Bornom kiselinom modificirani kitozanski nosači kemijski umreženi genipinom

Chitosan scaffolds are an effective biologically active material with versatile application in chemistry and medicine. Chitosan is a linear polysaccharide, a derivative of chitin, with great biocompatibility due to the possession of functional groups such as −OH and −NH2, which allow for biodegradability and antibacterial function. Chitosan has a polycation nature allowing complex formation with metal ions and many biomolecules such as DNA, proteins and lipids, while its specific structure and functional groups are responsible for antibacterial, hemostatic, and analgesic properties. To improve its angiogenic and antimicrobial potential, chitosan can be modified by boron (borate ions). The aim of this work was to prepare boric acid modified chitosan scaffolds, using boric acid as a boron precursor, as potential bioactive scaffolds for tissue regeneration. Borate ions tend to form complexes with hydroxyl groups, however, such physical interactions between boron and chitosan functional groups result in poor encapsulation efficiency. To ensure higher boron incorporation, chitosan scaffolds were cross-linked by genipin, a cross linker with lower cytotoxicity in contrast to glutaraldehyde commonly used to prepare stable chitosan-based materials. The degree of deacetylation (DD) and concentration of chitosan solution as well as the concentration of a solvent are important parameters that affect the crosslinking process. Moreover, the addition of boric acid could interfere with the crosslinking process by occupying chitosan functional groups. Here, chitosan scaffolds were modified with different concentrations of boric acid, while the concentrations of chitosan solution (1.2 w/v), genipin (2 % w/w), and acetic acid (0.5 % v/v) were kept constant. Obtained scaffolds were characterised by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), differential scanning calorimetry (DSC), Fourier transformation infrared spectroscopy (FTIR), while cytotoxicity was evaluated as a function of materials concentration and exposure time. The results indicated successful incorporation of boron into cross-linked chitosan scaffolds with highly porous structure and low cytotoxicity.Kitozanski nosači su efektivni biološki aktivni materijali sa širokom primjenom u kemiji i medicini. Kitozan je linearni polisaharid, derivat hitina, koji posjeduje dobru biokompatibilnost koja se pripisuje prisustvu funkcionalnih skupina kao što su −OH i −NH2 koje pridonose biorazgradljivim i antibakterijskim svojstvima. U kiselim vodenim otopinama kitozan je polikationske strukturne prirode, koja ima veliku sposobnost stvaranja kompleksa s različitim metalnim ionima i važnim biomolekulama, kao što su DNA, proteini i lipidi. Jedinstvena struktura, kao i uvođenje specifičnih funkcionalnih skupina odgovorni su za antibakterijska svojstva, hemostatsku aktivnost i analgetska svojstva tog biopolimera. Za poboljšanje angiogenih i antimikrobnih svojstava, kitozan se može modificirati borom (boratnim ionima). Cilj ovog rada bio je pripremiti bornom kiselinom modificirane kitozanske nosače, upotrebljavajući bornu kiselinu kao prekursor bora, u svrhu priprave potencijalnih bioaktivnih okosnica za regeneraciju tkiva. Boratni ioni imaju sklonost stvaranja kompleksa s hidroksilnim skupinama, međutim, takve interakcije između funkcionalnih skupina kitozana i bora rezultiraju slabijom učinkovitosti njegove inkapsulacije. Da bi se osigurala bolja ugradnja bora, kitozanski nosači su umreženi genipinom, manje toksičnim umreživalom u odnosu na glutaraldehid koji se obično upotrebljava za pripremu stabilnih materijala čiji se sastav temelji na kitozanu. Stupanj deacetilacije (DD) i koncentracija otopine kitozana kao i koncentracija otapala važni su parametri koji utječu na proces umreživanja. Nadalje, dodatak borne kiseline mogao bi utjecati na proces umreživanja zauzimanjem funkcionalnih skupina kitozana. U ovom radu kitozanski nosači modificirani su bornom kiselinom različite koncentracije, dok su koncentracija otopine kitozana (1,2 w/v), koncentracija genipina (2 % w/w) i koncentracija octene kiseline (0,5 % v/v) bile konstantne. Dobiveni nosači okarakterizirani su pretražnom elektronskom mikroskopijom (SEM), energetski disperzivnom rendgenskom spektroskopijom (EDS), diferencijalnom pretražnom kalorimetrijom (DSC), infracrvenom spektroskopijom s Fourierovom transformacijom (FTIR), dok je citotoksičnost procijenjena kao funkcija koncentracije materijala i vremena izloženosti stanica materijalu. Rezultati su pokazali uspješnu ugradnju bora u umrežene kitozanske nosače, visoko poroznu strukturu i nisku citotoksičnost

