Development and validation of embedded micro wireless strain sensor array for in vivo characterization of contact stress distribution in hip replacement

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SUMMARY Total hip arthroplasty (THA) is one of the most widely performed orthopedic surgeries in the US. Unfortunately, many follow-up revisions are often expensive and ineffective. Many simulation studies show that the failures are caused by edge loading and excess stresses resulting from inappropriate component positions or size selections during surgeries. The lack of an in vivo stress distribution characterization method at the joint interface currently prevents the fundamental understanding of the effect of surgery factors such as the positioning and choice of implants on the THA outcome. Our goal is to develop embedded, micro wireless strain sensors for in vivo characterization of the biomechanical stress distribution and validate their usefulness in THA. The project will harvest our recent breakthroughs in development of embeddable microfluidic sensors that are highly sensitive to micro-strains. These sensors will be further developed into arrays and embedded into the UHMWPE insert for in vivo measurement of the stress distributions. The sensor arrays embedded in UNMWPE will be calibrated and validated using cadaver testing. We will also study the effect of the radiographic inclination angles and anteversion angles on the stress distributions at the contact interface of the hip joint. The underlying hypothesis is that the femoral/acetabular bearing surface stress distribution is strongly correlated with the positioning, and the quantitative correlation (once established) can be used to guide THA and improve its outcome. We will pursue three specific aims. Aim 1: Develop and calibrate micro wireless strain sensors embedded within UHMWPE. Aim 2: Validate the strain mapping capability of the sensor array embedded UHMWPE using cadaver testing and finite element modeling. Aim 3: Preliminarily evaluate the embedded strain sensors in animal studies. This research is innovative in that it will provide a precise, in vivo stress distribution characterization method at the hip joint interface, which is currently greatly needed but unavailable. This research is significant in that we will 1) Establish the fabrication method of the highly sensitive, micro-sized, biocompatible, embedded wireless strain sensors; 2) Enable the analysis of surface stress distribution with different implant positioning; 3) Provide a useful tool for future fundamental studies on the interrelated effects of other THA parameters, such as the component sizes and ligament tension, on the biomechanical environment at femoral head/UHMWPE insert interface. Providing a new tool for in vivo characterization of the stress distribution, this project integrates with the COBRE's research theme in virtual human trial to improve musculoskeletal health.