Abstract
Silica is one of the most abundant minerals in the Earth’s crust, and over time it has been introduced first into human life and later into engineering. Silica is present in the food chain and in the human body. As a biomaterial, silica is widely used in dentistry, orthopedics, and dermatology. Recently amorphous sol-gel SiO2 nanoparticles (NPs) have appeared as nanocarriers in a wide range of medical applications, namely in drug/gene target delivery and imaging diagnosis, where they stand out for their high biocompatibility, hydrophilicity, enormous flexibility for surface modification with a high payload capacity, and prolonged blood circulation time. The sol-gel process is an extremely versatile bottom-up methodology used in the synthesis of silica NPs, offering a great variety of chemical possibilities, such as high homogeneity and purity, along with full scale pH processing. By introducing organic functional groups or surfactants during the sol-gel process, ORMOSIL NPs or mesoporous NPs are produced. Colloidal route, biomimetic synthesis, solution route and template synthesis (the main sol-gel methods to produce monosized silica nanoparticles) are compared and discussed. This short review goes over some of the emerging approaches in the field of non-porous sol-gel silica NPs aiming at medical applications, centered on the syntheses processes used.
Highlights
Silica (SiO2 ) has been used throughout history in the manufacturing of glass, ceramics, concrete, mortar, sandstone and silicones [1]
Dissolution rates of amorphous silica phases, which involves an equilibrium between the solid phase and dissolve disorder enabled the loss of surface (SiO4 )4− Q3 units into solution and keeping unchanged the a-SiO2 surface Gibbs energy
A bottom-up strategy holds a large number of techniques but research has been focused on sol-gel, as the synthesis is straightforward, scalable, controllable, time and energy saving
Summary
Silica (SiO2 ) has been used throughout history in the manufacturing of glass, ceramics, concrete, mortar, sandstone and silicones [1]. Stand out for their global market shares in sol-gel silica NPs. As to pharmaceutical and medical applications, the Canadian company PreveCeutical (Vancouver, BC, Canada) has developed (and patented) a sol-gel delivery platform for Nose-to-Brain Delivery of Therapeutic Compounds® , the first. Sol-gels are taken via nasal (systemic) administration and rapidly gel upon contact with mucosal tissue allowing a direct nose-to-brain delivery by slow releasing of drug/therapeutic molecules. USA Cd Creative Diagnostics (Shirley, NY, USA) has commercialized a wide range of plain and core-shell (iron oxide magnetic core) sol-gel silica NPs while the French company NH TherAguix (Crolles, France) provides ultra-small sol-gel silica-based bismuth/gadolinium contrast agents. The Israeli (clinical-stage) company Sol Gel Technologies (Ness Ziona, Israel) focuses on developing and commercializing topical dermatological drug products, based on its proprietary sol-gel microencapsulation delivery system.
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