Modeling Liver Biology and the Tissue Response to Injury in Bioprinted Human Liver Tissues

Abstract

The rapid advancement of additive manufacturing technologies and their extension into biological systems have led to the emergence of a new category of cell-based models, namely bioprinted tissues. By combining automation and spatially controlled deposition of distinct components, such as cells, hydrogels, and mixtures thereof, the tissue engineer can now design and build tissues with far more control over the architecture of the end product. Bioprinted human liver tissues (BHLT) were one of the first commercial examples of a tissue model fabricated from three or more specific cell types using a custom-built robotic bioprinting platform. Significant progress has been made toward characterizing BHLT and evaluating their performance in a broad spectrum of applications, including in vitro safety and efficacy testing, and disease modeling. Like many multicellular and/or three-dimensional liver tissue models, BHLT exhibit enhanced longevity and persistent liver functions (protein synthesis, metabolism) compared with traditional monocellular or two-dimensional systems. BHLT are a compelling option for many in vitro applications due to several factors: (1) they contain cell-cell interfaces with direct contact between multiple cell types without interference from culture surfaces (polystyrene or polymeric membranes); (2) they have sufficient biomass to enable isolation of nucleic acids or proteins for use in genomic or proteomic analyses; and (3) they are compatible with histology techniques and thus enable detection of outcomes that require histological endpoints for interpretation, such as liver fibrosis and nonalcoholic steatohepatitis. The advantages and limitations of BHLT are highlighted herein through a series of exemplary case studies and related discussion.

Additive Manufacturing of Precision Biomaterials

“…This approach differs from several other biofabrication strategies in that the printed bioink is almost entirely cellular. The spatial arrangement of hepatocytes, stellate cells, and endothelial cells results in the formation of functional liver tissue units, which are used to study liver homeostasis and drug response . In a similar approach, bioprinted liver spheroids integrated into a liver‐on‐a‐chip platform demonstrated physiologic acetaminophen toxicity …”

Recommended Guidelines for Developing, Qualifying, and Implementing Complex In Vitro Models (CIVMs) for Drug Discovery

“…32 The reduced throughput and the ability to miniaturize bioprinted tissue can be challenges, however, potentially limiting bioprinting's application to target validation or LO. 33 In addition, a NASH-like phenotype-including steatosis, ballooning hepatocytes, excessive collagen production, and inflammation-could be observed after exposing the 3D printed tissues to high levels of sugar and fatty acids, mimicking a diet regimen typically associated with obesity. 33,34 Comparisons of gene expression profiles between healthy and diseased human liver tissues and vehicle versus TGFβ-treated 3D bioprinted liver tissues showed a 5% overlap between human organs and 3D printed tissues.…”

“…33 In addition, a NASH-like phenotype-including steatosis, ballooning hepatocytes, excessive collagen production, and inflammation-could be observed after exposing the 3D printed tissues to high levels of sugar and fatty acids, mimicking a diet regimen typically associated with obesity. 33,34 Comparisons of gene expression profiles between healthy and diseased human liver tissues and vehicle versus TGFβ-treated 3D bioprinted liver tissues showed a 5% overlap between human organs and 3D printed tissues. 33 Subsequently, understanding the domain of validity for any cell model is critical to deciding how to apply the model for target validation and development of drugs to treat liver fibrosis.…”

Reconstituted Human Organ Models as a Translational Tool for Human Organ Response: Definition, Expectations, Cases, and Strategies for Implementation in Drug Discovery and Development

“…Despite potential challenges, some studies have reported the successful determination of humanto-human differences. Emori et al 44) constructed and characterized 3D-cultures of fibroblast-like synoviocytes from rheumatoid arthritis (RA) patients and osteoarthritis (OA) patients. They showed that the 3D-RA and 3D-OA models differed in architecture and morphology.…”