Impact of adipose-derived stem cells on engineering hair follicle germ-like tissue grafts for hair regenerative medicine

Large-Scale Preparation of Hair Follicle Germs Using a Microfluidic Device

Hair follicle morphogenesis during embryonic development is driven by the formation of hair follicle germs (HFGs) via interactions between epithelial and mesenchymal cells. Bioengineered HFGs are potential tissue grafts for hair regenerative medicine because they can replicate interactions and hair follicle morphogenesis after transplantation. However, a mass preparation approach for HFGs is necessary for clinical applications, given that thousands of de novo hair follicles are required to improve the appearance of a single patient with alopecia. In this study, we developed a microfluidics-based approach for the large-scale preparation of HFGs. A simple flow-focusing microfluidic device allowed collagen solutions containing epithelial and mesenchymal cells to flow and generate collagen microbeads with distinct Janus structures. During the 3 days of culture, the collagen beads contracted owing to cellular traction forces, resulting in collagen- and cell-dense HFGs. The transplantation of HFGs into nude mice resulted in highly efficient de novo hair follicle regeneration. This method provides a scalable and robust tissue graft preparation approach for hair regeneration.

Exosomes for hair growth and regeneration

Exosomes are lipid bilayer vesicles, 30-200 nm in diameter, that are produced by cells and play essential roles in cell-cell communication. Exosomes have been studied in several medical fields including dermatology. Hair loss, a major disorder that affects people and sometimes causes mental stress, urgently requires more effective treatment. Because the growth and cycling of hair follicles are governed by interactions between hair follicle stem cells (HFSCs) and dermal papilla cells (DPCs), a better understanding of the mechanisms responsible for hair growth and cycling through exosomes may provide new insights into novel treatments for hair loss. In this review, we focused on the comprehensive knowledge and recent studies on exosomes in the field of hair development and regeneration. We classified exosomes of several cellular origins for the treatment of hair loss. Exosomes and their components, such as microRNAs, are promising drugs for effective hair loss treatment.

Biological and mechanical influence of three-dimensional microenvironment formed in microwell on multicellular spheroids composed of heterogeneous hair follicle stem cells

Hair loss caused by malfunction of the hair follicle stem cells (HFSCs) and physical damage to the skin is difficult to recover from naturally. To overcome these obstacles to hair follicle (HF) regeneration, it is essential to understand the three-dimensional (3D) microenvironment and interactions of various cells within the HFs. Therefore, 3D cell culture technology has been used in HF regeneration research; specifically, multicellular spheroids have been generally adapted to mimic the 3D volumetric structure of the HF. In this study, we culture HF-derived cells, which are mainly composed of HFSCs, in the form of 3D spheroids using a microwell array and discuss the effects of the 3D cellular environment on HF morphogenesis by expression measurements of Sonic hedgehog signaling and stem cell markers in the HF spheroids. Additionally, the influences of microwell depth on HF spheroid formation and biological conditions were investigated. The biomolecular diffusion and convective flow in the microwell were predicted using computational fluid dynamics, which allows analysis of the physical stimulations occurring on the spheroid at the micro-scale. Although a simple experimental method using the microwell array was adopted in this study, the results provide fundamental insights into the physiological phenomena of HFs in the 3D microenvironment, and the numerical analysis is expected to shed light on the investigation of the geometric parameters of the microwell system.

Cryopreservation of engineered hair follicle germs for hair regenerative medicine

Hair regenerative medicine must involve practical procedures, such as cryopreservation of tissue grafts. This can aid in evaluating tissue safety and quality, as well as transportation to a clinic and multiple transplants. Hair follicle germs (HFGs), identified during in vivo development, are considered effective tissue grafts for hair regenerative medicine. However, to the best of our knowledge, methods for cryopreserving HFGs have not been explored yet. This study investigated the efficacy of slow vitrification methods for freezing HFGs. Cryoprotectants such as dimethyl sulfoxide (DMSO) and carboxylated poly-l-lysine were used for vitrification. The results indicate that DMSO vitrification yielded the most efficient de novo hair regeneration in mouse skin, comparable to that of non-cryoprotected HFGs. A microfinger was fabricated to scale up the cryopreservation method, considering that thousands of tissue grafts were required per patient in clinical practice. The microfinger can be used for a series of processes, holding the HFG, replacing it with a cryopreservation solution, freezing it in liquid nitrogen, thawing it in a warm medium, and transplanting it into the skin. Although de novo hair regeneration by HFGs cryopreserved using microfingers was reduced by approximately 20 % compared to those cryopreserved using flat plates for fertilized eggs, it exceeded 50 %. These findings demonstrate that vitrification with DMSO and microfingers could be a useful approach for the cryopreservation of tissue grafts in hair regenerative medicine for hair loss.

