Spatial confinement affects the heterogeneity and interactions between shoaling fish.

Living objects are able to consume chemical energy and process information independently from others. However, living objects can coordinate to form ordered groups such as schools of fish. This work considers these complex groups as living materials and presents imaging-based experiments of laboratory schools of fish to understand how activity, which is a non-equilibrium feature, affects the structure and dynamics of a group. We use spatial confinement to control the motion and structure of fish within quasi-2D shoals of fish and use image analysis techniques to make quantitative observations of the structures, their spatial heterogeneity, and their temporal fluctuations. Furthermore, we utilize Monte Carlo simulations to replicate the experimentally observed data which provides insight into the effective interactions between fish and confirms the presence of a confinement-based behavioral preference transition. In addition, unlike in short-range interacting systems, here structural heterogeneity and dynamic activities are positively correlated as a result of complex interplay between spatial arrangement and behavioral dynamics in fish collectives.

Mexican jumping beans exhibit diffusive motion.

Organisms across many lengthscales generate specific strategies for motion that are crucial to their survival. Here, we detail the motion of a nontraditional organism, the Mexican jumping bean, where a larva encapsulated within a seed blindly moves the seed in search of shade. Using image analysis techniques, we quantitatively describe the motion of these objects as active particles. From this experimental data, we build a computational simulation that quantitatively captures the motion of these beans. And we further evaluate the effectiveness of using the observed diffusive strategy to find shade, suggesting that the random walk is an advantageous strategy for survival.

F-actin architecture determines constraints on myosin thick filament motion.

Active stresses are generated and transmitted throughout diverse F-actin architectures within the cell cytoskeleton, and drive essential behaviors of the cell, from cell division to migration. However, while the impact of F-actin architecture on the transmission of stress is well studied, the role of architecture on the ab initio generation of stresses remains less understood. Here, we assemble F-actin networks in vitro, whose architectures are varied from branched to bundled through F-actin nucleation via Arp2/3 and the formin mDia1. Within these architectures, we track the motions of embedded myosin thick filaments and connect them to the extent of F-actin network deformation. While mDia1-nucleated networks facilitate the accumulation of stress and drive contractility through enhanced actomyosin sliding, branched networks prevent stress accumulation through the inhibited processivity of thick filaments. The reduction in processivity is due to a decrease in translational and rotational motions constrained by the local density and geometry of F-actin.

Dynamic motions of molecular motors in the actin cytoskeleton.

During intracellular transport, cellular cargos, such as organelles, vesicles, and proteins, are transported within cells. Intracellular transport plays an important role in diverse cellular functions. Molecular motors walking on the cytoskeleton facilitate active intracellular transport, which is more efficient than diffusion-based passive transport. Active transport driven by kinesin and dynein walking on microtubules has been studied well during recent decades. However, mechanisms of active transport occurring in disorganized actin networks via myosin motors remain elusive. To provide physiologically relevant insights, we probed motions of myosin motors in actin networks under various conditions using our well-established computational model that rigorously accounts for the mechanical and dynamical behaviors of the actin cytoskeleton. We demonstrated that myosin motions can be confined due to three different reasons in the absence of F-actin turnover. We verified mechanisms of motor stalling using in vitro reconstituted actomyosin networks. We also found that with F-actin turnover, motors consistently move for a long time without significant confinement. Our study sheds light on the importance of F-actin turnover for effective active transport in the actin cytoskeleton.

Filament Nucleation Tunes Mechanical Memory in Active Polymer Networks.

Incorporating growth into contemporary material functionality presents a grand challenge in materials design. The F-actin cytoskeleton is an active polymer network which serves as the mechanical scaffolding for eukaryotic cells, growing and remodeling in order to determine changes in cell shape. Nucleated from the membrane, filaments polymerize and grow into a dense network whose dynamics of assembly and disassembly, or 'turnover', coordinates both fluidity and rigidity. Here, we vary the extent of F-actin nucleation from a membrane surface in a biomimetic model of the cytoskeleton constructed from purified protein. We find that nucleation of F-actin mediates the accumulation and dissipation of polymerization-induced F-actin bending energy. At high and low nucleation, bending energies are low and easily relaxed yielding an isotropic material. However, at an intermediate critical nucleation, stresses are not relaxed by turnover and the internal energy accumulates 100-fold. In this case, high filament curvatures template further assembly of F-actin, driving the formation and stabilization of vortex-like topological defects. Thus, nucleation coordinates mechanical and chemical timescales to encode shape memory into active materials.

Wound Healing Coordinates Actin Architectures to Regulate Mechanical Work.

