Tetracycline and propolis incorporation and release by bioactive glassy compounds

This study compares the release of tetracycline and propolis incorporated into four silica-based bioactive glassy systems. The bioactive glasses, with composition (SiO₂)x(P₂O₅)y(CaO)z, were prepared using a sol–gel process at room temperature. Tetraethoxysilane (TEOS), triethylphosphate, and calcium chloride were used as Si, P, and Ca precursors, respectively. The quantities of tetracycline and propolis incorporated were 2% in weight. For delivery assays, the samples were individually immersed in deionized water and buffered with tris-hydroxymethyl amino methane, pH 7.4, and kept in water bath (37 °C) for thirty days. Aliquots were withdrawn and analyzed by ultraviolet spectrophotometry in the tetracycline (270 nm) and propolis (420 nm) wavelengths. For the glass–tetracycline compounds, it was observed that four days after release had started all samples had released about 90% of the total tetracycline concentration. In contrast, 90% of the propolis was released in about 30 days’ time. Sample characterization was made using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopic (FTIR), and thermogravimetry (TG).     

Structure and non-linear optical performance of TeO2-Nb2O5-ZnO glasses

The non-linear optical performance and structure of TeO₂-Nb₂O₅-ZnO glasses was investigated as a function of ZnO content. The third-order non-linear optical susceptibility (χ⁽³⁾) as measured by a Degenerate Four Wave Mixing (DFWM) method, initially increased with increasing ZnO content to about 8.2 × 10⁻¹³ esu for a glass containing 2.5 wt% ZnO, and then decreased to 5.9 × 10⁻¹³ esu as the ZnO content increased to 10 wt%. There was no noticeable change as the ZnO content increased from 10 to 15 wt%. The non-linear optical response time, which caused electron cloud deformation, was from 450 to 500 fs. The structure of these glasses as analyzed by Raman spectroscopy and FT-IR spectra, was affected by the addition of ZnO up to 5 wt%, when, it is believed, the Zn²⁺ ions occupied the interstitial positions in the glass network by replacing the Nb⁵⁺ ions. The replaced Nb⁵⁺ ions occupied the network forming positions as the Te⁴⁺ ions. Increasing ZnO > 5 wt% did not have any further effect on the glass structure.     

Physicochemical studies of phosphate based P2O5-Na2O-CaO-TiO2 glasses for biomedical applications

Glasses P₂O₅-Na₂O-CaO-TiO₂ with different TiO₂ contents and fixed P₂O₅ (45 wt%) and CaO (24 wt%) have been prepared employing the normal melting and annealing technique. Measurements such as ultrasonic velocity, attenuation, solubility and pH have been carried out in all the compositions of the glasses. It is interesting to note that the above measured ultrasonic parameters exhibit an abnormal behavior (minimum) at 0.5 wt% of TiO₂ content, beyond which an increase in these parameters with increasing TiO₂ content is observed. The maximum pH values and Ca²⁺ ion release have been observed for the TiO₂ free glass those compositions with and the low TiO₂(?1.0 wt%) content. As the content of the TiO₂ increases, the solubility of the glasses decreases. The observed weight loss reveals two stages of phosphate dissolution kinetics i.e. the first stage, in which the weight loss is proportional to t^1/2, and a second stage in which a linear behavior is observed.     

Preparation and physical properties of (PVA)0.75(NH4Br)0.25(H2SO4)xM solid acid membrane

In this work, solid acid membrane consisting of poly(vinyl alcohol) (PVA), ammonium bromide (NH₄Br) and sulfuric acid (SA) has been prepared by a solution casting technique method. X-ray diffraction of the (PVA)_0.75(NH₄Br)_0.25(H₂SO₄)_xM polymer matrix and pure (PVA)_0.75(NH₄Br)_0.25 revealed the difference in crystallinity between them. The effect of different amounts of SA on the conductivity of the polymer electrolytes was studied. The ionic conductivity of the prepared electrolytes can reach 3.1 × 10⁻² S cm⁻¹ at room temperature. The conductivity measurements carried out at different temperatures indicate that all the films follow Arrhenius behavior and that the activation energy decreases with the increase in SA concentration. The a.c. conductivity seems to follow the universal power law.     

