Stretchable, tunable conducting polymer hydrogels for implantable devices and tissue engineering

Engineers in Prof. Zhenan Bao's lab have developed highly conductive, stretchable composite hydrogel materials that can be used as soft electrodes that match the mechanical properties of a range of biological tissues. This technology combines a biocompatible, conductive PEDOT:PSS-based hydrogel network with a secondary network of material to achieve stretchability or other desirable properties (e.g., adhesiveness, cell binding or self-healing). A prototype of this composite produced a conductive interpenetrating network (C-IPN) with an elastic modulus that could be tuned between 8kPA – 374 kPa without compromising stretchability (>100% strain) or conductivity (>10 S/m). In addition, the material could be easily molded into different shapes to accommodate desired device architectures or experimental setups.

C-IPN's are designed to resolve the mismatch between the elastic modulus of standard conductive electrodes and soft biological tissues. In wearable or implantable devices, this could prevent scarring and enhance stability of bioelectronics interfaces. In tissue culture applications, this could provide appropriate mechanical properties and 3D architecture for cell viability along with the ability to electronically stimulate cells.

Stretchable PEDOT:PSS/polyacrylic acid hydrogels can be tuned to enhance a variety of features and molded into a variety of shapes, depending on the target application. Sample geometries made by casting into silicon molds: b various large shapes (1?cm scale bars); c, d micropatterns of pyramidal structures with features as small as 10??m (scale bar is 200??m c and 100??m d).

Stage of Research
The inventors fabricated prototype C-IPN (conductive interpenetrating networks) materials using a low concentration PEDOT:PSS hydrogel combined with a second polyacrylic acid network. This composite enabled control over the bulk mechanical properties:
-up to 23 S/m conductivity (a record for stretchable PEDOT:PSS-based hydrogels)
-ultra-soft elastic modulus that could be tuned between 8kPA – 374 kPa without compromising stretchability (>100% strain) or conductivity (>10 S/m)