Light controlled release system based on photoresponsive bridged polysilsesquioxane nanocarriers

Abstract

Light-controlled release system plays an important role in the stimuli-responsive release application, due to light with its efficient controllability and non-contact. By adjusting the light irradiation of intensity, wavelength, time and location, the release behavior of the target molecule, such as the release rate, location and concentrations, can be performed by spatial and temporal control. Bridged polysilsesquioxanes have a -[A-SiO1.5] n -molecular chain structure (A is an organic group) which show good mechanical properties and biocompatibility. Due to the wide designability and tunability of the A organic group, bridged polysilsesquioxane materials with different properties can be prepared. This kind of hybrid inorganic-organic materials have potential application values on stimulus-responsive release, optical sensors and biological imaging. A novel photoresponsive controlled release system based on this material was designed and prepared in the present study. When target molecules are connected to nanocarriers with photoresponsive groups by a covalent bond, the covalently binding tends to affect the characteristics of the target molecules, and the chemical process of preparing the controlled release system is complex. Therefore, a photoresponsive controlled release system with simple preparation process and guaranteed target molecular characteristics is highly desired to be constructed. In the paper, a bridged silane containing 2-nitrobenzyl group (BS) was successfully prepared. First, 2-nitrobenzyl chloroformate was obtained by substitution reaction of 2-nitrobenzyl alcohol and triphosgene. Then, the photoresponsive bridged silane monomer BS was produced from 2-nitrobenzyl chloroformate and bis(trimethoxysilylpropyl)amine. The photoresponsive group 2-nitrobenzyl was covalently connected with the silane through an ester group. The synthesized BS was confirmed by nuclear magnetic resonance spectroscopies (1H NMR, 13C NMR, and 29Si NMR), FTIR and mass spectrometry. UV-vis spectra showed that BS was photoresponsive under 254 nm light. The characteristic absorption peaks of the BS at 300 and 224 nm obviously changed during the period of irradiation. Furthermore, the maximum photoreaction conversion was 70% at the irradiation time of 70 min. Further, photoresponsive bridged polysilsesquioxane nanoparticles (BPS) were prepared from BS using a sol-gel method. The prepared BPS nanoparticles were characterized by SEM and DLS. The results showed that the nanoparticles had a spherical morphology with an average particle size of 127 nm. The UV-vis spectra of BPS in an aqueous solution irradiated over different time testified the photoresponse property of BPS. More importantly, the surface charge of BPS nanoparticles could be reversed from negative (–28.20 mV) to positive (+22.86 mV) triggered by light. Upon irradiation, the secondary amine groups were exposed on the surface of BPS due to the photocleaved reaction of photosensitive groups. And the further protonation of amine groups in the aqueous solution increased the positive property of the surface of BPS. The properties indicated that the light-triggered charge reversal nanoparticles may be promising candidates for controlled drug release system. Doxorubicin (DOX) as a widely used clinical anticancer drug was used to evaluate the concept of charge reversal. It was easily combined on the BPS nanoparticles by electrostatic interaction. The nanoparticles could efficiently load 14.8wt% of DOX. The strategy to prepare drug-loaded nanocarriers is simple, mild and high efficiency. In vitro release results showed that the loaded DOX release rate had positive correlation with irradiation intensity and irradiation time (254 nm). The release behaviors under different laser power (60, 160 and 200 mW/cm2) were performed in PBS buffer (pH 7.4) at 37°C over a period of 16 h. There was no obvious release without light. The loaded DOX release rate increased with the increasing irradiation intensity or irradiation time. The highest release rate was 82.9% under 200 mW/cm2 irradiation over 16 h. Moreover, no sudden release behavior was found for the drug-loaded nanoparticles occurred within 6 h of irradiation. As a result, the drug release process can be precisely controlled by regulating the irradiation time and intensity. The prepared DOX@BPS drug-loaded nanoparticles exhibited good photoresponsive performance.