Cytogel: A Cell-Crosslinked Thermogel

Hydrogels are a three-dimensional network material with a high equilibrium water content where chemical, physical, or biomolecular crosslinking systems have been used for the network formation. In this study, we report a thermosensitive cytogel of lactobionic acid/butanoic acid-conjugated poly(ε-l-lysine) (PKLC4). The thermogelation of the aqueous PKLC4 solution (3.5 wt %) was induced by partial dehydration accompanying a random coil-to-β-sheet transition of the polymer. During the sol-to-gel transition, the modulus increased from <0.05 Pa at <10 °C to 1300-1360 Pa at 37 °C. When HepG2 cells were incorporated into the PKLC4 solution, the gel modulus at 37 °C increased to 2300-2670 Pa. Moreover, the gel modulus was significantly affected by the cell type, population of the HepG2 cells, and live/dead states of the HepG2 cells. The cells proliferate better in the biointeractive PKLC4 thermogel than in the bioinert PEG-PA thermogel. To conclude, by combining thermosensitivity and specific binding of the receptor to the substrate, the hydrogel attained a high modulus without delay in gel time. This study provides new insights into hydrogel preparation in that substrate-receptor binding can be utilized as a crosslinking system to control the hydrogel modulus as well as a design principle for three-dimensional cache that improves cytocompatibility for cells.