3D Bioprinted Liver-on-a-Chip for Drug Cytotoxicity Screening.

Tissues on a chip are sophisticated three-dimensional (3D) in vitro microphysiological systems designed to replicate human tissue conditions within dynamic physicochemical environments. However, the current fabrication methods for tissue spheroids on a chip require multiple parts and manual processing steps, including the deposition of spheroids onto prefabricated "chips." These challenges also lead to limitations regarding scalability and reproducibility. To overcome these challenges, we employed 3D printing techniques to automate the fabrication process of tissue spheroids on a chip. This allowed the simultaneous high-throughput printing of human liver spheroids and their surrounding polymeric flow chamber "chips" containing inner channels in a single step. The fabricated liver tissue spheroids on a liver-on-a-chip (LOC) were subsequently subjected to dynamic culturing by a peristaltic pump, enabling assessment of cell viability and metabolic activities. The 3D printed liver spheroids within the printed chips demonstrated high cell viability (>80%), increased spheroid size, and consistent adenosine triphosphate (ATP) activity and albumin production for up to 14 days. Furthermore, we conducted a study on the effects of acetaminophen (APAP), a nonsteroidal anti-inflammatory drug, on the LOC. Comparative analysis revealed a substantial decline in cell viability (<40%), diminished ATP activity, and reduced spheroid size after 7 days of culture within the APAP-treated LOC group, compared to the nontreated groups. These results underscore the potential of 3D bioprinted tissue chips as an advanced in vitro model that holds promise for accurately studying in vivo biological processes, including the assessment of tissue response to administered drugs, in a high-throughput manner.

Combinations of photoinitiator and UV absorber for cell-based digital light processing (DLP) bioprinting.

Digital light processing (DLP) bioprinting, which provides predominant speed, resolution, and adaptability for fabricating complex cell-laden three-dimensional (3D) structures, requires a combination of photoinitiator (PI) and UV absorber (UA) that plays critical roles during the photo-polymerization of bioinks. However, the PI and UA combination has not been highlighted for cell-based DLP bioprinting. In this study, the most used PIs and UAs in cell-based bioprinting were compared to optimize a combination that can ensure the maximum DLP printability, while maintaining the cellular activities during the process. The crosslinking time and printability of PIs were assessed, which are critical in minimizing the cell damage by the UV exposure during the fabrication process. On the other hand, the UAs were evaluated based on their ability to prevent the over-curing of layers beyond the focal layer and the scattering of light, which are required for the desirable crosslinking of a hydrogel and high resolution (25-50µms) to create a complex 3D cell-laden construct. Lastly, the cytotoxicity of PIs and UAs was assessed by measuring the cellular activity of 2D cultured and 3D bioprinted cells. The optimized PI and UA combination provided high initial cell viability (>90%) for up to 14 days in culture and could fabricate complex 3D structures like a perfusable heart-shaped construct with open vesicles and atriums. This combination can provide a potential starting condition when preparing the bioink for the cell-based DLP bioprinting in tissue engineering applications.

Fabrication of micro/nanoporous collagen/dECM/silk-fibroin biocomposite scaffolds using a low temperature 3D printing process for bone tissue regeneration.

Biomaterials must be biocompatible, biodegradable, and mechanically stable to be used for tissue engineering applications. Among various biomaterials, a natural-based biopolymer, collagen, has been widely applied in tissue engineering because of its outstanding biocompatibility. However, due to its low mechanical properties, collagen has been a challenge to build a desired/complex 3D porous structure with appropriate mechanical strength. To overcome this problem, in this study, we used a low temperature printing process to create a 3D porous scaffold consisting of collagen, decellularized extracellular matrix (dECM) to induce high cellular activities, and silk-fibroin (SF) to attain the proper mechanical strength. To show the feasibility of the scaffold, pre-osteoblast (MC3T3-E1) cells were grown on the fabricated scaffold. Various in vitro cellular activities (cell-viability, MTT assay, and osteogenic activity) for pure collagen, collagen/dECM, and collagen/SF/dECM scaffolds were compared.

Preparation and characterization of gelatin/α-TCP/SF biocomposite scaffold for bone tissue regeneration.

In this study, we suggest a new biocomposite scaffold composed of gelatin/α-TCP (tricalcium phosphate)/SF (silk-fibroin) (GTS) which has enhanced mechanical strength and high level of cellular activity. To fabricate GTS scaffold, a temperature-controlled 3D printing process was used and appropriate printing conditions were selected based on rheological data. To show the feasibility as a biomedical scaffold for bone tissue regeneration, the various physical and biological results, using MG63 (osteoblast-like cells), of the GTS scaffold were compared with those of a pure gelatin (G) and gelatin/α-TCP (GT) composite scaffold. GTS scaffolds showed enhanced mechanical properties in dry and wet state compared to those of the G and GT scaffolds. Also, significantly high cell-proliferation and differentiation of MG63 cells were observed in the GTS scaffold. Therefore, the GTS composite scaffold will be one of highly potential biomaterials to be used in bone regeneration.