Silicon-29 echo train coherence lifetimes and geminal 2J-couplings in network modified silicate glasses

The natural abundance ²⁹Si echo-train coherence lifetimes in network-modified silicate glasses were examined under static and magic-angle spinning (MAS) conditions. The nuclear magnetic properties of modifier cations were found to play a major role in determining ²⁹Si coherence lifetimes, leading to differences as large as three orders of magnitude. In compositions with abundant NMR active nuclei, such as alkali silicates, the ²⁹Si coherence lifetimes are dominated by coherent dephasing due to residual heteronuclear dipolar couplings, whereas in compositions dilute in NMR active nuclei, such as alkaline earth silicates, the ²⁹Si coherence lifetimes are dominated by incoherent dephasing due to paramagnetic impurities. Expressing the inverse of the coherence lifetime as a residual full width at half maximum (FWHM), we found that increasing rates of both MAS and a π-pulse train are effective in removing the residual ²⁹Si heteronuclear broadenings, with a near-linear relationship between FWHM and MAS rotor period and π-pulse spacing. Based on these results, we conclude that accurate ²⁹Si J coupling measurements will be the most challenging in lithium silicate glasses due to strong homonuclear dipolar couplings among ⁷Li nuclei, requiring MAS speeds up to 100 kHz, and be the least challenging in the alkaline earth silicate glasses. At a modest MAS speed of 14kHz, distributions of geminal J couplings across Si-O-Si linkages were measured in alkali and alkaline earth silicate glasses giving mean values of 4.2Hz and 5.1Hz in 0.4 CaO·0.6 SiO₂ and 0.33 Ba₂O·0.67 SiO₂ glasses, respectively, and 5.2Hz and 5.3Hz in 0.33 Na₂O·0.67 SiO₂ and 0.33 K₂O·0.67 SiO₂ glasses, respectively. We also observe greater variance in the J distributions of alkaline earth silicate glasses consistent with greater structural disorder due to increased modifier cation potential, i.e., the charge-to-radius ratio, Z/r of the cation.

Bioactive glass-biopolymers‑gold nanoparticle based composites for tissue engineering applications

Biomaterials based on bioactive glass with gold nanoparticle composites have many applications in tissue engineering due to their tissue regeneration and angiogenesis capacities. The objectives of the study were to develop new composites using bioactive glass with gold nanospheres (BGAuSP) and gold nanocages (BGAuIND), individually introduced in alginate-pullulan (Alg-Pll) polymer, to evaluate their biocompatibility potential, and to compare the obtained results with those achieved when β-tricalcium phosphate-hydroxyapatite (βTCP/HA) replaced the BG. The novel composites underwent structural and morphological characterization followed by in vitro viability testing on fibroblast and osteoblast cell lines. Additionally, the biomaterials were subcutaneously implanted in Sprague Dawley rats, for in vivo biocompatibility assessment during 3 separate time frames (14, 30 and 60 days). The biological effects were evaluated by histopathology and immunohistochemistry. The physical characterization revealed the cross-linking between polymers and glasses/ceramics and demonstrated a suitable thermal stability for sterilization processes. The in vitro assays demonstrated adequate form, pore size of composites ranging from few micrometers up to 100 μm, while the self-assembled apatite layer formed after simulated body fluid immersion confirmed the composites' bioactivity. Viability assays have highlighted optimal cellular proliferation and in vitro biocompatibility for all tested composites. Furthermore, based on the in vivo subcutaneous analyses the polymer composites with BGAuNP have shown excellent biocompatibility at 14, 30 and 60 days, exhibiting marked angiogenesis while, tissue proliferation was confirmed by high number of Vimentin positive cells, in comparison with the polymer composite that contains βTCP/HA, which induced an inflammatory response represented by a foreign body reaction. The obtained results suggest promising, innovative, and biocompatible composites with bioactive properties for future soft tissue and bone engineering endeavours.

Luminescence characteristics of Sm3+-doped lithium barium gadolinium silicate glasses for Orange LED's

Traditional melt-quenching technique is adopted for synthesis of Sm₂O₃ doped lithium barium gadolinium silicate (LBGS: Li₂O-BaO-Gd₂O₃-SiO₂) glasses. These glass samples are characterized by different spectroscopic techniques under ambient conditions. Density and molar volume of the present LBGS glass samples increase with increasing Sm³⁺ ion-concentration. JO intensity parameters Ω_λ (where λ = 2, 4 and 6) are evaluated by using Judd-Ofelt theory and Ω₄ > Ω₂ > Ω₆ trend is observed. Furthermore, these parameters are used to evaluate radiative properties like radiative transition probability, branching ratio, radiative lifetime and stimulated emission cross-section for state ⁴G_5/2 of Sm³⁺ ion. The measured color coordinates for the title glass fall within orange region of CIE diagram. For the present LBGS glasses, the correlated color temperature values are less than warm. The lifetime for the ⁴G_5/2 decreases from 2.468 to 0.566 ms when concentration increases from 0.1 to 2.0 mol% of Sm³⁺ ions. The analysis of non-exponential behavior of the decay profile through Inokuti-Hirayama model for S = 6 indicates that the energy transfer between Sm³⁺ ions is due to dipole-dipole interactions. Further energy transfer parameters (Q), critical distance (R_o, Å) and donor-acceptor interaction parameters (C_DA x 10^-40 cm⁶/s) of Sm³⁺ ions doped LBGS glasses were evaluated and compared to other glasses. From the evaluated results it is suggested that the present novelty of the work emphasizes on new matrix LBGS doped with Sm³⁺ ions showing increasing energy transfer rate with increasing in concentration of Sm₂O₃ content indicating these glasses are potential candidate for orange-light emitting device applications.

