C. Fagnano

Raman and infrared spectra on silica gel evolving toward glass

Abstract Infrared and Raman spectra of gels obtained from specially prepared solutions of Si(OC2H5)4 (TEOS) which have been thermally treated in the 40–800°C temperature range, are reported and discussed with reference to the spectra of fused quartz. The results show that the gel to glass transformation is an hydrolytic polycondensation process, which takes plase gradually and is practically completed in the samples treated at 800°C. Particularly revealing is the behaviour of the bands due to OH (associated and/or unassociated H-bonded) stretching modes, including those of water, which are weakened by increasing temperature; the behaviour of the band due to the SiOH stretching mode; the behaviour of the network bands, some of which become more intense with increasing temperature, due to asymmetric and symmetric stretching and the bending SiOSi modes. In the Raman spectra of gels heated at different temperatures two peaks also appear at ≈600 and ≈490 cm−1, which are also present in the Raman spectrum of fused quartz, they are related to network defects of the glass structure, for which no definite interpretation has yet been given in the literature.

Polylactic acid fibre-reinforced polycaprolactone scaffolds for bone tissue engineering.

The employment of composite scaffolds with a well-organized architecture and multi-scale porosity certainly represents a valuable approach for achieving a tissue engineered construct to reproduce the middle and long-term behaviour of hierarchically complex tissues such as spongy bone. In this paper, fibre-reinforced composites scaffold for bone tissue engineering applications is described. These are composed of poly-L-lactide acid (PLLA) fibres embedded in a porous poly(epsilon-caprolactone) matrix, and were obtained by synergistic use of phase inversion/particulate leaching technique and filament winding technology. Porosity degree as high as 79.7% was achieved, the bimodal pore size distribution showing peaks at ca 10 and 200 microm diameter, respectively, accounting for 53.7% and 46.3% of the total porosity. In vitro degradation was carried out in PBS and SBF without significant degradation of the scaffold after 35 days, while in NaOH solution, a linear increase of weight lost was observed with preferential degradation of PLLA component. Subsequently, marrow stromal cells (MSC) and human osteoblasts (HOB) reached a plateau at 3 weeks, while at 5 weeks the number of cells was almost the same. Human marrow stromal cell and trabecular osteoblasts rapidly proliferate on the scaffold up to 3 weeks, promoting an oriented migration of bone cells along the fibre arrangement. Moreover, the role of seeded HOB and MSC on composite degradation mechanism was assessed by demonstrating a more relevant contribution to PLLA degradation of MSC when compared to HOB. The novel PCL/PLLA composite scaffolds thus showed promise whenever tuneable porosity, controlled degradability and guided cell-material interaction are simultaneously requested.

Further investigations on Raman spectra of silica gel evolving toward glass

Abstract In a previous investigation a continuous evolution of silica gel structure toward that of v-SiO 2 was verified by Raman spectroscopy. Modifications on the intensity of some Raman bands usually associated in the literature to “defects” of the structure were observed. In the present work the study has been extended to the transformation with temperature of silica gels obtained from tetraethoxysilane (TEOS) with different H 2 O/TEOS molar ratios. Raman spectra as well as thermogravimetric data are discussed in terms of the effect of this ratio on the local structure and the sintering process of silica gel.

Effects of the sterilisation method on the wear of UHMWPE acetabular cups tested in a hip joint simulator

Ultra-high molecular-weight-polyethylene is the most commonly used bearing material in total joint replacement. Wear of polyethylene is a Serious Clinical problem that limits the longevity of orthopaedic implants. Information on degradative changes in the material properties and on the methods used for the sterilisation of polyethylene may help in the selection process of orthopaedic implants with the best wear resistance. This study was performed to investigate the effects of the sterilisation method (gamma irradiation and ethylene oxide treatment) on the wear and on the changes in physical properties of polyethylene acetabular cups. At this purpose, gamma-sterilised and ethylene oxide (EtO)-sterilised acetabular cups were tested against CoCr femoral heads in a hip joint simulator run for 5 million cycles in bovine calf serum. The crystallinity of the cups was evaluated by micro-Raman spectroscopy as a function of the inner surface position. The partial least square calibration was used to correlate the Raman spectra with the crystallinity of the polymer measured by differential scanning calorimetry. The analysis performed on soak control acetabular cups demonstrated that the gamma-sterilised cups are significantly more crystalline than the EtO-sterilised ones. The mean crystallinity values obtained for the gamma-sterilised and EtO-sterilised soak control cups were 65.0% and 63.4%, respectively. Weight loss measurements revealed that the gamma-sterilised acetabular cups exhibited a lower wear rate than that by EtO-sterilised. Thc Raman results obtained on gamma-sterilised and EtO-sterilised acetabular cups showed that the changes in surface crystallinity were mainly caused by irradiation rather than by the mechanical friction during the in vitro tests.

