Enhanced Mechanical and Electromechanical Properties of Compositionally Complex Zirconia Zr1-x(Gd1/5Pr1/5Nd1/5Sm1/5Y1/5)xO2-δ Ceramics.

Compositionally complex oxides (CCOs) or high-entropy oxides (HEOs) are new multielement oxides with unexplored physical and functional properties. In this work, we report fluorite structure-derived compositionally complex zirconia with composition Zr1-x(Gd1/5Pr1/5Nd1/5Sm1/5Y1/5)xO2-δ (x = 0.1 and 0.2) synthesized in solid-state reaction route and sintered via hot pressing at 1350 °C. We explore the evolution of these oxides' structural, microstructural, mechanical, electrical, and electromechanical properties regarding phase separation and sintering mechanisms. Highly dense ceramics are achieved by bimodal mass diffusion, composing nanometric tetragonal and micrometric cubic grains microstructure. The material exhibits an anomalously large electrostriction response exceeding the M33 value of 10-17 m2/V2 at room temperature and viscoelastic properties of primary creep in nanoindentation measurement under fast loading. These findings are strikingly similar to those reported for doped ceria and bismuth oxide derivates, highlighting the presence of a large concentration of point defects linked to structural distortion and anelastic behavior, which are characteristics of nonclassical ionic electrostrictors.

Effect of Simulated Mastication on Structural Stability of Prosthetic Zirconia Material after Thermocycling Aging.

Recent trends to improve the aesthetic properties-tooth-like color and translucency-of ceramic dental crowns have led to the development of yttria-stabilized zirconia (Y-TZP) materials with higher stabilizer content. These 5Y-TZP materials contain more cubic or t' phase, which boosts translucency. The tradeoff as a consequence of a less transformable tetragonal phase is a significant reduction of strength and toughness compared to the standard 3Y-TZP composition. This study aims at determining the durability of such 5Y-TZP crowns under lab conditions simulating the conditions in the oral cavity during mastication and consumption of different nutrients. The test included up to 10,000 thermal cycles from 5 °C to 55 °C "from ice cream to coffee" and a chewing simulation representing 5 years of use applying typical loads. The investigation of the stress-affected zone at the surface indicates only a very moderate phase transformation from tetragonal to monoclinic after different varieties of testing cycles. The surface showed no indication of crack formation after testing. It can, therefore, be assumed that over the simulated period, dental crowns of 5Y-TZP are not prone to fatigue failure.

Adjustment of Micro- and Macroporosity of ß-TCP Scaffolds Using Solid-Stabilized Foams as Bone Replacement.

To enable rapid osteointegration in bioceramic implants and to give them osteoinductive properties, scaffolds with defined micro- and macroporosity are required. Pores or pore networks promote the integration of cells into the implant, facilitating the supply of nutrients and the removal of metabolic products. In this paper, scaffolds are created from ß-tricalciumphosphate (ß-TCP) and in a novel way, where both the micro- and macroporosity are adjusted simultaneously by the addition of pore-forming polymer particles. The particles used are 10-40 wt%, spherical polymer particles of polymethylmethacrylate (PMMA) (Ø = 5 µm) and alternatively polymethylsilsesquioxane (PMSQ) (Ø = 2 µm), added in the course of ß-TCP slurry preparation. The arrangement of hydrophobic polymer particles at the interface of air bubbles was incorporated during slurry preparation and foaming of the slurry. The foam structures remain after sintering and lead to the formation of macro-porosity in the scaffolds. Furthermore, decomposition of the polymer particles during thermal debindering results in the formation of an additional network of interconnecting micropores in the stabilizing structures. It is possible to adjust the porosity easily and quickly in a range of 1.2-140 µm with a relatively low organic fraction. The structures thus prepared showed no cytotoxicity nor negative effects on the biocompatibility.

PA-12-Zirconia-Alumina-Cenospheres 3D Printed Composites: Accelerated Ageing and Role of the Sterilisation Process for Physicochemical Properties.

The aim of this study was to conduct artificial ageing tests on polymer-ceramic composites prepared from polyamide PA-12 polymer matrix for medical applications and three different variants of ceramic fillers: zirconia, alumina and cenospheres. Before ageing, the samples were subjected to ethyl oxide sterilization. The composite variants were prepared for 3D printing using the fused deposition modeling method. The control group consisted of unsterilized samples. Samples were subjected to artificial ageing in a high-pressure autoclave. Ageing conditions were calculated from the modified Hammerlich Arrhenius kinetic equation. Ageing was carried out in artificial saliva. After ageing the composites were subjected to mechanical (tensile strength, hardness, surface roughness) testing, chemical and structural (MS, FTIR) analysis, electron microscopy observations (SEM/EDS) and absorbability measurements.

