Chemical design of pH-sensitive nanovalves on the outer surface of mesoporous silicas for controlled storage and release of aromatic amino acid

Stimuli-Responsive Nanomachines and Caps for Drug Delivery

In this review we focus on methods that are used to trap and release on command therapeutic drugs from mesoporous silica nanoparticles (MSNs). The pores in the MSNs are large enough to accommodate a wide range of cargo molecules such as anticancer and antibiotic drugs and yet small enough to be blocked by a variety of bulky molecules that act as caps. The caps are designed to be tightly attached to the pore openings and trap the cargo molecules without leakage, but upon application of a designed stimulus detach from the nanoparticles and release the cargo. Of special emphasis in this review are nanomachines that respond to stimuli administered from external sources such as light or magnetic fields, or from chemical stimuli produced by the biological system such as a general change in pH or redox potential, or a highly specific chemical produced by a cancer cell or infectious bacterium. The goal is to release a high local concentration of the cargo only where and when it is needed, thus minimizing off-target side effects. We discuss sophisticated reversible nanomachines but also discuss some useful caps that simply break off from the nanoparticles in response to the selected stimulus. Many ingenious systems have been and are being designed; we primarily highlight those that have been demonstrated to operate in vitro and/or in vivo. In most cases the closed MSNs are endocytosed by diseased or infected cells and opened inside the cells to release the drugs. We begin with an overview of the nanoparticles and nanomachines and then present examples of drug release triggered by internal chemical stimuli from the organism and finally by external light and magnetic field stimuli.

Mesoporous silica nanoparticles equipped with surface nanovalves for pH-controlled liberation of doxorubicin

Silica carriers equipped with molecular and supramolecular pH-sensitive nanovalves were designed by combination of sol-gel synthesis and selective postsynthetic modification. Mesoporous structure of synthesized materials was characterized by low-temperature nitrogen adsorption-desorption, small-angle X-ray diffraction and transmission electron microscopy. Chemical immobilization of N-[N'-(N'-phenyl)-2-aminophenyl]aminoalkyl groups was confirmed by IR spectral and chemical analyses of surface layer. Loading and release behaviour of synthesized drug carriers was studied in phosphate buffer solutions with pH 5.0 and pH 7.0 using doxorubicin (Dox) as a test molecule. It was found that the loading efficiency of synthesized materials determined by UV spectroscopy measurements reached 59-76%, whereas cumulative value of Dox released from silica materials equipped with molecular and supramolecular nanovalves into the phosphate buffer solution with pH 5.0 reached up to 48% and 51%, respectively. It was proved that aromatic amino groups and surface supramolecular structures localized near pore openings play an essential role in pH-controlled Dox release.

Sol-Gel Synthesis of Ordered β-Cyclodextrin-Containing Silicas

New approaches for β-cyclodextrin-containing silicas synthesis were demonstrated. Materials with hexagonally ordered mesoporous structure were prepared by postsynthesis grafting and by co-condensation methods. β-Cyclodextrin activated by a N,N'-carbonyldiimidazole was employed for postsynthesis treatment of 3-aminopropyl-modified MCM-41 support as well as for sol-gel synthesis with β-cyclodextrin-containing organosilane and tetraethyl orthosilicate participation in the presence of cetyltrimethylammonium bromide. The successful incorporation of cyclic oligosaccharide moieties in silica surface layer was verified by means of FT-IR spectroscopy and chemical analysis. Obtained β-cyclodextrin-containing materials were characterized by X-ray diffraction, transmission electron microscopy, and low-temperature adsorption-desorption of nitrogen. In spite of commensurable loading of β-cyclodextrin groups attained by both proposed approaches (up to 0.028 μmol · m(-2)), it was found that co-condensation procedure provides uniform distribution of β-cyclodextrin functionalities in silica framework, whereas postsynthesis grafting results in modification of external surface of silica surface. Adsorption of benzene from aqueous solutions onto the surface of β-cyclodextrin-containing materials prepared by co-condensation method was studied as the function of time and equilibrium concentration. Langmuir and Freundlich models were used to evaluate adsorption processes and parameters. Adsorption experiments showed that β-cyclodextrin-containing silicas could be promising for the trace amount removal of aromatics from water.