Investigation of vessel occlusion during cell seeding process

Biomechanics and Modeling in Mechanobiology - The seeding of cells into an organ is an important step in cell therapy because the final functional properties of the organ are related to...     

Effectiveness of pedicle screw inclusion at the fracture level in short-segment fixation constructs for the treatment of thoracolumbar burst fractures: a computational biomechanics analysis

When treating thoracolumbar burst fractures (BF), short-segment posterior fixation (SSPF) represents a less invasive alternative to the traditional long-segment posterior fixation (LSPF) approach. However, hardware failure and loss of sagittal alignment have been reported in patients treated with SSPF. Including pedicle screws at the fracture level in SSPF constructs has been proposed to improve stiffness and reliability of the construct. Accordingly, the biomechanical performance of the proposed construct was compared to LSPF via a computational analysis. Pedicle screws at fracture level improved the performance of the short-segment construct. However, LSPF still represent a biomechanically superior option for treating thoracolumbar BF.     

Dynamic analysis of a simplified bone model during the process of fracture healing

The dynamic analysis of fracture healing is tackled numerically by means of a bone model which uses the finite element method. The model is of non-uniform cross-sectional area and moment of inertia. Shear and rotatory inertia are taken into account. Considerable variation of the upper natural frequencies is observed as the healing process progresses. The practical implications, as well as present limitations, of the technique are examined.     

Charge compensation during the phagocyte respiratory burst

The phagocyte NADPH oxidase produces superoxide anion (O₂^·−) by the electrogenic process of moving electrons across the cell membrane. This charge translocation must be compensated to prevent self-inhibition by extreme membrane depolarization. Examination of the mechanisms of charge compensation reveals that these mechanisms perform several other vital functions beyond simply supporting oxidase activity. Voltage-gated proton channels compensate most of the charge translocated by the phagocyte NADPH oxidase in human neutrophils and eosinophils. Quantitative modeling of NADPH oxidase in the plasma membrane supports this conclusion and shows that if any other conductance is present, it must be miniscule. In addition to charge compensation, proton flux from the cytoplasm into the phagosome (a) helps prevent large pH excursions both in the cytoplasm and in the phagosome, (b) minimizes osmotic disturbances, and (c) provides essential substrate protons for the conversion of O₂^·− to H₂O₂ and then to HOCl. A small contribution by K⁺ or Cl⁻ fluxes may offset the acidity of granule contents to keep the phagosome pH near neutral, facilitating release of bactericidal enzymes. In summary, the mechanisms used by phagocytes for charge compensation during the respiratory burst would still be essential to phagocyte function, even if NADPH oxidase were not electrogenic.     

Charge compensation during the phagocyte respiratory burst

The phagocyte NADPH oxidase produces superoxide anion (O(2)(.-)) by the electrogenic process of moving electrons across the cell membrane. This charge translocation must be compensated to prevent self-inhibition by extreme membrane depolarization. Examination of the mechanisms of charge compensation reveals that these mechanisms perform several other vital functions beyond simply supporting oxidase activity. Voltage-gated proton channels compensate most of the charge translocated by the phagocyte NADPH oxidase in human neutrophils and eosinophils. Quantitative modeling of NADPH oxidase in the plasma membrane supports this conclusion and shows that if any other conductance is present, it must be miniscule. In addition to charge compensation, proton flux from the cytoplasm into the phagosome (a) helps prevent large pH excursions both in the cytoplasm and in the phagosome, (b) minimizes osmotic disturbances, and (c) provides essential substrate protons for the conversion of O(2)(*-) to H(2)O(2) and then to HOCl. A small contribution by K+ or Cl- fluxes may offset the acidity of granule contents to keep the phagosome pH near neutral, facilitating release of bactericidal enzymes. In summary, the mechanisms used by phagocytes for charge compensation during the respiratory burst would still be essential to phagocyte function, even if NADPH oxidase were not electrogenic.     

Measurement of the microstructural fracture toughness of cortical bone using indentation fracture

The purpose of this work is to investigate the use of indentation fracture as a method of measuring toughness at the microscale in cortical bone. Indentation fracture employs sharp indenters to initiate cracks, whose length can be used to calculate the toughness of the material. Only a cube corner indenter tip is found to initiate cracks at a suitable size scale for microstructural measurement. Cracks from 7 to 56 microm in length are produced using loads from 0.05 to 3N. Preliminary data predicts rising toughness with increasing crack length (rising R-curve behaviour) at the microscale. This technique provides a new insight into fracture in cortical bone since it allows the investigator to observe mechanisms and measure toughness at a size scale at which in vivo damage is known to exist.     

