Thermal Behavior and Structural Study of SiO2/Poly(ε-caprolactone) Hybrids Synthesized via Sol-Gel Method.

SiO2-based organic-inorganic hybrids (OIHs) are versatile materials whose properties may change significantly because of their thermal treatment. In fact, after their preparation at low temperature by the sol-gel method, they still have reactive silanol groups due to incomplete condensation reactions that can be removed by accelerating these processes upon heating them in controlled experimental conditions. In this study, the thermal behavior of pure SiO2 and four SiO2-based OIHs containing increasing amount (6, 12, 24 and 50 wt %) of poly(ε-caprolactone) (PCL) has been studied by simultaneous thermogravimetry (TG) and differential scanning calorimetry (DSC). The FTIR analysis of the gas mixture evolved at defined temperatures from the samples submitted to the TG experiments identified the mechanisms of thermally activated processes occurring upon heating. In particular, all samples already release ethanol at low temperature. Moreover, thermal degradation of PCL takes place in the richest-PCL sample, leading to 5-hexenoic acid, H2O, CO2, CO and ε-caprolactone. After the samples' treatment at 450, 600 and 1000 °C, the X-ray diffraction (XRD) spectra revealed that they were still amorphous, while the presence of cristobalite is found in the richest-PCL material.

Zirconia/Hydroxyapatite Composites Synthesized Via Sol-Gel: Influence of Hydroxyapatite Content and Heating on Their Biological Properties.

Zirconia (ZrO2) and zirconia-based glasses and ceramics are materials proposed for use in the dental and orthopedic fields. In this work, ZrO2 glass was modified by adding different amounts of bioactive and biocompatible hydroxyapatite (HAp). ZrO2/HAp composites were synthesized via the sol-gel method and heated to different temperatures to induce modifications of their chemical structure, as ascertained by Fourier transform infrared spectroscopy (FTIR) analysis. The aim was to investigate the effect of both HAp content and heating on the biological performances of ZrO2. The materials' bioactivity was studied by soaking samples in a simulated body fluid (SBF). FTIR and scanning electron microscopy (SEM)) analyses carried out after exposure to SBF showed that all materials are bioactive, i.e., they are able to form a hydroxyapatite layer on their surface. Moreover, the samples were soaked in a solution containing bovine serum albumin (BSA). FTIR analysis proved that the synthesized materials are able to adsorb the blood protein, the first step of cell adhesion. WST-8 ([2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium, monosodium salt]) assay showed that no cytotoxicity effects were induced by the materials' extract. However, the results proved that bioactivity increases with both the HAp content and the temperature used for the thermal treatment, whereas biocompatibility increases with heating but is not affected by the HAp content.

Modification of Ti6Al4V implant surfaces by biocompatible TiO2/PCL hybrid layers prepared via sol-gel dip coating: Structural characterization, mechanical and corrosion behavior.

Surface modification of metallic implants is a promising strategy to improve tissue tolerance, osseointegration and corrosion resistance of them. In the present work, bioactive and biocompatible organic-inorganic hybrid coatings were prepared using a sol-gel dip coating route. They consist of an inorganic TiO2 matrix in which different percentages of poly(ε-caprolactone) (PCL), a biodegradable and biocompatible polymer, were incorporated. The coatings were used to modify the surface of Ti6Al4V substrates in order to improve their wear and corrosion resistance. The chemical structure of the coatings was analyzed by attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy. Coating microstructure, mechanical properties and ability to inhibit the corrosion of the substrates were evaluated as a function of the PCL amount. Scanning electron microscopy (SEM) showed that the polymer allows to obtain crack-free coatings, but when high percentages were added uncoated areas appear. Nano-indentation tests revealed that, as expected, surface hardness and elastic modulus decrease as the percentage of polymeric matrix increases, but scratch testing demonstrated that the coatings are effective in preventing scratching of the underlying metallic substrate, at least for PCL contents up to 20wt%. The electrochemical tests (polarization curves acquired in order to evaluate the corrosion resistance) allowed to asses that the coatings have a significant effect in term of corrosion potential (Ecorr) but they do not significantly affect the passivation process that titanium undergoes in contact with the test solution used (modified Dulbecco's phosphate-buffered saline or DPBS).

