TuningMolecular Weights of Bombyx mori (B. mori) Silk Sericinto Modify Its Assembly Structures and Materials Formation

摘要

Bombyx mori (B. mori) silk sericin is a protein with features desirable as a biomaterial, such as increased hydrophilicity and biodegradation, as well as resistance to oxidation, bacteria, and ultraviolet light. In contrast to other widely studied B. mori silk proteins such as fibroin, sericin is still unexplored as a building block for fabricating biomaterial, and thus a facile technique of processing it into a material is needed. Here, electrospinning technology was used to fabricate it into biomaterials from two forms of B. mori silk sericin with different molecular weights, one is a low (12.0 kDa) molecular sericin (LS) form and another is a high (66.0 kDa) molecular weight sericin (HS) form. Circular dichroism (CD) spectra showed that LS in hexafluoroacetone (HFA) solvent adopted a predominantly random coil conformation, whereas HS tended to form a β-sheet structure along with a large content of random coils. In addition, LS and HS in HFA solvent were found to form cylinder-like smaller nanoparticles and larger irregular aggregates before electrospinning, respectively. As a result, biomaterials based on microparticles and nanofibers were successfully fabricated by electrospinningof LS and HS dissolved in HFA, respectively. The cell viability anddifferentiation assay indicated that nanofibers and microparticlesimproved cell adhesion, growth, and differentiation, proving thatthe scaffolds electrospun from sericin are biocompatible regardlessof its molecular weight. The microparticles, not common in electrospinningof silk proteins reported previously, were found to promote the osteogenicdifferentiation of mesenchymal stem cells in comparison to the nanofibers.This study suggested that molecular weight of sericin mediates itssecondary structure and assembly structure, which in turn leads toa control of final morphology of the electrospun materials. The microparticlesand nanofibers of sericin can be potentially used as building blocksfor fabricating the scaffolds for tissue engineering.