Fibroblast growth and polymorphonuclear granulocyte activation in the presence of a new biologically active sol-gel glass

Investigation of bioactivity, biocompatibility and thermal behavior of sol-gel silica glass containing a high PEG percentage

SiO2/PEG organic-inorganic hybrid materials, which contain 60 or 70 weight percentage of PEG, were synthesized by the sol-gel technique. The materials were characterized and subjected to various tests to assess their application in the biomedical field. The evaluation of their morphology by scanning electron microscopy (SEM) confirms the homogeneity of the samples on the nanometer scale. Fourier transform infrared spectroscopy (FT-IR) indicated that the two components of the hybrids (SiO2 and PEG) are linked by hydrogen bonds. This feature makes them class I hybrids. Simultaneous thermogravimetry/differential thermal analysis (TG/DTA) was used to investigate their thermal behavior and to establish the best temperatures for their pre-treatment. The fundamental properties that a material must have to be used in the biomedical field are biocompatibility and bioactivity. The formation of a hydroxyapatite layer was observed on the hybrid surface by SEM/EDX and FTIR after soaking in simulated body fluid. This indicates that the materials are able to bond to bone tissue. Moreover, the biocompatibility of SiO2/PEG hybrids was assessed by performing WST-8 cytotoxicity tests on fibroblast cell NIH 3T3 after 24h of exposure. The cytotoxicity tests highlight that the cell viability is affected by the polymer percentage. The results showed that the synthesized materials were bioactive and biocompatible. Therefore, the results obtained are encouraging for the use of the obtained hybrids in dental or orthopedic applications.

Influence of the polymer amount on bioactivity and biocompatibility of SiO2/PEG hybrid materials synthesized by sol-gel technique

SiO2/PEG organic-inorganic hybrid materials, which differ in polyethylene glycol (PEG) content, were synthesized by sol-gel technique and the characterization of their structure and biological properties was carried out in order to evaluate the possible use in biomedical field. FT-IR spectroscopy detected that the two components of the hybrids (SiO2 and PEG) are linked by hydrogen bonds between the Si-OH groups of the inorganic phase and the terminal alcoholic groups and/or the ethereal oxygen atoms in the repeating units of polymer. X-ray diffraction analysis ascertained the amorphous nature of the gels and the observation of their morphology by SEM microscopy confirmed that the interpenetration of the two phases (organic and inorganic) occurs on nanometric scale. The biological characterization was carried out as a function of the polymer amount to study its influence on material behavior. The results showed that the synthesized materials were bioactive and biocompatible. The formation of a hydroxyapatite layer, indeed, was observed on their surface by SEM/EDX analysis after soaking in simulated body fluid. Moreover, the biocompatibility of SiO2/PEG hybrids was assessed performing MTT and SRB cytotoxicity tests on fibroblast cell NIH 3T3 after 24 and 48h of exposure, as well as Trypan Blue dye exclusion test. The response to the presence of the investigated materials was positive. The cell growth and proliferation showed dependence on polymer amount and time of exposure to the material extracts. Therefore, the obtained results are encouraging for the use of the obtained hybrids in dental or orthopedic applications.

Tailoring the degradation kinetics of mesoporous silicon structures through PEGylation

Injectable and implantable porosified silicon (pSi) carriers and devices for prolonged and controlled delivery of biotherapeutics offer great promise for treatment of various chronic ailments and acute conditions. Polyethylene glycols (PEGs) are important surface modifiers currently used in clinic mostly to avoid uptake of particulates by reticulo-endothelial system (RES). In this work we show for the first time that covalent attachment of PEGs to the pSi surface can be used as a means to tune degradation kinetics of silicon structures. Seven PEGs with varying molecular weights (245, 333, 509, 686, 1214, 3400, and 5000 Da) were employed and the degradation of PEGylated pSi hemispherical microparticles in simulated physiological conditions was monitored by means of ICP-AES, SEM, and fluorimetry. Biocompatibility of the systems with human macrophages in vitro was also evaluated. The results clearly indicate that controlled PEGylation of silicon microparticles can offer a sensitive tool to finely tune their degradation kinetics and that the systems do not induce release of proinflammatory cytokines IL-6 and IL-8 in THP1 human macrophages.

Silica-Polyethylene Glycol Matrix Synthesis by Sol-Gel Method and Evaluation for Diclofenac Diethyloammonium Release

Modified silica-polyethylene glycol xerogels were prepared by the sol-gel method to explore the possibilities of using these polymers as drug delivery systems. The synthesis was performed at room temperature and under atmospheric pressure using tetraethylorthosilicate (TEOS) as a precursor, low-molecular polyethylene-glycol (600) as a modifier, and acetic acid as a catalyst. The composition in a mole ratio of the initial sols corresponds to TEOS:H(2)O:EtOH:CH(3)COOH:PEG = 1:4:6:0.005:0.147. Diclofenac diethyloammonium was used as a model drug and encapsulated in predoping sol-gel process. After 5 days of gelation time of matrices at room temperature two different forms of xerogels were obtained: monolithic form of pellet and cracked, irregular-shaped of particles. The rate of release from the both forms of xerogels was controlled by the rate of diffusion of the drug through the pores. The dissolution testing for the loaded irregular-shaped xerogels showed an initial burst release followed by sustained release. The degradation of the PEG/silica xerogels followed a zero-order kinetics.

