Natural origin degradable materials : the barrier or the passage through the immune system?

Biodegradable materials perhaps hold much of the future potential for many biomedical applications due to their advantages when compared to non degradable materials, both in terms of their foreign body reaction and in their gradual elimination and therefore replacement. The stimulus or source of a tissue reaction is always present with non degradable biomaterials and might be the queue for chronic inflammation often culminating with failure. Natural-origin biodegradable materials have emerged, due to their similarities with biological systems, as having additional advantages over synthetic materials. In fact, natural-origin polymeric materials are generally more susceptible to enzymatic degradation and many of the enzymes responsible for that process are present in the human body. The degradation products are often comprised of molecules that can be incorporated in normal metabolic processes. In addition, it would be expected that any other molecules/fragments resulting from the degradation of natural origin implants, because of their nature, could be easily eliminated from the surrounding tissues, thus minimizing inflammation. However, several other aspects should be analyzed and taken into account when considering foreign-body reactions to biomaterials. This chapter will give an overview of the biological elements involved in the inflammatory response to biomaterials, as well as introduce the reader to the significant parameters of materials that might enable modulation and control of biological reactions with particular reference to degradable natural-origin materials