**1. Introduction**

Over 25 million people in the United States (USA) suffer from diabetes, with approximately 5% characterized as type 1 diabetes (T1DM). Diabetes is ranked as the seventh leading cause of death in the USA. T1DM is characterized by the autoimmune-mediated destruction of the β-cells of the pancreas, resulting in insulin deficiency [1]. The current method of treatment for T1DM is insulin injection to maintain blood glucose control, which treats the symptoms but not the underlying disease.

With the invention of the Edmonton protocol in 2000, islet transplantation has become an attractive treatment for T1DM. As a treatment option, islet transplantation meets the goal of treating the disease rather than the symptoms. The end goal of islet transplantation in patients is the elimination of exogenous insulin dependence, allowing for those with T1DM to return to normal lives without constant monitoring of their blood glucose levels. There have been a total of 677 islet transplant recipients from 2000 to 2010. The success of the treatment has improved as well, where 27% of recipients achieved 3 years of insulin independence before 2007. After 2007 that rate has increased to 44%. Compared to insulin injection regimen, islet transplantation resulted in significant reduction in episodes of hypoglycemia unawareness [2].

Islet transplantation faces two challenges from the host immune system: the rejection of the transplanted islets as foreign body and the existing autoimmunity against β-cells. Immunosuppressive drugs such as sirolimus and rapamycin used in the Edmonton protocol has toxic side effects on islets [3, 4]. As such, there is an impetus to move away from the use of immunosuppressive therapy and instead shift toward developing physical barriers against transplant rejection and autoimmunity.

Cell encapsulation to provide physical barrier has been tested in treating other diseases such as neurodegenerative diseases, pain, and epilepsy to name a few. So far, encapsulation has been used primarily to treat T1DM [5–9]. By providing a physical barrier to immune rejection, islet encapsulation has been shown to allow transplanted islet to function normally and avoid the use of immunosuppression [10, 11].
