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This paper focuses on improving tracking performance of totally uncoupled compliant micromanipulator based on robust control method of elliptical hysteresis model. The hysteresis model and hysteresis compensation model for proposed mechanism based on Piezoelectric transducer (PZT) are established by using elliptical model method. The values of elliptical hysteresis model parameters are identified by simulating method with different frequencies of control input. The uncertainty model is also established, the values of corresponding estimated parameters are conformed by experiment method. Based on the uncertainty model and elliptical hysteresis model, the robust tracking control method is presented and utilized to evaluate the tracking performance of proposed mechanism under inputting different tracking curves. The proposed method can accurately control the output displacement and improve tracking performance of this mechanism, which are validated and carried out by using experimental studies. Additionally, the coupling errors between two directions are kept within 0.14% and the tracking errors for different curves are within 2.5%.

A microrobot with untethered control in 3D space is a good choice to be applied in the fields of biomedicine with in small and confined workspace. In this paper, an electromagnetic actuation system (EMA) which combined with Helmholtz coil and Maxwell coil for the microrobot 5 DOF locomotion in 3D space is built. The magnetic field analysis of the proposed 3D EMA system was analyzed by finite-element-method (FEM) with multi-physics COMSOL software. The proposed EMA system can produce magnetic field with different characteristics such as a controllable uniform gradient magnetic field, a rotating magnetic field and a oscillating magnetic field in a three-dimensional space by independently changing the current in each coil. In this paper the 3D motion dynamic equation model of microrobot was established. A novel control method for the gravity compensation for the wireless locomotive microrobot was proposed. The proposed method has the property that the direction of magnetic flux and the locomotion path of the microrobot are independent. Meanwhile, it can achieve the horizontal motions or nearly horizontal motions and overcome the gravity well at the same time. It has been verified by experiments in 3D liquid environment. With the proposed method, the microrobot shows good performance in horizontal motions as well as various motions in the 3D space.

Reciprocating motion is a widely existing form of mechanical motion in the natural environment. Triboelectric nanogenerators (TENGs) that work in sliding mode are ideal for harnessing large-distance reciprocating motion, and their energy conversion efficiency could be greatly enhanced by adding springs to them. Herein, we focused on investigating the design and optimization principles of sliding mode TENGs by analyzing the effects of spring parameters and vibration frequency on the triboelectric output performance of typical cylindrical sliding TENGs (CS-TENGs). Experimental study and finite elemental analysis were carried out based on a CS-TENG model assembled using a polytetrafluoroethylene (PTFE) film as the negative layer and an aluminum film as the positive layer. The energy output was found to be mainly affected by the change of relative displacement between the two friction layers, rather than the reactive force applied by the springs or the velocity of the sliding motion. However, the frequency of the output signals could be improved when the stiffness coefficient of the springs and the CS-TENG vibration frequency were increased. This study provides valuable directions for the design and optimization of sliding mode TENGs containing springs, and will motivate in-depth research on the fundamental principles of TENG operation.

The polyamide (PA) reverse osmosis (RO) membranes prepared by interfacial polymerization at a free aqueous-organic interface always suffer from polymerization instability on the free-interface and low chlorine resistance. Focusing on these problems, in this study, a new approach was proposed which introduced an additional buffer layer to assist the free-interfacial polymerization (BLFIP). And due to the adjustment of the mitigation of the organic phase and water phase on the free-interface, defect-free PA membranes with significantly improved surface smoothness were successfully prepared by the proposed BLFIP process and the resultant membranes demonstrated superior desalination performance compared to the PA membranes prepared with the previous technique. With the optimized concentration of 0.3 wt.% trimesoyl chloride (TMC) and 0.6 wt.%, m-xylylenediamine, the prepared BLFIP PA membrane showed salt rejection rate of 92.55%, 92.01%, 83.99% and 95.16%, to Na2SO4, MgSO4, NaCl and methyl orange, respectively at 5 bar, while maintained a water flux of about 2 Lm-2 h-1 bar-1. More importantly, the BLFIP PA membrane possesses excellent long-term stability, and chlorine resistance comparing with traditional PA membranes based on TMC and m-phenylenediamine, which demonstrated the new method in this study paved a facile way for preparing RO filtration membranes with outstanding performance in seawater desalination. [ABSTRACT FROM AUTHOR]

