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Porous silicon nitride–based drug delivery carrier

Michal Hičák, Ľubomír Medvecký, Miroslav Hnatko, Radoslava Stulajterová, Mária Giretová, Monika Tatarková, Zoltán Lenčéš, Pavol Šajgalík

Abstract

Tetracalcium phosphate/monetite biocement was modified with the addition of 30 wt% highly porous silicon nitride/α-tricalcium phosphate (α-TCP) microgranules. The volume ratio of Si3N4 and α-TCP in microgranules was 1:1 and showed good in vitro simulated body fluid bioactivity with precipitation of hydroxyapatite particles. The intention of addition of microgranules to the biocement was to have a carrier of drug, which can be released into the body in due time. Granules prepared by the freeze granulation of starting mixture of silicon nitride and calcium phosphate and subsequent sintering at 1100°C have a suitable pore structure for the foreseen use. The pore volume was almost 1000 mm3/g with the open porosity of 77 vol%. This porosity and the biocompatible composition of silicon nitride–based granules gave a chance to fabricate a suitable composite cement for dexamethasone (DMZ) drug release into the human body. An accelerated release of dexamethasone from composite cement was observed and the full amount of DMZ was released from the composite biocement after 10 days. The presented results are a good base to adjust the total drug release time by the mixing of an appropriate amount of drug infiltrated ceramic granules with the tetracalcium phosphate/monetite cement.

Keywords

biocement, bioceramics, calcium phosphate, dexamethasone, drug release, silicon nitride

Physical properties of feeds for novel bioactives – encapsulating bead formation

Hansen, Mackenzie M.

Abstract

Encapsulation involves the entrapment of sensitive bioactive compounds with structure- forming food components to enhance protection and delivery. Blends of proteins and glass- forming carbohydrates are often used as encapsulation matrices and for structure formation. When bioactives intended for encapsulation are mixed with structuring proteins under acidic and neutral pH conditions and ambient temperatures, weak, non-covalent protein-bioactive interactions have been reported to occur. Complex formation may influence the physical properties of dispersions as well as dried products formed by feed mixtures. We hypothesized that: (i) Processes forming concentrated protein-carbohydrate feed dispersions into dry, solid beads could be developed, and (ii) formulation composition changes such as varied total solids, protein-carbohydrate ratios, protein isolates with different purities and structures, carbohydrate types, bioactives contents, and bioactives sources with diverse structures and sizes of predominant compounds would result in changes to the physico-chemical properties and drop formation abilities of dispersions, as well as the physical characteristics of dry beads formed. Key objectives of the present study were: (i) the development of two different simple, continuous processes forming feed dispersions into dried, novel bead structures, and (ii) characterization of the effects of changes in formulation compositions on the physical properties of liquid feeds and resulting dry beads.

Keywords

Protein, Bioactives, Encapsulation, Physico-chemical properties, Freeze granulation

Sintering and microstructure development of SFR MOX nuclear fuel

Julie Simeon

Abstract

For the manufacture of FNR (Fast Neutron Reactor) MOX (Mixed Oxide) fuel, (U,Pu)O2-x, consolidation of green compacts shaped from the raw powders, is performed by sintering at high temperature. Thus, the detailed study of the sintering is based on coupling of dilatometric tests in controlled reducing atmospheres to multi-scale microstructural characterizations in order to plot sintering maps and to establish predictive sintering models.In this study, three batches of powders were obtained by cryogenic granulation with target Pu/(U+Pu) contents of 15, 26 and 33 %mol. A single sintering trajectory was obtained from the relative density and grain size of each sample (raw and sintered). It is independent not only of the heat cycle (heating rate, sintering temperature and soak time) but also of the plutonium content and the oxygen stoichiometry.A batch with a Pu/(U+Pu) content of 26 %mol was prepared by direct co-milling (based on an industrial method for nuclear fuel fabrication). The trajectory observed for this batch differs from that of the three others.For all batches (granulated and co-milled), calculations of the diffusion coefficients from dilatometry data and the sintering map show that the densification is governed by the self-diffusion of plutonium at the grain boundaries. Furthermore, transmission electron microscopy results, in agreement with results obtained by X-ray diffraction, electron microprobe and Raman spectroscopy, show that grain growth is controlled by grain boundaries.A single sintering trajectory allows the calculation of the densification activation energy through methods exploiting the data collected by dilatometry. Thus, the activation energy of densification is evaluated at 454 ± 64 kJ/mol for all batches resulting from freeze granulation and at 548 ± 33 kJ/mol for the co-milled batch. These values allow the establishment of predictive sintering models that were used to lower the maximum temperature and duration required during sintering without affecting the fuel with the specifications.

