4D printing of PLA/PCL shape memory composites with controllable sequential deformation

Shape memory polymers(SMPs)are a promising class of materials for biomedical applications due to their favorable mechanical properties,fast response,and good biocompatibility.However,it is difficult to achieve controllable sequential shape change for most SMPs due to their high deformation temperature and the simplex deformation process.Herein,shape memory composites based on polylactic acid(PLA)matrix and semi-crystalline linear polymer polycaprolactone(PCL)are fabricated using 4D printing technology.Compared with pure PLA,with the rise of PCL content,the 4D-printed PLA/PCL composites show decreased glass transition temperature(Tg)from 67.2 to 55.2°C.Through the precise control of the deformation condition,controllable sequential deformation with an outstanding shape memory effect can be achieved for the PLA/PCL shape memory composites.The response time of shape recovery is less than 1.2 s,and the shape fixation/recov-ery rates are above 92%.In order to simulate sequential petal opening and sequential drug releasing effects,a double-layer bionic flower and a drug release device,respectively,are presented by assembling PLA/PCL samples with different PLA/PCL ratios.The results indicate the potential applications of 4D-printed PLA/PCL composites in the field of bio-inspired robotics and biomedical devices.

Bioinspired flexible piezoresistive sensor for high-sensitivity detection of broad pressure range

The human skin has the ability to sense tactile touch and a great range of pressures.Therefore,in prosthetic or robotic systems,it is necessary to prepare pressure sensors with high sensitivity in a wide measurement range to provide human-like tactile sensation.Herein,we developed a flexible piezoresistive pressure sensor that is highly sensitive in a broad pressure range by using lotus leaf micropatterned polydimethylsiloxane and multilayer superposition.By superposing four layers of micropatterned constructive substrates,the multilayer piezoresistive pressure sensor achieves a broad pressure range of 312 kPa,a high sensitivity of 2.525 kPa^(−1),a low limit of detection(LOD)of<12 Pa,and a fast response time of 45 ms.Compared with the traditional flexible pressure sensor,the pressure range of this sensor can be increased by at least an order of magnitude.The flexible piezoresistive pressure sensor also shows high robustness:after testing for at least 1000 cycles,it shows no sign of fatigue.More importantly,these sensors can be potentially applied in various human motion detection scenarios,including tiny pulse monitoring,throat vibration detection,and large under-feet pressure sensing.The proposed fabrication strategy may guide the design of other kinds of multifunctional sensors to improve the detection performance.

PEEK modified PLA shape memory blends:towards enhanced mechanical and deformation properties

Polylactic acid(PLA)is one of the most promising shape memory polymers with outstanding biocompatibility,while poly(ether ether ketone)(PEEK)is a special engineering plastic with excellent mechanical performance.In this work,PEEK was selected to modify PLA,and a series of PLA blended with different PEEK contents(PLA/PEEK blends)were obtained.The effects of PEEK on thermodynamic,mechanical and shape memory properties of PLA/PEEK blends were investigated.The results showed that the thermal stabillity of the PL A/PEEK blend was improved with the PEEK content increase.The tensile strength reached the highest value of 20.6 MPa when the PEEK content was 10%.While the best shape memory performance occurred with the PEEK content of 15%,the shape recovery time was less than 2 s,and the shape fixation/recovery ratio was more than 99%.Furthermore,the programmable mimetic flower opening process was achieved by using PLA/PEEK blends with different PEEK content ratios.The above results indicated that the blend of an appropriate proportion of PEEK had positive effects on mechanical and deformation performances of PLA.

High-performance Multilayer Flexible Piezoresistive Pressure Sensor with Bionic Hierarchical and Anisotropic Structure

Flexible pressure sensor that enables detection of multimodal signals has greater advantages in human–computer interaction,medical/health care,and other applications.To make a versatile flexible pressure sensor,hierarchical and anisotropy structure are key features to improve sensing performance and realize multi-signal detection.However,traditional flexible sensors usually have narrow linear range and single signal detection capability.Herein,a highly sensitive flexible piezoresistive pressure sensor which has broad linear range of pressure is developed by replicating one dimensional microstructures from reed leaf and using multilayer superposition of micropatterned polydimethylsiloxane(m-PDMS).Through superposing 4 layers of parallel micropatterned constructive substrates,the multilayer piezoresistive pressure sensor exhibits a high sensitivity of 2.54 kPa?1,a fast response time of 30 ms,and a broad linear range of 107 kPa.The flexible piezoresistive pressure sensor is also highly robust:there is no fatigue after testing for at least 1000 cycles.Due to the specific anisotropy of the micro-structure,the sensor can measure the tangential force in different directions.It permits multimode signal detection,including pressure,tangential force,and deformation.The versatile flexible pressure sensor enables effective monitoring of multisignals,it reveals great potential for medical and health care,flexible human–computer interaction,and intelligent robot.

二苯乙烯基蒽聚集诱导发光材料体系的研究进展

具有聚集诱导发光(AIE)性质的有机荧光分子由于其扭曲的分子构型,在聚集态或固态表现出显著增强的荧光发射,避免了传统有机荧光分子的浓度猝灭现象,因而在光电器件、生物传感等领域有着广泛的应用.本文着重介绍了具有AIE性质的二苯乙烯基蒽(DSA)衍生物及其在高效固态发光材料、刺激响应材料、生物成像和生物与化学传感等领域的研究进展.

A cyanostilbene-based molecule with aggregation-induced emission properties: amplified spontaneous emission, protonation effect and electroluminescence

A terpyridine-substituted cyanostilbene derivative(Z)-2-(4′-([2,2′:6′,2″-terpyridin]-4′-yl)-[1,1′-biphenyl]-4-yl)-3-phenylacrylonitrile(CNSTPy) was synthesized and characterized. The compound exhibits remarkable aggregation-induced emission phenomenon and its single crystal shows a blue emission with fluorescent efficiency as high as 45%. Based on its aggregation state behavior, multiple applications towards exploring its lasing, fluorescence switching and electroluminescence properties were realized. Amplified spontaneous emission(ASE) was observed from the crystal and verified by the variable pump strip method, with a threshold value of ～1.5 m J cm^(-2). The protonation/deprotonation processes accompanied by the formation of different molecular aggregation structure result in the distinct blue and yellow emissions. Additionally, the molecule also shows a moderate electroluminescence performance.

Organic molecular aggregates:From aggregation structure to emission property

Organic molecular aggregates have attracted widespread attention over the past decade owing to their unique optoelectronic properties in the aggregate state,which mainly involves the effects of aggregation structure as well as molecular packing mode.Although many examples of H-and J-aggregates defined by molecular exciton model have been found,there are also other types of unconventional aggregates,especially for aggregation-induced emission(AIE)system.In this review,the recent progress of some examples of basic and novel aggregate forms,as well as coassembled forms,presenting distinctive optical features,such as optical waveguide and polarization emission,polymorph-dependent emission and stimuli-responsive luminescence are presented.The systematic insight into the relationship between the aggregation structure and emission property is discussed.Guidelines are therefore anticipated and will direct the future preprogramming molecular design so as to fine-tune the emission feature through a specific aggregation model for developing organic molecular aggregates with desirable optoelectronic properties.