Surface enhancements accelerate bone bonding to CPC-coated strain gauges

Calcium phosphate ceramic (CPC)-coated strain gauges have been used for in vivo bone strain measurements for up to 18 weeks, but they require 6 to 9 weeks for sufficient bonding. Osteogenic protein-1 (OP-1), PepTite (a proprietary ligand), calcium sulfate dihydrate (CSD), transforming growth factor beta-1 (TGF-beta1 ), and an endothelial cell layer with and without TGF-beta1 were used as surface enhancements to accelerate bone-to-CPC bonding. Young male Sprague-Dawley rats were implanted with unenhanced and enhanced CPC-coated gauges. Animals were allowed normal activity for 3 weeks and then calcein labeled. Femurs were explanted following euthanasia. A gauge was attached with cyanoacrylate to the opposite femur in the same position as the CPC-coated gauge. Bones were cantilever-loaded to assess strain transfer. They were sectioned and stained with mineralized bone stain (MIBS) and examined with transmitted and ultraviolet light. Mechanical testing indicated increased sensing accuracy for TGF-beta1 and OP-1 enhancements to 105 +/- 14% and 92 +/- 12% versus 52 +/- 44% for the unenhanced gauges. The PepTite and the endothelial-cell-layer-enhanced gauges showed lower sensing accuracy, and histology revealed a vascular layer near CPC particles. TGF-beta1 increased bone formation when used prior to endothelial cell sodding. CSD prevented strain transfer to the femur. TGF-beta1 and OP-1 surface enhancements produced accurate in vivo strain sensing on the rat femur after 3 weeks.