A SiO2/pHEMA-Based Polymer-Infiltrated Ceramic Network Composite for Dental Restorative Materials

SiO2-poly(2-hydroxyethyl methacrylate) (pHEMA)-based composites have been widely used as biomaterials owing to their biocompatibility. However, they have not yet been applied as tooth restorative materials because of their poor mechanical properties. In the present paper, we develop a novel SiO2/pHEMA-based composite with a polymer-infiltrated network (PICN) structure for use in dental restorative materials. A mixture of SiO2 nanoparticles and a poly(vinyl alcohol) binder was sintered at 950 °C to fabricate a porous SiO2 block. A monomer mixture containing 70 wt%-HEMA/30 wt%-ethylene glycol dimethacrylate and a benzoyl peroxide initiator was infiltrated into the porous SiO2 block and heat-polymerized to fabricate the SiO2/pHEMA-based composite with a PICN structure. The composite was characterized according to its mechanical properties, surface free energy, and bonding properties with a dental adhesive. The flexural strength was 112.5 ± 18.7 MPa, the flexural modulus was 13.6 ± 3.4 GPa, and the Vickers hardness was 168.2 ± 16.1, which are similar values to human teeth. The surface free energy of the polar component of the composite was 19.6 ± 2.5 mN/m, suggesting that this composite has an active surface for bonding with the adhesive. The composite bonded well to the adhesive, in the presence of a silane coupling agent. The SiO2/pHEMA-based composite was demonstrated to be a potential candidate for dental restorative materials.

As-Grown Domain Structure in Calcium Orthovanadate Crystals

An as-grown domain structure in nominally pure and Mn-doped calcium orthovanadate (CVO) crystals was studied by several methods of domain imaging: optical microscopy, piezoelectric force microscopy, and Cherenkov-type second harmonic generation. The combination of imaging methods provided an opportunity for comprehensive study of the domain structure on the polar surface and in the bulk of the samples. It was shown that, in nominally pure CVO crystals, an irregular 3D maze of rounded domains, with charged walls, essentially tilted from the polar direction, was present. It was proposed that the domain structure was formed just below the phase transition temperature and persisted during subsequent cooling. Such behavior is due to effective bulk screening of the depolarization field and a low value of the pyroelectric field which appears during cooling. The revealed formation of triangular domains and flat fragments of domain walls in Mn-doped CVO was attributed to polarization reversal under the action of the polar component of the pyroelectric field, above the threshold value for domain switching. This fact represents the first observation of the domain switching in CVO crystals.

Microbial Adhesion and Biofilm Formation on Bioactive Surfaces of Ti-35Nb-7Zr-5Ta Alloy Created by Anodization

This study evaluated the microbial colonization (adhesion and biofilm) on modified surfaces of a titanium alloy, Ti-35Nb-7Zr-5Ta, anodized with Ca and P or F ions, with and without silver deposition. The chemical composition, surface topography, roughness (Ra), and surface free energy were evaluated before and after the surface modifications (anodizing). Adhesion and biofilm formation on saliva-coated discs by primary colonizing species (Streptococcus sanguinis, Streptococcus gordonii, Actinomyces naeslundii) and a periodontal pathogen (Porphyromonasgingivalis) were assessed. The surfaces of titanium alloys were modified after anodizing with volcano-shaped micropores with Ca and P or nanosized with F, both with further silver deposition. There was an increase in the Ra values after micropores formation; CaP surfaces became more hydrophilic than other surfaces, showing the highest polar component. For adhesion, no difference was detected for S. gordonii on all surfaces, and some differences were observed for the other three species. No differences were found for biofilm formation per species on all surfaces. However, S. gordonii biofilm counts on distinct surfaces were lower than S. sanguinis, A. naeslundii, and P. gingivalis on some surfaces. Therefore, anodized Ti-35Nb-7Zr-5Ta affected microbial adhesion and subsequent biofilm, but silver deposition did not hinder the colonization of these microorganisms.

