Soft matter dynamics: A versatile microgravity platform to study dynamics in soft matter.

We describe an experiment container with light scattering and imaging diagnostics for experiments on soft matter aboard the International Space Station (ISS). The suite of measurement capabilities can be used to study different materials in exchangeable sample cell units. The currently available sample cell units and future possibilities for foams, granular media, and emulsions are presented in addition to an overview of the design and the diagnostics of the experiment container. First results from measurements performed on ground and during the commissioning aboard the ISS highlight the capabilities of the experiment container to study the different materials.

Frequency dependence of lung volume changes during superimposed high-frequency jet ventilation and high-frequency jet ventilation.

BACKGROUND: Superimposed high-frequency jet ventilation (SHFJV) has proved to be safe and effective in clinical practice. However, it is unclear which frequency range optimizes ventilation and gas exchange. The aim of this study was to systematically compare high-frequency jet ventilation (HFJV) with HFJV by assessing chest wall volume variations (ΔEEV(CW)) and gas exchange in relation to variable high frequency. METHODS: SHFJV or HFJV were used alternatively to ventilate the lungs of 10 anaesthetized pigs (21-25 kg). The low-frequency component was kept at 16 min(-1) in SHFJV. In both modes, high frequencies ranging from 100 to 1000 min(-1) were applied in random order and ventilation was maintained for 5 min in all modalities. Chest wall volume variations were obtained using opto-electronic plethysmography. Airway pressures and arterial blood gases were measured repeatedly. RESULTS: SHFJV increased ΔEEV(CW) compared with HFJV; the difference ranged from 43 to 68 ml. Tidal volume (V(T)) was always >240 ml during SHFJV whereas during HFJV ranged from 92 ml at the ventilation frequency of 100 min(-1) to negligible values at frequencies >300 min(-1). We observed similar patterns for Pa(O2) and Pa(CO2). SHFJV provided generally higher, frequency-independent oxygenation (Pa(O2) at least 32.0 kPa) and CO2 removal (Pa(CO2) ∼5.5 kPa), whereas HFJV led to hypoxia and hypercarbia at higher rates (Pa(O2) <10 kPa and Pa(CO2)>10 kPa at f(HF)>300 min(-1)). CONCLUSIONS: In a porcine model, SHFJV was more effective in increasing end-expiratory volume than single-frequency HFJV, but both modes may provide adequate ventilation in the absence of airway obstruction and respiratory disease, except for HFJV at frequencies ≥300 min(-1).

Dissipative dark soliton in a complex plasma.

The observation of a dark soliton in a three-dimensional complex plasma containing monodisperse microparticles is presented. We perform our experiments using neon gas in the bulk plasma of an rf discharge. A gas temperature gradient of 500K/m is applied to balance gravity and to levitate the particles in the bulk plasma. The wave is excited by a short voltage pulse on the electrodes of the radio frequency discharge chamber. It is found that the wave propagates with constant speed. The propagation time of the dark soliton is approximately 20 times longer than the damping time.

Convective dust clouds driven by thermal creep in a complex plasma.

Steady-state clouds of microparticles were observed, levitating in a low-frequency glow discharge generated in an elongated vertical glass tube. A heated ring was attached to the tube wall outside, so that the particles, exhibiting a global convective motion, were confined vertically in the region above the location of the heater. It is shown that the particle vortices were induced by the convection of neutral gas, and the mechanism responsible for the gas convection was the thermal creep along the inhomogeneously heated tube walls. The phenomenon of thermal creep, which commonly occurs in rarefied gases under the presence of thermal gradients, should generally play a substantial role in experiments with complex plasmas.

Conformation-specific antibodies reveal distinct actin structures in the nucleus and the cytoplasm.

