Dendrimer directed assembly of dicarboxylated hairy nanocellulose

Dendrimer-directed assembly of electrosterically stabilized nanocrystalline cellulose (ENCC) to form network structures was studied. ENCC is a member of the family of hairy nanocelluloses and consists of a crystalline rod and dicarboxylated cellulose chains ("hairs") protruding from both ends, which are very reactive. We hypothesized that covalent linking of ENCC and dendrimers should lead to self-assembled hybrid network structures in which dendrimeric nodes connect cellulose nanorods.

Polyamidoamine (PAMAM) dendrimers were covalently linked to ENCC by a bioconjugation reaction with different ratios of ENCC to PAMAM. To control the self-assembly process and prevent aggregation, acid hydrolysis of ENCC was performed to obtain crew-cut ENCC with shorter hairs and less negative charge. The formation of self-assembled structures from different PAMAM concentrations were analyzed using atomic force microscopy.

It was observed that depending on the concentration of PAMAM, various linear, star-shaped, and closed-loop structures were formed. Also, networks were formed with dendrimers acting as the nodes, connecting long cellulose rods, thus producing a network with a characteristic length of around 100-200 nm, which is difficult to obtain otherwise. We have demonstrated that the reactions of dendrimers with ENCC are solely occurring at the hairs and not at the crystalline regions.