Soft Elastomeric Capacitor for Strain and Stress Monitoring on Sutured Skin Tissues.

Sutures are ubiquitous medical devices for wound closures in human and veterinary medicine, and suture techniques are frequently evaluated by comparing tensile strengths in ex vivo studies. Direct and nondestructive measurement of tensile force present in sutured biological skin tissue is a key challenge in biomechanical fields because of the unique and complex properties of each sutured skin specimen and the lack of compliant sensors capable of monitoring large levels of strain. The authors have recently proposed a soft elastomeric capacitor (SEC) sensor that consists of a highly compliant and scalable strain gauge capable of transducing geometric variations into a measurable change in capacitance. In this study, corrugated SECs are used to experimentally characterize the inherent biomechanical properties of canine skin specimens. In particular, an SEC corrugated with a re-entrant hexagonal honeycomb pattern is studied to monitor strain and stresses for three specific suture patterns: simple interrupted, cruciate, and intradermal patterns. Stress is estimated using constitutive models based on the Fractional Zener and the Kelvin-Voigt models, parametrized using a particle swarm algorithm from experimental data and results from a validated finite element model. Results are benchmarked against findings from the literature and show that SECs are valuable for clinical evaluation of tensile force in biological skins. It was found that both the ranking of suture pattern performance and the sutured skin's Young's modulus using the proposed approach agreed with data reported in the literature and that the estimated stress at the suture level closely matched that of an approximate finite element model.

A Tunable Resonance Cantilever for Cardiac Energy Harvesting.

PURPOSE: Energy harvesting from cardiac motion is an attractive means to avoid the use of batteries in implantable sensors and pacemakers. A single implantable device would ideally integrate both sensing and self-powering functionality. METHODS: This work describes a novel electromagnetic system that achieves high sensitivity detection of the heart rate while simultaneously providing adaptive energy harvesting capability using a tunable resonance cantilever mechanism. RESULTS: Our prototype design exhibits tunability of resonant frequency across the range of physiologic heart rates at a combination of lengths and angular orientations. Our initial prototype also produces between 3.0 [Formula: see text]W and 20.6 [Formula: see text]W of power at heart rates of 79-243 bpm, respectively. CONCLUSIONS: The prototype device can harvest sufficient energy to sustain implantable cardiac devices such as a leadless pacemaker. The system in this paper has the potential to eliminate batteries in certain implantable cardiac devices and thereby improve overall patient monitoring and treatment.