Effect of silicon content on the microstructure evolution, mechanical properties, and biocompatibility of ß-type TiNbZrTa alloys fabricated by laser powder bed fusion.

Beta-type titanium alloys are excellent candidates for biomedical applications because of their very low elastic modulus, excellent corrosion resistance, and biocompatibility. However, many traditional ß-type titanium alloys exhibit low yield strength. In this study, a small amount of Si (3 and 5 at.%) was added to a Ti-35Nb-7Zr-5Ta (wt%, TNZT) biomedical alloy prepared via laser powder bed fusion (LPBF) to increase its yield strength. The Si addition resulted in a significant increase in the compression yield strength of the alloy (from 802 to 1282 MPa). Meanwhile, the elastic moduli of the TNZT alloys (48.7-60.6 GPa) with 3 and 5 at.% Si were much lower than that of the Ti-6Al-4 V alloy (110 GPa), which is used extensively in clinical applications. The microstructural analyses indicated that the ultrahigh-strength of the TNZT alloy containing Si was due to the presence of ultrafine (Ti, Nb, Zr)5Si3 (S1) grains in the ß-Ti matrix. In addition, thin shell-shaped S1 and (Ti, Nb, Zr)2Si (S2) grains precipitated along the columnar ß-Ti grain boundaries in the TNZT alloys containing 3 and 5 at.% Si, respectively. Moreover, the introduction of Si to the TNZT alloy significantly refined the grains, weakened the cubic texture, decreased surface roughness, and improved Vickers hardness. The ultrahigh strength of the Si-containing TNZT alloys was due to grain boundary strengthening and precipitation strengthening. In addition, in vitro studies with MC3T3-E1 cells revealed that the cytocompatibilities of the LPBF-fabricated TNZT and Si-containing TNZT alloys were equivalent and were better than that of the LPBF-fabricated Ti-6Al-4 V alloy. In particular, the TNZT alloy with 3 at.% Si showed the best elastic modulus (48.7 ± 1.0 GPa), yield strength (1151 ± 17 MPa), and cell biological response among all the alloys investigated in this study, and hence was found to be a suitable candidate for application in load-bearing bone implants.

Effect of thermomechanical processing on the mechanical biofunctionality of a low modulus Ti-40Nb alloy.

Different hardening strategies were evaluated regarding their potential to improve the mechanical biofunctionality of the cast and solution-treated low modulus ß-Ti alloy Ti 40Nb. The strategies are based on thermomechanical treatments comprised of different hot- and cold-rolling steps, as well as annealing treatments aiming at the successive exploitation of different hardening mechanisms (grain boundary hardening, work hardening and precipitation hardening). Quasi-static tensile testing revealed that grain refinement by one order of magnitude has only a small impact on improving the mechanical biofunctionality of Ti-40Nb. However, work hardening effectively improves the tensile strength by 30% to a value of 650MPa, while retaining Young׳s modulus at 60GPa. The α-phase precipitation hardening was verified to have an increasing effect on both, strength and Young׳s modulus. Thereby, the change of Young׳s modulus dominates the change of the strength, even at low α-phase fractions. The pseudo-elastic behavior of Ti 40Nb is discussed under consideration of the microstructural changes due to the thermomechanical treatment. The texture changes evolving upon cold-rolling markedly influence the recrystallization behavior. However, the present results do not show a significant effect of the texture on the mechanical properties of Ti-40Nb.

Nanostructured Ti-Zr-Pd-Si-(Nb) bulk metallic composites: Novel biocompatible materials with superior mechanical strength and elastic recovery.

