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 β‐1 (TGF‐β1 ), and an endothelial cell layer with and without TGF‐β1 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‐β1 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‐β1 increased bone formation when used prior to endothelial cell sodding. CSD prevented strain transfer to the femur. TGF‐β1 and OP‐1 surface enhancements produced accurate in vivo strain sensing on the rat femur after 3 weeks. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res 56: 109–119, 2001