Regenerated Protein Fibers

Keywords

Bovine serum albumin • Solubility • Cross-linking • Aligned fiber • Globular core • Reproducing BSA • Recombinant B. mori

Bovine serum albumin was dissolved in water using dithiothreitol as a reducing agent at a pH of 4.7, and the solution obtained was poured onto glass plates. Proteins were dehydrated at 30 °C, and 30 % humidity and fibers were formed by pulling air over the solution at a constant flow rate leading to fibrillation [13Wu]. Fibers obtained were cross-linked with formaldehyde dissolved in metha­nol and additionally cross-linked again with 0.1 % glutaraldehyde or with EDC. Average length of the fibers obtained was 35 cm, and the diameter of the fibers was between 10 and 20 pm. Figure 53.1 shows the image of the fibers obtained. It was found that the fibers consisted of ordered p-sheets at the ends and with globular regions at the center as seen from the SEM image in Fig. 53.2. However, the structure and properties of the fibers were dependent on protein concentration, pH, degree of cross-linking, and other fiber-forming conditions. Fibers without cross-linking dissolved in water or 50 % methanol but reassembled into original fibers when the solvent was removed. Table 53.1 provides a comparison of the tensile properties of the albumin fibers with Bombyx mori silk. As can be inferred from the table, the albumin fibers have strength similar to that of silk, higher modulus, and similar elongation. Higher amounts of tightly packed p-sheets were suggested to provide good tensile properties to the fibers after cross-linking. Fibers were also dyed using acid dyes and spun into yarns. Pictures of the dyed fibers and yarns spun from the fibers are shown in Fig. 53.3.

Recombinant human serum albumin (rHSA) proteins were obtained using trans­genic silkworms with structure and properties similar to that of the native albumin [07Oga]. The DNA from HSA was introduced into silk glands through PiggyBac- based transformation vector, and the glands were transplanted into larvae and reared to produce silk fibers. To obtain HSA that could be easily collected without

Fig. 53.1 Digital image of albumin fibers produced via dehydration and cross-linking [13Wu]. Reproduced with permission from Wiley

Fig. 53.3 Digital picture of the yarns made from the albumin fibers (a) is 35 cm long yarn made using 0.2 grams of fibers having 180 turns per inch and (b) is yarn made from 0.5 grams of fibers having 220 turns per inch. [13Wu]. Reproduced with permission from Wiley

using harsh solvents or contamination from other proteins, the authors attempted to express the HSA genes in the sericin layer of the fibers since sericin dissolves in aqueous solvents. As seen from Fig. 53.4, the authors successfully produced BSA in the outer sericin layers. BSA up to 83 % in the sericin with a purity of up to 99 % was extracted from the cocoons by immersing the cocoons in PBS at 4 °C for 24 h and later precipitating the BSA using ammonium sulfate or blue-sepharose binding. The yield of protein ranged from 2.8 to 5.5 %. In terms of structure, the recombinant

BSA was found to have antiparallel p-sheets, and the primary and secondary structures were similar to that of native BSA [07Oga].

References

[07Oga] Ogawa, S., Tomita, M., Shimizu, K., Yoshizato, K.: J. Biotechnol. 128, 531 (2007) [13Wu] Wu, Y., Wang, K., Bushcle-Diller, G., Liles, M. R.: J. Appl. Polym. Sci. 129, 3591 (2013)