Sol-gel based materials for biomedical applications

The biorelated degradability and clearance of siliceous nanomaterials have been questioned worldwide, since they are crucial prerequisites for the successful translation in clinics. Typically, the degradability and biocompatibility of mesoporous silica nanoparticles (MSNs) have been an ongoing discussion in research circles. The reason for such a concern is that approved pharmaceutical products must not accumulate in the human body, to prevent severe and unpredictable side-effects. Here, the biorelated degradability and clearance of silicon and silica nanoparticles (NPs) are comprehensively summarized. The influence of the size, morphology, surface area, pore size, and surface functional groups, to name a few, on the degradability of silicon and silica NPs is described. The noncovalent organic doping of silica and the covalent incorporation of either hydrolytically stable or redox- and enzymatically cleavable silsesquioxanes is then described for organosilica, bridged silsesquioxane (BS), and periodic mesoporous organosilica (PMO) NPs. Inorganically doped silica particles such as calcium-, iron-, manganese-, and zirconium-doped NPs, also have radically different hydrolytic stabilities. To conclude, the degradability and clearance timelines of various siliceous nanomaterials are compared and it is highlighted that researchers can select a specific nanomaterial in this large family according to the targeted applications and the required clearance kinetics.

Degradability and Clearance of Silicon, Organosilica, Silsesquioxane, Silica Mixed Oxide, and Mesoporous Silica Nanoparticles.

An international initiative on long-term behavior of high-level nuclear waste glass

The remarkable chemical durability of silicate glass makes it suitable for a wide range of applications. The slowdown of the aqueous glass corrosion kinetics that is frequently observed at long time is generally attributed to chemical affinity effects (saturation of the solution with respect to silica). Here, we demonstrate a new mechanism and highlight the impact of morphological transformations in the alteration layer on the leaching kinetics. A direct correlation between structure and reactivity is revealed by coupling the results of several structure-sensitive experiments with numerical simulations at mesoscopic scale. The sharp drop in the corrosion rate is shown to arise from densification of the outer layers of the alteration film, leading to pore closure. The presence of insoluble elements in the glass can inhibit the film restructuring responsible for this effect. This mechanism may be more broadly applicable to silicate minerals.

Insight into silicate-glass corrosion mechanisms

Recent progress in antireflection and self-cleaning technology – From surface engineering to functional surfaces

Dissolution, selective leaching, and stress-corrosion cracking are all processes which can degrade the performance of silica and silicate glasses exposed to aqueous environments. Reactions which corrode glass in water include hydration, hydrolysis and condensation, and ion-exchange processes. Techniques such as solid-state nuclear magnetic resonance, Raman and Fourier transform infrared spectroscopies, pH stat titrations and elemental depth profiling have been used to establish the relative importance of the above reactions on glass degradation as a function of solution pH and composition, temperature and stress level. This paper reviews results obtained for silica, alkali silicate, and alkali boro- and aluminosilicate glasses. For most glasses, the rate at which water enters the glass structure controls the kinetics of the other glass-water reactions, explaining the corrosion characteristics of different glass compositions.

B.C. Bunker

Papers

Molecular mechanisms for corrosion of silica and silicate glasses