Search

We conducted a systematic numerical investigation of spherical, prolate and oblate particles in an inertial shear flow between two parallel walls, using smoothed particle hydrodynamics (SPH). It was previously shown that above a critical Reynolds number, spherical particles experience a supercritical pitchfork bifurcation of the equilibrium position in shear flow between two parallel walls, namely that the central equilibrium position becomes unstable, leading to the emergence of two new off-centre stable positions (Fox et al. , J. Fluid Mech. , vol. 915, 2021). This phenomenon was unexpected given the symmetry of the system. In addition to confirming this finding, we found, surprisingly, that ellipsoidal particles can also return to the centre position from the off-centre positions when the particle Reynolds number is further increased, while spherical particles become unstable under this increased Reynolds number. By utilizing both SPH and the finite element method for flow visualization, we explained the underlining mechanism of this reverse of bifurcation by altered streamwise vorticity and symmetry breaking of pressure. Furthermore, we expanded our investigation to include asymmetric particles, a novel aspect that had not been previously modelled, and we observed similar trends in particle dynamics for both symmetric and asymmetric ellipsoidal particles. While further validation through laboratory experiments is necessary, our research paves the road for development of new focusing and separation methods for shaped particles. [ABSTRACT FROM AUTHOR]

Nanoindentation probing on nacre obtained from Haliotis rufescens shells has demonstrated that nacre displays a combined viscoplastic-viscoelastic time dependent response. Additionally, it is found that the moisture/water content of nacre contributes to its time dependent behavior and overall mechanical properties. Detailed finite element simulations allow for the determination of constitutive parameters used to calibrate specific time dependent material models which are, in turn, compared to those found via independent measurement as reported in the literature. The results lead to a new paradigm for nacre’s attractive structural composite behavior and thereby to new potential pathways for biomimetics.

Various signals in tissue microenvironments are often unevenly distributed around cells. Cellular responses to asymmetric cell‐matrix adhesion in a 3D space remain generally unclear and are to be studied at the single‐cell resolution. Here, the authors developed a droplet‐based microfluidic approach to manufacture a pure population of single cells in a microscale layer of compartmentalized 3D hydrogel matrices with a tunable spatial presentation of ligands at the subcellular level. Cells elongate with an asymmetric presentation of the integrin adhesion ligand Arg‐Gly‐Asp (RGD), while cells expand isotropically with a symmetric presentation of RGD. Membrane tension is higher on the side of single cells interacting with RGD than on the side without RGD. Finite element analysis shows that a non‐uniform isotropic cell volume expansion model is sufficient to recapitulate the experimental results. At a longer timescale, asymmetric ligand presentation commits mesenchymal stem cells to the osteogenic lineage. Cdc42 is an essential mediator of cell polarization and lineage specification in response to asymmetric cell‐matrix adhesion. This study highlights the utility of precisely controlling 3D ligand presentation around single cells to direct cell polarity for regenerative engineering and medicine. [ABSTRACT FROM AUTHOR]

We verify both theoretically and by simulation that an AC electric field, with a frequency much higher than the dissociation rate, can significantly accelerate the dissociation rate of biological molecules under isothermal conditions. The cumulative effect of the AC field is shown to break a key bottleneck by reducing the entropy (and increasing the free energy of the local minimum) via the alignment of the molecular dipole with the field. For frequencies below a resonant frequency which corresponds to the inverse Debye dipole relaxation time, the dissociation rate can be accelerated by a factor that scales as ω ( ϵ ′ (ω) − 1) E 0 2 , where ω is the field frequency, E0 is the field amplitude, and ϵ′(ω) is the frequency-dependent real permittivity of the molecule. At large amplitudes, we find that the accelerated melting rate becomes universal, independent of duplex size and sequence, which is in drastic contrast to Ohmic thermal melting. We confirm our theory with isothermal all-atomic molecular dynamics simulation of short DNA duplexes with known melting rates, demonstrating several orders in enhancement with realistic fields. [ABSTRACT FROM AUTHOR]