(H-294) Force Tunable Pledget Sensors to Monitor Loading in Tendon and Ligament Sutures During Post-Operative Physical Therapy

Introduction:: Approximately 50% of all musculoskeletal injuries within the United States involve tendons and ligaments. When surgical repair is utilized in the treatment of partially or fully torn tendons and ligaments, post-operative physical therapy is vital to restoring tissue function. However, to effectively treat these injuries, the duration and intensity of rehabilitation need to be regulated to prevent tissue reinjury while promoting regeneration. Currently, physical therapy procedures following tendon and ligament repair rely on qualitative factors such as tissue swelling or patient pain tolerance, which can prevent optimal healing outcomes due to patient and medical caregiver variability. Therefore, the goal of this project was to develop and characterize a sensing platform to provide suture loading biofeedback in real-time during physical therapy exercises in order to facilitate personalized, evidence-based rehabilitation therapy. Specifically, this study built upon previous work to generate a portfolio of suture sensors for various orthopedic loading ranges.


Materials and Methods:: To generate clinically feasible implantable suture loading sensors, sensor circuitry was integrated into the design of existing suture pledget accessories and the sensor was engineered to be battery-free and operate wirelessly. Remote transfer of power and data was achieved via electromagnetic coupling with a wearable detection device that was incorporated into existing orthopedic braces. Suture loading force was transduced via bending of a resonant circuit embedded in the suture pledget structure as deformation alters the measured resonance characteristics. Since suture force sensing is based on elastic deformation of the pledget sensors, the geometry of the sensors was varied to achieve force loading ranges from 2-20 N, 10-50 N, and 20-80 N. After sensor manufacturing, sensitivity, loading ranges, and repeatability of the sensing platform were evaluated with a mechanical testing system. An external detection device that can be worn by the patient during physical therapy exercises was also engineered. The influence of alignment and distance between the implanted sensor and external detection device was characterized. Finally, the ex vivo functionality and the in vitro biocompatibility of pledget sensor were determined.


Results, Conclusions, and Discussions:: Results and Discussion:
Mechanical testing of the pledget sensors indicated that suture loading and unloading was linearly related to changes in sensor resonance frequency. Hysteresis associated with loading and unloading conditions of the pledget sensors did not exceed 5% of the full-scale output. Repetitive loading of the pledget sensors produced minimal drift and change in sensitivity over 1000 cycles of recurring loads demonstrating the repeatability of platform. The maximum detection distance between the sensor and external detection device was 8 mm as measured through synthetic gelatin. Radial alignment and tilt angle tests between the sensor and detection device indicated that accurate sensor readings were limited to 7 mm of radial misalignment and 40 degrees of angle misalignment. Pledget sensors sutured in ex vivo ovine tendon demonstrated sensor force sensitivity with applied loading. Finally, in vitro studies with L929 fibroblasts indicated that the pledget sensors were not cytotoxic ( >95% viability).

Conclusions:

Overall, the proposed sensor technology offers physical therapists and patients with a platform for determining suture loading in real-time to aid in providing personized rehabilitation guidance. Future work consists of designing the sensor pledget to be fully biodegradable through the use of bioresorbable metals and polymers and evaluating the biocompatibility and functionality of the pledget sensors in vivo.


Acknowledgements (Optional): : Funding Sources:
Wu Tsai Human Performance Alliance
National Science Foundation Graduate Research Fellowship Program

References (Optional): :