Evaluation of a New CPC-to-Gauge Bonding Technique with the Use of In Vitro Fluid Flow

Strain gauging enables the measurement of bone deformation during physical activity, leading to a better understanding of the physiological effects of loading on bone growth and remodeling. Development of a technology that will withstand long-term in vivo exposure and bond securely to bone is imperative for accurate, consistent measurement collection. Polysulfone is currently used to attach calcium-phosphate ceramic (CPC) particles, which promote bone-to-gauge bonding, to polyimide-backed strain gauges. This study evaluated the use of an implant-grade epoxy as an alternative CPC-polyimide adhesive. Polyimide-epoxy-CPC interfaces were loaded to failure and shear strengths calculated. In vitro studies providing a constant flow of medium over test specimens were designed, and long-term in vitro fluid exposure studies of the epoxy's shear strength were conducted. Average shear strength of polysulfone-polyimide interfaces were reported to be 7 MPa. The average shear strength of the epoxy-polyimide interface before long-term in vitro exposure was 17 MPa, which is stronger than the shear strength of the bone-CPC interface. The strength of the epoxy-polyimide interface decreased to 6.8 MPa after 24 weeks in vitro and 3 MPa after 24 weeks in vivo.