Bioprinting of hair follicle germs for hair regenerative medicine

Hair regenerative medicine is a promising approach to treat hair loss. The replication of in vivo tissue configurations and microenvironments, such as hair follicle germs, has been studied to prepare tissue grafts for hair regenerative medicine. However, such approaches should be scalable, because a single patient with alopecia requires thousands of tissue grafts. In this paper, we propose an approach for the scalable and automated preparation of highly hair-inductive tissue grafts using a bioprinter. Two collagen droplets (2 µL each) containing mesenchymal and epithelial cells were placed adjacent to each other to fabricate hair-follicle-germ-like grafts. During three days of culture, the pairs of microgel beads were spontaneously contracted by cell traction forces, whereas the two cell types remained separated, where the densities of the cells and collagen were enriched more than 10 times. This approach allowed us to fabricate submillimeter objects printed with millimeter-order accuracy, facilitating scalable and automated tissue graft preparation. Because of mesenchymal-epithelial interactions, hair microgels (HMGs, i.e., collagen- and cell-enriched microgels) efficiently regenerate hair follicles and shafts when transplanted into the back skin of mice. However, the generated hair shafts mostly remain under the skin. Therefore, we printed microgel beads onto surgical suture guides arrayed on a stage. The microgel beads were contracted along with the suture guides in culture prior to transplantation. The guide-inserted HMGs significantly improved hair-shaft sprouting through the skin, owing to the control of the orientation of the HMGs transplanted into the skin. This approach is a promising strategy to advance hair regenerative medicine. STATEMENT OF SIGNIFICANCE: This study proposes an approach for the scalable and automated preparation of highly hair-inductive grafts using a bioprinter. Two collagen droplets containing mesenchymal and epithelial cells were placed adjacently. Cell traction forces caused the pairs of microgel beads to spontaneously contract in culture. Because of mesenchymal-epithelial interactions, hair microgels (HMGs) efficiently regenerated hair follicles on the back skin of mice. However, the generated hair shafts remained mostly beneath the skin. Therefore, we printed microgel beads onto surgical suture guides arrayed on a stage. The guide-inserted HMGs significantly improved hair-shaft sprouting through the skin owing to the control of the orientation of the HMGs in the skin. This approach represents a promising strategy for advancing hair regenerative medicine.