Hydrogel co-networks of gelatin methacryloyl and poly(ethylene glycol)diacrylate sustain 3D functional in vitro models of intestinal mucosa
Anna Vila Giraut, Biomimetic systems for cell engineering Group
Conventional in vitro cell culture models do not possess the complexity that the native tissues offer. Because of this, the functional properties of the tissues are not properly mimicked, which causes poorly predictive capabilities. Engineered tissues, which combine biofabrication and tissue engineering techniques, try to overcome this gap by providing the cells with an environment similar to the native tissue, recapitulating (I) the physicochemical and mechanical properties of the cellular matrix, (II) the multicellular complexity of the different tissue compartments, and (III) the 3D structures of the tissues. These new engineered models are key factors to improve the platforms for basic research studies, testing new drugs or modelling diseases. Among all the engineered tissues, the intestinal mucosa is not well represented. The intestinal mucosa is formed by the epithelium, which is a multicellular monolayer laying on top of the lamina propria, a connective tissue containing several cell types (mesenchymal cells, immune cells). The gold standard intestinal models are based on epithelial cell lines derived from colon cancer cells grown on the hard porous membranes of the Transwell®
inserts. The lack of the intestinal stromal compartment and the growth on a hard surface give high transepithelial electrical resistance and low apparent permeability. Therefore, the development of better in vitro platforms, which integrates both compartments and provides epithelium-lamina propria cell interactions, is highly desirable.
In this work, we describe an easy and cost-effective method to engineer a 3D intestinal mucosa model that combines both the epithelium and the lamina propria compartments. To build the 3D scaffolds we chose hydrogels as materials to mimic the physicochemical and mechanical properties of intestinal tissue. Thus, hydrogel conetworks of gelatin methacryolyl (GelMA), a natural polymer, and poly(ethylene glycol) diacrylate (PEGDA), a synthetic polymer, are photopolymerized. On one hand, GelMA provides biodegradation and cell adhesion sequences but it lacks long-term mechanical stability. On the other hand, PEGDA, is non-biodegradable and does not present cell adhesion motifs. Nevertheless, it has good mechanical properties. By this technique, the lamina propria compartment of the intestinal mucosa can be reproduced in vitro. To do that, GelMA and PEGDA polymers are laden with mesenchymal cells (fibroblasts or myofibroblasts) and/or immune cells (macrophages). We demonstrated that GelMA – PEGDA hydrogel co-networks support the growth of these cells and epithelial monolayers on top of the scaffolds. Embedding fibroblasts or myofibroblasts on the hydrogel conetworks enhance the formation and the maturity of the Caco-2 epithelial monolayers, providing barrier properties similar to in vivo. The presence of the stromal cells also enhances the recovery of the epithelial integrity when the epithelium is temporally damaged. Finally, an immunocompetent model is obtained by the encapsulation of macrophages in the constructs. The presence of macrophages does not influence the formation of the epithelium. However, when the epithelial monolayer is disrupted, the presence of mesenchymal and immune cells in the stromal compartment increases cytokine secretion in a synergistic manner. Our model can successfully mimic the interactions between stromal and epithelial compartments found in vivo intestinal tissue, offering a potential platform to be used to study absorption and toxicity of drugs, as well as cell behaviour under physiological and pathological conditions.
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