Tribological performance of injection-molded microtextured surfaces for silicone oil-free syringes

Silicone oil in prefilled syringes causes issues with stability, contamination, and immune response. To solve these problems, this study explores surface texturing as an alternative way to reduce friction in silicone oil-free syringes. By fine-tuning microdimple size, especially area density and aspect ratio, the study aims to enhance glide performance without needing extra coatings. Two-photon polymerization was used to make microtextured test surfaces, and a factorial screening identified 60% area density and a 0.03 aspect ratio as the levels associated with the highest marginal mean reductions in the coefficient of friction within the investigated design space, and this combination was therefore selected. This setup was then replicated on polypropylene syringe prototypes through laser ablation of the mold core, followed by micro-injection molding. Tests on glide force showed that microtextured syringes decreased the mean glide force by approximately 36%, from 8.5 ± 1.0 N for the untextured, unsiliconized reference to 5.4 ± 0.9 N. While the friction reduction did not match that of siliconized syringes (0.6 ± 0.1 N), these results show that an application-specific microtexture can be selected and applied to injection-molded syringes, substantially lowering glide force without added barrel coatings. More research is needed to assess sealing integrity and dosing performance for pharmaceutical uses.