Development of Poly(Ethylene Glycol) Hydrogels for Salivary Gland Tissue Engineering Applications

Abstract

More than 40,000 patients are diagnosed with head and neck cancers annually in the United States with the vast majority receiving radiation therapy. Salivary glands are irreparably damaged by radiation therapy resulting in xerostomia, which severely affects patient quality of life. Cell-based therapies have shown some promise in mouse models of radiation-induced xerostomia, but they suffer from insufficient and inconsistent gland regeneration and accompanying secretory function. To aid in the development of regenerative therapies, poly(ethylene glycol) hydrogels were investigated for the encapsulation of primary submandibular gland (SMG) cells for tissue engineering applications. Different methods of hydrogel formation and cell preparation were examined to identify cytocompatible encapsulation conditions for SMG cells. Cell viability was much higher after thiol-ene polymerizations compared with conventional methacrylate polymerizations due to reduced membrane peroxidation and intracellular reactive oxygen species formation. In addition, the formation of multicellular microspheres before encapsulation maximized cell-cell contacts and increased viability of SMG cells over 14-day culture periods. Thiol-ene hydrogel-encapsulated microspheres also promoted SMG proliferation. Lineage tracing was employed to determine the cellular composition of hydrogel-encapsulated microspheres using markers for acinar (Mist1) and duct (Keratin5) cells. Our findings indicate that both acinar and duct cell phenotypes are present throughout the 14 day culture period. However, the acinar:duct cell ratios are reduced over time, likely due to duct cell proliferation. Altogether, permissive encapsulation methods for primary SMG cells have been identified that promote cell viability, proliferation, and maintenance of differentiated salivary gland cell phenotypes, which allows for translation of this approach for salivary gland tissue engineering applications.

Advances in multicellular spheroids formation

“…cell [82] synthesized polymers PEG -good biocompatibility -irreversible gelation leading to challenges in releasing MCSs from gel Huh7.5 cells [12], submadibular glands [83] PLG/PLGA -biodegradable and biocompatible hepatocytes [84], MCF-7, U87 [49] NIPAM-based hydrogel -thermally reversible to release MSCs during harvest -low viscoelasticity -porous structure with great nutrient, oxygen and waste transport HepG2 [85], HeLa [51], human pluripotent stem cells [7] poly(1-carpolacton)…”

Biomaterials-based strategies for salivary gland tissue regeneration

“…Encapsulation of pre-assembled multicellular spheroids improved cell viability, promoted cell proliferation, and established and preserved cell-cell contacts. 41 …”

Tuning Hydrogel Properties to Promote the Assembly of Salivary Gland Spheroids in 3D

“…One report of primary mouse submandibular gland cells, cultured within covalently crosslinked PEG gels, describes viability and phenotype retention for pre-aggregated cells encapsulated under specific crosslinking chemistries. 7 Stably crosslinked HA gels that effectively promoted the formation of prostate cancer spheroids 8–11 failed to promote the formation of salivary spheroids from individually-encapsulated salivary gland epithelial cells. Although covalently crosslinked HA/PEG gels allowed for the growth of lobular structures two weeks after 3D cell encapsulation, 12–13 the underlying mechanism has not been elucidated and thorough integration of implanted cell-gel constructs with host tissues is challenging owing to their relatively low in vivo stability.…”