Excellent Shape Memory Effect Research Articles

Shape memory and shape recovery characterization of thermoplastic urethane

ABSTRACT Polyurethane shape memory polymer, as a smart material, has been becoming more and more popular due to its greater multifunctionality in various industrial and biomedical applications. Here, the authors reported the characterization, and comprehensive methodology and acquired the results of thermoplastic urethane (SMTPU) as a shape memory polymer, with 35°C as the glass transition temperature, by examining its creep. This smart polymer exhibits excellent shape memory behaviour due to its steady, chemically cross-linked network. Such behaviour of shape memory polymer determines its usability in various functional applications. Furthermore, the activation temperature range of SMPTPU is close to body temperature and room temperature as well, so it can be employed in more demanding industrial applications. Thus, it becomes essential to investigate the shape-changing/memory behaviour of commercial SMTPU. A quantitative analysis was done to determine the effects of programming temperature, maximum uniaxial strain, and compressive strain on shape memory characteristics viz. the shape recovery ratios and shape fixity ratios. Along with the excellent shape memory effect, this material also exhibits high creep and elasticity at room temperature, indicating that it may be used for various industrial and biomedical applications.

Thermadapt shape memory AB-copolymer networks exhibiting tunable properties and kinetics of topological rearrangement

Polycaprolactone (PCL) based thermadapt shape memory polymers (SMPs) have exhibited superiority over traditional analogues by allowing shape-editing to reconfigure permanent shapes into more complex geometrical shapes, driven by the pursuit of advanced functionalities for high-value applications. Nevertheless, although transesterification-based PCL networks exhibit impressive shape reconfigurability as prototypical thermadapt SMPs, there are still constraints in terms of the need for significant flexibility in architectural adjustment and property modulation without compromising reconfigurability, which would be relevant for practical applications. Here, we present a simple yet efficient strategy to create PCL-based thermadapt SMPs that possess a highly tunable structure and properties, as well as exceptional reconfigurability. The family of SMPs, called thermadapt shape memory AB copolymer networks (AB-CPNs), was synthesized by UV-initiated free radical polymerization between PCL diacrylate as crosslinker and 4-hydroxybutyl acrylate (HBA) as comonomer. The thermadapt AB-CPNs allow for significant structural alterations with 0 wt% to 70 wt% HBA while maintaining excellent shape memory and shape reconfigurability effects. The insertion of the polymer segment containing free hydroxyls not only promises tunable material properties but also makes network rearrangement easier since dynamic hydroxy-ester bonds are more active than dynamic ester-ester bonds. It is envisioned that the thermadapt shape memory AB-CPNs with widely tunable macroscopic properties will drive progress in the real-world applications of SMP devices with complicated geometric structures.

Construction of CO2‐based thermoplastic elastomer via combining aliphatic polycarbonate and polyamide: A multiblock copolymer PPC‐mb‐PA6

AbstractA CO2‐based thermoplastic elastomer, poly(propylene carbonate)‐multiblock‐polyamide6 (PPC‐mb‐PA6) copolymer, was constructed through coupling amorphous/soft PPC blocks with crystalline/hard PA6 blocks. The PPC‐mb‐PA6 copolymers with different block length pairs were designed and synthesized, and then fully characterized by structural, thermal, and mechanical analysis. The proton nuclear magnetic resonance (1H‐NMR), diffusion ordered spectroscopy (DOSY), heteronuclear multiple‐bond correlation (HMBC) and gel permeation chromatography (GPC) results confirm that the multiblock sequence structure of PPC‐mb‐PA6. The differential scanning calorimetry (DSC) tests show that all PPC‐mb‐PA6s possess melting points around 179–206°C. The thermal and mechanical analysis indicates improved service temperatures (T5% up to 270°C) and tensile strength ranging from 15.8 to 39.6 MPa with higher PA6 content. The dynamic mechanical analysis demonstrates excellent shape memory effect of PPC‐mb‐PA6 with thermal stimuli responsiveness derived from the micro phase separation between soft PPC and hard PA6 domains. And the characteristic strain fixity parameter (Rf) and deformation recovery rate (Rr) are 98% and 100%, respectively, which are comparable with other excellent shape memory polymers.