How cells with diverse morphologies and cytoskeletal architectures modulate their mechanical behaviors to drive robust collective motion within tissues is poorly understood. During wound repair within epithelial monolayers in vitro, cells coordinate the assembly of branched and bundled actin networks to regulate the total mechanical work produced by collective cell motion. Using traction force microscopy, we show that the balance of actin network architectures optimizes the wound closure rate and the magnitude of the mechanical work. These values are constrained by the effective power exerted by the monolayer, which is conserved and independent of actin architectures. Using a cell-based physical model, we show that the rate at which mechanical work is done by the monolayer is limited by the transformation between actin network architectures and differential regulation of cell-substrate friction. These results and our proposed mechanisms provide a robust physical model for how cells collectively coordinate their non-equilibrium behaviors to dynamically regulate tissue-scale mechanical output.

Entropy production rate is maximized in non-contractile actomyosin.

The actin cytoskeleton is an active semi-flexible polymer network whose non-equilibrium properties coordinate both stable and contractile behaviors to maintain or change cell shape. While myosin motors drive the actin cytoskeleton out-of-equilibrium, the role of myosin-driven active stresses in the accumulation and dissipation of mechanical energy is unclear. To investigate this, we synthesize an actomyosin material in vitro whose active stress content can tune the network from stable to contractile. Each increment in activity determines a characteristic spectrum of actin filament fluctuations which is used to calculate the total mechanical work and the production of entropy in the material. We find that the balance of work and entropy does not increase monotonically and the entropy production rate is maximized in the non-contractile, stable state of actomyosin. Our study provides evidence that the origins of entropy production and activity-dependent dissipation relate to disorder in the molecular interactions between actin and myosin.

Silk Molecular Weight Influences the Kinetics of Enzymatically Cross-linked Silk Hydrogel Formation.

We transform reconstituted silk solutions into robust hydrogels through covalent dityrosine cross-linking resulting from an enzymatic reaction. The bulk rheological properties and the covalent dityrosine bond formation of these gels are measured during polymerization. We compare the time-resolved bond formation to the mechanical properties, where we find that the gelation process is consistent with a model of percolation. The molecular weight of the protein determines whether a secondary mode of growth postpercolation exists, indicating that molecular weight changes affect the mechanisms by which these gels polymerize.

Cooperation of dual modes of cell motility promotes epithelial stress relaxation to accelerate wound healing.

Collective cell migration in cohesive units is vital for tissue morphogenesis, wound repair, and immune response. While the fundamental driving forces for collective cell motion stem from contractile and protrusive activities of individual cells, it remains unknown how their balance is optimized to maintain tissue cohesiveness and the fluidity for motion. Here we present a cell-based computational model for collective cell migration during wound healing that incorporates mechanochemical coupling of cell motion and adhesion kinetics with stochastic transformation of active motility forces. We show that a balance of protrusive motility and actomyosin contractility is optimized for accelerating the rate of wound repair, which is robust to variations in cell and substrate mechanical properties. This balance underlies rapid collective cell motion during wound healing, resulting from a tradeoff between tension mediated collective cell guidance and active stress relaxation in the tissue.

Acid-induced assembly of a reconstituted silk protein system.

Silk cocoons are reconstituted into an aqueous suspension, and protein stability is investigated by comparing the protein's response to hydrochloric acid and sodium chloride. Aggregation occurs for systems mixed with hydrochloric acid, while sodium chloride over the same range of concentrations does not cause aggregation. We measure the structures present on the protein and aggregate length scales in these solutions using both optical and small-angle neutron scattering, while mass spectrometry techniques shed light on a possible mechanism for aggregate formation. We find that the introduction of acid modulates the aggregate size and pervaded volume of the protein, an effect that is not observed with salt.

Silk Fibroin Degradation Related to Rheological and Mechanical Properties.

Regenerated silk fibroin has been proposed as a material substrate for biomedical, optical, and electronic applications. Preparation of the silk fibroin solution requires extraction (degumming) to remove contaminants, but results in the degradation of the fibroin protein. Here, a mechanism of fibroin degradation is proposed and the molecular weight and polydispersity is characterized as a function of extraction time. Rheological analysis reveals significant changes in the viscosity of samples while mechanical characterization of cast and drawn films shows increased moduli, extensibility, and strength upon drawing. Fifteen minutes extraction time results in degraded fibroin that generates the strongest films. Structural analysis by wide angle X-ray scattering (WAXS) and Fourier transform infrared spectroscopy (FTIR) indicates molecular alignment in the drawn films and shows that the drawing process converts amorphous films into the crystalline, ß-sheet, secondary structure. Most interesting, by using selected extraction times, films with near-native crystallinity, alignment, and molecular weight can be achieved; yet maximal mechanical properties for the films from regenerated silk fibroin solutions are found with solutions subjected to some degree of degradation. These results suggest that the regenerated solutions and the film casting and drawing processes introduce more complexity than native spinning processes.

