Phospholipid- and gold-induced gelation of Thai silk fibroin and its applications for cell and drug delivery

Abstract

Recently, an in situ gelation, which is a rapid sol-to-gel transition under mild conditions, has been employed, allowing an entrapment of cells or substances in 3D structures as well as tailorable geometries and point-of-care uses. Silk fibroin (SF), a natural polymer from Bombyx mori silkworm cocoons, was chosen in this study as a substrate for the in situ hydrogel fabrication, due to self-assembly characteristic and a presence of modifiable functional groups. However, regenerated SF solution poses a slow gelation (several days or weeks) which is impractical for an in situ application. Therefore, a phospholipid, dimyristoyl glycerophosphoglycerol (DMPG), and a gold salt (Au3+) were introduced as chemical inducers to accelerate the gelation process of SF.

SF hydrogels induced by DMPG can be obtained within 10-40 min depending on the concentration of DMPG. Electrostatic and hydrophobic interactions were proposed as driving forces for inducing SF structural transition. Encapsulated L929 and NIH/3T3 fibroblasts in the hydrogel displayed a normal proliferation, confirming the cytocompatibility of DMPG-induced SF hydrogel. Subsequently, DMPG-based liposomes were prepared and loaded with an anticancer drug, curcumin. The liposomes can enhance loading amount and extend curcumin stability as well as induce the rapid gelation of SF. Curcumin released from liposome-SF hydrogels can inhibit the growth of cancer cells. When using the hydrogel as a substrate for cell culture, low cell survival was observed, possibly due to the combination of low cell attachment on SF and cytotoxicity of curcumin. Moreover, an addition of a gold salt (Au3+) in regenerated and thiolated SF solutions can accelerate the sol-to-gel transition. Dityrosine formation was proposed as an underlying mechanism of gelation for regenerated SF, while the formation of disulfide and Au-S bonds was proposed for thiolated SF. The obtained hydrogels exhibited good cytocompatibility with L929 fibroblasts.

In summary, the rapid gelation of SF can be achieved by the addition of DMPG or Au3+ salt. Different gelation mechanisms were proposed, and the obtained hydrogels showed the in vitro cytocompatibility, indicating the potential uses as a biomaterial for different biomedical applications.