Xianhu Liu

Continuously prepared highly conductive and stretchable SWNT/MWNT synergistically composited electrospun thermoplastic polyurethane yarns for wearable sensing

Highly conductive and stretchable yarns have attracted increasing attention due to their potential applications in wearable electronics. The integration of conductive yarns with large stretching capability renders the composite yarns with new intriguing functions, such as monitoring human body motion and health. However, simultaneously endowing the yarns with high conductivity and stretchability using an easily scalable approach is still a challenge. Here, highly conductive and stretchable yarns based on electrospun thermoplastic polyurethane (TPU) fiber yarns successively decorated with multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs) were prepared by a combined electrospinning, ultrasonication adsorbing, and bobbin winder technique. The improved thermal stability of the SWNT/MWNT/TPU yarn (SMTY) indicated strong interfacial interactions between the CNTs and electrospun TPU fibers. The synergism between the successively decorated SWNTs and MWNTs significantly enhanced the conductivity of the TPU yarns (up to 13 S cm−1). The as-fabricated yarns can be easily integrated into strain sensors and exhibit high stretchability with large workable strain range (100%) and good cyclic stability (2000 cycles). Moreover, such yarn can be attached to the human body or knitted into textiles to monitor joint motion, showing promising potential for wearable electronics, such as wearable strain sensors.

Mapping the Electrical Conductivity of Poly(methyl methacrylate)/Carbon Black Composites Prior to and after Shear

In this letter, the electrical conductivity of disklike poly(methyl methacrylate)/carbon black composite samples was investigated prior to and after a shear process. Novel electrical conductivity maps of the samples as a function of the position were obtained. It was found that the electrical conductivity after angular averaging of the static (nonsheared) sample is, as expected, independent of the radius. However, for the sheared sample, the electrical conductivity is decreasing from the center to the outer rim of the sample. This is attributed to the interplay of destruction and buildup effects of the applied linear shear stress on the agglomerate network.

Conductivity and phase morphology of carbon black-filled immiscible polymer blends under creep: an experimental and theoretical study.

Blends of carbon black (CB)-filled co-continuous immiscible polystyrene/poly(methyl-methacrylate) (PS/PMMA) with a PS/PMMA ratio of 50/50 and CB selectively located in the PS phase have been prepared by melt blending. The simultaneous evolution of conductivity and phase morphology of blend composites was investigated under shear and in the quiescent state at 200 °C. It was found that shear deformation had a significant influence on the conductivity of the unfilled PS/PMMA blend and its composites, which was attributed to the change of phase morphology during shear. After the shear stress of 10 kPa, the conductivity of PS/PMMA blends filled with 2 vol% of CB decreased by about two orders of magnitude and the phase morphology transformed from a fine co-continuous structure into a highly elongated lamellar structure. The deformation of phase morphology and the decrease of conductivity were weakened upon decreasing the shear stress or increasing the CB concentration. During subsequent recovery, pronounced phase structure coarsening was observed in the mixture and the conductivity increased as well. A simple model describing the behavior of conductivity under shear deformation was derived and utilized for the description of the experimental data. For the first time, the Burgers model was used to describe the conductivity, and the viscoelastic and viscoplastic parameters were deduced by fitting the conductivity under shear. The results obtained in this study provide a deeper insight into the evolution of phase structure in the conductive polymer blend composite induced by shear deformation.

Electric Field-Assisted Orientation of Short Phosphate Glass Fibers on Stainless Steel for Biomedical Applications

Structural and compositional modifications of metallic implant surfaces are being actively investigated to achieve improved bone-to-implant bonding. In this study, a strategy to modify bulk metallic surfaces by electrophoretic deposition (EPD) of short phosphate glass fibers (sPGF) is presented. Random and aligned orientation of sPGF embedded in a poly(acrylic acid) matrix is achieved by vertical and horizontal EPD, respectively. The influence of EPD parameters on the degree of alignment is investigated to pave the way for the fabrication of highly aligned sPGF structures in large areas. Importantly, the oriented sPGF structure in the coating, owing to the synergistic effects of bioactive composition and fiber orientation, plays an important role in directional cell migration and enhanced proliferation. Moreover, gene expression of MC3T3-E1 cells cultured with different concentrations of sPGF is thoroughly assessed to elucidate the potential stimulating effect of sPGF on osteogenic differentiation. This study represents an innovative exploitation of EPD to develop textured surfaces by orientation of fibers in the macroscale, which shows great potential for directional functionalization of metallic implants.

