Silica biocompatibility

Z. Stmad, J. Sestak, J. Strnad, N. Koga Thermodynamics ofhon-bridging oxygen in silica biocompatible glasses J. Thermal Anal. Calor. 71(2003)927 and 76(2004)17... 

The realization of the reasons for poor biocompatibility of general alkoxides with biopolymers led to the development of approaches to minimize or eliminate the problem of the detrimental effect of alcohols. This can be done in two ways modification of the sol-gel processing or the silica precursor. This is considered in some detail below. 

It should be pointed out that the addition of substances, which could improve the biocompatibility of sol-gel processing and the functional characteristics of the silica matrix, is practiced rather widely. Polyethylene glycol) is one of such additives [110— 113]. Enzyme stabilization was favored by formation of polyelectrolyte complexes with polymers. For example, an increase in the lactate oxidase and glycolate oxidase activity and lifetime took place when they were combined with poly(N-vinylimida-zole) and poly(ethyleneimine), respectively, prior to their immobilization [87,114]. To improve the functional efficiency of entrapped horseradish peroxidase, a graft copolymer of polyvinylimidazole and polyvinylpyridine was added [115,116]. As shown in Refs. [117,118], the denaturation of calcium-binding proteins, cod III parvalbumin and oncomodulin, in the course of sol-gel processing could be decreased by complexation with calcium cations. 

It did not give rise to phase separation or precipitation. Similar behavior was observed when other types of polysaccharides were examined [53,54]. By now all the commercially important polysaccharides have been applied to the fabrication of hybrid silica nanocomposites in accordance with Scheme 3.2. What is more, various proteins have been entrapped in silica by the same means. In all instances the THEOS demonstrated good biocompatibility with biopolymers, even though its amount in formulations was sometimes up to 60 wt%. Biopolymer solutions after the precursor admixing remained homogeneous to the point of transition into a gel state. 

Ferrer, M.L., Yuste, L., Rojo, F. and Del Monte, F. (2003) Biocompatible sol-gel route for encapsulation of living bacteria in organically modified silica matrixes. Chemistry of Materials 15, 3614-3618. 

Schiraldi et al. [64] have developed this kind of material by combining silica particles and pHEMA. pHEMA is a biocompatible hydrogel that has been widely studied in the past decades due to its chemical-physical structure and mechanical properties. It has been widely used in ophthalmic prostheses (contact or intraocular lenses), vascular prostheses, drug delivery systems and soft-tissue replacement [65]. These authors have shown that by incorporating silica nanoparticles, the resulting hybrid material is highly biocompatible and promotes bone cell adhesion and proliferation of bone cells seeded on it.1 ... 

Although the biocompatibility and biodegradability of these materials were rapidly determined, the bioactivity of Si02-PCL hybrid materials was not studied until recently [99]. In order to provide bioactivity to Si02-PCL hybrid materials, Rhee prepared triethoxysilane end-capped poly(s-caprolactone) which was then cocondensed with tetraethyl orthosilicate and calcium nitrate via the sol-gel method. The Ca-containing PCL/silica hybrid so obtained showed in vitro bioactivity and biodegradability. The hybridization procedure between the a,co-hydroxyl PCL and silica phases was proposed to be as follows ... 

Silica-based materials obtained by the sol-gel process are perhaps the most promising class of functional materials capable to meet such a grand objective. In the sol-gel process liquid precursors such as silicon alkoxides are mixed and transformed into silica via hydrolytic polycondensation at room temperature. Called soft chemitry or chimie douce, this approach to the synthesis of glasses at room temperature and pressure and in biocompatible conditions (water, neutral pH) has been pioneered by Livage and Rouxel in the 1970s, and further developed by Sanchez, Avnir, Brinker and Ozin. 

Template synthesized silica nanotubes (SNTs) provide unique features such as end functionalization to control drug release, inner voids for loading biomolecules, and distinctive inner and outer surfaces that can be differentially functionalized for targeting and biocompatibility.50 A general path to synthesize nanotubes utilizes anisotropic materials as template. They are coated with silica using Si(OR)4 precursors and nanotubes of Si02 are obtained after removal of the template (Figure 1.24). 

Biocompatible silica nanoparticles prepared by analogous sol formation followed by emulsification and doped with the antibiotic... 

As was demonstrated, a variety of polymeric materials are used for preparation of dye-doped beads. Dye-doped silica beads are also extremely popular due to their chemical robustness, biocompatibility and simplicity in preparation and further functionalization of the surface [55]. Thus, polymeric, silica and Ormosil beads (which occupy intermediate position) are widely used as nanosensors and labels. On the other hand, quantum dots possess much higher cytotoxicity which often limits their application in biological systems. 

Owing to the instability of silica gel based columns at pH values <2.0 or >8.0, mobile phases must have a pH range of 2.1-7.5. Within this range, a large number of solvent systems have been described. Solvent systems are selected on the basis of several criteria optimal resolution, volatility, LTV transparency, biocompatibility, selectivity, viscosity, and cost. 

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