a-method-for-determination-simulation-permeability-diffusion-3d

A Method for Determination and Simulation of Permeability and Diffusion in a 3D Tissue Model in a Membrane Insert System for Multi-well Plates

In vitro cultivated skin models have become increasingly relevant for pharmaceutical and cosmetic applications, and are also used in drug development as ...

Vessel sealing has been well-established in surgical practice in recent years. Bipolar radiofrequency-induced thermofusion (BIRTH) of intestinal tissue might replace traditionally used staples or sutures in the near future. In this experimental study, the influence of compressive pressure, fusion temperature, and duration of heating on the quality of intestinal anastomosis was investigated to obtain the relevant major parameters for the in vivo use of this system.

Pilot study of bipolar radiofrequency-induced anastomotic thermofusion-exploration of therapy parameters ex vivo.

Across many tissues and organs, the ability to create an organoid, the smallest functional unit of an organ, in vitro is the key both to tissue engineering and preclinical testing regimes. The hair follicle is an organoid that has been much studied based on its ability to grow quickly and to regenerate after trauma. But hair follicle formation in vitro has been elusive. Replacing hair lost due to pattern baldness or more severe alopecia, including that induced by chemotherapy, remains a significant unmet medical need. By carefully analyzing and recapitulating the growth conditions of hair follicle formation, we recreated human hair follicles in tissue culture that were capable of producing hair. Our microfollicles contained all relevant cell types and their structure and orientation resembled in some ways excised hair follicle specimens from human skin. This finding offers a new window onto hair follicle development. Having a robust culture system for hair follicles is an important step towards improved hair regeneration as well as to an understanding of how marketed drugs or drug candidates, including cancer chemotherapy, will affect this important organ.

De novo formation and ultra-structural characterization of a fiber-producing human hair follicle equivalent in vitro.

Hair follicle cycling is driven by epithelial-mesenchymal interactions (EMI), which require extracellular matrix (ECM) modifications to control the crosstalk between key epithelial- and mesenchymal-derived growth factors and cytokines. The exact roles of these ECM modifications in hair cycle-associated EMI are still unknown. Here, we used differential microarray analysis of laser capture-microdissected human scalp hair follicles (HF) to identify new ECM components that distinguish fibroblasts from the connective tissue sheath (CTS) from those of the follicular dermal papilla (DP). These analyses provide the first evidence that normal human CTS fibroblasts are characterized by the selective in situ-transcription of cartilage oligomeric matrix protein (COMP). Following this up on the protein level, COMP was found to be hair cycle-dependent, suggesting critical role in this process: COMP is expressed during telogen and early anagen at regions of EMI and is degraded during catagen (only the CTS adjacent to the bulge remains COMP+ during catagen). Notably, COMP gene expression in vitro suggests direct correlation with the expression of TGFβ2 in CTS fibroblasts. This raises the question whether COMP expression undergoes regulation by transforming growth factor, beta (TGFβ) signalling. The intrafollicular COMP expression suggests to be functionally important and deserves further scrutiny in hair biology as indicated by the fact that altered COMP expression might be associated with scant fine hair in the case of some chondrodysplasia and scleroderma patients. Together these results reveal for the first time that COMP is part of the ECM and suggests its important role in normal human HF biology.

Cartilage oligomeric matrix protein (COMP) forms part of the connective tissue of normal human hair follicles.

Various factors, including the phylogenetic distance between laboratory animals and humans, the discrepancy between current in vitro systems and the human body, and the restrictions of in silico modelling, have generated the need for new solutions to the ever-increasing worldwide dilemma of substance testing. This review provides a historical sketch on the accentuation of this dilemma, and highlights fundamental limitations to the countermeasures taken so far. It describes the potential of recently-introduced microsystems to emulate human organs in 'organ-on-a-chip' devices. Finally, it focuses on an in-depth analysis of the first devices that aimed to mimic human systemic organ interactions in 'human-on-a-chip' systems. Their potential to replace acute systemic toxicity testing in animals, and their inability to provide alternatives to repeated dose long-term testing, are discussed. Inspired by the latest discoveries in human biology, tissue engineering and micro-systems technology, this review proposes a paradigm shift to overcome the apparent challenges. A roadmap is outlined to create a new homeostatic level of biology in 'human-on-a-chip' systems in order to, in the long run, replace systemic repeated dose safety evaluation and disease modelling in animals.

'Human-on-a-chip' developments: a translational cutting-edge alternative to systemic safety assessment and efficiency evaluation of substances in laboratory animals and man?

Substantial progress has been achieved over the last few decades in the development of skin equivalents to model the skin as an organ. However, their static culture still limits the emulation of essential physiological properties crucial for toxicity testing and compound screening. Here, we describe a dynamically perfused chip-based bioreactor platform capable of applying variable mechanical shear stress and extending culture periods. This leads to improvements of culture conditions for integrated in vitro skin models, ex vivo skin organ cultures and biopsies of single hair follicular units.