Electrical Properties of Two Types of Lithium-Based Glass Ceramics

Abstract The dental ceramic materials are constantly being developed due to their continuous clinical appli- cation in the eld of esthetic dentistry. Glass ceramics (GC) materials are also of special interest for dental application due to their speci c properties ; and thus, they can be applied as crowns, veneers and small bridges. Purpose: However, due to a variety of different GC materials, it is of keen inter- est to inspect their morphology and ion-diffusion, which also governs aging properties. Material and methods: In this study, two different GC materials were processed, i.e., lithium silicate (LS-10) and lithium disilicate (LS-20). The aforementioned properties can be inspected by using impedance spec- troscopy (IS) and scanning electron microscopy (SEM). Results: SEM study suggested that LS-10 ma- terial is harder to mechanically process by computer-aided design/computer-aided manufacturing (CAD/CAM) technology. Furthermore, IS measurements showed that LS-20 (vs. LS-10) has more pro- nounced resistance properties. Conclusion: According to IS data, it was concluded that LS-20 (vs. LS- 10) has more pronounced resistance properties that point out to hindered ion- diffusion and to bet- ter aging properties

Structural and magnetic properties of Ag-doped CuO nanopowders

The influence of Ag doping on the crystal structure and magnetic properties of CuO nanopowders was investigated. Nanoparticles of copper–silver oxide solid solutions with composition Cu1−xAgxO(x=0.01–0.05) were successfully produced by using self–propagating room temperature synthesis using reaction between metal nitrates and sodium hydroxide. Prepared powders were calcinated at 700 °C for 2 h. The diffraction pattern was recorded at room temperature and atmospheric pressure in the absence of any re-heating of the sample. A fitting refinement procedure using the Rietveld method was performed which showed the incorporation of Ag3+ ions in the CuO crystal lattice, where they substitute Cu 2+ ions. Magnetic behaviour of synthesized materials was investigated by SQUID magnetometer in temperature interval 2-400 K. Copper(II) oxide exhibits ferroelectricity driven by magnetic order at temperature as high as 230 K [1]. Multiferroic phase is present above the first order phase transition at TN1= 213 K and exists up to the subsequent first order phase transition TN2= 230 K . It was shown that disorder in the form of impurities can stabilize the ferroelectric phase what was a motivate to dope CuO with Ag in order to improve further its multiferroic properties.InCu1-x Ag x Osmall change of magnetic properties were observed if compared to CuO.IX Serbian Ceramic Society Conference - Advanced Ceramics and Application : new frontiers in multifunctional material science and processing : program and the book of abstracts; September 20-21, 2021; Belgrad

Surface Characterization and Conductivity of Two Types of Lithium-Based Glass Ceramics after Accelerating Ageing

In this study, two different dental ceramics, based on zirconia-reinforced lithium-silicate (LS1) glass-ceramics (Celtra Duo, Dentsply Sirona, Bensheim, Germany) and lithium disilicate (LS2) ceramics (IPS e.max CAD, Ivoclar, Vivadent, Schaan, Liechtenstein) were examined. They were tested prior to and after the crystallization by sintering in the dental furnace. Additionally, the impact of ageing on ceramic degradability was investigated by immersing it in 4% acetic acid at 80 ◦C for 16 h. The degradability of the materials was monitored by Impedance Spectroscopy (IS), X-Ray Powder Diffraction (XRPD), and Field Emission Scanning Electron Microscope (FE-SEM) techniques. It was detected that LS2 (vs. LS1) samples had a lower conductivity, which can be explained by reduced portions of structural defects. XRPD analyses also showed that the ageing increased the portion of defects in ceramics, which facilitated the ion diffusion and degradation of samples. To summarize, this study suggests that the non-destructive IS technique can be employed to probe the ageing properties of the investigated LS1 and LS2 ceramics materials

