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Understanding Acoustic Cavitation Initiation by Porous Nanoparticles: Toward Nanoscale Agents for Ultrasound Imaging and Therapy
journal contribution
posted on 2016-08-09, 16:21 authored by Adem Yildirim, Rajarshi Chattaraj, Nicholas
T. Blum, Andrew P. GoodwinUltrasound
is widely applied in medical diagnosis and therapy due
to its safety, high penetration depth, and low cost. In order to improve
the contrast of sonographs and efficiency of the ultrasound therapy,
echogenic gas bodies or droplets (with diameters from 200 nm to 10
μm) are often used, which are not very stable in the bloodstream
and unable to penetrate into target tissues. Recently, it was demonstrated
that nanobubbles stabilized by nanoparticles can nucleate ultrasound
responsive microbubbles under reduced acoustic pressures, which is
very promising for the development of nanoscale (<100 nm) ultrasound
agents. However, there is still very little understanding about the
effects of nanoparticle properties on the stabilization of nanobubbles
and nucleation of acoustic cavitation by these nanobubbles. Here,
a series of mesoporous silica nanoparticles with sizes around 100
nm but with different morphologies were synthesized to understand
the effects of nanoparticle porosity, surface roughness, hydrophobicity,
and hydrophilic surface modification on acoustic cavitation inception
by porous nanoparticles. The chemical analyses of the nanoparticles
showed that, while the nanoparticles were prepared using the same
silica precursor (TEOS) and surfactant (CTAB), they revealed varying
amounts of carbon impurities, hydroxyl content, and degrees of silica
cross-linking. Carbon impurities or hydrophobic modification with
methyl groups is found to be essential for nanobubble stabilization
by mesoporous silica nanoparticles. The acoustic cavitation experiments
in the presence of ethanol and/or bovine serum albumin (BSA) demonstrated
that acoustic cavitation is predominantly nucleated by the nanobubbles
stabilized at the nanoparticle surface not inside the mesopores. Finally,
acoustic cavitation experiments with rough and smooth nanoparticles
were suggested: a rough nanoparticle surface is needed to largely
preserve surface nanobubbles after coating the surface with hydrophilic
macromolecules, which is required for in vivo applications of nanoparticles.