Fostering hydroxyapatite bioactivity and mechanical strength by Si-doping and reinforcing with multiwall carbon nanotubes.

The aim of the present study was to prepare resorbable hydroxyapatite (HA) based bone graft materials reinforced with carbon nanotubes as a way to cope with the inability of pure HA to resorb and its intrinsic brittleness and poor strength that restrict its clinical applications under load-bearing conditions. With this purpose, a Si-doped HA nanopowder (n-Si0.8HA) was prepared by chemical synthesis and used as composite matrix reinforced with different amounts of functionalized multiwall carbon nanotubes (MWCNTs). The effect of the added amounts of MWCNTs on the mechanical properties of nanocomposites and their in vitro biomineralization was assessed by bending strength measurements, immersing tests in simulated body fluid solution (SBF), scanning electron microscopy (SEM), and inductively coupled plasma atomic emission spectroscopy analysis (ICP-AES). The bioactivity and bending strength were enhanced, reaching maximum balanced values for an optimum addition of 3 wt.% f-MWCNTs. These results might contribute to broaden the potential applications of HA-based bone grafts.

Physicochemical, structural, and functional characterization of pectin extracted from quince and pomegranate peel: A comparative study.

Pectin's physicochemical, structural, and functional characteristics vary widely depending on the source of extraction. In this study, pectins were extracted from seedless quince and pomegranate peel, and their physicochemical, structural, and functional properties were investigated. A Box-Behnken Design with three factors and three levels was applied to optimize the pectin extraction yield from each matrix. As a result, the best extraction yields for quince pectin (QP) and pomegranate peel pectin (PPP) were 11.44 and 12.08 % (w/w), respectively. Both extracted pectins exhibit a linear structure, with the homogalacturonan domain dominating the rhamnogalacturonan I. Both pectins are highly methyl-esterified (DM > 69 %) with a higher degree of acetylation for PPP than QP, with 12 and 8 %, respectively. Unlike QP, PPP has a narrow, homogenous distribution and greater molecular weight (120 kDa). Regarding functionality, 1 g of QP could retain 4.92 g of water, and both pectin emulsions were more stable at room temperature than at 4 °C. When the concentration of QP is increased, rheological measurements demonstrate that it exhibits pseudoplastic behavior. Finally, QP can be used as a thickener, whereas PPP can be utilized as starting material for chemical changes to create multifunctional pectins.

Elemental and experimental analysis of modified stent's structure under uniaxial compression load.

Additive manufacturing has enabled the fabrication of lightweight complex metamaterials that possess high energy absorption and impact resistance properties. Stents, a typical 3D auxetic material, have significant self-expanding behavior, and their mechanical properties can be finely tuned over a wide range. In this study, we systematically analyzed three distinctive elastic-plastic regions using experimental, numerical simulations, and theoretical analysis, focusing on investigating the energy absorption capability of a designed structure by varying tessellated unit cell numbers in two section views in X- and Y-direction. Two batches of 5 specimens each were 3D printed using FDM techniques. The results showed that designing a self-expanding stent with innovative capabilities was possible, with the yield stress ranging between 1.5 MPa and 2.0 MPa and extended effective elastic moduli derived from the deformation mode of tessellated unit cells. The maximum energy absorption for all structures ranged between 7.1J and 18J, with similar capabilities observed for the designed stents. However, increasing unit cells along the X-direction resulted in a significant increase in SEA, while the Y-direction remained unchanged. Therefore, these structures have a significant influence on areas requiring energy absorption. In addition, they are the ideal class of energy absorbers for cushioning applications. Furthermore, their energy-absorption capacity can be easily tailored to meet specific end-use requirements by varying their structural parameters using unit cell tessellation.

A review on borate bioactive glasses (BBG): effect of doping elements, degradation, and applications.

Because of their excellent biologically active qualities, bioactive glasses (BGs) have been extensively used in the biomedical domain, leading to better tissue-implant interactions and promoting bone regeneration and wound healing. Aside from having attractive characteristics, BGs are appealing as a porous scaffold material. On the other hand, such porous scaffolds should enable tissue proliferation and integration with the natural bone and neighboring soft tissues and degrade at a rate that allows for new bone development while preventing bacterial colonization. Therefore, researchers have recently become interested in a different BG composition based on borate (B2O3) rather than silicate (SiO2). Furthermore, apatite synthesis in the borate-based bioactive glass (BBG) is faster than in the silicate-based bioactive glass, which slowly transforms to hydroxyapatite. This low chemical durability of BBG indicates a fast degradation process, which has become a concern for their utilization in biological and biomedical applications. To address these shortcomings, glass network modifiers, active ions, and other materials can be combined with BBG to improve the bioactivity, mechanical, and regenerative properties, including its degradation potential. To this end, this review article will highlight the details of BBGs, including their structure, properties, and medical applications, such as bone regeneration, wound care, and dental/bone implant coatings. Furthermore, the mechanism of BBG surface reaction kinetics and the role of doping ions in controlling the low chemical durability of BBG and its effects on osteogenesis and angiogenesis will be outlined.

In vitro hemocompatibility studies on small-caliber stents for cardiovascular applications.

