A Biocompatible Pressure Sensor Based on Styrene-Isobutylene-Styrene (SIBS) and Carbon Black

The effect of carbon black (CB) loading percentage on the pressure-sensing capability of a thermoplastic elastomer (SIBS) composite was investigated. SIBS is well-known for its excellent biocompatibility and lack of foreign body reaction during in vivo use. As such, the goal of this effort is the exploitation of this characteristic to develop implantable and/or external (stick-to-skin) pressure sensors. This study represents an initial analysis of sensing performance as a function of carbon black content; a necessary step toward probing the interaction between the competing design goals of retained biocompatibility, suitable mechanical strength, flexibility, and sufficient carbon black content to meet or exceed the percolation threshold as required for sensor functionality. The SIBS/CB composites were manufactured through solution casting in toluene and a combination of high-shear mixing and ultrasonication. The dependence on carbon black content and optimum carbon loading for pressure sensing applications was determined for these composites by measuring the change in voltage (5V max) across the bulk film as a function of pressure via a custom Arduino/Matlab voltmeter. The highest sensitivity was recorded for samples with 20% CB by weight, which exhibited a voltage drop of 1.9 V at the maximum loading of 4861 Pa and a maximum rate of 0.380 mV/Pa. The optimum carbon black loading for maximum sensitivity, 20% by weight, is considerably higher than typical loadings intended to improve mechanical performance. Accordingly, design of pressure-sensing composites based on SIBS will likely require careful tradeoff studies specific to the requirements of each application. Fortunately, SIBS-based composites are uniquely suited to this type of application-specific tailoring due to the ability to adjust molecular weight, styrene content, and carbon black loading to achieve a wide range of material performance and functionality.