A 3D printable self-healing composite conductive polymer for sensitive temperature detection

Recent development of self-healing material has attracted tremendous attention,owing to its biomimetic ability to restore structure and functionality when encountering damages.Here,we develop a threedimensional(3D)printable self-healing composite conductive polymer by mixing hydrogen-bond-based supramolecular polymer with low-cost carbon black.It has a room-temperature self-healing capability in both conductivity and mechanical property,while its shear-thinning behavior enables fabrication of a self-healable circuit by 3D printing technology.As an application,the circuit shows an excellent temperature-dependent behavior of the resistance,indicating its great potential fo r practical application in the artificial intelligence field.     

Properties of conductive polymer hydrogels and their application in sensors

Conductive polymer hydrogels (CPHs), which combine the unique advantages of hydrogels and organic conductors, have received wide attention due to their adjustable mechanical properties, biocompatibility, self‐healing, hydrophilicity, and ease of preparation. With doping engineering and incorporation with other functional nanomaterials, CPHs have exhibited excellent physical/chemical properties. CPHs have been widely used in various electronic devices, especially in the field of sensors due to its sensitivity to external stimuli. This review summarizes recent progress in CPHs from the aspect of the CPHs' properties and their application in advanced sensor technology. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1606–1621     

聚苯胺/顺丁橡胶复合导电膜的制备与性能

采用溶液共混与浇铸法制备聚苯胺（PAn ）/顺丁橡胶（BR）复合导电膜,确定了本征态聚苯胺以顺丁橡胶为弹性基体材料,甲苯为溶剂,过氧化二苯甲酰为交联剂,十二烷基苯磺酸作为共混分散剂和聚苯胺掺杂剂的复合膜制备工艺,并对复合膜的导电性能和形态结构进行了测试与表征.     

A Stereolithography‐Based 3D Printed Hybrid Scaffold for In Situ Cartilage Defect Repair

Damage to articular cartilage can over time cause degeneration to the tissue surrounding the injury. To address this problem, scaffolds that prevent degeneration and promote neotissue growth are needed. A new hybrid scaffold that combines a stereolithography‐based 3D printed support structure with an injectable and photopolymerizable hydrogel for delivering cells to treat focal chondral defects is introduced. In this proof of concept study, the ability to a) infill the support structure with an injectable hydrogel precursor solution, b) incorporate cartilage cells during infilling using a degradable hydrogel that promotes neotissue deposition, and c) minimize damage to the surrounding cartilage when the hybrid scaffold is placed in situ in a focal chondral defect in an osteochondral plug that is cultured under mechanical loading is demonstrated. With the ability to independently control the properties of the structure and the injectable hydrogel, this hybrid scaffold approach holds promise for treating chondral defects.     

Dynamic postpolymerization of 3D‐printed photopolymer nanocomposites: Effect of cellulose nanocrystal and postcure temperature

Cellulose nanocrystal (CNC) reinforced methacrylate (MA) resin nanocomposite was prepared by 3D stereolithography printing. A postcure process, where the printed nanocomposite was heat‐treated under different temperatures, was applied to improve the property of the printed nanocomposites. To investigate the effect of CNC and postcure temperature on the kinetic behavior of the postpolymerization of printed nanocomposites, Fourier‐transform infrared spectroscopy and differential scanning calorimetry measurement of the printed nanocomposites before and after postcure were analyzed. The postpolymerization of MA nanocomposites was promoted at a postcure temperature of 140 °C for the printed 0.5% CNC/MA nanocomposites compared to the printed MA resin. The addition of CNC retarded the polymerization of MA resin during 3D printing, resulting in poorer mechanical properties of the printed nanocomposites compared to the printed MA resin. However, after postcure, the mechanical properties of the printed nanocomposites were improved by the postpolymerization of the MA nanocomposites. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 935–946     

3D printed polylactic acid nanocomposite scaffolds for tissue engineering applications

