To improve the magnetorheological (MR) properties and dispersion stability of the carbonyl iron (CI) particles, bidisperse magnetorheological (BMR) fluids consisting of magnetic micron-sized CI and nanoparticles dual-coated with gelatin and multi-walled carbon nanotubes (MWCNTs) were synthesized for the first time. Gelatin was used as a grafting agent to improve the stability of bidisperse magnetic particles and restrict the oxidation of nanoparticles (Fe 3 O 4 ). And a dense network composed of MWCNTs on the surface of gelatin-coated bidisperse particles was fabricated based on the self-assembly of MWCNTs to produce considerably rough surfaces. The influence of functional dual-coated layer on rheological performance such as shear stress and yield stress behavior was investigated by a rotational rheometer upon various magnetic field applications. Additionally, the dispersion stability was measured through sedimentation tests. The results showed that CI-Fe 3 O 4 -Gelatin-MWCNTs (CI-Fe 3 O 4 -G-NT) magnetic microspheres possessed enhanced MR properties compared with those from CI-Fe 3 O 4 -Gelatin (CI-Fe 3 O 4 -G) microspheres, while the dispersion stability of CI-Fe 3 O 4 -G-NT microspheres was still maintained.

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Tubular cell apoptosis has been implicated in the development of ischemic renal failure. In in vitro models, ATP depletion-induced apoptosis of tubular cells is mediated by the intrinsic pathway involving Bax translocation, cytochrome c release, and caspase activation. While the apoptotic cascade has been delineated, much less is known about its regulation. The current study has examined the regulation of ATP depletion-induced tubular cell apoptosis by acidic pH, a common feature of tissue ischemia. Cultured renal tubular cells were subjected to 3 h of ATP depletion with azide and then recovered in full culture medium. The treatment led to apoptosis in ∼40% of cells. Apoptosis was significantly reduced, if the pH of ATP depletion buffer was lowered from 7–7.4 to 6–6.5. This was accompanied by the inhibition of caspase activation. However, acidic pH did not prevent Bax translocation and oligomerization in mitochondria. Cytochrome c release from mitochondria was not blocked either, suggesting that acidic pH inhibited apoptosis at the postmitochondrial level. To determine the postmitochondrial events that were blocked by acidic pH, we conducted in vitro reconstitution experiments. Exogenous cytochrome c, when added into isolated cell cytosol, induced caspase activation. Such activation was abrogated, when pH during the reconstitution was lowered to 6 or 6.5. Nevertheless, acidic pH did not prevent the recruitment and association of caspase-9 by Apaf-1, as shown by coimmunoprecipitation. Together, this study demonstrated the inhibition of tubular cell apoptosis following ATP depletion by acidic pH. A critical step blocked by acidic pH seems to be caspase-9 activation in apoptosome.

In this study, a novel flexible conductive sodium alginate/chitosan (SA/CS) foam with double-network structure based on dual-coated magnetic particles (MPs) was prepared by a biological crosslinking process of natural biopolymers. The structural characterization, response deformation and magnetic-field-dependent electric performance for different foams were investigated, and they were significantly dependent on the mass ratio of SA/CS, the contents of glycerol and MPs. By increasing SA and CS, the electrostatic interactions of double-network enhanced, leading to an increase in its binding force with the MPs, so the magnetic-responsive performance was strongly improved. Meanwhile, the resistance displayed a remarkable variation under the magnetic fields. For instance, the resistance of the sample with a mass ratio of 3:3 decreased with the magnetic flux densities (0.10-0.40 T) and it ranged from 14.8-6.83 kΩ, which reduced by about 53.9%. Moreover, the periodic measurements were applied so as to verify its recoverability and repeatability. Furthermore, a possible mechanism was provided to explain the magnetic-responsive behavior of the samples. Because of the superior magnetic controllability and preeminent mechanical performance, the conductive porous foam is promising in the fields of artificial electric skins, soft sensors and actuators.

