Hydrogel films and coatings by swelling-induced gelation

Significance This work reports a processing route to fabricate hydrogel films through their rapid and spontaneous growth in aqueous solutions. This approach exploits the strong solvent depletion created at the surface of a polymer substrate swelling in a polymer solution. By immersing substrates that swell in associative polymer solutions, we showed that this local suction effect induces the gelation and growth of hydrogel films. Experiments and a simple model captured how the kinetics of this process can be deliberately controlled by handy processing parameters. Other solutes can be easily incorporated in the so-formed hydrogel films to provide other functionalities. We demonstrated this potential by coating complex shapes with bioceramic particles and by encapsulating mammalian cells in freestanding membranes. Hydrogel films used as membranes or coatings are essential components of devices interfaced with biological systems. Their design is greatly challenged by the need to find mild synthesis and processing conditions that preserve their biocompatibility and the integrity of encapsulated compounds. Here, we report an approach to produce hydrogel films spontaneously in aqueous polymer solutions. This method uses the solvent depletion created at the surface of swelling polymer substrates to induce the gelation of a thin layer of polymer solution. Using a biocompatible polymer that self-assembles at high concentration [poly(vinyl alcohol)], hydrogel films were produced within minutes to hours with thicknesses ranging from tens to hundreds of micrometers. A simple model and numerical simulations of mass transport during swelling capture the experiments and predict how film growth depends on the solution composition, substrate geometry, and swelling properties. The versatility of the approach was verified with a variety of swelling substrates and hydrogel-forming solutions. We also demonstrate the potential of this technique by incorporating other solutes such as inorganic particles to fabricate ceramic-hydrogel coatings for bone anchoring and cells to fabricate cell-laden membranes for cell culture or tissue engineering.