In this study, biodegradable polylactic acid (PLA) and PLA nanocomposite scaffolds reinforced with magnetic and conductive fillers, were processed via fused filament fabrication additive manufacturing and their bioactivity and biodegradation characteristics were examined. Porous 3D architectures with 50% bulk porosity were 3D printed, and their physicochemical properties were evaluated. Thermal analysis confirmed the presence of ~18 wt% of carbon nanostructures (CNF and GNP; nowonwards CNF) and ~37 wt% of magnetic iron oxide (Fe₂O₃) particles in the filaments. The in vitro degradation tests of scaffolds showed porous and fractured struts after 2 and 4 weeks of immersion in DMEM respectively, although a negligible weight loss is observed. Greater extent of degradation is observed in PLA with magnetic fillers followed by PLA with conductive fillers and neat PLA. In vitro bioactivity study of scaffolds indicate enhancement from ~2.9% (PLA) to ~5.32% (PLA/CNF) and ~ 3.12% (PLA/Fe₂O₃). Stiffness calculated from the compression tests showed decrease from ~680 MPa (PLA) to 533 MPa and 425 MPa for PLA/CNF and PLA/Fe₂O₃ respectively. Enhanced bioactivity and faster biodegradation response of PLA nanocomposites with conductive fillers make them a potential candidate for tissue engineering applications such as scaffold bone replacement and regeneration.     

Concentration of lambda concatemers using a 3D printed device

Identifying significant variations in genomes can be cumbersome, as the variations span a multitude of base pairs and can make genome assembly difficult. However, large DNA molecules that span the variation aid in assembly. Due to the DNA molecule's large size, routine molecular biology techniques can break DNA. Therefore, a method is required to concentrate large DNA. A bis-acrylamide roadblock was cured in a proof-of-principle 3D printed device to concentrate DNA at the interface between the roadblock and solution. Lambda concatemer DNA was stained with YOYO-1 and loaded into the 3D printed device. A dynamic range of voltages and acrylamide concentrations were tested to determine how much DNA was concentrated and recovered. The fluorescence of the original solution and the concentrated solution was measured, the recovery was 37% of the original sample, and the volume decreased by a factor of 3 of the original volume.     

A novel strategy for fabrication,activation and cleaning of fully 3D printed flexible planar electrochemical platforms

In recent years, 3D printing of carbon-based conductive filaments has received growing attention for assembling electrodes to be used in a wide variety of electroanalytical devices and applications. Despite the large amount of work present in literature concerning the development of three-dimensional (3D) conductive structures, its potential as dry deposition method for assembling two-dimensional (2D) electrodes to be used in planar configuration is still largely unexplored. In fact, the possibility to rapidly change the geometry of the electrochemical circuits, associated with the reduction of waste and the absence of solvents, which are instead important components of ink and paste formulations, makes this strategy a valid green and efficient alternative to other deposition approaches such as screen-printing technology. We report here a rapid and solvent-free method for assembling fully 3D printed flexible planar electroanalytical platforms (3DEPs) to be used with microliters of liquid. At the same time, a novel protocol for the surface pre-treatment of 3D printed electrodes based on ultrasonication in aqueous NaOH solution followed by electrochemical activation using the same medium, is presented. In addition, the same procedure has proved to be efficient for cleaning the electrode surface after electrochemical passivation, thus confirming the validity of both time-efficient and environmentally-friendly assembling and activation/cleaning procedures developed which allow efficient and reusable electrodes to be produced. Finally, 3DEPs were tested by a proof-of-concept quantification of a commonly used food dye (Brilliant Blue, E-133) in commercial solutions used for homemade food coloring.     

Mechanical evaluation of polymeric filaments and their corresponding 3D printed samples

3D printing technologies permits to produce functional parts with complex geometries, optimized topologies or enhanced internal structures. The relationship between mechanical performance and manufacturing parameters should be exhaustively analyzed to warrant the long term success of printed products. In this work, the mechanical performance of filaments based on acrylonitrile butadiene styrene (ABS), polylactic acid (PLA) and polylactic acid/polyhydroxyalkanoate (PLA/PHA) was investigated and also compared with their corresponding 3D printed samples. In general, the specimen dimensional deviations were found to be within the tolerances defined by the standard testing protocols. Density values revealed a high level of filament fusion promoting a nearly solid internal structure. The filaments exhibited improved tensile performance with respect to their corresponding printed samples. Tensile and bending performance looked quite independent of the raster angle. Izod impact behavior was increased, for ABS systems printed with the ±45° raster orientation. Quasi-static fracture tests displayed improved crack initiation resistance with the 0°/90° raster angle. The crack propagation observed for the ±45° specimens, through the bonding of the inter-layers, suggests weak entanglements.     

