An all-in-one microfluidic cryopreservation system and protocols with gradually increasing CPA concentration

In regular biosample cryopreservation operations, dropwise pipetting and continuous swirling are ordinarily needed to prevent cell damage (e.g. sudden osmotic change, toxicity and dissolution heat) caused by the high-concentration cryoprotectant (CPA) addition process. The following CPA removal process after freezing and rewarming also requires multiple sample transfer processes and manual work. In order to optimize the cryopreservation process, especially for trace sample preservation, here we present a microfluidic approach integrating CPA addition, sample storage, CPA removal and sample resuspension processes on a 30 × 30 × 4 mm³ three-layer chip. The sample solution could be added into CPA solution with pre-generated increasing concentration to decrease possible osmotic damage. Utilizing specially designed microfluidic structure and fluid field analysis, on-chip sample enrichment and CPA removal were achieved. A novel dead-end micro valve strategy with a simplified control module was applied and evaluated to assist on-chip mixing and sample pellet resuspension. The entire biosample cryopreservation process was also performed that verified the functions of the integrated microfluidic platform. Altogether, this developed platform could be an effective approach to realize automatic, all-in-one, low-damage cryopreservation operation.