Effect of Calcination Temperature on the Phase Composition, Morphology, and Thermal Properties of ZrO2 and Al2O3 Modified with APTES (3-aminopropyltriethoxysilane).

This paper describes the effect of calcination temperature on the phase composition, chemical composition, and morphology of ZrO2 and Al2O3 powders modified with 3-aminopropyltriethoxysilane (APTES). Both ceramic powders were modified by etching in piranha solution, neutralization in ammonia water, reaction with APTES, ultrasonication, and finally calcination at 250, 350, or 450 °C. The obtained modified powders were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, particle size distribution (PSD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS), and thermogravimetric analysis (TGA).

Alumina and Zirconia-Reinforced Polyamide PA-12 Composites for Biomedical Additive Manufacturing.

This work aimed to prepare a composite with a polyamide (PA) matrix and surface-modified ZrO2 or Al2O3 to be used as ceramic fillers (CFs). Those composites contained 30 wt.% ceramic powder to 70 wt.% polymer. Possible applications for this type of composite include bioengineering applications especially in the fields of dental prosthetics and orthopaedics. The ceramic fillers were subjected to chemical surface modification with Piranha Solution and suspension in 10 M sodium hydroxide and Si3N4 to achieve the highest possible surface development and to introduce additional functional groups. This was to improve the bonding between the CFs and the polymer matrix. Both CFs were examined for particle size distribution (PSD), functional groups (FTIR), chemical composition (XPS), phase composition (XRD), and morphology and chemical composition (SEM/EDS). Filaments were created from the powders prepared in this way and were then used for 3D FDM printing. Samples were subjected to mechanical tests (tensility, hardness) and soaking tests in a high-pressure autoclave in artificial saliva for 14, 21, and 29 days.

Additive Manufacturing of ß-Tricalcium Phosphate Components via Fused Deposition of Ceramics (FDC).

Bone defects introduced by accidents or diseases are very painful for the patient and their treatment leads to high expenses for the healthcare systems. When a bone defect reaches a critical size, the body is not able to restore this defect by itself. In this case a bone graft is required, either an autologous one taken from the patient or an artificial one made of a bioceramic material such as calcium phosphate. In this study ß-tricalcium phosphate (ß-TCP) was dispersed in a polymer matrix containing poly(lactic acid) (PLA) and poly(ethylene glycole) (PEG). These compounds were extruded to filaments, which were used for 3D printing of cylindrical scaffolds via Fused Deposition of Ceramics (FDC) technique. After shaping, the printed parts were debindered and sintered. The components combined macro- and micropores with a pore size of 1 mm and 0.01 mm, respectively, which are considered beneficial for bone healing. The compressive strength of sintered cylindrical scaffolds exceeded 72 MPa at an open porosity of 35%. The FDC approach seems promising for manufacturing patient specific bioceramic bone grafts.

Mechanical behaviour of extremely tough TZP bioceramics.

Tetragonal Zirconia Polycrystals (TZP) is attractive for structural biomedical applications because of their excellent mechanical properties at room-temperature, which include high strength, fracture toughness and wear resistance. In this work, zirconia stabilized with Y or Yb or Yb+Nd, all containing 0.5 vol.% Al2O3, were prepared by hot-pressing (HP) at 50-60 MPa and sintered at 1300-1350 °C for 1 h. Microstructural features, phase composition and mechanical properties were investigated. The strength was measured by 4-point bending (4P-B), piston-on-three-balls (P-3B) and three-balls-on-three-balls (3B-3B) biaxial methods. Toughness was determined by indentation strength in bending (ISB). Vickers hardness (Hv) and the Young modulus (E) were also estimated. Preliminary aging behaviour (LTD) was also here considered. Measured biaxial strength was significantly higher (until 1.83 times) than the uniaxial one because of the tetragonal to monoclinic (t-m) zirconia phase transformation which is strongly influenced by the loading configuration. The variation of the strength with the testing method is attributed to the compressive stresses generated by the phase transformation which is particularly favoured under P-3B tests and also to the calculation of the stresses from elastic theories. LTD preliminary tests showed excellent aging resistance of 3Yb-0.5A ceramics.

