The sol-gel process is based on the hydrolysis and condensation of metal or silicon alkoxides and is used to obtain a variety of high-purity inorganic oxides or hybrid inorganic-organic materials that are simple to prepare. This process can be employed for the synthesis of functionalized silica with controlled particle size and shape. Apart from the several applications mentioned in the first paragraph of this chapter, more recently, biomaterials have been utilized as drug delivery systems (DDSs). In this sense, polymers and biodegradable polymers emerge as potential materials, since they promote temporal and targeted drug release. Indeed, biomaterials have had an enormous impact on human health care. Applications include medical devices, diagnosis, sensors, tissue engineering, besides the aforementioned DDSs.

In the latter field, an ideal drug deliverer should be able to lead a biologically active molecule at the desired rate and for the desired duration to the desired target, so as to maintain the drug level in the body at optimum therapeutic concentrations with minimum fluctuation. The use of DDSs overcomes the problems related to conventional administration routes, such as oral and intravenous administration. Several biomaterials have been applied as DDSs. This is because they are biocompatible and/or biodegradable, which allows for consecutive administrations. Hydroxyapatite-based materials, natural and synthetic polymers, silica, clays and other layered double hydroxides, and lipids are some examples of biomaterials that have been employed for the delivery of active molecules through the body. Liposomes, solid lipid nanoparticles, polymeric nano and microparticles, micelles, dendrimers, metallic nanoparticles, and nanoemulsion are currently utilized as DDSs. Special attention has been given to DDSs comprised of biodegradable polymers and silica.

In polymeric DDSs, the drugs are incorporated into a polymer matrix. Since biodegradable polymers are degraded to non-toxic substances, they do not have to be removed after implantation. So they have become attractive candidates for DDS applications. The rate of drug release from polymeric matrices depends on several parameters such as the nature of the polymer matrix, matrix geometry, drug properties, initial drug loading, and drug– matrix interaction. Moreover, the drugs can be effectively released by bioerosion of the matrices. Thus, both natural, frequently polysaccharides, and synthetic biodegradable polymers, usually aliphatic polyesters such as PLA, PGA, and their copolymer (PLGA), are the most extensively investigated biodegradable materials for drug delivery applications [1]. Inorganic materials, like silica, can offer the necessary properties for a nanoparticle to be applied as DDS, especially nontoxicity, biocompatibility, high stability, and a hydrophilic and porous structure.

The drug release rate from the silica structures could be controlled by adjusting particle size and porous structure. The sol-gel technology is also employed in the preparation of inorganic ceramic and glass materials. This technique was first used in the mid-1800s, when Ebelman and Graham carried out studies on silica gels. Initially, the sol-gel process was utilized in the preparation of silicate from tetraethylorthosilicate (TEOS, Si(OC2H5)4), which is mixed with water and a mutual solvent, to form a homogeneous solution. Recently, new reagents have appeared, so novel inorganic oxides and hybrid organic-inorganic materials can be synthesized using this methodology.

Thanks & Regards,
Nicola B
Editorial Team
Journal of Biochemistry & Biotechnology