Optimizing Mechanical Stretching Protocols for Hypertrophic and Anti-apoptotic Responses in H9c2 Cardiomyocytes

Background: Cardiomyocytes are sensitive to mechanical loading, possessing the ability to respond to mechanical stimuli by reprogramming their gene expression. In this study, signaling as well as expression responses of myogenic, anabolic, inflammatory, atrophy and pro-apoptotic genes to different mechanical stretching protocols were examined in differentiated cardiomyocytes.Methods: H9C2 cardiomyoblasts were cultured on elastic membranes up to their 5th day of differentiation (myotubes) and then subjected to three different stretching protocols by altering their strain, frequency and duration characteristics, using an in vitro cell tension system. cells were harvested and lysed 24 hours after the completion of each stretching protocol and Real Time-PCR was used to monitor changes in mRNA expression of myogenic regulatory factors (MyoD, Myogenin, MRF4), the IGF-1 isoforms (IGF-1Ea, IGF-1Eb), as well as atrophy (Atrogin-1), pro-apoptotic (FoxO, Fuca), and inflammatory (IL-6) factors in response to the different mechanical loading conditions. The activation of Akt and Erk 1/2 signaling proteins following the various stretching protocols was also evaluated by Western blot analysis.Results: We documented that the low strain (2.7% elongation), low frequency (0.25 Hz) and intermediate duration (12 hrs) stretching protocol was overall the most effective in inducing beneficial responses in differentiated cardiomyoblasts as it increased the expression of IGF-1 isoforms and phosphorylation of Akt and Erk1/2 (p<0.05), while it provoked the downregulation of all the other factors examined (p<0.05-0.001). Conclusion: These findings demonstrated that a low strain, low frequency of intermediate duration stretching protocol is the most effective in inducing a hypertrophic and anti-apoptotic response in H9C2 cardiomyotubes, in vitro.

Experimental and Simulation Study on the Response Characteristics of Engine Blades Under Thermo-Acoustic-Vibration Load

Thermal, acoustic, and vibration loads are important to affect the strength and durability of many aerospace products, especially the compressor blades, solar wings, antennas, etc. In extreme cases, a strong acoustic load combined with vibration and thermal loads may cause blade fatigue damage or even failure. In the study, an experimental device is designed to simulate the thermo-acoustic-vibration comprehensive load. Based on the tested strain data, the response characteristics under the thermo-acoustic-vibration load are investigated experimentally. Besides, a finite element method (FEM) model considering the acoustic-vibration coupling and material parameters dependent on temperature is presented applying software ansys-workbench to calculate stress and strain frequency responses of the blades, and the results agree well with the experimental results. The work will help understand failure mechanism of aerospace products under a comprehensive load of thermo-acoustic-vibration.

Structural Damage Identification Based on Strain Frequency Response Functions

Damage identification using the sensitivity of the dynamic characteristics of the structure of concern has been studied considerably. Among the dynamic characteristics used to locate and quantify structural damages, the frequency response function (FRF) data has the advantage of avoiding modal analysis errors. Additionally, previous studies demonstrated that strains are more sensitive to localized damages compared to displacements. So, in this study, the strain frequency response function (SFRF) data is utilized to identify structural damages using a sensitivity-based model updating approach. A pseudo-linear sensitivity equation which removes the adverse effects of incomplete measurement data is proposed. The approximation used for the sensitivity equation utilizes measured natural frequencies to reconstruct the unmeasured SFRFs. Moreover, new approaches are proposed for selecting the excitation and measurement locations for effective model updating. The efficiency of the proposed method is validated numerically through 2D truss and frame examples using incomplete and noise polluted SFRF data. Results indicate that the method can be used to accurately locate and quantify the severity of damage.

Viscoelastic Large Strain Model of Bitumen Used for Corrosion Protection in Subsea Cables and Umbilicals

Bitumen is used as anticorrosion material to protect armor wires in subsea cables and umbilicals. Establishing bitumen’s viscoelastic properties is essential for developing analytical models of how bitumen influences the cable’s mechanical properties, in particular the bending stiffness. A new laboratory instrument has been developed for establishing the viscoelastic properties of bitumen subject to equally large strains as in real-life cables. This paper presents the basic principle of the new instrument and derives how to calculate bitumen’s viscoelastic properties from the measurements logged by the instrument. The paper also models bitumen’s viscoelastic properties as function of strain amplitude, strain frequency, and bitumen temperature, using multi-variable data analysis. These models show that the viscoelastic properties are highly temperature dependent. Bitumen’s shear stress / shear strain amplitude ratio grows with increasing rate as the temperature decreases.

Measuring of Low Frequency Internal Friction in Solids

The principles and apparatus of measuring low frequency internal friction are described in this paper. The low frequency internal friction apparatus have been evidently improved in automation and functions since the Ke,s pendulum was invented in 1947. The degree of automation of the internal friction apparatus is elevated and the functions of the apparatus are increased/ strengthened. The resolution of internal friction is increased. The accuracy of strain and frequency is also enhanced. The scope of measuring parameters such as temperature, strain, frequency and so on is enlarged.