High Stiffness (high + stiffness)

Distribution by Scientific Domains

Selected Abstracts

Contractility of single human dermal myofibroblasts and fibroblasts

CYTOSKELETON, Issue 2 2002
Louise K. Wrobel
Abstract Human dermal myofibroblasts, characterised by the expression of ,-smooth muscle actin, are part of the granulation tissue and implicated in the generation of contractile forces during normal wound healing and pathological contractures. We have compared the contractile properties of single human dermal fibroblasts and human dermal myofibroblasts by culturing them on flexible silicone elastomers. The flexibility of the silicone substratum permits the contractile forces exerted by the cells to be measured [Fray et al., 1998: Tissue Eng. 4:273,283], without changing their expression of ,-smooth muscle actin. The mean contractile force produced by myofibroblasts (2.2 ,N per cell) was not significantly different from that generated by fibroblasts (2.0 ,N per cell) when cultured on a substrata with a low elastomer stiffness. Forces produced by fibroblasts were unaffected by increases in elastomer stiffness, but forces measured for myofibroblasts increased to a mean value of 4.1 ,N/cell. This was associated with a higher proportion of myofibroblasts being able to produce wrinkles on elastomers of high stiffness compared to fibroblasts. We discuss the force measurements at the single cell level, for both fibroblast and myofibroblasts, in relation to the proposed role of myofibroblasts in wound healing and pathological contractures. Cell Motil. Cytoskeleton 52:82,90, 2002. © 2002 Wiley-Liss, Inc. [source]

Plastic Dissipation Mechanisms in Periodic Microframe-Structured Polymers

Lifeng Wang
Abstract Novel lightweight micro- and nanostructured materials are being used as constituents in hierarchically structured composites for providing high stiffness, high strength, and energy absorbing capability at low weight. Three dimensional SU-8 periodic microframe materials with submicrometer elements exhibit unusual large plastic deformations. Here, the plastic dissipation and mechanical response of polymeric microframe structures is investigated using micromechanical modeling of large deformations. Finite element analysis shows that multiple deformation domains initiate, stabilize, and then spread plasticity through the structure; simulated deformation mechanisms and deformation progression are found to be in excellent agreement with experimental observation. Furthermore, the geometry can be used to tailor aspects of 3D behavior such as effective lateral contraction ratios (elastic and plastic) during tensile loading as well as negative normal stress during simple shear deformation. The effects of structural geometry on mechanical response are also studied to tailor and optimize mechanical performance at a given density. These quantitative investigations enable simulation-based design of optimal lightweight material microstructures for dissipating energy. [source]

Rotational molding of two-layered polyethylene foams

Shih-Jung Liu
Rotational molding of polyethylene foams has increasingly become an important process in industry because of its resultant thicker walls, low sound transfer, high stiffness, and good thermal insulation. This report assesses the rotomoldability of two-layer polyethylene foamed parts. The polymeric material used in this study was linear low-density polyethylene and the foaming material was an endothemic chemical blowing agent. Two different molding methods, by powder and by pellet, were used to mold the multilayer foamed parts. Rotational molding experiments were carried out in a laboratory scale uniaxial machine, capable of measuring internal mold temperature in the cycle. Characterization of molded part properties was performed after molding. Optical microscopy was also employed to determine the bubble distribution in foamed parts. The final goal of this study was to investigate how the blowing agent and processing conditions can influence the process of rotational molding and the final product quality. It was found that the rotational molding of two-layer polyethylene foams produced parts of better impact properties, as well as fine outside surfaces. In addition, rotational molding of foamed parts by pellets saves the cost of powder grinding, but is counteracted by uneven inner surfaces. © 2001 John Wiley & Sons, Inc. Adv Polym Techn 20: 108,115, 2001 [source]

Recycled PET nanocomposites improved by silanization of organoclays

Milan Krá, alík
Abstract Recycled PET/organo-modified montmorillonite nanocomposites were prepared via melt compounding as a promising possibility of the used beverage bottles recovery. According to our previous work, the three suitable commercial organoclays Cloisite 25A, 10A, and 30B were additionally modified with [3-(glycidyloxy)propyl]trimethoxysilane, hexadecyltrimethoxysilane and (3-aminopropyl)trimethoxysilane. The selected organoclays were compounded in the concentration 5 wt % and their degree of intercalation/delamination was determined by wide-angle X-ray scattering and transmission electron microscopy. Modification of Cloisite 25A with [3-(glycidyloxy)propyl]trimethoxysilane increased homogeneity of silicate layers in recycled PET. Additional modification of Cloisite 10A and Cloisite 30B led to lower level of delamination concomitant with melt viscosity reduction. However, flow characteristics of all studied organoclay nanocomposites showed solid-like behavior at low frequencies. Silanization of commercial organoclays had remarkable impact on crystallinity and melt temperature decrease accompanied by faster formation of crystalline nuclei during injection molding. Thermogravimetric analysis showed enhancement of thermal stability of modified organoclays. The tensile tests confirmed significant increase of PET-R stiffness with organoclays loading and the system containing Cloisite 25A treated with [3-(glycidyloxy)propyl]trimethoxysilane revealed combination of high stiffness and extensibility, which could be utilized for production of high-performance materials by spinning, extrusion, and blow molding technologies. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source]

A Novel Concept for Highly Oriented Carbon Nanotube Composite Tapes or Fibres with High Strength and Electrical Conductivity

Hua Deng
Abstract A new concept is described for the creation of multifunctional polymer nanocomposite tapes (or fibres) that combines high stiffness and strength with good electrical properties and a low percolation threshold of carbon nanotubes (CNTs). The concept is based on a bicomponent tape (or fibre) construction consisting of a highly oriented polymer core and a conductive polymer composite (CPC) skin based on a polymer with a lower melting temperature than the core, enabling thermal annealing of these skins to improve conductivity through a dynamic percolation process while retaining the properties of the core and hence those of the tape (or fibre). The percolation threshold in the CPC skins of the highly drawn conductive bicomponent tapes could be decreased from 5.3 to 1.1,wt.-% after annealing. [source]

Foaming of PS/wood fiber composites using moisture as a blowing agent

Ghaus Rizvi
This paper presents an experimental study on foam processing of polystyrene (PS) and high-impact polystyrene HIPS/wood-fiber composites in extrusion using moisture as a blowing agent. Wood-fiber inherently contains moisture that can potentially be used as a blowing agent. Undried wood-fiber was processed together with PS and HIPS materials in extrusion and wood-fiber composite foams were produced. The cellular morphology and volume expansion ratios of the foamed composites were characterized. Because of the high stiffness of styrenic materials, moisture condensation during cooling after expansion at high temperature did not cause much contraction of the foamed composite and a high volume expansion ratio up to 20 was successfully obtained. The experimental results showed that the expansion ratio could be controlled by varying the processing temperature and the moisture content in the wood fiber. The effects of a small amount of a chemical blowing agent and mineral oil on the cell morphologies of plastic/wood-fiber composite foams were also investigated. [source]