Researchers at the University of Illinois Chicago have developed a method to create 3D printed cell-loaded bioink constructs that can change shape over time, just like tissues in the body do. Incorporating crosslinking molecules into the printed hydrogels, some of which are UV light-sensitive, allows the constructs to undergo shape changes after printing. The technique could help scientists model the development of tissues that also undergo shape changes in response to external stimuli, such as bone or cartilage, or during healing and development. The UIC researchers have dubbed the technique as “4D printing,” with the fourth dimension represented by morphological changes over time. 3D printing has unlocked the wildest fantasies of researchers in tissue engineering, allowing them to print complex shapes that consist of a biocompatible ink and encapsulated cells. The technique holds huge promise in creating replacements for tissues or even organs, but there is a lot of work to do before we reach that point. This latest development allows researchers to create 3D shapes that undergo preprogrammed shape changes later on. These can be designed to happen automatically over time or on demand, and involve the careful incorporation of gradients of crosslinking molecules that bind the structure together at a molecular level, resulting in predictable shape changes. The bioink consists of flake-shaped microgels that have been tightly packed together, and the researchers also incorporated living cells and light-sensitive crosslinking molecules into the printed structures. “This bioink system provides the opportunity to print bioconstructs capable of achieving more sophisticated architectural changes over time than was previously possible,” said Eben Alsberg, a researcher involved in the study. “These cell-rich structures with pre-programmable and controllable shape morphing promise to better mimic the body’s natural developmental processes and could help scientists conduct more accurate studies of tissue morphogenesis and achieve greater advances in tissue engineering.” The shape-shifting performance of the printed constructs could be useful for researchers who wish to better emulate shape-shifting tissues within our bodies. Bone, for example, has a remarkable capacity to remodel itself in response to physical stimuli, but to date a shape-shifting biomaterial that emulates this was not available. “The bioinks have what are called shear-thinning and rapid self-healing properties that enable smooth extrusion-based printing with high resolution and high fidelity without a supporting bath,” said Alsberg. “The printed bioconstructs, after further stabilization by light-based crosslinking, remain intact while, for example, bending, twisting or undergoing any number of multiple deformations. With this system, cartilage-like tissues with complex shapes that evolve over time could be bioengineered.” Source
