A new generation of materials for neural recording electrodes comprises shape memory polymers (SMPs). These materials have the capability to undergo softening after insertion in the body, and therefore reduce the mismatch in modulus that usually exists between the device and the tissue. We want to understand how a key material property, stiffness, influences the robustness of implantable neuroprosthetic technology. Therefore, we have developed novel intracortical probes which differ only by their ability to soften and become compliant at physiological conditions. We have applied a new testing protocol to provide accurate thermomechanical measurements of thin SMP films and demonstrate variable compositions to reliably adjust the glass transition temperature (Tg) from 40 to 90 °C in the dry state. Furthermore, we tested test devices in aqueous environments and found that Tg shifts by approximately 10 to 15 °C after plasticization of thin films. Depending on the monomer composition, the polymers could undergo various degrees of softening under physiological conditions, ranging non-softening to softening over 2 magnitudes of order. Important for the applicability of self-softening, SMP based devices in vivo is, that they can be sterilized without altering their thermomechanical properties. Hence, we have studied the response of our SMPs to various sterilization methods listed in the FDA guidance for industry. We have found, that the sterilization with ethylene oxide is an appropriate method for our temperature sensitive polymers. To get a better understanding of the robustness of the devices, we are currently studying the mechanical durability of the base material and the electrochemical integrity of test devices against accelerated aging in physiological solution at elevated temperatures. For my future career, I want to focus my research on the enteric nervous system (ENS). Many gastrointestinal diseases are related to dysfunctions of the ENS, but they are not well understood. I want to use my expertise in structure-property relationships of polymers and my knowledge about neural devices, to develop conformal electrode arrays for recording and stimulation of the gut.

Self-softening shape memory polymers as a substrate for bioelectronic devices

254th National Meeting (2017)

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