Hydrogel-Solid Hybrid Materials for Biomedical Applications Enabled by Surface-Embedded Radicals

Combinations of hydrogels and solids provide high level functionality for devices such as tissue engineering scaffolds and soft machines. However, the weak bonding between hydrogels and solids hampers functionality. Here, a versatile strategy to develop mechanically robust solid-hydrogel hybrid materials using surface embedded radicals generated through plasma immersion ion implantation (PIII) of polymeric surfaces is reported. Evidence is provided that the reactive radicals play a dual role: inducing surface-initiated, spontaneous polymerization of hydrogels; and binding the hydrogels to the surfaces. Acrylamide and silk hydrogels are formed and covalently attached through spontaneous reactions with the radicals on PIII activated polymer surfaces without cross-linking agents or initiators. The hydrogel amount increases with incubation time, monomer concentration, and temperature. Stability tests indicate that 95% of the hydrogel is retained even after 4 months in PBS solution. T-peel tests show that failure occurs at the tape-hydrogel interface and the hydrogel-PIII-treated PTFE interfacial adhesion strength is over 300 N m(-1). Cell assays show no adhesion to the as-synthesized hydrogels; however, hydrogels synthesized with fibronectin enable cell adhesion and spreading. These results show that polymers functionalized with surface-embedded radicals provide excellent solid platforms for the generation of robust solid-hydrogel hybrid structures for biomedical applications.