Energy transfer phenomenon of Gd3+ to excited ground state of Eu3+ ions in Li2O-BaO-Gd2O3-SiO2-Eu2O3 glasses

Li₂O-BaO-Gd₂O₃-SiO₂ glasses with different concentration of Eu³⁺ ions were developed by the traditional melt quenching technique and characterized via FTIR, absorption, excitation, emission and CIE color coordinates analysis for visible red emission application. The FTIR shows strong band at position 740 cm^-1 which is attributed to Si-O-Si symmetric stretching mode. Density and molar volume of LBGSEu glasses increases with Eu³⁺ ions concentration. The covalent nature of bond between the Eu³⁺ ions and surrounding ligands was confirmed from the bonding parameter (δ). From absorption spectra JO-parameters and oscillator strength are evaluated for LBGSEu6 glass. From JO-parameters, Eu³⁺ ions have asymmetric coordination environment and stronger covalency. The phonon line PSB (22,522 cm^-1) confirm the phonon energy ≈971 cm^-1, that corresponds to the energy of one phonon associated with maximum energy of the vibrational mode couple to Eu³⁺ ions. Under 275 nm and 393 nm excitation, intense red emission was observed at 613 nm, we observe efficient energy transfer phenomena from Gd³⁺ → Eu³⁺ in these glasses. Increasing trend of I_R with increasing concentration of Eu₂O₃ indicates the asymmetric environment around Eu³⁺ ions in LBGS. Moreover, from JO analysis, LBGS glasses have high capability for red laser device with high lasing power and energy extraction ratio. The fluorescence lifetimes show decreasing trend in lifetime with increasing concentration of Eu₂O₃ is due to radiative transition. From CIE color coordinate, the CIE color coordinates of LBGSEu6 glass fall in reddish region close to orange region and can be useful for optical display devices.

A novel tantalum-containing bioglass. Part I. Structure and solubility

Bioglasses are employed for surgical augmentation in a range of hard tissue applications. Tantalum is a bioactive and biocompatible transition metal that has been used as an orthopedic medical device. It has a range of biological and physical properties that make its incorporation into ionic form into bioactive glass systems promising for various clinical applications. The work herein reports the characterization and properties of novel tantalum-containing glasses. A series of glasses based on the system 48SiO₂-(36-X)ZnO-6CaO-8SrO-2P₂O₅-XTa₂O₅ with X varying from 0mol% (TA0) to 0.5mol% (TA2) were synthesized. The addition of small amounts of Ta₂O₅ did not cause crystallization of the glasses but increasing Ta₂O₅ content at the expense of ZnO was found to result in an increased number of bridging oxygens (BOs). This, along with the data recorded by differential thermal analysis (DTA) and magic angle spinning-nuclear magnetic resonance (MAS-NMR), confirms that Ta acts as a glass former in this series. Solubility experiments showed that minor changes in the glass structure caused by Ta incorporation (0.5mol%) exhibited greater cumulative % weight loss, pH values and cumulative Zn²⁺ and Sr²⁺ ion concentration over a period of 30days of maturation, when compared to Ta₂O₅-free glasses. The results presented in this article confirm that replacing ZnO with Ta₂O₅ in silicate glasses results in the formation of stronger bonds within the glass network without any adverse effects on the solubility of the glasses prepared from them.

Two heteronuclear dipolar results at the price of one: quantifying Na/P contacts in phosphosilicate glasses and biomimetic hydroxy-apatite

The analysis of S{I} recoupling experiments applied to amorphous solids yields a heteronuclear second moment M(2)(S-I) that represents the effective through-space dipolar interaction between the detected S spins and the neighboring I-spin species. We show that both M(2)(S-I) and M(2)(I-S) values are readily accessible from a sole S{I} or I{S} experiment, which may involve either S or I detection, and is naturally selected as the most favorable option under the given experimental conditions. For the common case where I has half-integer spin, an I{S} REDOR implementation is preferred to the S{I} REAPDOR counterpart. We verify the procedure by (23)Na{(31)P} REDOR and (31)P{(23)Na} REAPDOR NMR applied to Na(2)O-CaO-SiO(2)-P(2)O(5) glasses and biomimetic hydroxyapatite, where the M(2)(P-Na) values directly determined by REAPDOR agree very well with those derived from the corresponding M(2)(Na-P) results measured by REDOR. Moreover, we show that dipolar second moments are readily extracted from the REAPDOR NMR protocol by a straightforward numerical fitting of the initial dephasing data, in direct analogy with the well-established procedure to determine M(2)(S-I) values from REDOR NMR experiments applied to amorphous materials; this avoids the problems with time-consuming numerically exact simulations whose accuracy is limited for describing the dynamics of a priori unknown multi-spin systems in disordered structures.