Limitations of current techniques for the evaluation of the biohazards and biocompatibility of new candidate materials.

The reasons for the limitations of current techniques for the evaluation of the biohazards and biocompatibility of new candidate materials may be summarized as follows: (1) There is no agreement on how these materials are to be standardized interms of chemical, physical, mechanical, or biological criteria; (2) basic bioengineering data, needed to serve as specifications for reconstruction materials, are lacking for mosttissues in the body; (3) there is a lack of agreement as to what constitutes a valid biological test and its interpretation(s) (4) many in vitro and in vivo tests in animals have limited predictability for humans; (5) there has been an overemphasis on studies of the effect of materials on the biological environment at the expense of bioengineering and biodegration studies; (6) except in cases of obvious problems, there has been relatively little follow-up of the large numbers of patients receiving implanted materials. Little effort has been exerted to exploit this important opportunity to obtain human data: (i) By registering each implant material; (ii) by collecting data on performance; (iii) by collecting data on local or systemic side effects; (iv) by collecting data on biodegradation; (v) by obtaining biopsy or autopsy material whenever possible; and (vi) by examining implants following removal. The limitations of current techniques for the evaluation of new materials are due not so much to the lack of availability of potential test approaches as to a lack of willingness to select, adopt, and actually conduct comparative, objective tests of high predictive value for human patient response. In fact, the confusing array of test approaches and the lack of coordination and completeness of testing efforts has become one of the key factors limiting further progress in materials research, making it difficult for materials scientists and engineers to determine whether their product is likely to be of use in human patients, whether its performance is better or worse than similar products already developed, and hence its potential value as a marketable product. It is proposed that a systematic approach to the development of safe and suitable implant materials focus on three areas of investigation, namely: (1) Matching of the engineering properties of the materials and finished devices with those of the corresponding human tissues; (2) Properties of the implant materials which might exert an effect on the biological system; and (3) properties of the biological environment which might have an effect on the material. To date research on the biocompatibility and biohazards of materials has focused almost entirely on the second area of investigation to the exclusion of the other two. It can be expected that greater attention to the bioengineering specifications of living tissues, and the effects of the biological environment on materials will result in safer materials, exhibiting a closer correspondence to the tissues they are intended to replace. Also greater future emphasis on follow-up human patient material can be expected to substantially advance the knowledge necessary for the development of new implant materials.