Rheology of reconstituted silk fibroin protein gels: the epitome of extreme mechanics.

In nature, silk fibroin proteins assemble into hierarchical structures with dramatic mechanical properties. With the hope of creating new classes of on demand silk-based biomaterials, Bombyx mori silk is reconstituted back into stable aqueous solutions that can be reassembled into functionalized materials; one strategy for reassembly is electrogelation. Electrogels (e-gels) are particularly versatile and can be produced using electrolysis with small DC electric fields. We characterize the linear and nonlinear rheological behavior of e-gels to provide fundamental insights into these distinct protein-based materials. We observe that e-gels form robust biopolymer networks that exhibit distinctive strain hardening and are recoverable from strains as large as γ=27, i.e. 2700%. We propose a simple microscopic model that is consistent with local restructuring of single proteins within the e-gel network.

Clinical presentation and outcome of perforating ocular injuries due to BB guns: a case series.

PURPOSE: To describe the clinical presentations and treatment modalities of a series of BB gun-related perforating ocular injuries. METHODS: Clinical records of all consecutive cases of perforating BB gun injuries to the globe seen between September 2004 and September 2008 were reviewed retrospectively. At the time of the trauma and after final treatment, all patients underwent a complete ocular examination, including visual acuity,applanation tonometry for intraocular pressure, slit lamp biomicroscopy, indirect ophthalmoscopy and fundus photography, if possible. In all cases, primary globe repair was performed in the first session, and then appropriate surgery took place based on the individual situation. RESULTS: In this study, 13 patients (11 males and 2 females) with a mean age of 20.8 years (range 9­50 years) were enrolled. The mean follow-up period was 7.2 4.3 months (range 1­25 months). Initial visual acuity (VA) ranged from no-light perception (NLP) to finger counting (CF). Vitreous haemorrhage and retinal detachment were present in all involved eyes. Hyphema (30.76%), uveal and retinal prolapse (30.8%), retinalin carceration (30.8%) and retinal haemorrhage (53.8%) were other ocular findings. VA remained stable in 46.2% of the patients (6 cases). The best achieved final VA was CF at 2 min one case after 6 months follow-up.After several surgical procedures, enucleation was necessary in only 2/13 (15.4%) cases. CONCLUSION: Despite several surgical procedures which decreased the number of enucleations, BB gunperforating ocular injuries still lead to a grim visual outcome. This implies the importance of political strategies targeting on education of parents and restriction for children to access to these guns.

Protein Z circulates in plasma in a complex with protein Z-dependent protease inhibitor.

Protein Z (PZ) is a vitamin K-dependent plasma protein that forms a Ca++-dependent complex with factor Xa at phospholipid surfaces. This interaction between PZ and factor Xa enhances by >1,000-fold the inhibition of factor Xa by the serpin called protein Z-dependent protease inhibitor (ZPI). These experiments show that PZ also binds ZPI in a process that does not require Ca++ or phospholipids. In pooled normal plasma, which contains excess ZPI relative to PZ, all the PZ appears to be bound in a complex with ZPI. The binding of PZ to ZPI reduces the rate and extent of factor XIa inhibition produced by ZPI. During the course of these studies, it was noted that a PZ purification procedure, that included NaSCN (2.0 M) elution of PZ from an immunoaffinity column, produced aggregated, inactive forms of PZ.

Prenatal development of the muscles in the floor of the mouth in human embryos and fetuses from 6.9 to 76 mm CRL.

The development of the muscles in the floor of the mouth is described in 10 human embryos and fetuses ranging from 6.9 to 76 mm CRL by means of computer-aided graphical 3D-reconstructions. All primordia of the muscles in the floor of the mouth could be identified from the 15.6 mm CRL stage on. The proportions and insertion lines of the early muscles were found to be different from adult anatomy. Each muscle first inserted in the medial surface of Meckels cartilage, but during the developmental period between 19 and 68 mm CRL the insertion lines were gradually transposed to the bony ridges of the mandible which progrediently embraced Meckels cartilage. The fibers of the mylohyoid muscles left the anterior region near the symphysis mentalis free during all stages of this study. The digastric muscle revealed only one belly with a constriction of its continuous fibers where it passed the hyoid bone primordium. There was no attachment of digastric muscle fibers to the hyoid; only geniohyoid and mylohyoid fibers. Geniohyoid and genioglossus muscles basically correspond to their definite arrangement, but they underwent proportional changes. Individual specimens embodied irregularities such as accessory geniohyoid and hyoid portions and muscle fibers separate from the mylohyoide muscle.