Evaluation of Silicon Dioxide–Based Coating Enriched with Bioactive Peptides Mapped on Human Vitronectin and Fibronectin:In VitroandIn VivoAssays

A wide range of biochemical signals promoting cell functions (adhesion, migration, proliferation, and differentiation) and thereby improving the osseointegration process are currently investigated. Unfortunately, their application for the production of bioactive implantable devices is often hampered by their insolubility; instability; and limited availability of a large amount of inexpensive, high-purity samples. An attractive alternative is the use of short peptides carrying the minimum active sequence of the natural factors. Synthetic peptides mapped on fibronectin and vitronectin have been demonstrated to enhance cell adhesion both to polystyrene and acellular bone matrix; in particular, a nonapeptide sequence from human vitronectin works via an osteoblast-specific adhesion mechanism. In this study, we incorporated these peptides into a sol-gel silica dressing applied to coat sand-blasted and acid-attacked titanium samples; measured the kinetic of peptide release; and used titanium disks, coated with a peptide-enriched film, as substrates to determine the peptide concentration that maximizes cell adhesion in vitro. We also evaluated in vivo the capacity of the vitronectin-derived peptide to improve osteogenic activity: histologic analysis revealed markedly improved osteogenic activity around peptide-enriched samples. This article also discusses the role of surface characteristics and the importance of bioactive peptides.

Assessment of polyglycolic acid mesh and bioactive glass for soft-tissue engineering scaffolds

Sufficient neovascularization of neotissue is currently a limiting factor for the engineering of large tissue constructs. 45S5 Bioglass has been investigated extensively in bone tissue engineering but there has been relatively little previous research on its application to soft-tissue engineering. The objectives of this study were to investigate the use of 45S5 Bioglass in soft-tissue engineering scaffolds using in vitro and in vivo models. A fibroblast cell line (208F) was used for in vitro evaluation of surfaces coated with 45S5 Bioglass. Increased proliferation of fibroblasts was observed after growth on polystyrene surfaces coated with low concentrations (0.01-0.2%wt/vol) of 45S5 Bioglass for 24 h in vitro, determined as a change in total cell number by measuring lactate dehydrogenase. At higher concentrations of 45S5 Bioglass and longer periods of incubation (48 and 72 h) on coated surfaces, cell proliferation was reduced. Light microscopy revealed that the morphology of fibroblasts grown on 45S5 Bioglass-coated surfaces was not altered at low concentrations, but at higher concentrations fibroblasts became vacuolated. Enzyme-linked immunosorbent assay of conditioned culture medium collected from fibroblasts grown for 24 h on surfaces coated with low concentrations of 45S5 Bioglass (0.01%wt/vol) was found to contain significantly higher concentrations of vascular endothelial growth factor. Histological examination of polyglycolic acid (PGA)/45S5 Bioglass composite scaffolds that had been implanted subcutaneously into rats revealed that 45S5 Bioglass-coated meshes were well tolerated. Light microscopy revealed that neovascularization into 45S5 Bioglass-coated meshes was significantly increased at 28 and 42 days. Electron microscopy revealed fibroblasts adhering closely to the PGA mesh but not to 45S5 Bioglass particles. The apparent ability of 45S5 Bioglass incorporated into scaffolds to increase neovascularization would be extremely beneficial during the engineering of larger soft-tissue constructs.

Silica xerogel as an implantable carrier for controlled drug delivery--evaluation of drug distribution and tissue effects after implantation

The purpose of the present study was to examine controlled delivery of toremifene citrate from subcutaneously implanted silica xerogel carrier and to evaluate silica xerogel related tissue effects after implantation. Toremifene citrate was incorporated into hydrolyzed silica sol in a room temperature process. Toremifene citrate treated silica xerogel implants were tested both in vitro and in vivo using healthy mice. Silica xerogel with tritium-labelled toremifene was implanted subcutaneously in mice for 42 d. To determine the amount of tritiated toremifene remaining in the silica discs at the implantation site, the discs were excised periodically and radioactivity measured. The amount of tritiated toremifene in the implant after 42 d was still about 16% and the amount of silica xerogel about 25%. In a histopathological study silica xerogel did not show any tissue irritation at the site of the implantation. A fibrotic capsule was formed around the implant. No silica xerogel related histological changes in liver, kidney, lymph nodes and uterus were observed during the implantation period. The silica xerogel discs showed a sustained release of toremifene citrate over 42 d. Histologically, toremifene-related changes in the uterus were also detectable at all studied time points. These findings suggest that silica xerogel is a promising carrier material for implantable controlled drug delivery system.

In vitro release behavior of toremifene citrate from sol-gel processed sintered silica xerogels

Factors affecting the adsorption and desorption of toremifene citrate (TC) on sintered silica xerogels were investigated in vitro. TC was attached onto sol-gel processed sintered silica xerogel grains or disks by adsorption. The adsorption of TC on the surface of silica was pH dependent. The results support the conclusion that large pore size results in highest drug adsorption. Adsorption of TC was most effective in xerogels sintered at 700 degrees C and containing the largest pores and lowest specific surface area of the silica xerogels studied in the adsorption tests. The release of TC from the xerogel matrix was linear with respect to the square root of time. The release of TC from the grains was very rapid for the first 5 hr, followed by a slower release. All drug was released from the grains, and 60% to 80% was released from the disks in 24 hr. All drug-silica xerogel formulations showed sustained in vitro release profiles.