The microstructure, mechanical behaviour, and biocompatibility (cell culture, morphology, and cell adhesion) of nanostructured Ti45 Zr15 Pd35- x Si5 Nbx with x = 0, 5 (at. %) alloys, synthesized by arc melting and subsequent Cu mould suction casting, in the form of rods with 3 mm in diameter, are investigated. Both Ti-Zr-Pd-Si-(Nb) materials show a multi-phase (composite-like) microstructure. The main phase is cubic ß-Ti phase (Im3m) but hexagonal α-Ti (P63/mmc), cubic TiPd (Pm3m), cubic PdZr (Fm3m), and hexagonal (Ti, Zr)5 Si3 (P63/mmc) phases are also present. Nanoindentation experiments show that the Ti45 Zr15 Pd30 Si5 Nb5 sample exhibits lower Young's modulus than Ti45 Zr15 Pd35 Si5 . Conversely, Ti45 Zr15 Pd35 Si5 is mechanically harder. Actually, both alloys exhibit larger values of hardness when compared with commercial Ti-40Nb, (HTi-Zr-Pd-Si ≈ 14 GPa, HTi-Zr-Pd-Si-Nb ≈ 10 GPa and HTi-40Nb ≈ 2.7 GPa). Concerning the biological behaviour, preliminary results of cell viability performed on several Ti-Zr-Pd-Si-(Nb) discs indicate that the number of live cells is superior to 94% in both cases. The studied Ti-Zr-Pd-Si-(Nb) bulk metallic system is thus interesting for biomedical applications because of the outstanding mechanical properties (relatively low Young's modulus combined with large hardness), together with the excellent biocompatibility.

Chemical nanoroughening of Ti40Nb surfaces and its effect on human mesenchymal stromal cell response.

Samples of low modulus beta-type Ti40Nb and cp2-Ti were chemically treated with 98% H2 SO4 + 30% H2 O2 (vol. ratio 1:1) solution. Surface analytical studies conducted with HR-SEM, AFM, and XPS identified a characteristic nanoroughness of the alloy surface related with a network of nanopits of ∼25 nm diameter. This is very similar to that obtained for cp2-Ti. The treatment enhances the oxide layer growth compared to mechanically ground states and causes a strong enrichment of Nb2 O5 relative to TiO2 on the alloy surface. The in vitro analyses clearly indicated that the chemical treatment accelerates the adhesion and spreading of human mesenchymal stromal cells (hMSC), increases the metabolic activity, and the enzyme activity of tissue non-specific alkaline phosphatase (TNAP). Surface structures which were generated mimic the cytoplasmic projections of the cells on the nanoscale. Those effects are more pronounced for the Ti40Nb alloy than for cp2-Ti. The relation between alloy surface topography and chemistry and cell functions is discussed.

Porous low modulus Ti40Nb compacts with electrodeposited hydroxyapatite coating for biomedical applications.

Porous ß-type non-toxic Ti40Nb alloy was prepared by compaction of mechanically alloyed powder mixed with NaCl or Mg particles as space-holder material. The compacts with porosity of 36-80% demonstrated a very low Young's modulus of ~1.5-3 GPa and compression strength of ~10-35 MPa, which is suitable for potential implant material application. Porous samples were electrochemically covered with hydroxyapatite. The influence of the deposition time and of the electrolyte concentrations on the morphology of the hydroxyapatite coating was studied. It is demonstrated that a homogenous coating of hydroxyapatite crystals with different shape and size can be obtained on the surface of the porous samples.

Available processing resources influence encoding-related brain activity before an event.

Effective cognitive functioning not only relies on brain activity elicited by an event, but also on activity that precedes it. This has been demonstrated in a number of cognitive domains, including memory. Here, we show that brain activity that precedes the effective encoding of a word into long-term memory depends on the availability of sufficient processing resources. We recorded electrical brain activity from the scalps of healthy adult men and women while they memorized intermixed visual and auditory words for later recall. Each word was preceded by a cue that indicated the modality of the upcoming word. The degree to which processing resources were available before word onset was manipulated by asking participants to make an easy or difficult perceptual discrimination on the cue. Brain activity before word onset predicted later recall of the word, but only in the easy discrimination condition. These findings indicate that anticipatory influences on long-term memory are limited in capacity and sensitive to the degree to which attention is divided between tasks. Prestimulus activity that affects later encoding can only be engaged when the necessary cognitive resources can be allocated to the encoding process.

