Effects of platelet-rich plasma on in vitro hair follicle germ preparation for hair regenerative medicine

Development of in vitro hair pigmentation model using hair follicle organoids

Hair color is formed through a series of processes such as melanin synthesis and storage in melanosomes, transfer from melanocytes, and reception by hair matrix cells in the hair bulb. Because gray hair is caused by the deterioration of a single or multiple of these processes, understanding the mechanisms responsible for these processes is crucial for developing therapeutic strategies. Recently, a robust approach for preparing hair follicle organoids (HFOs) was reported, in which hair follicle morphogenesis, including hair shaft elongation, was tracked in vitro. Here, we investigated whether HFOs could be used to assess genes involved in hair pigmentation. HFOs generated hair follicles and pigmented shafts during the in vitro culturing process. The knockdown of genes associated with melanosome production (Bcl2 and Mitf) and transport (MyoX, PAR2, and Rab11b) significantly increased the number of gray hairs in HFOs. This organoid model may be a promising platform for better understanding hair pigmentation and screening drugs for gray hair.

The promising prospect of human hair follicle regeneration in the shadow of new tissue engineering strategies

Hair loss disorder (alopecia) affects numerous people around the world. The low effectiveness and numerous side effects of common treatments have prompted researchers to investigate alternative and effective solutions. Hair follicle (HF) bioengineering is the knowledge of using hair-inductive (trichogenic) cells. Most bioengineering-based approaches focus on regenerating folliculogenesis through manipulation of regulators of physical/molecular properties in the HF niche. Despite the high potential of cell therapy, no cell product has been produced for effective treatment in the field of hair regeneration. This problem shows the challenges in the functionality of cultured human hair cells. To achieve this goal, research and development of new and practical approaches, technologies and biomaterials are needed. Based on recent advances in the field, this review evaluates emerging HF bioengineering strategies and the future prospects for the field of tissue engineering and successful HF regeneration.

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.

Potential application of PBM use in hair follicle organoid culture for the treatment of androgenic alopecia

Androgenic alopecia is a hereditary condition of pattern hair loss in genetically susceptible individuals. The condition has a significant impact on an individual's quality of life, with decreased self-esteem, body image issues and depression being the main effects. Various conventional treatment options, such as minoxidil, finasteride and herbal supplements, aim to slow down hair loss and promote hair growth. However, due to the chronic nature of the condition the financial cost of treatment for androgenic alopecia is very high and conventional treatment options are not universally effective and come with a host of side effects. Therefore, to address the limitations of current treatment options a novel regenerative treatment option is required. One promising approach is organoids, organoids are 3D cell aggregates with similar structures and functions to a target organ. Hair follicle organoids can be developed in vitro. However, the main challenges are to maintain the cell populations within the organoid in a proliferative and inductive state, as well as to promote the maturation of organoids. Photobiomodulation is a form of light therapy that stimulates endogenous chromophores. PBM has been shown to improve cell viability, proliferation, migration, differentiation and gene expression in dermal papilla cells and hair follicle stem cells. Therefore, photobiomodulation is a potential adjunct to hair follicle organoid culture to improve the proliferation and inductive capacity of cells.

Recent Trends in Macromolecule-Based Approaches for Hair Loss Treatment

Macromolecules are large, complex molecules composed of smaller subunits known as monomers. The four primary categories of macromolecules found in living organisms are carbohydrates, lipids, proteins, and nucleic acids; they also encompass a broad range of natural and synthetic polymers. Recent studies have shown that biologically active macromolecules can help regenerate hair, providing a potential solution for current hair regeneration therapies. This review examines the latest developments in the use of macromolecules for the treatment of hair loss. The fundamental principles of hair follicle (HF) morphogenesis, hair shaft (HS) development, hair cycle regulation, and alopecia have been introduced. Microneedle (MN) and nanoparticle (NP) delivery systems are innovative treatments for hair loss. Additionally, the application of macromolecule-based tissue-engineered scaffolds for the in vitro and in vivo neogenesis of HFs is discussed. Furthermore, a new research direction is explored wherein artificial skin platforms are adopted as a promising screening method for hair loss treatment drugs. Through these multifaceted approaches, promising aspects of macromolecules for future hair loss treatments are identified.

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.

