Qualification of the Low-pressure Cold Gas Spraying for the Additive Manufacturing of Copper-Nickel-Diamond Grinding Wheels

Grinding wheels are usually manufactured by powder metallurgical processes, i.e., by molding and sintering. Since this requires the production of special molds and the sintering is typically carried out in a continuous furnace, this process is time-consuming and cost-intensive. Therefore, it is only worthwhile for medium and large batches. Another influencing factor of the powder metallurgical process route is the high thermal load during the sintering process. Due to their high thermal sensitivity, superabrasives such as diamond or cubic boron nitride are very difficult to process in this way. In this study, a novel and innovative approach is presented, in which superabrasive grinding wheels are manufactured by thermal spraying. For this purpose, flat samples as well as grinding wheel bodies were coated by low-pressure (LP) cold gas spraying with a blend of a commercial Cu-Al2O3 cold gas spraying powder and nickel-coated diamonds. The coatings were examined metallographically in terms of their composition. A well-embedded superabrasive content of 12 % was achieved. After the spraying process, the grinding wheels were conditioned and tested for the grinding application of cemented carbides and the topographies of both the grinding wheel and the cemented carbide were evaluated. Surface qualities of the ground surface that are comparable to those of other finishing processes were reached. This novel process route offers great flexibility in the combination of binder and hard material as well as a cost-effective single-part and small-batch production.

Analysis of stress gradients in physical vapour deposition multilayers by X-ray diffraction at fixed depth intervals

The objective of this article is to develop and apply a model for the design and evaluation of X-ray diffraction experiments to measure phase-specific residual stress profiles in multilayer systems. Using synchrotron radiation and angle-dispersive diffraction, the stress measurements are performed on the basis of the sin2ψ method. Instead of the traditional Ω or χ mode, the experiments are carried out by a simultaneous variation of the goniometer angles χ, Ω and φGto ensure that the penetration and information depth and the measuring direction φ remain unchanged when the polar angle ψ is varied. The applicability of this measuring and evaluation strategy is demonstrated by the example of a multilayer system consisting of Ti and TiAlN layers, alternately deposited on a steel substrate by means of physical vapour deposition.

In vitro and in vivo evaluation of biodegradable, open-porous scaffolds made of sintered magnesium W4 short fibres

A cytocompatible and biocompatible, degradable, open-porous, mechanically adaptable metal scaffold made of magnesium alloy W4 melt-extracted short fibres was fabricated by liquid phase sintering. Cylindrical samples (3×5 mm) of sintered W4 short fibres were evaluated under in vitro (L929, HOB, eudiometer, weight loss) and in vivo conditions (rabbits: 6 and 12 weeks). The in vitro corrosion environment (e.g., temperature, flow, composition of corrosion solution, exposure time) significantly influenced the corrosion rates of W4 scaffolds compared with corrosion in vivo. Corrosion rates under cell culture conditions for 72 h varied from 1.05 to 3.43 mm y(-1) depending on the media composition. Corrosion rates measured in eudiometric systems for 24 h were ~24-27 times higher (3.88-4.43 mm y(-1)) than corrosion in vivo after 6 weeks (0.16 mm y(-1)). Moreover, it was found that the cell culture media composition significantly influences the ionic composition of the extract by selectively dissolving ions from W4 samples or their corrosion products. A pilot in vivo study for 6 and 12 weeks demonstrated active bone remodelling, no foreign body reaction and no clinical observation of gas formation during W4 scaffold implantation. Long-term in vivo studies need to be conducted to prove complete degradation of the W4 scaffold and total replacement by the host tissue.

Severe cerebral venous sinus thrombosis and dural arteriovenous fistula in an infant with protein S deficiency

A 12-month-old infant presented with cerebral seizures and neurological deficits. MRI scan of the brain and angiography showed massive cerebral venous sinus thrombosis complicated by a dural arteriovenous fistula. Subsequent clotting analysis revealed a protein S deficiency. Screening for inherited coagulation inhibitor deficiency is recommended in children with unexplained or atypical thrombotic events.