Influence of press-fit parameters on the primary stability of uncemented femoral resurfacing implants.

Primary stability is essential to the success of uncemented prostheses. It is strongly influenced by implantation technique, implant design and bone quality. The goal of this study was to investigate the effect of press-fit parameters on the primary stability of uncemented femoral head resurfacing prostheses. An in vitro study with human specimens and prototype implants (nominal radial interference 170 and 420 microm) was used to investigate the effect of interference on primary stability. A finite element model was used to assess the influence of interference, friction between implant and bone, and bone quality. Primary stability was represented by the torque capacity of the implant. The model predicted increasing stability with actual interference, bone quality and friction coefficient; plastic deformation of the bone began at interferences of less than 100 microm. Experimentally, however, stability was not related to interference. This may be due to abrasion or the collapse of trabecular bone structures at higher interferences, which could not be captured by the model. High nominal interferences as tested experimentally appear unlikely to result in improved stability clinically. An implantation force of about 2,500 N was estimated to be sufficient to achieve a torque capacity of about 30 N m with a small interference (70 microm).

[Comparative analysis of in vitro test procedures for evaluating hemocompatibility of cardiovascular stents]. / Vergleichende Analyse von in vitro Testverfahren zur Beurteilung der Hämokompatibilität von kardiovaskulären Stents.

Within the scope of this study existing in vitro techniques for testing the hemocompatibility of coronary stents were analysed and optimised. Static and quasi-stationary systems were compared to a pulsed flow model with respect to platelet activity. The streamlines were visualized by dye injection. Blood flow was measured by ultrasonic Doppler velocity meter and electromagnetic flow meter. Uncoated stainless steel (316 L) stents were tested. Surrogate parameters of the hemocompatibility were the change in surface morphology after blood contact and the rise of biomechanical activation markers as C3a and beta-thromboglobulin. The results were correlated to the stent design and to the flow characteristics of the test systems.

Pulmonary surfactant in birds: coping with surface tension in a tubular lung.

As birds have tubular lungs that do not contain alveoli, avian surfactant predominantly functions to maintain airflow in tubes rather than to prevent alveolar collapse. Consequently, we have evaluated structural, biochemical, and functional parameters of avian surfactant as a model for airway surfactant in the mammalian lung. Surfactant was isolated from duck, chicken, and pig lung lavage fluid by differential centrifugation. Electron microscopy revealed a uniform surfactant layer within the air capillaries of the bird lungs, and there was no tubular myelin in purified avian surfactants. Phosphatidylcholine molecular species of the various surfactants were measured by HPLC. Compared with pig surfactant, both bird surfactants were enriched in dipalmitoylphosphatidylcholine, the principle surface tension-lowering agent in surfactant, and depleted in palmitoylmyristoylphosphatidylcholine, the other disaturated phosphatidylcholine of mammalian surfactant. Surfactant protein (SP)-A was determined by immunoblot analysis, and SP-B and SP-C were determined by gel-filtration HPLC. Neither SP-A nor SP-C was detectable in either bird surfactant, but both preparations of surfactant contained SP-B. Surface tension function was determined using both the pulsating bubble surfactometer (PBS) and capillary surfactometer (CS). Under dynamic cycling conditions, where pig surfactant readily reached minimal surface tension values below 5 mN/m, neither avian surfactant reached values below 15 mN/m within 10 pulsations. However, maximal surface tension of avian surfactant was lower than that of porcine surfactant, and all surfactants were equally efficient in the CS. We conclude that a surfactant composed primarily of dipalmitoylphosphatidylcholine and SP-B is adequate to maintain patency of the air capillaries of the bird lung.

Dispiro[fluorene-9,5'-[1,2,3,4]tetrathiane-6',9"-fluorene.

