Unique Biological Degradation Behavior of Stöber Mesoporous Silica Nanoparticles from Their Interiors to Their Exteriors

The degradation behavior of mesoporous silica nanoparticles (MSNs) influences their biological applications. The present study was a systematic investigation of the biological degradation behavior of mesoporous silica synthesized by the Stöber method. Different sized Stöber mesoporous silica nanoparticles were prepared and immersed in simulated body fluid, and degradation curves were obtained by measuring the dissolved silicon content of the fluid. Structural changes during degradation were observed by transmission electron microscope (TEM). The Stöber mesoporous silica nanoparticles tended to become hollow during the degradation process, and each particle was almost completely degradable from its interior to its exterior. Because of this unique degradation behavior, the morphology of the Stöber mesoporous silica nanoparticles can be retained even after over 85% of the silica degraded. Thus, during degradation, the dispersibility of the silica particles was superior to that of MSNs prepared in aqueous phases. Furthermore, the degradation behavior, intracellular distribution, and structural transformation of Stöber mesoporous silica nanoparticles in human embryo kidney 293T cells were investigated by measuring the silicon content in culture medium and analyzing TEM images. When these silica nanoparticles degraded in cells, their size and dispersibility remained unchanged, which would reduce the biological toxicity associated with the accumulation of silica aggregates in tissues. Overall, these results demonstrate that Stöber mesoporous silica nanoparticles can degrade in biological medium from inside to outside and maintain their good dispersibility, which suggests that these nanoparticles have great potential for applications as degradable biomedical materials such as drug carriers.