A novel method for targeting lymphatic vessel imaging: methylene blue nanoparticle integrated with dissolvable microneedles

The lymphatic system serves many more functions than simply maintaining tissue fluid homeostasis, and its structural and functional changes indicate the occurrence of disease. Current clinical methods for the assessment of the lymphatic system, however, are severely limited because of their nontargeting ability, invasiveness, high cost, and radiation risk. Herein, we propose a simple and painless method for visualizing and quantifying the lymphatic system. This method is based on the noninvasive administration of a novel lymphatic tracer via dissolvable microneedles, followed by the application of a portable detection device for near-infrared (NIR) imaging. The tracer is prepared by incorporating the clinically approved NIR fluorescent dye methylene blue (ME) into the nanomaterial monomethoxyl poly(ethylene glycol)-b-poly(ε-caprolactone) (MPEG-PCL@ME). This novel tracer displays superior fluorescence properties, stability, biocompatibility, and targeting features in comparison with ME solution alone. Lymphography with MPEG-PCL@ME in vivo clearly revealed the lymphatic vessel morphology. Notably, compared with ME and indocyanine green, MPEG-PCL@ME can easily identify the dominant lymphatic vessels and nodes in rats with higher imaging quality. Furthermore, a series of segmental contracting sections are detected with MPEG-PCL@ME, allowing straightforward identification of the lymphatic pump, which provides direct evidence for exquisitely evaluating lymphatic functions.