Sorting of large particles as a model for use in islet cryopreservation

Pancreatic islet transplantation offers a potential curative approach to diabetes but has been limited in application due to the lack of adequate islet supply needed at the time of transplant (∼300,000 islets for a possible reversal of diabetes). Cryopreservation of pancreatic endocrine cells could circumvent supply chain challenges for quality and required islet equivalence (IEQ). Cryopreservation protocols are more effective when tailored to the size and volume of the biological sample (CPA loading protocols, cooling, and warming rates). Human islets vary in size ranging from 50-400μm, and our group has recently demonstrated a generalized cryopreservation protocol to preserve them. However, protocols specific to IEQ could further improve outcomes, but this requires a platform for high throughput sorting. Additionally, clinical translation will require purification of the isolated cell products (e.g., removal of acinar tissue). Microfluidic platforms provide a unique opportunity to screen and manipulate islets. Recent work on using surface acoustic waves-based devices to actuate small particles (< 50μm) and cells has shown great potential in performing high throughput separation. This work aims to separate large (>50μm) biomaterials such as pancreatic islets by size using travelling surface acoustic waves. We demonstrate high throughput label free sorting of polyethylene particles by size. Particles were focused into narrow streamlines inside the device and were optically interrogated for their size. Particles larger than a set cut-off diameter (150μm) were actuated into a separate outlet using acoustic pulses. We tested the effect of control parameters (actuation signal, flowrates, sample dilution) on efficacy of sorting. Our device can sort relevant particle samples at about 25,000-100,000 particle-mixture/hour rate. Translation of this work to islets provides a key technology for improving outcomes in islet cryopreservation and transplant. This sorting technology can also be used for other biological systems such as embryos, and stem cell spheroid clusters.