Materials for bioelectronic applications

Abstract

Robust hydrogels, which are biocompatible, transducing, and stable in water for at least 25 days were synthesised with mechanical properties appropriate for the spinal cord. Hyaluronic acid, a naturally occurring polymer, was chemically crosslinked to function as a scaffold and a doping agent in a bioelectronic device. HA is a glycosaminoglycan which provides it with inherent biocompatibility and is therefore an excellent starting material in the production of a bioelectronic device. An organic electrochemical transistor has been designed which mimics the biological communication which occurs in the spinal cord. A key property for this device is its softness, which must be similar to that of the spinal cord. The elastic modulus provides a means of quantifying the softness. Previous studies indicate that the target modulus for the device should be between 5 and 100 kPa. The scaffold presented has a modulus of 20-30 kPa achieved using an indentation method. The aim of the device is to provide information about cellular communication if used in vivo, such as how neurons carry a potential through the body to send a message. To carry out this function an active layer must be present, which consists of either poly(3,4-ethylenedioxythiophene), PEDOT, or poly[bis(3,4 ethylenedioxythiophene)-3-thiophene butyric acid, sodium salt], (PETE-S). For PEDOT to function as a semiconductive material a doping agent must also be present. Fortunately, the carboxylic acid group of hyaluronic acid presents as a natural doping agent to PEDOT. Early scaffolds containing both active layers were characterised as transistors, finding they both display good transistor switching ability and output characteristics.