Photoacoustic imaging, using targeted plasmonic metallic nanoparticles, is a promising noninvasive molecular imaging method. Analysis of the photoacoustic signal generated by plasmonic metallic nanoparticles is complex because of the dependence upon physical properties of both the nanoparticle and the surrounding environment. We studied the effect of the aggregation of gold nanoparticles on the photoacoustic signal amplitude. We found that the photoacoustic signal from aggregated silica-coated gold nanoparticles is greatly enhanced in comparison to disperse silica-coated gold nanoparticles. Because cellular uptake and endocytosis of nanoparticles results in their aggregation, these results have important implications for the application of plasmonic metallic nanoparticles towards quantitative molecular imaging.
Mesenchymal stem cells (MSCs) are versatile in many tissue engineering applications and have the potential to be used
for cellular therapies because they can differentiate into many cell types. Specifically, the use of MSCs for the treatment
of ischemic disease is promising because MSCs can express characteristics of vascular cells. MSCs can promote vascular
growth at the site of injury after delivery using a PEGylated fibrin gel. In order to quantitatively assess in vivo delivery
and differentiation of MSCs, a non-invasive and high-resolution imaging technique is required. In this study, the
combined ultrasound and photoacoustic imaging was demonstrated to monitor MSCs labeled with citrate-stabilized gold
nanoparticles (Au NPs). It was observed that uptake of nanoparticles did not have a significant effect on cell viability and
proliferation over a two-week period. Four different cell concentrations of either the non-labeled MSCs or the Au NP
labeled MSCs were embedded in the tissue mimicking gelatin phantom. The ultrasound and photoacoustic signals were
acquired and quantitatively analyzed to assess sensitivity and accuracy of the developed imaging approach. Furthermore,
based on the results, the feasibility of in vivo ultrasound and photoacoustic imaging of MSCs was discussed.
Stem cells can differentiate into multiple cell types, and thus have the potential to be used for tissue repair and
regeneration. However, the participation of stem cells in wound repair and neovascularization is not well
understood. As a result, there is a need to monitor and track stem cells in vivo in order to obtain a better
understanding of the mechanisms of the wound healing response. Noninvasive, long-term imaging is ideal in order
to track stem cells within a single animal model. Thus, we are interested in developing an imaging approach to track
gold nanoparticle loaded mesenchymal stem cells (MSCs) in vivo after delivery via a hydrogel. This study assessed
the effect on cell function of loading MSCs with gold nanoparticles. We examined the loading of MSCs with gold
nanoparticles of various sizes and surface coatings using darkfield microscopy. We also examined the effect of
nanoparticle loading on cell viability, proliferation, and differentiation. The feasibility of imaging nanoparticle
loaded MSCs was examined by assessing cell viability and MSC tubulogenesis following laser irradiation. Our
results demonstrate that loading MSCs with gold nanoparticles does not compromise cell function. These findings
lend to the possibility of imaging MSCs in vivo with optical imaging.
Quantitative and qualitative monitoring of neovascular growth is required in many vascular tissue engineering
applications. For example, the contribution of progenitor cells in growing microvasculature has been demonstrated;
however, the process of vascularization from progenitor cells is not well understood. Therefore, there is a need for an
imaging technique that is consistent, easy to use, and can quantitatively assess the dynamics of vascular growth or
regression in a three-dimensional environment. In this study, we evaluate the ability of combined ultrasound and
photoacoustic imaging to assess the dynamics of vascular growth. The experiments were performed using hydrogels that
spontaneously promote tube formation from implanted mesenchymal stem cells (MSCs). Specifically, PEGylated fibrin
gels, supporting the development of capillary growth were implanted in a Lewis rat. After one week, the rat was
euthanized and the gel implants were excised and positioned in water cuvettes for imaging. Simultaneous ultrasound and
photoacoustic images were obtained using single-element, focused ultrasound transducers interfaced with a nanosecond
pulsed laser source. To image samples, ultrasound transducers operating at either 25 MHz or 48 MHz and interfaced
with laser sources operating at either 532 nm or within 680-800 nm wavelengths were used. The 3-D ultrasound and
photoacoustic images were acquired by mechanically scanning the transducer over the region of interest and capturing
spatially co-registered and temporally consecutive photoacoustic transients and ultrasound pulse-echo signals. The
ultrasound and photoacoustic images agree well with the overall anatomy and vascular structure in the gel samples. The
results suggest that the photoacoustic and ultrasound imaging could be used to sequentially monitor the growth of
neovasculature in-vivo.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.