Effect of Mechanically and Chemically Altered Alginate Hydrogels on Fibroblastic Reticular Cell Function

• Ethan Neidich, Biomedical Engineering, University of Delaware

• Brian Kwee, Biomedical Engineering, University of Delaware

Fibroblastic reticular cells (FRCs) are stromal cells that make up the structure of our lymph nodes and help mount immune responses by secreting chemokines. When FRCs are isolated from the body and grown on tissue culture plastic (TCPS) in a lab, FRCs lose key functions, such as the ability to secrete chemokines. Alginate hydrogels, a biomaterial derived from seaweed, have been used as an alternative material to culture cells due to their ability to better mimic in vivo matrices compared to traditional TCPS. The purpose of this study was to evaluate how alginate can be an alternate material to culture FRCs in the lab and determine what fundamental properties of the hydrogels regulate their function in vitro.  Here, we fabricated covalently-crosslinked, elastic alginate hydrogels and calcium-crosslinked, stress-relaxing alginate hydrogels and modified them with integrin mimetic peptide RGD or cadherin mimetic peptide HAVDI. We then cultured commercially available human FRCs on the hydrogels in 2D and evaluated their adhesion, proliferation, and spreading. This is an essential first step in determining whether the function of FRCs can be better maintained on alginate hydrogels in vitro. Elastic and stress-relaxing hydrogels were used to better understand how hydrogel viscoelasticity affects cell function, where stress-relaxing hydrogels better mimic the mechanical properties of native tissues. By using these combinations of mechanical and chemical properties, preliminary results suggest that FRCs have greater adhesion on the stress-relaxing hydrogels modified with RGD or  HAVDI compared to their elastic counterparts. Additionally, better cell spreading was observed on the RGD-modified alginate hydrogels compared to the HAVDI-modified alginate hydrogels, regardless of the hydrogel’s mechanical properties, and no cell proliferation was observed during the course of the experiment, as measured by the incorporation of EdU into cells with newly synthesized DNA. Further testing must be performed to substantiate these results and ensure repeatability. If further testing proves that alginate hydrogels with particular properties are a suitable culture substrate for FRCs in vitro, future work will explore how FRCs harvested from tonsil tissues can be cultured on the gels.