Effects of Covalent Functionalization on the Biocompatibility Characteristics of Multi-Walled Carbon Nanotubes

Abstract

We report the effect of chemical modification of multi-walled carbon nanotubes (MWNTs) on their activation of the human serum complement system, as well as the adsorption of human plasma proteins on MWNTs. Four different types of chemically-modified MWNTs were tested for complement activation via the classical and alternative pathways using haemolytic assays. Human plasma protein binding was also tested using an affinity chromatography technique based on carbon nanotube-Sepharose matrix. Covalent functionalization of MWNTs greatly altered the level of activation of the complement system via the classical pathway. For example, MWNTs functionalised with epsilon-caprolactam or L-alanine showed respectively >90% and >75% reduction in classical pathway activation compared with unmodified MWNTs. These results demonstrate for the first time that these types of chemical modification are able to alter considerably the levels of specific complement proteins bound by pristine MWNTs (used as a control experiment). The reduced levels of complement activation via the classical pathway, that are likely to increase biocompatibility, were directly correlated with the amount of C1q protein bound to chemically modified carbon nanotubes. An inverse correlation was also observed between the amount of complement factor H bound to chemically modified MWNTs and the level of complement consumption via the alternative pathway. Binding of human plasma and serum proteins to pristine and modified MWNTs was highly selective. The chemical modifications studied generally increased nanotube dispersibility in aqueous media, but diminished protein adsorption.

Innate immune humoral factors, C1q and factor H, with differential pattern recognition properties, alter macrophage response to carbon nanotubes

“…The innate immune system plays a key role in the recognition and clearance of pathogens, altered-self, and synthetic particles including nanoparticles [1,3,[6][7][8]. The complement system is one of the key innate immune mechanisms and is activated through three pathways.…”

The winding road for carbon nanotubes in nanomedicine

“…Recent understanding of CNT-protein interactions is suggesting convergence on the fact that CNT functionalization plays a key role in fine-tuning (and potentially reducing) protein binding [50,[74][75][76], albeit no protocol has succeeded in completely eliminating complement activation [77]. For instance, non-covalent binding of proteins such as albumin, fibrinogen, and C1q to DWCNTs is not competitive as it occurs at different sites, therefore, complement activation is prevented by neither albumin-nor fibrinogen-coating of CNTs [78].…”

The Role of the Protein Corona in Fiber Structure-Activity Relationships

“…For SWCNT that had been modified with polyethylene glycol (PEG), the pattern of adsorbed proteins was affected in dependence of the conformation of the PEG [53,76]. The natural protein binding affinity to SWCNTs is reduced or even eliminated by covalent functionalization of the CNTs with PEG moieties [77], which in turn changes the cellular uptake [42].…”