A temporary self-expanding metallic stent for malignant colorectal obstruction

AIM:To investigate the clinical safety and efficacy of a temporary self-expanding metallic stent(SEMS) for malignant colorectal obstruction.METHODS:From September 2007 to June 2012,33 patients with malignant colorectal obstruction were treated with a temporary SEMS.The stent had a tubular configuration with a retrieval lasso attached inside the proximal end of the stent to facilitate its removal.The SEMS was removed one week after placement.Clinical examination,abdominal X-ray and a contrast study were prospectively performed and both initial and follow-up data before and at 1 d,1 wk,and 1 mo,3 mo,6 mo and 12 mo after stent placement were obtained.Data collected on the technical and clinical success of the procedures,complications,need for reinsertion and survival were analyzed.RESULTS:Stent placement and removal were technically successful in all patients with no procedurerelated complications.Post-procedural complications included stent migration(n = 2) and anal pain(n = 2).Clinical success was achieved in 31(93.9%) of 33 patients with resolution of bowel obstruction within 3 d of stent removal.Eleven of the 33 patients died 73.81 ± 23.66 d(range 42-121 d) after removal of the stent without colonic re-obstruction.Clinical success was achieved in another 8 patients without symptoms of obstruction during the follow-up period.Reinsertion of the stent was performed in the remaining 12 patients with re-obstruction after 84.33 ± 51.80 d of follow-up.The mean and median periods of relief of obstructive symptoms were 97.25 ± 9.56 d and 105 ± 17.43 d,respectively,using Kaplan-Meier analysis.CONCLUSION:Temporary SEMS is a safe and effective approach in patients with malignant colorectal obstruction due to low complication rates and good medium-term outcomes.

Thermally Conductive,Healable Glass Fiber Cloth Reinforced Polymer Composite based onβ-Hydroxyester Bonds Crosslinked Epoxy with Improved Heat Resistance

To simultaneously endow thermal conductivity,high glass transition temperature(Tg)and healing capability to glass fiber/epoxy(GFREP)composite,dynamic crosslinked epoxy resin bearing reversibleβ-hydroxyl ester bonds was reinforced with boron nitride nanosheets modified glass fiber cloth(GFC@BNNSs).The in-plane heat conduction paths were constructed by electrostatic self-assembly of polyacrylic acid treated GFC and polyethyleneimine decorated BNNSs.Then,the GFC@BNNSs were impregnated with the mixture of lower concentration(3-glycidyloxypropyl)trimethoxysilane grafted BN micron sheets,3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate and hexahydro-4-methylphthalic anhydride,which accounted for establishing the through-plane heat transport pathways and avoiding serious deterioration of mechanical performances.The resultant GFREP composite containing less boron nitride particles(17.6 wt%)exhibited superior in-plane(3.29 W·m^(-1)·K^(-1))and through-plane(1.16 W·m^(-1)·K^(-1))thermal conductivities,as well as high Tg of 204℃(Tg of the unfilled epoxy=177℃).The reversible transesterification reaction enabled closure of interlaminar cracks within the composite,achieving decent healing efficiencies estimated by means of tensile strength(71.2%),electrical breakdown strength(83.6%)and thermal conductivity(69.1%).The present work overcame the disadvantages of conventional thermally conductive composites,and provided an efficient approach to prolong the life span of thermally conductive GFREP laminate for high-temperature resistant integrated circuit application.

Topological Confinement in Reversibly Interlocked Polymer Networks

Recently, we reported a series of reversibly interlocked polymer networks(RILNs), whose mechanical robustness and functionalities improvement was believed to be derived from topological interlocking of two sub-networks, although the direct evidence for the deduction is still lacking. Herein, a specially-designed RILNs system, in which the inter-component hydrogen bonds can be shielded as needed, was prepared and used to study the micro-structures of RILNs, aiming to verify the existence of mechanical interlocking in RILNs. By changing the pH of the swelling solvent, the effect exerted by the inter-component non-covalent bonds was eliminated, so detailed information of the networks structure was exposed. The small angle X-ray scattering(SAXS) and small-angle neutron scattering(SANS) results indicated that swelling-induced structural evolution of the two sub-networks mutually affected each other, even when the inter-component hydrogen bonds were absent, proving the presence of topological interlocking. The findings may help to draw a more accurate physical image and reveal the detailed structureproperty relationship of RILNs.

Imparting Pulley Effect and Self-healability to Cathode Binder of Li-S Battery for Improvement of the Cycling Stability

To construct structurally stable sulfur cathode of Li-S battery with improved cycling performance,poly(acrylic acid)(PAA)crosslinked by cationic hydroxypropyl polyrotaxane(HPRN+)via dynamically reversible boronic ester bonds is synthesized and serves as the cathode binder.The smart polymer networks offer multifunction including buffering the volume change of the cathode during charge/discharge through the pulley effect of polyrotaxanes(PR),suppressing the shuttle effect by adsorption of polysulfide using the plentiful carboxyl,hydroxyl and quaternary ammonium cationic groups,and self-healing the micro-damages to ensure stable conduction pathways of the electrode.As a result,the Li-S batteries based on this novel multifunctional binder and simple commercial sulfur/carbon composites cathode exhibit excellent specific capacity and cycling stability.In particular,the specific capacity decay per cycle of the cell is only 0.064%along with high Coulombic efficiency after 550 cycles at 1.0 C,which is superior to most of the reported binders.Even under high sulfur loading,moreover,the cathode can deliver superior areal capacity and cycling stability.This proposed binder provides a new way for the design of high-stability sulfur cathodes.

