Controlled release of fibroin repeat-tagged proteins from silk hydrogel

Abstract

Protein-based biologic drugs such as growth factors are playing important roles in modern medicine. These proteins can be used to stimulate local tissue repair. Growth factors are often incorporated into a scaffold, such as a hydrogel, and then put into the desired area of the body to achieve therapeutic effects. However, diffusion of these growth factors outside of the designated area or inappropriate release time can have deleterious consequences, such as inducing tumors in other areas of the body or uncontrolled inflammation. Therefore, this project aims to create a model to study diffusion of protein from hydrogel by using green fluorescent protein (GFP) as a biologics model and silk hydrogel as a scaffold to investigate the drug release behavior from the hydrogel. To investigate the bioactive release profile, GFP fused to silk repeating units (GAGAGS)n-GFP was used as a model. In this study, the gelation time of the silk fibroin hydrogel containing GFP is faster than the pure silk fibroin hydrogel. The release of (GAGAGS)n-GFP from silk fibroin hydrogel reduces the burst release effect and sustained release profile, especially silk fibroin hydrogel containing six repeats of SF tagged GFP. These results indicate that increasing the number of silk repeating unit(s) help sustain the model protein release from silk fibroin hydrogel. In addition, the release mechanism was investigated by FTIR and XRD method. The result showed that the release profile of GFP was not dependent on the β-sheet content of hydrogel but could be occur from hydrophobic interaction between repeating unit of peptide and repeating unit of SF hydrogel scaffold. After determining the optimal number of repeating units, the six repeating units tagged-basic fibroblast growth factor (bFGF) is produced and showed the function. The bFGF-incorporated hydrogel is examined for bFGF release and stimulated of cell proliferation in cell culture. These results indicate that six repeating units-tagged bFGF can sustain release of bFGF detected by NIH3T3 proliferation.