In this study, we present a fast and convenient liquid foam templating route to generate gelatin methacryloyl (GM) foams. Microfluidic bubbling was used to generate monodisperse liquid foams with bubble sizes ranging from 220 to 390 μm. The continuous phase contained 20 wt % GM and 0.7 wt % lithium phenyl-2,4,6-trimethylbenzoylphosphinate as photoinitiator. Gelation was achieved via UV-initiated radical cross-linking of GM. After cross-linking, the hydrogel foams were either swollen in water or freeze-dried. The pore sizes of the dry foams were 15−20% smaller than the bubble sizes of the liquid templates, whereas the pore sizes of the swollen porous hydrogels were in the range of the bubble sizes of the liquid templates. Compared to commonly used methods for the fabrication of biopolymer scaffolds, our route neither involves cryogenic treatment nor toxic chemicals or organic solvents and potentially allows for the photoencapsulation of cells.

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The influence of gelatin methacryloyl hydrogel morphology on the sorption and release behavior of metoprolol was studied for both equilibrium and non-equilibrium conditions. For samples examined in equilibrium conditions, no influence of the sample morphology was observed. The maximum sorption capacity q max was determined to be 530 μmol g −1 . Furthermore, up to 100% of the sorbed drug was released from both foamed and non-foamed samples upon immersion into salt solutions, which demonstrates the regenerability of the material. By contrast, the sample morphology strongly influenced the sorption and release kinetics. We found that the sorption and release rate coefficients k increased up to 10 times for foamed hydrogels as compared to non-foamed hydrogels. Furthermore, k increased with increasing ion concentration in the sorption and release medium. This effect was more pronounced for non-foamed hydrogels. The obtained results indicate that the sorption and release rate can be controlled by the morphology of the sorbents and, to some extent, by the ion concentration of the surrounding medium.

Hydrogel foams provide an aqueous environment that is very attractive for the immobilization of enzymes. To this end, functional polymers are needed that can be converted into hydrogel foams and that enable bioconjugation while maintaining high enzyme activity. The present study demonstrates the potential of biotinylated gelatin methacryloyl (GM10EB) for this purpose. GM10EB is synthesized in a two-step procedure with gelatin methacryloyl (GM10) being the starting point. Successful biotinylation is confirmed by 2,4,6-trinitrobenzene sulfonic acid and 4'-hydroxyazobenzene-2-carboxylic acid/avidin assays. Most importantly, a high methacryloyl group content (DM) is maintained in GM10EB, so that solutions of GM10EB show both a sufficiently low viscosity for microfluidic foaming and a pronounced curing behavior. Thus, foamed and nonfoamed GM10EB hydrogels can be prepared via radical crosslinking of the polymer chains. Within both sample types, biotin groups are available for bioconjugation, as is demonstrated by coupling streptavidin-conjugated horseradish peroxidase to the hydrogels. When assessing the substrate conversion rate r A in foamed hydrogels by enzymatic conversion of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), a value for r A 12 times higher than the value for nonfoamed hydrogels of the same mass is observed. In other words, r A can be successfully tailored by the hydrogel morphology.