Engineering In Vitro Vascularized Tissues Using FRESH 3D Bioprinted Collagen Scaffolds

Andrew Hudson, MS

Carnegie Mellon University, Regenerative Bioaterials Therapeutic Group (Adam Feinberg PhD), PhD Student

Abstract: One of the foremost challenges remaining to engineer large (>1 cm3), transplantable tissues is creating the microvasculature necessary to promote cell viability and eventual tissue function. Given the intricate 3D architecture of native tissues, 3D bioprinting aims to build complex geometries that would otherwise be unobtainable through traditional methods, seeking to create viable tissues and organs. Two major hurdles to bioprinting large tissues are 3D printing extracellular matrix (ECM) proteins at high fidelity and generating the microvasculature necessary to maintain cell viability. The mechanical instability of soft (E < 150 kPa) ECM proteins causes significant deformation during printing that hinders the immediate creation of patent microvasculature. Recently, improvements to our 3D bioprinting method Freeform Reversible Embedding of Suspended Hydrogels (FRESH) have allowed us to print ECM components like collagen with a high degree of geometric complexity at a fidelity down to 20 μm.

With a major obstacle largely addressed, we have begun to work towards developing an in vitro vascularization system for vessel templates FRESH printed from collagen. This system is based on leveraging two phenomena in tissue engineering – microporosity and cellular remodeling. By increasing tissue scaffold porosity, we show an increase rate of diffusion through a collagen matrix translates to improved cellular viability while in vivo data shows porosity improves host-driven angiogenesis. By introducing endothelial cells to our porous bioprinted vessel templates, we seek to create an in vitro vascularization system that results in a large, vascularized tissue for transplantation.

Dynamic Loading of Human Engineered Heart Tissue Enhances Contractile Function and Drives Desmosome-linked Disease Phenotype

Jaci Billey, MS

Carnegie Mellon University, Regenerative Biomaterials Therapeutic Group (Adam Feinberg PhD), PhD Student

Abstract: Heart failure is a significant concern affecting more than 5 million adults in the U.S. alone. Hemodynamic loads, including preload (stretch on heart muscle) and afterload (pressure the heart must work against to eject blood), can lead to maladaptive structural and functional changes in the heart, specifically ventricular dilation and reduced force generation. Engineered heart tissues (EHTs) have the potential to provide insight into loading-induced disease progression but current 3D EHT approaches are constrained (length is held constant), which limits their ability to model the altered loads experienced during heart failure, the tissue morphological changes that occur, and the consequences that these have on heart muscle tissue force generation. Here, we have developed a dynamic EHT (dyn-EHT) model that addresses these limitations by integrating EHTs with an elastic polydimethylsiloxane (PDMS) strip, which provides active preload and a contractile force measurement based on strip bending during EHT contraction. Our results demonstrate that dynamic loading is beneficial in wild-type EHTs leading to improved alignment, conduction velocity, and contractility. For disease modeling, we use hiPSC–derived cardiomyocytes from a patient with arrhythmogenic cardiomyopathy due to mutations in desmoplakin. We demonstrate that manifestation of this desmosome-linked disease state requires the dyn-EHT conditioning and that it cannot be induced using 2D or standard 3D EHT approaches. Thus, a dynamic loading strategy is necessary to provoke a disease phenotype (tissue lengthening, reduction of desmosome counts, and reduced contractility), which are akin to primary endpoints of clinical disease, such as chamber thinning and reduced cardiac output.