Hemocompatibility of styrenic block copolymers for

Authors: Jacob Brubert Stefanie Krajewski Hans Peter Wendel Sukumaran Nair Joanna Stasiak Geoff D Moggridge

Publish Date: 2015/12/24

Volume: 27, Issue: 2, Pages: 32-

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Abstract

Certain styrenic thermoplastic block copolymer elastomers can be processed to exhibit anisotropic mechanical properties which may be desirable for imitating biological tissues The exvivo hemocompatibility of four triblock hard–soft–hard copolymers with polystyrene hard blocks and polyethylene polypropylene polyisoprene polybutadiene or polyisobutylene soft blocks are tested using the modified Chandler loop method using fresh human blood and direct contact cell proliferation of fibroblasts upon the materials The hemocompatibility and durability performance of a heparin coating is also evaluated Measures of platelet and coagulation cascade activation indicate that the test materials are superior to polyester but inferior to expanded polytetrafluoroethylene and bovine pericardium reference materials Against inflammatory measures the test materials are superior to polyester and bovine pericardium The addition of a heparin coating results in reduced protein adsorption and exvivo hemocompatibility performance superior to all reference materials in all measures The tested styrenic thermoplastic block copolymers demonstrate adequate performance for blood contacting applicationsPolymeric elastomers have widespread uses as biomaterials but the full scope of their potential use has not been realised Elastomeric materials are attractive as their properties are tuneable and their mechanical properties are similar to native biological materials A subset of polymeric elastomers possess another property giving them a desirable analogy with biological materials anisotropic mechanical properties that can be induced during processing for some types of block copolymers 1 In particular styrenic block copolymers can exhibit a cylindrical morphology when the fraction of styrene is approximately 18–30  and the other block is a polyolefin such as polyethylene polyisoprene or polyisobutylene 2 Styrenic block copolymers are relatively easy to process via extrusion or injection moulding and the process of shearing or stretching during moulding can be used to align the cylinders and this alignment is preserved upon cooling 3 4 The alignment of the glassy polystyrene cylinders results in macroscopic anisotropic properties Such triblock copolymers also exhibit a form of physical crosslinking between the polystyrene domains which improves their durabilityThe opportunity to fabricate heart valve prostheses from thermoplastic elastomers shows great potential 3 39 Bioprosthetic valves are a current gold standard prosthesis used to treat heart valve disease Unfortunately their durability is a significant shortcoming 5 Alternatively mechanical valves have lifelong durability but are accompanied by the requirement for anticoagulation therapy Polymeric valves have been hailed as offering a potential solution which may be able to overcome issues of durability while not requiring anticoagulant drug regime 6The anisotropic mechanical properties of native heart valves are well characterised and are recognised as essential requirements for the observed durability of native heart valves 7 Given this premise the use of cylinder forming block copolymers which have anisotropic mechanical properties is a promising application In this study we investigate the hemocompatibility of a selection of styrenic block copolymers We selected one of these polymers for a prosthetic heart valve application which was coated with a commercial heparin coating The selected material also underwent direct contact cell viability testingPolystyreneblockisobutyleneblockstyrene SIBS is already in use as a biomaterial for bloodcontacting applications as part of the TAXUS stent It has also been tested as a polymeric prosthetic heart valve material 8 Other cylinderforming block copolymers have been used to fabricate valves for which the hydrodynamics are good 9 In this study we publish ex vivo hemocompatibility data for a range of saturated and unsaturated cylinderforming block copolymer materials which may be used in a prosthetic heart valveStyrenic block copolymers are produced by anionic polymerisation Four cylinderforming block copolymers were examined polystyreneblockpolyisopreneblockpolystyrene containing 30 wt styrene commercial product name Kraton D1164P polystyreneblockpolyisopreneblockpolybutadieneblockpolystyrene commercial product name Kraton D1171 PT with a polystyrene content of 19  denoted as SI/BS19 polystyreneblockpolyethylenepolypropyleneblockpolystyrene commercial product name Kraton G1730 with a polystyrene content of 22  and polystyreneblockpolyisobutyleneblockpolystyrene having 30  wt styrene manufactured by Innovia LLC denoted in this paper as SIS30 SIBS19 SEPS22 and SIBS30 respectively All are linear block copolymersWe also compared our selected polymer to a commercially available glutaraldehydefixed Bovine Pericardium patch trade name PeriGuard with Apex Processing Synovis Life Technologies Inc MN USA In ‘Apex Processing’ the patch is chemically sterilized using ethanol and propylene oxide and treated with 1 molar sodium hydroxide for 60–75 min at 20–25 °C This results in 5 ppm residual glutaraldehyde and is a method used to reduce calcification and improve the hemocompatibility of bioprosthetic heart valves

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