In vitro and in vivo investigation of thermosensitive chitosan hydrogels containing silica nanoparticles for vaccine delivery.

In this work silica nanoparticles (SNP) containing the model antigen ovalbumin (OVA) were incorporated into a thermosensitive chitosan hydrogel, and the resulting formulation investigated for its potential to act as a particulate sustained release vaccine delivery system. OVA-loaded SNP and chitosan hydrogels containing OVA-loaded SNP were prepared and characterised in vitro, and examined for their ability to elicit OVA-specific immune responses in vivo. Optimised SNP were found to be approximately 300nm in size with a moderate level of heterogeneity, a highly negative zeta potential, and an entrapment efficiency of approximately 7%. A porous particulate structure was indicated both by electron microscopy and a rapid release of fluorescently-labelled OVA (FITC-OVA) from SNP. Following successful incorporation of SNP into chitosan hydrogels, the release of both soluble and SNP-associated antigen from gel systems was quantified. Approximately 16% of total protein was released in a particulate form over a 14-day period, while approximately 35% was released as soluble antigen. Gel-based systems containing SNP-associated or soluble antigen in the presence or absence of the adjuvant Quil A (QA) demonstrated an ability to stimulate both cell mediated and humoral immunity in vivo. Chitosan gels containing OVA-loaded SNP and the adjuvant QA showed a significantly greater ability to induce CD4(+) T cell proliferation than chitosan gel containing soluble OVA and QA, indicating the future promise for such a system.

Electrostatic self-assembly of PEG copolymers onto porous silica nanoparticles.

A critical requirement toward the clinical use of nanocarriers in drug delivery applications is the development of optimal biointerfacial engineering procedures designed to resist biologically nonspecific adsorption events. Minimization of opsonization increases blood residence time and improves the ability to target solid tumors. We report the electrostatic self-assembly of polyethyleneimine-polyethylene glycol (PEI-PEG) copolymers onto porous silica nanoparticles. PEI-PEG copolymers were synthesized and their adsorption by self-assembly onto silica surfaces were investigated to achieve a better understanding of structure-activity relationships. Quartz-crystal microbalance (QCM) study confirmed the rapid and stable adsorption of the copolymers onto silica-coated QCM sensors driven by strong electrostatic interactions. XPS and FT-IR spectroscopy were used to analyze the coated surfaces, which indicated the presence of dense PEG layers on the silica nanoparticles. Dynamic light scattering was used to optimize the coating procedure. Monodisperse dispersions of the PEGylated nanoparticles were obtained in high yields and the thin PEG layers provided excellent colloidal stability. In vitro protein adsorption tests using 5% serum demonstrated the ability of the self-assembled copolymer layers to resist biologically nonspecific fouling and to prevent aggregation of the nanoparticles in physiological environments. These results demonstrate that the electrostatic self-assembly of PEG copolymers onto silica nanoparticles used as drug nanocarriers is a robust and efficient procedure, providing excellent control of their biointerfacial properties.

Formation of silica nanoparticles in microemulsions.

Silica nanoparticles for controlled release applications have been produced by the reaction of tetramethylorthosilicate (TMOS) inside the water droplets of a water-in-oil microemulsion, under both acidic (pH 1.05) and basic (pH 10.85) conditions. In-situ FTIR measurements show that the addition of TMOS to the microemulsion results in the formation of silica as TMOS, preferentially located in the oil phase, diffuses into the water droplets. Once in the hydrophilic domain, hydrolysis occurs rapidly as a result of the high local concentration of water. Varying the pH of the water droplets from 1.05 to 10.85, however, considerably slows the hydrolysis reaction of TMOS. The formation of a dense silica network occurs rapidly under basic conditions, with IR indicating the slower formation of more disordered silica in acid. SAXS analysis of the evolving particles shows that approximately 11 nm spheres are formed under basic conditions; these are stabilized by a water/surfactant layer on the particle surface during formation. Under acidic conditions, highly uniform approximately 5 nm spheres are formed, which appear to be retained within the water droplets (approximately 6 nm diameter) and form an ordered micelle nanoparticle structure that exhibits sufficient longer-range order to generate a peak in the scattering at q approximately equal to 0.05 A-1. Nitrogen adsorption analysis reveals that high surface area (510 m2/g) particles with an average pore size of 1 nm are formed at pH 1.05. In contrast, base synthesis results in low surface area particles with negligible internal porosity.

Quantum dot and silica nanoparticle doped polymer optical fibers.

A novel and highly versatile doping method has been developed to allow active dopants, including materials incompatible with the polymer matrix, to be incorporated into microstructured polymer optical fibers through the use of nanoparticles. The incorporation of quantum dots and silica nanoparticles containing Rhodamine isothiocyanate is demonstrated.

Quantification of the contribution of surface outgrowth to biocatalysis in sol-gels: oxytetracycline production by Streptomyces rimosus.

A technique was developed for differentiating the activity of microbes solely within sol gels by using the contribution of biomass outgrowth. Streptomyces rimosus was immobilised in colloidal silica gels and biomass growth, oxytetracycline synthesis, pH and carbohydrate consumption were compared for UV surface-sterilised gels, untreated gels, and liquid cultures. Absolute and biomass specific oxytetracycline yields were higher for non-sterile gels than for liquid culture. Biomass solely within colloidal silica gels (1.7 mg ml(-1)), and gels obtained from colloidal silica modified by addition of larger silica particles (1.2 mg ml(-1)) yielded 27 and 21 microg ml(-1) oxytetracycline compared with 97 and 104 microg ml(-1) for unsterilised gels (3.6 and 5.2 mg ml(-1) biomass) displaying outgrowth. It was therefore apparent that biomass and antibiotic production within the gels was limited and that optimisation requires gel modification.

Vibrational Spectra and Molecular Association of Titanium Tetraisopropoxide.

The Fourier transform-infrared (FT-IR) and polarized FT-Raman spectra of titanium tetraisopropoxide (tetraisopropoxytitanium, TPT), in pure and diluted forms, and of 2-propanol have been investigated in conjunction with previous assignments for related compounds to obtain a comprehensive assignment of the vibrational spectra. Evidence was obtained for the presence of both monomeric and associated species of TPT. The latter are formed by coordination expansion through bridging isopropoxy ligands. For both monomeric and associated TPT species, vibrational modes of isopropoxy ligands with nu(C-O) mode character were coupled to nu(s)(Ti-O) and nu(as)(Ti-O) modes (interligand coupling). The symmetrically coupled ligand modes gave rise to intense, strongly polarized bands in the Raman spectrum. The antisymmetrically coupled ligand modes gave rise to strong bands in the IR spectrum at lower wavenumbers than the corresponding Raman bands. Molecular association of TPT produced negligible shifts in the ligand modes coupled to the nu(s)(Ti-O) mode in the Raman spectrum. In contrast, the degeneracy of the strong ligand modes coupled to the nu(as)(Ti-O) mode was lifted upon molecular association, yielding band shifts and splittings in the IR spectrum of neat TPT.