(T1530-01-06) Properties and Printability of Recycled Pharmaceutical Powder Blend in SLS 3D Printing

Purpose: The aim of this study was to investigate the printability and properties of pharmaceutical powder after recycling in selective laser sintering 3D printing process.

Methods: Phenytoin sodium (PS) was used as a model drug. The powder blend was composed of PS (20%), Kollidon VA 64 (58%), Kollicoat (20%), Candurin®NXT Ruby Red (2%). All powders were blended using a V-Blender (Model VH-2). Color was added to the formulations to aid printability and enhance energy absorption from the laser. Cylindrical printlet models of 5 mm diameter and 3 mm height was designed using Solidworks (Solidworks Inc., USA). The printlets were printed using Sintratec central software version 1.1.13. Powder reservoir (150 × 150 × 150 mm) of the Desktop SLS printer (Sintratec Kit, AG, Brugg, Switzerland). The reservoir chamber was filled with the blend and moved to the printing build area in 0.1 mm thickness by a roller creating a uniform layer. The surface and chamber temperatures were maintained at 120 °C and 70°C respectively during printing process. A 2.3 W blue diode laser sintered the layered powder with a scanning speed of 50 mm/sec. The process continued as the reservoir moved upward and the printing platform moved downward thus sintering the powder layer by layer into the final shape of the tablet. Upon completion of the printing process, the printer was allowed to cool down, the printlets were removed from the powder bed, and the excess powder was collected, sieved and reloaded in the chamber. The recycling process was repeated 3 times. The recycled powder samples and respective printlets were characterized for assay, dissolution, physicochemical properties (FTIR, NIR and XRD), uniformity in color (NIR-chemical imaging) and surface morphology (scanning electron microscopy, SEM).

Results: The dissolution was more than 98% in 30 min from first and second recycled powder and printlets and about 95% in the third recycled powder however, the third recycled printlets showed a decrease in drug release by 5%. The assay values were ≤ 95% in all the samples except the third recycled printlet. This decrease may be due to the degradation of PS or excipients caused by laser, which is supported by the XRD, FTIR and NIR data. A prominent change in the intensity of the color on the surface between the first, second and third recycled printlets was seen on NIR-chemical images. This could be due to laser absorption by the drug or the excipient. The SEM images of the first and second recycled printlets can clearly show the sintering of individual powder particles.

Conclusion: Based on the findings, a methodology for powder recycling is proposed for SLS-3D printing in relation to the temperature and time at which the material is exposed to the laser in the chamber. It allows for more efficient use of the API and excipients as well as improved control of the input material properties.