Stimuli-sensitive hydrogels can have dramatic and reversible changes in volume under external stimuli, a characteristic crucial in drug delivery, tissue engineering, and sensing applications. Free-standing nanothin hydrogels would be desirable for those applications where substrate-free materials are needed. Indeed, free-standing films can be used as membranes, sensors, wound dressings, catalytic films, micromechanical devices, or even artificial organs. A significant limitation of releasing ultrathin hydrogels from a substrate is associated with their fragile nature. To mediate these drawbacks, we have developed an approach to obtain nanothin free-floating poly(methacrylic acid) (PMAA) hydrogel films through the dissolution of a sacrificial SiO2 layer. The hydrogel films were produced by chemical crosslinking of PMAA in the PMAA/poly(N-vinylpyrrolidone) (PVPON) hydrogen-bonded precursors assembled through spin-assisted multilayer assembly. Surface-anchored precursor films and hydrogels were released from silicon templates into an aqueous solution via etching the thick sacrificial SiO2 layer of the templates. We studied the impact of the release method on the surface morphology, thickness, and elasticity of the released (PMAA/PVPON)60 and (PMAA)60 films using Atomic Force Microscopy (AFM) and demonstrated that these properties were affected neither by the film release nor by their following transfer onto Si wafers. We found that 16-hour crosslinked (PMAA)60 hydrogels and their more swollen 8-hour crosslinked counterparts produced free-floating films with good mechanical integrity and strength. We showed that the elastic moduli of a 16-hour crosslinked (PMAA)60 film decreased by 25 and 136-times upon hydration at pH 5 and 6.5, correspondingly. We also showed that incorporating Zr(IV) into twice thinner, (PMAA)30 hydrogels (60 nm dry thickness), improved film mechanical robustness and allowed their successful release and transfer onto Si wafers. In contrast, Zr-free (PMAA)30 were less tolerant to the release/transfer procedure due to mechanical fragility. The temporary coordination links between Zr(IV) and the hydrogel could be removed from the network by an EDTA chelator. The free-floating hydrogels obtained by this method can be used as transferrable platforms to develop lab-on-a-chip systems, nanocomposite pressure sensing platforms, rapid optical biosensors, and responsive platforms for regulating cell adhesion and more effective cell sheet recoveries.

Free-standing nanothin hydrogels: Effects of composition and pH-dependent hydration on mechanical properties

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.