For many years the existence of actin in the nucleus has been doubted because of the lack of phalloidin staining as well as the failure to document nuclear actin filaments by electron microscopy. More recent findings reveal actin to be a component of chromatin remodeling complexes and of the machinery involved in RNA synthesis and transport. With distinct functions for nuclear actin emerging, the quest for its conformation and oligomeric/polymeric structure in the nucleus has resumed importance. We used chemically cross-linked 'lower dimer' (LD) to generate mouse monoclonal antibodies specific for different actin conformations. One of the resulting antibodies, termed 1C7, recognizes an epitope that is buried in the F-actin filament, but is surface-exposed in G-actin as well as in the LD. In immunofluorescence studies with different cell lines, 1C7 selectively reacts with non-filamentous actin in the cytoplasm. In addition, it detects a discrete form of actin in the nucleus, which is different from the nuclear actin revealed by the previously described 2G2 [Gonsior, S.M., Platz, S., Buchmeier, S., Scheer, U., Jockusch, B.M., Hinssen, H., 1999. J. Cell Sci. 112, 797]. Upon latrunculin-induced disassembly of the filamentous cytoskeleton in Rat2 fibroblasts, we observed a perinuclear accumulation of the 1C7-reactive actin conformation. In addition, latrunculin treatment led to the assembly of phalloidin-staining actin structures in chromatin-free regions of the nucleus in these cells. Our results indicate that distinct actin conformations and/or structures are present in the nucleus and the cytoplasm of different cell types and that their distribution varies in response to external signals.

Contraction-mediated pinocytosis of RGD-peptide by dermal fibroblasts: inhibition of matrix attachment blocks contraction and disrupts microfilament organisation.

Force generation in collagen and matrix contraction are basic functions of fibroblasts and important elements of tissue repair. Cell-matrix attachment is critical to this contraction, involving RGD-binding integrins. We have investigated how this process operates, in terms of force generation (in the Culture Force Monitor) and cytoskeletal structure, using a synthetic RGD-decapeptide. The RGD-peptide blocked force generation over the first 6 h, followed by near complete recovery by 20 h. However, dose response was complex indicating multiple processes were operating. Analysis of cytoskeletal structure after treatment with RGD-peptide indicated major disruption with condensed aggregates of actin and microtubular fragmentation. Fluorescent labeling and tracking of the RGD-peptide demonstrated intracellular uptake into discrete cytoplasmic aggregates. Critically, these RGD-peptide pools co-localised with the condensed actin microfilament aggregates. It is concluded that RGD-peptide uptake was by a form of contraction-mediated pinocytosis, resulting from mechanical tension applied to the untethered RGD-peptide-integrin, as contractile microfilament were assembled. These findings emphasize the importance of sound mechanical attachment of ligand-occupied integrins (e.g., to extracellular matrix) for normal cytoskeletal function. Conversely, this aspect of unrestrained cytoskeletal contraction may have important pathogenic and therapeutic applications.

Vertical pairing of identical particles suspended in the plasma sheath.

It is shown experimentally that vertical pairing of two identical microspheres suspended in the sheath of a radio-frequency (rf) discharge at low gas pressures (a few Pa) appears at a well-defined instability threshold of the rf power. The transition is reversible, but with significant hysteresis on the second stage. A simple model which uses measured microsphere resonance frequencies and takes into account, in addition to the Coulomb interaction between negatively charged microspheres, their interaction with positive-ion-wake charges, seems to explain the instability threshold quite well.

Levitation of cylindrical particles in the sheath of an rf plasma.

Microrods were levitated in the collisional sheath of a rf plasma. Rods below a critical length settle vertically, parallel to the electric field, while longer rods float horizontally. Usually rods with other inclinations spin about a vertical axis. These experimental features fit well with a model that includes a theoretical profile for the sheath, a plasma model for the screening length, which increases going deeper in the sheath, and a plasma theory for the charging of the rod's elements. Despite the agreement this paper highlights the need for a better understanding of the charging mechanism of bodies in sheaths and of the transition region in collisional sheaths.

NonliNEAR vertical oscillations of a particle in a sheath of a rf discharge.

A new simple method to measure the spatial distribution of the electric field in the plasma sheath is proposed. The method is based on the experimental investigation of vertical oscillations of a single particle in the sheath of a low-pressure radio-frequency discharge. It is shown that the oscillations become strongly nonlinear as the amplitude increases. The theory of anharmonic oscillations provides a good quantitative description of the data and gives estimates for the first two anharmonic terms in an expansion of the sheath potential around the particle equilibrium.

Three-dimensional strongly coupled plasma crystal under gravity conditions.

Experiments were carried out to investigate a three-dimensional (3D) plasma crystal. A method of determining the positions of each individual microparticle has been developed. A crystal volume of about 2x10(4) particles in 19 horizontal planes was analyzed. Direct imaging and the 3D pair correlation function show that "domains" of fcc and hcp lattices coexist in the crystal. Other structures, in particular, the theoretically predicted bcc lattice, were not observed.

Specific types of prosomes distribute differentially between intermediate and actin filaments in epithelial, fibroblastic and muscle cells.