Accessory muscle activation during the superimposed burst technique

Quadriceps muscle activation is assessed using the superimposed burst technique. This technique involves percutaneous muscle stimulation superimposed during maximal isometric volitional knee extension. It is unknown whether accessory muscle activation during maximal knee extension influences estimates of quadriceps muscle activation. Our aim was to compare accessory muscle activation while performing the superimposed burst technique using investigator delivered verbal instruction to constrain the system (CS) and a participant preferred (PP) technique. Twenty five healthy, active individuals (13M/12F, age=23.8 ± 3.35, height=72.73 ± 14.51 cm, and weight=175.29 ± 9.59 kg) were recruited for this study. All participants performed superimposed burst testing with (CS) and without (PP) verbal instruction to encourage isolated quadriceps activation during maximal isometric knee extension. The main outcome variables measured were knee extension torque, quadriceps central activation ratio and mean EMG of vastus lateralis, biceps femoris, and lumbar paraspinal muscles. There were significant differences in knee extension torque (CS=2.87 ± 0.93 Nm/kg, PP=3.40 ± 1.12 Nm/kg, p<0.001), superimposed burst torque (CS=3.40 ±0.98 Nm/kg, PP=3.75 ± 1.11 Nm/kg, p=0.002) and quadriceps CAR (CS=84.1 ± 12.0%, PP=90.2 ± 9.9%, p<0.001) between the techniques. There was also a significant difference in lumbar paraspinal EMG (CS=6.40 ± 8.52%, PP=11.86 ± 14.89%, p=0.043) between the techniques however vastus lateralis EMG was not significantly different. Patient instruction via verbal instruction to constrain proximal structures may help patient minimize confounders to knee extension torque generation while maximizing quadriceps activation.     

A finite element inverse analysis to assess functional improvement during the fracture healing process

Assessment of the restoration of load-bearing function is the central goal in the study of fracture healing process. During the fracture healing, two critical aspects affect its analysis: (1) material properties of the callus components, and (2) the spatio-temporal architecture of the callus with respect to cartilage and new bone formation. In this study, an inverse problem methodology is used which takes into account both features and yields material property estimates that can analyze the healing changes. Six stabilized fractured mouse tibias are obtained at two time points during the most active phase of the healing process, respectively 10 days (n=3), and 14 days (n=3) after fracture. Under the same displacement conditions, the inverse procedure estimations of the callus material properties are generated and compared to other fracture healing metrics. The FEA estimated property is the only metric shown to be statistically significant (p=0.0194) in detecting the changes in the stiffness that occur during the healing time points. In addition, simulation studies regarding sensitivity to initial guess and noise are presented; as well as the influence of callus architecture on the FEA estimated material property metric. The finite element model inverse analysis developed can be used to determine the effects of genetics or therapeutic manipulations on fracture healing in rodents.     

Measurement of chlorine dioxide penetration in dairy process pipe biofilms during disinfection

Biofilms are considered a significant health risk in the food and dairy industries because they can harbor pathogens, and direct contact with them can lead to food contamination. Biofilm control is often performed using strong oxidizing agents like chlorine and peracetic acid. Although chlorine dioxide (ClO₂) is being used increasingly to control microbiological growth in a number of different industries, not much is known about disinfection in biofilms using chlorine dioxide. In this study, a microelectrode originally made for chlorine detection was modified to measure the profiles of chlorine dioxide in biofilm as a function of depth into the biofilm. In addition, discarded microelectrodes proved useful for in situ direct measurement of biofilm thicknesses. The chlorine dioxide microelectrode had a linear response when calibrated up to a ClO₂ concentration of 0.4 mM. ClO₂ profiles showed depletion of disinfectant at 100 μm in the biofilm depth, indicating that ClO₂ may not reach bacteria in a biofilm thicker than this using a 25 mg/l solution.     

Controlled sinus arrhythmia during burst stimulation of the vagus nerve

In experiments on anesthesized cats and rats the desynchronization of the heart rate and burst stimulation of the vagus brought about severe sinus arrhythmia. Analysis of the functional dependence between the P--S interval (atrial wave of the ECG--moment of vagus stimulation) and the P--P interval showed periodical alterations in pacemaker sensitivity to the effect of the vagus during each cardiac cycle. It is supposed that natural vagus arrhythmia is the result of discoordination between heart automacy and efferent vagus bursts of central origin.     

Endovascular treatment of a blunt thoracic aortic laceration due to thoracolumbar spine fracture

A 36-year-old woman sustained an aortic laceration at the level of the diaphragmatic hiatus owing to a displaced thoracolumbar spine fracture (TLS). We herein report the first case of aortic trauma secondary to a TLS fracture treated with a thoracic stent-graft.     

