Sensing and Sensibility: Single‐Islet‐based Quality Control Assay of Cryopreserved Pancreatic Islets with Functionalized Hydrogel Microcapsules

Abstract

Despite decades of research and clinical studies of islet transplantations, fi nding simple yet reliable islet quality assays that correlate accurately with in vivo potency is still a major challenge, especially for real-time and singleislet-based quality assessment. Herein, proof-of-concept studies of a cryopreserved microcapsule-based quality control assays are presented for single islets. Individual rat pancreatic islets and fl uorescent oxygen-sensitive dye (FOSD) are encapsulated in alginate hydrogel microcapsules via a microfl uidic device. To test the susceptibility of the microcapsules and the FOSD to cryopreservation, the islet microcapsules containing FOSD are cryopreserved and the islet functionalities (adenosine triphosphate, static insulin release measurement, and oxygen consumption rate) are assessed after freezing and thawing steps. The cryopreserved islet capsules with FOSD remain functional after encapsulation and freezing/thawing procedures, validating a simple yet reliable individual-islet-based quality control method for the entire islet processing procedure prior to transplantation. This work also demonstrates that the functionality of cryopreserved islets can be improved by introducing trehalose into the routinely used cryoprotectant dimethyl sulfoxide. The functionalized alginate hydrogel microcapsules with embedded FOSD and optimized cryopreservation protocol presented in this work serve as a versatile islet quality assay and offer tremendous promise for tackling existing challenges in islet transplantation procedures.

Current Advancements in Pancreatic Islet Cryopreservation Techniques

“…In addition to cyroprotective abilities, the microcapsules treated with ROS demonstrated viable oxygen sensitivity during OCR measurements. This study demonstrates the use of multiple cyroprotective parameters to mitigate potential damage during cryopreservation [94]. Other studies have demonstrated the benefits of alginate microencapsulation use during cryopreservation as the 3D barrier is porous and can resist stress/strain associated with ice formation [94,96,97].…”

“…Islets were encapsulated with alginate coating containing ruthenium-based oxygen-sensitive fluorophore (ROF) after which the encapsulated islets were subjected to a 10% DMSO with or without 50x10 −3 M trehalose and stored for 1-7 days. Encapsulated islets undergoing cryopreservation showed significantly higher insulin stimulation behavior than bare islets at Day 1 and 7 [94]. In addition to cyroprotective abilities, the microcapsules treated with ROS demonstrated viable oxygen sensitivity during OCR measurements.…”

“…Alginate-microencapsulation has recently been applied to the field of islet cryopreservation in order to characterize its effect on islet survivability [33]. Chen et al reported the development of an oxygen-sensing alginate coating to encapsulate islets prior to cryopreservation [94,95]. Islets were encapsulated with alginate coating containing ruthenium-based oxygen-sensitive fluorophore (ROF) after which the encapsulated islets were subjected to a 10% DMSO with or without 50x10 −3 M trehalose and stored for 1-7 days.…”

Hydrogel Encapsulation Facilitates Rapid‐Cooling Cryopreservation of Stem Cell‐Laden Core–Shell Microcapsules as Cell–Biomaterial Constructs

“…Cryovials and conventional plastic straw (PS) have been widely used for low-CPA (1–2 mol L −1 ) slow freezing with controlled rate freezer (or cryogenic refrigerator) [2, 9, 46] and high-CPA (~8 mol L −1 ) vitrification by plunging into LN 2 [8, 22, 47] , respectively. Therefore, we used PS for the large-volume-alginate hydrogel-encapsulation based cryopreservation of stem cells by rapid cooling with low concentrations of CPAs in this study.…”

Current Perspective and Advancements of Alginate-Based Transplantation Technologies

“…Transplantation research has particularly benefited from use of alginate technologies during cryopreservation. Recent studies in pancreatic islet transplantation have demonstrated that use of alginate microencapsulation helps maintain islet viability during preservation and improves islet secretory function during transplantation [67,78,79]. A 10 years study using encapsulated rat, pig, human islets showed that alginate encapsulated islets maintained significantly higher viability, secretory function, and yield compared to nonencapsulated islets after cryopreservation for 10 years [80].…”