Development of Novel Polymer Ultrasound Contrast Agents Incorporating Nested Carbon Nanodots
Wednesday, September 11, 2024
2:30 PM-4:30 PM
BIOMED PhD Thesis Defense
Title:
Development of Novel Polymer Ultrasound Contrast Agents Incorporating Nested Carbon Nanodots
Speaker:
Matthew A. Shirley, PhD Candidate
School of Biomedical Engineering, Science and Health Systems
Drexel University
Advisor:
Margaret A. Wheatley, PhD
John M. Reid Professor
School of Biomedical Engineering, Science and Health Systems
Drexel University
Details:
In 2024, a total of over 2 million people in the United States are expected to be newly diagnosed with cancer. and over 600,000 people in the country are expected to succumb to the disease. These facts, along with the recent $150 million reinvestment in the Cancer Moonshot initiative, highlight the urgent necessity for novel cancer detection and treatment strategies. Great progress has been made over the years; however, the systemic delivery of non-specific and toxic chemotherapeutic regimes is still a hallmark of many current treatment options in use today. Several theranostic strategies have been investigated, including the usage of microbubbles, or ultrasound contrast agents (UCAs).
Microbubble-mediated ultrasound therapy has gained significant attention due to its non-invasive nature and targeted delivery potential. The Microencapsulation Lab has developed a drug-loaded polymer microbubble that can be used as a UCA, and the polylactic acid (PLA) microbubbles have the robust capability of being able to load nanoparticles, as well. However, current polymer microbubbles still face limitations in terms of their functionality and the capabilities of polymer microbubbles can still be enhanced, particularly regarding the imaging performance and functional versatility of the platform.
In this context, the integration of carbon nanodots (CNDs) with polymer microbubbles presents an exciting avenue for the improvement of microbubbles. CNDs are emerging nanoscale (<10 nm), photoluminescent particles with unique properties that exhibit drug loading and delivery capabilities, including rapid cellular uptake, and strong biological imaging potential. Economically, CNDs are also cost-effective to produce and can be synthesized from a wide variety of carbon sources in minimal steps. Encapsulation of CNDs within the polymer shell of MBs can provide multifunctionality, combining the imaging and drug-retaining capabilities of CNDs with the drug delivery and imaging potential of microbubbles.
Herein this dissertation describes a research effort towards the development of a CND-loaded microbubble to enhance the theranostic potential of the UCA platform. By encapsulating CNDs within the PLA microbubbles, we hypothesize that the resulting MB system will display improved imaging capabilities, allow tracking of collapsed polymer fragments and shells, and potentially improve loading capabilities of drug, all while maintaining the vital acoustic properties of a functional ultrasound contrast agent. To our knowledge, this is the first study to explore incorporating CNDs into a polymer microbubble shell. This study improves upon previous research by incorporating fluorescent, non-toxic carriers, while potentially keeping the drug delivery platform clinically relevant.
In an effort to establish a proof-of-concept CND-loaded polymer UCA, carbon quantum dots (CQDs) were incorporated into the PLA microbubble water/oil/water emulsion fabrication process. This integration led to enhanced acoustic properties, with CQD-loaded MBs exhibiting a ~10% improved acoustic enhancement and a >50% improved acoustic stability compared to unloaded microbubbles. In addition to this, the CQDs did not significantly change the physical characteristics of the UCA. However, although the presence of CQD in the polymer shell was confirmed through TEM, confocal microscopy was needed to detect visual fluorescence.
To further establish the CND-microbubble loading capabilities, three different graphene quantum dots (GQDs) were compared by organic loading onto the UCA. These unmodified (U-), carboxylated (C-), and aminated GQDS (A-GQDs) effected the UCA in a variety of ways. All UCA experimental groups maintained vital acoustic properties. More uniquely, the U-GQDs increased the microbubble concentration and acoustic enhancement to the highest of the group, while also imbuing fluorescence on the shell. The C-GQDs decreased the size and enhancement, and did not exhibit additional fluorescence. However, while the A-GQDs maintained improved physical and acoustic microbubble characteristics compared to the unloaded control, they exhibited the most advantageous fluorescence and loading capabilities.
To continue expanding the platform capabilities, the method of loading A-GQDs was then studied. Three different loading weights were evaluated in two different loading conditions: organic loading or aqueous loading. All A-GQD loaded UCA groups performed similarly except in a couple areas. The 1wt% loaded A-GQD groups significantly increased particle counts in the microbubble size range, which decreased as loading weight went up, and scanning electron microscopy ultimately showed that 1wt% loading contains non-bubble PLA material while 5wt% aqueous loading of A-GQDs appears to stabilize uniform bubble formation. In terms of nanoparticle loading efficiency, the aqueous loadings consistently showed greater loading efficiencies over the equivalent organic loading group, with 3wt% having the highest efficiency.
Co-loading of A-GQD and Doxorubicin (Dox) was then examined. This led to poor results, showing barely any microbubble formation, let alone drug-nanoparticle-loaded microbubbles. However, pivoting to examining Dox loading on C-GQDs revealed that Dox + C-GQD-loaded UCAs made intact microbubbles and improved acoustic behavior over unloaded or Dox-loaded UCAs individually, while also improving the drug loading of Dox compared to Dox alone by almost ~150%.
Overall, this work represents a step towards developing multifunctional theranostic agents. This was accomplished by maintaining the acoustic properties of UCAs, while fabricating novel fluorescent CND-loaded UCAs, and incorporating a chemotherapeutic agent. This study contributes to the field of nanoparticle-loaded UCAs and opens the way towards future applications in agile targeted cancer therapies and diagnostic imaging.
Contact Information
Natalia Broz
njb33@drexel.edu