To overcome the drawbacks of in vitro liver testing during drug development, numerous liver-on-a-chip models have been developed. However, current liver-on-a-chip technologies are labor-intensive, lack extracellular matrix (ECM) essential for liver cells, and lack a biliary system essential for excreting bile acids, which contribute to intestinal digestion but are known to be toxic to hepatocytes. Therefore, fabrication methods for development of liver-on-a-chip models that overcome the above limitations are required. Cell-printing technology enables construction of complex 3D structures with multiple cell types and biomaterials. We used cell-printing to develop a 3D liver-on-a-chip with multiple cell types for co-culture of liver cells, liver decellularized ECM bioink for a 3D microenvironment, and vascular/biliary fluidic channels for creating vascular and biliary systems. A chip with a biliary fluidic channel induced better biliary system creation and liver-specific gene expression and functions compared to a chip without a biliary system. Further, the 3D liver-on-a-chip showed better functionalities than 2D or 3D cultures. The chip was evaluated using acetaminophen and it showed an effective drug response. In summary, our results demonstrate that the 3D liver-on-a-chip we developed is promising in vitro liver test platform for drug discovery.

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Tissue engineering has emerged as a promising approach to viable small-diameter vascular grafts that may be used to treat cardiovascular diseases. One challenge in constructing such blood vessels is proper localization of endothelial cells and smooth muscle cells, as well as promotion of their cellular functions to generate functional tissues. Thus far, construction of small-diameter vascular substitutes with both endothelial and muscular tissues, which is essential for the grafts to acquire antithrombosis function and sufficient strength to avoid thrombus formation as well as to withstand blood pressure, has not yet been demonstrated. In this study, we engineer small-diameter blood vessel grafts containing both functional endothelial and muscular cell layers, which has been demonstrated in vivo in a living rat model. Our construction of the blood vessel grafts uses vascular-tissue-derived extracellular matrix bioinks and a reservoir-assisted triple-coaxial cell printing technique. The prematured vessel was implanted for three weeks as a graft of rat abdominal aorta in a proof-of-concept study where all implants showed great patency, intact endothelium, remodeled smooth muscle, and integration with host tissues at the end of the study. These outcomes suggest that our approach to tissue-engineered biomimetic blood vessels provides a promising route for the construction of durable small-diameter vascular grafts that may be used in future treatments of cardiovascular diseases.

As the main precursor of cardiovascular diseases, atherosclerosis is a complex inflammatory disorder that preferentially occurs in stenotic, curved, and branched arterial regions. Although various in vitro models are established to understand its pathology, reconstructing the native atherosclerotic environment that involves both co‐cultured cells and local turbulent flow singling remains challenging. This study develops an arterial construct via in‐bath coaxial cell printing that not only facilitates the direct fabrication of three‐layered conduits with tunable geometry and dimensions but also maintains structural stability. Functional vascular tissues, which respond to various stimulations that induce endothelial dysfunction, are rapidly generated in the constructed models. The presence of multiple vascular tissues under stenotic and tortuous turbulent flows allows the recapitulation of hallmark events in early atherosclerosis under physiological conditions. Furthermore, the fabricated models are utilized to investigate the individual and synergistic functions of cell co‐culture and local turbulent flows in regulating atherosclerotic initiation, as well as the dose‐dependent therapeutic effect of atorvastatin. These outcomes suggest that the constructed atherosclerotic model via a novel fabrication strategy is a promising platform to elucidate the pathophysiology of atherosclerosis and seek effective drugs and therapies.

Autologous cartilages or synthetic nasal implants have been utilized in augmentative rhinoplasty to reconstruct the nasal shape for therapeutic and cosmetic purposes. Autologous cartilage is considered to be an ideal graft, but has drawbacks, such as limited cartilage source, requirements of additional surgery for obtaining autologous cartilage, and donor site morbidity. In contrast, synthetic nasal implants are abundantly available but have low biocompatibility than the autologous cartilages. Moreover, the currently used nasal cartilage grafts involve additional reshaping processes, by meticulous manual carving during surgery to fit the diverse nose shape of each patient. The final shapes of the manually tailored implants are highly dependent on the surgeons’ proficiency and often result in patient dissatisfaction and even undesired separation of the implant. This study describes a new process of rhinoplasty, which integrates three-dimensional printing and tissue engineering approaches. We established a serial procedure based on computer-aided design to generate a three-dimensional model of customized nasal implant, and the model was fabricated through three-dimensional printing. An engineered nasal cartilage implant was generated by injecting cartilage-derived hydrogel containing human adipose-derived stem cells into the implant containing the octahedral interior architecture. We observed remarkable expression levels of chondrogenic markers from the human adipose-derived stem cells grown in the engineered nasal cartilage with the cartilage-derived hydrogel. In addition, the engineered nasal cartilage, which was implanted into mouse subcutaneous region, exhibited maintenance of the exquisite shape and structure, and striking formation of the cartilaginous tissues for 12 weeks. We expect that the developed process, which combines computer-aided design, three-dimensional printing, and tissue-derived hydrogel, would be beneficial in generating implants of other types of tissue.