Reversal phenomena of molten immiscible polymer blends during creep-recovery in shear

In this work, the creep-recovery behavior of immiscible poly (styrene)/poly (methyl methacrylate) blends and their pure components in the molten state were systematically investigated. A stationary plateau in the recoverable compliance of pure components is observed. Unexpectedly, for immiscible polymer blends, the recoverable compliances show different phenomena. For blends with a fine co-continuous morphology, the recoverable compliances exhibit a one-reversal phenomenon, whereas a two-reversal phenomenon is found in the blends with a sea-island morphology. Moreover, these reversal behaviors become less pronounced with decreasing temperature, increasing creep stress, increasing annealing time, or incorporation of nanoparticles. Three competitive effects, i.e., the recovery of oriented polymer matrix, the interfacial tension which drives the deformed droplets to their equilibrium shape, and the phase coarsening process, are used here to explain the different behaviors.

Suppression of the hierarchical structure of water-assisted injection moulded iPP in the presence of a β-nucleating agent and lamellar branching of a β-crystal

The thickness of oriented zones in water-assisted injection moulded β-iPP parts increased with the increasing of β-nucleating agent (β-NA) content. More interestingly, the high β-NA content suppressed the hierarchical structure effectively, which is consistent with the almost invariable crystallinity and orientation. Meanwhile, an unexpected lamellar branching of the β-crystal was observed.

A Facile Flow-Casting Production of Bioactive Glass Coatings on Porous Titanium for Bone Tissue Engineering

Additive manufacturing enabled the fabrication of porous titanium (PT) with customized porosity and mechanical properties. However, functionalization of PT surfaces with bioactive coatings is being challenged due to sophisticated geometry and highly porous structure. In this study, a facile flow-casting technique was developed to produce homogeneous 45S5 bioactive glass (BG) coatings on the entire surface of PT. The coating weight as a function of BG concentration in a BG-PVA slurry was investigated to achieve controllable coating yield without blocking macropore structure. The annealing-treated BG coating not only exhibited compact adhesion confirmed by qualitative sonication treatment, but also enhanced the mechanical properties of PT scaffolds. Moreover, in-vitro assessments of BG-coated PT cultured with MC3T3-E1 cells was carried out having in mind their potential as bioactive bone implants. The experimental results in this study offer a simple and versatile approach for the bio-functionalization of PT and other porous biomedical devices.

Electrically Conductive Polymer Composites for Smart Flexible Strain Sensors: A Critical Review

The rapid development of wearable smart devices has contributed to the enormous demands for smart flexible strain sensors. However, to date, the poor stretchability and sensitivity of conventional metals or inorganic semiconductor-based strain sensors have restricted their application in this field to some extent, and hence many efforts have been devoted to find suitable candidates to overcome these limitations. Recently, novel resistive-type electrically conductive polymer composites (ECPCs)-based strain sensors have attracted attention based on their merits of light weight, flexibility, stretchability, and easy processing, thus showing great potential applications in the fields of human movement detection, artificial muscles, human–machine interfaces, soft robotic skin, etc. For ECPCs-based strain sensors, the conductive filler type and the phase morphology design have important influences on the sensing property. Meanwhile, to achieve a successful application toward wearable devices, several imperative features, including a self-healing capability, superhydrophobicity, and good light transmission, need to be considered. The aim of the present review is to critically review the progress of ECPCs-based strain sensors and to foresee their future development.

Electrophoretic deposition of dexamethasone-loaded gelatin nanospheres/chitosan coating and its dual function in anti-inflammation and osteogenesis

Surface modification of metallic implants with bioactive and biodegradable coatings could be a promising approach for bone regeneration. The objective of this study was to prepare chitosan/gelatin nanospheres (GNs) composite coating for the delivery of dexamethasone (DEX). GNs with narrow size distribution and negative surface charge were firstly prepared by a two-step desolvation method. Homogeneous and stable gelatin nanospheres/chitosan (GNs/CTS) composite coatings were formed by electrophoretic deposition (EPD). Drug loading, encapsulation efficiency and in vitro release of DEX were estimated using high performance liquid chromatography (HPLC). The anti-inflammatory effect of DEX-loaded coatings on macrophage RAW 264.7 cells was assessed by the secretion of tumour necrosis factor (TNF) and inducible nitric oxide synthase (iNOS). Osteogenic differentiation of MC3T3-E1 osteoblasts on DEX-loaded coatings was investigated by osteogenic gene expression and mineralization. The DEX in GNs/CTS composite coating showed a two-stage release pattern could not only suppress inflammation during the burst release period, but also promote osteogenic differentiation in the sustained release period. This study might offer a feasible method for modifying the surface of metallic implants in bone regeneration.