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Here, we propose an immune-responsive human Microbiota-Intestine axis on-chip as a platform able to reproduce the architecture and vertical topography of the microbiota with a complex extracellular microenvironment consisting of a responsive extra cellular matrix (ECM) and a plethora of immune-modulatory mediators released from different cell populations such as epithelial, stromal, blood and microbial species in homeostatic and inflamed conditions. Firstly, we developed a three-dimensional human intestine model (3D-hI), represented by an instructive and histologically competent ECM and a well-differentiated epithelium with mucus-covered microvilli. Then, we replicated the microenvironmental anaerobic condition of human intestinal lumen by fabricating a custom-made microbiota chamber (MC) on the apical side of the Microbiota-human Intestine on chip (MihI-oC), establishing the physiological oxygen gradient occurring along the thickness of human small intestine from the serosal to the luminal side. The complexity of the intestinal extracellular microenvironment was improved by integrating cells populations that are directly involved in the inflammatory response such as peripheral blood mononuclear cells (PBMCs) and two species of the intestinal commensal microbiota (Lactobacillus rhamnosus and Bifidobacterium longum). We found that lipopolysaccharide (LPS)-induced inflammation elicits microbiota's geographical change and induce Bifidobacterium longum iper-proliferation, highlighting a role of such probiotic in anti-inflammatory process. Moreover, we proved, for the first time, the indirect role of the microbiota on stromal reshaping in immune-responsive MihI-oC in terms of collagen fibers orientation and ECM remodeling, and demonstrated the role of microbiota in alleviating gastrointestinal, immunological and infectious diseases by analyzing the release of key immune-mediators after inflammatory stimulus (reactive oxygen species (ROS), pro- and anti-inflammatory cytokines).

We fabricated three-dimensional microtissues with the aim to replicate in vitro the composition and the functionalities of the tumor microenvironment. By arranging either normal fibroblasts (NF) or cancer-activated fibroblasts (CAF) in two different three dimensional (3D) configurations, two kinds of micromodules were produced: spheroids and microtissues. Spheroids were obtained by means of the traditional cell aggregation technique resulting in a 3D model characterized by high cell density and low amount of extracellular proteins. The microtissues were obtained by culturing cells into porous gelatin microscaffolds. In this latter configuration, cells assembled an intricate network of collagen, fibronectin and hyaluronic acid. We investigated the biophysical properties of both 3D models in terms of cell growth, metabolic activity, texture and composition of the extracellular matrix (via histological analysis and multiphoton imaging) and cell mechanical properties (via Particle Tracking Microrheology). In the spheroid models such biophysical properties remained unchanged regardless to the cell type used. In contrast, normal-microtissues and cancer-activated-microtissues displayed marked differences. CAF-microtissues possessed higher proliferation rate, superior contraction capability, different micro-rheological properties and an extracellular matrix richer in collagen fibronectin and hyaluronic acid. At last, multiphoton investigation revealed differences in the collagen network architecture. Taken together, these results suggested that despite to cell spheroids, microtissues better recapitulate the important differences existing in vivo between normal and cancer-activated stroma representing a more suitable system to mimic in vitro the stromal element of the tumor tissues. Statement of Significance This work concerns the engineering of tumor tissue in vitro. Tumor models serve as biological equivalent to study pathologic progression and to screen or validate the drugs efficacy. Tumor tissue is composed by malignant cells surviving in a microenvironment, or stroma. Stroma plays a pivotal role in cancer progression. Current in vitro models, i.e. spheroids, can’t replicate the phenomena related to the tumor stroma remodeling. For this reason, to better replicate the tumor physiology in vitro that include functional and morphological changes, a novel 3D cancer model is proposed.

Tissue-engineered constructs can be fabricated by the assembly of smaller building blocks in order to mimic much of the native biology that is often made from repeating functional units. Our aim was to realize a three-dimensional (3-D) tissue-like construct in vitro by inducing the assembly of functional micrometric tissue precursors (microTPs). MicroTPs were obtained by dynamic cell seeding of bovine fibroblasts on porous gelatine microcarriers using a spinner flask bioreactor. During the dynamic seeding, cells adhered, proliferated and synthesized a thin layer of extracellular matrix (ECM) in and around the macroporous beads, generating the microTPs. The analysis showed that the ECM produced was rich in type I collagen. The cells and ECM layer around the microTPs allowed their biological sintering via cell-cell and cell-matrix interaction after only a few days of dynamic seeding. The assembling ability of microTPs was exploited by placing them in a maturation chamber. After 1 week of culture disc-shaped constructs (1cm in diameter, 1mm in thickness) of completely assembled microTPs were collected. The biohybrid obtained presented both a homogeneous and compact aspect. Moreover, histological and immunohistochemical analyses revealed an abundant ECM, rich in type I collagen, interconnecting the microTPs. The results obtained in this survey pave the way to realizing a 3-D dermal tissue equivalent by means of a bottom-up tissue engineering approach.