Keywords

Microstructure, Sintering, Nuclear Fuel

Formation of dry beads for bioactives encapsulation by freeze granulation

Mackenzie M. Hansen, Richard W. Hartel, Yrjö H. Roos

Abstract

Solid beads formed by whey protein isolate (WPI) and various sugars/polyols with a wide range of glass transition temperatures showed potential as structures for encapsulation of Aronia berry bioactives. Whey protein isolate (WPI), Aronia extract, and carbohydrates (maltitol, sucrose, or trehalose) were mixed into water to form concentrated liquid feed dispersions with varied pH. Microstructures were imaged and physical properties including complex viscosities, surface tensions, particle size distributions, and centrifuge separation were measured to investigate the effects of carbohydrate type, WPI:sugar ratio, and Aronia polyphenols (PP) concentration on liquid properties. Feed dispersions were used to produce dry beads with an adapted freeze granulation method, where individual drops were pumped into liquid nitrogen for flash freezing and harvested for subsequent freeze-drying to remove water. Dry bead diameters, water contents, and water activities were measured prior to measuring hardness and glass transition temperatures. While formulating with different sugars did not meaningfully impact liquid feed characteristics that impact processing, compositional differences were found to influence characteristics of the final dried beads more notably.

Porous silicon nitride-based drug delivery carrier

Hicak, Michal; Medvecky, L’ubomir; Hnatko, Miroslav; Stulajterova, Radoslava; Giretova, Maria; Tatarkova, Monika; Lences, Zoltan; Sajgalik, Pavol

Abstract

Tetracalcium phosphate/monetite biocement was modified with the addition of 30 wt% highly porous silicon nitride/alpha-tricalcium phosphate (alpha-TCP) microgranules. The volume ratio of Si3N4 and alpha-TCP in microgranules was 1:1 and showed good in vitro simulated body fluid bioactivity with precipitation of hydroxyapatite particles. The intention of addition of microgranules to the biocement was to have a carrier of drug, which can be released into the body in due time. Granules prepared by the freeze granulation of starting mixture of silicon nitride and calcium phosphate and subsequent sintering at 1100 degrees C have a suitable pore structure for the foreseen use. The pore volume was almost 1000 mm(3)/g with the open porosity of 77 vol%. This porosity and the biocompatible composition of silicon nitride-based granules gave a chance to fabricate a suitable composite cement for dexamethasone (DMZ) drug release into the human body. An accelerated release of dexamethasone from composite cement was observed and the full amount of DMZ was released from the composite biocement after 10 days. The presented results are a good base to adjust the total drug release time by the mixing of an appropriate amount of drug infiltrated ceramic granules with the tetracalcium phosphate/monetite cement.

Formulation of mixed alumina/kaolin systems : Application to the elaboration of multi-layer materials by co-pressing

Rana Al Tahan

Abstract

Multilayer ceramic architectures generally exhibit improved mechanical properties in regards with individual monolithic constituents. In alumina-based materials, addition of kaolin can advantageously promote i) mullite crystallisation and ii) internal residual stresses by monitoring thermal expansion mismatch between layers. From powders prepared by freeze granulation whose formulations contain a reduce amount of organic additives, alumina/mullite composites shaped by uniaxial pressing have been developed and characterized. Two different kaolins are used in this study, with different characteristics in terms of crystallinity, grain shape, layering and basal/lateral face ratio. The originality of this work consisted in studying in detail the dispersion mechanisms of kaolinite suspensions in aqueous media by acoustophoresis, and in highlighting the relationship between kaolinite’s electrokinetic properties, physicochemical characteristics and thermal pretreatment between 200 and 800°C. The sintering properties of mixed alumina/kaolinite formulations were studied as a function of kaolinite crystallinity and content (0-25%vol). This thesis studies the integrated chain of a ceramic process, starting with the selection of kaolinite as a raw material (acoustophoresis, MAS NMR), its crystallochemical transformation into mullite (thermal analyses, dilatometry) and its incorporation into an alumina matrix for an original architecture of multilayer materials with modified properties of toughness and fracture resistance. The multi-layer materials developed show good interfacial adhesion despite the presence of a porous zone close to the layer interface. Compared to the monolithic materials, the most efficient multilayer configurations exhibit a failure stress improved by 30%.