Influence of Ho doping on magnetic properties of bismuth ferrite nanopowders

Bismuth ferrite (BiFeO3) is one of the most studied multiferroic systems mainly because of BiFeO3 material possesses both antiferromagnetic and ferroelectric properties observed at room temperature, which opens great possibilities for industrial and technological application. The influence of Ho doping on the crystal structure and magnetic properties of bismuth ferrite (BFO) nanopowders was investigated. BiFeO3 and Bi1-xHoxFeO3 ultrafine nanopowders were synthesized by the hydrothermal method. Here we use simple, low-cost and energy-saving hydrothermal method, which has advantages over the conventional methods. The diffraction pattern was recorded at room temperature and atmospheric pressure in the absence of any re-heating of the sample. A fitting refinement procedure using the Rietveld method was performed which showed the incorporation of Ho 3+ ions in the BiFeO3 crystal lattice, where they substitute Bi 3+ ions. All the samples belong to R3c space group. Magnetic behavior of synthesized materials was investigated by SQUID magnetometer in wide temperature interval (2-800 K).Temperature dependence of magnetization shows antiferromagnetic transition at TN ~ 630 K and below this temperature weak ferromagnetism is observed, which becomes enhanced with the Ho-dopingSeventeenth Young Researchers' Conference Materials Sciences and Engineerin

Magnetic behaviour of Ag doped BiFeO3

Bismuth ferrite (BFO) is one of a few room temperature magneto-electric multiferroics. High ferroelectric and magnetic transition temperatures (1100 and 630 K, respectively) make it interesting for possible technological application. The problem with BFO bulk ceramic is low net magnetic moment of its ordered antiferomagnetic phase. To disturb the antiferromagnetic order and induce bigger magnetic moment, BFO is often doped with different elements, usually heavy rare earth elements or transition metal ions. In this study we have investigated magnetic behaviour of Ag doped BFO. Compounds of BiFeO3, with metal ions substituted by different percentage of silver, were synthesized using hydrothermal method. Structural characterization of synthesized samples was performed using X-ray diffraction. Magnetization of polycrystalline samples measured in a wide temperature range, from 2 to 720 K, showed that the transition temperature for all the samples is nearly the same, TN = 630 K. The development of weak ferromagnetism with doping was observed as enhanced splitting between zero field cooled (ZFC) and field cooled (FC) curves, together with increased magnetization seen also in M(H) curves. The peculiar behaviour of ZFC and FC curves expressed at lower temperatures, where the FC curve crossed the ZFC curve attaining lower values of magnetization then the ZFC curve, could be attributed to the competition of exchange interactions within and between the sublattices.V Serbian Ceramic Society Conference : program and the book of abstracts; June 11-13, 2019; Belgrad

The effect of Y3+ addition on morphology, structure, and electrical properties of yttria-stabilized tetragonal zirconia dental materials

Zirconia (ZrO2), a widely known material with an extensive range of applications, is espe- cially suitable for dental applications. This kind of dental material is produced in the form of blocks or discs (mostly discs—depending on CAD/CAM machines) by cold isostatic pressing (CIP). Such discs are subsequently milled by CAM/CAD technology into a desirable form. Due to the application of CIP, the resulting discs consist of different yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) powders, additives and pigments. The diverse composition of the discs (e.g., different Y3+ content) governs material properties, such as hardness, toughness and translucence. The aim of this work was to investigate the impact of Y3+ addition on the grains and grain boundaries, on the ZrO2 phases lattice parameter values and on the electrical equivalent circuit parameters of the prepared Y- TZP samples. The disc-shaped samples were prepared by using CAM/CAD technology. It was observed that the grain size and the grain density were increased by Y3+ addition. The sample with the lowest Y3+ content was characterized by the highest portion of the tetragonal phase, whilst the disc with the highest Y3+ addition consisted mainly of the cubic phase. It was also observed that at the higher Y3+ ion concentrations, these ions mainly incorporated the tetragonal phase. Furthermore, conductivity investigations showed that the resistivity of the grains in the samples with the higher Y3+ concentrations was decreased as these ions were mainly trapped in the grain boundary. On the other hand, the Y3+ trapping increased the capacitance of the grain boundary