Issues in nanocomposite ceramic engineering: focus on processing and properties of alumina-based composites.

Ceramic nanocomposites, containing at least one phase in the nanometric dimension, have received special interest in recent years. They have, in fact, demonstrated increased performance, reliability and lifetime with respect to monolithic ceramics. However, a successful approach to the production of tailored composite nanostructures requires the development of innovative concepts at each step of manufacturing, from the synthesis of composite nanopowders, to their processing and sintering.This review aims to deepen understanding of some of the critical issues associated with the manufacturing of nanocomposite ceramics, focusing on alumina-based composite systems. Two case studies are presented and briefly discussed. The former illustrates the benefits, in terms of sintered microstructure and related mechanical properties, resulting from the application of an engineering approach to a laboratory-scale protocol for the elaboration of nanocomposites in the system alumina-ZrO2-YAG (yttrium aluminium garnet). The latter illustrates the manufacturing of alumina-based composites for large-scale applications such as cutting tools, carried out by an injection molding process. The need for an engineering approach to be applied in all processing steps is demonstrated also in this second case study, where a tailored manufacturing process is required to obtain the desired results.

Hemolytic characteristics of three commercially available centrifugal blood pumps.

OBJECTIVE: As compared with traditional extracorporeal roller-occlusion blood pumps, nonocclusive centrifugal pumps offer the benefits of requiring a smaller circuit surface area and, thus, a smaller prime volume. However, centrifugal blood pumps have been reported to generate unacceptable levels of hemolysis. We hypothesize that the newer generation centrifugal pumps have an incidence of hemolysis similar to the traditional roller head pumps and, thus, could be used for extracorporeal membrane oxygenation circuits. DESIGN: Randomized, prospective, bench study. SETTING: University research laboratory. INTERVENTIONS: Three centrifugal blood pumps (Cobe Revolution, Jostra Rotaflow, and Medtronic BioMedicus) were compared with a roller occlusion blood pump (Cobe Century). Hemolysis generation was examined during 6 hrs of continuous use. Two test runs per group were randomly performed on three consecutive days for a total of six test runs for each of the four pumps (n = 24). MEASUREMENTS AND MAIN RESULTS: Plasma free hemoglobin values were determined using a Spectra MaxPlus spectrophotometer. A normalized index of hemolysis was calculated to compare the individual trials. The Cobe Revolution and the Jostra Rotaflow compared favorably with the Cobe Century roller occlusion blood pump in the amount of hemolysis produced. CONCLUSIONS: These data are encouraging for the development of a low-prime, mobile neonatal extracorporeal membrane oxygenation circuit using centrifugal pump technology.

Soluble alpha2-macroglobulin receptor is increased in endotracheal aspirates from infants and children after cardiopulmonary bypass.

OBJECTIVE: Cytokine dysregulation contributes to the systemic inflammatory response after cardiopulmonary bypass. Clearance of cytokine binding proteins may be important in the resolution of inflammation. Our aim was to determine whether the cytokine binding protein alpha 2 -macroglobulin and its soluble receptor were upregulated in endotracheal aspirates from infants and children undergoing cardiopulmonary bypass. METHODS: Seventy tracheal aspirates were collected before and after cardiopulmonary bypass from 35 infants and children undergoing surgical correction of congenital heart defects. alpha 2 -Macroglobulin and the soluble alpha 2 -macroglobulin receptor were identified by Western blot. With the use of multi-analyte cytokine profiling, pro-inflammatory and anti-inflammatory cytokines were quantified, normalized to total protein, and expressed as ratios. Paired t tests and Wilcoxon signed-rank tests were performed between prebypass and postbypass samples. Correlations were examined among alpha 2 -macroglobulin, soluble alpha 2 -macroglobulin receptor, cytokine ratios, and the clinical variables of cardiopulmonary bypass, aortic crossclamp, and circulatory arrest times. RESULTS: alpha 2 -Macroglobulin increased by 50% (mean densitometry increase 82,683 +/- 184,594, P = .012), and soluble alpha 2 -macroglobulin receptor increased by 17% (mean densitometry increase 506,148 +/- 687,037, P = .0001) after cardiopulmonary bypass. The ratio of interleukin-8/interleukin-4 increased by 136% ( P = .0001), and interleukin-8/interleukin-10 increased by 102% ( P = .001). The increase in soluble alpha 2 -macroglobulin receptor was positively correlated with the ratios of interleukin-8/interleukin-4 and interleukin-8/interleukin-10. There were no statistically significant positive correlations between the increase in alpha 2 -macroglobulin or soluble alpha 2 -macroglobulin receptor and measured clinical variables. CONCLUSIONS: We report for the first time the upregulation of alpha 2 -macroglobulin and soluble alpha 2 -macroglobulin receptor in tracheal aspirates after cardiopulmonary bypass in infants and children. Soluble alpha 2 -macroglobulin receptor correlates with increased alpha 2 -macroglobulin and a disproportionate increase in pro-inflammatory to anti-inflammatory cytokine ratios.

