A Biodegradation Study of SBA-15 Microparticles in
Simulated Body Fluid and <i>in Vivo</i>
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Abstract
Mesoporous silica has received considerable
attention as a drug
delivery vehicle because of its large surface area and large pore
volume for loading drugs and large biomolecules. Recently, mesoporous
silica microparticles have shown potential as a three-dimensional
vaccine platform for modulating dendritic cells via spontaneous assembly
of microparticles in a specific region after subcutaneous injection.
For further <i>in vivo</i> applications, the biodegradation
behavior of mesoporous silica microparticles must be studied and known.
Until now, most biodegradation studies have focused on mesoporous
silica nanoparticles (MSNs); here, we report the biodegradation of
hexagonally ordered mesoporous silica, SBA-15, with micrometer-sized
lengths (∼32 μm with a high aspect ratio). The degradation
of SBA-15 microparticles was investigated in simulated body fluid
(SBF) and in mice by analyzing the structural change over time. SBA-15
microparticles were found to degrade in SBF and <i>in vivo</i>. The erosion of SBA-15 under biological conditions led to a loss
of the hysteresis loop in the nitrogen adsorption/desorption isotherm
and fingerprint peaks in small-angle X-ray scattering, specifically
indicating a degradation of ordered mesoporous structure. Via comparison
to previous results of degradation of MSNs in SBF, SBA-15 microparticles
degraded faster than MCM-41 nanoparticles presumably because SBA-15
microparticles have a pore size (∼8 nm) and a pore volume larger
than those of MCM-41 mesoporous silica. The surface functional groups,
the residual amounts of organic templates, and the hydrothermal treatment
during the synthesis could affect the rate of degradation of SBA-15.
In <i>in vivo</i> testing, previous studies focused on the
evaluation of toxicity of mesoporous silica particles in various organs.
In contrast, we studied the change in the physical properties of SBA-15
microparticles depending on the duration after subcutaneous injection.
The pristine SBA-15 microparticles injected into mice subcutaneously
slowly degraded over time and lost ordered structure after 3 days.
These findings represent the possible <i>in vivo</i> use
of microsized mesoporous silica for drug delivery or vaccine platform
after local injection