Dendritic nanotubes self-assembled from stiff polysaccharides as drug and probe carriers
Dendritic nanotubes (DNTs) with hydrophobic cavities were constructed directly from rigid branched β-1,3-D-glucan (AF1) in aqueous solution, and the AF1 sample was isolated from the fruiting bodies of Auricularia auricula-judae, a household nutritional food. The structure of AF1 dendritic nanotubes was demonstrated with a transmission electron microscope (TEM) and a scanning electron microscope (SEM), and a schematic diagram was proposed to describe the formation process, which was supported by the results of static/dynamic light scattering (SLS/DLS) and atomic force microscopy (AFM). In solution, a sequential self-assembly of the AF1 chains in a parallel manner occurred to form lamellas followed by self-curling into nanotubes with the mean diameters from 20 to 80 nm, depending on the concentration and molecular weight of AF1, through hydrogen bonding and hydrophilic/hydrophobic interaction. As a result of the dendritic structure, the AF1 aggregates exhibited highly condensed hydrophobic regions, which could be used as carriers to achieve a high concentration of the target molecules. In our findings, the anticancer drug DOX and the fluorescent probe TPA-BMO could be loaded into the hydrophobic region of DNTs. Interestingly, DOX-loaded DNTs of AF1 exhibited high drug loading capacity and pH-triggered sustained release behaviors (>23 days) with reduced cytotoxicity in vitro. Moreover, the bioimaging experiment demonstrated that TPA-BMO-loaded DNTs of AF1 induced stronger fluorescence intensity than TPA-BMO alone, and maintained a longer duration time (18 days) in vivo. Therefore, the DNTs of AF1 have promising applications as bioactive carriers, especially in the fields of drug delivery and bioimaging.