First observed as components of non-translated mRNP complexes, prosomes harbour RNase and several proteinase activities; they are also the central constituent of the "Multicatalytic Proteinase (MCP) complexes" or "26S-proteasomes". In two recent publications (Arcangeletti et al., 1997b; De Conto et al., 1997) we have shown, by applying a new fixation technique, that these particles distribute differentially between the cytoskeletal networks of intermediate filament (IF) and actin types; previously they had been observed exclusively on the intermediate filaments. Here we further investigate the distribution of prosomes of several types, distinct by their subunit composition, between the IF of vimentin type and the actin network, as well as in the 3D space of the cell. It is shown that subtypes of prosomes occupy specific networks of the cytoskeleton, and that this pattern is specific for a given cell type. Confocal microscopy shows that prosome cytodistribution is not homogeneous in the 3D space: in the perinuclear area they colocalize most strongly with the IF, and more peripherally with the microfilament/stress fiber system; connections may exist between the two networks. Furthermore, new data indicate that the prosome-actin interaction may participate in the molecular structure of the stress fibers.

Visualization of prosomes (MCP-proteasomes), intermediate filament and actin networks by "instantaneous fixation" preserving the cytoskeleton.

A new "instantaneous" fixation/extraction procedure, yielding good preservation of intermediate filaments (IFs) and actin filaments when applied at 37 degrees C, has been explored to reexamine the relationships of the prosomes to the cytoskeleton. Prosomes are protein complexes of variable subunit composition, including occasionally a small RNA, which were originally observed as trans-acting factors in untranslated mRNPs. Constituting also the proteolytic core of the 26S proteasomes, they are also called "multicatalytic proteinase (MCP) complexes" or "20S-Proteasomes." In Triton X-100-extracted epithelial, fibroblastic, and muscle cells, prosome particles were found associated primarily with the IFs (Olink-Coux et al., 1994). Application of "instantaneous fixation" has now led to the new observation that a major fraction of prosome particles, composed of specific sets of subunits, is distributed in variable proportions between the IFs and the microfilament/ stress fiber system in PtK1 epithelial cells and human fibroblasts. Electron microscopy using gold-labeled antibodies confirms this dual localization on classical whole mounts and on cells exposed to instantaneous fixation. In contrast to the resistance of the prosome-IF association, a variable fraction of the prosome particles is released from the actin cytoskeleton by Triton X-100 when applied prior to fixation. Moreover, in vitro copolymerization of prosomes with G-actin made it possible to observe "ladder-like" filamentous structures in the electron microscope, in which the prosome particles, like the "rungs of a ladder," laterally crosslink two or more actin filaments in a regular pattern. These results demonstrate that prosomes are bound in the cell not only to IFs but also to the actin cytoskeleton and, furthermore, not only within large M(r) complexes (possibly mRNPs and/or 26S proteasomes), but also directly, as individual prosome particles.

Punch-wounded, fibroblast populated collagen matrices: a novel approach for studying cytoskeletal changes in three dimensions by confocal laser scanning microscopy.

Depending on growth conditions and cell type, collagen matrices populated with viable cells, i.e. commonly with fibroblasts, contract in a manner resembling wound contraction in vivo. If matrix cultures can be grown to provide the environment of contracting wounds in vitro, other conditions may be established under which fibroblasts grow reminiscent of those in normal dermis. Wounding such dermal equivalents may then initiate cells to change their phenotype in space and time in an in vivo-like environment. In turn, such a system should allow to study the underlying cytoskeletal changes at the onset of tissue repair and beyond. To test this hypothesis, we established the conditions for human skin-derived fibroblasts (KD cells) to grow within collagen matrices without contraction. We then excised from the center of such "attached, low-contracting dermal equivalents" (ALDE) "punch biopsies" with a diameter of 1 mm, and monitored the cell's shape and their microtubular networks and F-actin-containing structures over time by i) conventional fluorescence microscopy and ii) by confocal laser scanning microscopy in combination with optical sectioning and volume rendering software. Prior to wounding and in non-wounded controls up to 8 days post seeding (ps), cells predominantly exhibited an elongated, spindle-shaped morphology with distinct microtubular networks and F-actin-containing structures. Wounding induced most of the fibroblasts lining the wound edge to immediately round up. The round cells still revealed a microtubular network but only diffuse labeling for F-actin. One day post wounding (pw), these fibroblasts had resumed their spindle-shaped structure. They displayed the microtubular network and again thin F-actin-containing structures. From 2 days pw on and up to 6 days pw, the number of fibroblasts in the wound zone had increased, forming dense, multilayered patches oriented parallel to the wound surface, and the cells lining the wound margin showed the most extensive and massive F-actin-containing stress fiber-like structures. Quantification of the cell densities at the wound margin and in adjacent zones corroborated this increase, which is reminiscent of the fibroblasts migrating to the wound edge in the early phase of connective tissue repair.

