Skin-on-a-chip strategies for human hair follicle regeneration

Targeted self-assembled anti-NFκB AuNCs-aptamer nanoplatform for precise theranostics via tailored follicle regeneration

NFκB is a vital transcription factor for the regulation of hair follicle cycle. As a therapeutic target, NFκB is specifically blocked by RNA aptamer with negligible side effects, but the targeted transmembrane transport of anti-NFκB aptamer remains a challenge due to its negative charge under physiological conditions. In this study, taking advantage of the depilation-induced oxidative stress microenvironment (OSM), it was confirmed for the first time that self-assembled gold nanoclusters and aptamer (AuNCs-Aptamer) complexes formed in the skin and enhanced the therapeutic effect of anti-NFκB aptamer drugs, effectively blocking the NFκB-mediated inflammatory response and inhibiting hair follicle regeneration. The hematoxylin-eosin (HE) staining of tissue section and hematology analysis demonstrated that OSM-responsive self-assembled AuNCs-Aptamer caused no toxicity to the living organism. Moreover, self-assembly occurred only in the oxidative stress-injured skin cells rather than the normal cells, which revealed that this self-assembly was a targeted, safe and effective therapy for hypertrichosis.

Organs on chips: fundamentals, bioengineering and applications

Human body constitutes unique biological system containing specific fluid mechanics and biomechanics. Traditional cell culture techniques of 2D and 3D do not recapitulate these specific natures of the human system. In addition, they lack the spatiotemporal conditions of representing the cells. Moreover, they do not enable the study of cell-cell interactions in multiple cell culture platforms. Therefore, establishing biological system of dynamic cell culture was of great interest. Organs on chips systems were fabricated proving their concept to mimic specific organs functions. Therefore, it paves the way for validating new drugs and establishes mechanisms of emerging diseases. It has played a key role in validating suitable vaccines for Coronavirus disease (COVID-19). Herein, the concept of organs on chips, fabrication methodology and their applications are discussed.

Advancements in 3D skin bioprinting: processes, bioinks, applications and sensor integration

This comprehensive review explores the multifaceted landscape of skin bioprinting, revolutionizing dermatological research. The applications of skin bioprinting utilizing techniques like extrusion-, droplet-, laser- and light-based methods, with specialized bioinks for skin biofabrication have been critically reviewed along with the intricate aspects of bioprinting hair follicles, sweat glands, and achieving skin pigmentation. Challenges remain with the need for vascularization, safety concerns, and the integration of automated processes for effective clinical translation. The review further investigates the incorporation of biosensor technologies, emphasizing their role in monitoring and enhancing the wound healing process. While highlighting the remarkable progress in the field, critical limitations and concerns are critically examined to provide a balanced perspective. This synthesis aims to guide scientists, engineers, and healthcare providers, fostering a deeper understanding of the current state, challenges, and future directions in skin bioprinting for transformative applications in tissue engineering and regenerative medicine.

Advances in Microengineered Platforms for Skin Research

The skin plays a critical role in human physiology, acting both as a barrier to environmental insults and as a window to environmental stimuli. Disruption of this homeostasis leads to numerous skin disorders. Human and animal skin differ significantly, limiting the translational potential of animal-based investigations to advance therapeutics to human skin diseases. Hence, there is a critical need for physiologically relevant human skin models to explore novel treatment strategies. Recent advances in microfluidic technologies now allow design and generation of organ-on-chip devices that mimic critical features of tissue architecture. Skin-on-a-chip and microfluidic platforms hold promise as useful models for diverse dermatology applications. Compared with traditional in vitro models, microfluidic platforms offer improved control of fluid flow, which in turn allows precise manipulation of cell and molecular distribution. These properties enable the generation of multilayered in vitro models that mimic human skin structure while simultaneously offering superior control over nutrient and drug distribution. Researchers have used microfluidic platforms for a variety of applications in skin research, including epidermal-dermal cellular crosstalk, cell migration, mechanobiology, microbiome-immune response interactions, vascular biology, and wound healing. In this review, we comprehensively review state-of-the-art microfluidic models for skin research. We discuss the challenges and promise of current skin-on-a-chip technologies and provide a roadmap for future research in this active field.

Advances in Skin-on-a-Chip Technologies for Dermatological Disease Modeling

Skin-on-a-chip (SoC) technologies are emerging as a paradigm shift in dermatology research by replicating human physiology in a dynamic manner not achievable by current animal models. Although animal models have contributed to successful clinical trials, their ability to predict human outcomes remains questionable, owing to inherent differences in skin anatomy and immune response. Covering areas including infectious diseases, autoimmune skin conditions, wound healing, drug toxicity, aging, and antiaging, SoC aims to circumvent the inherent disparities created by traditional models. In this paper, we review current SoC technologies, highlighting their potential as an alternative to animal models for a deeper understanding of complex skin conditions.

Optimization of hair follicle spheroids for hair-on-a-chip

Currently, most models for hair follicle research have the limitation of not replicating some key features of the hair follicle microenvironment. To complement this, we transfected various factors for hair growth into dermal papilla cells (DPCs) by electroporation and cultured the spheroids with keratinocytes (KCs). We optimized the cell number and culture period for applying spheroids to hair-on-a-chip. Furthermore, we investigated the expression of hair growth factors in spheroids depending on the presence or absence of human umbilical vein endothelial cells (HUVECs) and transfection. In spheroids in which DPCs, KCs, and HUVECs were co-cultured for 21 days, the expression of lymphoid enhancer factor 1 (LEF1), T-cell factor 1 (TCF1), and keratin 25 (K25) in the center of the spheroid, the expression of keratin 17 (K17) on the outer surface of the spheroid, and the shape of hair extending outward from the spheroid surface were observed. From these results, it is expected that a hair-on-a-chip experiment in which short-term cultured TKH spheroids are injected into the dermis and co-cultured with KC will enable the production of full-thickness skin equivalents containing hair in vitro without transplantation into animals.

Recent advances in understanding the role of the skin microbiome in the treatment of atopic dermatitis

The skin is the largest organ in the human body, and histologically consists of the epidermis, dermis and subcutaneous tissue. Humans maintain a cooperative symbiotic relationship with their skin microbiota, a complex community of bacteria, fungi and viruses that live on the surface of the skin, and which act as a barrier to protect the body from the inside and outside. The skin is a 'habitat' and vast 'ecosystem' inhabited by countless microbes; as such, relationships have been forged through millions of years of coevolution. It is not surprising then that microbes are key participants in shaping and maintaining essential physiological processes. In addition to maintaining barrier function, the unique symbiotic microbiota that colonizes the skin increases the immune response and provides protection against pathogenic microbes. This review examines our current understanding of skin microbes in shaping and enhancing the skin barrier, as well as skin microbiome-host interactions and their roles in skin diseases, such as atopic dermatitis (AD). We also report on the current status of AD therapeutic drugs that target the skin microbiome, related research on current therapeutic strategies, and the limitations and future considerations of skin microbiome research. In particular, as a future strategy, we discuss the need for a skin-on-a-chip-based microphysiological system research model amenable to biomimetic in vitro studies and human skin equivalent models, including skin appendages.

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.