Influence of the red blood cell Ca2+-ion concentration on the erythrocyte aggregation in stasis

Ca2+ ions were transported into the cell by incubation of the erythrocyte suspension with ionophore A23187, a lipophil electric neutral ion complexing substance. Erythrocyte aggregation could be increased twice, when doubling the intracellular Ca2+-ion concentration. Our measurements lead to the suggestion that an increase of the cytoplasmatic Ca2+ ion changes the physical and/or biochemical properties of the aggregation receptors on the membrane surface, i.e., cell-protein interactions are regulated by alteration of the intracellular Ca2+-ion concentration.

[Continuous subcutaneous deferoxamine infusions in thalassemia major. Improvement in glucose tolerance]

Exocrine and endocrine pancreatic functions were studied in 30 patients with homozygotic beta-thalassaemia. All were treated with continuous subcutaneous deferoxamine infusions for a mean period of 30 months. Three patients (aged 18-22 years) had insulin-dependent diabetes, two before and one shortly after the onset of deferoxamine administration. There was no improvement during the treatment. An abnormal glucose tolerance test was demonstrated in 14 patients (47%) before and in seven (23%) during deferoxamine infusion. Enzyme activity of alpha-amylase and lipase as an expression of exocrine pancreatic function was normal in all during the observation period. Improvement in endocrine pancreatic function was apparently age-dependent: the younger the patient at the onset of treatment the more likely is normalization of the oral glucose tolerance test.

[Specific immunoglobulin and acyclovir in the prevention and treatment of varicella zoster infections in children with neoplastic diseases]

Immunocompromised children with acute leukemias and solid tumors are at high risk of fatal varicella infection. Reviewing a total of 242 patients at risk we have found that zoster immune plasma from reconvalescent patients (ZIP) and commercially available specific varicella/zoster immune globulin (VZIG) both prevent fatal disease. In addition, Acyclovir was effective against VZV-infections in this group of patients. We summarize our present policy of prophylaxis and treatment of immunocompromised children with neoplastic disease who have been exposed to VZV.

[Longitudinal growth of patients with homozygote beta-thalassemia during continuous subcutaneous infusion of deferoxamine]

Subcutaneous continuous infusions of deferoxamine were administered to 28 children with thalassaemia major. Longitudinal growth beyond the eleventh year was favourably influenced. The normal growth spurt during puberty was not demonstrable in six patients (three boys and three girls) during their puberty. Taking into account standard height allowing for parents' height, prospective final height and ethnic origin, the treatment favourably influenced longitudinal growth in 26 of the 28 children.

[Frequent occurrence of Yersinia infection in hemosiderosis]

Antibodies against Yersinia were found in 12 of 50 patients with hemosiderosis, in 11 of 47 patients with thalassemia major and in one of three patients with Blackfan-Diamond anemia. All patients were treated with subcutaneous continuous deferoxamin-infusions. A systemic yersiniosis occurred in seven patients, all with homozygous beta-thalassemia, in five during and in two before treatment with deferoxamin. Hemosiderosis and infusions with deferoxamin seem to increase the risk of yersinia septicemia.

[Continuous subcutaneous deferoxamine treatment in thalassemia major. Decrease of hemosiderosis and improvement of liver function]

Liver function during continuous subcutaneous deferoxamine therapy was investigated in 29 patients with homozygotic beta-thalassaemia. Average duration of treatment was 26 months (range 8-51 months). A decrease in haemosiderosis and an improvement in liver function was observed in 27 patients: Mean liver density, determined by computed tomography, decreased from 98 to 84 HU, mean serum ferritin concentration fell from 8028 to 3661 ng/ml, mean serum GOT activity from 44 to 13 U/l and GPT from 51 to 16 U/l. Mean cholinesterase activity, reflecting the improved synthetic activity of the liver, increased from 4063 to 4530 U/l.

