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

High-Throughput Screening of 3-Dimensional Co-culture Hair Follicle Mimetic Tissue with an Enhanced Extracellular Matrix for the Screening of Hair Growth-Promoting Compounds

Hair follicle cells reside within a complex extracellular matrix (ECM) environment in vivo, where physical and chemical cues regulate their behavior. The ECM is crucial for hair follicle development and regeneration, particularly through epithelial-mesenchymal interactions. Current in vitro models often fail to replicate this complexity, leading to inconsistencies in evaluating hair loss treatments. Advanced 3-dimensional (3D) culture systems that better mimic in vivo ECM dynamics are needed for more effective therapeutic assessments. Here, we introduce a 3D co-culture system designed to replicate in vivo ECM dynamics. The system incorporates primary dermal papilla cells from human patients, co-cultured with neonatal keratinocytes. This platform facilitates uniform spheroid formation through cell sliding and aggregation, enabling the evaluation of approximately 60 spheroids per well. The model is optimized for high-throughput screening, allowing precise assessments of hair-loss-inducing compounds under consistent conditions. We successfully generated dermal papilla cell and keratinocyte spheroids that closely resemble the native ECM structure, providing an optimal microenvironment for studying hair follicle biology. The 3D co-culture model supported efficient spheroid formation with consistent cellular organization and polarization, along with enhanced ECM-related gene expression crucial for hair follicle regeneration. Uniform spheroid formation and reproducibility were demonstrated across experiments. Overall, the novel 3D co-culture system provides a robust platform for replicating in vivo-like ECM conditions, enabling effective assessment of potential hair loss treatments through epithelial-mesenchymal interactions. Its high-throughput capacity, combined with reproducibility and ease of use, makes it a valuable tool for screening therapeutic candidates and advancing hair loss treatment development.

Materials-based hair follicle engineering: Basic components and recent advances

The hair follicle (HF) is a significant skin appendage whose primary function is to produce the hair shaft. HFs are a non-renewable resource; skin damage or follicle closure may lead to permanent hair loss. Advances in biomaterials and biomedical engineering enable the feasibility of manipulating the HF-associated cell function for follicle reconstruction via rational design. The regeneration of bioengineered HF addresses the issue of limited resources and contributes to advancements in research and applications in hair loss treatment, HF development, and drug screening. Based on these requirements, this review summarizes the basic and recent advances in hair follicle regulation, including four components: acquisition of stem cells, signaling pathways, materials, and engineering methods. Recent studies have focused on efficiently combining these components and reproducing functionality, which would boost fabrication in HF rebuilding ex vivo, thereby eliminating the obstacles of transplantation into animals to promote mature development.

Epidermal stem cells: skin surveillance and clinical perspective

The skin epidermis is continually influenced by a myriad of internal and external elements. At its basal layer reside epidermal stem cells, which fuels epidermal renovation and hair regeneration with powerful self-renewal ability, as well as keeping diverse signals that direct their activity under surveillance with quick response. The importance of epidermal stem cells in wound healing and immune-related skin conditions has been increasingly recognized, and their potential for clinical applications is attracting attention. In this review, we delve into recent advancements and the various physiological and psychological factors that govern distinct epidermal stem cell populations, including psychological stress, mechanical forces, chronic aging, and circadian rhythm, as well as providing an overview of current methodological approaches. Furthermore, we discuss the pathogenic role of epidermal stem cells in immune-related skin disorders and their potential clinical applications.

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.

iPSC-based approach for human hair follicle regeneration

Hair follicles (HFs) are a multifunctional structure involved in physical protection, thermoregulation, sensational detection, and wound healing. Formation and cycling of HFs require dynamic interaction between different cell types of the follicles. Although the processes have been well studied, the generation of human functional HFs with a normal cycling pattern for clinical utilization has yet to be achieved. Recently, human pluripotent stem cells (hPSCs) serve as an unlimited cell source for generating various types of cells including cells of the HFs. In this review, HF morphogenesis and cycling, different cell sources used for HF regeneration, and potential strategies for HF bioengineering using induced pluripotent stem cells (iPSCs) are depicted. Challenges and perspectives toward the therapeutic use of bioengineered HFs for hair loss disorder are also discussed.