The tetrathiane ring of the title compound, C26H16S4, has a chair conformation and the molecule has approximate C2 symmetry. Each of the two fluorene ring systems is virtually planar, with the ring planes intersecting at an angle of 67.58 (5) degrees. This novel compound has been formed as a side product from the treatment of 9H-fluorene-9-thione with methyl N-[(benzylidene)phenyl]glycinate in the presence of LiBr and 1,6-diazabicyclo[5.4.0]undecane.

Morphology and immunology of the human palatine tonsil.

At the surface of the respiratory and digestive organs the organism first comes into contact nasally and orally with various foreign agents and substances in the air and in food. The palatine tonsils are located at the centre of this strategic region. Immunological processes, both humoral and cellular, are initiated in the different specialised compartments of the palatine tonsils, such as the crypt epithelium, lymphoid follicles and extrafollicular region. Each compartment has a typical composition of lymphocytes and dendritic cell subsets. This review summarises current data on the anatomy, histology, and pathology of the human palatine tonsils, describes their fundamental immunological functions, and provides insight into the various interactions involved in the initiation of immune responses. The palatine tonsil is the only easily accessible human lymphoid organ and is often taken as an example for lymphoid organs. Although affections of the palatine tonsils constitutes an essential part in the clinical routine, it is still controversial whether tonsillectomy is of general benefit. This is of increasing importance since it has been discovered in the last few years that the palatine tonsils are reservoir and replication sites of HIV.

[The mechanisms of antigen uptake in the small and large intestines: the roll of the M cells for the initiation of immune responses]. / Mechanismen der Antigenaufnahme im Dünn- und Dickdarm: die Rolle der M-Zellen für die Initiierung von Immunantworten.

The gut-associated lymphoid tissues, e.g., the Peyer's patches and the appendix, constantly internalize antigenic material to rapidly generate an immune response, if necessary. This sampling of antigens is performed by specialized epithelial cells, the "membranous" or "microfold" (M) cells of the dome epithelia. M cells possess a unique ultrastructure and are typically in contact with lymphoid cells. They endocytose macromolecules and particles, including entire microorganisms, at their apical membrane, transport these in vesicles to their basolateral membrane, and exocytose them to the intercellular space. This article reviews the structural and functional characteristics of M cells in the digestive tract in humans and other species. Specializations of M cells for antigen uptake and transport comprise the composition of their apical membrane, a modified cytoskeleton as compared to enterocytes, and a large pocket-like invagination of the basolateral membrane populated by lymphocytes. Besides ultrastructural characteristics, histochemical markers are listed that are available for detecting M cells. The origin and differentiation pathways of M cells and enterocytes of the dome epithelium are outlined and critically commented on. Because M cells are known entry sites of various pathogens and, in the future, might be employed for the oral application of drugs and vaccines, the clinical relevance of M cells in health and disease is discussed.

Commercial versus native surfactants. Surface activity, molecular components, and the effect of calcium.

Despite their broad clinical use, there is no standardized comparative study on the functional, biochemical, and morphologic differences of the various commercial surfactants in relation to native surfactant. We investigated these parameters in Alveofact, Curosurf, Exosurf, and Survanta, and compared them with native bovine (NBS) and porcine (NPS) surfactant. For Curosurf and Alveofact the concentrations necessary for minimal surface tensions < 5 mN/m were six to 12 times higher (1.5 and 3 mg/ml, respectively) than with NPS and NBS. Exosurf and Survanta only reached 22 and 8 mN/m, respectively. Increasing calcium to nonphysiologic concentrations artificially improved the function of Alveofact and Curosurf, but it had little effect on Exosurf and Survanta. Impaired surface activity of commercial versus native surfactants corresponded with their lack in surfactant protein SP-A and decreased SP-B/C. The higher surface activity of Curosurf compared with Alveofact corresponded with its higher concentration of dipalmitoylphosphatidylcholine (DPPC). Despite their enrichment in DPPC Survanta and Exosurf exhibited poor surface activity because of low or absent SP-B/C. Ultrastructurally, Curosurf and Alveofact consisted mainly of lamellar and vesicular structures, which were also present in NPS and NBS. Exosurf contained crystalline structures only, whereas the DPPC-enriched Survanta contained separate lamellar/vesicular and crystalline structures. We conclude that in vitro surface activity of commercial surfactants is impaired compared with native surfactants at physiologic calcium concentrations. In the presence of SP-B/C, surface activity corresponds to the concentration of DPPC. Our data underscore the importance of a standardized protocol at physiologic calcium concentrations for the in vitro assessment of commercial surfactants.

