Nanodynamics of dendritic core-multishell nanocarriers.

The molecular dynamics of polymeric nanocarriers is an important parameter for controlling the interaction of nanocarrier branches with cargo. Understanding the interplay of dendritic polymer dynamics, temperature, and cargo molecule interactions should provide valuable new insight for tailoring the dendritic architecture to specific needs in nanomedicine, drug, dye, and gene delivery. Here, we have investigated polyglycerol-based core-multishell (CMS) nanotransporters with incorporated Nile Red as a fluorescent drug mimetic and CMS nanotransporters with a covalently bound fluorophore (Indocarbocyanine) using fluorescence spectroscopy methods. From time-resolved fluorescence depolarization we have obtained the rotational diffusion dynamics of the incorporated dye, the nanocarrier, and its branches as a function of temperature. UV/vis and fluorescence lifetime measurements provided additional information on the local dye environment. Our results show a distribution of the cargo Nile Red within the nanotransporter shells that depends on solvent and temperature. In particular, we show that the flexibility of the polymer branches in the unimolecular state of the nanotransporter undergoes a temperature-dependent transition which correlates with a larger space for the mobility of the incorporated hydrophobic drug mimetic Nile Red and a higher probability of cargo-solvent interactions at temperatures above 31 °C. The measurements have further revealed that a loss of the cargo molecule Nile Red occurred neither upon dilution of the CMS nanotransporters nor upon heating. Thus, the unimolecular preloaded CMS nanotransporters retain their cargo and are capable to transport and respond to temperature, thereby fulfilling important requirements for biomedical applications.