Fabrication of a transforming growth factor β1 functionalized silk sericin hydrogel through genetical engineering to repair alveolar bone defects in rabbit

Cleft palate is one of the most prevalent congenital craniofacial birth defects in human congenital facial anomaly. Severe cleft palate is usually accompanied by alveolar bone defects (ABDs). Growth factors (GFs) are considered as desirable opportunity to promote the craniofacial healing post the surgery. However, limited resource, susceptibility to degradation, and lack of appropriate delivery systems greatly hinder the clinic application of GFs in the ABDs repair. In this study, a transforming growth factor β1 variant (eTGF-β1) with enhanced extracellular matrix (ECM) binding efficiency was engineered to generate transgenic silkworm using the silk gland biosynthesizing system for cost effective and massive bio-synthesis of the eTGF-β1 functionalized silk fibers. The eTGF-β1 achieved a highly-efficient expression in the middle silk gland (MSG) cells of transgenic silkworm, and secretion and distribution in the sericin layer of silk fiber which accounted for approximately 5.57 ± 0.72 % of the cocoon shell weight. The eTGF-β1 functionalized silk sericin hydrogel (eTGF-β1 SH) was then fabricated with excellent mechanical and processing properties, injectability, biocompatibility, biodegradability, sustained release of eTGF-β1, and capability to promote cell proliferation, which significantly accelerated the bone defect repair particularly the osteoblast maturation and new bone formation through regulating the expressions of the bone formation-related genes in a rabbit alveolar process cleft model. This study provides a valuable strategy for future the treatments of ABDs in rabbit with cleft palate using the genetically engineered eTGF-β1 silk sericin hydrogel.