Abstract
We demonstrate that the release of a poorly soluble molecule from nanoporous carriers is a complex process that undergoes heterogeneous surface nucleation events even under significantly diluted release conditions, and that those events heavily affect the dynamics of release. Using beta-carotene and porous silicon as loaded molecule and carrier model, respectively, we show that the cargo easily nucleates at the pore surface during the release, forming micro- to macroscopic solid particles at the pores surface. These particles dissolve at a much slower pace, compared to the rate of dissolution of pure beta-carotene in the same solvent, and they negatively affect the reproducibility of the release experiments, possibly because their solubility depends on their size distribution. We propose to exploit this aspect to use release kinetics as a better alternative to the induction time method, and to thereby detect heterogenous nucleation during release experiments. In fact, release dynamics provide much higher sensitivity and reproducibility as they average over the entire sample surface instead of depending on statistical analysis over a small area to find clusters.
Highlights
Nanoporous materials posess several properties that render them of interest for a wide range of different uses
We demonstrate that the release of a poorly soluble molecule from nanoporous carriers is a complex process that undergoes heterogeneous surface nucleation events even under significantly diluted release conditions, and that those events heavily affect the dynamics of release
We demonstrate that the release of poorly soluble molecules from nanoporous materials is a complex process that might stimulate heterogeneous nucleation (HN) at carrier surface if the loaded amount of molecule is above a certain threshold
Summary
Nanoporous materials posess several properties that render them of interest for a wide range of different uses. Nanoporous materials are ideal candidates to develop effective drug delivery systems (DDS) with tailored properties and release characteristics. Their large surface area, well controlled pore size distribution, tunable chemistry, and top-down fabrication techniques are some of the parameters that render them of interest in both research and industrial applications [13,14,15,16,17,18,19,20,21]. Among the plethora of materials studied for these purposes, porous silica and porous silicon (PSi) are some of the most investigated inorganic carriers thanks to their many interesting properties, such as: chemical stability and inertness, well-known and controlled surface chemistry, large tunability of the porous architectures spanning from the “truly” nanometric range (e.g., MCM41) up to micron-sized pores (e.g., macroporous silicon and reverse opals) and, their biocompatibility (they are both approved for medical uses)
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