Patterning porosity in hydrogels by arresting phase separation
MetadataShow full item record
Poly (ethylene glycol) (PEG) hydrogels have been used extensively in biological and tissue engineering, because of their outstanding biocompatibility and processability. However, it is not yet possible to process soft materials like PEG hydrogels with the requisite precision and throughput needed to recapitulate macroscopic biological tissue with control over every hierarchical scale. In this study, porous PEG hydrogels are processed by a phase separation method and patterned in a single photolithographic step. The thermodynamics of the temperature triggered spinodal decomposition of a ternary mixture of water, salt, and polymer are studied resulting in a ternary phase diagram and a spinodal temperature plot. Importantly, the state of porosity can be frozen by exposing the hydrogel to UV light to form a crosslinked hydrogel network. The average pore size can be tuned by changing delay between the application of heat and UV exposure. By utilizing grey-scale photomasks, a single process can be used to define regions of pure hydrogel, porous hydrogel with a programmed average pore size, and blank substrate with no hydrogel. In addition to representing a combination of a top-down and a bottom-up processes that enables the realization of complex samples, the simplicity of this process and the versatility of the resultant patterns could provide a useful capability for the definition of hydrogel samples for the development of advanced biomaterials.