Toward pharmaceutical selective laser sintering 3D printing - a thermal and temperature-dependent analysis...

The potential advantages of pharmaceutical additive manufacturing (AM) are thoroughly described in the literature. Challenges related to pharmaceutical AM are less discussed. Selective laser sintering (SLS) is one of the AM methods possible for pharmaceutical applications. The article addresses aspects of SLS that are not typically explored in pharmaceutical studies. The literature research was conducted in parallel for both non-pharmaceutical (technical) and pharmaceutical SLS. As a result, in-depth studies on the temperature-dependent properties (rheological and optical) and thermal properties of powders for general technical printing are presented, along with the characterization of the laser sintering process. Special attention is given to the development of the "processing window" and "energy density" terms, as they continue to evolve. An application of a wide range of thermal analysis techniques is presented, including fast differential calorimetry, hot-stage microscopy, thermovision, and dielectric thermal analysis. Next, the complexity, regarding crystalline/semicrystalline/amorphous substances combination and their melt miscibility for pharmaceutical powders is marked. Pharmaceutical SLS studies are also analyzed, with emphasis on thermal aspects. Generally, pharmaceutical studies lack meaningful temperature-dependent and thermal analysis. The only significant exception is studies on drug substance amorphization during the SLS process. The main message is that pharmaceutical SLS should benefit from the methods and ideas developed for technical SLS. In particular, the research directions should include: (1) conscious powder design regarding the specificity of SLS manufacturing method, which completely different from powder compression (API - excipients matching), (2) extending the set of research methods, (3) consolidation process elucidation, (4) powder reusing or powder reusing avoiding, (5) searching for potential new carriers/excipients dedicated to pharmaceutical SLS process.