Abstract

Microscopic Laser Photolithography for Designing In Situ Architectures in 3D Cell-Laden Hydrogels

Dror Seliktar, Associate Professor, Faculty of Biomedical Engineering, Technion-Israel Institute of Technology

One of the key advantages in using light-sensitive hydrogel biomaterials is the ability to spatially structure cell scaffolds with three-dimensional mechanical cues that guide cellular morphogenesis. However, creating unique mechanical landscapes within these materials – with resident cells present – has proven difficult because of the high toxicity associated with the localized photochemical interactions. To overcome this challenge, we developed a new paradigm in micro-patterning using a reversible temperature-induced phase transition from liquid to solid vis-à-vis lower critical solubility temperature (LCST) in order to facilitate reduced transport kinetics of the polymer chains in solution, thus enabling mild microscopic photo-chemical crosslinking that is truly compatible with cell-laden 3D culture. Temperature responsive bioactive hydrogels were made from fibrinogen and Pluronic®F127 (FF127) that are physically crosslinked at physiologic temperatures and can be locally altered by mild in situ chemical cross-linking using microscopic photolithography, without compromising cellular viability. FF127 constructs made with rhodamine-labeled F127-Acrylate were used to pinpoint the patterned regions of chemical crosslinking in the physically crosslinked hydrogels, while particle tracking microrheology was used to study the local mechanical properties of these heterogeneous networks. Cellularized constructs where patterned to reveal a difference in morphogenesis between chemically crosslinked “stiffer” and physically crosslinked “softer” regions. Emphasizing the importance of mechanical heterogeneity in cellular morphogenesis, the results validate cutting-edge technology that can provide scientists with a robust set of tools for engineering cell and tissue growth in three dimensions.