A Mild Strategy To Encapsulate Enzyme into Hydrogel Layer Grafted on Polymeric Substrate

Although the hydrogel network has been widely investigated as a carrier for enzyme immobilization, to in situ encapsulate enzymes into a hydrogel network in an efficient, practical, and active way is still one of the great challenges in the field of biochemical engineering. Here, we report a new protocol to address this issue by encapsulating enzyme into poly(ethylene glycol) (PEG) hydrogel network grafted on polymeric substrates. In our strategy, isopropyl thioxanthone semipinacol (ITXSP) dormant groups were first planted onto the surface of a plastic matrix with low density polyethylene (LDPE) film as a model by a UV-induced abstracting hydrogen-coupling reaction. As a proof of concept, lipase, which could catalyze esterification of glucose with palmitic acid, then was in situ net-immobilized into a PEG-based hydrogel network layer through a visible light-induced surface controlled/living graft cross-linking polymerization. This strategy demonstrates the following novel significant merits: (1) in comparison with the UV irradiation or high temperature, the visible light and room temperature used provide a friendly condition to maintain activity of enzyme during immobilization; (2) the uniqueness of controlled/living cross-linking polymerization not only makes it easy to form a uniform PEG hydrogel network, which is a benefit to avoid the leakage of net-immobilizing enzyme, but also to tune the net-thickness or capacity to accommodate enzyme; and (3) as compared to systems of nanoparticles and porous matrixes, the flexible/robust end-products of the surface net-immobilizing enzyme with polymer film are more suitable to be applied in a bioreactor due to their features of easier separation and reuse. We confirmed that this catalytic film could retain almost all of its initial activity after seven batches of 24 h esterifications. The proposed strategy provides an extremely simple, effective, and flexible method for enzyme immobilization.