This review discusses the reported studies investigating the use of bioprinting to develop functional organ-on-chip systems from a manufacturing perspective. These organ-on-chip systems model the liver, kidney, heart, lung, gut, bone, vessel, and tumors to demonstrate the viability of bioprinted organ-on-chip systems for disease modeling and drug screening. In addition, the paper highlights the challenges involved in using bioprinting techniques for organ-on-chip system fabrications and suggests future research directions. Based on the reviewed studies, it is concluded that bioprinting can be applied for the automated and assembly-free fabrication of organ-on chip systems. These bioprinted organ-on-chip systems can help in the modeling of several different diseases and can thereby expedite drug discovery by providing an efficient platform for drug screening in the preclinical phase of drug development processes.

Copper contamination of drinking water and marine areas is detrimental to human health and the environment. Physical and chemical approaches currently used for copper removal from water tend to be expensive and may introduce chemicals to the water. Using suspended algae to remove copper is a biological approach. Its cost is relatively low, and algae can be used for other purposes after being used for copper removal. However, this approach using algae is currently limited in its usefulness due to technological barriers. For example, chemical agents used to remove suspended algae from water after copper is absorbed, can cause secondary contamination. Using immobilized algae instead of suspended algae can overcome these problems. In this preliminary study, hydrogel filters containing algae cells and those containing no algae cells are printed on an extrusion-based 3D printer. They were used in a custom-build filtration setup for copper removal. Experimental results show that hydrogel filters containing algae cells reduced copper concentration in the test solution by about 83% (from 3 to 0.5 ppm) after one hour of filtration, while hydrogel filters containing no algae cells reduced copper concentration in the test solution by about 50% (from 3 to 1.5 ppm) after one hour of filtration.

Bioprinting is the fabrication of structures based on layer-by-layer deposition of biomaterials. Applications of bioprinting using plant or algae cells include the production of metabolites for use in pharmaceutical, cosmetic, and food industries. Reported studies regarding effects of extrusion pressure and needle diameter on cell viability in bioprinting have used animal cells. There are no reports regarding effects of extrusion pressure and needle diameter on cell viability using plant or algae cells. This paper fills this knowledge gap by reporting an experimental investigation on effects of extrusion pressure and needle diameter on cell quantity (an indicator of cell viability) in extrusion-based bioprinting of hydrogel-based bioink containing Chlamydomonas reinhardtii algae cells. Extrusion pressure levels used in this study were 3, 5, and 7 bar, and needle diameter levels were 200, 250, and 400 µm. Algae cell quantity in printed samples was measured on the third day and sixth day post bioprinting. Results show that, when extrusion pressure increases or needle diameter decreases, algae cell quantity in printed samples will decrease.

Process variables of bioprinting (including extrusion pressure, nozzle size, and bioink composition) can affect the shape fidelity and cell viability of printed constructs. Reported studies show that increasing extrusion pressure or decreasing nozzle size would decrease cell viability in printed constructs. However, a smaller nozzle size is often necessary for printing constructs of higher shape fidelity, and a higher extrusion pressure is usually needed to extrude bioink through nozzles with a smaller diameter. Because values of printing process variables that increase shape fidelity can be detrimental to cell viability, the optimum combination of variables regarding both shape fidelity and cell viability must be determined for specific bioink compositions. This paper reports a designed experimental investigation (full factorial design with three variables and two levels) on bioprinting by applying layer-by-layer photo-crosslinking and using the alginate-methylcellulose-GelMA bioink containing algae cells. The study investigates both the main effects and interaction effects of extrusion pressure, nozzle size, and bioink composition on the shape fidelity and cell viability of printed constructs. Results show that, as extrusion pressure changed from its low level to its high level, shape fidelity and cell viability decreased. As nozzle size changed from its low level to its high level, shape fidelity decreased while cell viability increased. As bioink composition changed from its low level (with more methylcellulose content in the bioink) to its high level (with less methylcellulose content in the bioink), shape fidelity and cell viability increased.

Bioprinting has many potential applications in drug screening, tissue engineering, and regenerative medicine. In extrusion-based bioprinting, the extruded strand is the fundamental building block for printed constructs, and needs to be of good quality and continuous in shape. In recent years, many studies have been conducted on extrusion-based bioprinting. However, values of process parameters leading to continuous extrusion of strands have rarely been reported. In this paper, feasible regions of bioink composition, extrusion pressure, and needle size for continuous strand extrusion have been evaluated. The information on feasible regions for extruding continuous strands, provided in this paper, can be useful in deciding appropriate extrusion pressure and needle size for bioink of different compositions (ratios of alginate:methylcellulose) in extrusion-based bioprinting.