Dietary fiber and type 2 diabetes.

This article addresses the current theory, research, and implications of dietary fiber in the management of type 2 diabetes mellitus (DM; non-insulin-dependent DM). Dietary fiber shows promise in the management of type 2 DM. The inclusion of sufficient dietary fiber in a meal flattens the postprandial glycemic and insulinemic excursions and favorably influences plasma lipid levels in patients with type 2 DM. Water-soluble fiber appears to have a greater potential to reduce postprandial blood glucose, insulin, and serum lipid levels than insoluble fiber. Viscosity of the dietary fiber is important; the greater the viscosity, the greater the effect. Possible mechanisms for metabolic improvements with dietary fiber include delay of glucose absorption, increase in hepatic extraction of insulin, increased insulin sensitivity at the cellular level, and binding of bile acids. Patients with type 2 DM should increase their dietary fiber intake to 20 to 35 g/d and be aware of the considerations when increasing fiber intake. The nurse practitioner is in an ideal position to promote dietary fiber intake in such patients.

The use of visible light-cured resin system in maxillofacial prosthetics and neuro-orthopedic surgery.

The use of visible light-cured (VLC) resin was evaluated in contrast to more traditional chemical-cured resins for reconstruction of the spine in experimental rats. Such procedures are used to reconstruct vertebra in humans following corpectomy for neoplastic destruction of the spine. Numerous disadvantages exist in the use of chemical-cured resins, including excessive heat generated during the polymerization, cytotoxic effects of the nonpolymerized monomers on adjacent tissues, increased risk of infection due to impaired immunity, and distortion problems with the polymers. A new visible light-cured resin, Triad, was tested for use in maxillofacial prosthetics and for vertebral body replacement in neuro-orthopedic surgery. This study evaluated the biocompatibility of the VLC resin system as a bone implant material. The results of this study have shown the VLC resins underwent polymerization without substantial exothermic reaction and the biologic testing indicated that they are nontoxic and biocompatible. Some of the advantages noticed by using VLC resin are accuracy of fit and ease of fabrication and manipulation.

The use of visible light-curing resin for vertebral body replacement.

The technology of visible light-curing resin has recently been developed for use in removable prosthodontics. A quartz halogen lamp producing a 400- to 500-nanometer wave-length spectrum of visible light is used to polymerize high-molecular-weight acrylic resin monomers. While several in vitro and in vivo studies of visible light-curing resin are found in the dental literature, no studies have yet been performed to evaluate it as an intracorporeal implant in surgery. The authors have designed a rat model of microcervical corpectomy to assess vertebral body replacement with visible light-curing resin in comparison to conventional autopolymerizing methyl methacrylate. Spinal cord function tests, spinal-implant stability assessments, and histological evaluations were made in a total of 41 rats at 2, 4, or 6 months postimplant. No animal developed a neurological deficit or radiographic instability, and at sacrifice there was no evidence of implant fracture-extrusion. In addition, there were no signs of adverse reaction in the surrounding tissues. Morphological investigation of the resin/bone interface at 6 months revealed very good implant anchorage. Visible light-curing resin was found to be far superior to methyl methacrylate for construction of spinal implants. Its waxy consistency makes it easy to handle. It remains pliable until light is applied, allowing adjustments in shape for a well-fitted implant without time constraints. Applied in layers, adjustments can be made even after polymerization of a previous layer. This new implantable resin will allow safer, immediate stabilization in patients with neoplastic destruction of the spine, and may also be advantageous for other neurosurgical applications, such as cranioplasty.

Edge location to subpixel values in digital imagery.

A new method for locating edges in digital data to subpixel values and which is invariant to additive and multiplicative changes in the data is presented. For one-dimensional edge patterns an ideal edge is fit to the data by matching moments. It is shown that the edge location is related to the so-called ``Christoffel numbers.'' Also presented is the study of the effect of additive noise on edge location. The method is extended to include two-dimensional edge patterns where a line equation is derived to locate an edge. This in turn is compared with the standard Hueckel edge operator. An application of the new edge operator as an edge detector is also provided and is compared with Sobel and Hueckel edge detectors in presence and absence of noise.