Structural implications of water and boron dissolution in albite glass

A combined nuclear magnetic resonance, infrared and Raman spectroscopic study on the effect of water dissolution on the structure of B-bearing aluminosilicate glasses is presented. The base composition was albite (NaAlSi₃O₈) to which different amounts of B₂O₃ (4.8, 9.1, 16.7 wt%) were added. Hydrous glasses containing 4.4 ± 0.1 wt% water were synthesized at pressures of 2000 bar. The results show that B dissolves in both dry and hydrous glasses by forming predominantly trigonal BO₃ groups although some tetrahedral BO₄ is also present. In anhydrous glasses prepared at high pressures (above 10 kbar) the fraction of BO₄ increased. The hydrous glasses contain more BO₄ groups compared to the dry counterparts, suggesting that this species is stabilized by water. The Raman and NMR (¹⁷O, ²⁷Al, ²⁹Si) spectra show that B interacts with the aluminosilicate network by formation of Si-O-B and probably Al-O-B units. In the hydrous glasses the water speciation changes significantly towards higher hydroxyl concentrations with increasing B-content. The NIR peaks, which are related to OH groups and molecular H₂O, develop additional shoulders, suggesting that possibly B-OH complexes are formed.     

Fabrication of mesoporous hydroxycarbonate apatite for oral delivery of poorly water-soluble drug carvedilol

The main aim of this study was to prepare nanosized hydroxycarbonate apatite (HCA) as a drug carrier to improve the dissolution rate and increase the bioavailability of poorly soluble drugs, intended to be administered orally. In the present study, uniform mesoporous HCA nanoparticles were synthesized using CaCO₃ as a sacrificial template by the hydrothermal method in the presence of cetyltrimethylammonium bromide (CTAB) as a surfactant. The prepared HCA was used as a drug carrier to investigate the drug uptake and release properties employing carvedilol (CAR) as a model drug. The structure and morphology of mesoporous HCA, and the successful storage/release of CAR were systematically studied by N₂ adsorption, scanning electron microscopy (SEM), powder X-Ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric (TG) analysis, Fourier transform infrared (FT-IR) spectroscopy, and UV–VIS spectrophotometry. In vitro drug dissolution tests showed that mesoporous HCA produced burst release of CAR in comparison with micronized CAR in simulated gastric fluid and intestinal fluid. Stability test result indicated that amorphous state of CAR loaded in HCA nanoparticles had a good physical stability after room storage for 6 months. Hence, mesoporous HCA nanoparticles are excellent drug carriers for the oral delivery of poorly soluble drugs.     

An easy and economic method for preparing completely reduced basalt glass

Four basalt glass samples were prepared by fusing basalt rock (powder) with different amounts of sulfur in a platinum crucible at 1550 °C for 30 min. Each melt was quenched in air. Sulfur addition to the basalt powder was changed from 0 to 5, 10 and 15 wt%. The prepared glass samples were pulverized for measuring the Mössbauer spectra by the constant acceleration method. The basalt rock spectrum can be analyzed into four peaks; two sites due to Fe³⁺ with octahedral (Oh) and tetrahedral (Td) symmetry, and the other two due to Fe²⁺ with Oh and Td symmetry. Pure basalt glass (sulfur-free) consists of four doublets; two of them represent Fe²⁺(Oh) sites and the third represents Fe²⁺(Td); while the fourth doublet belongs to Fe³⁺(Td). The sample containing 5 wt% sulfur has four iron sites also, although there is a slight difference in the relative absorption area when compared with sulfur-free sample. The fraction of Fe³⁺ in the 5% sulfur sample was estimated to be only 7.1%; i.e., the fraction of Fe²⁺ was 92.9%. Three iron sites present in the 10% sulfur sample, two of them represent Fe²⁺ with (Oh) symmetry, while the third one represents Fe²⁺(Td) site. Mössbauer spectrum of 15 wt% sulfur sample is essentially the same as that of the sample which contains 10 wt%. It is noteworthy that the sulfur content shows a linear relationship with the Fe²⁺ fraction which is calculated from the Mössbauer spectra of basalt glasses. 7.5 wt% of sulfur is large enough to completely reduce the iron in basalt glass. The reduction of glasses could occur easily and economically using sulfur as a reducing agent. This method is a very easy and economic method for the preparation of completely reduced oxide glass.     

Preparation of bioactive glass ceramic nanoparticles by combination of sol-gel and coprecipitation method

SiO₂-CaO-P₂O₅ ternary bioactive glass ceramic nanoparticles were prepared via the combination of sol-gel and coprecipitation processes. Precursors of silicon and calcium were hydrolyzed in acidic solution and gelated in alkaline condition together with ammonium dibasic phosphate. Gel particles were separated by centrifugation, followed by freeze drying, and calcination procedure to obtain the bioactive glass ceramic nanoparticles. The investigation of the influence of synthesis temperature on the nanopartilce’s properties showed that the reaction temperature played an important role in the crystallinity of nanoparticle. The glass ceramic particles synthesized at 55 °C included about 15% crystalline phase, while at 25 °C and 40 °C the entire amorphous nanopowder could be obtained. In vitro testing showed that the bioactive glass ceramic nanoparticles can induce the formation of hydroxylaptite from simulated body fluid rapidly. As a result, this bioactive glass ceramic nanoparticle with excellent bioactivity would be a promising filler material for bone tissues engineering.     

