Shear lap adhesion testing. Glass substrates functionalised with different thiol densities were firstly placed faced to each other at a distance of 1 mm. The photocurable PEGDA hydrogel solutions were then injected into the gap between two glass substrates until reaching the desired dimension (15x25 mm). The glass-gel-glass geometry was then irradiated by UV light (94 mW/cm 2 , 2 min) before being carefully placed into the tensile testing machine (Instron 3342 system with a 10 N static load cell and lap shear rig installed) for the shear lap experiments by tensile loading with a strain rate of 0.1 mm/mm/min. The shear adhesion strength was determined at the point of detachment and the measurement were repeated in triplicate for each experimented condition.