Changing Concepts in Biomaterials Specification

Abstract: Traditionally, biomaterials have been used in areas of medical technology that have been largely dependent on the ability of these materials to perform their mechanical or physical functions for the desired length of time without provoking any undesirable responses from the tissues of the human body. This essential requirement has resulted in the selection of materials for the vast majority of devices which are chemically and biologically as inert as possible.  Thus, most long term implantable devices are constructed from the most corrosion resistant alloys, including some titanium alloys, cobalt-chromium and platinum – iridium, the most degradation resistant polymers such as PTFE, silicones and PMMA, inert oxide ceramics and carbons.  In some situations, a compromise has had to be made when functionality is not found within materials of optimal biocompatibility, including less-than-biostable thermoplastic elastomers and corrosion-susceptible shape memory alloys.  There have been several cases of long term implantable devices where the critically of this functional biocompatibility equilibrium has not been fully appreciated and clinical failures have followed.  At the same time, however, biomaterials are being used in situations that are far removed from these implantable devices, and where these specifications are no longer appropriate or sufficient.  The obvious examples are tissue engineering scaffolds, non-viral vectors for gene transfer, nanoscale drug delivery systems, MEMS devices and biomaterial – based arrays in biotechnological diagnostic systems.  These situations require different concepts of biocompatibility, different specifications and different evaluation procedures. This lecture will explore some of the crucial issues within this changing environment.