Characterization of Hybrid Materials Prepared by Sol-Gel Method for Biomedical Implementations. A Critical Review

The interaction between tissues and biomaterials (BM) has the purpose of improving and replacing anatomical parts of the human body, avoiding the occurrence of adverse reactions in the host organism. Unfortunately, the early failure of implants cannot be currently avoided, since neither a good mixture of mechanical and chemical characteristics of materials nor their biocompatibility has been yet achieved. Bioactive glasses are recognized to be a fine class of bioactive substances for good repair and replacement. BM interact with living bones through the formation of a hydroxyapatite surface layer that is analogous to bones. Bioglasses’ composition noticeably affects their biological properties, as does the synthesis method, with the best one being the versatile sol-gel technique, which includes the change of scheme from a ‘sol’ fluid into a ‘gel’. This process is widely used to prepare many materials for biomedical implants (e.g., hip and knee prostheses, heart valves, and ceramic, glassy and hybrid materials to serve as carriers for drug release). Nanoparticles prepared by the sol-gel method are interesting systems for biomedical implementations, and particularly useful for cancer therapy. This review provides many examples concerning the synthesis and characterization of the above-mentioned materials either taken from literature and from recently prepared zirconia/polyethylene glycol (PEG) hybrids, and the corresponding results are extensively discussed

Sol-Gel synthesis, spectroscopic and thermal behavior study of SiO2/PEG composites containing different amount of chlorogenic acid

In this work, new phenol-based materials have been synthesized by the sol-gel method, in which different amounts of the phenolic antioxidant chlorogenic acid (CGA) (from 5 wt % to 20 wt %) were embedded in two different silica matrices: pure silica and silica-based hybrids materials, containing 50 wt % of polyethylene glycol (PEG). The incorporation of CGA in different sol-gel matrices might protect them from degradation, which could cause the loss of their properties. The two series of materials were chemically characterized by Fourier transform infrared (FTIR) spectroscopy. In addition, the thermal behavior of both series of materials containing CGA was studied by thermogravimetry under both air and inert N2flowing gas atmosphere. The bioactivity was evaluated by soaking the synthesized hybrids in a simulated body fluid, showing that the bioactivity of the silica matrix is not modified by the presence of PEG and CGA

Thermal behavior and antibacterial studies of a carbonate Mg–Al-based layered double hydroxide (LDH) for in vivo uses

The goal of this work is to study the thermal behavior and the antibacterial properties of a MgAl-CO3 layered double hydroxide (LDH), which demonstrated high efficiency in removing chromium (VI) from contaminated industrial wastewater. The compound has been synthesized via co-precipitation route (direct method) followed by hydrothermal treatment, obtaining nanoscopic crystallites with a partially disordered (turbostratic) structure. After its synthesis, the compound was characterized by means of X-ray powder diffraction, field emission scanning electron microscope, inductively coupled plasma atomic emission spectroscopy and analysis and Fourier transform infrared spectroscopy. On the other hand, with the view to check the drug delivery and surgical tools usage of MgAl-CO3, antibacterial tests, performed according to the Kirby–Bauer method, revealed the inability the growth of the pathogenic bacterial strains. Thermogravimetry and differential thermal analysis revealed that evolution of water from the material occurs in two stages upon heating and a noticeable interaction takes place between water (in the vapor phase) and MgAl-CO3. Kinetic analysis of both steps provides almost constant values of activation energy, with the following average values in the range 0.1 < a < 0.9: E1 = (66 ± 9) kJ mol‒1; E2 = (106 ± 7) kJ mol‒1. Finally, prediction of reasonable reaction times extrapolated at 25 and 37 °C has been made from kinetic parameters of the first step, while almost unrealistic reaction time values were determined using the same procedure with kinetic parameters related to the second step

Thermal and spectroscopic (TG/DSC-FTIR) characterization of mixed plastics for materials and energy recovery under pyrolytic conditions

Seven waste thermoplastic polymers (polypropylene, polyethylene film, polyethylene terephthalate, polystyrene, acrylonitrile–butadiene–styrene, high-impact polystyrene and polybutadiene terephthalate, denoted as PP, PE (film), PET, PS, ABS, HIPS and PBT, respectively) and four synthetic mixtures thereof with different compositions representing commingled postconsumer plastic waste and waste of electrical and electronic equipment were studied by means of simultaneous thermogravimetry/differential scanning calorimetry coupled with Fourier transform infrared spectroscopy (TG/DSC–FTIR) under pyrolytic conditions (inert atmosphere). By summing all the heat change contributions due to physical and/or chemical processes occurring (i.e., melting, decomposition), an overall energy, defined as the degradation heat, was determined for both single component and their mixtures. It was found to be about 4–5 % of the exploitable energy of the input material. Vapors evolved during the pyrolysis of single-component polymers and their mixtures, analyzed using the FTIR apparatus, allowed identifying the main reaction products as monomers or fragments of the polymeric chain. Results from TG/DSC runs and FTIR analysis show that there is no interaction among the plastic components of the mixtures during the occurrence of pyrolysis