3D打印便携式凝胶电泳装置用于蛋白质的快速检测

随着现场分析对于快速、便携和经济型检测的需求,分析仪器的便携化和微型化备受关注。3D打印技术的不断发展,将会极大推动小型化、便携式实验设备的开发和研制。分析仪器的微型化有助于促进资源不足地区在医疗现场、食品安全和环境污染等方面的现场监测。目前,用于蛋白质分离的凝胶电泳装置多为实验室用小型化分析仪器,可用于现场快速分离蛋白质的小型化仪器尚未见报道。该研究设计加工了一款便携式凝胶电泳装置,用于蛋白质的快速分离检测。首先,通过3D打印加工的凝胶电泳装置可在实验室内方便、快捷、低成本的复制。其次,通过对预染蛋白质相对分子质量标准的分离测试,对该系统结构进行优化。优化后该凝胶电泳装置电泳槽的尺寸仅为15 mm×20 mm×17 mm,采用3D打印技术可在5 h内加工完成,耗费打印材料10 mL。正负极所用电泳缓冲液共需4 mL,所使用的25 V锂电池可实现100 h左右的工作时间。装置优化后可实现蛋白质的快速高效分离。随后,在5种常用蛋白质相对分子质量标准的分离中,该装置与商业化平板凝胶电泳分离效果相当,同时具备更快的分离速度。该研究在便携式凝胶电泳装置的开发及其在蛋白质快速分离方面取得了初步成...     

High-speed on-demand 3D printed bioresorbable vascular scaffolds

Recent development of the high-resolution Micro-Continuous Liquid Interface Production (μCLIP) process has enabled 3D printing of biomedical devices with micron-scale precision. Despite our recent success in demonstrating fabrication of bioresorbable vascular scaffolds (BVS) via μCLIP, key technical obstacles remain. Specifically, achieving comparable radial stiffness to nitinol stents required strut thickness of 400 μm. Such large struts would negatively affect blood flow through smaller coronary vessels. Low printing speed also made the process impractical for potential on-demand fabrication of patient-specific BVSs. Lack of a systematic optimization strategy capturing the sophisticated process-materials-performance dependencies impedes development of on-demand fabrication of BVSs and other biomedical devices. Herein, we developed a systematic method to optimize the entangled process parameters, such as materials strength/stiffness, exposure dosage, and fabrication speed. A dedicated speed working curve method was developed to calibrate the μCLIP process, which allowed experimental determination of dimensionally-accurate fabrication parameters. Composition of the citric acid-based bioresorbable ink (B-Ink?) was optimized to maximize BVS radial stiffness, allowing scaffold struts at clinically-relevant sizes. Through the described dual optimization, we have successfully fabricated BVSs with radial stiffness comparable to nitinol stents and strut thickness of 150 μm, which is comparable to the ABSORB GT1BVS. Fabrication of 2-cm long BVS with 5 μm, 10 μm, and 15 μm layer slicing can now be accomplished within 26.5, 15.3, and 11.3 min, respectively. The reported process optimization methods and high-speed, high-resolution 3D printing capability demonstrate a promising solution for on-demand fabrication of patient-specific biomedical devices.     

Development of 3D printed mesofluidic devices to elute and concentrate DNA

To understand structural variation for personal genomics, an extensive ensemble of large DNA molecules will be required to span large structural variations. Nanocoding, a whole‐genome analysis platform, can analyze large DNA molecules for the construction of physical restriction maps of entire genomes. However, handling of large DNA is difficult and a system is needed to concentrate large DNA molecules, while keeping the molecules intact. Insert technology was developed to protect large DNA molecules during routine cell lysis and molecular biology techniques. However, eluting and concentrating DNA molecules has been difficult in the past. Utilizing 3D printed mesofluidic device, a proof of principle system was developed to elute and concentrate lambda DNA molecules at the interface between a solution and a poly‐acrylamide roadblock. The matrix allowed buffer solution to move through the pores in the matrix; however, it slowed down the progression of DNA in the matrix, since the molecules were so large and the pore size was small. Using fluorescence intensity of the insert, 84% of DNA was eluted from the insert and 45% of DNA was recovered in solution from the eluted DNA. DNA recovered was digested with a restriction enzyme to determine that the DNA molecules remained full length during the elution and concentration of DNA.     

