To evaluate the mechanical properties of elastomer-hydrogel hybrids generated through thiol-ene coupling, we selected a thiol-ene PDMS formulation with Young's modulus of 0.25 MPa 19 , formed through the combination of thiolated PDMS (PDMS-SH) and a vinyl-terminated silicone (vinyl-PDMS), together with a series of gels displaying a range of chemistries and mechanical properties (Figure ). As a conventional acrylate-based gel, reactive through radical polymerisation, poly(ethylene glycol) diacrylate (PEGDA) was selected, which can readily form hydrogels with relatively high moduli, depending on monomer concentrations . In addition, two hydrogels cured through thiol-ene radical coupling were selected: polycationic hydrogels formed from poly(dimethylpentenylaminoethyl methacrylate) (PDMAEMA-Pent) and polyanionic hydrogels formed from carboxymethyl cellulose functionalised with allyl residues (CMC-Allyl). These hydrogels can be readily crosslinked with poly(ethylene glycol) bis-thiol terminated (PEGDT), and afford materials with a moderate range of mechanical properties, depending on polymer concentration and crosslinking ratio (ratio of thiol to alkene functions) . PDMAEMA-Pent hydrogels, with their high degree of alkene functionality, displayed a broader range of mechanical properties (1-300 kPa). CMC-Allyl based hydrogels displayed softer mechanical properties (0.5-20 kPa), as a result of their lower density of alkene residues, lower achievable concentration (higher viscosity) and more moderate crosslinking efficiency . However, CMC-Allyl gels are relevant to the design of platforms enabling the embedding and culture of cells in vitro, alongside other alkene-functionalised hydrogels formed through thiol-ene crosslinking from backbones such as hyaluronic acid, PEG, poly(2-alkyl-2-oxazoline) or dextran . To prepare elastomer-hydrogel hybrids suitable for tensile testing, we generated elastomer samples in moulds that were then cut and re-positioned to form 5 mm gaps in which hydrogel precursor solutions were deposited. After further photoirradiation to crosslink the hydrogel phase, the samples were carefully removed from the mould and mounted into the clamps of an Instron tensile tester. Therefore sample configuration generated allowed direct mechanical testing of hybrids and probing of the bonding between different phases and failure mechanism. In addition, this allowed the extraction of apparent Youngs' moduli, mostly associated with the mechanical properties of the gel phase. Videos of the samples were captured during deformation to visualise sample deformation and investigate failure (Figure ).