Methylene blue-filled biodegradable polymer particles as a contrast agent for optical coherence tomography

Area of Science:

• Biomedical Optics
• Materials Science
• Nanotechnology

Background:

• Optical coherence tomography (OCT) lacks molecular specificity, limiting its diagnostic capabilities.
• Methylene blue (MB) is a clinically relevant dye but suffers from toxicity and reduced contrast in OCT.
• Developing effective molecular contrast agents is crucial for advancing OCT applications.

Purpose of the Study:

• To develop biodegradable micro/nano-spheres loaded with methylene blue (MB) as molecular contrast agents for OCT.
• To improve signal strength and reduce toxicity associated with MB in OCT imaging.
• To demonstrate targeted delivery of these contrast agents for specific molecular imaging.

Main Methods:

• Biodegradable polymer micro/nano-spheres were synthesized and loaded with methylene blue (MB).
• The spheres' optical properties and MB release kinetics were characterized.
• Contrast-enhanced OCT imaging was performed using pump-probe and photothermal OCT techniques with 830 nm and 1.3 µm OCT systems.
• Functionalization of spheres for targeted delivery to VCAM receptors was demonstrated.

Main Results:

• MB-loaded spheres significantly reduced singlet oxygen and leuco-MB production, enhancing safety and contrast.
• The strongly scattering nature of the spheres improved signal localization and strength in OCT images.
• Successful imaging of the contrast agents was achieved using both pump-probe and photothermal OCT modalities.
• Targeted functionalization enabled specific receptor binding, as shown with VCAM targeting.

Conclusions:

• Biodegradable MB-loaded spheres are effective molecular contrast agents for OCT.
• These agents offer improved safety, signal strength, and localization compared to free MB.
• The developed contrast agents show potential for targeted molecular imaging, particularly for inflammatory conditions.