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.