Effect of frit size on sintering, crystallization and electrical properties of wollastonite glass-ceramics

Wollastonite glass-ceramics were prepared through pressureless sintering. The sinterability of the prepared samples of the glassy powder in the system (SiO₂-CaO-Na₂O-Fe₂O₃-WO₃) was investigated in the temperature range 720-900 °C and soaking time of 180 min. The influence of the increase in the glass powder particle size on the sinterability and dielectric properties of the glass-ceramic samples was studied.The sintered specimens were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods. XRD analysis revealed that wollastonite was the main crystalline phase in the sintered glass-ceramics. Dielectric properties such as dielectric constant and dielectric loss were measured via a network analyzer at 10 GHz.It was observed that the increase of the glassy powder particle size improved the sinterability and dielectric properties of the glass-ceramic specimens. Wollastonite glass-ceramics with 16 μm particle size had maximum constant and minimum loss (ε_r = 10.10 and tan δ = 0.005) compared with the other glass-ceramics.     

Energy transfer between Tm and Er ions in a TeO2-based glass pumped at diode laser wavelength

In this paper we investigate the energy transfer processes in Tm³⁺/Er³⁺ doped telluride glass pumped at the commercial diode laser pump wavelength ∼800 nm. Tailoring the rare-earths content in the glass matrix, seven main energy transfer channels within the doping range considered were identified. A 6-fold enhancement of the Er³⁺ visible frequency upconversion fluorescence at ∼660 nm is observed due to the inclusion of Tm³⁺ ions. This is evidence of the relevant contribution of the route Er₁(⁴I_11/2) + Er₂(⁴I_13/2) → Er₁(⁴I_15/2) + Er₂(⁴F_9/2) to the process. Energy migration among pumped ⁴I_9/2 level reducing the efficiency of the upconversion emission rate (³H_11/2, ⁴S_3/2, and ⁴F_9/2) is observed for Er³⁺ above 1.5 wt%. The rate equations regarding the observed energy transfer routes are determined and a qualitative analysis of the observed processes is reported.     

Structure and crystallization of potassium titanium phosphate glasses containing B2O3 and SiO2

Transparent glasses composition of which can be expressed by the formula: (100−x) · (K₂O · 2TiO₂ · P₂O₅) · x(K₂O · 2B₂O₃ · 7SiO₂), where x=5, 10, 15 and 20 mol% (KTP-xKBS), were obtained by melt quenching technique. The structure and crystallization behavior of these glasses have been examined by Fourier transform infrared spectroscopy, differential thermal analysis and X-ray diffraction. In spite of their nominal composition, the studied glasses exhibit a similar oxygen polyhedra distribution. However, significant differences were found in the trigonal BO₃ units amount. During DTA runs all the examined glasses devitrify in two steps. In the former, very small crystals of an unknown crystalline phase are produced. In KTP-5KBS and KTP-10KBS glasses anatase phase was also detected. Attempts were made in order to identify the unknown phase (UTP) for which a AB₃(XO₄)₂(OH)₆ Crandallite-type structure was proposed where the A, B and X sites were occupied by K, Ti and/or Al, and P, respectively. In the second devitrification step the crystallization of the KTiOPO₄ phase occurs while the UTP phase previously formed disappears. Isothermal heat treatments performed at temperature just above T_g have allowed one to obtain transparent crystal-glass nanocomposites, formed by crystalline nanostructure of the UTP phase uniformly dispersed in the amorphous matrix.     

Phase separation, crystallization and leaching of microporous glass ceramics in the CaO-TiO2-P2O5 system

Microporous glass ceramics belonging to the CaO-TiO₂-P₂O₅ system were prepared with the assumption of a 2:1 mole ratio for β-Ca₃(PO₄)₂:CaTi₄(PO₄)₆, the anticipated crystalline phases in the end product. The glasses formulated according to the above composition were melted and cast onto a steel mold and were crystallized to glass ceramics containing the above phases. Dilatometric/differential thermal analysis (DTA) techniques were utilized to determine the appropriate phase separation-nucleation and crystallization temperatures. The crystalline products and resulting microstructures in various stages of process were determined and observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). By leaching the resulting glass ceramics in HCl, β-Ca₃(PO₄)₂ was dissolved out leaving a porous skeleton of CaTi₄(PO₄)₆. It was found that the volume porosity, specific surface area and mean pore diameter of microporous glass ceramics can be managed through the proper selection of heat treatment conditions. In the optimized conditions for fabricating glass ceramics of minimum mean pore size the values of 41 ± 4%, 26 ± 3 m²/g and 14.3 ± 2 nm were obtained for porosity, surface area and pore diameter respectively.     

