A strategy to engineer vascularized tissue constructs by optimizing and maintaining the geometry

Abstract

The success of engineered tissues is limited by the need for rapid perfusion of a functional vascular network that can control tissue engraftment and promote survival after implantation. Diabetic conditions pose an additional challenge, because high glucose and lipid concentrations cause an aggressive oxidative environment that impairs vessel remodeling and stabilization and impedes integration of engineered constructs into surrounding tissues. Thus, to achieve rapid vasculogenesis, angiogenesis, and anastomosis, hydrogels incorporating cells in their structure have been developed to facilitate formation of functional vascular networks within implants. However, their transport diffusivity decreases with increasing thickness, preventing the formation of a thick vascularized tissue. To address this, we used diffusion-based computational simulations to optimize the geometry of hydrogel structures. The results show that the micro-patterned constructs improved diffusion, thus supporting cell viability, and spreading while retaining their mechanical properties. Thick cell-laden bulk, linear, or hexagonal infill patterned hydrogels were implanted; and structural stability due to skin mobility was improved by the protective spacer. Larger and thicker perfused vascular networks formed in the hexagonal structures (∼17 mm diameter, ∼1.5 mm thickness) in both normal and diabetic mice on day 3, and they became functional and uniformly distributed on day 7. Moreover, transplanted islets were rapidly integrated subcutaneously in this engineered functional vascular bed, which significantly enhanced islet viability and insulin secretion. In summary, we developed a promising strategy for generating large, thick vascularized tissue constructs, which may support transplanted islet cells. These constructs showed potential for engineering other vascularized tissues in regenerative therapy. STATEMENT OF SIGNIFICANCE: Diffusion-based computational simulations were used to optimize the geometry of hydrogel structures, i.e., hexagonal cell-laden hydrogels. To maintain the hydrogel's structural integrity, a spacer was designed and co-implanted subcutaneously to increase the permeability of explants. The spacer provides the structural integrity to improve the permeability of the implanted hydrogel. Otherwise, the implanted hydrogel may be easily squeezed and deformed by compression from the skin mobility of mice. Here, we successfully developed a cell-based strategy for rapidly generating large, functional vasculature (diameter ∼17 mm and thickness ∼1.5 mm) in both normal and diabetic mice and demonstrated its advantages over currently available methods in a clinically-relevant animal model. This concept could serve as a basis for engineering and repairing other tissues in animals.

Keywords: Cell-laden hydrogel structures; Diffusion-based computational simulations; Vascularized tissues.