Bioprinting: Mechanical Stabilization and Reinforcement Strategies in Regenerative Medicine

Bioprinting describes the printing of biomaterials and cell-laden or cell-free hydrogels with various combinations of embedded bioactive molecules. It encompasses the precise patterning of biomaterials and cells to create scaffolds for different biomedical needs. There are many requirements that bioprinting scaffolds face, and it is ultimately the interplay between the scaffold's structure, properties, processing, and performance that will lead to its successful translation. Among the essential properties that the scaffolds must possess-adequate and appropriate application-specific chemical, mechanical, and biological performance-the mechanical behavior of hydrogel-based bioprinted scaffolds is the key to their stable performance in vivo at the site of implantation. Hydrogels that typically constitute the main scaffold material and the medium for the cells and biomolecules are very soft, and often lack sufficient mechanical stability, which reduces their printability and, therefore, the bioprinting potential. The aim of this review article is to highlight the reinforcement strategies that are used in different bioprinting approaches to achieve enhanced mechanical stability of the bioinks and the printed scaffolds. Enabling stable and robust materials for the bioprinting processes will lead to the creation of truly complex and remarkable printed structures that could accelerate the application of smart, functional scaffolds in biomedical settings. Impact statement Bioprinting is a powerful tool for the fabrication of 3D structures and scaffolds for biomedical applications. It has gained tremendous attention in recent years, and the bioink library is expanding to include more and more material combinations. From the practical application perspective, different properties need to be considered, such as the printed structure's chemical, mechanical, and biological performances. Among these, the mechanical behavior of the printed constructs is critical for their successful translation into the clinic. The aim of this review article is to explore the different reinforcement strategies used for the mechanical stabilization of bioinks and bioprinted structures.