Experimental measurement of dynamic fluid shear stress on the aortic surface of the aortic valve leaflet

Aortic valve (AV) calcification is a highly prevalent disease with serious impact on mortality and morbidity. Although exact causes and mechanisms of AV calcification are unclear, previous studies suggest that mechanical forces play a role. Since calcium deposits occur almost exclusively on the aortic surfaces of AV leaflets, it has been hypothesized that adverse patterns of fluid shear stress on the aortic surface of AV leaflets promote calcification. The current study characterizes AV leaflet aortic surface fluid shear stresses using Laser Doppler velocimetry and an in vitro pulsatile flow loop. The valve model used was a native porcine valve mounted on a suturing ring and preserved using 0.15% glutaraldehyde solution. This valve model was inserted in a mounting chamber with sinus geometries, which is made of clear acrylic to provide optical access for measurements. To understand the effects of hemodynamics on fluid shear stress, shear stress was measured across a range of conditions: varying stroke volumes at the same heart rate and varying heart rates at the same stroke volume. Systolic shear stress magnitude was found to be much higher than diastolic shear stress magnitude due to the stronger flow in the sinuses during systole, reaching up to 20 dyn/cm² at mid-systole. Upon increasing stroke volume, fluid shear stresses increased due to stronger sinus fluid motion. Upon increasing heart rate, fluid shear stresses decreased due to reduced systolic duration that restricted the formation of strong sinus flow. Significant changes in the shear stress waveform were observed at 90 beats/min, most likely due to altered leaflet dynamics at this higher heart rate. Overall, this study represents the most well-resolved shear stress measurements to date across a range of conditions on the aortic side of the AV. The data presented can be used for further investigation to understand AV biological response to shear stresses.     

Propagation of Turing patterns in a plankton model

The paper is devoted to a reaction-diffusion system of equations describing phytoplankton and zooplankton distributions. Linear stability analysis of the model is carried out. Turing and Hopf stability boundaries are found. Emergence of two-dimensional spatial structures is illustrated by numerical simulations. Travelling waves between various stationary solutions are investigated. Transitions between homogeneous in space stationary solutions and Turing structures are studied.     

In-vivo transducer to measure dynamic mitral annular forces

Limited knowledge exists regarding the forces which act on devices implanted to the heart's mitral valve. Developing a transducer to measure the peak force magnitudes, time rates of change, and relationship with left ventricular pressure will aid in device development. A novel force transducer was developed and implanted in the mitral valve annulus of an ovine subject. In the post-cardioplegic heart, septal-lateral and transverse forces were continuously measured for cardiac cycles reaching a peak left ventricular pressure of 90 mmHg. Each force was seen to increase from ventricular diastole and found to peak at mid-systole. The mean change in septal-lateral and transverse forces throughout the cardiac cycle was 4.4±0.2 N and 1.9±0.1 N respectively. During isovolumetric contraction, the septal-lateral and transverse forces were found to increase at peak rate of 143±8 N/s and 34±9 N/s, respectively. Combined, this study provides the first quantitative assessment of septal-lateral and transverse forces within the contractile mitral annulus. The developed transducer was successful in measuring these forces whose methods may be extended to future studies. Upon additional investigation, these data may contribute to the safer development and evaluation of devices aimed to repair or replace mitral valve function.     

Knee moments during run-to-cut maneuvers are associated with lateral trunk positioning

Non-contact anterior cruciate ligament (ACL) injuries account for approximately 70% of ACL ruptures and often occur during a sudden change in direction or pivot. Decreased neuromuscular control of the trunk in a controlled perturbation task has previously been associated with ACL injury incidence, while knee abduction moments and tibial internal rotation moments have been associated with ACL strain and ACL injury incidence. In this study, the association between movement of the trunk during a run-to-cut maneuver and loading of the knee during the same activity was investigated. External knee moments and trunk angles were quantified during a run-to-cut maneuver for 29 individuals. The trunk angles examined were outside tilt (frontal plane angle of the torso from vertical), angle between the ground reaction force (GRF) and the torso in the plane containing the GRF and shoulders (torso-GRF_shoulders); and angle between GRF and torso in the plane containing the GRF and pelvis (torso-GRF_pelvis). Significant positive associations were found between torso angles and peak knee abduction moments (outside tilt, p=0.002; and torso-GRF_shoulders, p=0.036) while a significant negative association was found between peak tibial internal rotation moment and outside tilt (p=0.021). Because the peaks of these moments occur at different times and minimal axial rotation moment is observed at peak knee abduction moment (-0.29±0.46%BW*ht), the positive association between peak knee abduction moment and torso lean suggests that increasing torso lean may increase ACL load and risk of injury.     

