The insulin-secreting cells of people with type 1 diabetes are destroyed by their immune systems and daily insulin injections are required to treat the condition. Pancreatic islet transplantation is an effective treatment that can dramatically reduce daily doses or even eliminate dependence on external insulin. Insulin-producing cells are injected into a recipient’s liver, and after an adaptation period, they start to produce the insulin the patient needs.
However, the collection, preservation, and transportation of these islet cells are still very challenging. Research published in Advanced Healthcare Materials by scientists from the Okinawa Institute of Technology and Science Graduate University (OIST) in collaboration with the University of Washington and Wuhan University of Technology offers a solution for some of these problems.
Production and secretion of insulin occur in the pancreas-an endocrine gland in the digestive system. Cells secreting insulin are clustered in pancreatic islets. Unfortunately, so far, only human islets can be transplanted, and their supply is small.
Cryopreservation, or deep freezing, is the method commonly used for the islet preservation and transportation. But it is not completely safe. As the cells are cooled, water in and around them freezes. Ice crystals have sharp edges that can pierce membranes and compromise cell viability. This also becomes problematic during thawing.
A multidisciplinary group of researchers led by Amy Shen, PhD, head of the Micro/Bio/Nanofluidics Unit at OIST, developed a novel cryopreservation method that not only helps protect pancreatic islets from ice damage, but also facilitates real-time assessments of cell viability. Moreover, this method may reduce transplant rejection and, in turn, decrease use of immunosuppressant drugs, which can be harmful to patient health.
The technique employs a droplet microfluidic device to encapsulate pancreatic islets in hydrogel made of alginate, a natural polymer extracted from seaweed. These capsules have a unique microstructure: a porous network and considerable amount of nonfreezable water. There are three types of water in the hydrogel: free water, freezable bound water, and nonfreezable bound water. Free water is regular water: It freezes at 0°C, producing ice crystals. Freezable bound water also crystallizes, but the freezing point is lower. Nonfreezable bound water does not form ice due to the strong association between water molecules and the hydrogel networks. Hydrogel capsules with large amounts of nonfreezable bound water protect the cells from ice damage and reduce the need for cryoprotectants-special substances that minimize or prevent freezing damage and can be toxic in high concentrations.
Another innovation proposed by the group is the use of a fluorescent oxygen-sensitive dye in hydrogel capsules. The porous structure of the capsules does not impede oxygen flow to the cells. And this dye functions as a real-time single-islet oxygen sensor. Fluorescence indicates whether cells are consuming oxygen and, therefore, are alive and healthy. It is a simple, time-efficient, and cheap method of assessing viability, both of individual islets or populations thereof.
The microencapsulation method can help to overcome some major challenges in pancreatic islet transplantation, including the scarcity of available islets and the lack of simple and reliable control methods, especially for individual islet assessment. It offers hope to patients suffering from type 1 diabetes to return to a “normal” life, free of insulin injections.
This article was based on information provided by OIST.
