The extracellular matrix (ECM) provides biochemical and structural support to the surrounding cells in living tissues. Comprising proteins and polysaccharides arranged in an intricate porous network, ECM incorporates cells, enzymes and growth factors. Recreating its complexity in vitro, in terms of composition, structure, and mechanical properties, is a challenging task. The use of 3D bioprinting to fabricate 3D constructs with a hierarchical architecture similar to the native tissue could meet some of these challenges. Bioinks hence need to be formulated to give the biochemical cues for cell adhesion and proliferation, which may be missing in commonly used polymers. Decellularized ECM (dECM), obtained from the decellularization of ECM, is a promising candidate to that respect. dECM gels preserve the composition of ECM and thereby contain protein domains essential for cell stimulation. Here, we aim to fabricate 3D printed constructs from dECM bioinks with tunable rheological properties, and investigate their interactions with cells.

dECM bioinks were obtained from the decellularization of porcine skin tissue, followed by an enzymatic digestion. The efficiency of the decellularization process was assessed with biochemical assays to measure the DNA removal and the maintenance of collagen and glycosaminoglycans levels in the dECM. Gelation kinetics at physiological pH and shear viscosity were assessed as a function of the concentration of dECM in the bioink. dECM hydrogels with a storage modulus ranging from ca 100 Pa to 1 kPa were obtained after 10 min at 37 °C for concentrations of dECM up to 10 mg.mL-1. Bioinks with different rheological properties were then processed through extrusion printing to obtain 3D constructs of variable porosity and topography, as observed by optical- and electron microscopy. The cellular behavior of fibroblasts and T-cells seeded on top or encapsulated inside the gels was evaluated. Cell proliferation was monitored over a week and compared between gels of different stiffness. Finally, compression tests with or without the encapsulated cells were used to assess how the presence of cells affect the mechanical properties of the construct.

Using dECM bioinks with tunable properties, we were able to fabricate 3D printed constructs. Thanks to the similarity of dECM with native tissues, these constructs can stimulate cell attachment and proliferation, which is of great interest for their further use in tissue engineering.