Ultrafast diffusion-controlled thiol-ene based crosslinking of silicone elastomers with tailored mechanical properties for biomedical applications

Polysiloxanes are commonly used in a wide range of applications, but their crosslinking is typically relatively slow, requires metal catalysts (for hydrosilylation or to catalyse condensation) and depends on storage and curing conditions (humidity level). Thiol-ene click chemistry, on the other hand, is a promising strategy to post-functionalise and cross-link polymers or to introduce different biofunctionalities for applications in the biomedical field. In the present work, we explore the use of the photo-initiated thiol-ene reaction to cross-link a side-chain thiol-functionalised poly(dimethylsiloxane) (PDMS) with telechelic vinyl-PDMS chains at ambient temperature. We investigate the impact of different curing parameters on the network properties and gelation kinetics, using in situ photo-rheology. It is shown that the curing reaction occurs rapidly and very efficiently even in the presence of oxygen in the system. Whilst the mechanical properties of the cross-linked networks are strongly affected by the ratios between thiol and alkene moieties, the molecular weight, and therefore viscosity, of starting macromonomers and UV light intensity showed very small variation in the resulting storage moduli of the formed PDMS networks. The potential of using such materials in biomedical applications and cell culture were highlighted by the good cytocompatibility of thiol-ene PDMS substrates with varying mechanical properties. In addition, by utilising remaining thiol-moieties in the crosslinked networks, strong adhesion between thiol-ene matrices and the acrylate pre-treated glass surfaces was established, in mild conditions. These findings indicate an ability to systematically tailor the mechanical properties of the resulting networks whilst manipulating their surface functionalities, attractive features for a range of applications including 3D printing, microfabrication and cell culture.