A new electrospinning approach for fabricating vascular grafts with a layered, circumferentially aligned, and micro-wavy fibrous structure similar to natural elastic tissues has been developed. The customized electrospinning collector was able to generate wavy fibers using the dynamic "jump rope" collecting process, which also solved the sample removal problem for mandrel-type collectors. In this study, natural silk fibroin and synthetic thermoplastic polyurethane (TPU) were combined at different weight ratios to produce hybrid small-diameter vascular grafts. The purpose of combining these two materials was to leverage the bioactivity and tunable mechanical properties of these natural and synthetic materials. Results showed that the electrospun fiber morphology was highly influenced by the material compositions and solvents employed. All of the TPU/fibroin hybrid grafts had mechanical properties comparable to natural blood vessels. The circumferentially aligned and wavy biomimetic configuration provided the grafts with a sufficient toe region and the capacity for long-term usage under repeated dilatation and contraction. Cell culture tests with human endothelial cells (EC) also revealed high cell viability and good biocompatibility for these grafts. [ABSTRACT FROM AUTHOR]

Carbon-based aerogels have been recognized as a promising 3D superabsorbent material for oil absorption due to their high absorption capacity. However, their selective absorption efficiency is limited because of their relatively low hydrophobicity. Here, we report the fabrication of a fluorinated hybrid aerogel (FHA) consisting of graphene oxide (GO), cellulose nanofibrils (CNFs), and silica nanoparticles by one-pot hydrothermal synthesis and subsequent freeze-drying and chemical vapor deposition modification. The CNFs in FHA prevented volume shrinkage, greatly reduced the bulk density, and increased the surface area, while the GO retained its mechanical strength and the free-standing characteristic of FHA. Silica particles and CNFs created hierarchical structures on pore walls, and the grafted fluorochains reduced the surface energy. The synergistic effect of the hierarchical structure and low surface energy contributed to the excellent superhydrophobicity (water contact angle of 157°) and water repellency (contact angle hysteresis less than 1°) of FHA. Meanwhile, FHA maintained superoleophilicity and showed extraordinary absorption efficiency (∼100%) and relatively high absorption capacity (39-68 times weight gain) to various oils and chemical solvents. This high performance can be maintained in repetitive use. Furthermore, a self-driven oil collection device assembled with FHA demonstrated its diverse applications in water remediation. [ABSTRACT FROM AUTHOR]

Fabrication of small-diameter vascular scaffolds has been a challenge in recent years, especially scaffolds with multiple layers. In this study, two approaches were proposed to fabricate triple-layered vascular scaffolds based on the electrospinning method and the thermally induced phase separation (TIPS) method. It was found that the electrospun fibers had a compact fibrous structure that provided good mechanical properties. The porous TIPS layer had high porosity and pore interconnectivity to facilitate cell penetration; however, this structure alone could not ensure sufficient mechanical properties for surgical applications. The triple-layered scaffolds, which consisted of electrospun TPU, TIPS TPU, and electrospun PPC layers, showed the highest mechanical properties and best structure and dimensions for vascular graft applications. Preliminary endothelial cell culture results showed that the cells could attach to and proliferate on the inside surface of the scaffolds with >95% viability. [ABSTRACT FROM AUTHOR]

Biodegradable poly(lactic acid) (PLA)based poly(butylenes succinate)(PBS) foams with open cell structure were prepared via batch foamingmethod using supercritical carbon dioxide as blowing agent. It wasfound that PLA was immiscible with PBS, and PBS phase was dispersedas tiny spheres or large domains at various concentrations. The additionof PBS reduced the viscosity of the blends. During the foaming process,the PLA/PBS interfaces acted as cell nucleation sites and the lowmelt strength PBS contributed to the formation of cell connectionchannels, which resulted in open cell structure. The investigationof PBS content and foaming temperature found that PLA/PBS (80/20)foamed at 100 °C, obtaining the highest cell opening rate (96%).Two-step depressurization foaming experiments proved that bimodalcell structure PLA/PBS foams with high cell opening rate (97%) wereable to be fabricated. [ABSTRACT FROM AUTHOR]

Thermoplastic polyurethane (TPU)/hydroxyapatite (HA) scaffolds were fabricated via electrospinning. The effects of TPU properties and HA particle size on scaffold physical properties and osteoblast-like cell performance were investigated. It was found that the addition of micro-HA (mHA), which was inlayed in the fiber, decreased the electrospun fiber diameter. On the contrary, nano-HA (nHA), which was either embedded or existed inside of the fiber, increased the fiber diameter for both soft and hard TPUs. The soft TPU had a much lower Young's modulus and higher strain-at-break than the hard TPU. The addition of both mHA and nHA decreased the tensile properties; this decrease was more significant with mHA. The cells on the hard scaffolds actively proliferated and migrated compared to those on the soft scaffolds. On the other hand, cells on the soft scaffolds more effectively induced osteogenesis of human mesenchymal stem cells (hMSCs) than those on the hard scaffolds. In addition, our data suggest that the soft scaffolds with supplementation of nHA further enhanced osteogenesis of hMSCs compared to those without nHA. The soft TPU scaffolds containing nano-HA have the potential to be used in bone tissue engineering applications. [ABSTRACT FROM AUTHOR]