Bonding of hydrogel to silicone elastomer using a self-healing hydrogel–elastomer two-phase material

Hypothesis: Bonding of hydrogel with silicone elastomers may allow fusion of conductivity and biodegradability of hydrogel with the mechanical integrity and flexibility of silicone, desirable for many applications in flexible electronics, ionotronics and microfluidics. However, hydrogels do not bond with silicone unless silicone is suitably functionalized. We hypothesize that a two-phase glue made by blending a self-healing hydrogel (SHH) made of starch, PVA and borax, with silicone will form a bridge between the two materials eliminating need for surface and bulk modification processes. Experiment: The glue was made by dispersing drops of the SHH in silicone, followed by forming a thin layer of this dispersion on a typical silicone surface. Curing of the dispersion bonds it with the later. To bond hydrogel to this glue, its top surface was removed mechanically or chemically, to expose the gel phase to the surface, on which the SHH prepolymer mix was crosslinked. Results: The hydrogel particles in the glue acted as anchors for the hydrogel layer to bond to it; the silicone phase of it, bonded to the elastomeric layer, thereby creating strong attachment between the two. The bonding strength of SHH-TPG was estimated via pull-off experiments which showed that debonding force increases linearly with solid fraction of SHH and sub-linearly with the ageing time of the bonded interface . The SHH-glue interface also exhibits repeated bonding/ debonding for multiple cycles.