Anaesthetic management of infants with glycogen storage disease type II: a physiological approach.

Pompe or Glycogen Storage Disease type II (GSD-II) is a genetic disorder affecting both cardiac and skeletal muscle. Historically, patients with the infantile form usually die within the first year of life due to cardiac and respiratory failure. Recently a promising enzyme replacement therapy has resulted in improved clinical outcomes and a resurgence of elective anaesthesia for these patients. Understanding the unique cardiac physiology in patients with GSD-II is essential to providing safe general anaesthesia.

North American neonatal extracorporeal membrane oxygenation (ECMO) devices: 2002 survey results.

In mid 2002, surveys of active extracorporeal membrane oxygenation (ECMO) centers in the United States and Canada were conducted via E-mail regarding neonatal equipment and personnel. Seventy-four out of 99 (75%) North American ECMO centers listed in the Extracorporeal Life Support Organization (ELSO) directory responded to the survey. Of the responding centers, 95% use roller pumps, and the remaining 5% use centrifugal pumps. Silicone membrane oxygenators were used by 97% of the respondents, while 3% used hollow fiber oxygenators. Of the silicone membrane oxygenator users, 82% used the Medtronic ECMOtherm heat exchanger, 15% used a Gish heat exchanger, and 3% used the Dideco D720 heat exchanger. Sixty-one percent of the responding centers used some form of in-line blood gas monitoring. Five percent of the centers used a bubble trap in the arterial line, and 12% used an arterial line filter. A bladder was used by 92% of the centers, and 29% used a mechanical bladder box for servo regulation, the remaining 71% used pressure servo regulation. An air bubble detector was used by 65% of the responding centers, although 81% had the device available. Heparin coating was used by 5% of the centers on all their neonatal ECMO patients. The average low range ACT was 183 seconds, and the average high range ACT was 216 seconds. At 49% of the responding centers, perfusionists were involved with the ECMO program, registered nurses were involved at 84% of the centers, and respiratory therapists were involved at 61% of the centers, perfusion assistants were involved at one center (1%), and biomedical engineers were involved at one of the centers. When compared to a 1990 survey, a shift away from using bladder boxes and toward using air bubble detectors is apparent. But other than those two shifts, ECMO is done in much the same manner as it was done 12 years ago.

A clinical comparison of two commercially available pediatric hemoconcentrators.

Hemoconcentration is a technique that involves selective removal of plasma water and some dissolved solutes by way of an ultrafiltration membrane. Hemoconcentrators (HC) are routinely used during pediatric cardiopulmonary bypass (CPB) to remove free plasma water and various inflammatory mediators. This paper examines two different commercial HCs, the Dideco DHF0.2 and the Minntech Hemocor HPH 400. Both products were evaluated when used for prebypass ultrafiltration (Pre-BUF), and postbypass modified ultrafiltration (MUF). Five HCs were evaluated for each product, and the two groups were compared during the two different phases of the cardiac procedure. During the pre-BUF period, both groups of HCs were tested at a transmembrane pressure (TMP) gradient of 500 millimeters of mercury (mmHg). The mean amount of ultrafiltrate (UF) removed by the Dideco DHF0.2 was 81.4 milliliters per minute (mL/min), and the mean amount of UF removed by the Minntech Hemocor HPH 400 was 90.8 mL/min during the pre-BUF period. During the peribypass period flow parameters were much harder to define. As a result, these data are not reported. During the MUF procedure, the mean amount of UF removed by the Dideco DHF0.2 was 74.2 mL/min at an average MUF flow rate of 130 mL/min. The mean amount of UF removed by the Minntech Hemocor HPH 400 was 81.4 mL/min at an average MUF flow rate of 127 mL/min. Both products performed adequately under the clinical circumstances described above. The Minntech HPH 400 produced a hemofiltrate that was consistently tinged with a slight red color. The Dideco DHF0.2 consistently produced a hemofiltrate that was noticeably clearer than that of the Minntech device.