Current 3D printing of tissue is restricted by the use of biomaterials that do not recapitulate the native properties of the extracellular matrix (ECM). These restrictions have thus far prevented optimization of composition and structure of the in vivo tissue microenvironment. The artificial nature of currently used biomaterials affects cellular phenotype and function of the bioprinted tissues, and results in inaccurate modeling of disease and drug metabolism significantly. Collagen type I is the major structural component in the ECM, and is widely used as a 3D hydrogel, but is less applicable for 3D bioprinting due to low viscosity and slow polymerization. We have hypothesized that a combination of hyaluronic acid with collagen I yields a bioink with the properties required for extrusion bioprinting, while supporting native cell–matrix interactions and preservation of the native microenvironment properties. To test this hypothesis, we tested the viscoelastic properties of three bioink formulations –2:1, 3:1, and 4:1 collagen type I to hyaluronic acid, and examined cellular behavior in order to determine an optimal formulation that allows for bioprinting while supporting biological activity. We then employed this formulation to bioprint 3D liver tissue constructs containing primary human hepatocytes and liver stellate cells and tested the effects of acetaminophen, a common liver toxicant. Our results have shown that the combination of methacrylated collagen type I and thiolated hyaluronic acid yield a simple, printable bioink that allows for modulation that was directly related to stromal cell elongation. Further, the bioink adequately allowed for implementation as a support hydrogel for hepatocytes which were able to remain viable over two weeks and responded to drug treatment appropriately.

The field of three-dimensional (3D) bioprinting has advanced rapidly in recent years. Significant reduction in the costs associated with obtaining functional 3D bioprinting hardware platforms is both a cause and a result of these advances. As such, there are more laboratories than ever integrating bioprinting methodologies into their research. However, there is a lack of standards in the field of biofabrication governing any requirements or characteristics to support cross-compatibility with biomaterial bioinks, hardware, and different tissue types. Here we describe a modular extracellular matrix (ECM) inspired bioink comprised of collagen and hyaluronic acid base components that: 1) employ reversible internal hydrogen bonding forces to generate thixotropic materials that dynamically reduce their elastic moduli in response to increased shear stress, thus enabling increased compatibility with printing hardware; and 2) modular addons in the form of chemically-modified fibronectin and laminin that when covalently bound within the bioink support a variety of tissue types, including liver, neural, muscle, pancreatic islet, and adipose tissue. These features aim to accelerate the deployment of such bioinks for tissue engineering of functional constructs in the hands of various end users.