Blockade of leucocyte function-associated antigen-1 (LFA-1) decreases lymphocyte trapping in the normal pulmonary vasculature: studies in the isolated buffer-perfused rat lung.

Adhesion molecules regulate the migration of lymphocytes in lymphoid and non-lymphoid organs. In the lung, little is known about lymphocyte sticking and migration through the pulmonary vascular endothelium in physiological or pathological situations. Therefore the isolated buffer-perfused rat lung was used to investigate the mobilization of lymphocytes out of the normal lung into the venous effluent and to the bronchoalveolar space. The lymphocyte subset composition was characterized in the venous effluent, the lung tissue and the bronchoalveolar lavage (BAL) using immunocytology. Lymphocytes continuously left the normal lung at a total of 5.0 +/- 0.7 x 106 cells within the first hour of perfusion. The injection of 200 x 106 lymphocytes via the pulmonary trunk increased the venous release of lymphocytes by 170%. To investigate the effect of LFA-1 and CD44 on the adhesion of lymphocytes to the pulmonary endothelium, lymphocytes preincubated with an anti-LFA-1 MoAb, which blocks the interaction of LFA-1 and intercellular adhesion molecule-1 (ICAM-1), or lymphocytes preincubated with an anti-CD44 MoAb, were injected. The injection of LFA-1-blocked lymphocytes led to an increase by 70% of injected cells recovered in the perfusate within the first hour, whereas anti-CD44 treatment of injected lymphocytes had no effect. The LFA-1-blocked lymphocytes showed higher numbers of T and B cells in the effluent. Thus, the present experiments demonstrate that LFA-1 influences the trapping of lymphocytes in the vasculature of the healthy rat lung.

The apical membrane of intestinal brush cells possesses a specialised, but species-specific, composition of glycoconjugates--on-section and in vivo lectin labelling in rats, guinea-pigs and mice.

Brush cells are specialised epithelial cells that are assumed to represent chemoreceptors of the digestive tract. They comprise a small population of the epithelial cells lining the intestine, possess a unique ultrastructure and, in many aspects, resemble the receptor cells of taste buds. To characterise glycoconjugates possibly involved in a sensory function, we investigated brush cells in the small intestine of three species using lectin histochemistry in confocal light and thin-section electron microscopy. Brush cells of rats were selectively labelled by the sialic acid-specific lectin Maackia amurensis agglutinin, those of guinea-pigs by the D-galactose-specific lectin Bandeiraea simplicifolia agglutinin, isolectin B4 and those of mice by the L-fucose-specific lectin Ulex europaeus agglutinin lectin I. Lectin binding sites were consistently located in the glycocalyx of the apical membrane and in that of cytoplasmic vesicles. In vivo lectin labelling revealed that the glycoconjugates of the apical membrane are accessible under physiological conditions, that brush cells do not endocytose and that they probably possess a high membrane turnover rate. The results show that specialisations exist in the composition of glycoconjugates forming the glycocalyx of brush cells in all species investigated. The presence of brush cell-specific glycoconjugates would be in accordance with the current hypothesis of a receptive function of brush cells. Differences in the specific glycosylation patterns among rats, guinea-pigs and mice indicate that species-specific adaptations exist.

