Photo-Induced Modification of Nanocellulose: The Design of Self-Fluorescent Drug Carriers

Nanocellulose is an excellent carrier to deliver drugs, as the material is biocompatible and has a desirable non-spherical shape. However, nanocellulose displays low solubility in aqueous solution and needs to be modified with water-soluble polymers in order to achieve high colloidal stability. In this study, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl or (2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl (TEMPO)-oxidized cellulose nanofibers bearing carboxylic acid moieties (TOCNs) are modified by nitrile imine-mediated tetrazole/carboxylic acid ligation. The advantage of this reaction is that TOCNs do not need to be modified further and the polymer with tetrazole end-functionalities can be directly clicked onto the TOCNs forming fluorescent functional groups. Poly(2-hydroxyethyl acrylate) with a tetrazole end-functionality is prepared using RAFT polymerization. The polymer is mixed with TOCNs and after irradiation at lambda = 326 nm for 10 h, fluorescent pHEA-g-TOCNs are obtained. The polymer-grafted nanocellulose is found to disperse well in water and has only limited albumin binding. The uptake of these nanoparticles by MCF-7 breast cancer cell lines can now be monitored by fluorescent microscopy without further modification. Excess negatively charged carboxylic groups of TOCNs allow doxorubicin loading by electrostatic interactions at various drug-loading capacities. Higher drug loading is more efficient in inhibiting the cell proliferation, highlighting the effect of drug loading on toxicity.