Expansion Culture of Hair Follicle Stem Cells through Uniform Aggregation in Microwell Array Devices

Hair regeneration using hair follicle stem cells (HFSCs) and dermal papilla cells is a promising approach for the treatment of alopecia. One of the challenges faced in this approach is the quantitative expansion of HFSCs while maintaining their hair induction capacity. In this study, HFSC expansion was achieved through the formation of uniform-diameter cell aggregates that were subsequently encapsulated in Matrigel. We designed a microwell array device, wherein mouse HFSCs were seeded, allowed to form loosely packed aggregates for an hour, and then embedded in Matrigel. Quantitative analysis revealed a 20-fold increase in HFSC number in 2 weeks through this culture device. Gene expression of trichogenic stem cell markers in the device-grown cells showed a significant increase compared with that of typical flat substrate Matrigel suspension culture cells. These microwell array-cultured HFSCs mixed with freshly isolated embryonic mesenchymal cells indicated vigorous hair regeneration on the skin of nude mice. Furthermore, we examined the feasibility of this approach for the expansion of human HFSCs from androgenetic alopecia patients and found that the ratio of CD200⁺ cells was improved significantly in comparison with that of cells cultured in a typical culture dish or in a Matrigel suspension culture on a flat substrate. Therefore, the novel approach proposed in this study may be useful for HFSC expansion in hair regenerative medicine.

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.

Reprogramming of three-dimensional microenvironments for in vitro hair follicle induction

During embryonic development, reciprocal interactions between epidermal and mesenchymal layers trigger hair follicle morphogenesis. This study revealed that microenvironmental reprogramming via control over these interactions enabled hair follicle induction in vitro. A key approach is to modulate spatial distributions of epithelial and mesenchymal cells in their spontaneous organization. The de novo hair follicles with typical morphological features emerged in aggregates of the two cell types, termed hair follicloids, and hair shafts sprouted with near 100% efficiency in vitro. The hair shaft length reached ~3 mm in culture. Typical trichogenic signaling pathways were up-regulated in hair follicloids. Owing to replication of hair follicle morphogenesis in vitro, melanosome production and transportation were also monitored in the hair bulb region. This in vitro hair follicle model might be valuable for better understanding hair follicle induction, evaluating hair growth and inhibition of hair growth by drugs, and modeling gray hairs in a well-defined environment.

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.

Design of In Vitro Hair Follicles for Different Applications in the Treatment of Alopecia-A Review

The hair research field has seen great improvement in recent decades, with in vitro hair follicle (HF) models being extensively developed. However, due to the cellular complexity and number of various molecular interactions that must be coordinated, a fully functional in vitro model of HFs remains elusive. The most common bioengineering approach to grow HFs in vitro is to manipulate their features on cellular and molecular levels, with dermal papilla cells being the main focus. In this study, we focus on providing a better understanding of HFs in general and how they behave in vitro. The first part of the review presents skin morphology with an emphasis on HFs and hair loss. The remainder of the paper evaluates cells, materials, and methods of in vitro growth of HFs. Lastly, in vitro models and assays for evaluating the effects of active compounds on alopecia and hair growth are presented, with the final emphasis on applications of in vitro HFs in hair transplantation. Since the growth of in vitro HFs is a complicated procedure, there is still a great number of unanswered questions aimed at understanding the long-term cycling of HFs without losing inductivity. Incorporating other regions of HFs that lead to the successful formation of different hair classes remains a difficult challenge.

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

Hair regenerative medicine has emerged as a promising treatment strategy for severe hair loss, such as end-stage androgenetic alopecia. Various approaches to engineering three-dimensional tissue grafts have been explored since they drive the ability to regenerate hair follicles when transplanted. In the present study, we demonstrated the assembly of human adipose-derived stem cells (hASCs) into hair follicle germ (HFG)-like aggregates for de novo hair regeneration. We mixed human dermal papilla cells (hDPCs), murine embryonic epithelial cells, and hASCs in suspension, and allowed them to form aggregates. During three days of culture, cells initially formed a single aggregate with a random distribution of the three cell types, but the epithelial and dermal papilla cells subsequently separated from each other and formed a dumbbell-shaped HFG, with hASCs localized on the hDPC aggregate side. The involvement of hASCs significantly increased gene expression associated with hair morphogenesis compared to HFGs without hASCs. The self-organization of the three cell types was observed in our scalable lab-made chip device. HFGs containing hASCs efficiently generated hair shafts upon transplantation to nude mice, while only a few shafts were generated with HFGs without hASCs. This approach may be a promising strategy for fabricating tissue grafts for hair regenerative medicine.