Biodegradable shape-memory polymers as implant materials

Abstract

Biodegradable polymers are widely used as implant materials, e.g. for surgical suture. Recently, a group of biodegradable materials with shape-memory (SM) has been developed. SM polymers have the capability to change their shape upon exposure to an external stimulus. One problem in suturing is that the suture becomes loose after swelling of tissue went down. Sutures made of SM polymers could provide a subsequent tightening of suture initiated by an external thermal stimulus. Also for knot formation in minimally invasive surgery these polymers are promising materials. In this study we examined the biocompatibility of biodegradable polymers with and without SM effect to assess them for application in contact with endothelium. Two biodegradable thermoplastic polymers were synthesized from approved building blocks. These multi-block copolymers were poly(p-dioxanone)/poly(ɛ-caprolactone) (PPDO/PCL)40/60 and 50/50 with SM properties and PPDO/poly(alkylenglycole adipinate) (PPDO/Diorez) 50/50 without SM effect. The polymers were formed to discs (13 mm in diameter, 1 mm thick) and sterilized with ethylenoxide. Polypropylene was reference material. 3T3 fibroblasts and human umbilical endothelial cells (HUVEC) were used for biocompatibility testing with respect to cytotoxicity, adhesion, proliferation, morphology and functional activity. The materials tested according ISO 10993-5 caused no cytotoxic effects. The studies with HUVEC on the cell-material interaction concerning adhesion, proliferation, morphology and functional activity showed good biocompatibility for PPDO/Diorez. Adhesion of HUVECs on pure PPDO/PCL’s was low. Cell-material interaction was improved after surface modification with adhesion proteins (fibronectin, fibrinogen, collagen) especially for the PPDO/PCL’s. The biodegradable polymers tested are promising materials for application as implant materials.