Aggregate formation of erythrocytes and diabetic retinopathy in children, adolescents, and adults with diabetes mellitus (type I)

In vitro measurements were carried out to study the aggregation of erythrocytes in 33 children and young adolescents, three older adolescents, and 38 adults with type I diabetes. The aggregate formation of erythrocytes in stasis was increased in adult patients with both "good" and "poor" metabolic control when compared to control values. The aggregation of red cells in all children and the younger adolescents, both those under good and poor metabolic control, did not statistically differ from those of controls. Each of the three older adolescents showed an increased aggregate formation of their erythrocytes compared to controls. All adult patients under poor metabolic control exhibited various stages of diabetic retinopathy as shown by fluorescence angiography. Only one child under poor metabolic control showed an early stage of retinopathy (stage I according to Malone). The three older adolescents showed an increased aggregate formation of their erythrocytes. These patients exhibited also stage I of retinopathy. We suggest that the increased aggregation of erythrocytes of both adult and older adolescent patients may be one of the reasons for the development of diabetic retinopathy. Moreover, the normal erythrocyte aggregation of the diabetic children and younger adolescents could help to explain the rare occurrence of microangiopathies in childhood diabetes.

[Deferoxamine in hemosiderosis. Fecal iron excretion during continuous subcutaneous infusion]

Faecal iron excretion during continuous subcutaneous deferoxamine infusion was measured by flameless atom-absorption spectral photometry in 21 patients with homozygous ss-thalassaemia and one patient with Blackfan-Diamond anaemia. Taking into account faecal and urinary iron excretion, more iron was eliminated than was taken up during transfusion and by intestinal absorption. Urine contained 37.9%, faeces 62.1% of the amount of iron eliminated.

[Antibiotic prophylaxis and therapy of febrile aplastic children with acute leukemia]

One hundred and twenty-one febrile episodes (FE) were studied in 58 aplastic children with acute leukemia. All patients received a prophylactic regimen of trimethoprim-sulfamethoxazole (TS) and colistin sulfate orally, and amphotericin B locally from the beginning of their antineoplastic therapy. Eighty episodes were analysed retrospectively. Forty-one episodes in 24 patients were treated prospectively with a standard regimen of gentamicin + cefotaxime. The results show that the prophylactic regimen does not eradicate potentially pathogenic organisms from the throat, urine, or stools. Sixty-three per cent of FE were of unknown origin (FUU). 40.5% of all isolated organisms were TS resistant. In the prospective group, 9 of 41 FE (22%) responded to gentamicin + cefotaxime with lysis of fever within 48 hours, and 63% required no further antibiotics. Defeverescence occurred in the whole group within 5 +/- 4 days. No patients were lost to infectious complications. The combination of gentamicin + cefotaxime as initial therapy of a febrile episode must be supplemented within 48 to 72 hours by additional antibiotics in the absence of clinical improvement.

Erythrocyte pyruvate kinase deficiency: characterization of a new variant (PK "Aarau")

A new PK variant with moderate hemolytic anemia is described. The enzymes of the nonanemic parents show sigmoidal reaction kinetics, with normal kinetic parameters, but differ with respect to nucleotide specificity, thermostability, and the concentrations of the glycolytic intermediates in the erythrocytes. The most characteristic features of the patient's (daughter) enzyme are a 30% activity, hyperbolic reaction kinetics and only two bands in the SDS-gel electrophoresis instead of three bands observed with the parental enzymes. Moreover, the pH-optimum is shifted to the acidic range, the affinity for PEP and ADP is decreased, ATP inhibition is negligible and FDP-activation is roughly ten times smaller than with controls. The concentrations of 2,3-DPG, 2-PG and PEP in the erythrocyte are increased, but ATP decreased. As there is no consanguinity in the parents and their enzymes are different this PK mutant can be considered to be compound-heterozygous for two different mutant PK alleles.

