Dynamic fatigue of beta tricalcium phosphate bioceramics

Abstract

Tricalcium phosphate (TCP) ceramics are particularly attractive ,candidates for application as temporary implants in the human body to fill parts of skeleton. TCP possesses many favourable properties such as biocompatibility with bone tissue; bioactivity, e.g. ability to form strong bonding with bone tissue, and significant biodegradation behaviour. The lifetime of TCP ceramic implants can be strongly influenced not only by the biodegradation processes but also by fracture mechanics phenomena (subcritical crack growth) when implants are under the action of external mechanical loads and environment (body fluids). Subcritical crack growth results in a time dependence of strength, or delayed failure. This type of failure must be taken into account to avoid structural failure of temporary implant before the completion of bonding reactions or osteogenesis. There are three characteristic regions of subcritical crack growth in ceramics [1, 2]. For delayed failure of ceramic implants in human body, region I, at low values of stress intensity factor, K, is most important. Slow crack growth in region I is attributable to stress-enhanced chemical reactions between ceramics and environment, and the rate of growth is reaction-rate controlled [2]. This part of the K versus crack growth rate, v, diagram is usually described by the relation