Entrapping quercetin in silica/polyethylene glycol hybrid materials: Chemical characterization and biocompatibility.

Sol-gel synthesis was exploited to entrap quercetin, a natural occurring antioxidant polyphenol, in silica-based hybrid materials, which differed in their polyethylene glycol (PEG) content (6, 12, 24 and 50wt%). The materials obtained, whose nano-composite nature was ascertained by Scanning Electron Microscopy (SEM), were chemically characterized by Fourier Transform InfraRed (FT-IR) and UV-Vis spectroscopies. The results prove that a reaction between the polymer and the drug occurred. Bioactivity tests showed their ability to induce hydroxyapatite nucleation on the sample surfaces. The direct contact method was applied to screen the cytotoxicity of the synthetized materials towards fibroblast NIH 3T3 cells, commonly used for in vitro biocompatibility studies, and three nervous system cell lines (neuroblastoma SH-SY5Y, glioma U251, and pheochromocytoma PC12 cell lines), adopted as models in oxidative stress related studies. Using the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay NIH 3T3 proliferation was assessed and the morphology was not compromised by direct exposure to the materials. Analogously, PC-12, and U-251 cell lines were not affected by new materials. SH-SY5Y appeared to be the most sensitive cell line with cytotoxic effects of 20-35%.

Sol-gel synthesis and characterization of SiO2/PCL hybrid materials containing quercetin as new materials for antioxidant implants.

The development of biomaterials with intrinsic antioxidant properties could represent a valuable strategy for preventing peri-implant disease onset. In this context quercetin, a naturally occurring flavonoid, has been entrapped, at different weight percentages in a silica/poly(ε-caprolactone)-based hybrid material by a sol-gel route. FT-IR and UV spectroscopic techniques were employed in order to characterize the hybrids. FT-IR analysis indicated changes in stretching frequencies of the quercetin dienonic moiety, suggesting that a flavonol oxidized derivative was formed during the sol-gel process. The establishment of hydrogen-bonded interactions between quercetin and silica and polymer matrices,was strongly affected by the amount of polymer. Poly(ε-caprolactone) did not interact with quercetin when it was loaded at high doses (50 wt.%). The morphology of the synthesized materials was observed by using SEM. The obtained images proved that the materials are hybrid nanocomposites. Their bioactivity was shown by the formation of a hydroxyapatite layer on samples' surface soaked in a fluid simulating the composition of the human plasma. The antiradical properties of the investigated systems were evaluated by DPPH and ABTS methods and their cytotoxicity by the MTT assay. Data obtained revealed that the synthesized materials are biocompatible and that the hybrid system,with 6 wt.% of PCL and 15 wt.% of quercetin, produced the strongest antiradical efficacy.

Silica/quercetin sol-gel hybrids as antioxidant dental implant materials.

The development of biomaterials with intrinsic antioxidant properties could represent a valuable strategy for preventing the onset of peri-implant diseases. In this context, quercetin, a naturally occurring flavonoid, has been entrapped at different weight percentages in a silica-based inorganic material by a sol-gel route. The establishment of hydrogen bond interactions between the flavonol and the solid matrix was ascertained by Fourier transform infrared spectroscopy. This technique also evidenced changes in the stretching frequencies of the quercetin dienonic moiety, suggesting that the formation of a secondary product occurs. Scanning electron microscopy was applied to detect the morphology of the synthesized materials. Their bioactivity was shown by the formation of a hydroxyapatite layer on sample surface soaked in a fluid that simulates the composition of human blood plasma. When the potential release of flavonol was determined by liquid chromatography coupled with ultraviolet and electrospray ionization tandem mass spectrometry techniques, the eluates displayed a retention time that was 0.5 min less than quercetin. Collision-activated dissociation mass spectrometry and untraviolet-visible spectroscopy were in accordance with the release of a quercetin derivative. The antiradical properties of the investigated systems were evaluated by DPPH and ABTS methods, whereas the 2,7-dichlorofluorescein diacetate assay highlighted their ability to inhibit the H2O2-induced intracellular production of reactive oxygen species in NIH-3T3 mouse fibroblast cells. Data obtained, along with data gathered from the MTT cytotoxicity test, revealed that the materials that entrapped the highest amount of quercetin showed notable antioxidant effectiveness.