In vitro hair follicle growth model for drug testing

In vitro models of human hair follicle-like tissue could be fundamental tools to better understand hair follicle morphogenesis and hair drug screening. During prenatal development and postnatal cyclic hair regeneration, hair follicle morphogenesis is triggered by reciprocal interactions and the organization of the epithelial and mesenchymal cell populations. Given this mechanism, we developed an approach to induce hair peg-like sprouting in organoid cultures composed of epithelial and mesenchymal cells. Human fetal/adult epithelial and mesenchymal cells were cultured in a medium supplemented with a low concentration of either Matrigel or collagen I. These extracellular matrices significantly enhanced the self-organization capabilities of the epithelial and mesenchymal cells, resulting in spherical aggregation and subsequent hair peg-like sprouting. The length of the hair peg sprouting and associated gene expression significantly increased in the presence of a well-known hair drug, minoxidil. This approach may be beneficial for testing hair growth-promoting drug candidates.

Impacts of manipulating cell sorting on in vitro hair follicle regeneration

Hair follicle morphogenesis is triggered by epithelial-mesenchymal interactions. Several approaches have been developed for preparing hair follicle organoids using epithelial and mesenchymal cells; however, the current understanding of the relevance of in vitro spontaneous organization processes to hair regeneration is limited. In the present study, we used Y27632, a rho-associated kinase inhibitor, to investigate the effects of manipulation of cell sorting on hair regeneration in vitro. Dissociated hair follicle-inducible epithelial and mesenchymal cells were cultured in Y27632-containing media in 96-well plates or polydimethylsiloxane microarray plates. We found that Y27632 supplementation modulated the spatial distribution of epithelial and mesenchymal cells from a dumbbell shape to a core-shell configuration via a spontaneous organization process. New hair follicles with typical morphological features emerged in the Y27632-treated core-shell-shaped aggregates, and hair shafts sprouted with approximately 100% efficiency in vitro. Gene chip analysis and pathway-inhibition experiments revealed that the phosphatidylinositol-3-kinase/protein kinase B- and Ras-signaling pathways were involved in hair-like sprouting in the Y27632-treated hair follicle organoids. Our findings enhance the understanding of hair follicle organogenesis and the development of hair follicle organoids.

Cell-repellent polyampholyte for conformal coating on microstructures

Repellent coatings are critical for the development of biomedical and analytical devices to prevent nonspecific protein and cell adhesion. In this study, prevelex (polyampholytes containing phosphate and amine units) was synthesized for the fine coating of microdevices for cell culture. The dip-coating of the prevelex on hydrophobic substrates altered their surfaces to be highly hydrophilic and electrically neutral. The range of prebake temperature (50–150 °C) after dip-coating was moderate and within a preferable range to treat typical materials for cell culture such as polystyrene and polydimethylsiloxane. Scanning electron microscopy revealed a conformal and ultra-thin film coating on the micro/nano structures. When compared with poly(2-hydroxyethyl methacrylate) and poly(2-methacryloyloxyethyl phosphorylcholine), prevelex exhibited better characteristics for coating on microwell array devices, thereby facilitating the formation of spheroids with uniform diameters using various cell types. Furthermore, to examine cellular functionalities, mouse embryonic epithelial and mesenchymal cells were seeded in a prevelex-coated microwell array device. The two types of cells formed hair follicle germ-like aggregates in the device. The aggregates were then transplanted to generate de novo hair follicles in nude mice. The coating material provided a robust and fine coating approach for the preparation of non-fouling surfaces for tissue engineering and biomedical applications.

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.

Electrical stimulation to human dermal papilla cells for hair regenerative medicine

Hair follicle dermal papilla cells (DPCs) are specialized mesenchymal cells that play pivotal roles in hair formation, growth, and cycles, and they are considered as a cell source in hair regenerative medicine. Rodent dermal papilla cells have been shown to induce de novo hair follicle generation in the skin of recipients following transplantation, suggesting that dermal papilla cells can reprogram epidermal microenvironments. However, human DPCs (hDPCs) lose their ability to generate de novo hair follicles under conventional culture methods. We investigated the effects of electrical stimulation (ES) on hDPCs to restore the depressed trichogenic activity. We demonstrated that ES with a polypyrrole (PPy)-modified electrode upregulated trichogenic gene expression in hDPCs in vitro, and the activated cells when transplanted into mice generated double the number of hairs compared to that without the ES. Using specific inhibitors, we revealed that the mechanisms behind the electrical activation are associated with voltage-gated ion channels. Further, ES can be adapted for hDPCs from a patient with androgenic alopecia. Thus, this approach is potentially beneficial in preparing hDPCs for hair regenerative medicine.

Regenerative engineering: a review of recent advances and future directions

Regenerative engineering is defined as the convergence of the disciplines of advanced material science, stem cell science, physics, developmental biology and clinical translation for the regeneration of complex tissues and organ systems. It is an expansion of tissue engineering, which was first developed as a method of repair and restoration of human tissue. In the past three decades, advances in regenerative engineering have made it possible to treat a variety of clinical challenges by utilizing cutting-edge technology currently available to harness the body's healing and regenerative abilities. The emergence of new information in developmental biology, stem cell science, advanced material science and nanotechnology have provided promising concepts and approaches to regenerate complex tissues and structures.