Morphological growth dynamics, mechanical stability, and active microtubule mechanics underlying spindle self-organization.

The spindle is a dynamic intracellular structure self-organized from microtubules and microtubule-associated proteins. The spindle's bipolar morphology is essential for the faithful segregation of chromosomes during cell division, and it is robustly maintained by multifaceted mechanisms. However, abnormally shaped spindles, such as multipolar spindles, can stochastically arise in a cell population and cause chromosome segregation errors. The physical basis of how microtubules fail in bipolarization and occasionally favor nonbipolar assembly is poorly understood. Here, using live fluorescence imaging and quantitative shape analysis in Xenopus egg extracts, we find that spindles of varied shape morphologies emerge through nonrandom, bistable self-organization paths, one leading to a bipolar and the other leading to a multipolar phenotype. The bistability defines the spindle's unique morphological growth dynamics linked to each shape phenotype and can be promoted by a locally distorted microtubule flow that arises within premature structures. We also find that bipolar and multipolar spindles are stable at the steady-state in bulk but can infrequently switch between the two phenotypes. Our microneedle-based physical manipulation further demonstrates that a transient force perturbation applied near the assembled pole can trigger the phenotypic switching, revealing the mechanical plasticity of the spindle. Together with molecular perturbation of kinesin-5 and augmin, our data propose the physical and molecular bases underlying the emergence of spindle-shape variation, which influences chromosome segregation fidelity during cell division.

Collective motion of epithelial cells along a wrinkled 3D-buckled hydrogel.

Epithelial cells migrate autonomously by aligning and inducing a collective motion. Controlling the collective motion of epithelial cells in geometrically confined environments is important for understanding physiological processes such as wound healing and self-organized morphogenesis. However, collective migration under a three-dimensional (3D) curved surface resembling living epithelial tissue has not yet been explored. In this study, we investigated the collective motion of a 3D-buckled polyacrylamide (PAAm) gel that mimics the shape of folds and wrinkles of epithelial tissue to understand the geometric effects of collective motion. We found that the velocity correlation in the space near the hydrogel boundary showed a periodic change that correlated with the wrinkled folding of the hydrogel pattern. Furthermore, the characteristic length of the velocity correlation increased proportionally with the wavelength of wrinkled folding. These observations indicated that the hydrogel pattern could steer the collective motion of epithelial cells over long distances. Our study also suggests that the wrinkled design of the hydrogel is a versatile platform for studying the geometric effect of a curved surface on complex epithelial cell dynamics.

Protein Needles Designed to Self-Assemble through Needle Tip Engineering.

The dynamic process of formation of protein assemblies is essential to form highly ordered structures in biological systems. Advances in structural and synthetic biology have led to the construction of artificial protein assemblies. However, development of design strategies exploiting the anisotropic shape of building blocks of protein assemblies has not yet been achieved. Here, the 2D assembly pattern of protein needles (PNs) is controlled by regulating their tip-to-tip interactions. The PN is an anisotropic needle-shaped protein composed of ß-helix, foldon, and His-tag. Three different types of tip-modified PNs are designed by deleting the His-tag and foldon to change the protein-protein interactions. Observing their assembly by high-speed atomic force microscopy (HS-AFM) reveals that PN, His-tag deleted PN, and His-tag and foldon deleted PN form triangular lattices, the monomeric state with nematic order, and fiber assemblies, respectively, on a mica surface. Their assembly dynamics are observed by HS-AFM and analyzed by the theoretical models. Monte Carlo (MC) simulations indicate that the mica-PN interactions and the flexible and multipoint His-tag interactions cooperatively guide the formation of the triangular lattice. This work is expected to provide a new strategy for constructing supramolecular protein architectures by controlling directional interactions of anisotropic shaped proteins.

Opto-thermal diffusiophoresis of soft biological matter: from physical principle to molecular manipulation.

Transport of ions and molecules under external field gradients is fundamental phenomena relevant to many biological systems including molecular motors in nature. As inspired from such biological transport, novel optical manipulation by using local solute gradient and the creation of self-propulsive particles are being developed using this technology. In this review article, we describe the basic principles behind those transport phenomena under a temperature and a solute concentration gradient and discuss novel manipulation tools for soft biological materials. The control of such micron-scale transport will bring new insight in design principles of functional materials showing autonomous motion as seen in molecular motors.

Thermal molecular focusing: tunable cross effect of phoresis and light-driven hydrodynamic focusing.

The control of solute flux by either microscopic phoresis or hydrodynamic advection is a fundamental way to transport molecules, which are ubiquitously present in nature and technology. We study the transport of large solutes such as DNA driven by a time-dependent thermal field in a polymer solution. Heat propagation of a heat spot moving back and forth gives rise to the molecular focusing of DNA with frequency-tunable control. We develop a model where the viscoelastic expansion of a solution and the viscosity gradient of a smaller solute are coupled, which explains the underlying hydrodynamic focusing. This effect offers novel non-invasive manipulation of soft and biological materials in a frequency-tunable manner.

