Surface PEGylation of nanodiamond through a facile Michael addition reaction for intracellular drug delivery

Nanodiamond (ND) has been regarded as one of the most fascinating carbon nanomaterials for biomedical applications owing to its excellent physicochemical and biological properties. The biomedical application of ND-based materials mainly depends on its surface chemistry and properties, so the surface modification of ND is very important to improve its final biomedical application performance. In this work, a novel route for the surface modification of ND was developed via the combination of esterification reaction and Michael addition reaction. Simply, the pristine ND was first functionalized with ethylene diamine to immobilize the amino groups on the surface of ND. Then, a hydrophilic and biocompatible poly (ethylene glycol) methyl ether methacrylate (PEGMA) was further conjugated onto ND surface through Michael addition reaction to obtain PEGylated ND (ND@PEGMA) composites, which were ascertained by a series of characterization techniques. The dispersibility and potential biomedical applications of ND@PEGMA were examined and results demonstrated that ND@PEGMA displayed enhanced dispersibility and low cytotoxicity. Finally, doxorubicin hydrochloride as an anticancer drug model was successfully loaded on the prepared ND based composites, and the drug release and intracellular delivery of the drug-loaded composites (ND@PEGMA-DOX) were further studied and the results indicate that ND@PEGMA composites could be utilized as promising candidates for intracellular drug delivery.