Influence of PCL on mechanical properties and bioactivity of ZrO2-based hybrid coatings synthesized by sol-gel dip coating technique.

The biological properties of medical implants can be enhanced through surface modifications such as to provide a firm attachment of the implant. In this study, organic-inorganic hybrid coatings have been synthesized via sol-gel dip coating. They consist of an inorganic ZrO2 matrix in which different amounts of poly(ε-caprolactone) have been entrapped to improve the mechanical properties of the films. The influence of the PCL amount on the microstructural, biological and mechanical properties of the coating has been investigated. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses have shown that the hybrids used for the coating are homogenous and totally amorphous materials; Fourier transform infrared spectroscopy (FT-IR) has demonstrated that hydrogen bonds arise between the organic and inorganic phases. SEM and atomic force microscopy (AFM) have highlighted the nanostructured nature of the film. SEM and EDS analyses, after soaking the samples in a simulated body fluid (SBF), have pointed out the apatite formation on the coating surface, which proves the bone-bonding ability of the nanocomposite bioactive films. Scratch and nano-indentation tests have shown that the coating hardness, stiffness and Young's modulus decrease in the presence of large amounts of the organic phase.

Release kinetics of anti-inflammatory drug, and characterization and bioactivity of SiO2+PCL hybrid material synthesized by sol-gel processing.

BACKGROUND: Controlled and local drug delivery systems of anti-inflammatory agents are drawing increasing attention thanks to their possible pharmaceutical and biomedical applications. These systems have extended therapeutic effects and reduced side effects.
 METHODS: A single-step sol-gel process was used to prepare organic-inorganic hybrid materials based on silica (SiO2) and poly-ε-caprolactone, containing ketoprofen for controlled drug delivery applications. Fourier transform infrared spectroscopy analysis proved formation of H-bonds among the carbonyl groups of the polymer chains and Si-OH group of the inorganic matrix. X-ray diffraction analysis highlighted the amorphous nature of the synthesized materials. Scanning electron microscopy and atomic force microscope topography showed their homogeneous morphology and nanostructure nature. 
 RESULTS: The bioactivity of the synthesized hybrid materials was shown by the formation of a layer of hydroxyapatite on the surface of samples soaked in a simulated body fluid (SBF). 
 CONCLUSION: Release kinetics in SBF were subsequently investigated by means of UV-VIS spectroscopy. A large amount of drug release occurred during the first few hours, then a slower drug release supplied a maintenance dose until the end of the experiment.

Preparation, characterization, and biological properties of organic-inorganic nanocomposite coatings on titanium substrates prepared by sol-gel.

When surface-reactive (bioactive) coatings are applied to medical implants by means of the sol-gel dip-coating technique, the biological proprieties of the surface of the implant can be locally modified to match the properties of the surrounding tissues to provide a firm fixation of the implant. The aim of this study has been to synthesize, via sol-gel, organoinorganic nanoporous materials and to dip-coat a substrate to use in dental applications. Different systems have been prepared consisting of an inorganic zirconium-based matrix, in which a biodegradable polymer, the poly-ε-caprolactone was incorporated in different percentages. The materials synthesized by the sol-gel process, before gelation, when they were still in sol phase, have been used to coat a titanium grade 4 (Ti-4) substrate to change its surface biological properties. Thin films have been obtained by means of the dip-coating technique. A microstructural analysis of the obtained coatings was performed using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy. The biological proprieties have been investigated by means of tests in vitro. The bone-bonding capability of the nanocomposite films has been evaluated by examining the appearance of apatite on their surface when plunged in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. The examination of apatite formation on the nanocomposites, after immersion in SBF, has been carried out by SEM equipped with energy-dispersive X-ray spectroscopy. To evaluate cells-materials interaction, human osteosarcoma cell line (Saos-2) has been seeded on specimens and cell vitality evaluated by WST-8 assay.