The eVe reference polarisation lidar system for Cal/Val of Aeolus L2A product

The eVe dual-laser/dual-telescope lidar system is briefly given here, focusing on the optical and mechanical parts of system’s emission and receiver units. The compact design of linear/circular emission unit along with the linear/circular analyser in the receiver unit, allows eVe to simultaneously reproduce the operation of the ALADIN lidar on board Aeolus as well as the operation of a traditional ground-based polarisation lidar system with linear emission. As such, eVe lidar aims to provide: (a) ground reference measurements for the validation of the Aeolus L2A aerosol products, and (b) the atmospheric conditions for which linear polarisation lidar systems can be considered for Aeolus L2A validation, by identifying any possible biases arisen from the different polarisation state in the emission between ALADIN and these systems, and the detection of only the co-polar component of the returned signal from ALADIN for the L2A products retrieval. In addition, a brief description is given concerning the polarisation calibration techniques that are applied in the system, as well as the developed software for the analysis of the collected signals and the retrieval of the optical products. More specifically, the system’s dual configuration enables the retrieval of the optical properties of particle backscatter and extinction coefficients originating from the two different polarisation states of the emission, the linear and circular depolarisation ratios, as well as the direct calculation of the Aeolus like backscatter coefficient, i.e., the backscatter coefficient that Aeolus would measure from ground. Two cases, one with slightly-depolarising particles and one with moderately-depolarising particles, were selected from the first conducted measurements of eVe in Athens, in order to give a glimpse of the system’s capabilities. In the slightly depolarising scene, the Aeolus like backscatter coefficient agrees well with the actual backscatter coefficient, which is also true when non-depolarising particles are present. The agreement however fades out for strongly depolarising scenes, where an underestimation of ~17 % of the Aeolus like backscatter coefficient is observed when moderately-depolarising particles are probed.

The Influence of Battery Acid on the Destruction of Acrylic Coatings of Car Bodies

Renovation coatings of car bodies undergo destruction under the influence of operational factors. Like ultraviolet radiation, erosion, and aggressive media (among others, battery acid). This article concerns the evaluation of the influence of battery acid on the destruction of acrylic coatings previously non-aged, as well as aged climatically for 2 years. Ageing of the coatings with battery acid contributed to a degradation increase of their chemical structure. It was supported by a considerable increase in the polar component of surface free energy (SFE) of the coatings. In the case of prior climate ageing, the increase in the polar component was even higher. Moreover, the coating’s ability to absorb battery acid increased, which induced blistering. The DSC method revealed that the action of battery acid caused more intense oxidation of coating material, and as a result, the brittleness increased, leading to chipping of the coating surface layers. This led to the increase in surface roughness, measured using an interferometric method. The coatings previously climatically aged for 2 years presented higher values of surface roughness parameters than the non-aged ones. The increase in the surface roughness contributed to a substantial decrease in the gloss of coatings. A sharp difference in colour escalating with the lengthening of the ageing period was also observed using the spectrophotometric method.

Chemical Modification as a Method of Improving Biocompatibility of Carbon Nonwovens

It was shown that carbon nonwoven fabrics obtained from polyacrylonitrile fibers (PAN) by thermal conversion may be modified on the surface in order to improve their biological compatibility and cellular response, which is particularly important in the regeneration of bone or cartilage tissue. Surface functionalization of carbon nonwovens containing C–C double bonds was carried out using in situ generated diazonium salts derived from aromatic amines containing both electron-acceptor and electron-donor substituents. It was shown that the modification method characteristic for materials containing aromatic structures may be successfully applied to the functionalization of carbon materials. The effectiveness of the surface modification of carbon nonwoven fabrics was confirmed by the FTIR method using an ATR device. The proposed approach allows the incorporation of various functional groups on the nonwovens’ surface, which affects the morphology of fibers as well as their physicochemical properties (wettability). The introduction of a carboxyl group on the surface of nonwoven fabrics, in a reaction with 4-aminobenzoic acid, became a starting point for further modifications necessary for the attachment of RGD-type peptides facilitating cell adhesion to the surface of materials. The surface modification reduced the wettability (θ) of the carbon nonwoven by about 50%. The surface free energy (SFE) in the chemically modified and reference nonwovens remained similar, with the surface modification causing an increase in the polar component (ɣp). The modification of the fiber surface was heterogeneous in nature; however, it provided an attractive site of cell–materials interaction by contacting them to the fiber surface, which supports the adhesion process.