Corrosion and tribocorrosion resistance of superhydrophobic LPBF-NiTi alloys surface fabricated by nanosecond laser and ultrasonic fluorination

NiTi alloys have been extensively studied for their excellent super-elasticity (SE) and shape memory effects (SME). With the development of laser powder bed fusion (LPBF), it is possible to process the complex structure of NiTi alloy, which results in the mechanical properties of LPBF-NiTi alloys receiving great attention. However, the processing method is different from the traditional one, which not only has an impact on the mechanical properties but also seriously affects the anti-corrosion resistance and causes a substantial deterioration. In the research work of this paper, nanosecond laser processing was used to fabricate the bionic mastoid-shaped micro-nano structure on the LPBF-NiTi alloys. An efficient and convenient ultrasonic fluorination treatment was used to achieve the full surface coverage of FAS-17 in 10 min, and the superhydrophobic LPBF-NiTi alloy surface (CA ~ 157°) was successfully achieved. The constructed superhydrophobic LPBF-NiTi alloy surface exhibits excellent anti-corrosion resistance compared with the original surface, and the icorr from (4.42 ± 0.5) × 10−7 A·cm−2 reduced to (3.21 ± 0.5) × 10−9 A·cm−2. Meanwhile, the superhydrophobic surface showed outstanding stability in the 15-day immersion test n 3.5 wt% NaCl solution. And it is also stable after the tribocorrosion tests in 3.5 wt% NaCl solution at 1 N and 5 N pressures. The remarkable anti-corrosion resistance and stability of the superhydrophobic surface can be attributed to the micro-nano structure rich in the TiO2 oxide layer, the air layer formed by the superhydrophobic surface insulates the corrosive liquid and the stable hydrophobic agent film.

From dynamic molecular bridging to achieving Healable, recyclable, photo/magnetic-responsive shape memory EVA@Fe3O4 hybrid network

Dynamic networks show great potential in shape memory polymers (SMPs) not only because they can display excellent shape memory effects (SMEs), but also possess good recyclability and reprocessability due to their dynamic features. Additionally, multiple responsiveness is also an attractive characteristic for SMPs to meet diverse applications. while incorporating functional fillers into SMPs has been explored as a feasible solution, their performance relies heavily on the interface interactions. In this study, we present a facile strategy to construct a dynamic hybrid network that combines excellent multi-responsive SMEs and recyclability. This is achieved by using dihydroxyphenylpropionic acid (CA) to bridge EVA chains and multi-responsive Fe3O4 particles through transesterification and metal-ligand coordination. The hybrid networks exhibited favorable dynamic characteristics. Specifically, EVA-CA@Fe3O410% demonstrates remarkable thermal and light healing efficiency, exhibiting a mechanical strength recovery (ησ) of 102% and elongation at break recovery (ηε) of 95% after healing at 140 °C for 2 h, and a ησ of 107% and ηε of 92% when healing under near-infrared light (NIR) irradiation for 2 min, respectively. Furthermore, good recyclability was demonstrated by maintaining mechanical performance after three reprocessing cycles. Moreover, the hybrid networks exhibited excellent SMEs, enabling multifunctional deformation triggered by heat, NIR and alternating magnetic fields.

Graphene Oxide-Enhanced and Dynamically Crosslinked Bio-Elastomer for Poly(lactic acid) Modification.

Being a bio-sourced and biodegradable polymer, polylactic acid (PLA) has been considered as one of the most promising substitutes for petroleum-based plastics. However, its wide application is greatly limited by its very poor ductility, which has driven PLA-toughening modifications to be a topic of increasing research interest in the past decade. Toughening enhancement is achieved often at the cost of a large sacrifice in strength, with the toughness-strength trade-off having remained as one of the main bottlenecks of PLA modification. In the present study, a bio-elastomeric material of epoxidized soybean oil (ESO) crosslinked with sebacic acid (SA) and enhanced by graphene oxide (GO) nanoparticles (NPs) was employed to toughen PLA with the purpose of simultaneously preserving strength and achieving additional functions. The even dispersion of GO NPs in ESO was aided by ultrasonication and guaranteed during the following ESO-SA crosslinking with GO participating in the carboxyl-epoxy reaction with both ESO and SA, resulting in a nanoparticle-enhanced and dynamically crosslinked elastomer (GESO) via a β-hydroxy ester. GESO was then melt-blended with PLA, with the interfacial reaction between ESO and PLA offering good compatibility. The blend morphology, and thermal and mechanical properties, etc., were evaluated and GESO was found to significantly toughen PLA while preserving its strength, with the GO loading optimized at ~0.67 wt%, which gave an elongation at break of ~274.5% and impact strength of ~10.2 kJ/m2, being 31 times and 2.5 times higher than pure PLA, respectively. Moreover, thanks to the presence of dynamic crosslinks and GO NPs, the PLA-GESO blends exhibited excellent shape memory effect and antistatic properties.