Impact of Sandblasting on Morphology, Structure and Conductivity of Zirconia Dental Ceramics Material

Over the last decade, zirconia (ZrO2)-based ceramic materials have become more applicable to modern dental medicine due to the sustained development of diverse computer-aided design/computer-aided manufacturing (CAD/CAM) systems. However, before the cementation and clinical application, the freshly prepared zirconia material (e.g., crowns) has to be processed by sandblasting in the dental laboratory. In this work, the impact of the sandblasting on the zirconia is monitored as changes in morphology (i.e., grains and cracks), and the presence of impurities might result in a poor adhesive bonding with cement. The sandblasting is conducted by using Al2O3 powder (25, 50, 110 and 125 µm) under various amounts of air-abrasion pressure (0.1, 0.2, 0.4 and 0.6 MPa). There has been much interest in both the determination of the impact of the sandblasting on the zirconia phase transformations and conductivity. Morphology changes are observed by using Scanning Electron Microscope (SEM), the conductivity is measured by Impedance Spectroscopy (IS), and the phase transformation is observed by using Powder X-Ray Diffraction (PXRD). The results imply that even the application of the lowest amount of air-abrasion pressure and the smallest Al2O3 powder size yields a morphology change, a phase transformation and a material contaminatio

Sodium-Ion Conductivity and Humidity-Sensing Properties of Na2O-MoO3-P2O5 Glass-Ceramics

A series of glass-ceramics were prepared by heat- treatments of 40Na2O-30MoO3-30P2O5 (in mol%) glass in a temperature range from 380 (Tg) to 490 °C (Tc) and for 1–24 h. The prepared glass-ceramics contain from 2 to 25 wt.% of crystalline NaMoO2PO4. The sodium-ion conductivity in these materials decreases up to one order of magnitude with an increase in the degree of crystallization due to the immobilization of sodium ions in crystalline NaMoO2PO4. The transport of sodium ions in these materials occurs primarily through the dominant continuous glassy phase, and it is weakly affected by the sporadically distributed crystalline grains. However, the prepared glassceramics exhibit high proton conductivity in a humid atmosphere and remarkable humidity-sensing properties ; this could be related to crystalline NaMoO2PO4, which provides sites for water adsorption. The glass-ceramic prepared at 450 °C for 24 h shows the best humidity-sensing performance among all samples, showing an increase in proton conductivity for more than seven orders of magnitude with the increase in relative humidity from 0% to 95%. Under a highly humid atmosphere (95% relative humidity and 25 °C), the proton conductivity of this glass-ceramic reaches 5.2 ×10−3 (Ω cm)−1. Moreover, the electrical response of these materials on the change in the relative humidity is linear and reversible in the entire range of the relative humidity, which indicates that they are novel promising candidates for application as humidity sensors

Humidity-Sensing Properties of an 1D Antiferromagnetic Oxalate-Bridged Coordination Polymer of Iron(III) and Its Temperature-Induced Structural Flexibility

A novel one-dimensional (1D) oxalate-bridged coordination polymer of iron(III), {; ; [NH(CH3) (C2H5)2][FeCl2(C2O4)]}; ; n (1), exhibits remarkable humidity-sensing properties and very high proton conductivity at room temperature (2.70 × 10−4 (W·cm)−1 at 298 K under 93% relative humidity), in addition to the independent antiferromagnetic spin chains of iron(III) ions bridged by oxalate groups (J = −7.58(9) cm−1). Moreover, the time-dependent measurements show that 1 could maintain a stable proton conductivity for at least 12 h. Charge transport and magnetic properties were investigated by impedance spectroscopy and magnetization measurements, respectively. Compound 1 consists of infinite anionic zig-zag chains [FeCl2(C2O4)]nn− and interposed diethylmethylammonium cations (C2H5)2(CH3)NH+, which act as hydrogen bond donors toward carbonyl oxygen atoms. Extraordinarily, the studied coordination polymer exhibits two reversible phase transitions: from the high-temperature phase HT to the mid-temperature phase MT at T ~213 K and from the mid-temperature phase MT to the low-temperature phase LT at T ~120 K, as revealed by in situ powder and single-crystal X-ray diffraction. All three polymorphs show large linear thermal expansion coefficients