Mechanical Stimulation of Growth Plate Chondrocytes: Previous Approaches and Future Directions

Growth plate cartilage resides near the ends of long bones and is the primary driver of skeletal growth. During growth, both intrinsically and extrinsically generated mechanical stresses act on chondrocytes in the growth plate. Although the role of mechanical stresses in promoting tissue growth and homeostasis has been strongly demonstrated in articular cartilage of the major skeletal joints, effects of stresses on growth plate cartilage and bone growth are not well established. Here, we review the literature on mechanobiology in growth plate cartilage at macroscopic and microscopic scales, with particular emphasis on comparison of results obtained using different methodological approaches, as well as from whole animal and in vitro experiments. To answer these questions, macroscopic mechanical stimulators have been developed and applied to study mechanobiology of growth plate cartilage and chondrocytes. However, the previous approaches have tested a limited number of stress conditions, and the mechanobiology of a single chondrocyte has not been well studied due to limitations of the macroscopic mechanical stimulators. We explore how microfluidics devices can overcome these limitations and improve current understanding of growth plate chondrocyte mechanobiology. In particular, microfluidic devices can generate multiple stress conditions in a single platform and enable real-time monitoring of metabolism and cellular behavior using optical microscopy. Systematic characterization of the chondrocytes using microfluidics will enhance our understanding of how to use mechanical stresses to control the bone growth and the properties of tissue-engineered growth plate cartilage.

     

Temperature‐dependent kinetics for the ozonolysis of selected chlorinated alkenes in the gas phase

The ozonolysis of olefinic species is an important tropospheric process impacting on climate and human health. However, few studies have investigated these reactions as a function of temperature and even less information is available upon the effects of alkene heteroatomic substitution on the Arrhenius parameters. The electron‐withdrawing capacity of substituents about the olefinic bond strongly influences the rate of alkene ozonolysis. To understand better the effect of these substitutions, the temperature‐dependence of a series of ozone–chloroalkene reactions is investigated. Experiments were conducted in the EXTreme RAnge (EXTRA) chamber, over the range of 292–409 K and 760 Torr. The experimentally determined rate coefficients were fitted using an Arrhenius‐type analysis to yield the following activation energies: 30.80 ± 0.79, 23.18 ± 0.59, 65.2 ± 2.8, 116.9 ± 5.6, 29.5 ± 1.8, and 18.67 ± 0.96 kJ mol^?1 and preexponential A‐factors 1.22^+0.39_?0.29×10^?15, 9.3^+6.7_?5.4×10^?16, 1.6^+2.5_?1.0×10^?10, 6⁺²²_?3.9×10^?4, 1.7^+1.6_?0.8×10^?14, and 4.2^+1.9_?1.3×10^?15 cm³ molecule^?1 s^?1 for cis‐1,2‐dichloroethene, trans‐1,2‐dichloroethene, trichloroethene, tetrachloroethene, 2‐chloropropene, and 3‐chloro‐1‐butene, respectively. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 120–129, 2011     

Random preorders and alignments

A preorder consists of linearly ordered equivalence classes called blocks, and an alignment is a sequence of cycles. We investigate the block structure of a preorder chosen uniformly at random among all preorders on n elements, and also the distribution of cycles in a random alignment chosen uniformly at random among all alignments on n elements, as n→∞.     

Functionalized single graphene sheets derived from splitting graphite oxide

A process is described to produce single sheets of functionalized graphene through thermal exfoliation of graphite oxide. The process yields a wrinkled sheet structure resulting from reaction sites involved in oxidation and reduction processes. The topological features of single sheets, as measured by atomic force microscopy, closely match predictions of first-principles atomistic modeling. Although graphite oxide is an insulator, functionalized graphene produced by this method is electrically conducting.     

Anisotropic adsorption of molecular assemblies on crystalline surfaces

Orientational order of surfactant micelles and proteins on crystalline templates has been observed but, given that the template unit cell is significantly smaller than the characteristic size of the adsorbate, this order cannot be attributed to lattice epitaxy. We interpret the template-directed orientation of rodlike molecular assemblies as arising from anisotropic van der Waals interactions between the assembly and crystalline surfaces where the anisotropic van der Waals interaction is calculated using the Lifshitz methodology. Provided the assembly is sufficiently large, substrate anisotropy provides a torque that overcomes rotational Brownian motion near the surface. The probability of a particular orientation is computed by solving a Smoluchowski equation that describes the balance between van der Waals and Brownian torques. Torque aligns both micelles and protein fibrils; the interaction energy is minimized when the assembly lies perpendicular to a symmetry axis of a crystalline substrate. Theoretical predictions agree with experiments for both hemi-cylindrical micelles and protein fibrils adsorbed on graphite.     

Differential non-destructive image current detection in a fourier transform quadrupole ion trap

Dual-detector differential non-destructive Fourier transform detection in a quadrupole ion trap is shown to improve signal intensity and reduce noise compared with spectra recorded using a single detector. A larger area detector in each end-cap electrode is machined to fit its hyperbolic shape and so minimize field imperfections on the z-axis. Argon, acetophenone and bromobenzene spectra were recorded to allow a comparison between single- and dual-detector (differential) modes of detection and to demonstrate the improvement achieved with differential detection. Copyright 1999 John Wiley & Sons, Ltd.     

Kinetic barriers and ordering of non-covalently bound states

Binding of a dimer of a glycopeptide antibiotic to two molecules of a ligand that are bound to a membrane surface (by a hydrocarbon anchor) has been investigated. This binding on a surface is cooperatively enhanced (surface enhancement) relative to the binding in solution, because the former occurs intramolecularly on a template. Previously a correlation between surface enhancement and thermodynamic stability of the dimer in free solution (Kdimsol) was hypothesised. However, we found that two weakly dimerising antibiotics (vancomycin and ristocetin A) with similar Kdimsol give very different surface enhancements. We propose a model to explain the data correlating surface enhancement to the kinetic barrier to dissociation of the dimer. The surface enhancement of binding can be expected to increase with increasing tightness of the non-covalent interactions formed at the dimer interface. The effect should be found in general where cooperativity is exercised within an organised template (e.g., DNA duplexes and proteins).     

Pseudo-steady-state solutions for solidification in a wedge

Polubarinova-Kochina's analytical differential equation methodis used to determine the pseudo-steady-state solution to problemsinvolving the freezing (solidification) of wedges of liquidwhich are initially at their fusion temperature. In particular,we consider four distinct problems for wedges which are: freezingwith the same constant boundary temperature, freezing with thesame constant boundary heat fluxes, freezing with distinct constantboundary temperatures and freezing with distinct constant fluxesat the boundaries. For the last two problems, a Heun's differentialequation with an unknown singularity is derived, which in bothcases admits a particularly elegant simple solution for thespecial case when the wedge angle is . The moving boundariesobtained are shown pictorially.     

Complete pulse characterization at 1.5 mum by cross-phase modulation in optical fibers

Cross-phase modulation in optical fibers has been used for complete characterization of ultrashort pulses by a modified frequency-resolved optical gating (FROG) measurement technique. This technique has been used for characterization of picosecond pulses at 1.5mum with energy as low as 24 pJ, and the results are in excellent agreement with second-harmonic generation (SHG)-FROG characterization. The use of an optical waveguide gives measurement sensitivity comparable with that of SHG-FROG but without any temporal ambiguity in the retrieved pulse.