PubMed Health⌕ Search
Home/Archive/PubMed

PubMed · 12959588

Load distribution in native cellulose.

Barbara Hinterstoisser·Margaretha Akerholm·Lennart Salmén
View original source ↗Export metadata ↓

Abstract

The properties of cellulose materials are dependent on interactions between and within the cellulose chains. To investigate the deformation behavior of cellulose and its relation to molecular straining, sheets with fibers oriented preferably in one direction were studied by dynamic FT-IR spectroscopy. Celluloses with different origins (spruce pulp, Cladophora cellulose, cotton linters) were used. The sheets were stretched sinusoidally at low strains and small amplitudes while being irradiated with polarized infrared radiation. The cellulose fibers showed mainly an elastic response. The cellulose fibers showed mainly an elastic response. The glucose rings and the C-O-C bridges connecting adjacent rings, as well as the O(3)H.O(5) intramolecular hydrogen bonds are the components mainly deformed under stress, whereas the O(2)H.O(6) intramolecular hydrogen bonds play a minor role. The load distribution was also found to be different in the different allomorphic forms of cellulose I, namely, I(alpha) and I(beta).

Explore related subjects

Biomechanical PhenomenaCelluloseCotton FiberMolecular StructurePiceaSpectroscopy, Fourier Transform InfraredComparative StudyJournal ArticleResearch Support, Non-U.S. Gov't

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Barbara Hinterstoisser, Margaretha Akerholm, Lennart Salmén. Load distribution in native cellulose.. https://doi.org/10.1021/bm030017k

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2003

Positive force feedback in bouncing gaits?

During bouncing gaits (running, hopping, trotting), passive compliant structures (e.g. tendons, ligaments) store and release part of the stride energy. Here, active muscles must provide the required force to withstand the developing tendon strain and to compensate for the inevitable energy losses. This requires an appropriate control of muscle activation. In this study, for hopping, the potential involvement of afferent information from muscle receptors (muscle spindles, Golgi tendon organs) is investigated using a two-segment leg model with one extensor muscle. It is found that: (i) positive feedbacks of muscle-fibre length and muscle force can result in periodic bouncing; (ii) positive force feedback (F+) stabilizes bouncing patterns within a large range of stride energies (maximum hopping height of 16.3 cm, almost twofold higher than the length feedback); and (iii) when employing this reflex scheme, for moderate hopping heights (up to 8.8 cm), an overall elastic leg behaviour is predicted (hopping frequency of 1.4-3 Hz, leg stiffness of 9-27 kN m(-1)). Furthermore, F+ could stabilize running. It is suggested that, during the stance phase of bouncing tasks, the reflex-generated motor control based on feedbacks might be an efficient and reliable alternative to central motor commands.

Biomechanical Phenomena↗
PubMed2003

Biomechanical comparison of cervical spine reconstructive techniques after a multilevel corpectomy of the cervical spine.

STUDY DESIGN: An in vitro biomechanical study of several reconstructive techniques after a two-level cervical corpectomy. OBJECTIVES: To evaluate, compare, and quantitate the stability of several reconstructive strategies (anterior, posterior, or anterior/posterior with or without instrumentation) after a multilevel cervical corpectomy. SUMMARY OF BACKGROUND DATA: Several clinical and biomechanical studies have questioned the stability of stand-alone long-segment anterior plate fixation after a multilevel (>or=2) corpectomy. The large cantilever forces generated within the stabilized construct, particularly at the caudal screw-bone interface, have led to plate and screw dislodgement and the need for further surgical intervention. The addition of posterior segmental instrumentation has been shown to improve overall stability and decrease local stresses on the anterior fusion construct (graft and plate). MATERIALS AND METHODS: Seven fresh-frozen cadaveric human cervical spines (C1-T1) were harvested. The C1-C2 and C7-T1 vertebral bodies were embedded in poly-methylmethacrylate (PMMA). Three VICON cameras tracked three-dimensional segmental motions at the ends of the fusion construct after a two-level corpectomy and placement of a strut graft with or without instrumentation. Pure moments (flexion/extension, lateral bending, and axial rotation) were applied to the C1 level of each specimen. The motion segments were loaded to a maximum of 2 Nm using dead weights. Testing was first performed on the intact specimens. Then, a two-level corpectomy at the C4 and C5 levels was performed. A PMMA strut graft was then placed into the corpectomy site. Biomechanical testing was then repeated among three different reconstruction techniques: 1) anterior cervical locking plate (PEAK; Depuy-Acromed, Raynham, MA) with dual unicortical screw fixation at C3 and C6; 2) posterior cervical instrumentation (Summit; Depuy-Acromed) using a 3.0-mm rod with segmental lateral mass screw fixation from C3 to C6; and 3) a combined anterior-posterior instrumentation using the anterior PEAK plate and posterior Summit rod system. RESULTS: In all pure moments tested (flexion/extension/lateral bending/axial rotation) the combined anterior-posterior instrumentation reconstruction model and the posterior-only instrumentation model were significantly more rigid than the anterior-only instrumentation model (P < 0.05). Interestingly, no statistically significant difference was noted between the combined anterior plate/posterior instrumentation model and the posterior instrumentation-only model. CONCLUSION: The biomechanical results obtained suggest that posterior segmental instrumentation confers significant stability to a multilevel cervical corpectomy regardless of the presence or absence of anterior instrumentation. In cases in which the stability of a multilevel reconstruction procedure is tenuous, the surgeon should strongly consider the placement of segmental posterior instrumentation to significantly improve the overall stability of the fusion construct.

Biomechanical Phenomena↗
PubMed2003

Forces associated with pneumatic power screwdriver operation: statics and dynamics.

The statics and dynamics of pneumatic power screwdriver operation were investigated in the context of predicting forces acting against the human operator. A static force model is described in the paper, based on tool geometry, mass, orientation in space, feed force, torque build up, and stall torque. Three common power hand tool shapes are considered, including pistol grip, right angle, and in-line. The static model estimates handle force needed to support a power nutrunner when it acts against the tightened fastener with a constant torque. A system of equations for static force and moment equilibrium conditions are established, and the resultant handle force (resolved in orthogonal directions) is calculated in matrix form. A dynamic model is formulated to describe pneumatic motor torque build-up characteristics dependent on threaded fastener joint hardness. Six pneumatic tools were tested to validate the deterministic model. The average torque prediction error was 6.6% (SD = 5.4%) and the average handle force prediction error was 6.7% (SD = 6.4%) for a medium-soft threaded fastener joint. The average torque prediction error was 5.2% (SD = 5.3%) and the average handle force prediction error was 3.6% (SD = 3.2%) for a hard threaded fastener joint. Use of these equations for estimating handle forces based on passive mechanical elements representing the human operator is also described. These models together should be useful for considering tool handle force in the selection and design of power screwdrivers, particularly for minimizing handle forces in the prevention of injuries and work related musculoskeletal disorders.

Biomechanical Phenomena↗