Designing of polymeric gels mimicking the normal and fibrotic liver tissues: Effect of viscoelasticity on cells adhesion and survival

Chronic hepatitis B/C virus, alcohol abuse, and non-alcoholic fatty liver disease are the major causes of liver fibrosis (LF), that leads to the progressive impairment of liver function (cirrhosis), often resulting in hepatocellular carcinoma. Despite the etiology, a key element in LF generation is represented by hepatic stellate cells (HSCs) that, from a quiescent condition, differentiate into proliferative and migratory myofibroblasts (cell activation) which secrete Extra Cellular Matrix (ECM) making the tissue increasingly stiffer. Interestingly, HCS activation is triggered by stiff environments, typical of fibrotic liver tissues (shear modulus G > (5 - 6) kPa for human beings). To study the activation process and novel drugs to down-modulate HSC activation, we developed proper substrates which can effectively mimic the viscoelastic properties of healthy and pathological liver tissue. Therefore, we designed alginates-based gels resembling the healthy and the pathological liver tissues from a viscoelastic point of view. For this purpose, hydrogels characterized by different alginate concentrations were produced to indicatively match healthy and pathological stiffness (crosslinking by CaCl2). Then, to improve cells adhesion and survival on the gel surface, the water phase was substituted by a proper culture medium. Furthermore, additional studies were carried out in order to add ECM-like substrates to the alginate solution, like collagen or fibronectin or matrigel, to promote cells-gel interactions. Each gels was characterized by stress and frequency sweep tests to get the linear viscoelastic range, the relaxation spectrum (generalized Maxwell model fitting to frequency sweep data) and the shear modulus G (stiffness). Finally, the optimal gel systems effectively mimicking healthy or pathological liver tissues were successfully considered for cell seeding and followed their adhesion and survival up to three days