Structural and magnetic behaviour of lead-bismuthate glasses containing rare earth ions

Lead-bismuthate glasses containing rare earth ions in the xR₂O₃(1 − x)[3Bi₂O₃⋅ PbO] (R = Nd, Eu, Er and Gd), xCeO₂(1 − x)[3Bi₂O₃⋅ PbO] and xTb₄O₇(1 − x)[3Bi₂O₃⋅ PbO] vitreous systems with x up to 0.25 were prepared and investigated by density, IR spectroscopy and magnetic susceptibility measurements. Density data show that the gradual addition of the rare earth ions leads not only to a simple incorporation of the rare earth ions in the host glass matrix but also generates structural changes of the vitreous matrix. FTIR data permitted to determine the Bi³⁺/Bi⁶⁺ ratio of the samples and to follow the compositional evolution of the structural changes for the studied systems. Magnetic susceptibility data show that the magnetic rare earth ions appear as isolated species for low rare earth oxide contents (x ≤ 0.03 ÷ 0.05) and as both isolated and magnetically coupled species for higher contents. All the magnetic rare earth ions present a very accentuated clustering tendency. Some of the studied rare earth ions appear in the host glass matrix in a single valence state (neodymium, gadolinium, and erbium), namely the 3+ one. Other rare earth ions appear in two valence states (i.e., cerium, europium and terbium), but the 3+ one is the most stable.     

Porous characteristics of carbon-coated silica gel beads prepared by liquid phase deposition of organic colloidal nanoparticles

Carbon-coated silica gel beads could be prepared by immersing porous silica gel beads in a resorcinol–formaldehyde (RF) aqueous solution and then following by drying and pyrolysis in nitrogen atmosphere. With the proposed method, deposition of colloidal nanoparticles formed during the sol–gel polycondensation of the RF solution was successfully prepared on the mesopores of the silica gel beads. Both size and concentration of the colloidal particles could be controlled by the gelation time and the mixing ratio (V_EtOH/V_RF) of the RF solution to ethanol. The porous characteristics of the prepared carbon-coated silica gel beads and the amounts of deposited carbon could be controlled by changing V_EtOH/V_RF. Without any significant decrease in mesoporosity, the maximal carbon contents of carbon-coated silica gel beads could be increased up to 18 wt% in the inner part and 53 wt% on the outer surface, respectively.     

Generation and annealing of defects in virgin fused silica (type III) upon ArF laser irradiation: Transmission measurements and kinetic model

The transmission of ArF laser pulses in virgin fused silica (type III) samples changes during N = 10⁶ pulses at an incoming fluence H_in = 5 mJ cm⁻² pulse⁻¹. The related absorption is determined by the pulse energy absorption coefficient α(N, H_in) using a modified Beer’s law, yielding initial values α_ini around 0.005 cm⁻¹, a maximum α_max ? 0.02 cm⁻¹ at N = 10³-10⁴ and stationary values 0.0045 cm⁻¹ ? α_end ? 0.0094 cm⁻¹ after N ≈ 6 × 10⁵ pulses. The development α(N, H_in = const.) is simulated by a rate equation model assuming a pulse number dependent E′ center density E′(N). E′(N) is determined by a dynamic equilibrium between E′ center generation and annealing. Generation occurs photolytically from the precursors ODC II and unstable SiH structures upon single photon absorption and from strained SiO bonds via two-photon excitation. Annealing in the dark periods between the laser pulses is dominated by the reaction of E′ with H₂ present in the SiO₂ network. The development α(N, H_in = const.) is observed for the very first sample irradiation only (virgin state). The values α_end are not accessible by simple spectrophotometer measurements.     

Synthesis and Judd-Ofelt analysis of a sol-gel material doped with a Ln2(Benzoate)6(Phen)2 (Ln = Er/Yb) complex

In this work, we have prepared a sol-gel derived hybrid material directly doped with Er_1.4Yb_0.6(Benzoate)₆(Phen)₂ (Phen = 1,10-phenanthroline) complex, which was reported with intramolecular Yb-Er energy-transfer process in our previous work. The infrared (IR) spectra of the pure complex and hybrid gel material were investigated. The NIR photoluminescence (PL) spectrum of hybrid gel material shows strong characteristic emission of Er³⁺ with broad full width at half-maximum (FWHM) of 70 nm. Judd-Ofelt theory was used in order to analyze the optical properties of Er³⁺ ions in the hybrid gel material.     