Thermal behavior study of pristine and modified halloysite nanotubes: A modern kinetic study

Pristine halloysite nanotubes (HNTs) were studied by thermogravimetry (TG) up to 800 C. Etching of alumina from inside the tube (causing a significant increase in tube lumen) was realized by treating the material with an acidic H2SO4 solution at 50 C. Both materials were characterized by TG-FTIR techniques and their thermal behaviors were compared with that of kaolinite. The coupling of TG with FTIR enables to detect the gases evolved during the TG experiments, thus confirming that only pristine HNTs undergo dehydration with the loss of interlayer water molecules at around 245 C, while dehydroxylation occurs in all these materials in close temperature ranges around 500 C. TG runs at five different heating rates (2, 5, 10, 15 and 20 C min-1), was carried out in the same experimental conditions used for the thermal analysis study with the aim to investigate dehydration and dehydroxylation kinetics using some isoconversional methods recommended by the ICTAC kinetic committee, and thermogravimetric data under a modulated rising temperature program. Finally, the results of the kinetic analysis were discussed and explained in terms of the strengths of the hydrogen bonds broken during these processes

Nanostructured Poly-l-lactide and Polyglycerol Adipate Carriers for the Encapsulation of Usnic Acid: A Promising Approach for Hepatoprotection

The present study investigates the utilization of nanoparticles based on poly-l-lactide (PLLA) and polyglycerol adipate (PGA), alone and blended, for the encapsulation of usnic acid (UA), a potent natural compound with various therapeutic properties including antimicrobial and anticancer activities. The development of these carriers offers an innovative approach to overcome the challenges associated with usnic acid’s limited aqueous solubility, bioavailability, and hepatotoxicity. The nanosystems were characterized according to their physicochemical properties (among others, size, zeta potential, thermal properties), apparent aqueous solubility, and in vitro cytotoxicity. Interestingly, the nanocarrier obtained with the PLLA-PGA 50/50 weight ratio blend showed both the lowest size and the highest UA apparent solubility as well as the ability to decrease UA cytotoxicity towards human hepatocytes (HepG2 cells). This research opens new avenues for the effective utilization of these highly degradable and biocompatible PLLA-PGA blends as nanocarriers for reducing the cytotoxicity of usnic acid

Vapor pressures and standard molar enthalpies, entropies and Gibbs energies of sublimation of two hexachloro herbicides using a TG unit

The vapor pressures above the solid hexachlorobenzene (HCB) and above both the solid and liquid 1,2,3,4,5,6-hexachlorocyclohexane (lindane) were determined in the ranges 332-450 K and 347-429 K, respectively, by measuring the mass loss rates recorded by thermogravimetry under both isothermal and nonisothermal conditions. The results obtained were compared with those taken from literature. From the temperature dependence of vapor pressure derived by the experimental thermogravimetry data the molar enthalpies of sublimation Delta(g)(cr)H(m)degrees() were selected for HCB and lindane as well as the molar enthalpy of vaporization Delta(g)(1)H(m)degrees() for lindane only, at the middle of the respective temperature intervals. The melting temperatures and the molar enthalpies of fusion Delta(1)(cr)H(m)degrees(T(fus)) of lindane were measured by differential scanning calorimetry. Finally, the standard molar enthalpies of sublimation Delta(g)(cr)H(m)degrees D(298.15 K) were obtained for both chlorinated compounds at the reference temperature of 298.15 K using the Delta(g)(cr)H(m)degrees(), Delta(g)(1)H(m)degrees() and Delta(1)(cr)H(m)degrees(T(fus)) values, as well as the heat capacity differences between gas and liquid and the heat capacity differences between gas and solid, Delta(g)(1)C(p,m)degrees and Delta(g)(cr)C(p,m)degrees, respectively, both estimated by applying a group additivity procedure. Therefore, the averages of the standard (p degrees = 0.1 MPa) molar enthalpies, entropies and Gibbs energies of sublimation at 298.15 K, have been derived: [GRAPHICS] (C) 2009 Elsevier B.V. All rights reserved