Engineering poly (ethylene glycol) diacrylate-based microstructures to develop an in vitro model of small intestinal epithelium

[eng] Most of the current in vitro cell culture models do not reproduce the anatomy of tissues and physiological behavior of cells in vivo and provide misleading results when compared to the real tissue. Microfabrication technologies can be used to go one step beyond the conventional 2D in vitro tissue culture models and reliably reproduce in vivo tissue microenvironments.1 For the small intestinal epithelium, this approach has been explored through the fabrication of collagen and poly (lactic-co-glycolic acid) villi-like scaffolds, using sequential micromolding.2–4 Although that has been an innovative and interesting approach, the nature of the employed materials does not allow fine-tuning of the system properties and the molding method is laborious, requiring several intermediate molding steps. Here we describe a simple and cost-effective method to fabricate soft 3D villi-like microstructures with the anatomical architecture. We use poly (ethylene glycol) diacrylated (PEGDA) and acrylic acid that copolymerize and form soft hydrogels upon crosslinking through UV photolithography. And we demonstrate that our technology allows producing functional monolayers of polarized Caco-2 epithelial cells. Hydrogels are networked materials with high water content, which allow easy diffusion of soluble factors and oxygen.5,6 PEG-based hydrogels possess highly tunable chemical and mechanical properties and have become trendy materials to mimic and are the extracellular matrix and tissue basement membranes.7,8 To get 3D villi-like microstructures, 2D photomasks were used in a UV light-dependent polymerization process. During this process, several variable factors, such as UV exposure time, photoinitiator concentration, and PEGDA molecular weight and concentration, were studied to understand the mechanisms that allow the formation of high aspect ratio soft microstructures. Then, these variables were adjusted to control the microstructure dimensions and to obtain villi-like microstructures resembling the in vivo villi dimensions, physical and mechanical properties. To allow cell adhesion and growth, we copolymerize PEGDA (non-bioactive) with acrylic acid and we took advantage of the exposed carboxylic groups of the acrylic acid to covalently incorporate laminin through the EDC/NHS coupling reaction. We have stablished the ratio between PEGDA and acrylic acid to obtain on the one hand, a successful copolymerization and villi-like structures formation and, on the other a pro