Why bioprinting in regenerative medicine should adopt a rational technology readiness assessment.

Recent years have seen a surge of interest in the potential use of 3D bioprinting technologies for the development of tissues and organs with the aim of restoring, maintaining, or improving tissue function. Bioprinting studies frequently claim to be close to clinical translation, yet only report research at very early stages of the translational pipeline. Technology readiness levels (TRLs) are a systematic metric used to objectively assess the maturity of a technology, allowing researchers and stakeholders to understand how far a particular project has progressed from the conceptual stage towards clinical application. Bioprinting is an annex of additive manufacturing, as defined by the American Society for Testing and Materials (ASTM) and International Organization for Standardization (ISO) standards, characterized by the automated deposition of living cells and biomaterials. The tissue engineering and regenerative medicine (TE&RM) community has eagerly adopted bioprinting, while review articles regularly herald its imminent translation to the clinic as functional tissues and organs. Here we argue that such proclamations are premature and counterproductive; they place emphasis on technological progress while typically ignoring the critical stage-gates that must be passed through to bring a technology to market. We suggest the technology readiness level (TRL) scale as a valuable metric for gauging the relative maturity of a bioprinting technology in relation to how it has passed a series of key milestones. We suggest guidelines for a bioprinting-oriented scale and use this to discuss the state-of-the-art of bioprinting in regenerative medicine (BRM) today. Finally, we make corresponding recommendations for improvements to BRM research that would support its progression to clinical translation. [ABSTRACT FROM AUTHOR]