A Gentle Sedimentation Process for Size-Selecting Porous Silicon Microparticles to Be Used for Drug Delivery Via Fine Gauge Needle Administration

Biodegradable porous silicon (pSi) particles are under development for drug delivery applications. The optimum particle size very much depends on medical use, and microparticles can outperform nanoparticles in specific instances. Here we demonstrate the ability of sedimentation to size-select ultrasmall (1–10 μm) nanoporous microparticles in common solvents. Size tunability is quantified for 1–24 h of sedimentation. Experimental values of settling times in ethanol and water are compared to those calculated using Stokes’ Law. Differences can arise due to particle agglomeration, internal gas generation and incomplete wetting. Air-dried and supercritically-dried pSi powders are shown to have, for example, their median diameter d (0.5) particle sizes reduced from 13 to 1 μm and from 20 to 3 μm, using sedimentation times of 6 and 2 h respectively. Such filtered microparticles also have much narrower size distributions and are hence suitable for administration in 27 gauge microneedles, commonly used in intravitreal drug delivery.