TAMI-60. MODULATION OF CELL BIOMECHANICS THROUGH GUIDANCE RECEPTOR PLEXIN-B2 FACILITATES GLIOBLASTOMA INFILTRATION

Infiltrative growth is a major cause of the high lethality of malignant brain tumors such as glioblastoma (GBM). The study of the contribution of biomechanical processes to GBM invasion is an emerging field. We show here that GBM cells upregulate the guidance receptor Plexin-B2 to gain invasiveness by modulating their biomechanical properties. Deletion of Plexin-B2 in GBM stem cells limited tumor spread and shifted invasion paths from axon fiber tracts to perivascular routes. On a cellular level, Plexin-B2 adjusts cell adhesiveness, migratory responses to different matrix stiffness, and actomyosin dynamics, thus empowering GBM cells to leave stiff tumor bulk and infiltrate softer brain parenchyma. Correspondingly, gene signatures affected by Plexin-B2 were associated with locomotor regulation, matrix interactions, and cellular biomechanics. On a molecular level, the intracellular Ras-GAP domain contributed to Plexin-B2 function, while the signaling relationship with downstream effectors Rap1/2 appeared variable between GBM stem cell lines, reflecting intertumoral heterogeneity. Our studies have established Plexin-B2 as a modulator of cell biomechanics that is usurped by GBM cells to gain invasiveness. Ongoing investigations focus on the regulation of the biomechanical properties of cell membrane and cell actomyosin cortex through plexins that provide GBM cells with the mechanical dynamics to penetrate to restricted space.

Numerical analysis of crimping behaviour of triaxial braided structures

The mechanical properties of tubular braided structures influence their inherent performance during application as biomedical materials. In their use as stents, braided structures are forced to conform to the topology of the host tissues. Triaxial braided structures have had limited use in tissue repair and organ support even though they have the potential of offering equal if not better performance compared to bi-axial braided structures. A study of the mechanical dynamics of tri-axial braids would be crucial in the potential design of customised structures for advanced tissue repair and organ support. This study therefore uses Finite Element Methods (FEM) to design and develop triaxial braided structures and investigate their crimping behaviour using parametric modeling and numerical analysis in their potential application as biomedical materials. The results in this study portrayed that the presence of axial yarns in tubular braided structure offers improved performance in terms of stability of the structure.

On the mechanism of three-body adhesive wear in turning

The paper reveals a hypothesis regarding the adhesive mechanism in metal cutting and its mechanical dynamics. One steel grade, 34CrNiMo 6, 285 HB, and one set of coatings on the cutting tool are reviewed. The adhesive mechanism is a transient vibration, including a feedback system limited by the plastic deformation in the chip. The vibration shows as a cluster of waves with stochastic duration in time. It starts up again after a stochastic lapse of silence. The cycle frequency is around 12.5 kHz and the internal excitation is twice that frequency, as the cutting speed and feed are 200 m/min and 0.2 mm, respectively. The adhesive frequency and amplitude are influenced by the cutting speed and the current wear status. The adhesion is monitored by the sound waves emanating from vibrations in the chip, the part still in the workpiece.

Nanomechanics of negatively supercoiled diaminopurine-substituted DNA

ABSTRACTSingle molecule experiments have demonstrated a progressive transition from a B- to an L-form helix as DNA is gently stretched and progressively unwound. Since the particular sequence of a DNA segment influences both base stacking and hydrogen bonding, the conformational dynamics of B-to-L transitions should be tunable. To test this idea, DNA with diaminopurine replacing adenine was synthesized to produce linear fragments with triply hydrogen-bonded A:T base pairs. Triple hydrogen bonding stiffened the DNA by 30% flexurally. In addition, DAP-substituted DNA formed plectonemes with larger gyres for both B- and L-form helices. Both unmodified and DAP-substituted DNA transitioned from a B- to an L-helix under physiological conditions of mild tension and unwinding. This transition avoids writhing by DNA stretched and unwound by enzymatic activity. The intramolecular nature and ease of this transition likely prevent cumbersome topological rearrangements in genomic DNA that would require topoisomerase activity to resolve. L-DNA displayed about tenfold lower persistence length indicating it is much more contractile and prone to sharp bends and kinks. However, left-handed DAP DNA was twice as stiff as unmodified L-DNA. Thus, significantly doubly and triply hydrogen bonded segments have very distinct mechanical dynamics at physiological levels of negative supercoiling and tension.

Sensorless Self-Excited Vibrational Viscometer with Two Hopf Bifurcations Based on a Piezoelectric Device

In this study, we propose a high-sensitivity sensorless viscometer based on a piezoelectric device. Viscosity is an essential parameter frequently used in many fields. The vibration type viscometer based on self-excited oscillation generally requires displacement sensor although they can measure high viscosity without deterioration of sensitivity. The proposed viscometer utilizes the sensorless self-excited oscillation without any detection of the displacement of the cantilever, which uses the interaction between the mechanical dynamics of the cantilever and the electrical dynamics of the piezoelectric device attached to the cantilever. Since the proposed viscometer has fourth-order dynamics and two coupled oscillator systems, the systems can produce different self-excited oscillations through different Hopf bifurcations. We theoretically showed that the response frequency jumps at the two Hopf bifurcation points and this distance between them depends on the viscosity. Using this distance makes measurement highly sensitive and easier because the jump in the response frequency can be easily detected. We experimentally demonstrate the efficiency of the proposed sensorless viscometer by a macro-scale measurement system. The results show the sensitivity of the proposed method is higher than that of the previous method based on self-excited oscillation with a displacement sensor.

Actuation and dynamic mechanical characteristics of a core free flat dielectric electro-active polymer soft actuator

Various complex shapes of dielectric electro-active polymer (DEAP) actuator have been promoted for several types of applications. In this study, the actuation and mechanical dynamics characteristics of a new core free flat DEAP soft actuator were investigated. This actuator was developed by Danfoss PolyPower. DC voltage of up to 2000 V was supplied for identifying the actuation characteristics of the actuator and compare with the existing formula. The operational frequency of the actuator was determined by dynamic testing. Then, the soft actuator has been modelled as a uniform bar rigidly fixed at one end and attached to mass at another end. Results from the theoretical model were compared with the experimental results. It was found that the deformation of the current actuator was quadratic proportional to the voltage supplied. It was found that experimental results and theory were not in good agreement for low and high voltage with average percentage error are 104% and 20.7%, respectively. The resonance frequency of the actuator was near 14 Hz. Mass of load added, inhomogeneity and initial tension significantly affected the resonance frequency of the soft actuator. The experimental results were consistent with the theoretical model at zero load. However, due to inhomogeneity, the frequency response function’s plot underlines a poor prediction where the theoretical calculation was far from experimental results as values of load increasing with the average percentage error 15.7%. Hence, it shows the proposed analytical procedure not suitable to provide accurate natural frequency for the DEAP soft actuator.