Directing and Boosting of Cell Migration by the Entropic Force Gradient in Polymer Solution.

Noncontact manipulation of nano/micromaterials presents a great challenge in fields ranging from biotechnology to nanotechnology. In this study we developed a new strategy for the manipulation of molecules and cells based on diffusiophoresis driven by a concentration gradient of a polymer solute. By using laser focusing in a microfluidic device, we created a sharp concentration gradient of poly(ethylene glycol) (PEG) in a solution of this polymer. Because diffusiophoresis essentially depends on solute gradients alone, PEG solute contrast resulted in trapping of DNA and eukaryotic cells with little material dependence. Furthermore, quantitative analysis revealed that the motility of migrating cells was enhanced with the PEG concentration, consistent with a theoretical model of boosted cell migration. Our results support that a solute contrast of polymer can exert an interfacial force gradient that physically propels objects and may have application for the manipulation of soft materials.

Safety and efficacy of oral rehydration therapy until 2 h before surgery: a multicenter randomized controlled trial.

PURPOSE: In many countries, patients are generally allowed to have clear fluids until 2-3 h before surgery. In Japan, long preoperative fasting is still common practice. To shorten the preoperative fasting period in Japan, we tested the safety and efficacy of oral rehydration therapy until 2 h before surgery. METHODS: Three hundred low-risk patients scheduled for morning surgery in six university-affiliated hospitals were randomly assigned to an oral rehydration solution (ORS) group or to a fasting group. Patients in the ORS group consumed up to 1,000 ml of ORS containing balanced glucose and electrolytes: 500 ml between 2100 the night before surgery and the time they woke up the next morning and 500 ml during the morning of surgery until 2 h before surgery. Patients in the fasting group started fasting at 2100 the night before surgery. Primary endpoints were gastric fluid volume and pH immediately after anesthesia induction. Several physiological measures of hydration and electrolytes including the fractional excretion of sodium (FENa) and the fractional excretion of urea nitrogen (FEUN) were also evaluated. RESULTS: Mean (SD) gastric fluid volume immediately after anesthesia induction was 15.1 (14.0) ml in the ORS group and 17.5 (23.2) ml in the fasting group (P = 0.30). The mean difference between the ORS group and fasting group was -2.5 ml. The 95% confidence interval ranged from -7.1 to +2.2 ml and did not include the noninferior limit of +8 ml. Mean (SD) gastric fluid pH was 2.1 (1.9) in the ORS group and 2.2 (2.0) in the fasting group (P = 0.59). In the ORS group, mean FENa and FEUN immediately after anesthesia induction were both significantly greater than those in the fasting group (P < 0.001 for both variables). The ORS group reported they had been less thirsty and hungry before surgery (P < 0.001, 0.01). CONCLUSIONS: Oral rehydration therapy until 2 h before surgery is safe and feasible in the low-risk Japanese surgical population. Physicians are encouraged to use this practice to maintain the amount of water in the body and electrolytes and to improve the patient's comfort.

[Excessive bleeding in the patients with past history of Hassab's operation].

We report two cases of massive perioperative bleeding and multiple organ failure with past history of Hassab's operation. Massive bleeding occurred during laparotomy and thoracocentesis in each case. After Hassab's operation, collateral circulation and coagulation disorders could develop, and unanticipated massive bleeding might occur. Preparations for excessive bleeding and postoperative intensive care would be required for the patients who have past history of Hassab's operation.

[Blood lactate levels during fast-track cardiac anesthesia].

BACKGROUND: Lactate is a very sensitive marker of outcomes in critically ill patients. The aim of this study was to investigate the significance of blood lactate measurement during fast-track cardiac anesthesia. METHODS: We examined arterial blood lactate levels of 12 patients following coronary artery bypass graft surgery under intermittent aortic cross clamping with fast-track cardiac anesthesia. Anesthesia was induced with propofol and fentanyl, and maintained with propofol, fentanyl (total 400-1000 micrograms) and isoflurane. Blood samples were collected from a radical artery catheter. RESULTS: At the termination of the extracorporeal circulation, the blood lactate was 10.3 +/- 2.0 (7.4-12.5) mmol.l-1. This value decreased slowly to 1.5 +/- 0.4 mmol.l-1 on the second postoperative day. All patients were extubated within 4 hours after surgery. Vital signs were stable, and no cardiac events occurred perioperatively. CONCLUSIONS: A continuous decline in blood lactate levels was related to a favorable postoperative course. Further research might be required to prevent transient hyperlactecemia at the end of cardiopulmonary bypass.