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Additional file 4. The primer sequences used in this study.

Additional file 6. Figs. S1-S7.

Additional file 5. Information of the antibody used in IHC.

Additional file 3. The siRNA sequences used in this study.

Additional file 2. Five kinds of immune infiltration algorithm principles.

Adding flow channel between main and annular chambers in same strut of roll-coupled Hydro-pneumatic Inter-connected Suspension (HIS) can effectively avoid the negative hydraulic pressure caused by the high damping factor of connected pipes under high velocity condition. This flow channel is usually closed in previous research in HIS area. In this study, the effect of orifice between main and annular chambers in same strut to the dynamic properties of HIS under the different road excitations is investigated by the established AMEsim half-car simulation model. The bounce and roll displacement/acceleration of the sprung mass are used to evaluate the dynamic properties of HIS. The results illustrate that (1) the added orifice can reduce the roll displacement/acceleration with slight influence on the vertical displacement/acceleration under the transient and road loop excitations; (2) the added orifice will not change the resonance frequency of the bounce and roll modes; (3) comparing with the traditional HIS design (without the added orifices), the maximum roll transmissibility can decrease 30.17% with 2.89% increase of the maximum vertical transmission for the added orifice with 2 mm2 area. Overall, the results suggest that the proper size of the orifices will significantly increase the roll-stability properties with slight effect on the bounce mode under the road excitations.

The dynamic properties of one kind of Inter-Connected Hydro-Pneumatic Struts (IC HPS), which is designed based on the developed double-gas-chamber compacted Hydro-Pneumatic Struts (HPS) integrating double inner gas chambers, will be investigated in this research. Comparing with the traditional IC HPS designs based on single gas chamber compacted HPS, the proposed IC HPS can postpone the force distortion, and then increase the working envelop, provide good stiffness performance and be stable in both In-Phase and Out-of-Phase working condition. The equation of motion of the proposed IC HPS will be derived firstly. And then based on the established dynamic model, the related simulating model will be established utilizing the AMEsim software, and the validity of the established simulating model will be verified on the basis of experimental data and available literatures. The validity and performance of the proposed IC HPS will be verified and investigated through comprehensive comparison with traditional IC HPS designs. Finally, the detailed sensitivity analysis of the essential design parameter of the proposed IC HPS will be presented to illustrate the advantage of the proposed IC HPS design.

The dynamic properties of a compact hydro-pneumatic suspension strut integrating the gas chamber are investigated analytically and experimentally. A comprehensive experiment was designed to experimentally characterize the dependence of friction force on the strut operating pressure in addition to the pressure/force–displacement and pressure/force–velocity properties of the prototype under broad ranges of excitations. An analytical model of the strut is formulated to incorporate the polytropic gas process, nonlinear and hysteretic friction force and turbulent flows across the piston orifices. Owing to dominant effect of friction due to seals of the floating piston separating the gas and oil media, and strong dependence of friction force on the operating pressure, the Coulomb and Stribeck friction effects are described by a nonlinear function in the operating pressure. Furthermore, the viscoelastic O-ring-type seals contributed to notable hysteresis at very low velocities, which is described by a hyperbolic tangent function in velocity. The discharge coefficient of flows through orifices is also identified from the measured fluid pressures. The validity of the proposed model is demonstrated through comparisons of force–displacement and force–velocity responses of the model with the corresponding measured data under broad ranges of excitations. The comparisons revealed that the model could predict dynamic behavior of the strut reasonably well. The effects of charge pressure and gas volume are further investigated to seek guidance on tuning of the strut for realizing desired load carrying capacity and suspension stiffness.

A programming methodology, which can be applied to soft-magnetic-material-based magneto-active elastomers (MAEs), to catch the predefined specific objective curves is proposed in this study. The objective curves have been equally separated into a couple of segments, which will be filled by the designed MAE elements. Furthermore, the designed MAE segments with different chain angles, in which the deformation orientation of each element under applied homogeneous magnetic fields has been investigated based on the designed experimental setup, are arrayed based on the proposed programming methodology to constitute the MAE composite to catch the orientation of the objective curve. The experimental results show that based on the proposed programming methodology, the MAE composites can describe different curves, which include harmonic, tangential and arc tangential functions under applied homogeneous magnetic fields with good agreement. Furthermore, on the basis of the proposed programming methodology, the MAE composites are utilized to mimic the typical biomimetic behavior (the peeking-up behavior of snakes and the flapping behavior of birds) with smooth curvature properties, in which the dynamic procedures present continuous curves.

Magnetoactive elastomers (MAEs), one kind of typical novel magnetoactive driver applied in the soft robotic area, have become one of the research hotspots as they can provide biologically friendly driving methods with safe, preprogrammed, and easy-to-implement properties. In this study, novel MAEs embedding soft magnetic iron microparticles with radial chains, which can be molded in one piece, achieve 3D deformation, and co-work between multiple MAEs under single homogeneous stimuli, are proposed. Then, two kinds of novel magnetoactive drivers are established based on the proposed MAEs, which can achieve the synchronous pumping behavior of heart and the extension behavior of muscle under applied homogeneous magnetic fields. The experimental data show that (1) for the pumping behavior, the maximum instantaneous flow rate and total pumping volume can reach 200.1 and 52.3 mL/min, respectively, under 120 BPM applied harmonic magnetic field with 0-300 mT amplitude; (2) the muscle extension behavior can achieve a strain of 0.925 without a loading mass and carry a load of 40 times its own weight with a pronounced dynamic movement. It should be emphasized that the behavior of the proposed magnetoactive drivers can be excited by remote homogeneous magnetic fields, and it has great application potential in biomimetic or bioinspired soft driving systems.

The dynamic properties of two types of interconnected hydro-pneumatic struts (HPSs), which are designed based on two different types of the HPSs with integrated gas chamber, have been investigated through the setup experiment on the designed prototypes and established numerical model on the basis of the AMEsim software in this research work. Detailed analysis of the dynamic properties has been posted on the experimental data, including the in-phase and out-of-phase tests. Special emphasis has been placed on the analysis of some unusual phenomenon shown in the experiment, such as the negative output force, output force distortion, and small stiffness, and so on, which are seldom reported by researchers in this area. Then, the effect of the structural parameters, which include the length/diameter of the interconnected pipes and the size of orifices, to the dynamic properties, especially to the unusual phenomenon shown in the experiment, will be discussed through the established AMEsim model, in which the validity of the AMEsim model has been verified through the experiment. The presented research work provides the fundamental investigation on two types of interconnected HPSs, which have great potential application in the area of a vehicle suspension system.

A dynamic model based on a novel hydro-pneumatic damper will be proposed on this paper. The non-linear properties of the polytropic state, friction, and the orifices have been considered in the proposed model. The validity of the proposed model has been verified through the experimental set-up.