Normal phase thin layer chromatography for aromatic derivatives of 3-chloro-1,4-naphtochinone

The chromatographic characteristics were investigated for eight aromatic derivatives of 3-chloro-1,4-naphthoquinone under conditions of normal-phase thin-layer chromatography for benzene-based binary mobile phase and such polar solvents as chloroform, acetone, acetonitrile, methanol and propan-2-ol. The slope of linear retention dependencies for the investigated compounds on the concentration of the polar component in the mobile phase satisfactorily correlates with the area occupied by the adsorbed analyte molecule in the stationary phase. The intercept in the Soczewinski equation depends on the polar component of the mobile phase.

Evidence for intermolecular forces involved in ladybird beetle tarsal setae adhesion

Why can beetles such as the ladybird beetle Coccinella septempunctata walk vertically or upside-down on a smooth glass plane? Intermolecular and/or capillary forces mediated by a secretion fluid on the hairy footpads have commonly been considered the predominant adhesion mechanism. However, the main contribution of physical phenomena to the resulting overall adhesive force has yet to be experimentally proved, because it is difficult to quantitatively analyse the pad secretion which directly affects the adhesion mechanism. We observed beetle secretion fluid by using inverted optical microscopy and cryo-scanning electron microscopy, which showed the fluid secretion layer and revealed that the contact fluid layer between the footpad and substrate was less than 10–20 nm thick, thus indicating the possibility of contribution of intermolecular forces. If intermolecular force is the main physical phenomenon of adhesion, the force will be proportional to the work of adhesion, which can be described by the sum of the square roots of dispersive and polar parts of surface free energy. We measured adhesion forces of ladybird beetle footpads to flat, smooth substrates with known surface free energies. The adhesive force was proportional to the square-root of the dispersive component of the substrate surface free energy and was not affected by the polar component. Therefore, intermolecular forces are the main adhesive component of the overall adhesion force of the ladybird beetle. The footpads adhere more strongly to surfaces with higher dispersive components, such as wax-covered plant leaves found in the natural habitat of ladybird beetles. Based on the present findings, we assume ladybird beetles have developed this improved performance as an adaptation to the variety of plant species in its habitat.

Assessment of Bleached and Unbleached Nanofibers from Pistachio Shells for Nanopaper Making

Cellulose and lignocellulose nanofibrils were extracted from pistachio shells utilizing environmentally friendly pulping and totally chlorine-free bleaching. The extracted nanofibers were used to elaborate nanopaper, a continuous film made by gravimetric entanglement of the nanofibers and hot-pressed to enhance intramolecular bonding. The elaborated nanopapers were analyzed through their mechanical, optical, and surface properties to evaluate the influence of non-cellulosic macromolecules on the final properties of the nanopaper. Results have shown that the presence of lignin augmented the viscoelastic properties of the nanopapers by ≈25% compared with fully bleached nanopaper; moreover, the hydrophobicity of the lignocellulose nanopaper was achieved, as the surface free energy was diminished from 62.65 to 32.45 mNm−1 with an almost non-polar component and a water contact angle of 93.52°. On the other hand, the presence of lignin had an apparent visual effect on the color of the nanopapers, with a ΔE of 51.33 and a ΔL of −44.91, meaning a substantial darkening of the film. However, in terms of ultraviolet transmittance, the presence of lignin resulted in a practically nonexistent transmission in the UV spectra, with low transmittance in the visible wavelengths. In general, the presence of lignin resulted in the enhancement of selected properties which are desirable for packaging materials, which makes pistachio shell nano-lignocellulose an attractive option for this field.