When you print out photos with dazzling hues, chances are the colors don’t always turn out the right way. Colors aside, the difference between design and the final outcome has been a persistent problem for printing complex three-dimensional (3D) structures, especially living ones like cells and organs.
By mimicking natural structures, biomaterials like hydrogels can be printed to serve as platforms for growing tissues that may replace damaged counterparts or for training surgeons with realistic models. Though delicate tissues like cartilage and brain tissue may be fabricated from soft hydrogels, it has proven challenging to print such configurations. Until now, elaborate supports have to be put into place to maintain the tissue’s structural integrity.
Trade-offs may also arise between speed, cell viability and the level of detail in tissue structure captured, noted Cyrus Beh. As Principal Investigator at A*STAR’s Institute of Bioengineering and Bioimaging and Senior Scientist at the Institute of Molecular and Cell Biology (IMCB), Beh leads a team that develops novel 3D bioprinting methods.
Their recent innovation, dubbed the Fluid-supported Liquid Interface Polymerization (FLIP), uses a dense support fluid that generates buoyant forces, keeping the hydrogel precursor afloat and effectively keeping the material upright. As the hydrogel solidifies near the liquid surface, printing carries on seamlessly rather than having to build on top of the initial layers step by step.
“FLIP uses buoyant forces and a liquid projection screen to allow the continuous—and hence, much faster—printing of soft hydrogels, without requiring additional support structures,” shared Beh.
Besides mimicking the softness and complexity of biological support structures, the FLIP-printed hydrogels can also contain channels that ensure that cells receive sufficient nutrients. “The need to supply cells with nutrients through channels is one of the key challenges in bioprinting,” Beh said. Typically, hydrogels are manufactured in between two solid surfaces, namely the projection screen containing the target pattern and the print bed below. “But while channels can be directly printed as gaps in the structure, they tend to become clogged unless printing conditions are tightly controlled.”
By instead projecting the pattern directly onto the floating precursor layer, FLIP creates space for an additional component to deposit fibers while the printing is ongoing. The precursor solution then flows over the fibers, embedding them as channels in the structure. “Taking advantage of the unique configuration of FLIP, we can introduce channels into hydrogel discs, through which cells in the gel can be supplied with nutrients,” Beh explained.
To advance the system a step further, the team hopes to manufacture more complex structures resembling the body’s networks of blood vessels, providing nutrient supply channels for lab-made organoids. As Beh envisions, these structures could be more readily integrated into the body, minimizing the risk of implant failure during tissue replacement operations.