The doping of biologically meaningful ions into biphasic calcium phosphate (BCP) bioceramics, which exhibit biocompatibility with human body parts, has led to their effective use in biomedical applications in recent years. Doping with metal ions while changing the characteristics of the dopant ions, an arrangement of various ions in the Ca/P crystal structure. In our work, small-diameter vascular stents based on BCP and biologically appropriate ion substitute-BCP bioceramic materials were developed for cardiovascular applications. The small-diameter vascular stents were created using an extrusion process. FTIR, XRD, and FESEM were used to identify the functional groups, crystallinity, and morphology of the synthesized bioceramic materials. In addition, investigation of the blood compatibility of the 3D porous vascular stents was carried out via hemolysis. The outcomes indicate that the prepared grafts are appropriate for clinical requirements.

Surfactant-assisted hydrothermal synthesis of hydroxyapatite nanopowders.

Rod-like hydroxyapatite nanoparticles (n-HAp) with a highly ordered nanostructure were prepared by hydrothermal synthesis from calcium chloride, and phosphoric acid, as calcium and phosphorus sources, respectively. Various surfactant families such as cationic (CTAB), anionic (SDS) and nonionic (Triton X-100) were used as regulators of the nucleation and crystal growth. The synthesized nanopowders were characterized using X-ray diffraction (XRD), Fourier transform infrared spectrograph (FTIR) and transmission electron microscopy (TEM). The rod-like morphology was obtained regardless of the surfactant used during the hydrothermal treatment, but the aspect ratio of the crystals was found to be surfactant dependent. The mechanism of crystal growth as well-oriented nanostructure is discussed.

Acellular bioactivity and drug delivery of new strontium doped bioactive glasses prepared through a hydrothermal process.

This work aims to study the kinetics of apatite layer formation on the surface of strontium doped binary bioactive glasses (BG: 63S37C) prepared for the first time by a hydrothermal process and evaluate their potential for drug loading and release using ibuprofen (IBU) as an anti-inflammatory drug vector. First, the binary glass 63S37C was doped with various amounts of strontium, from 0.2 to 1 mol%. Subsequently, the amorphous state of the samples and the microstructure were assessed by TGA, XRD, FTIR, ICP-AES, and SEM-EDS. Next, the in vitro bioactivity was evaluated by following the surface morphology and composition changes of soaked samples for up to 14 days at 37 °C in simulated bodily fluid (SBF). Finally, SEM-EDS spectroscopy showed clearly the appearance of needle-shaped apatite on amorphous glass substrates at the earlier stages of immersion for bioglasses doped with strontium. These findings are also confirmed with XRD and FTIR analysis. Furthermore, 63S37C BG proved that the drug release increased with increasing strontium content. Altogether, this novel class of bioactive glasses may be considered to have a promising future for biomedical applications.

[Performance of orthodontic aligners in the aging process: systematic review and in vitro study]. / La performance des aligneurs orthodontiques à l'épreuve du vieillissement : revue systématique et étude in vitro.

INTRODUCTION: The objective of this study was to evaluate, through a systematic review of the literature and an in vitro study, the alteration of the mechanical and chemical properties of aligners after aging in artificial saliva and in the oral cavity. MATERIALS AND METHODS: A systematic literature review was carried out, through an electronic consultation of three databases: PubMed, EBSCO and Sciencedirect, between September 2018 and January 2020. The search was guided by the use of several specific keywords. In our in vitro study, the mechanical properties of our sample of aligners were evaluated using the 3-point bending test after a water immersion. RESULTS AND DISCUSSION: Of the 189 articles found, only six articles met our inclusion criteria. In the light of the studies selected in this systematic review and of our in vitro study, it can be concluded that the orthodontic aligners undergo an alteration in their mechanical properties after stay in the mouth. However, the real impact of these modifications on their clinical performance remains to be demonstrated and it is difficult to make a final judgment on their chemical stability. Other controlled clinical studies, with protocols better suited to the clinical criteria studied, are necessary to objectively assess the aging phenomenon of orthodontic aligners.

Mesoporous bioactive glass nanoparticles doped with magnesium: drug delivery and acellular in vitro bioactivity.

The effects of the magnesium doping of binary glass (Si-Ca) on particle texture, on the biomineralization process in simulated body fluid (SBF) as well as on drug loading and release were examined. For this purpose, magnesium-doped binary bioglass nanoparticles (85SiO2-(15 - x)CaO-xMgO, with x = 1, 3, 5 and 10 mol%) were prepared by a base catalysed sol-gel method. N2 adsorption isotherm analysis showed an enhancement in specific surface area as the Mg molar fraction increased. In addition, the FTIR spectra of the samples after soaking in SBF for various periods of time confirmed the presence of new chemical bonds related to the apatite phase, as was also confirmed by SEM observations. XRD patterns of the samples after soaking revealed that the crystallization to form a more stable apatite-like phase was hindered with increasing magnesium content in the glass composition. Furthermore, it was proved that the kinetics of drug release improved with increasing magnesium content. The porosity and the specific surface area were found to be responsible for this improvement.

