“…A penetrating probe that is too soft will deform upon insertion into the tissue and fail to reach its intended target, and a surface device which is too rigid may not remain flush with the curved and convoluted surfaces typical of anatomy, causing its electrodes to be too far from the targeted cells to function effectively. Implantable bioelectronics with penetrating structures have traditionally been constructed of rigid materials with high moduli of elasticity (100-1000 GPa) to facilitate insertion; however, since neural tissues are soft (1-10 kPa), recent advances in implantable bioelectronics have focused on reducing the mechanical mismatch between the device and the tissue by using soft tissue-like materials as device substrates [31,33,[65][66][67][68][69][70][71], with the intended effect of enhancing device integration and reducing the body's response to the implanted device. Nonetheless, every substrate material has its own advantages, challenges, and requirements which must be understood in order to select the optimal material for the desired application.…”