Proinflammatory cytokines trigger MUC gene expression and mucin release in the intestinal cancer cell line LS180.

OBJECTIVES AND DESIGN: Proinflammatory cytokines and a defective mucus layer are involved in the pathogenesis of colitis. Therefore, we determined cytokine effects on MUC gene expression and mucin secretion. MATERIALS AND METHODS: LS180 cells were characterized by light and electron microscopy and subsequently exposed to interleukin 1 (IL-1, 1 ng/ml), interleukin 6 (IL-6, 10 ng/ml), or tumor necrosis factor-alpha (TNFalpha, 10 ng/ml). MUC gene (MUC2, MUC5AC, MUC5B, MUC6) mRNA expression was assessed by RT-PCR, the encoded proteins were identified by immunocytochemistry and Western blotting, and the released mucins were isolated and chromatographically characterized. RESULTS: Thirty to 40% of the cells contained intracellular mucin granules. Incubation with IL-1 transiently stimulated the mRNA expression of MUC2 and MUC5AC, whereas IL-6 induced an early response of MUC2, MUC5B and MUC6. TNFalpha upregulated the expression of MUC2 and MUC5B for 3 hours, and had no effect on the expression of MUC 5AC and MUC6. Immunocytochemistry and Western blotting confirmed TNFalpha effects on MUC2 and MUC5AC on the protein levels. All cytokines stimulated the release of less glycosylated mucins and considerably modulated their carbohydrate composition. CONCLUSION: Our data demonstrate differential cytokine effects on mucin synthesis, secretion and composition. These alterations may contribute to the defective mucus layer in colitis.

Human polymorphonuclear neutrophils express a B7-1-like molecule.

Polymorphonuclear neutrophils (PMN) are part of the innate immune system and are first-line effector cells in acute inflammatory responses. On activation PMNs secrete cytokines and oxygen metabolites that might be involved in the regulation of the acquired immune response. We show here that peripheral blood PMNs constitutively express a B7-1-like molecule as detected by immunostaining with several B7-1 antibodies. Reverse transcriptase-polymerase chain reaction using three sets of primers spanning different regions of B7-1 indicate dissimilarities at the mRNA level. B7-1 mRNA is expressed in bone marrow cells and lipopolysaccharide (LPS)-stimulated but not in unstimulated PMNs. The B7-1-like molecule is localized to the cytoplasmic granules and translocated to the cell surface after stimulation with LPS or interleukin-12 in some donors. Binding of CTLA4-Ig suggests that the B7-1-like molecule can interact with functional B7 ligand and might be important in the immunobiology of PMNs.

Matrix expression and proliferation of primary gingival fibroblasts in a three-dimensional cell culture model.

The growth of cultured primary human gingival fibroblasts and the three-dimensional arrangement of the extracellular matrix in a polyester carrier system was investigated using various histological techniques. The results were compared with monolayer cultures. Collagen types I, III, V, and VI were investigated by conventional and fluorescence microscopy, scanning and transmission electron microscopy, and confocal laser scanning microscopy. Human gingival fibroblasts were obtained from tissue biopsies of five donors and were cultivated up to 5 weeks under three-dimensional culture conditions. The cells displayed an elongated, spindle-like or stellate morphology resembling the in vivo situation. Collagen type I revealed thick fiber bundles, and collagens type III and V were distributed as fine fibrils or small bundles throughout the culture system. Frequently, the fibers were oriented parallel to the long axis of the cells. Type VI collagen formed thin fibers and revealed a reticular pattern. In histological sections the cultured cells exhibited a morphology clearly different from that of cells cultured in monolayers. Their shape and spatial distribution resembled that of cells in tissue biopsies more closely. The culture system presented here promotes a dynamic model for performing studies for instance on the interactions of cultured cells with extracellular matrix molecules, on the pathogenesis of inflammatory processes or on the interactions with biomaterials, thus providing qualitative and quantitative information.