In this study, we prepared and characterized enzyme (α-chymotrypsin or lactase)-encapsulating core-shell fibermats by electrospinning. The hydrophilic copolymer of acrylamide (AM) and diacetone acrylamide (DAAM), poly(AM/DAAM), was used as the base material to obtain the core unit of nanofibers. During electrospinning, poly(AM/DAAM) was crosslinked with the bifunctional crosslinker adipic acid dihydrazide (ADH) in the presence of enzyme molecules. The cores were wrapped with hydrophobic poly(ε-caprolactone) (PCL) layers as shell unit. Different from the fibermats of only poly(AM/DAAM)/ADH, the core-shell fibermat of poly(AM/DAAM)/ADH and PCL exhibited sufficient mechanical strength and stability of the stacked nanofibrous structure in a neutral-pH buffer. Furthermore, when the PCL-shell thickness was controlled to be less than 150 nm, the encapsulated enzymes exhibited an apparent activity of >70–80% for low-molecular weight substrates in an immersion buffer. These results indicate that the core-shell fibermats of poly(AM/DAAM)/ADH and PCL (or other hydrophobic polymer) could be used as effective enzyme-immobilizing platforms.

Background: A core-shell fiber mat is one of the attractive platforms for this purpose. However, very few details the importance of choosing the suitable material for the shell units that can endow efficient release properties. The tailored design of cytokine-releasing scaffolds aiming at in situ regenerative therapy is still one of the crucial issues to be studied. Objective: In this study, we characterized the effectiveness of core-shell fiber mats that possess cross-linked gelatin (CLG) as the shell layer of constituent nanofibers, as a protein-releasing cell-incubation scaffold. Methods: We utilized a crosslinked copolymer of poly (acrylamide)-co-poly (diacetone acrylamide) (poly (AM/DAAM)) and adipic acid dihydrazide (ADH), poly (AM/DAAM)/ADH for the core nanofibers in the core-shell fiber mats. By coaxial electrospinning and the subsequent crosslinking of the gelatin layer, we successfully constructed core-shell fiber mats consisting of double-layered nanofibers of poly (AM/DAAM)/ADH and CLG. Using fluorescein isothiocyanate-labeled lysozyme (FITC-Lys) as a dummy guest protein, we characterized the release behavior of the core-shell fiber mats containing a CLG layer. Upon loading essential fibroblast growth factor (bFGF) as cargo in our fiber mats, we also characterized the impacts of the released bFGF on the proliferation of the incubated cells. Results: Although the single-layered poly (AM/DAAM)/ADH nanofiber fiber mats did not adhere to the mammalian cells, the core-shell fiber mat with the CLG shell layer exhibited good adherence and subsequent proliferation. A sustained release of the preloaded FITC-Lys over 24 days without any burst release was observed, and the cumulative amount of released protein reached over 65% after 24 days. Upon loading bFGF in our fiber mats, we succeeded in promoting cell proliferation and highlighting its potential for therapeutic applications. Conclusion: We successfully confirmed that core-shell fiber mats with a CLG shell layer around the constituent nanofibers were practical as protein-releasing cell-incubation scaffolds.