Keywords

Kaolinite, Aluminous multilayer materials, Residual stresses, Co-Pressing, Mullite

Modified Freeze-granulation method for fabricating Li2TiO3 ceramic tritium breeding pebbles

Shufeng Zhang, Wei Lu, Youfu Jiang, Xinyu Gao, Delin Chu, Weihua Wang

Abstract

Lithium metatitanate (Li2TiO3) ceramic is an important candidate for tritium breeding material in fusion reactor blanket. Nevertheless, mass production has become an important factor restricting the application of Li2TiO3 pebbles. In this paper, freeze-granulation method is innovatively modified by drying frozen pebbles in acetone. The principle of modified freeze-granulation method is explained in detail. Influence of PVA content, sintering temperature and sintering time on mechanical performance of frozen pebbles dried in acetone are carefully discussed. The modified process could shorten the drying time in 30 min under the premise of good crushing load and thus conducive to improve the efficiency of mass production of tritium breeding ceramic pebbles potentially in the future. Finally, the Li2TiO3 pebbles present good sphericity, high average crushing load (38 N), abundant and uniform pores which are beneficial to tritium release.

Enhancing the density and crush load of Li2TiO3 tritium breeding ceramic pebbles by adding LiNO3-Li2CO3

Yichao Gong, Qingze Na, Chao Dang, Yijiang Yang, Mingxiang Tang, Zhanwen Liu, Guojun Zhang

Abstract

The fabrication of Li2TiO3 ceramic pebbles with satisfactory density and excellent crush load while maintaining a fine grain structure is one of the research objectives of solid tritium breeders. However, densification and grain refinement are often contradictory in lithium-containing ceramics during the sintering process. In this work, LiNO3-Li2CO3 was added during the preparation of Li2TiO3 green spheres by the wet process, and the formation of LiNO3-Li2CO3 molten salt resulted in the significant sintering improvement of Li2TiO3 ceramic pebbles. The addition of LiNO3-Li2CO3 increased the density of Li2TiO3 ceramic pebbles by 10.47 % (92.63 % vs. 82.16 %) and the crush load by more than four times (144.54 N vs. 28.2 N). ICP-OES analysis showed that the lithium content of the Li2TiO3 ceramic pebbles was slightly increased by the addition of LiNO3-Li2CO3. Overall, the difficulty of balancing grain refinement and densification in lithium-containing tritium breeders can be addressed by the proposed method.

Comparative sintering behaviour of MOX powders synthesized through the freeze granulation or dry-cogrinding routes

Guillaume Bernard-Granger, Florent Lebreton, Laure Ramond, Marion Le Guellec, Gabriella Cunha Costa Miranda, Abibatou Ndiaye, Thierry Gervais

Abstract

Two MOX powders containing 11 mol% Pu/(U+Pu) have been synthesized using the freeze granulation or dry-cogrinding routes. The sintering behaviour of green compacts has been investigated up to 1700 °C in an Ar/4.3 vol% H2 humidified with 1200 vpm H2O. The evolution of the sintering trajectory (grain size as a function of relative density) is identical up to approximately 94% relative density. Above this value, grain growth becomes significant in compacts made with the powder obtained by freeze granulation and densification becomes more modest. As for it, the sintering trajectory relating to the compacts shaped from the co-grinded powder continues up to approximately 97.5% relative density, without remarkable grain growth. Beyond this value, grain growth occurs and densification slows down. It has also been shown that the plutonium distribution is more homogeneous in the case of a sample sintered from the powder obtained by freeze-granulation (relative density around 97–99%).

Optimization of freeze granulation and sintering behavior of MgO granules for thermal interface materials

Hyojung Cho, Rokhyeon Kim, Haewon Jung, Joo-Hwan Han, In Chul Jung, Jungho Ryu

Abstract

Heat management of high-performance secondary batteries, used in various applications that require high charging and discharging rates, such as electric vehicles and electronic devices, has recently been attracting increased attention. One of the most popular heat management technologies involves the use of thermal interface materials (TIMs) for heat dissipation. TIMs are composites of thermally conductive granulated fillers uniformly dispersed in a polymer matrix. In this study, the freeze granulation process is optimized to prepare MgO granules with high thermal conductivity as an alternative to commercial alumina fillers for TIMs. The heat dissipation characteristics of TIMs are directly related to their thermal properties, size distribution, shape, density, and filler content. Therefore, a suspension is optimized with high solid content and low viscosity for proper spraying. The size distribution and sintered granule density are analyzed for various spraying distances and pressures to optimize the process for producing high-quality TIMs. Finally, a TIM with MgO granules formed by freeze granulation dispersed in silicone-based resin is fabricated, with a high thermal conductivity exceeding 5.425 W/m∙K (with an interfacial thermal resistance of 0.343 K∙ cm2/W) and low density of 2.78 g/cm3.