Bonding of Hydrogel to Silicone Elastomer Using a Self-Healing Hydrogel–Elastomer Two-Phase Material

Bonding hydrogels with silicone elastomers may allow fusion of the conductivity and biodegradability of hydrogels with the mechanical integrity and flexibility of silicone, which is desirable for many applications in flexible electronics, ionotronics, and microfluidics. However, hydrogels do not bond with silicone unless both materials are suitably functionalized. We show here that a two-phase composite (TPC) glue prepared by blending a self-healing hydrogel (SHH) made of starch, PVA, and borax with silicone forms a bridge between the two materials, eliminating the need for surface and bulk modification processes. 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 the dispersion bonds it with the latter. To bond a 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 cross-linked. The SHH microparticles in the glue acted as anchors for the SHH layer to bond to it; the silicone phase of it at the other side bonded to the elastomeric layer, thereby creating a strong attachment between the two. The bonding strength of the SHH–TPC interface was estimated via pull-off experiments, which revealed that the debonding force scales as n 1/3 ( x p x M 2/3 ) g 2/3, where n is the number of SHH particles in the TPC, g is the SHH weight fraction in the TPC, and x p and x M are the solid contents in the SHH in TPC and the SHH layer, respectively. The SHH–glue interface also exhibits reversible bonding/debonding for multiple cycles.