Stability of alginate scaffolds for stromal and salivary gland epithelial cell growth

Abstract

There is a need for understanding and recreating salivary gland stromal and epithelial cell interactions to enable simulation of the process of branching morphogenesis to create gland structure and induce polarization of salivary epithelial cells to enable gland function. Previously our lab designed a method to create biocompatible “off-the-shelf” alginate hydrogel microtubes to mimic the microenvironment of salivary gland cells. Alginate hydrogels provide a useful option for a 3D scaffold due to their biocompatibility and proven use for 3D cell culture and tissue engineering. However, alginate hydrogels, in particular, those crosslinked by Ca2+ are not especially stable in the presence of phosphate, which exists in cell culture media and is required for cell growth. To address the instability of alginate hydrogels due to degradation/disassociation in the presence of phosphate, CaCl2 is needed to supplement the cell culture medium.

This need leads to our current focus on addressing the following two questions: i) What is the optimal minimal concentration of CaCl2 to stabilize alginate hydrogel microtubes; and ii) What is the maximal CaCl2 concentration that allows cells to continue to grow once released from these microtubes? In this study, CaCl2 was supplemented at various concentrations between 0 mM and 50 mM (i.e., 0, 1, 2, 3.125, 6.25, 12.5, 25, and 50 mM) to determine the lowest effective concentration to stabilize alginate hydrogel microtubes while supporting cell growth and organization. The purpose of this project is to focus on the effect of CaCl2 on alginate hydrogel microtube porosity and stability, as well as its effect on cell growth and regrowth after release from alginate hydrogel microtubes. We used mouse NIH 3T3 fibroblasts as model stromal cells and salivary gland epithelial SCA-9 cells as model epithelial cells to evaluate the effects of CaCl2 concentration in monoculture and also in co-culture of these cells in alginate hydrogel microtubes. By determining the optimal CaCl2 concentration, we were able to maintain the structural integrity of our alginate hydrogel microtubes while allowing stromal and epithelial cells to grow, interact, and organize into cell clusters. This work lays a foundation for future organoid culture in alginate hydrogels for the salivary gland and beyond.