Abstract
Constructs of magnetic nanocomposite hydrogels microencapsulated with stem cells are of great interest as smart materials for tissue engineering and regenerative medicine. Due to the short shelf life of such biocomposites at an ambient temperature, their long-term storage and banking at cryogenic temperatures are essential for the "off-the-shelf" availability of such biocomposites for widespread clinical applications. However, high-quality cryogenic recovery of stem cell-nanocomposite hydrogel constructs has not yet been achieved due to the damage to cells and/or microstructures of hydrogel constructs caused by ice formation, particularly during warming from cryogenic temperatures. Herein, stem cell-magnetic nanocomposite hydrogel constructs, which have an inherent magnetothermal property provided by embedded magnetic nanoparticles, are explored to achieve ultra-rapid cryogenic warming. The binding of water molecules by the hydrogel combined with the magnetothermal heating greatly suppressed ice formation during both cryogenic cooling and warming. Thus, the cryogenic recovery of nanocomposite hydrogel constructs with intact microstructures and fully functional stem cells from ultra-low temperatures was successfully achieved. We further demonstrated that magnetic nanocomposite hydrogels microencapsulated with stem cells could be conveniently manipulated for a self-assembled 3D culture. Together, we have developed a highly efficient and easy-to-perform approach for the cryogenic recovery of stem cell-encapsulated magnetic nanocomposite hydrogel constructs. Our results will facilitate the applications of such stem cell-magnetic nanocomposite hydrogels in regenerative medicine and tissue engineering.