PubMed · 10794872
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J M Thijssen. 2000. Spectroscopy and image texture analysis.. https://doi.org/10.1016/s0301-5629(00)00161-7
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Under a stretching force, the sugar ring of polysaccharide molecules switches from the chair to the boat-like or inverted chair conformation. This conformational change can be observed by stretching single polysaccharide molecules with an atomic force microscope. In those early experiments, the molecules were stretched at a constant rate while the resulting force changed over wide ranges. However, because the rings undergo force-dependent transitions, an experimental arrangement where the force is the free variable introduces an undesirable level of complexity in the results. Here we demonstrate the use of force-ramp atomic force microscopy to capture the conformational changes in single polysaccharide molecules. Force-ramp atomic force microscopy readily captures the ring transitions under conditions where the entropic elasticity of the molecule is separated from its conformational transitions, enabling a quantitative analysis of the data with a simple two-state model. This analysis directly provides the physico-chemical characteristics of the ring transitions such as the width of the energy barrier, the relative energy of the conformers, and their enthalpic elasticity. Our experiments enhance the ability of single-molecule force spectroscopy to make high-resolution measurements of the conformations of single polysaccharide molecules under a stretching force, making an important addition to polysaccharide spectroscopy.
The influence of an external electric field on a poorly conductive membrane such as a lipid bilayer is studied theoretically. The unbalanced electric stress created by an ionic current across a non-perfectly flat membrane gives rise to a destabilizing surface energy enhancing undulations. The deformation of a membrane attached to a frame is derived and the electrohydrodynamic instability of a free floating membrane is studied. We find a most unstable mode of undulation, of wavelength in the microm range, connected to the crossover between membrane and solvent dominated dissipations.
A new artificial loop ligament (LL) without mechanical weak points, such as a knot, has been developed to connect the EndoButton and hamstring tendons for anterior or posterior cruciate ligament (CL) reconstruction. This study assessed the mechanical properties of the LL and sutures (No. 5 Ethibond thread, EndoButton tape) and those of the different CL constructs with these materials and fixation devices commonly used in CL reconstruction. The LL had a significantly higher ultimate tensile load (UTL) and stiffness value (p < 0.001) than No. 5 Ethibond thread or EndoButton tape in static and fatigue tests (50--500 N, 1.08 million cycles). The LL-tendons-Leeds-Keio artificial ligament-staple construct complex also had significantly higher UTL and stiffness value than the Ethibond loops or EndoButton tape loop-tendons-Ethibond sutures-postscrew-fixed construct complex. Furthermore, the LL construct complex elongated the least after cyclic loading (50--150 N, 90,000 cycles). These findings suggested that using the LL construct complex might avoid a bungee cord effect and elongation before biological healing between the construct and bony socket. The LL construct complex could be a safe substitute for use during the postoperative period.