Examples of biomedical materials
The first biomaterials used were gold and ivory for replacements of cranial defects. This was done by Egyptians and Romans. Biological materials such as placenta was used since the 1900s. Celluloid was the first man-made plastic used for cranial defects a polymethyl methacrylate (PMMA) was one of the first polymers accepted since World War II.
The Williams Dictionary of Biomaterials (Williams 1999) defined biocompatibility as “ability of a material to perform with an appropriate host response in a specific situation”. Although this definition seems vague and unhelpful at first glance, it represented a quantum leap forward at the time of its introduction. Prior to this definition, the prevailing view was that successful materials played largely inert roles the body.
A long list of ‘non-properties’ had evolved for ‘successful’ biomaterials: non-toxic, non-immunogenic, non-thrombogenic, non-carcinogenic, and so forth. The above definition required that materials not only provide some function, but also recognized that the interface created by introduction of the material will elicit a biological response. Thus, the idea that the material could be truly inert was essentially rejected with the adoption of this definition. Given today’s level of understanding of our bodies as sophisticated, complex biological environments, the idea that one could place a foreign material without some sort of response seems naive.
Based on the reaction of the tissue to the biomaterial, these are classified into three distinct categories:
Biotolerant Materials: which are separated from bone tissue by a layer of fibrous tissue.
Bioactive materials: which have the property of establishing chemical bonds with bone tissue, known as osseointegration. The collagen and mineral phase of the adjacent bone is deposited directly on the implant surface.
Bioinert Materials: in this class it is possible, under certain conditions, to have direct contact with the adjacent bone tissue. No chemical reactions shall occur between the implant and the tissue.
Recognition of an active interface between biomaterials and biological systems led to several important basic ideas about biocompatibility. These ideas persist today and comprise the essence of biocompatibility.
The first idea is that the interactions at the material–tissue interface occur for both; the material elicits a response from the body and the body elicits a response from the material. All materials will be changed at some level by their introduction into a biological environment—either via corrosion, chemical modification, deposition of substance, degradation, or other mechanism.
This exchange of responses leads to a second idea: that the material–tissue interface is dynamic. As the material and biological tissue are modified by each other, the changes themselves may suppose other changes. Thus, the interface is not static, but is changing over its lifetime. Furthermore, because the human buccal conditions are always changing—by aging, by developing systemic or local diseases by adopting new activities, by eating differently, etc.—any equilibrium established at a material–tissue interface is subject to perturbation.