Synergistic Flame-retardant Effect of Epoxy Resin Combined with Phenethyl-bridged DOPO Derivative and Graphene Nanosheets

Phenethyl-bridged DOPO derivative(DiDOPO)was combined with graphene nanosheets(GNSs)in epoxy resin(EP)to improve its flame retardancy.The results indicated that the introduction of only 1.5 wt%DiDOPO/1.5 wt%GNS in EP increased the limited oxygen index(LOI)from 21.8%to 32.2%,hence meeting UL 94 V-0 rating.The thermogravimetric analyses revealed that char yield rose in presence of GNSs to form thermally stable carbonaceous char.The decomposition and pyrolysis products in gas phase were characterized by thermogravimetry-Fourier transform infrared spectroscopy(TG-FTIR),and the release of large amounts of phosphorus was detected in the gas phase.The evaluation of flame-retardant effect by cone calorimetry demonstrated that GNSs improved the protective-barrier effect of fire residue of EP/DiDOPO/GNS.The latter was further confirmed by digital photography and scanning electron microscopy(SEM).Also,Raman spectroscopy showed that GNSs enhanced graphitization degree of the resin during combustion.Overall,the combination of DiDOPO with GNSs provides an effective way for developing high-performance resins with improved flame retardancy.

IMPROVEMENT OF CREEP RESISTANCE OF POLYTETRAFLUOROETHYLENE FILMS BY NANO-INCLUSIONS

To improve creep resistance of directional polytetrafluoroethylene （PTFE） films, epoxy grafted nano-SiO2 is mixed with PTFE powder before sintering and calender rolling. The aligned macromolecular chains （especially those in amorphous region） of the composite films can be bundled up by the nanoparticles to share the applied stress together. In addition, incorporation of silica nanoparticles increases crystallinity of PTFE and favors microfibrillation of PTFE in the course of large deformation. As result, PTFE films exhibit lower creep strain and creep rate, and higher tensile strength and hardness. The work is believed to open an avenue for manufacturing high performance fluoropolymers by nano-inclusions.

Reversible Mechanochemistry Enabled Autonomous Sustaining of Robustness of Polymers—An Example of Next Generation Self-healing Strategy

Even under low external force,a few macromolecules of a polymer have to be much more highly stressed and fractured first due to the inherent heterogeneous microstructure.When the materials keep on working under loading,as is often the case,the minor damages would add up,endangering the safety of use.Here we show an innovative solution based on mechanochemically initiated reversible cascading variation of metal-ligand complexations.Upon loading,crosslinking density of the proof-of-concept metallopolymer networks autonomously increases,and recovers after unloading.Meanwhile,the stress-induced tiny fracture precursors are blocked to grow and then restored.The entire processes reversibly proceed free of manual intervention and catalyst.The proposed molecular-level internal equilibrium prevention mechanisms fundamentally enhance durability of polymers in service.

Self-Healing Polymeric Materials:On a Winding Road to Success

Self-healing represents a next-generation technology in response to the common demands of polymeric materials for long-term stability and durability.It mimics the capability of naturally occurring species like living organisms to autonomously recover nonfatal harm.The damages inevitably generated during fabrication and service are allowed to be unconsciously repaired on a microscopic scale,and would no longer develop into macroscopic failures like the case of conventional materials.

SbF_5-loaded microcapsules for ultrafast self-healing of polymer

To accelerate self-healing speed of epoxy materials,epoxy-SbF5 cure was introduced into the healing chemistry.Due to the high activity of SbF5,a milder SbF5-ethanol complex with improved processability was prepared,but it was still quite active and cannot be encapsulated by conventional encapsulation techniques like in situ polymerization.Accordingly,a novel route was proposed.Hollow silica microcapsules were firstly synthesized via sol-gel technique,which were then steeped in ethanol solution of SbF5-ethanol complex under vacuum,allowing infiltration of the latter into the capsules.The optimal formulation for creating the hollow silica capsules was studied in detail.Moreover,the results of optical pyrometry demonstrated that the encapsulated chemical retained its high reactivity toward the epoxy.

PREFACE

We are delighted to present this special-themed issue of the Chinese Journal of Polymer Science(CJPS)devoted to the recent advances in self-healing polymeric materials.Self-healing has been recognized as one of the most attractive topics for advaneed polymers in the past few years,enabling their reworkability,durability and reliability.Since the emergence of the concept,self-healing polymeric materials have been rapidly evolving and have revolutionized many aspects of polymer sciences.Nowadays,this type of smart materials has found broad prospects for both structural and functional applications including space vehicles,aircrafts,artificial skins,soft robots,energy devices,coatings,and sensors.This special issue consists of 3 feature articles,2 review articles,and 6 regular articles,focusing on the latest research achievements in dynamic networks,self-healing elastomers,supramolecular polymers,hybrid polymers,and so on.