In-vitro wall shear measurements at aortic valve prostheses

Wall shear distributions during the cardiac cycle at the valve rings of Starr-Edwards, Björk-Shiley and Lillehei-Kaster aortic valves are measured and compared with thresholds reported for shear-induced trauma of blood components. Further, for the disk valves, the influence of pulse rate on wall shear stresses is evaluated. Hot film anemometry with flush-mounted wall shear probes is used as measurement technique in a pulsatile flow mock circuit. The experimental systolic data support the better hemodynamic characteristics of the disk valves over the ball valve also with respect to the threshold shear stresses of flow induced blood trauma. These results are confirmed by postoperative clinical studies, where lower LDH-values are found with the disk than with the ball valves. During diastole, however, high shear stresses are measured and calculated at the valve ring of the Björk-Shiley prosthesis, which can be referred to the non-overlapping closing mechanism. This result is discussed with respect to the often observed thrombus formation at the disk downstream of the smaller orifice of the Björk-Shiley valve.

[Infection prevention following splenectomy: protective effect of a new 17-valent pneumococcal vaccine]

The antibody response to a new, 17-valent pneumococcal vaccine (Moniarix; Smith Kline-RIT) was tested in 43 splenectomised or functionally asplenic patients. The vaccine contained the following types of capsular antigens: 1, 2, 3, 4, 6A, 7F, 8, 9N, 11A, 12F, 14, 15F, 17F, 18C, 19F, 23F, 25 (Danish nomenclature). The vaccination was well tolerated. Local, reversible reddening and swelling was seen in 22 patients. The only systemic side effect was a rise of temperature in 13 patients. Serum titers of more than 300 ng/ml of specific antibodies were considered protective. A complete immunization of all patients was reached only with the capsular antigens 11A and 19F. The other antigens only induced protective serum concentrations in some of the patients. Considering the frequency of infections with the different types of antigens in Western Europe, percentage of asplenic patients at risk for infections with all pneumococcal types has been reduced by the vaccination to about 34%. It is proposed that the combination of pneumococcal vaccine and penicillin-prophylaxis provide effective protection for splenectomised patients against bacterial infections. The duration of penicillin-prophylaxis depends on the age of the patient at the time of splenectomy and the basic disease.

On the temperature- and salt-dependent conformation change in human erythrocyte pyruvate kinase

The influence of temperature, K+, Mg2+ and fructose 1,6-bisphosphate on human red cell pyruvate kinase was investigated. Kinetic measurements between 4 degrees C and 43 degrees C revealed a remarkable influence of the temperature on the allosteric behaviour of the enzyme. Below a transition region between 15 degrees C and 20 degrees C (as obtained from an Arrhenius plot) the enzyme shows non-cooperative behaviour, as can be deduced from Michaelis-Menten, Hill and Scatchard plots. At temperatures above 20 degrees C cooperativity increases with rising temperature. This effect becomes even more pronounced at higher temperatures upon addition of increasing amounts of K+ and Mg2+ accompanied by a slight decrease of the reaction velocity. Fructose 1,6-bisphosphate, however, abolishes cooperativity at every temperature and salt concentration measured. Difficulties which arise in evaluating the correct values of V, Km and the Hill coefficient nH with cooperative systems are met by using a computer program of Wieker, Johannes and Hess, especially designed for the determination of kinetic parameters obtained from sigmoidal steady-state kinetics.

[Puberty-specific gonadotropin rhythm in girls with homozygous beta-thalassemia during continuous subcutaneous desferrioxamine infusions and a simultaneous blood transfusion regimen]

The aim of the study was to find endocrinological parameters for the effectiveness of both, s.c. desferrioxamine therapy and a blood transfusion regimen, in 5 girls with homozygous beta-thalassemia treated in this way over 12-18 months. Physiologically, a sleep-dependent rhythm of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) secretion is detectable during early to mid puberty. Girls with homozygous beta-thalassemia develop persistant hypogonadotropic hypogonadism in the course of untreated hypothalamo-pituitary hemosiderosis and do not show this rhythm. All our patients developed a sleep-dependent gonadotropin rhythm, increased estradiol concentrations as well as secondary sex characteristics, including menarche in one girl. The occurence of sleep-dependent gonadotropin rhythms in previously hypogonadotropic girls emphasizes the effectiveness of s.c. desferrioxamine therapy of hypothalamo-pituitary hemosiderosis in combination with a blood transfusion regimen.

