Advancements in high-resolution 3D bioprinting: Exploring technological trends, bioinks and achieved resolutions

3D bioprinting is a rapidly evolving field that has seen significant advancements in technologies, materials, and strategies. It enables the production of living tissues and complex biological structures, offering great potential for regenerative medicine, drug testing, and personalized medical treatments. Notable progress has been done, particularly in developing materials that mimic the physiological environment and promote tissue growth. However, much work is still needed to fabricate complex, large-scale, heterocellular constructs. High-resolution printing and technological development are crucial to this goal. Despite the significance of this topic, the literature lacks comprehensive reviews focused on analyzing the achieved resolution and metrics for its quantification in bioprinting. Additionally, no previous work examines all the most relevant technologies, critically highlighting technological advantages such as resolution and identifying limitations like the characteristic dimensions of constructs. This review examines various aspects of 3D bioprinting, focusing on the most commonly used technologies, including Extrusion-Based Bioprinting, Vat Photopolymerization, Inkjet, Laser-Induced Forward Transfer, and Two-Photon Polymerization. Additionally, it examines the biomaterials and crosslinking strategies compatible with each of these technologies. The primary focus is on the importance of resolution characterization, assessing technical advantages, and summarizing common metrics from the literature. The review evaluates the resolutions achieved across different bioprinting methods, correlating such data with the applicability and limitations of each technology, as resolution alone is not sufficient for producing functional structures. Some strategies to overcome typical resolution limits of some technologies have been reported. In doing so, the focus is kept on works aimed at biological patterning and producing scaffolds for tissue engineering, therefore involving the use of live cells. • 3D bioprinting is rapidly growing, with extrusion and light-based processes dominating the literature. • The characterization of resolution is crucial in 3D bioprinting, with several different metrics used for its quantification. • Two-photon polymerization offers the highest resolution, but its characteristic dimension is limiting for tissue engineering. • GelMA and alginate-based bioinks are the most used materials, relying on photo- and ionic crosslinking.