Results of Biocompatibility Testing of Novel, Multifunctional Polymeric Implant Materials In-Vitro and In-Vivo

Abstract

Extensive in vitro and in vivo evaluation of the biocompatibility of biomaterials intended for clinical applications is necessary to provide informationon the interactions that take place between the organism and these materials under specific implant conditions. Sterilization of polymer-based implant materials is a basic requirement but can lead to their damage or destruction. Low-temperature plasma (LTP) or ethylene oxide (EO) sterilization are objects of intensive research and were applied on the materials used in this program. After 4 weeks of polymer incubation in cell culture medium, samples, sterilized by LTP, gave a markedly higher mean cell lysis rate (3.7 ± 2.5%) than EO sterilized samples (0.9 ± 0.3%). To achieve relevant in vitro results on biomaterial-cell interactions, biocompatibility testing was carried out with cultures of locotypical cells, e.g. cells of the upper aerodigestive tract (ADT). Primary cell cultures of the oral cavity, the pharynx and the esophagus showed region-typical varying relationships between epithelial, fibroblastic and smooth muscle cells. Proper wound healing is thought to be required for the integration of biomaterials and angiogenesis is a prerequisite for this process. A focus of the present work was the influence of polymer-based implant materials and their degradation products on angiogenesis in vivo. After 48 h, none of the polymer samples demonstrated development of an avascular region in the chorioallantoic membrane (CAM) test. A key process in proper wound healing is the tightly controlled degradation and regeneration of the extracellular matrix (ECM). Matrix metalloproteinases (MMP’s) cleave the components of the ECM and are specifically inhibited by tissue inhibitors of matrix metalloproteinases (TIMP’s). Well balanced MMP and TIMP activities are important for the functionality of the ECM. The kinetics of MMP-1, MMP-2 and TIMP activity of oral and pharyngeal cells demonstrated similar surface dependent patterns. The same contrast in surface dependent MMP and TIMP activity levels was not found for esophageal cells. A biomaterial for the reconstruction of the upper ADT is subjected to varying pH values and enzymatic, bacterial and mechanical stress during the digestive and the swallowing process. These complex conditions can currently only be investigated in vivo in an animal model. As a model the stomach of the rat was selected, in which a biomaterial can be investigated under extreme chemical, enzymatic, bacteriological and mechanical conditions. Other parameters investigated are the impermeability of the polymer tissue closure and the tissue regeneration after defect reconstruction. The fluid tight integration of a long term resorbable AB copolymer network in the surrounding tissue of the gastric wall of Sprague Dawley rats could be demonstrated.