The scarcity of donors and need for immunosuppression limit pancreatic islet transplantation to a few patients with labile type 1 diabetes. Transplantation of encapsulated stem cell-derived islets (SC islets) might extend the applicability of islet transplantation to a larger cohort of patients. Transplantation of conformal-coated islets into a confined well-vascularized site allows long-term diabetes reversal in fully MHC-mismatched diabetic mice without immunosuppression. Here, we demonstrated that human SC islets reaggregated from cryopreserved cells display glucose-stimulated insulin secretion in vitro. Importantly, we showed that conformally coated SC islets displayed comparable in vitro function with unencapsulated SC islets, with conformal coating permitting physiological insulin secretion. Transplantation of SC islets into the gonadal fat pad of diabetic NOD-scid mice revealed that both unencapsulated and conformal-coated SC islets could reverse diabetes and maintain human-level euglycemia for more than 80 days. Overall, these results provide support for further evaluation of safety and efficacy of conformal-coated SC islets in larger species.

matrix-type devices, without requiring surgical removal. [7-9] Enzymatic and hydrolytic degradation are the two major physiologically relevant mechanisms that confer degradability to hydrogel matrices. Enzymatic degradation is generally preferred in tissue engineering, where matrix degradation must be synchronized with native cell infiltration and tissue deposition. [10,11] Enzymatically degradable gels have also shown great potential for celldemanded growth factor delivery, where growth factors are released upon local proteolytic gel degradation by cells. [12,13] Hydrolytic degradation is also advantageous in controlled release applications, such as drug or protein delivery, because the rate of degradation does not depend on enzymes and can be controlled by the hydrogel's chemical and physical properties. [14] In addition, hydrolytically degradable materials could be made at lower cost compared to enzymatically degradable ones. Degradable hydrogels can be formed from both natural and synthetic polymers. Synthetic hydrogels offer advantages in reproducibility, availability, and tailoring physical and chemical properties to specific applications. [15] The synthetic hydrogel poly(ethylene glycol) (PEG) is widely used due to the advantages of being non-immunogenic, inert, and biocompatible. [16] However, the PEG polymer is not readily degradable under physiologic conditions at physiologically relevant time frames. Note that in the long-term PEG can be degradable by oxidative degradation from reactive oxygen species. [17] For short-term degradation, degradable moieties must be introduced to fabricate degradable PEG hydrogels and several techniques have been employed, such as incorporating enzymatically cleavable peptide crosslinkers [18,19] or hydrolytically degradable monomers or copolymers, such as polylactic (PLA) and polyglycolic acid (PGA) to either linear [20,21] or star PEG. [22] Each method has advantages and drawbacks. A reliance on enzymes to cleave crosslinkers can result in inconsistent degradation rates. PEG-PLA and PEG-PGA hydrogels are hydrolytically degradable, but copolymer hydrophobicity and acidic degradation products can denature proteins. [23] Hydrogels prepared from PEG-diacrylate (PEGDA) have also been shown degradable by hydrolytic degradation of the endgroup acrylate esters, when implanted subcutaneously in a rat model. [24] In another example, multiarm PEG-amine crosslinked with an ester-containing amine-reactive PEG derivative has been described as a hydrolytically degradable scaffold for Hydrogels, whose degradability can be controlled while also preserving cell viability or biomolecule stability, are in demand. Degradable polyethylene glycol crosslinkers are hydrolytically designed for use in hydrogels. Degradation is controlled by crosslinker chemical structure, such as introducing local hydrophobicity, steric hindrance, or electron-withdrawing moieties near a degradable ester moiety. Hydrogels made using these crosslinkers have gelation times from 1 to 22 min, storage moduli from 3 to 1...

Polyethylene glycol (PEG)–based conformal coating (CC) encapsulation of transplanted islets is a promising β cell replacement therapy for the treatment of type 1 diabetes without chronic immunosuppression because it minimizes capsule thickness, graft volume, and insulin secretion delay. However, we show here that our original CC method, the direct method, requiring exposure of islets to low pH levels and inclusion of viscosity enhancers during coating, severely affected the viability, scalability, and biocompatibility of CC islets in nonhuman primate preclinical models of type 1 diabetes. We therefore developed and validated in vitro and in vivo, in several small- and large-animal models of type 1 diabetes, an augmented CC method—emulsion method—that achieves hydrogel CCs around islets at physiological pH for improved cytocompatibility, with PEG hydrogels for increased biocompatibility and with fivefold increase in encapsulation throughput for enhanced scalability.

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Pancreatic islet transplantation improves metabolic control and prevents complications in patients with brittle type 1 diabetes (T1D). However, chronic immunosuppression is required to prevent allograft rejection and recurrence of autoimmunity. Islet encapsulation may eliminate the need for immunosuppression. Here, we analyzed in parallel two microencapsulation platforms that provided long-term diabetes reversal in preclinical T1D models, alginate single and double capsules versus polyethylene glycol conformal coating, to identify benefits and weaknesses that could inform the design of future clinical trials with microencapsulated islets. We performed in vitro and in vivo functionality assays with human islets and analyzed the explanted grafts by immunofluorescence. We quantified the size of islets and capsules, measured capsule permeability, and used these data for in silico simulations of islet functionality in COMSOL Multiphysics. We demonstrated that insulin response to glucose stimulation is dependent on capsule size, and the presence of permselective materials augments delays in insulin secretion. Non-coated and conformally coated islets could be transplanted into the fat pad of diabetic mice, resulting in comparable functionality and metabolic control. Mac-2+ cells were found in conformally coated grafts, indicating possible host reactivity. Due to their larger volume, alginate capsules were transplanted in the peritoneal cavity. Despite achieving diabetes reversal, changes in islet composition were found in retrieved capsules, and recipient mice experienced hypoglycemia indicative of hyperinsulinemia induced by glucose retention in large capsules as the in silico model predicted. We concluded that minimal capsule size is critical for physiological insulin secretion, and anti-inflammatory modulation may be beneficial for small conformal capsules.