Fig. 1 Immobilization of BSA or GOX in alginate-based microfibers. (a) Fluorescence imaging of FITC-BSA loaded microfibers. Scale bar = 100 μm. (b) Encapsulation efficiency of BSA in microfibers. (c) Cumulative release of BSA from the microfibers. (d) Relative activity of the encapsulated GOX (mean ± SD, n = 3).
To check the feasibility of microfibers for enzyme immobilization, BSA was used as a model to measure the protein loading capacity and release behavior of protein-encapsulated microfibers because BSA shows similar pI to GOX (Singh et al., 2014; Zore et al., 2017). Fluorescence images of FITC-BSA loaded microfibers demonstrated the successful encapsulation of protein, suggesting the potential for the immobilization of enzymes (Fig. 1a ). The EE of BSA in the selected microfibers at varying feeding concentrations was higher than 95% (Fig. 1b ). The BSA loading capacity (LC) of microfibers increased with BSA content in the inner phase (Fig. S3 ). When the concentration of feeding BSA was 40 mg/mL, the LC was as high as 66%, indicating the excellent performance for protein loading. However, BSA was readily released from the microfibers which were constructed by the physical encapsulation of BSA in the alginate blend when the microfibers were incubated with deionized water (Fig. 1c ). There were only 35%-40% proteins remaining in the microfibers after 3 h incubation. During the preparation of microfibers, the concentrate PEG outer phase was able to constrain the alginate stream and suppress the diffusion of BSA from the inner phase. When the microfibers were transferred to deionized water, loosely bound BSA was prone to diffuse across the macropore of alginate fibers to aqueous phase (Gao et al., 2015; Kahya & Erim, 2019). The leakage of physically adsorbed proteins was further confirmed by the catalytic assays of GOX-loaded microfibers (Fig. 1d ). The relative activity of microfibers decreased to 30% after reuse for 3 times.