| Monitoring strain within biological tissues in real me will help better understand biomechanical behaviors of the tissues and facilitate the development of biomechanical prostheses, diagnostic devices and assistive rehabilitation. However, currently available devices for measuring strain are too large (typically 2 ∼ 5 mm) to provide measurements with suitable resolution. These gauges are also difficult to mount on hard tissues, such as bone, because of their large size and the bone's irregular surface topology. In addition, they cannot sustain the high strain level (as much as 30%) of those in soft tissues including muscles, ligaments, tendons, and heart valves. Hence, in this work, we present two Micro Electromechanical Systems (MEMS) based implantable devices to provide high-resolution mechanical data from bone surface and muscle in real time. The strain sensitivities obtained from the Parylene-based strain gauge were found to be higher than those of the commercial gauges. The three-point bending on the chicken tibia demonstrated the capability of the strain gauges monitoring the surface strains in real-time, even up to the fracture point of the bone. We have also done feasibility studies of the carbon black filled polydimethylsiloxane (PDMS) as the sensing element for strain measurement of soft tissues. The high sensitive piezoresistive and flexible behavior of the composite device was observed.; Furthermore, we have developed a sensitive compliance measurement system for determining the stiffness of the adult rat brain tissue, especially the hippocampus. Through MEMS technology, the device has been successfully fabricated which consists of two strain gauges incorporated in the SU-8 based cantilever. The cantilever-sensor has been fully characterized and its strain sensitivity was found to be approximately 2.5. The in vitro testing on the brain tissue has demonstrated that the system is sensitive to provide distinctive direct stiffness measurements on various hippocampal regions. |