Non‐oxidized graphene/elastomer composite films for wearable strain and pressure sensors with ultra‐high flexibility and sensitivity

It remains challenging to prepare wearable strain and pressure sensors with excellent mechanical properties, ultra‐high flexibility and sensitivity. Electrically conductive graphene platelets (GnPs) with high structural integrity are used in making a composite film fabricated using robust fabrication techniques. The gauge factor for the strain is up to 100 at 0%‐5% strain and 50 at 5%‐30% strain, and the sensitivity to pressure is 2.7×10^‐2 kPa^‐1 between 0 and 10 kPa and 1.5×10^‐4 kPa^‐1 between 300 and 1000 kPa. In addition, the flexible sensor demonstrates good repeatability and durability after 1000 cycles of tensile and compression tests. The flexible sensor has fast response ability and a wide operating temperature range, suggesting the excellent response to temperature. The flexible sensor is applied in monitoring several human motions as a wearable device with high accuracy. The ability to detect strain, pressure and temperature of the flexible sensor extends its applications to multifunctional wearable devices.     

用于柔性应变传感器的离子凝胶的研究进展

随着生活智能化和生产数字化的发展,人们对于柔性传感器、柔性储能器件、柔性显示屏等柔性电子器件的需求和要求逐渐提升,这迫切需要开发具有优良拉伸性能、高透明度和适用温度范围大的柔性导电材料。离子凝胶是一种将离子液体限制在固态三维网络结构的导电弹性材料,其在耐热性、稳定性和力学性能等方面有着明显优势,在柔性电子器件的制造中有着巨大应用潜力。本文将从构成离子凝胶的固态三维网络的分类、结构与性质的改进来综述离子凝胶在柔性应变传感器的研究进展并对离子凝胶的研究发展趋势进行展望。     

Dimensional considerations on the mechanical properties of 3D printed polymer parts

Additive manufacturing offers a useful and accessible tool for prototyping and manufacturing small volume functional parts. Polylactic acid (PLA) and thermoplastic polyurethane (TPU) are amongst the most commonly used materials. Characterising 3D printed PLA and TPU is potentially important for both designing and finite element modelling of functional parts. This work explores the mechanical properties of additively manufactured PLA/TPU specimens with consideration to design parameters including size, and infill percentage. PLA/TPU specimens are 3D-printed in selected ISO standard geometries with 20%, 60%, 100% infill percentage. Tensile and compression test results suggest that traditional ISO testing standards might be insufficient in characterising 3D printed materials for finite element modelling or application purposes. Infill percentage in combination to design size, may significantly affect the mechanical performance of 3D printed parts. Dimensional variation may cause inhomogeneity in mechanical properties between large and small cross section areas of the same part. The effect was reduced in small cross section parts where reducing the nominal infill had less effect on the resulting specimens. The results suggest that for 3D printed functional parts with significant dimensional differences between sections, the material properties are not necessarily homogeneous. This consideration may be significant for designers using 3D printing for applications, which include mechanical loading.     

Multifunctional flexible and stretchable polyurethane/carbon nanotube strain sensor for human breath monitoring

Flexible and stretchable polyurethane/carbon nanotube composite with strain detection ability was used for human breath monitoring. The composite material consisted of a network of multiwalled carbon nanotubes and thermoplastic high elastic polyurethane. It was found that elongation of the composite led to a macroscopic increase in electrical resistance, which can be used as a principle for applied strain detection. This detection was reversible, durable, and sensitive with gauge factor reaching very promising value, as, for example, ~46 at applied deformation of 8.7%. Further, the composite could be elongated to very large extend of deformation without discontinuity in measured resistance change reaching gauge factor ~ 450 at composite mechanical break at ~300% of strain. Sensor durability was also confirmed by sine wave deformation cycling when any decrease in the sensor properties for more than 10³ cycles was observed. Simultaneously, the prepared composite possessed other utility properties also and was considered as multifunctional when it was tested as an organic solvent vapor sensor, an element for Joule heating and finally as a microstrip antenna.     