Measurement of strut chordal forces of the tricuspid valve using miniature C ring transducers

Tricuspid valve (TV) leaflets, papillary muscles (PM), and tendinous chords must work together to ensure proper coaptation. Alterations in valvular mechanics, including chordal forces, may lead to improper coaptation resulting in tricuspid regurgitation. Little is known about TV mechanics as right-sided heart diseases have been overlooked. We sought to fill this gap by understanding the role of TV strut chords with the objective to understand how strut chordal force varies depending on papillary muscle (PM) origin and leaflet attachment in the normal state. Additionally we investigated how these forces are altered with abnormal geometry. Porcine TVs (n=18) were studied in a right-heart simulator capable of reproducing physiological and pathological conditions. Miniature force transducers were placed on strut chords to measure forces throughout the cardiac cycle. In the normal state, chordal force depended upon PM attachment in which chords branching from the septal PM (SPM) carried significantly less force compared to those branching from the anterior PM (APM) (p≤0.05). Annular dilatation resulted in significant increase in chordal force (p≤0.05) on all strut chords. Severe PM displacement led to increased chordal force in chords attaching the APM to the posterior leaflet as well as chords attaching the PPM to the septal leaflet. Elevated chordal force due to isolated annular dilatation was further increased only with addition of apical displacement of the APM. These results provide initial knowledge of TV chordal force mechanics and may be applied to future studies on TV repair techniques.     

Nanocapsulated curcumin: oral chemopreventive formulation against diethylnitrosamine induced hepatocellular carcinoma in rat

Toxic outcome of chemical therapeutics as well as multidrug resistance are two serious phenomena for their inacceptance in cancer chemotherapy. Antioxidants like curcumin (Cur) have gained immense importance for their excellent anticarcinogenic activities and minimum toxic manifestations in biological system. However, Cur is lipophilic and thus following oral administration hardly appears in blood indicating its potential therapeutic challenge in cancer therapy. Nanocapsulated Cur has been used as a drug delivery vector to focus the effectiveness of these vesicles against hepatocellular carcinoma. The theme of work was to evaluate effectiveness in oral route of polylactide co-glycolide (PLGA) Nanocapsulated curcumin (Nano Cur) against diethylnitrosamine (DEN) induced hepatocellular carcinoma (HCC) in rat. Nano Cur of average diameter 14nm and encapsulation efficiency of 78% were prepared. Fourier Transform Infra Red (FTIR) analysis revealed that there is no chemical interaction between drug and the polymer. Three i.p. injections of the chemical hepatocarcinogen DEN at 15days interval causes hepatotoxicity, the generation of reactive oxygen species (ROS), lipid peroxidation, decrease in plasma membrane microviscosity and depletion of antioxidant enzyme levels in liver. Nano Cur (weekly oral treatment for 16weeks at 20mg/kg b.wt) in DEN induced HCC rats exerted significant protection against HCC and restored redox homeostasis in liver cells. Nanocapsulated Cur caused cancer cell apoptosis as visualized by ApoBrdU analysis. Histopathological analysis confirmed the pathological improvement in the liver. Nano Cur was found to be a potential formulation in oral route in combating the oxidative damage of hepatic cells and eliminating DEN induced hepatocellular cancer cells in rat whereas identical amount of free Cur treatment was found almost ineffective.     

Genome Sequence of the Alkaliphilic Bacterium Nitritalea halalkaliphila Type Strain LW7, Isolated from Lonar Lake,India

An alkaliphilic bacterium, Nitritalea halalkaliphila LW7, which belongs to the family Cyclobacteriacae in the phylum Bacteroidetes, was isolated from Lonar Lake in Maharastra, India. Here we announce the draft genome sequence of the type strain LW7, which contains 3,633,701 bp with a G+C content of 48.58%.     

Expandase-like activity mediated cell-free conversion of ampicillin to cephalexin by Streptomyces sp. DRS I

Cell-free extracts of Streptomyces sp. DRS I converted ampicillin to cephalexin, presumably due to the activity of the enzyme, expandase. The extract was fractionated and characterized by colorimetric and chromatographic measurements coupled with disc-agar diffusion bioassay against an ampicillin-resistant, cephalexin-sensitive E. coli strain. Though expandase could not be identified, the presence of a hitherto unreported expandase in Streptomyces sp. DRS I is suggested.