Pharmaceutical and personal care industries require human representative models for testing to ensure the safety of their products. A major route of penetration into our body after substance exposure is via the skin. Our aim was to generate robust culture conditions for a next generation human skin-on-chip model containing neopapillae and to establish proof-of-concept testing with the sensitizer, cinnamaldehyde. Reconstructed human skin consisting of a stratified and differentiated epidermis on a fibroblast populated hydrogel containing neopapillae spheroids (RhS-NP), were cultured air-exposed and under dynamic flow for 10 days. The robustness of three independent experiments, each with up to 21 intra-experiment replicates, was investigated. The epidermis was seen to invaginate into the hydrogel towards the neopapille spheroids. Daily measurements of lactate dehydrogenase (LDH) and glucose levels within the culture medium demonstrated high viability and stable metabolic activity throughout the culture period in all three independent experiments and in the replicates within an experiment. Topical cinnamaldehyde exposure to RhS-NP resulted in dose-dependent cytotoxicity (increased LDH release) and elevated cytokine secretion of contact sensitizer specific IL-18, pro-inflammatory IL-1β, inflammatory IL-23 and IFN-γ, as well as anti-inflammatory IL-10 and IL-12p70. This study demonstrates the robustness and feasibility of complex next generation skin models for investigating skin immunotoxicity.

Background/Objectives: The barrier properties of the human small intestine play a crucial role in regulating digestion, nutrient absorption and drug metabolism. Current in vitro organotypic models consist only of an epithelium, which does not take into account the possible role of stromal cells such as fibroblasts or the extracellular matrix (ECM) which could contribute to epithelial barrier properties. Therefore, the aim of this study was to determine whether these stromal cells or ECM were beneficial or detrimental to barrier function when incorporated into an organotypic human small intestine model. Methods: Intestinal epithelial cell lines or primary cell organoids derived from the epithelial stem cells of the small intestine were cultivated either on a porous Transwell membrane (epithelial model) or on a primary small intestinal stromal cell-populated collagen-fibrin hydrogel (full thickness model). Results: Both models expressed villin (enterocytes), lysozyme (Paneth cells), Ki67 (proliferative cells) and zonula occludens-1 (tight junctions). The polarized epithelial barriers of the full thickness models demonstrated a significant decrease in transepithelial electrical resistance (TEER) with values comparable to that found in the native small intestine in contrast to the higher TEER values observed in the epithelial models. This correlated to an increase in secreted zonulin, a regulator of intestine permeability, in the full thickness models. The decreased TEER values were due to both the stromal cells and the choice of the hydrogel versus the Transwell membrane. Moreover, erythropoietin and epithelial growth factor secretion, which have roles in regulating barrier integrity, directly correlated with the changes in TEER and permeability. Conclusions: This study emphasizes the importance of different cell types being incorporated into small intestine models and, also, the influence of the scaffold or matrix used.

For in vitro organ models, perfused vasculature is crucial to overcome nutrient diffusion limits and to generate immunocompetent models by allowing trans‐endothelial migration of immune cells in and out of the tissue. However, vasculature is often disregarded due to its complexity to generate and the necessity to integrate flow. The aim here is to overcome these limitations by combining 3D printing and multi‐organ‐chip technology to generate a vascularized, fibroblast‐populated connective tissue matrix on‐chip. A 3D printed, sacrificial, water‐dissolvable structure is incorporated into a multi‐organ‐chip to generate hollow channels within a collagen/fibrin hydrogel. Subsequently, the channels are populated with endothelial cells. Different hydrogel concentrations of fibrin are used to mimic healthy and early granulation tissue. The vessels are perfused, and stable metabolic/viability conditions (lactate dehydrogenase, glucose, lactate) acquired after 3 days for 7 days total. In high fibrin gels, angiogenic sprouting and increased secretion of angiogenic cytokines is observed. Perfusion with monocytes revealed differentiation into macrophages and migration across the endothelium into the tissue. In conclusion, the versatile, easy method to pattern hydrogels in multi‐organ‐chips can serve as the basis to build the next generation of vascularized, immunocompetent human organ models, and opens new possibilities to study health and disease.

For in vitro organ models, perfused vasculature is crucial to overcome nutrient diffusion limits and to generate immunocompetent models by allowing trans-endothelial migration of immune cells in and out of the tissue. However, vasculature is often disregarded due to its complexity to generate and the necessity to integrate flow. The aim here was to overcome these limitations by combining 3D printing and multi-organ-chip technology to generate a vascularized, fibroblast-populated connective tissue matrix on-chip. A 3D printed, sacrificial, water-dissolvable structure was incorporated into a multi-organ-chip to generate hollow channels within a collagen/fibrin hydrogel. Subsequently, the channels were populated with endothelial cells. Different hydrogel concentrations of fibrin were used to mimic healthy and early granulation tissue. The vessels were perfused, and stable metabolic/viability conditions (lactate dehydrogenase, glucose, lactate) acquired after 3 days for 7 days total. In high fibrin gels, angiogenic sprouting and increased secretion of angiogenic cytokines was observed. Perfusion with monocytes revealed differentiation into macrophages and migration across the endothelium into the tissue. In conclusion, the versatile, easy method to pattern hydrogels in multi-organ-chips can serve as the basis to build the next generation of vascularized, immunocompetent human organ models, and opens new possibilities to study health and disease.