In vivo, natural tissues are rarely physically or mechanically homogenous, but rather exhibit a range of elasticities and textures/topographies. Additionally, cells in native tissues reside in a dynamic environment in which the physical environment may change spatially and/or temporally (i.e., during tissue remodeling). Hydrogels are extensively investigated as two- and three-dimensional scaffolds for cells because of their high water content, tunable mechanical and physicochemical properties and their ability to be formed in the presence of biological materials such as cells, proteins and DNA. Therefore, hydrogels in which both topography and elasticity are dynamically tunable undoubtedly represent an important tool for investigating the synergistic effects of inhomogeneities in the physical environment on cell behavior, and better mimic the native microenvironment for tissue engineering applications. Many strategies and materials to produce hydrogels with controllable and patternable elastic moduli and topographic features have been explored, including techniques such as photolithography, micromolding and microcontact printing. Although physically and mechanically patterned materials are obtained, these techniques generally allow either topographic patterning or elastic patterning, but no hydrogel with controlled variations in both topography and elasticity has been reported. Secondly, most of the demonstrated hydrogel patterns are static or predefined, and cannot be altered dynamically, especially once cells have been introduced into the scaffold. Finally, topography control is typically exerted in a “one-way” manner. Here we report a photodegradable hydrogel substrate in which the elastic modulus and hydrogel topography are precisely controlled using light. We exploit changes in hydrogel crosslink density induced via photodegradation to create hydrogels exhibiting complex patterns of both elasticity and topography. These photodegradable hydrogels can act as both positive and pseudo-negative photoresists, depending on exposure time and wavelength. By carefully controlling the aspect ratio (surface area to depth) of micropatterned features, unique swelling-induced ordered microstructures can be formed on the surface. These dual-tone hydrogel photoresists therefore allow dynamic tunability in both topography and elasticity, enabling the fabrication of complex and anisotropic biomaterials.

Dynamic substrate control: Dual-tone hydrogel photoresists

249th National Meeting (2015)

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