Skin and hair on-a-chip: in vitro skin models versus ex vivo tissue maintenance with dynamic perfusion.

A chip-based system mimicking the transport function of the human cardiovascular system has been established at minute but standardized microsystem scale. A peristaltic on-chip micropump generates pulsatile shear stress in a widely adjustable physiological range within a microchannel circuit entirely covered on all fluid contact surfaces with human dermal microvascular endothelial cells. This microvascular transport system can be reproducibly established within four days, independently of the individual endothelial cell donor background. It interconnects two standard tissue culture compartments, each of 5 mm diameter, through microfluidic channels of 500 μm width. Further vessel branching and vessel diameter reduction down to a microvessel scale of approximately 40 μm width was realised by a two-photon laser ablation technique applied to inserts, designed for the convenient establishment of individual organ equivalents in the tissue culture compartments at a later time. The chip layout ensures physiological fluid-to-tissue ratios. Moreover, an in-depth microscopic analysis revealed the fine-tuned adjustment of endothelial cell behaviour to local shear stresses along the microvasculature of the system. Time-lapse and 3D imaging two-photon microscopy were used to visualise details of spatiotemporal adherence of the endothelial cells to the channel system and to each other. The first indicative long-term experiments revealed stable performance over two and four weeks. The potential application of this system for the future establishment of human-on-a-chip systems and basic human endothelial cell research is discussed.

Integrating biological vasculature into a multi-organ-chip microsystem.

During hair transplantation as an effective therapy for androgenetic alopecia, hair follicles were typically trans-located from the nonaffected occipital to the balding frontal or vertex region of the scalp. Although this is an autologous intervention, the donor and recipient hair follicle tissue differ in composition and local environment.

Hair Follicle Plasticity with Complemented Immune-modulation Following Follicular Unit Extraction.

Follicular unit transplantation is the most commonly performed technique in modern restorative hair transplantation surgery. It relies on the acquisition of intact follicular units from microdissected scalp skin strips and their subsequent transplantation into the recipient regions affected by alopecia. Ideally, the translocation of follicular units from the balding-resistant areas of the scalp (usually the occipital region) to the recipient site should not result in any morphological change in the grafts. Nevertheless, the insults associated with surgical intervention present grafted follicles to mechanical and chemical cues differently from those of the physiological steady-state conditions in undamaged skin. This disruption of the normal follicular microenvironment might alter important aspects of hair biology in grafts, for example, hair cycle and pigmentation, and, in turn, could lead to differences in hair appearance, eventually culminating in a diminished esthetical outcome of the surgery. In this study, the authors analyzed native and grafted scalp hair follicles (HFs) from 2 patients who had undergone follicular unit transplantation surgeries formerly. Scanning electron microscopy and light microscopy-based histomorphometry revealed a marked enlargement of follicular structures in the grafts with a concomitant increase in hair shaft diameter. Immunohistological staining confirmed a thickening of the dermal sheath in transplanted HFs that also harbored a denser vascular network. Taken together, these results show that the grafted HFs analyzed were subjected to marked morphological changes during their residence in the recipient site and that this phenomenon is associated with a modulation of follicular vascularization.

Alterations in Hair Follicle Morphology and Hair Shaft Production After Follicular Unit Transplantation.

The Norwood classification system is commonly used to ascertain the progress of androgenetic alopecia (AGA) with a robust and quick assessment, but it lacks precision in the frontal region, notably during the onset of male pattern hair loss.

Article	Year
Pilot study of bipolar radiofrequency-induced anastomotic thermofusion-exploration of therapy parameters ex vivo. International journal of colorectal disease\| PubMed ID: 19705133	2010
De novo formation and ultra-structural characterization of a fiber-producing human hair follicle equivalent in vitro. Journal of biotechnology\| PubMed ID: 21277344	2011
Cartilage oligomeric matrix protein (COMP) forms part of the connective tissue of normal human hair follicles. Experimental dermatology\| PubMed ID: 21355885	2011
'Human-on-a-chip' developments: a translational cutting-edge alternative to systemic safety assessment and efficiency evaluation of substances in laboratory animals and man? Alternatives to laboratory animals : ATLA\| PubMed ID: 23215661	2012
Skin and hair on-a-chip: in vitro skin models versus ex vivo tissue maintenance with dynamic perfusion. Lab on a chip\| PubMed ID: 23674126	2013
Integrating biological vasculature into a multi-organ-chip microsystem. Lab on a chip\| PubMed ID: 23743770	2013
Hair Follicle Plasticity with Complemented Immune-modulation Following Follicular Unit Extraction. International journal of trichology\| PubMed ID: 25878444	2015
Alterations in Hair Follicle Morphology and Hair Shaft Production After Follicular Unit Transplantation. The American Journal of dermatopathology\| PubMed ID: 26844618	2016
Asymmetry of the Receding Hairline in Men With Early Androgenetic Alopecia. Journal of cutaneous medicine and surgery\| PubMed ID: 27421295	2016

Gerd Lindner

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