Effect of surface texturing on friction behaviour of 3D printed polylactic acid (PLA)

Additive manufacturing is gaining a remarkable importance in manufacturing industries because of the ability to build parts with complex and intricate shapes. The most widely used material in additive manufacturing is the polymer. In this paper, circular textures have been 3D printed on the surface of Polylactic Acid (PLA) polymer using fused deposition modelling technique. Experiments were performed under dry and lubricated conditions by varying the texture size. The results were obtained for high and low speeds with varying loads of 10, 20, 30, 40 and 50 N. It was observed that coefficient of friction was minimum for texture T₂ at both high and low speeds under dry sliding conditions. This is due to the less real area of contact than texture T₁ and more effective formation of transfer film in case of texture T_3. The entrapment of wear debris is more effective which helps in the formation of transfer layer that acts as solid lubricant. Under lubricated conditions, it was observed that for low speed, texture T₃ has least coefficient of friction while at high speed texture T₁ resulted in the minimum coefficient of friction. This is mainly due to the more retention of lubricating oil for texture T₃ at low speed in comparison to the high speed. Surface analysis carried out for all the textures under dry sliding conditions revealed that the wear is mainly to adhesive and abrasive action.     

Reduced surface adsorption in 3D printed acrylonitrile butadiene styrene micro free-flow electrophoresis devices

We have 3D printed and fabricated micro free-flow electrophoresis (µFFE) devices in acrylonitrile butadiene styrene (ABS) that exhibit minimal surface adsorption without requiring additional surface coatings or specialized buffer additives. 2D, nano LC–micro free flow electrophoresis (2D nLC × µFFE) separations were used to assess both spatial and temporal broadening as peaks eluted through the separation channel. Minimal broadening due to wall adsorption was observed in either the spatial or temporal dimensions during separations of rhodamine 110, rhodamine 123, and fluorescein. Surface adsorption was observed in separations of Chromeo P503 labeled myoglobin and cytochrome c but was significantly reduced compared to previously reported glass devices. Peak widths of < 30 s were observed for both proteins. For comparison, Chromeo P503 labeled myoglobin and cytochrome c adsorb strongly to the surface of glass µFFE devices resulting in peak widths >20 min. A 2D nLC × µFFE separation of a Chromeo P503 labeled tryptic digest of BSA was performed to demonstrate the high peak capacity possible due to the low surface adsorption in the 3D printed ABS devices, even in the absence of surface coatings or buffer additives.     

Highly sensitive,stretchable and durable strain sensors based on conductive double-network polymer hydrogels

Hydrogel-based strain sensors have been attracting immense attention for wearable electronic devices owing to their intrinsic soft characteristics and flexibility. However, developing hydrogel sensors with hightensile strength, stretchability, and strain sensitivity remains a great challenge. Herein, we report a technique to synthesize highly sensitive hydrogel-based strain sensors by integrating carbon nanofibers (CNFs) with a double-network (DN) polymer hydrogel matrix comprising of a physically cross-linked agar network and a covalently cross-linked polyacrylamide (PAAm) network. The resultant nanocomposite sensors display superior piezoresistive sensitivity with a hightrue gauge factor (GF_T = 1.78) at an ultrahigh strain of 1,000%, a fast response time and linear correlation of ln(R/R₀) and ln(L/L₀) up to 1,000% strain. Most significantly, these sensors possess highmechanical strength (~0.6 MPa) and superb durability (>1,000 cycles at strain of 100%), stemming from the effective energy dissipation mechanism of the first agar network acting as sacrificial bonds and the CNFs serving as dynamic nanofillers. The combination of highstrain sensitivity and ultrahigh stretchability of hydrogel sensors makes it possible to sense both small mechanical deformations induced by human motions and large strain up to 1,000%.     

Fracture resistance measurement of fused deposition modeling 3D printed polymers

A method is presented to characterize the fracture resistance and interlayer adhesion of fused deposition modeling (FDM) 3D printed materials. Double cantilever beam (DCB) specimens of acrylonitrile butadiene styrene (ABS) were designed and printed with a precrack at the layers' interface. The DCBs were loaded in an opening mode and the load-displacement curves were synchronized with the optical visualization of the crack tip to detect the critical load at the crack initiation. A finite element model, coupled with J-integral method and fracture surface analysis was then developed to obtain the apparent fracture resistance (J_cr,a) and the interlayer fracture resistance (J_cr,i), as a measure of the interlayer adhesion. The maximum J_cr,i was measured to be 4017 J/m², a value close to the fracture resistance of bulk ABS. Both J_cr,a and J_cr,i increased with the printing temperature. This method can find a great importance in the structural applications of printed materials.