Are functionalized multi-walled carbon nanotubes biodegraded within the living body?
Carbon nanomaterials (CNMs) such as carbon nanotubes (CNTs) and carbon nanohorns (CNHs) have attractive in the application for drug delivery systems, biosensors, and biomaterials. Although carbon materials are believed to be unchangeable or non-biodegradable within the living body, the stability and metabolism of CNMs are of great significance for the human bodies and biogeocenosis as a fundamental knowledge. Recently, Kagan and colleagues reported on the enzymatic biodegradation of carboxylated single-walled carbon nanotubes (COOH-SWCNTs) in vitro, in neutrophils. In contrast, to our knowledge, the chemically-modified short CNTs or CNHs was taken into not neutrophils but macrophages, in vivo. It is a commonplace to say that oxidative ability of macrophages to foreign body is much weaker than that of neutrophils. Are CNMs biodegraded in macrophage in vivo? Here, we report on the implantation of multi-walled carbon nanotubes (MWCNTs) modified with carboxyl groups, in the subcutaneous tissue of rats over 2 years and the structural deformation of these MWCNTs in phagocytes studied using high-resolution transmission electron microscopy (HRTEM) and Raman scattering spectroscopy.