[Recommendations for initial diagnosis and therapy in acute blood coagulation disorders]. / Empfehlungen zur initialen Diagnostik und Therapie bei akuten Gerinnungsstörungen.

Acute disturbances of blood coagulation during operations and intensive therapy require quick and precise action in order to avoid life-threatening situations. This paper reports on a simple system for the diagnosis and therapy of acute disturbances of blood coagulation. In the initial phase of bleeding, determination of fibrin monomers, d-dimers, reptilase time, number of platelets and AT III enables diagnosis of disseminated intravascular coagulation (DIC), hyperfibrinolysis and consumption coagulopathy. Particular attention is paid to local hyperfibrinolysis, a relatively rare complication but of high diagnostic importance. After some remarks on the recommended clinical test parameters, the principles of the treatment of various coagulation disturbances are described. AT III is of special importance for the treatment of DIC, where as different opinions exist regarding the application of heparin. Aprotinin has long proved successful in the specific treatment of hyperfibrinolysis. Using clinical examples, the practicability of the recommended diagnostic and therapeutic measures is demonstrated.

The structural basis for the intrinsic disorder of the actin filament: the "lateral slipping" model.

Three-dimensional (3-D) helical reconstructions computed from electron micrographs of negatively stained dispersed F-actin filaments invariably revealed two uninterrupted columns of mass forming the "backbone" of the double-helical filament. The contact between neighboring subunits along the thus defined two long-pitch helical strands was spatially conserved and of high mass density, while the intersubunit contact between them was of lower mass density and varied among reconstructions. In contrast, phalloidinstabilized F-actin filaments displayed higher and spatially more conserved mass density between the two long-pitch helical strands, suggesting that this bicyclic hepta-peptide toxin strengthens the intersubunit contact between the two strands. Consistent with this distinct intersubunit bonding pattern, the two long-pitch helical strands of unstabilized filaments were sometimes observed separated from each other over a distance of two to six subunits, suggesting that the intrastrand intersubunit contact is also physically stronger than the interstrand contact. The resolution of the filament reconstructions, extending to 2.5 nm axially and radially, enabled us to reproducibly "cut out" the F-actin subunit which measured 5.5 nm axially by 6.0 nm tangentially by 3.2 nm radially. The subunit is distinctly polar with a massive "base" pointing towards the "barbed" end of the filament, and a slender "tip" defining its "pointed" end (i.e., relative to the "arrowhead" pattern revealed after stoichiometric decoration of the filaments with myosin subfragment 1). Concavities running approximately parallel to the filament axis both on the inner and outer face of the subunit define a distinct cleft separating the subunit into two domains of similar size: an inner domain confined to radii less than or equal to 2.5-nm forms the uninterrupted backbone of the two long-pitch helical strands, and an outer domain placed at radii of 2-5-nm protrudes radially and thus predominantly contributes to the outer part of the massive base. Quantitative evaluation of successive crossover spacings along individual F-actin filaments revealed the deviations from the mean repeat to be compensatory, i.e., short crossovers frequently followed long ones and vice versa. The variable crossover spacings and diameter of the F-actin filament together with the local unraveling of the two long-pitch helical strands are explained in terms of varying amounts of compensatory "lateral slipping" of the two strands past each other roughly perpendicular to the filament axis. This intrinsic disorder of the actin filament may enable the actin moiety to play a more active role in actin-myosin-based force generation than merely act as a rigid passive cable as has hitherto been assumed.

[Multiple coagulation disorders following cesarean section]. / Multiple Gerinnungsstörungen nach Sectio caesarea.

We refer to a case report describing the diagnostic and therapeutic problems resulting in multiple intra- and postoperative coagulation disorders. Differential diagnostic indications respecting to the most important disorders within the coagulation system are described especially. Local hyperfibrinolysis is accounted in detail; besides we inform about our own therapeutic experiences.