Mouse and human islets survive and function after coating by biosilicification

Abstract

Inorganic materials have properties that can be advantageous in bioencapsulation for cell transplantation. Our aim was to engineer a hybrid inorganic/soft tissue construct by inducing pancreatic islets to grow an inorganic shell. We created pancreatic islets surrounded by porous silica, which has potential application in the immunoprotection of islets in transplantation therapies for type 1 diabetes. The new method takes advantage of the islet capsule surface as a template for silica formation. Mouse and human islets were exposed to medium containing saturating silicic acid levels for 9 -15 min. The resulting tissue constructs were then cultured for up to 4 wk under normal conditions. Scanning electron microscopy and energy dispersive Xray spectroscopy was used to monitor the morphology and elemental composition of the material at the islet surface. A cytokine assay was used to assess biocompatibility with macrophages. Islet survival and function were assessed by confocal microscopy, glucose-stimulated insulin release assays, oxygen flux at the islet surface, expression of key genes by RT-PCR, and syngeneic transplant into diabetic mice. islet; encapsulation; silica; coating; tissue engineering TO CREATE 3D TISSUE CONSTRUCTS for transplantation therapies, cells are typically encapsulated within organic polymers, either synthetic or natural, such as collagen or alginate. For applications requiring protection from the immune system, however, inorganic or hybrid (inorganic/organic) materials may offer a different set of useful functions and properties to be used as alternatives to or in conjunction with the organic polymers. Porous silica is an attractive material for these applications because of its mesoporosity, potential to create hierarchical structures, optical transparency, capacity for biofunctionalization, performance in precision size exclusion, and bioactivity.Our work focuses on primary pancreatic islets because of their importance in therapies for type 1 diabetes. The Edmonton protocol of islet transplantation in humans (40) has demonstrated remarkable short-term success, with 80% of individuals achieving insulin independence at 1 yr posttransplant; however, this rate decreases to only about 10 -15% at 5 yr (3). Multiple mechanisms contribute to the progressive loss of graft function but likely include an immediate blood-mediated response (IBMR) (1, 37), poor revascularization and hypoxia (9, 16), and ongoing auto-and alloimmune responses (38). Protection of islets or stem cell-derived pseudo-islets by protective membranes could significantly improve transplant outcomes for patients.The sol-gel synthesis method of forming solid porous silica under biologically friendly temperatures and pH has been used to encapsulate first biomolecules and later living cells since the early 1990s. Early attempts to use silica as a microencapsulation matrix for islets employed bulk sol-gel techniques, resulting in islets encased in thick silica slabs or spheres (34, 35). These implants were able to supply enough insulin...

Sol-Generating Chemical Vapor into Liquid (SG-CViL) deposition – a facile method for encapsulation of diverse cell types in silica matrices

“…S5) is in contrast to work by Jaroch et. al ., 42 who encapsulated murine and human islet cells in silica without a polycation treatment. This is likely due to the higher concentration of silica utilized by Jaroch et.…”

Glucose Effectiveness

“…Again, obtained findings have been interpreted to show normal insulin release dynamics, however, without accurate insulin or c-peptide determinations in conjunction with glucose infusion. 2,[8][9][10][11][12][13][14][15]31 In contrast, in vitro studies show a significant delay in insulin release from encapsulated when compared with nonencapsulated islets. 30 A finding in agreement with the results presented herein demonstrate that the reported normal glucose disposal during an IVGTT could equally well be achieved with an encapsulation device with poor glucose and insulin diffusion dynamics resulting in baseline insulin release comparable with that from a slow-release device, such as the Linplant.…”

“…However, insulin, or c-peptide, release during the IVGTT has in most studies not been determined. 2,[8][9][10][11][12][13][14][15] Even so, normalization of glucose dynamics during an IVGTT has been interpreted as evidence of also active insulin secretion even if it has been known since the time of Soskin et al 16,17 that glucose could influence its own disposal independent of changes in the plasma insulin level.…”

Islet Encapsulation: Physiological Possibilities and Limitations

“…Notably, dynamic insulin, or C-peptide release, during the IVGTT has not been determined in most studies on encapsulation (20)(21)(22)(23)(24)(25)(26)(27)(28). Even so, normalization of glucose dynamics during an IVGTT has been interpreted as evidence of active insulin secretion, even though it has been known since 1934 (29) that glucose influences its own disposal, independent of changes in the plasma insulin level.…”