Thermoset Polymers for Bioelectronic Interfaces - Engineering of Thermomechanical Properties

In this work, we present three compositions of thiol-click polymers engineered to soften at various degrees upon implantation into the living body. Dynamic mechanical analysis has been used to assess the softening process and the storage modulus under simulated physiological conditions. In detail, we present polymers that are engineered to soften under physiological conditions within 10 to 20 minutes from 1.7-2.5 GPa to 1.7 GPa, 800 MPa, or 20 MPa, dependent on their composition. Critical material parameters such as the glass transition temperature and the cross-link density can be tuned by the choice of monomers and their relative proportions within the pre-polymer solution, as well as by the specific curing conditions used in the polymerization process. Because these polymers are used as substrate material for bioelectronic interfaces, we also present their electrical properties under simulated physiological conditions. For this, electrochemical impedance spectroscopy was used to assess dielectric constant and electrical resistivity. Typical relative permittivity of our compositions ranges from 4 to 6, while volume resistivity ranges from 10E10 to 10E13 Ohm*m, both measured at 37 ° C temperature in phosphate buffered saline solution. We discuss the results in the perspective of building functional electrical circuits on the presented polymer substrates.