Biomechanical effects of posterior pedicle fixation techniques on the adjacent segment for the treatment of thoracolumbar burst fractures: a biomechanical analysis

Abstract

Posterior pedicle fixation technique is a common method for treating thoracolumbar burst fractures, but the effect of different fixation techniques on the postoperative spinal mechanical properties has not been clearly defined, especially on adjacent segments. A finite element model of T10-L2 with moderate T12 vertebra burst fracture was constructed to investigate biomechanical behavior of three posterior pedicle screw fixation techniques. Compared with traditional short-segment 4 pedicle screw fixation (TS-4) and intermediate long-segment 6 pedicle screw fixation (IL-6), mono-segment 4 pedicle screw fixation (MS-4) provides a safer surgical selection to prevent the secondary degeneration of adjacent segments in the long-term.     

Role of the actin cytoskeleton during respiratory burst in chemoattractant-stimulated neutrophils

The aim of this study was to clarify the role of the actin cytoskeleton during chemotactic peptide fMet-Leu-Phe (fMLF)-stimulated respiratory burst in human neutrophil granulocytes. Reactive oxygen species (ROS) was measured as luminol-amplified chemiluminescence (CL) and F-actin content as bodipy phallacidin fluorescence in neutrophils treated with latrunculin B or jasplakinolide, an inhibitor and activator of actin polymerization, respectively. Latrunculin B markedly decreased, whereas jasplakinolide increased, the F-actin content in neutrophils, unstimulated or stimulated with fMLF. Latrunculin B enhanced the fMLF-triggered ROS-production more than tenfold. Jasplakinolide initially inhibited the fMLF-induced CL-response, however, caused a potent second sustained phase (>400% of control). Both actin drugs triggered a substantial CL-response when added 5-25 min after fMLF. This was also valid for chemotactic doses of fMLF, where latrunculin B and jasplakinolide amplified the ROS-production 5-10 times. By using specific signal transduction inhibitors, we found that the NADPH oxidase activation triggered by destabilization of the actin cytoskeleton occurs downstream of phospholipase C and protein kinase C but is mediated by Rho GTPases and tyrosine phosphorylation. In conclusion, rearrangements of the actin cytoskeleton are a prerequisite in connecting ligand/receptor activation, generation of second messengers and assembly of the NADPH oxidase in neutrophil granulocytes.     

Peering into the birth canal during ion channel parturition

Recent studies have provided detailed structures of the N-terminal T1 domain of Kv channel alpha subunits that mediates contranslational subunit assembly. In this issue of Neuron, Kosolapov et al. probe T1 domain structure within the ribosomal tunnel. They find that the T1 domain forms secondary structure within the tunnel, in preparation for its immediate role in governing channel assembly upon exit.     

A burst-feedback model of fast-phase burst generation during nystagmus

 Vestibular and optokinetic nystagmus are characterized by alternating slow-phase eye rotations that stabilize the retinal image, and fast-phase eye rotations that reset eye position. Nystagmus is coordinated in the brainstem by burst neurons that fire an intense, temporally circumscribed burst that terminates the slow phase and drives the fast phase. This paper demonstrates that such a burst can be generated during nystagmus using a simple neural network model containing only known brainstem neurons and their interconnections. These include the feedback connections of the burst neuron (burst feedback). The burst neuron excites itself directly, and disinhibits itself by inhibiting the pause neuron (positive feedback). It also inhibits itself by inhibiting the vestibular neuron (negative feedback). The burst neuron begins to fire after its inhibitory bias is overcome by excitation from the vestibular neuron, and burst neuron positive feedback then produces an intense burst with an abrupt onset. The burst causes the vestibular and pause neurons to pause. The benefit of the pause neuron loop is that it contributes to burst neuron positive feedback when it is needed at burst onset, but that contribution is eliminated when the pause neuron pauses and opens the loop. The burst can then terminate, with an offset duration proportional to burst amplitude, under the control of burst neuron self-excitation and inhibitory bias. Model neuron behavior is comparable to that of real brainstem neurons. Synchronized bursts can be produced over the population of burst neurons in a distributed version of the network. Variability in connection weights in the distributed network results in variability in prelude activity among burst neurons that is similar to the spread in lead observed for real burst neurons during nystagmus. Received: 11 April 1996 / Accepted in revised form: 6 August 1996     

Microtubules during formation of the micropylar canal in Drosophila melanogaster

The micropylar apparatus in Drosophila melanogaster contains a 0,8μm wide canal through which sperm entry occurs. During oogenesis the canal is formed by deposition of extracellular material (chorion) around long cellular processes filled with microtubules.