Fabrication and properties of recyclable tung oil–based polymer coatings based on dual cross-linked dynamic covalent polymer networks

The exploration of reprocessability and high-adhesion biomass polymer coatings is in line with the concept of green materials and is conducive to energy conservation and environmental protection. Here, a series of novel recyclable tung oil–based polymer coatings based on dual cross-linked dynamic covalent networks were reported. Tung oil polymerized maleic anhydride (TOA) was firstly prepared and further reacted with furfuryl alcohol. Then tung oil-polymerized maleic furanol ester (TOAFA) containing reactive conjugated double bond and carboxyl groups was prepared. FTIR and 1H NMR demonstrated the reactive monomer TOAFA was successfully synthesized. Then TOAFA was cross-linked with bismaleimide and different epoxy resins to fabricate target polymer networks based on dynamic Diels-Alder(D-A) bonds and dynamic transesterification. The shape memory, reprocessing, and mechanical and thermal stability of the copolymerized systems with different crosslinking states were investigated. The coating performances were characterized with solvent resistance, adhesion strength, hardness and glossiness tests. It was found that the dynamic D-A covalent bonds were perfectly combined with transesterification in the polymerization systems. The copolymerized systems possessed excellent thermal stability and mechanical properties. The rigid and flexible properties of the polymer networks can be controlled by adjusting the component weight ratios and the type of epoxy resin in the polymerization system. The rigid polymerization system had the highest tensile strength of 28 MPa, and its elongation at break was up to 57 % of the flexible polymerization system. Coating adhesion test showed the adhesion property reached level 1. The polymer coatings displayed excellent solvent corrosion resistance, and relative high gloss. The polymer networks also showed certain reprocessing performance and excellent shape memory effect.

Shape memory behavior of 4D printed CF/PEKK high temperature composite under subsequent thermomechanical cycles

Shape memory effect (SME) in high temperature polymers (HTPs) has great significance in space for making self-deployable structures, needing high strength and stiffness during operation, signifying the necessity of exploring HTP composite with SME. This work investigates the SME of 4D printed carbon fiber/polyether ketone ketone (CF/PEKK) HTP composite under subsequent thermomechanical cycles for the first time. Scanning electron microscopy (SEM) revealed a uniform distribution of CFs in the developed composite, the extruded composite filament, and the composite prints with seamless raster and layer deposition, confirming a suitable selection of processing parameters. The CF/PEKK composite prints exhibited an excellent shape fixity, Rf = 90 % and 91 %, and shape recovery, Rr = 96 % and 89 % in the first and the tenth cycle, respectively. A significant loss of 7 % in Rr is observed in the tenth cycle. Glass transition (Tg) and degradation temperature (Td) of the CF/PEKK composite prints are observed to be 162 °C and 568 °C, while storage modulus is found 157.69 % and 38.69 % higher than the existing PEKK and PEEK, respectively. This study revealed an excellent SME of 4D printed CF/PEKK composite with outstanding Tg and Td, showing great potential for space applications.

