Silk fibroin (SF) composed of heavy chains (Fib-H), light chains (Fib-L), and fibrohexamerin, is a desirable material for many tissue engineering applications due to its superior moldability and biocompatibility. In this work, we produced transgenic silkworm lines, which express a recombinant protein comprising the basic fibroblast growth factor (bFGF)-binding P7 peptide with homology to bFGF receptors introduced at the C-terminus of the fibroin L-chain, using the piggyBac vector. As a result, one transgenic line 2-23 expressed recombinant fibroin L-chain protein at a relative amount of 26.75 % of all L-chains (which also comprise endogenous L-chains), which indicates high bFGF binding affinity of recombinant SF compared to that of the control (non-transgenic silkworm SF). Our result will contribute to the development of medical application of recombinant SF.
In this study, to develop silk fibroin (SF)-based sponges used in the field of skin esthetics and skin tissue engineering, the influence of the SF solution and the SF sponge on gene expressions in three-dimensional (3-D) reconstructed human keratinocytes with or without melanocytes as a skin equivalent model was evaluated by quantitative reverse transcription-polymerase chain reaction (RT-PCR) experiments. Commercially available collagen (Col) solution and sponge were used for comparison. In the 3-D skin model made from keratinocytes, no marked changes in the expressions of genes related to differentiations and barrier functions of epidermis were observed between both solutions and sponges of SF and Col. RT-PCR experiments using the 3-D skin model with both keratinocytes and melanocytes revealed that gene expression levels of melanogenesis-related factors on the 3-D skin models stimulated with the SF sponge were slightly higher than that on the Col sponge. Measurements of pigment areas in the 3-D skin models with melanocytes indicated that almost identical areas of black melanin were detected in the 3-D skin models stimulated with medium, SF sponge, and Col sponge. This study indicates that SF-based materials are biologically inert to human skin epidermis, similar to collagen-based materials.