Magnetic hydrogel encapsulation combined with on-chip processing enhances straw vitrification of mouse oocytes

Oocyte cryopreservation represents a cornerstone technology in assisted reproductive medicine and biodiversity conservation. In this field, microfluidic chips have emerged as promising tools for minimizing osmotic shock and other damage through programmed and automated addition of cryoprotectants (CPAs). Nevertheless, existing microfluidic platforms still face significant challenges in inefficient cell loading/retrieval and operational complexity, which compromise the efficacy of oocyte cryopreservation, hindering their development and application. Here, we developed a novel microfluidic chip and combined it with magnetic hydrogel microencapsulation technology, to establish a comprehensive strategy for optimizing oocyte cryopreservation. Unlike previous microfluidic systems hindered by fluid shear stress or complex capture designs, our platform incorporates a quick-sealing cover for efficient retrieval and magnetic hydrogel immobilization, effectively preventing cell drift and loss without requiring intricate microchannel structures. This innovation not only simplifies operation but also enhances reproducibility. Furthermore, the magnetic hydrogel enables external magnetic control of oocytes in the microchannel, avoid the complex capture structure design of microchannels and provide physical shielding for oocytes during cryopreservation. Compared with conventional straw vitrification, this approach significantly improved oocyte survival rate (86.63% (n = 53) vs. 57.47% (n = 73)) and better preserved mitochondrial activity, cytoskeleton structure, and embryonic development potential. This work presents a combined cryopreservation method that marries high-efficiency protection with operational simplicity, offering a new scheme for oocyte cryopreservation with significant translational potential.