The functional maturation and preservation of hepatic cells derived from human induced pluripotent stem cells (hiPSCs) are essential to personalized in vitro drug screening and disease study. Major liver functions are tightly linked to the 3D assembly of hepatocytes, with the supporting cell types from both endodermal and mesodermal origins in a hexagonal lobule unit. Although there are many reports on functional 2D cell differentiation, few studies have demonstrated the in vitro maturation of hiPSC-derived hepatic progenitor cells (hiPSC-HPCs) in a 3D environment that depicts the physiologically relevant cell combination and microarchitecture. The application of rapid, digital 3D bioprinting to tissue engineering has allowed 3D patterning of multiple cell types in a predefined biomimetic manner. Here we present a 3D hydrogel-based triculture model that embeds hiPSC-HPCs with human umbilical vein endothelial cells and adiposederived stem cells in a microscale hexagonal architecture. In comparison with 2D monolayer culture and a 3D HPC-only model, our 3D triculture model shows both phenotypic and functional enhancements in the hiPSC-HPCs over weeks of in vitro culture. Specifically, we find improved morphological organization, higher liver-specific gene expression levels, increased metabolic product secretion, and enhanced cytochrome P450 induction. The application of bioprinting technology in tissue engineering enables the development of a 3D biomimetic liver model that recapitulates the native liver module architecture and could be used for various applications such as early drug screening and disease modeling.3D bioprinting | in vitro hepatic model | iPSC | tissue engineering | biomaterials T he liver plays a critical role in the synthesis of important proteins and the metabolism of xenobiotic; the failure of these functions is closely related to disease development and drug-induced toxicity (1). For these reasons, in vitro liver models have been extensively developed to serve as platforms for pathophysiological studies and as alternatives to animal models in drug screening and hepatotoxicity prediction (2-4). Human primary hepatocytes, considered one of the most mature liver cell sources, lose many liver-specific functions rapidly when cultured in vitro due to the great discrepancies between the native and culture environments (5, 6). In addition, the practical difficulties in obtaining liver biopsy samples from every patient further hinder their use in personalized liver models. Consequently, hepatocytes derived from human induced pluripotent stem cells (hiPSCs), with the potential to be patient specific and easily accessible, have been widely acknowledged as the most promising cell source for developing personalized human hepatic models (4, 7).Many groups have reported monolayer differentiation of hiPSCs into hepatocyte-like cells (HLCs) and their ability to metabolize drugs (7-9). Nevertheless, hiPSC-derived HLCs are still considered immature in terms of many liver-specific gene expressions, functions, and...

Living tissues rely heavily on vascular networks to transport nutrients, oxygen and metabolic waste. However, there still remains a need for a simple and efficient approach to engineer vascularized tissues. Here, we created prevascularized tissues with complex three-dimensional (3D) microarchitectures using a rapid bioprinting method – microscale continuous optical bioprinting (μCOB). Multiple cell types mimicking the native vascular cell composition were encapsulated directly into hydrogels with precisely controlled distribution without the need of sacrificial materials or perfusion. With regionally controlled biomaterial properties the endothelial cells formed lumen-like structures spontaneously in vitro. In vivo implantation demonstrated the survival and progressive formation of the endothelial network in the prevascularized tissue. Anastomosis between the bioprinted endothelial network and host circulation was observed with functional blood vessels featuring red blood cells. With the superior bioprinting speed, flexibility and scalability, this new prevascularization approach can be broadly applicable to the engineering and translation of various functional tissues.

Since the advent of additive manufacturing, known commonly as 3D printing, this technology has revolutionized the biofabrication landscape and driven numerous pivotal advancements in tissue engineering and regenerative medicine. Many 3D printing methods were developed in short course after Charles Hull first introduced the power of stereolithography to the world. However, materials development was not met with the same enthusiasm and remained the bottleneck in the field for some time. Only in the past decade has there been deliberate development to expand the materials toolbox for 3D printing applications to meet the true potential of 3D printing technologies. Herein, we review the development of biomaterials suited for light-based 3D printing modalities with an emphasis on bioprinting applications. We discuss the chemical mechanisms that govern photopolymerization and highlight the application of natural, synthetic, and composite biomaterials as 3D printed hydrogels. Because the quality of a 3D printed construct is highly dependent on both the material properties and processing technique, we included a final section on the theoretical and practical aspects behind light-based 3D printing as well as ways to employ that knowledge to troubleshoot and standardize the optimization of printing parameters.

Decellularized extracellular matrices (dECMs) have demonstrated excellent utility as bioscaffolds in recapitulating the complex biochemical microenvironment, however, their use as bioinks in 3D bioprinting to generate functional biomimetic tissues has been limited by their printability and lack of tunable physical properties. Here, we describe a method to produce photocrosslinkable tissuespecific dECM bioinks for fabricating patient-specific tissues with high control over complex microarchitecture and mechanical properties using a digital light processing (DLP)-based scanningless and continuous 3D bioprinter. We demonstrated that tissue-matched dECM bioinks provided a conducive environment for maintaining high viability and maturation of human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes and hepatocytes. Microscale patterning also guided spontaneous cellular reorganization into predesigned striated heart and lobular liver structures through biophysical cues. Our methodology enables a light-based approach *

Hepatocellular carcinoma (HCC), as the fifth most common malignant cancer, develops and progresses mostly in a cirrhotic liver where stiff nodules are separated by fibrous bands. Scaffolds that can provide a 3D cirrhotic mechanical environment with complex native composition and biomimetic architecture are necessary for the development of better predictive tissue models. Here, we developed photocrosslinkable liver decellularized extracellular matrix (dECM) and a rapid light-based 3D bioprinting process to pattern liver dECM with tailorable mechanical properties to serve as a platform for HCC progression study. 3D bioprinted liver dECM scaffolds were able to stably recapitulate the clinically relevant mechanical properties of cirrhotic liver tissue. When encapsulated in dECM scaffolds with cirrhotic stiffness, HepG2 cells demonstrated reduced growth along with an upregulation of invasion markers compared to healthy controls. Moreover, an engineered cancer tissue platform possessing tissue-scale organization and distinct regional stiffness enabled the visualization of HepG2 stromal invasion from the nodule with cirrhotic stiffness. This work demonstrates a significant advancement in rapid 3D patterning of complex ECM biomaterials with biomimetic architecture and tunable mechanical properties for in vitro disease modeling.