Skip to main content
2023 BMES Annual Meeting Main banner
Icon Legend
This session is not in your schedule.
This session is in your schedule. Click again to remove it.
Back

    Biomaterials

    (C-107) Cell-Releasing Hydrogel Carrier for Mesenchymal Stem Cell Delivery

    Friday, October 13, 2023
    9:30 AM – 10:30 AM PDT
    Location: Exhibit Hall - Row C - Poster # 107
    Introduction:: Mesenchymal stem cells (MSCs) exhibit unique therapeutic characteristics that have implicated them as potential tools for bone regeneration.1,2 Despite these regenerative qualities, therapeutic delivery of MSCs within clinical settings has seen limited success due to poor cell retention and decreased viability upon immune attack.3 We have previously demonstrated sustained viability and osteogenic potential of MSCs following encapsulation within a poly(ethylene glycol)-based injectable hydrogel system.4 Such systems, which implement mechanical barriers for retention and protection of cells, may mitigate the challenges in efficacy of stem cell therapy. Fundamental to successful stem cell delivery is an optimal hydrogel carrier degradation profile; because multiple environmental factors, such as inflammation and oxidative stress5, become significant at different stages following injection, it is necessary to investigate impacts of degradative profiles on cell viability. We have designed a hydrogel system which combines poly(ethylene glycol) diacrylate (PEGDA) and poly(ethylene glycol) dithioester acrylamide (PEGDTEA)6, a hydrolytically labile macromer, capable of achieving variable degradation profiles without changes in bulk properties; here, we demonstrate the maintenance of bulk properties along with varying degradation profiles across hydrogels of different macromer ratios. Currently, we are investigating the effects of these variable macromer ratios, and associated variable degradation rates, on sustained viability and osteogenic potential of MSCs.

    Materials and Methods:: Hydrogels of varying PEGDTEA:PEGDA ratios (100:0, 90:10, 80:20, 70:30, 60:40, 50:50, 0:100) were fabricated by preparing 10 wt% precursor solutions in reverse osmosis water. Precursor solutions were loaded into double-barrel syringes equipped with mixing heads, with half the solution containing ammonium persulfate (APS, 0.75 mM) and the other half containing iron gluconate dihydrate (IG, 1.5 mM). Solutions were injected between Sigmacote-treated coverslips spaced 1 mm apart and allowed to crosslink for 2 minutes at 37˚C, as previously established.7 For each composition, specimens (n = 6, 6 mm diameter, 1 mm height) were taken from hydrogel slabs to measure equilibrium swelling ratio. Following fabrication, specimens were swollen in phosphate-buffered saline (PBS) for 3 hours and weighed (Ws); specimens were then dried under vacuum for 24 hours and weighed (Wd). Swelling ratio (Q) was calculated from the equilibrium mass swelling ratio (Q = Ws / Wd). Swelling ratio was monitored over time to characterize in vitro hydrolytic degradation profiles of hydrogels as functions of composition and macromer molecular weight. Hydrogel specimens (n = 6, 6 mm diameter, 1 mm height) of varying PEGDTEA: PEGDA ratios (100:0, 90:10, 80:20, 70:30, 60:40, 50:50, 0:100) were prepared and taken from slabs as previously described. Following fabrication, specimens were dried under vacuum for 24 hours and weighed (Wd); hydrogel disks were then incubated at 37˚C in PBS supplemented with 1% penicillin-streptomycin with weekly solution changes. Swollen masses (Ws) were measured at discrete time points, and swelling ratio was calculated as previously described.

    Results, Conclusions, and Discussions::

    Results and Discussion: Hydrogels composed of macromers of equal molecular weights (6 kDa or 20 kDa) and varying PEGDTEA:PEGDA ratios (100:0, 90:10, 80:20, 70:30, 60:40, 50:50) exhibited similar swelling ratios to that of PEGDA hydrogel controls (Fig. 1A, 1B). Hydrogel degradation was monitored through changes in swelling ratio under the assumption that chain scission results in reduced crosslinking density and subsequently increased swelling ratio. As expected, PEGDA control hydrogels of both 6 kDa and 20 kDa molecular weights demonstrated minimal in vitro degradation over the 3-day period (Fig. 1C, 1D). Although the degradation profiles are not fully characterized through this data, we see a more rapid increase in swelling ratio of 20 kDa hydrogels; this is demonstrated by the significant change in swelling ratio of 20 kDa hydrogels with a 70:30 PEGDTEA:PEGDA composition as opposed to non-significant differences within 6 kDa hydrogels of the same composition. This may be attributable to the higher initial swelling ratio of 20 kDa hydrogels roughly 2X that of 6 kDa hydrogels, which allows for increased hydrogel water absorption and expedited hydrolysis.


    Conclusion: Hydrogel encapsulation is a potential solution for protecting mesenchymal stem cells from the obstacles imposed during the initial hostile conditions of injection and implantation. Ongoing studies are fully characterizing the degradation profiles of the variable hydrogel compositions and investigating the effects of these different degradation profiles on sustained cell viability and osteogenic potential post-release.



    Acknowledgements (Optional): :

    References (Optional): :

    1Walmsley, Graham G., et al. "Stem cells in bone regeneration." Stem cell reviews and reports 12 (2016): 524-529.


    2Gómez‐Barrena, Enrique, et al. "Bone regeneration: stem cell therapies and clinical studies in orthopaedics and traumatology." Journal of cellular and molecular medicine 15.6 (2011): 1266-1286.


    3Lukomska, Barbara, et al. "Challenges and controversies in human mesenchymal stem cell therapy." Stem cells international 2019 (2019).


    4Whitely, Michael, et al. "Improved in situ seeding of 3D printed scaffolds using cell-releasing hydrogels." Biomaterials 185 (2018): 194-204.


    5Wang, Xinlong, et al. "Advanced functional biomaterials for stem cell delivery in regenerative engineering and medicine." Advanced Functional Materials 29.23 (2019): 1809009.


    6Green, Mykel, et al. “New Synthetic Route to Improve Uniformity of Cell-Releasing PEG-based Hydrogel Carriers.” MRS communications (2023).


    7Cereceres, Stacy, et al. "In Vivo Characterization of Poly (ethylene glycol) Hydrogels with Thio-β Esters." Annals of biomedical engineering 48 (2020): 953-967.