Additive Manufacturing of Hydrogels for Vascular Tissue Engineering

Abstract

One of the major technical challenges with creating 3D artificial tissue constructs is the lack of simple and effective methods to integrate vascular networks within them. Without these vascular-like networks, the cells embedded within the constructs quickly become necrotic. This thesis details the use of a commercially available, low-cost, 3D printer modified with a microfluidic printhead in order to generate instantly perfusable vascular-like networks integrated within gel scaffolds seeded with cells. The printhead featured a coaxial nozzle that allowed the fabrication of hollow, gel tubes (500µm–2mm) that can be easily patterned to create single or multi-layered constructs. Media perfusion of the channels caused a significant increase in cell viability. This microfluidic nozzle design was further modified to allow for multi-axial extrusion in order to 3D print and pattern bi- and tri-layered hollow channel structures. Most available methodologies lack the ability to create multi-layered concentric conduits inside natural extracellular matrices, which would more accurately replicate the hierarchal architecture of biological blood vessels. The nozzle used in this work allowed, for the first time, for these hierarchal structures to be embedded within layers of gels in a fast, simple and low cost manner. This scalable design allowed for versatility in material incorporation, thereby creating heterogeneous structures that contained distinct concentric layers of different cell types and biomaterials. This thesis also demonstrates the use of non-extrusion based 3D biofabrication involving planar processing by means of hydrogel adhesion. There remains a lack of effective adhesives capable of composite layer fusion without affecting the integrity of patterned features. Here, silicon carbide was found for the first time to be an effective and cytocompatible adhesive to achieve strong bonding (0.39±0.03kPa) between hybrid hydrogel films. Multi-layered, heterogeneous constructs with embedded high-resolution microchannels (150µm-1mm) were fabricated in this way. With the new 3D fabrication technology developed in this thesis, gel constructs with embedded arrays of hollow channels can be created and used as potential substitutes for blood vessel networks as well as in applications such as drug discovery models and biological studies.