Tissue-Like Conductive Hydrogel Materials

Conductive hydrogels are polymeric networks that are electrically conductive and with applications ranging from tissue engineering scaffolds to bioelectronic interfaces in implantable surface arrays. The mechanical softness, biocompatibility, and tissue-like properties of hydrogels is compromised by the high volume fraction of conductive fillers needed to create composites that are highly conductive. We describe a technique to fabricate conductive hydrogels by mechanically suspending various conductive particles in an alginate matrix. Our approach allows for tunability of the electrical, mechanical, chemical, and structural properties of the gels. While metal microparticles (e.g. tungsten) can be added up to 60% weight/volume in the gel, we are able to fabricate conductive formulations using carbon nanomaterials with less than 2% weight/volume additives. By adjusting the molecular weight and crosslinking density of the alginate, we can precisely control the stiffness and viscoelasticity of the gels, to match the properties of fresh mammalian brain (~1 kPa in modulus, tan(d) ~0.35) while keeping a conductivity &gt;10 S/m. Interpenetrating networks of alginate and polyacrylamide can produce highly stretchable (&gt;300%) gels, with less than a 2x increase in resistance. The alginate can also be functionalized with cell-binding ligands, such as RGD, to promote cell integration into the networks. If we freeze the gels before crosslinking the formulations, we can create microporous materials (pores~1 µm – 150 µm, by adjusting the freezing temperature). After characterizing the properties of these bioinspired electronic materials, we have incorporated multiple cell types (D1 MSC, primary neurons) into the scaffolds to see how the structure and conductivity affect resulting cell-material interfaces and networks. Finally, we have processed these conductive hydrogels and integrated them in fully viscoelastic surface electrode arrays to stimulate and record <i>in vivo. </i>