A critical review of traditional and advanced characterisation tools to drive formulators towards the rational development of 3D printed oral dosage forms

The high degree of precision and control of 3D printing has given formulators the autonomy to engineer so-phisticated and personalised medicines, starting a revolution in pharmaceutics. In addition, dosage forms with tailored drug release profile can be produced by changing some parameters of the 3D printing processes. Therefore, 3D printed medicines must be characterised in an orthogonal approach, to establish their physico-chemical and biopharmaceutical features, and consequently to understand how these characteristics can be customised by changing the formulation and process parameters to ensure medicines' safety and efficacy. Given the recent regulation and commercialisation of 3D printed medicines, several methods and techniques have been transposed from official compendia; however, formulators must still make a critical assessment of their practical implications. A comprehensive review of the findings obtained by the characterisation of 3D printed oral dosage forms using traditional and advanced techniques is therefore presented here, to drive formulators towards a rational pharmaceutical development pathway. The characterisation methods have been classified in terms of their physicochemical or biopharmaceutical character. Interestingly, beyond the rise of modern characterisation techniques, the reassessment of data obtained by traditional methods has provided knowledge and a solid foundation to support the evolution of 3D printing techniques in pharmaceutics.