Introduction: The Body Fights Back – Degradation of Materials in the Biological Environment

The biological environment, seemingly a mild, aqueous salt solution at 37°C, is, in fact, surprisingly aggressive and can lead to rapid or gradual breakdown of many materials. Some mechanisms of biodegradation have evolved over millennia specifically to rid the living organism of invading foreign substances – these same mechanisms now attack our contemporary biomaterials. Other breakdown mechanisms have their basis in well-understood chemical and physical principles, and will occur in a living organism or in a beaker on a laboratory bench. After this introduction, four chapters (II.4.2, II.4.3, II.4.4, and II.4.5) Chapter II.4.2 Chapter II.4.3 Chapter II.4.4 Chapter II.4.5 ) directly address degradation. The first three of these consider breakdown in the biological environment. Chapter II.4.5 describes another type of degradation, calcification, which can lead to device failure and can exacerbate other degradation mechanisms. In addition, many of the textbook chapters address degradation in other contexts. Chapter I.2.6 reviews the chemistry of polymers designed to be biodegradable. Chapter III.1.3 addresses device failure, sometimes related to unintentional degradation. Most of the device-specific chapters consider degradation issues. Biodegradation as a subject is broad in scope, and critical to device performance. It rightfully should command considerable attention for the biomaterials scientist. This section introduces biodegradation issues for a number of classes of materials, and provides a basis for further study on this complex but critical subject.