Erythrocyte pyruvate kinase deficiency. A kinetic study of the membrane-localised and cytoplasmatic enzyme from six patients

Investigations on the activity and the kinetic behavior of red cell pyruvate kinase in the erythrocyte membrane and hemolysate of 6 patients with pyruvate kinase (PK) deficiency are presented and compared with those of normal individuals. Hemolysate: The PK in the hemolysate of normal individuals showed the well-known allosteric properties, reflected by sigmoidal reaction kinetics (Hill-coefficient greater than 1). In contrast to these findings the enzymes of 4 of the patients which had not been splenectomised and which were all in satisfactory condition showed between 15 and 35% of the PK activity of normal individuals in the hemolysates, whereas in the case of the 2 splenectomised patients only 5 and 15% of this activity could be measured. All of the patients' enzymes showed non allosteric (hyperbolic) reaction kinetics (Hill-coefficient approximately 1.0). Red cell membranes: Our studies confirmed earlier reports that not only the hemolysate of the patients, but also their red cell membranes ('ghosts') exhibit PK activity. In normal individuals the activity of the membrane-localised PK is about 5% of the cytoplasmatic one. In case of the membrane-localised enzyme of all patients--irrespective if they were splenectomised or not--the activity is decreased to 30-50%, compared to the activity of ghosts of the control persons. Reaction kinetic studies on the PK isolated from red cell membranes from normal individuals as well as from all 6 patients exhibited hyperbolic Michaelis-Menten kinetics with Hill coefficients around 1.0.

Flexibility of erythrocytes in juvenile diabetes mellitus

The rheological properties of erythrocytes of 47 diabetic children and adolescents were studied. Deformability of red cells of 32 patients under "poor" metabolic control was markedly decreased while the deformability of red cells of patients (15 individuals) under "good" control was normal. This diminished flexibility of erythrocytes of patients under "poor" control can be explained partly by an increased concentration of free fatty acids in plasma. Moreover we found a decreased fluidity of the intracellular hemoglobin caused possibly by a decreased concentration of 2, 3-diphosphoglycerate in the cells.

Role of the spleen in congenital stomatocytosis associated with high sodium-low potassium erythrocytes

A girl of German origin with severe congenital hemolytic anemia was found to have overhydrated erythrocytes with markedly increased sodium and reduced potassium concentrations. The cells were stomatocytic with increased osmotic fragility and autohemolysis. Their excessively increased energy production was mainly used for active cation transport. The cells were highly vulnerable to metabolic depletion. Their normal deformability was reduced rapidly during deprivation of glucose. In acidic, hypoglycemic environment of the splenic pulp the cells become swollen and lysed. After splenectomy anemia improved though increased hemolysis persisted.

Endocrine studies in Blackfan-Diamond anemia: evidence for hypothalamic-pituitary dysfunction under frequent transfusion therapy

A 13 year old boy with Blackfan-Diamond anemia treated with frequent transfusions was investigated for endocrine abnormalities. Prepubertal plasms LH and FSH values, lack of sleep-related hormone rhythms of the gonadotropins, as well as prepubertal responses of LH and FSH to acute stimulation with LHRH strongly suggests that a hypothalamic-pituitary abnormality is the cause of the hypogonadotropic hypogonadism observed in this patient. As a result of impaired stimulation of the gonads plasm testosterone was prepubertal. A three-to fourfold increase of basal plasma PRL values was found without any signs of a typical sleep-dependent increase. Values obtained ranged between 21 ng/ml and 24 ng/ml (normal range 5-8 ng/ml). A normal response to TRH stimulation was found. These results suggest that hemosiderosis may be responsible for the hyperprolactinemia as a result of hypothalamic-pituitary dysfunction. Furthermore, dysfunction is demonstrated by prepubertal responses of LH and FSH to LHRH stimulation.