Synthesis of SiO2 system via sol-gel process: biocompatibility tests with a fibroblast strain and release kinetics.

SiO2 glass has been synthesized via sol-gel process and enriched with 5 wt % sodium ampicillin. To verify the biocompatibility of the obtained biomaterial, fibroblasts have been grown on a glass surface and were tested for viability after 24 h. The results of the Water-Soluble Tetrazolium (WST)-8 analysis suggest that SiO2 glass has an adequate biocompatibility. The amorphous nature of the gels has been ascertained by X-ray diffraction analysis. Release kinetics have been subsequently investigated in a simulated body fluid. The amount of sodium ampicillin released has been detected by ultraviolet-visible spectroscopy. The release kinetics seems to occur in more than one stage. High-performance liquid chromatography analysis has also been carried out to ensure the integrity of ampicillin after the synthesis treatment.

Anti-inflammatory entrapment in polycaprolactone/silica hybrid material prepared by sol-gel route, characterization, bioactivity and in vitro release behavior.

AIM: A novel organic/inorganic hybrid material, based on poly(ε-caprolactone) (PCL) and silica (SiO2), were synthesized by the sol-gel method. An anti-inflammatory agent (indomethacin) was incorporated into the hybrid material to verify its local controlled drug delivery system. METHODS: The structure of the interpenetrating network was investigated by Fourier transform infrared spectroscopy. The morphology of the materials was studied by scanning electron microscopy. The structure of a molecular level dispersion was disclosed by atomic force microscopy. The bioactivity of the synthesized hybrid materials was revealed by the formation of a layer of hydroxyapatite on the surface of samples soaked in a simulated body fluid (SBF). Release kinetics in SBF were subsequently investigated. The amount of drug released was detected by UV-VIS spectroscopy. RESULTS: Pure anti-inflammatory agent exhibited linear release with time; in contrast, sol-gel silica entrapped drugs were released with a logarithmic time dependence starting with an initial burst effect followed by a gradual decrease. CONCLUSIONS: SiO2/PCL (3, 6, 9 and 12 %wt) materials, prepared via sol-gel process, are organic/inorganic hybrid and bioactive materials. All the materials showed a good release and therefore could be used as drug delivery system.

Poly(ε-caprolactone) reinforced with sol-gel synthesized organic-inorganic hybrid fillers as composite substrates for tissue engineering.

PURPOSE: The importance of polymer-based composite materials to make multifunctional substrates for tissue engineering and the strategies to improve their performances have been stressed in the literature. Bioactive features of sol-gel synthesized poly(ε-caprolactone)/TiO2 or poly(ε-caprolactone)/ZrO2 organic-inorganic hybrid materials are widely documented. Accordingly, the aim of this preliminary research was to develop advanced composite substrates consisting of a poly(ε-caprolactone) matrix reinforced with sol-gel synthesized PCL/TiO2 or PCL/ZrO2 hybrid fillers. METHODS: Micro-computed tomography and atomic force microscopy analyses allowed to study surface topography and roughness. On the other hand, mechanical and biological performances were evaluated by small punch tests and Alamar Blue™ assay, respectively. RESULTS: Micro-computed tomography and atomic force microscopy analyses highlighted the effect of the preparation technique. Results from small punch tests and Alamar Blue™ assay evidenced that PCL reinforced with Ti2 (PCL=12, TiO2=88 wt%) and Zr2 (PCL=12, ZrO2=88 wt%) hybrid fillers provided better mechanical and biological performances. CONCLUSIONS: PCL reinforced with Ti2 (PCL=12, TiO2=88 wt%) and Zr2 (PCL=12, ZrO2=88 wt%) hybrid fillers could be considered as advanced composite substrates for hard tissue engineering.