This study is an investigation to evaluate how the controlled release of different growth factors affects the hair follicle growth of mice in the second anagen stage of hair cycle. For the controlled release of basic fibroblast growth factor (bFGF) and hepatocyte growth factor (HGF), they were incorporating into biodegradable gelatin hydrogels, while a biodegradable collagen hydrogel was used for incorporation of vascular endothelial growth factor (VEGF). After subcutaneous implantation of the different hydrogels incorporating each growth factor or injection of phosphate buffered saline (PBS) containing the same dose of growth factor into the back of mice, the hair follicle growth was evaluated photometrically and histologically based on four parameters: the skin color of reverse side of the implanted or injected site, the number of vessels newly formed, the area occupied by hair follicle tissue, and the hair length.
The area in close proximity to the implanted site of hydrogels incorporating growth factor was still dark in color 10 days after application. The hydrogel incorporating any type of growth factor enabled the hair follicles to increase the size, leading significantly enhanced area occupied by hair follicles per unit area of tissue. Implantation of the hydrogels incorporating growth factor increased significantly the number of blood vessels newly formed. Moreover, the length of hair shaft was elongated by the hydrogel incorporating growth factor to a significantly higher extent than the corresponding growth factor. Neither empty gelatin nor collagen hydrogels affected the hair follicle growth.
These results indicate that the hydrogel incorporating growth factor induced the anagen-preservable activity. We conclude that the controlled release enabled growth factors to positively act on the hair growth cycle of mice, irrespective of the factor type.