Lauric Acid Sophorolipid: Accelerating the Gelation of Silk Fibroin.

Silk fibroin (SF) hydrogels find wide applications in tissue engineering. However, their scope has been limited due to the long gelation time in ambient conditions. This paper shows the reduction in gelation time of silk fibroin to minutes upon doping with a newly synthesized lauric acid sophorolipid (LASL). LASL comprises a fatty acid, lauric acid (with a 12-carbon aliphatic chain), that is derivatized by glucose molecules using a non-pathogenic yeast Candida bombicola. LASL was characterized using spectroscopic (Fourier transform infrared spectroscopy) and chromatographic (high-performance liquid chromatography, thin-layer chromatography, and high-resolution mass spectrometry) methods. This gelation of SF is comparable to the effect of an anionic surfactant, sodium dodecyl sulfate (SDS). The microstructure of SF-LASL hydrogels was investigated by small-angle neutron scattering (SANS) measurements and exhibited the beads-on-a-necklace model. The rheological properties of these hydrogels show similarity to SF-SDS hydrogels, therefore presenting a greener alternative for tissue engineering applications.

Silk Fibroin-Sodium Dodecyl Sulfate Gelation: Molecular, Structural, and Rheological Insights.

A gelling agent is necessary to accelerate sol to gel transition in an aqueous solution of silk fibroin (SF), which otherwise takes several days to complete. In this paper, we investigate the mechanism of gelation of Bombyx mori SF by a model anionic surfactant, sodium dodecyl sulfate (SDS). Even though interactions between SDS and proteins have been extensively investigated, most of these studies have focused on globular proteins, which undergo denaturation. The interaction with a fibrous protein such as SF is different and results in an altered secondary structure leading to gelation. In this work, the concentration-dependent gelation process of the SF-SDS system is examined using rheology, SANS, FTIR, and NMR. We observed preferential binding of SDS to specific regions on the SF chain, which aids structural changes favoring ß-sheet formation. We propose a mechanism for the accelerated sol-gel transition in the SF-SDS system.

Glycomonoterpene-Functionalized Crack-Resistant Biocompatible Silk Fibroin Coatings for Biomedical Implants.

Surface coatings for biomedical implants have been used to prevent premature failure of the implant due to bacterial biofilm formation and foreign body reaction. Delamination, cracking, crazing, etc. are frequent problems associated with coatings when implants are subjected to mechanical deformation either during surgical handling or during use. We demonstrate here a novel process that results in the formation of a coating that is stable under mechanical stresses in tensile, torsion, and bending modes. The coating process involves a combination of two conventional coating processes, namely, dip coating and electrospinning. Polydimethylsiloxane was selected as the substrate owing to its wide use in biomedical implants. Silk fibroin, a natural biocompatible protein polymer obtained from the Bombyx mori silkworm, was used for demonstrating the process of coating. The coating was also further functionalized using a green biomolecule , glycomonoterpene prepared using citronellal and glucose. These functional compounds are being touted as the next-generation antibiofilm molecules on account of quorum sensing inhibitory activity. We have demonstrated that the quorum-quenching activity of the biomolecule is retained during the processing steps and that the coatings exhibited an excellent antibiofilm activity against common infection-causing bacteria, Pseudomonas aeruginosa and Staphylococcus epidermidis. These silk fibroin-glycomonoterpene coatings can be used for implants in biomedical applications such as breast implants and catheter tubings.