solid phase composite polymeric structure to elute the sacrificial polymeric component therefrom.

7. The composition of claim 6, wherein: said block copolymer component comprises SIBS material.

8. The composition of claim 5, wherein: said sacrificial polymeric component comprises polyethylene oxide.

9. The composition of claim 1 , wherein: said porous polymeric material is formed by i) mixing a prepolymer comprising polyisobutylene and the sacrificial polymer component, ii) subsequent to the mixing, end-terminating the prepolymer with vinyl groups to form a thermoset polymer, and iii) processing the thermoset polymer to form a solid phase polymeric structure; wherein the liquid solution is applied to the solid phase polymeric structure to elute the sacrificial polymeric component therefrom.

10. The composition of claim 1 , wherein: said block copolymer component comprises SIBS material.

11. The composition of claim 1 , wherein: said sacrificial polymeric component includes one of polyethylene oxide, sulfonated polystyrene, non-crosslinked polyvinylpyrrolidone, and non-crosslinked poly(2-hydroxyethylmethacrylate).

12. The composition of claim 1 , wherein: said sacrificial polymeric component is water soluble and said liquid solution includes water.

13. A method for making a porous polymeric material comprising the steps of: a) forming a polymeric material comprising a polyisobutylene-based component and a sacrificial polymeric component; and b) forming pores within said polymeric material by dissolving said sacrificial polymeric component in a liquid solution.

14. The method of claim 13, wherein: said pores are round pores.

15. The method of claim 13, wherein: said pores have a pore size not greater than one micrometer.

16. The method of claim 13, wherein: said porous polymeric material is biocompatible, compliant, and has a hardness between about Shore 1OA and Shore 9OA.

17. The method of claim 13, wherein: in a), said polymeric material is formed by compounding a block polymer component comprising polyisobutylene and the sacrificial polymer component in a melt phase to thereby form a melt phase composite polymeric structure, and processing the melt phase composite structure to form a solid phase composite polymeric structure; and in b), the liquid solution is applied to the solid phase composite polymeric structure to elute the sacrificial polymeric component therefrom.

18. The method of claim 17, wherein: said block copolymer component comprises SIBS material.

19. The method of claim 17, wherein: said sacrificial polymeric component comprises polyethylene oxide.

20. The method of claim 13, wherein: in a), said porous polymeric material is formed by i) mixing a prepolymer comprising polyisobutylene and the sacrificial polymer component, ii) subsequent to the mixing, end-terminating the prepolymer with vinyl groups to form a thermoset polymer, and iii) processing the thermoset polymer to form a solid phase polymeric structure; and in b), the liquid solution is applied to the solid phase polymeric structure to elute the sacrificial polymeric component therefrom.

21. The method of claim 13, wherein: said polyisobutylene-based component comprises SIBS material.

22. The method of claim 13, wherein: said sacrificial polymeric component includes one of polyethylene oxide, sulfonated polystyrene, non-crosslinked polyvinylpyrrolidone, and non-crosslinked poly(2-hydroxyethylmethacrylate).

23. The method of claim 13, wherein: said sacrificial polymeric component is water soluble and said liquid solution includes water.

24. A composition of matter, comprising: a porous polymeric material comprising polyisobutylene with pores, said porous polymeric material being biocompatible, compliant, and having a hardness between about Shore 1OA and Shore 9OA.

25. The composition of claim 24, wherein: said pores have a pore size not greater than one micrometer.

26. The composition of claim 24, wherein: the porous polymeric material has a permeability of at least 3.66 x 10^~9 cm².

27. An implantable medical device comprising: a structure realized from a porous polymeric material comprising polyisobutylene with pores formed by the dissolution of a sacrificial polymeric component by a liquid solvent.

28. An implantable medical device according to claim 27, wherein: said structure provides a lumen for blood flow therethrough.

29. An implantable medical device according to claim 28, wherein: said structure comprises an elongate tubular structure for use as a vascular graft.

30. An implantable medical device according to claim 27, wherein: said structure is supported by a load bearing material.

31. An implantable medical device according to claim 30, wherein: said device is used as a patch for hernia repair.

32. An implantable medical device according to claim 30, wherein: said load bearing material comprises PET fabric.

33. An implantable medical device according to claim 32, wherein: said PET fabric is laminated to said structure before dissolution of the sacrificial polymeric component.

34. An article of manufacture implantable comprising: a structure realized from a porous polymeric material comprising polyisobutylene with pores formed by the dissolution of a sacrificial polymeric component by a liquid solvent.

35. An article of manufacture according to claim 34, wherein: said structure is supported by a load bearing material.

36. An article of manufacture according to claim 35, wherein: said load bearing material comprises PET fabric.

37. An article of manufacture according to claim 36, wherein: said PET fabric is laminated to said structure before dissolution of the sacrificial polymeric component.