Silica-Based Stimuli-Responsive Systems for Antitumor Drug Delivery and Controlled Release

The administration of cytotoxic drugs in classical chemotherapy is frequently limited by water solubility, low plasmatic stability, and a myriad of secondary effects associated with their diffusion to healthy tissue. In this sense, novel pharmaceutical forms able to deliver selectively these drugs to the malign cells, and imposing a space-time precise control of their discharge, are needed. In the last two decades, silica nanoparticles have been proposed as safe vehicles for antitumor molecules due to their stability in physiological medium, high surface area and easy functionalization, and good biocompatibility. In this review, we focus on silica-based nanomedicines provided with specific mechanisms for intracellular drug release. According to silica nature (amorphous, mesostructured, and hybrids) nanocarriers responding to a variety of stimuli endogenously (e.g., pH, redox potential, and enzyme activity) or exogenously (e.g., magnetic field, light, temperature, and ultrasound) are proposed. Furthermore, the incorporation of targeting molecules (e.g., monoclonal antibodies) that interact with specific cell membrane receptors allows a selective delivery to cancer cells to be carried out. Eventually, we present some remarks on the most important formulations in the pipeline for clinical approval, and we discuss the most difficult tasks to tackle in the near future, in order to extend the use of these nanomedicines to real patients.

Alkali-etching growth of nest-like Ag@mTiO2 hierarchical nanostructures and their potential applications

Porous nanomaterials have attracted extensive interests in adsorption, catalysis, biosensors, and biomedicine due to their high surface area, well-defined pore structure and tunable pore size. However, how to obtain porous nanomaterials of desirable component and unique structure with multifunctionalities and synergetic properties is still a great challenge. In this work, a novel nest-like Ag@mTiO₂ hierarchical nanostructure with Ag nanoparticle as the core and a mesoporous crystalline TiO₂ as the protective shell was successfully prepared by layer-by-layer assembly technique and alkali-etching hydrothermal route. By simply changing the conditions of alkali etching, different nanostructures could be obtained, such as core-shell or rattle type. In the process, the thickness of coating silica layer and TiO₂ shell both played important roles for the formation of desired nanostructures. The as-prepared products had a large specific surface area of 301m²/g and a tailored TiO₂ outer shell. Raman spectra results showed perfect SERS signal of the tags enhanced and remained good stability even after one month. Doxycycline (Doxy) was chosen to evaluate their drug loading and controlled release properties. The results indicated that the obtained Ag@mTiO₂ nanoparticles exhibited good biocompatibility and excellent drug-loading capacity. Consequently, they are also expected to serve as ideal candidates for more potential applications including photocatalysis, drug controlled release, biosensor and cell imaging, etc.

Au nanoparticle-embedded SiO2–Au@SiO2 catalysts with improved catalytic activity, enhanced stability to metal sintering and excellent recyclability

Au NP-embedded SiO₂ (SiO₂–Au@SiO₂) particles with the improved molecule accessibility, catalyst stability and catalytic performance were successfully synthesized by post-treatments such as calcination and/or etching with water or ammonia.

Gd–Si oxide mesoporous nanoparticles with pre-formed morphology prepared from a Prussian blue analogue template

A novel approach to the synthesis of Gd–Si oxide mesoporous nanoparticles is carried out by using a Prussian blue analogue as a sacrificial template and a further pseudomorphic transformation.

Hydrothermal synthesis of mesoporous silica spheres: effect of the cooling process

Hydrothermal methods have been widely used in the fabrication of silica-based micro-/nanomaterials. In this paper, we comprehensively investigated dissolution/regrowth kinetics of solid silica in alkaline media under relatively high temperature hydrothermal conditions (typically 180 °C). A decoupled dissolution and regrowth mechanism was proposed to explain the transformation of solid silica to mesoporous silica spheres in the presence of CTAB surfactant. Especially, we discovered that the "post-synthesis" sample cooling process plays a great role in the present hydrothermal process. The proposed mechanism can be utilized for the preparation of mesoporous silica spheres from various silica sources. Moreover, the mechanism is also applicable to other nonsurfactant hydrothermal processes.

Spontaneous deposition of gold nanoparticle nanocomposite on polymer surfaces through sol-gel chemistry

A aminosilica nanocomposite layer containing a monolayer of gold nanoparticles (d = 18-22 nm) with a well-defined spacing was spontaneously deposited on an unmodified polystyrene surface via a sol-gel reaction when the reduction reaction was carried out under 1:8 molar ratio (gold(III):aminosilane). The amount of aminosilica and spacing between gold nanoparticles were found to be a function of the aminosilane:water molar ratio, which contributes to the plasmonic property of the films with its absorption wavelength ranging between 701 and 548 nm. Furthermore, the nanocomposite film that consists of a monolayer of nanoparticles in aminosilica has also been deposited on the surface of polystyrene beads. This core-shell structure was found capable of storing electrostatic charges and forming a well-separated 2D array.