4D-bioprinting introduces "time" into the printing process, allowing printed structures to evolve. Researchers from the University of Illinois Chicago used oxidized and methacrylated alginate (OMA) to develop a bioink for 4D bioprinting. They made OMA into precursor beads, then transformed them into a "microgel" that could be easily printed into stable 3D constructs. Mixed with cells, the microgel became a bioink, which was printed into complex structures. The printed constructs could be further crosslinked to create 3D scaffolds that could change shape due to differential swelling, adding the 4th dimension, "time," to the printing process.

Recent advancements in 3D-bioprinting have opened the possibility of creating engineered tissues mimicking human native tissues. However, reproducing the extracellular matrix (ECM) composition and microscopic architecture within the biomaterial ink remains challenging. To tackle this, a research group from the AO Research Institute Davos developed a bioink containing both collagen type 1 and tyramine derivative hyaluronan for tissue engineering. They used optimal concentrations of these two components, along with human bone marrow-derived mesenchymal stromal cells. Two crosslinking pathways were used to induce gelation and create a 3D scaffold that was then printed using the bioink's shear-thinning properties. They successfully printed an anisotropic hydrogel, achieving control over the microscopic organization of the matrix. This breakthrough could pave the way for better mimicry of native human tissues, especially anisotropic ones, in tissue engineering applications.