Rheological properties of young and aged human erythrocytes

Rheological properties were studied of young and old human erythrocytes from healthy adults. Viscosity measurements of packed erythrocyte suspensions as well as filtration of cells through polycarbonate sieves show that young cells are more flexible than aged ones. Since deformability of erythrocytes is the product of cell shape, flexibility of the membrane and fluidity of the intracellular hemoglobin, we studied the manner in which these factors are relevant to the diminished flexibility of aged erythrocytes. The biconcave cell shape is maintained during the process of aging. The viscosity of packed ghost suspensions from aged erythrocytes is increased versus that of young ones. The diminished flexibility of old ghosts correlates well with their smaller cell volume. The fluidity of the hemoglobin in the interior of the cells is decreased as indicated by an increased hemoglobin content of the isolated ghosts. We conclude that aged erythrocytes loose their deformability as a result of both a decreased fluidity of the intracellular hemoglobin and a diminished flexibility of the membrane.

Deformability of erythrocytes in iron deficiency anemia

The rheological properties of erythrocytes of 14 patients with iron deficiency anemia were studied by filtration of cells through polycarbonate filters with a nominal pore diameter of 5 micron and by viscosity measurements of erythrocyte suspensions with a hematocrit of 80%. Erythrocytes of the patients passed through the filter pores more slowly than the cells from controls. The diminished deformability of the erythrocytes of the patients was solely due to an unfavorable ratio of cell surface area to microcytic cell volume. The viscosity of the ghost suspensions of the patients showed a normal flexibility. The hemoglobin content of the isolated ghosts was diminished, indicating an increased hemoglobin fluidity in the interior of the intact cells. The viscosity of erythrocytes of the patients was slightly increased at low shear rates but was normal at intermediate and high shear rates. We suggest that the decreased erythrocyte flexibility of microcytosis at low shear rates is no longer present at higher shear rates because of an increased fluidity of the intracellular hemoglobin. We discuss whether or not this mechanism also operates in vivo. The in vitro diminished deformability of erythrocytes explains the shortened survival of the patients' erythrocytes in vivo.

[Severe cardiogenic hemolytic anemia with decreased flexibility of erythrocytes following surgical correction of mitral valve stenosis (author's transl)]

After surgical correction of a common atrium and closure of a mitral cleft, a mitral stenosis developed in a 5 year old girl. Postoperatively a pronounced hemolysis developed necessitating multiple blood transfusions. Rheologic measurements showed that hemolysis was due to a loss of erythrocyte deformability after mechanical damage. On the basis of these measurements it was concluded that the mitral stenosis was most likely responsible for this mechanical damage. Following another surgical correction of the mitral valve there was no hemolysis anymore.

Rheological properties of erythrocytes in heterozygous and homozygous beta thalassaemia

The rheological properties of erythrocytes were studied in 12 heterozygous and nine homozygous beta thalassaemia patients, using filtration of erythrocytes through polycarbonate sieves with a pore diameter of 5 micron and viscosity measurements of erythrocyte and ghost suspensions. Erythrocyte deformability of all patients was decreased. In the heterozygous patients moderately diminished flexibility of cells was due to microcytosis of erythrocytes. Rigidity of erythrocytes in homozygous patients was due to altered cell shape, diminished fluidity of haemoglobin, and in splenectomized patients to the presence of inclusion bodies. Membrane flexibility of erythrocytes remained unaltered. We suggest that the decreased fluidity of haemoglobin as well as the presence of inclusion bodies result from the excess of alpha chains in erythrocytes of homozygous patients. The haemoglobin fluidity of erythrocytes of one patient with thalassaemia intermedia was unchanged. The flexibility of these cells was only moderately altered. In four patients who needed transfusions every 1--4 weeks deformability of transfused erythrocytes was likewise decreased when compared to controls. Erythrocyte suspensions obtained from the splenic artery and vein during splenectomy showed decreased flexibility of transfused cells after their passage through the spleen.