Effect of shear on phase-separation in polystyrene/poly(vinyl methyl ether)/ organoclay nanocomposites.

Blends of polystyrene (PS)/poly(vinyl methyl ether) (PVME) modified with two types of organoclay were prepared by solution casting from toluene. The effect of clay addition on the phase separating morphology of PS/PVME blend with critical composition (25/75) was examined both under quiescent conditions and under shear flow. The variation in critical temperature of phase separation was assessed by rheology, small angle laser light scattering (SALLS) and by on-line laser light transmission during shearing at fixed shear rate during heating. Transmission electron microscopy and X-ray diffraction analyses were used to examine the state of delamination and distribution of clay nanoparticles with the blend matrix.

Dispersion characteristics and properties of poly(methyl methacrylate)/multi-walled carbon nanotubes nanocomposites.

The preparation, characterization, and properties of poly(methyl methacrylate) (PMMA)/multi-walled carbon nanotubes (MWCNTs) nanocomposites are described. Nanocomposites have been prepared by melt-blending in a batch mixer. Both unmodified and surface modified MWCNTs have been used for the nanocomposites preparation. Using both unmodified and modified MWCNTs, the effect of surface modification in nanocomposites is investigated by focusing on three major aspects: dispersion characteristics, mechanical properties, and electrical conductivity measurements. Dispersion of the MWCNTs in the PMMA matrix is examined by scanning and transmission electron microscopy that revealed a homogeneous distribution-dispersion of MWCNTs in the PMMA matrix for both unmodified and modified MWCNTs. Thermomechanical behavior is studied by dynamic mechanical analyzer and results showed a substantial improvement in the mechanical properties of PMMA in conjunction to an increase in the elastic behavior. The tensile properties of neat PMMA moderately improved after nanocomposites preparation with both modified and unmodified MWCNTs, however, electrical conductivity of neat PMMA significantly improved after nanocomposites preparation with 2 wt% unmodified MWCNTs. For example, the through plane conductivity increased from 3.6 x 10(-12) S x cm(-1) for neat PMMA to 3.6 x 10(-9) S x cm(-1) for nanocomposite. The various property measurements have been conducted and results have shown that, in overall, surface modifications have very little or no effect on final properties of neat PMMA.

Phase separation in PS/PVME thin and thick films.

Phase separation in both thin and thick films of polystyrene (PS) and poly(vinyl methyl ether) (PVME) was studied by small-angle laser light scattering (SALLS), atomic force microscopy (AFM), optical microscopy, and X-ray photoelectron spectroscopy (XPS). Blend films with controlled thickness were obtained by spin-coating polymer-toluene solutions with various concentrations. Films with thicknesses smaller and larger than the maximum wavelength of concentration fluctuations were considered. Morphology of the blend films was characterized during and after phase separation. The obtained peculiar morphology was related to surface enrichment with the lower-surface-energy component, as was verified by XPS analyses.

Phase separation of polystyrene/poly(vinylmethylether)/organoclay nanocomposites.

The effect of addition of organically modified montmorillonite (OMMT) on the phase separation of polystyrene (PS)/poly(vinyl methyl ether) (PVME) blend was examined. Using two types of OMMT modified with two different kinds of surfactants, the effect of organic modification on nanocomposites was investigated by focusing on three major aspects: phase transition, morphological study, and melt rheological behavior both below and above the critical transition temperature. X-ray diffraction (XRD) patterns revealed the formation of intercalated nanocomposites and transmission electron micrographic (TEM) observations showed that the ordering of silicate layers in blend matrix is well matched with the XRD patterns. The addition of clay was found to affect both the mechanism of phase separation and the final morphology. Such effects resulted in uncommon rheological behavior of the blend both below and above the critical transition temperature. Surface phase separation of thin films for virgin blend and nanocomposites was also examined by atomic force microscopy (AFM). Morphology resulting after phase separation was found to be dependent on the nature and the amount of OMMT added to the polymer blend.

Degradation of the mechanical properties of orthodontic NiTi alloys in the oral environment: an in vitro study.

Appropriate characterization studies are needed to demonstrate the mechanical and biological effects of interaction between archwires and the oral environment. The aim of this study was to investigate, in vitro, the impact of this acidic and fluoridated environment on the electrochemical behavior and the mechanical properties of orthodontic alloys in nickel titanium and in stainless steel (controls) for the following parameters: Young's modulus (E), elastic limit (σe) and the maximum tensile load (σm). Six samples of each archwire alloy were used to assess these parameters. An Instron universal test apparatus (model - 88512) was used for the traction tests on the wires after immersion in solutions at different concentrations of fluoride and at various pH levels. Observations were made using an electron scanning microscope (ESM) to evaluate the surface and an ICP (inductively coupled plasma) mass spectroscopy analysis was made to quantify the substances released into the immersion solution. For the NiTi archwires, immersion in the fluoridated and acidic medium showed a statistically significant reduction of the Young's modulus (E), the elastic limit (σe) and the maximum tensile load (σm). Similarly, a higher level of released nickel proportionate to the increase in the fluoride concentration and acidity was observed in the immersion solutions. ESM observations revealed the status of the surface of the different alloys and the presence of corrosive pitting.