(498e) Length-Dependent Uptake, Inflammation, and Intracellular Processing of Single-Walled Carbon Nanotubes in Macrophages

Single-walled carbon nanotubes (SWCNTs) are increasingly being investigated for biomedical applications due to their chemical inertness, high surface area-to-volume ratio, and optical properties. Understanding cellular uptake and intracellular processing of SWCNTs while preserving their inherent properties is important for realizing SWCNT-based drug delivery and imaging systems. Especially, understanding immune-cell specific processing of SWCNTs is of great interest since immune cells involve in many physiological conditions including wound healing, inflammation, and cancer. Macrophages, a type of immune cell, have shown to take up larger number of SWCNTs than other cell types. They are professional phagocytes capable of two distinct size-dependent cellular entry mechanisms; endocytosis and phagocytosis. To determine how SWCNT lengths affect uptake and intracellular processing in macrophages, we non-covalently dispersed SWCNTs with average lengths of 50 nm (ultra-short, US) and 150 nm (short) with bovine serum albumin, which maintains SWCNT optical properties while promoting cellular uptake without affecting cell viability. Using confocal Raman imaging and spectroscopy, we quantify uptake, intracellular dispersion state, and recovery as a function of SWCNT lengths in macrophages. As expected from previous studies, macrophages uptake SWCNTs in dose-dependent manner for both short- and US- SWCNTs. However, uptake amount was significantly larger in a case for US-SWCNTs compared to short-SWCNTs. Interestingly, short-SWCNTs become highly bundled in phase dense regions of macrophages uptake and mostly retained for at least 24 h, whereas US-SWCNTs remain comparatively individualized and exocytosed over time. Phase contrast imaging of macrophages engulfed of SWCNTs revealed distinct phase dense regions, which co-registered with high SWCNT Raman signal. Further analysis of these regions revealed that they were mostly consisting of SWCNT bundles. In addition, we observed more numerous vacuoles and larger cell area for US-SWCNTs laden macrophages. This lead us to hypothesized that macrophages may have length-dependent inflammation upon exposure to SWCNTs, which may affect their uptake and intracellular trafficking in macrophages. The differential length-dependent inflammation and intracellular processing in macrophages may contribute to tailoring SWCNT properties for their usage in therapy and imaging. While high loading and subsequent release of individualized US-SWCNTs and triggering pro-inflammatory behavior in macrophages are more preferential for cancer therapy and drug delivery applications, high retention of short-SWCNTs in macrophages may be desirable for macrophage tracking in vivo and biomedical imaging applications.