Rheotaxis and migration of cells in a flow field have been investigated intensively owing to their importance in biology, physiology and engineering. In this study, first, we report our experiments showing that the microalgae Chlamydomonas can orient against the channel flow and migrate to the channel centre. Second, by performing boundary element simulations, we demonstrate that the mechanism of the observed rheotaxis and migration has a physical origin. Last, using a simple analytical model, we reveal the novel physical mechanisms of rheotaxis and migration, specifically the interplay between cyclic body deformation and cyclic swimming velocity in the channel flow. The discovered mechanism can be as important as phototaxis and gravitaxis, and likely plays a role in the movement of other natural microswimmers and artificial microrobots with non-reciprocal body deformation.
In-situ synthesis of HAp/TiO2 coating on titanium was performed via anaphoretic deposition of HAp and simultaneous anodization of Ti to produce highly adherent and strengthened composite coating. The prepared coatings were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray difraction and electron dispersive spectroscopy. HAp on anodized titanium was prepared at constant voltage of 60 V and deposition time of 45 s, which provided uniform and adherent HAp/TiO2 composite coating on Ti. Since smaller size of HAp crystals within highly porous coating structures is of improved binding ability to various biomolecules, our coating is expected to be of excellent coverage and compactness. The obtained coating can be good candidate for bone implants due to reduced brittleness and improved adhesion.
The aim of this work was to investigate
corrosion resistivity,
bioactivity, and antibacterial activity of novel nano-amorphous calcium
phosphate (ACP) potentially multifunctional composite coatings with
and without chitosan oligosaccharide lactate (ChOL), ACP + ChOL/TiO2 and ACP/TiO2 ACP + ChOL/TiO2, respectively,
on the titanium substrate. The coatings were obtained by new single-step
in situ anodization of the substrate to generate TiO2 and
the anaphoretic electrodeposition process of ACP and ChOL. The obtained
coatings were around 300 ± 15 μm thick and consisted of
two phases, namely, TiO2 and hybrid composite phases. Both
ACP/TiO2 and ACP + ChOL/TiO2 have improved corrosion
stability, whereas the ACP + ChOL/TiO2 coating showed better
corrosion stability. It was shown that at the very start of the deposition
process, the formation of the ChOL/TiO2 layer takes place
predominantly, which is followed by the inclusion of ChOL into ACP
with simultaneous growth of TiO2. This deposition mechanism
resulted in the formation of strongly bonded uniform stable coating
with high corrosion resistance. In vitro bioactivity was investigated
by immersion of the samples in simulated body fluid (SBF). There is
in-bone-like apatite formation on both ACP/TiO2 and ACP
+ ChOL/TiO2 surfaces upon immersion into SBF, which was
proven by X-ray diffraction and Fourier transform infrared spectroscopy.
While ACP/TiO2 shows no antibacterial activity, ACP + ChOL/TiO2 samples exhibited three- to fourfold decreases in the number
of Staphylococcus aureus and Pseudomonas aeruginosa, respectively, after 420 min.
The probable mechanism is binding ChOL with the bacterial cell wall,
inhibiting its growth, altering the permeability of the cell membrane,
and leading to bacterial death.
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