Bioengineering the Vascularized Endocrine Pancreas: A Fine-Tuned Interplay Between Vascularization, Extracellular-Matrix-Based Scaffold Architecture, and Insulin-Producing Cells

Abstract

Intrahepatic islet transplantation is a promising β-cell replacement strategy for the treatment of type 1 diabetes. Instant blood-mediated inflammatory reactions, acute inflammatory storm, and graft revascularization delay limit islet engraftment in the peri-transplant phase, hampering the success rate of the procedure. Growing evidence has demonstrated that islet engraftment efficiency may take advantage of several bioengineering approaches aimed to recreate both vascular and endocrine compartments either ex vivo or in vivo. To this end, endocrine pancreas bioengineering is an emerging field in β-cell replacement, which might provide endocrine cells with all the building blocks (vascularization, ECM composition, or micro/macro-architecture) useful for their successful engraftment and function in vivo. Studies on reshaping either the endocrine cellular composition or the islet microenvironment have been largely performed, focusing on a single building block element, without, however, grasping that their synergistic effect is indispensable for correct endocrine function. Herein, the review focuses on the minimum building blocks that an ideal vascularized endocrine scaffold should have to resemble the endocrine niche architecture, composition, and function to foster functional connections between the vascular and endocrine compartments. Additionally, this review highlights the possibility of designing bioengineered scaffolds integrating alternative endocrine sources to overcome donor organ shortages and the possibility of combining novel immune-preserving strategies for long-term graft function.

Keywords: 3D- bioprinting; alternative endocrine sources; beta cell replacement; bioengineering; biomaterials; extracellular matrix; type 1 diabetes; vascularized endocrine pancreas.

FIGURE 1

The vascularized endocrine niche within the pancreatic tissue. Pancreatic endocrine niche is enclosed within the pancreatic exocrine tissue and it is constituted by three main components: the extracellular matrix, islet of Langerhans and fenestrated vascular network. Islet is mainly composed of insulin-secreting β-cells, glucagon-secreting α-cells, somatostatin-secreting δ-cells, pancreatic polypeptide-secreting PP-cells, and macrophages. The microvasculature within the endocrine cell cluster is fundamental both for sustaining the endocrine cells viability and for accomplishing for their function.

FIGURE 2

Bioengineering the vascularized endocrine pancreas—building blocks assembly. Strategies mostly used for recreating the endocrine niche in order to improve the endocrine cells viability, their engraftment and function. All of them are aimed to accelerate the vasculature-building block to shorten the hypoxic with different approaches.