Fine-tuning of membrane permeability by reversible photoisomerization of aryl-azo derivatives of thymol embedded in lipid nanoparticles

Responsiveness of liposomes to external stimuli, such as light, should allow a precise spatial and temporal control of release of therapeutic agents or ion transmembrane transport. Here, some aryl-azo derivatives of thymol are synthesized and embedded into liposomes from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine to obtain light-sensitive membranes whose photo-responsiveness, release behaviour, and permeability towards Cl- ions are investigated. The hybrid systems are in-depth characterized by dynamic light scattering, atomic force microscopy and Raman spectroscopy. In liposomal bilayer the selected guests undergo reversible photoinduced isomerization upon irradiation with UV and visible light, alternately. Non-irradiated hybrid liposomes retain entrapped 5(6)-carboxyfluorescein (CF), slowing its spontaneous leakage, whereas UV-irradiation promotes CF release, due to guest trans-to-cis isomerization. Photoisomerization also influences membrane permeability towards Cl- ions. Data processing, according to first-order kinetics, demonstrates that Cl- transmembrane transport is enhanced by switching the guest from trans to cis but restored by back-switching the guest from cis to trans upon illumination with blue light. Finally, the passage of Cl- ions across the bilayer can be fine-tuned by irradiation with light of longer λ and different light-exposure times. Fine-tuning the photo-induced structural response of the liposomal membrane upon isomerization is a promising step towards effective photo-dynamic therapy.

Controlled Self-Assembly of Multiple-Responsive Superamphiphilc Polymers Based on Host-Guest Inclusions of a Modified PEG with β-Cyclodextrin

Superamphiphilic polymers (SAPs) constructed by host-guest inclusion can self-assemble into various nanostructures in solution, which can find applications in many fields such as nanodevices, drug delivery, and template synthesis. Herein, we report the controlled self-assembly of multiple-responsive SAP based on a selective host-guest inclusion of β-cyclodextrin (β-CD) with a modified poly(ethylene glycol) (PEG) (FcC₁₁AzoPEG) consisting of a ferrocene (Fc) end group, a C₁₁ alkyl chain, an azobenzene (Azo) block, and a poly(ethylene glycol)methyl ether (PEG) chain. These SAPs can self-assemble into interesting nanostructures in water upon exposure to different stimuli because β-CD can be selectively included with different guests, such as Fc, Azo, and C₁₁ alkyl chain, under different stimuli. The inclusion complex of Fc with β-CD (Fc@β-CD SAP) can form nanowire micelles in aqueous solution. The nanowire micelles can be transformed into spindle micelles with the addition of oxidant because the majority of β-CDs dissociated from the complex Fc@β-CD SAP due to a conversion of Fc to Fc⁺ and will preferentially include with Azo group to form another dominant inclusion complex (Azo@β-CD SAP). After UV irradiation, the spindle micelles can be further transformed into spherical micelles because most of β-CDs are excluded from the complex Azo@β-CD SAP due to a trans- to cis-Azo conversion and then form a dominant inclusion complex with C₁₁ alkyl chains (C₁₁@β-CD SAP). This work not only demonstrates the selective host-guest inclusion of stimuli-responsive groups modified PEG with β-CD but also provides a useful approach for construction of diverse morphologies.

Photocontrollable Intermittent Release of Doxorubicin Hydrochloride from Liposomes Embedded by Azobenzene-Contained Glycolipid

Azobenzene-contained glycolipids GlyAzoCns, newly structured azobenzene derivatives, which have an azobenzene moiety between the galactosyl and carbon chains of various sizes, have been synthesized. The GlyAzoCns undergo reversible photoinduced isomerization in both ethanol solution (free state) and liposomal bilayer (restricted state) upon irradiation with UV and vis light alternately. The drug release of Liposome@Gly induced by isomerization was found to be an instantaneous behavior. The photoinduced control of DOX release from liposome was investigated in various modes. The Liposome@Glys have been found to keep the entrapped DOX stably in the dark with less than 10% leakage in 10 h but release nearly 100% of cargos instantaneously with UV irradiation. The molecular structure of GlyAzoCns and the property of the liposomal bilayer were considered as important factors influencing drug release. Among the synthesized GlyAzoCns, GlyAzoC7 was shown to be the most efficient photosensitive actuator for controlling drug release. A lower proportion of cholesterol in Liposome@Glys was conducive to promote the release amount. Results indicated that the synthesized GlyAzoCns could act as a role of smart actuators in the liposome bilayer and control the drug to release temporarily and quantitatively.