Vibrational spectroscopy of ultra-high molecular weight polyethylene hip prostheses: influence of the sterilisation method on crystallinity and surface oxidation

Abstract Due to its high strength and low creep, ultra-high molecular weight polyethylene (UHMWPE) has been used for 30 years in the replacement of damaged articulating cartilage for total joint replacement surgery. In this study, micro-Raman spectroscopy was used to investigate the effects of the sterilisation method (gamma and ethylene oxide (EtO) treatment) on the crystallinity changes of UHMWPE acetabular cups. The crystallinity of the cups was evaluated by micro-Raman spectroscopy coupled to the partial least square (PLS) regression as a function of the inner surface position. Unworn gamma-sterilised cups were found to be significantly more crystalline than the EtO-sterilised ones. No significant differences were observed between the crystallinity values of worn (in in vitro tests) and unworn cups for each type of sterilisation, showing that the changes in surface crystallinity were mainly caused by irradiation rather than by mechanical friction during the in vitro wear tests. These results were discussed in relation to gravimetric measurements, which revealed at the end of the in vitro tests, a higher mean weight loss for the EtO-sterilised cups than for the gamma-sterilised ones. No significant amounts of oxidative degradation products were detected by IR spectroscopy in the inner surface of the EtO-sterilised worn and unworn cups. Regarding the gamma-sterilised cups, the oxidation level appeared to be slightly higher in the centre of the worn cups than on their borders.

Raman and FT IR ATR study of diethylsulfoxide/water mixtures

Abstract The Raman and FT IR ATR spectra of diethylsulfoxide (DESO)-water mixtures in the SO and C–H stretching vibration regions at different molar ratios are considered. Noticeable changes are observed in the ν SO region, suggesting the existence of strong H-bonds between DESO and water molecules; on the contrary the ν CH bands change only in a less extent, supporting the existence of SO⋯HC hydrogen bonds in pure DESO that gradually break in the presence of water. In addition, FT IR measurements confirm the existence of ‘free’ SO group at low concentrations of DESO. The results obtained are well explainable in frame of the cluster-structure model of liquid water.

Micro-Raman spectroscopy for the crystallinity characterization of UHMWPE hip cups run on joint simulators☆

Abstract In this work Raman microspectrometry was used to evaluate the crystallinity changes of hip cups made of ultra-high molecular weight polyethylene (UHMWPE). In vitro experiments were carried out using hip joint movement-wear simulators, run for five million cycles in water or bovine calf serum. The hip cups were subjected to mechanical friction with ceramic femoral heads (alumina–zirconia blend). The crystallinity of the polymer hip cups was studied as a function of inner surface position and thickness, from the stressed surface to the unstressed outer one. The Partial Least Square (PLS-l) calibration was used to correlate the Raman spectra with the crystallinity of the polymer measured with DSC calorimetry.

Raman and infrared spectra of As2Sx chalcogenide glasses with x ⩽ 3

Abstract Raman laser and far infrared spectra of As2Sx glasses with x ⩽ 3 are given and discussed. The purpose of the work is to bring a vibrational spectroscopic contribution to the study of these glasses and to the hypothesis, still under discussion in the literature, that they might be constituted either by a homogeneous vitreous phase or by a mixture of As2S3 and As4S4. Our results confirm a phase separation, with formation of s-As4S4, below a certain value of x, which depends not only on the preparation method of the samples but also on other factors such as melting time. Laser irradiation of s-As4S4 modifies its Raman spectrum. Such a phenomenon is attributable to two principal factors, either a partial polymerization or formation of a species richer in arsenic. A structural and formation model of the As2Sx glasses is given, starting from a more generalized structural model of vitreous As2S3 which is an accord with the vibrational results and those by the diffraction method in the literature.

Raman defect peaks in the spectra of Na2O silica gels evolving toward glass

Abstract In previous works the continuous thermal evolution toward v-SiO2 of gels obtained from tetraethoxysilane (TEOS) and with different H2O/TEOS molar ratios was studied by Raman spectroscopy; Raman defect peaks at ∼ 600 and ∼ 490 cm−1 were observed both in gels and in the v-SiO2. In this work the structural effects of small amounts of Na2O on silica gels evolving toward glass are studied in order to give a further experimental contribution to the problem of “Raman defect peaks”. Some considerations on the nature of these defect peaks are now presented considering all the results so far obtained.

Vibrational spectra of diethylsulfoxide

FT IR and Raman spectroscopic studies of pure diethylsulfoxide (DESO) in the liquid and in the solid states and its solutions in various solvents have been performed. Analysis of SO- and CH-stretching regions in a wide range of concentration shows that the bands may be fitted satisfactorily by considering seven components. In addition, fundamental frequencies have been assigned using ab initio calculations at the RHF/3-21G* levels. The results obtained confirm a viewpoint on a self-associative structure of DESO, and support the hypothesis of the existence of different types of intermolecular associates including both dipole-dipole and hydrogen bonding mechanisms.