Engineering Conducting Polymer Hydrogels for Additive Manufacturing and Biointerfaces

Hydrogels are insoluble polymer networks swollen with water (&gt;90% water by mass) and are used widely in biomedical applications for their similarities to native extracellular matrix. For bioelectronics, there are many efforts to build devices based on these materials to achieve tissue-matching stiffness and other tissue-inspired properties in order to improve the biointerface. For making electrodes and other device components based on semiconducting materials, conjugated polymers can be gelled into electronically conducting hydrogels. Such methods include simple mix-and-cast techniques, similar to other methods used widely in traditional (non-conducting) hydrogel processing. We have investigated conducting hydrogels based on the conjugated polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT<i>:</i>PSS) fabricated by mixing in a gelling agent, ionic liquid. We have studied how the hydrogel precursor formulation and other fabrication variables of this method affect gel properties, such as swelling, conductivity, and elastic modulus. Further, we have evaluated the potential of these PEDOT:PSS hydrogels for biointerfacing applications and have found that these gels when processed appropriately are stable in vitro and support mammalian cell culture. Finally, we are developing these conducting polymer hydrogels for compatibility with additive manufacturing to grant structural control of these soft bioelectronic interfaces. Such techniques provide manipulation of dimensions and microporosity, important for assembling these hydrogels into functional devices and optimizing tissue integration.