This paper presents a sensitive compliance measurement system for determining the stiffness of the adult rat hippocampus. 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. in vitro testing on the brain tissue has s...

This paper presents a novel flexible implantable device to provide high-resolution mechanical strain data from a bone surface in real time. The design of the device has been verified with finite-element analysis, and a prototype has been successfully fabricated which consists of a thin-film metal gauge encapsulated between two layers of parylene-C. The prototype has been characterized simultaneously with a commercial strain gauge using tensile testing. The results indicated that the strain sensitivities of the prototype were approximately 2.5 times greater than those of commercial gauges. In addition, real-time strain data collection has been successfully demonstrated on bone surfaces with the novel devices using mechanical testing of chicken tibiae in three-point bending.

We present a new micro-fabrication process to improve the yield of thin film metal strain gauges that are embedded in a poly-dimethyl-siloxane (PDMS) membrane. This work is directed towards the realization of a flexible, implantable sensor array for measuring surface strain on live bone. Although previous lift-off and peeling processes have been demonstrated to be feasible for fabricating the strain gauges in PDMS, they resulted in a very low yield, approximately 5%. Hence, we implemented a different process to improve the mechanical robustness and fabrication yield. One of the key improvements was the use of wet etching to pattern the thin metal film instead of conventional lift-off. The results demonstrated both an increase in yield to 50% and further miniaturization of the devices. Electromechanical testing results revealed that our metal thin-film gauges have greater gauge factors than commercially available ones, which will result in potentially more precise strain sensing. Various biocompatible adhesives were tested for fixing the micro strain sensor to imitation bone materials. Ultimately this strain gauge will be part of an implantable, wireless array for real-time in vivo monitoring of bone strain in the presence of disease and bone remodeling.

We present the design of a strain gauge embedded in polydimethylsiloxane (PDMS) that could be implanted and used for monitoring strain on surfaces of bones with high resolution. Our ultimate goal is to design and fabricate the device such that it could be used to provide real-time data of strain development in live subject. We have simulated the mechanical characteristics of thin-film metal strain gauges embedded in a flexible substrate made from polydimethyl-siloxane (PDMS) with various loading conditions using ANSYS/spl reg/ finite element analysis tool. Various gauge designs were subjected to stresses from several different directions. Linear relationships between fractional change of resistance and nominal resistance were found for both tensile and compressive stress applied on the gauges. Most significantly, the simulation demonstrated that external stresses were effectively transmitted through the PDMS layer to the thin-film metal, validating our approach.

We present micro-fabrication and device characterization results towards the realization of a flexible, implantable sensor array for measuring surface strain on live bone. Thin-film metal strain gauges were embedded in a poly-dimethyl-siloxane (PDMS) membrane. Various adhesives used to adhere the device to both imitation bone materials and cow bones were tested. The measured strain level and resolution indicates that the device is suitable for bone surface strain measurement. Ultimately this gauge will be part of an implantable, wireless array for real-time monitoring of bone disease and bone remodeling.