High oxygen preservation hydrogels to augment cell survival under hypoxic condition.

Cell therapy is a promising approach for ischemic tissue regeneration. However, high death rate of delivered cells under low oxygen condition, and poor cell retention in tissues largely limit the therapeutic efficacy. Using cell carriers with high oxygen preservation has potential to improve cell survival. To increase cell retention, cell carriers that can quickly solidify at 37 °C so as to efficiently immobilize the carriers and cells in the tissues are necessary. Yet there lacks cell carriers with these combined properties. In this work, we have developed a family of high oxygen preservation and fast gelation hydrogels based on N-isopropylacrylamide (NIPAAm) copolymers. The hydrogels were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of NIPAAm, acrylate-oligolactide (AOLA), 2-hydroxyethyl methacrylate (HEMA), and methacrylate-poly(ethylene glycol)-perfluorooctane (MAPEGPFC). The hydrogel solutions exhibited sol-gel temperatures around room temperature and were flowable and injectable at 4°C. They can quickly solidify (≤6 s) at 37°C to form flexible gels. These hydrogels lost 9.4~29.4% of their mass after incubation in Dulbecco's Phosphate-Buffered Saline (DPBS) for 4 weeks. The hydrogels exhibited a greater oxygen partial pressure than DPBS after being transferred from a 21% O2 condition to a 1% O2 condition. When bone marrow mesenchymal stem cells (MSCs) were encapsulated in the hydrogels and cultured under 1% O2, the cells survived and proliferated during the 14-day culture period. In contrast, the cells experienced extensive death in the control hydrogel that had low oxygen preservation capability. The hydrogels possessed excellent biocompatibility. The final degradation products did not provoke cell death even when the concentration was as high as 15 mg/ml, and the hydrogel implantation did not induce substantial inflammation. These hydrogels are promising as cell carriers for cell transplantation into ischemic tissues. STATEMENT OF SIGNIFICANCE: Stem cell therapy for ischemic tissues experiences low therapeutic efficacy largely due to poor cell survival under low oxygen condition. Using cell carriers with high oxygen preservation capability has potential to improve cell survival. In this work, we have developed a family of hydrogels with this property. These hydrogels promoted the encapsulated stem cell survival and growth under low oxygen condition.