Broadband infrared luminescence of Ni-doped silicate glass-ceramics containing lithium aluminate spinel nanocrystals

Transparent Ni²⁺-doped SiO₂-Al₂O₃-Ga₂O₃-Li₂O (LGAS) glass-ceramics embedding lithium aluminate spinel nanocrystals was prepared. After heat treatment, LiAl₅O₈ crystallite was precipitated in the glasses, and its size was about 3 nm. It was confirmed from the absorption spectra that the ligand environment of Ni²⁺ ions changed from the trigonal bi-pyramid fivefold sites in the as-made glass to the octahedral sites in the glass-ceramics. Upon excitation at 980 nm, broadband infrared luminescence centered at around 1250 nm with full width at half maximum (FWHM) more than 250 nm was observed originating from the ³T₂(³F) → ³A₂(³F) transition of Ni²⁺ in octahedral sites. The broadband near-infrared (NIR) emission from Ni²⁺-doped glass-ceramics can be as host materials for broadband optical amplifier.     

Dielectric study and ac conductivity of iron sodium silicate glasses

A series of glasses with formula (SiO₂)_0.7−x(Na₂O)_0.3(Fe₂O₃)_x with ( 0.0 ≤ x ≤ 0.20) were prepared and studied by means of AC measurements in the frequency range 20 kHz to 13 MHz at room temperature. The study of frequency dependence of both dielectric constant ε' and dielectric loss ε" showed a decrease of both quantities with increasing frequency. The results have been explained on the basis of frequency assistance of electron hopping besides electron polarization. From the Cole-Cole diagram the values of the static dielectric constant ε_s, infinity dielectric constant ε_∞, macroscopic time constant τ, and molecular time constant τ_m are calculated for the studied amorphous samples. The frequency dependence of the ac conductivity obeys a power relation, that is σ_ac (ω) = Α ω^s. The obtained values of the constant s lie in the range of 0.7 ≤ s ≤ 1 in agreement with the theoretical value which confirms the simple quantum mechanical tunneling (QMT) model. The increase in ac conductivity with iron concentration is likely to arise due to structural changes occurring in the glass network. The structure of a glass with similar composition was published and showed clustering of Fe²⁺ and Fe³⁺ ions which favor electron hopping and provide pathways for charge transport.     

Crystallization and dielectric properties of low temperature dielectrics containing Li2O filler

Crystallization and dielectric properties of typical low temperature co-fired ceramics (LTCC) consisting of calcium zinc aluminoborosilicate glass and Al₂O₃ filler were investigated by substituting the Al₂O₃ filler partially with Li₂O at the levels of 2-10 wt%. Depending on the content of Li₂O, densification was found significantly affected by early crystallization that resulted from the formation of unexpected crystalline phases including LiAlSiO₄, Ca₂SiO₄, LiAlO₂, and LiAlSi₃O₈. The effect of hindering sintering via earlier crystallization became enormous regardless of firing temperature when >5 wt% Li₂O substitution occurred. It was observed that the substitution of 2 wt% Li₂O for Al₂O₃ was beneficial in producing promising performance at the low temperature of 750 °C, which can be highlighted with k ∼ 8.7 and tan δ ∼ 0.009 at 1 MHz.     

Fluoride-containing bioactive glasses: Fluoride loss during melting and ion release in tris buffer solution

Melt-derived bioactive glasses (SiO₂-P₂O₅-CaO-Na₂O-CaF₂; CaF₂ 0 to 17.76 mol%) lost fluoride during melting, but nominal and analysed CaF₂ contents in the glass correlated linearly. Analysed CaO contents were increased, showing that fluoride was lost as hydrofluoric acid after reaction with atmospheric water during melting. Weight loss on ignition reduced linearly with increasing CaF₂, suggesting that CaF₂ impedes absorption of atmospheric water. pH changes in tris buffer solution showed that pH is controlled by the silicate matrix (via ion exchange processes), and fluoride release contributes less to the overall pH. Glasses formed apatite in tris buffer; phosphate concentration of the glass was the limiting factor, resulting in fluorite formation for increasing fluoride content in the glass and calcite formation for the fluoride-free composition. These results allow for tailoring of novel fluoride-containing bioactive glasses to address specific needs, particularly in dentistry and for remineralising toothpastes.