Strain transfer between a CPC coated strain gauge and cortical bone duringbending

The finite element method was used to simulate strain transfer from bone to a calcium phosphate ceramic (CPC) coated strain gauge. The model was const ructed using gross morphometric and histological measurements obtained from previous experimental studies. Material properties were assigned based on experiments and information from the literature. Boundary conditions simula ted experimental cantilever loading of rat femora. The model was validated using analytical solutions based on the theory of elasticity as well as dir ect comparison to experimental data obtained in a separate study. The inter face between the bone and strain gauge sensing surface consisted of layers of polysulfone, polysulfone/CPC, and CPC/bone. Parameter studies examined t he effect of interface thickness and modulus, gauge geometry, partial gauge debonding, and waterproofing on the strain transfer from the bone to the g auge sensing element. Results demonstrated that interface thickness and mod ulus have a significant effect on strain transfer. Optimal strain transfer was achieved for an interface modulus of approximately 2 GPa. Strain transf er decreased consistently with increasing interface thickness. Debonding al ong the lateral edges of the gauge had little effect, while debonding proxi mal and distal to the sensing element decreased strain transfer. A waterpro ofing layer decreased strain transfer, and this effect was more pronounced as the modulus or thickness of the layer increased. Based on these simulati ons, specific recommendations were made to optimize strain transfer between bone and CPC coated gauges for experimental studies. (C) 2001 John Wiley & Sons, Inc.