Bionic artificial muscle made from chitosan gel is an emerging type of the ionic electro active polymer with advantages of large deformation, low cost and environmental protection etc, which leads to a research focus and wide application in the fields of bionic engineering and intelligence material recently. In this paper, effects and improvement mechanisms of the direct casting and genipin cross-linking processes on response speed properties of the chitosan gel artificial muscle (CGAM) were mainly studied. Based on in-depth analysis of the CGAM response mechanism, a platform was built for testing the response performance of the CGAM, then its equivalent circuit and mathematical models were also established. Furthermore, control experiments were carried out to test and analyze several performances of the CGAM on response speed, electrical conductivity, mechanical properties and microstructure with different control variables. The experimental results illustrated that the CGAM assembled by direct casting enabled its electric actuating membrane and non-metallic electrode membrane tightly attached together with low contact resistance, which dramatically promoted the electrical conductivity of the CGAM resulting in nearly doubled response speed. Besides, different concentrations of genipin were adopted to cross-link the CGAM actuating membranes, and then it was found that the response speed of the uncross-linked CGAM was fast in the initial stage, but as time increased, it declined rapidly with poor steadiness. While there was no obvious decrease over time on the response speed of the CGAM cross-linked with low genipin concentration. Namely, its stability was getting better and better. In addition, the response speed of the CGAM cross-linked with low concentration of genipin was roughly the same as uncross-linked CGAM, which was quicker than that of high concentration. In this work, its internal mechanisms, feasible assembly technique and green modification method were provided to further explore the practical applications significantly.

The magnetorheology and dispersion stability of bidisperse magnetic particles (BMP)-based magnetorheological (MR) fluids were improved by applying a novel functional coating composed of gelatin and graphite oxide (GO) to the surfaces of the micron-sized carbonyl iron (CI) and nanoparticles Fe3O4. Gelatin acted as a grafting agent to reduce the aggregation and sedimentation of CI particles and prevent nanoparticles Fe3O4 from oxidation. In addition, a dense GO network on the surface of gelatin-coated BMP was synthesized by self-assembly to possess a better MR performance and redispersibility. The rheological properties of MR fluids containing dual-coated BMP were measured by a rotational rheometer under the presence of magnetic field and their dispersion stability was examined through sedimentation tests. The results showed that CI@Fe3O4@Gelatin@GO (CI@Fe3O4@G@GO) particles possessed enhanced MR properties and dispersion stability. In addition, the nanoparticle-enhancing effects on the dispersion stability of BMP-based MR fluids were investigated using Monte Carlo simulations.

This work reports a novel conductive composite matrix based on magnetically sensitive flexible sponges containing a porous polymeric matrix and bidisperse magnetic microspheres dual-coated with gelatin (GE) and multiwalled carbon nanotubes (MWCNTs). In comparison to the conventional continuous phase, the porous polymeric matrix herein is mainly constructed by sodium alginate (SA) and GE, which displays high flexibility, excellent deformability, and strong stability. The structural characterization, magneto-induced deformation, and magnetic− electric properties of the conductive composite matrix were investigated and they were significantly influenced by the contents of GE and magnetic microspheres. On increasing the GE contents, the electrostatic interactions increased owing to the increased entanglement points and cross-linking degree between polymer molecules, thus reducing the resistance performance of the samples. Meanwhile, the resistances of samples 12; 10 wt % and 12; 40 wt % are 6.83 and 3.94 kΩ under a 400 mT magnetic field, respectively, exhibiting a decreasing trend with the increase of magnetic microspheres. Additionally, the effects of MWCNTs on the electric conductivity were also illustrated. Furthermore, a potential mechanism was proposed to investigate the magnetic-fielddependent electrical properties of the products. Specifically, the iterative loading−unloading of the magnetic field was applied to verify the repeatability and recoverability of the conductive composite matrix. It was found that the electrical resistance and deformation could be synchronously and reversibly changed by the applied magnetic field, which provides a new idea for a new generation of intelligent sensors toward an artificial electric skin and micro-electromechanical system.

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