PLLA/(MWCNTs-ZnO)@PDA composite with NIR-light induced shape memory effect, antibacterial properties and 3D printability

PLLA based shape-memory polymer composites with multifunctions have attracted growing attention in biomedical applications. Generally, a single nanofiller has the problem of insufficient functionalization and easy aggregation. Therefore, we design and fabricate polydopamine (PDA) surface modified MWCNTs-ZnO hybrid nanostructure ((MWCNTs-ZnO)@PDA). The dispersion of (MWCNTs-ZnO)@PDA in PLLA is improved in comparison with the pristine MWCNTs or ZnO. The results indicate that the (MWCNTs-ZnO)@PDA nanosystem shows a synergistic effect on the mechanical properties and photothermal properties of the composites. Comparative analysis with neat PLLA demonstrates a remarkable 17% increase in tensile strength and a 19% increase in elongation at break for PLLA/(MWCNTs-ZnO)@PDA composite. Additionally, the composites exhibit excellent NIR light-induced shape memory effects with a shape recovery ratio reaching 100%. Moreover, PLLA/(MWCNTs-ZnO)@PDA composites show favorable antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Furthermore, the polymer composites display good 3D printability, and the 3D-printed porous scaffold possesses high compressive strength and modulus. Also, the PLLA/(MCNTs-ZnO)@PDA scaffold can be compressed into a compact size and recover its original shape under NIR light irradiation. This work provides an approach to prepare novel shape-memory polymer composites with multifunctions including high strength, light-induced shape-recovery, antibacterial properties and printability.

Enhancing the thermal stability and recoverability of ZrCu-based shape memory alloys via interstitial doping

ZrCu-based shape memory alloys (SMAs) are regarded as emerging smart materials with high phase transformation temperatures. However, unfavorable thermal stability and poor strain recovery rate hinder commercial applications. Herein, these issues were addressed by doping interstitial B atoms, and the impacts of B content on microstructure, martensitic transformation behavior and properties of ZrCu-based SMAs were systematically investigated. It was shown that (Zr50Cu25Ni7.5Co17.5)99.98B0.02 SMAs possessed excellent thermal stability and shape memory effect. The change of martensitic transformation temperature for this alloy was 15.7 °C after several cycles. The shape recovery rate reached 92.5 % at 8 % compressive pre-strain, which was attributed to the de-twinning of (0 0 1) compound twins and the appearance of (1 1 1) type I twins. Furthermore, it was elucidated for the first time by first-principles calculations that B atoms were covalently bonded with Zr and Cu atoms occupying the octahedral interstitial positions in the B19′ and Cm phases. This study offers an available pathway to exploit efficient and advanced products.

Development of vanillin-based crosslinking agent with phase-locked dynamic imine bonds for shape-memory polyurethanes

Scientists have gained so much attention due to one of polyurethane's tuneable and unique characteristics, i.e., the shape-memory effect. But, the simplistic fabrication of such materials persists a challenging work. In the current work, we report the synthesis and detailed characterization of shape-memory polyurethane obtained by incorporating lower concentrations of imine bonds, which readily undergo phase-locking systems beneficial for microphase separation. A symmetric imine moiety (DIM) was designed through the simple Schiff-base reaction of naphthalene diamine and vanillin. The tensile strength of the films reached up to 30 MPa with an %elongation of 87% by tuning the hard segment content and the concentration of imine bonds. Also, in the meantime, the films showed excellent shape memory effect, where the shape could recover its original form within 2 s at the highest loading of DIM. The remarkable balance between the mechanical properties and the shape memory effect could be associated with the two main factors. Firstly, incorporating symmetrical and rigid CN along with the naphthalene promoted the microphase separation and smoothened the orientation of the chain segments at the strain-induced crystallization at lower temperatures. Secondly, the phase locking occurred at lowered temperatures due to dynamic imine exchange reaction and H-bonding. The phase recovery started, and chains settled at their original positions once the temperature was elevated.

Analyses of the sliding wear behavior of NiTi shape memory alloys fabricated by laser powder bed fusion based on orthogonal experiments

Laser powder bed fusion of NiTi (LPBF-NiTi) alloys is gaining increasing attention and applications because of its flexible design for complex structures with excellent superelasticity and shape memory effects. Their wear behavior has a strong influence on the serviceability and safety, but the effects of their usage condition on the wear behavior are not clarified clearly. In the present work, the wear resistance of LPBF-NiTi (55.4 wt%Ni) alloys against 100Cr6 steel on a ball-on-slab tribometer and its response to sliding speed, normal load and sliding time were studied through orthogonal experiments. The results confirm that the wear rate of LPBF-NiTi alloys ranges from 1.1–2.5 × 10−3 mm3/m, which is comparable to that of NiTi alloys fabricated by conventional methods. In addition, the sliding speed has the largest influence with a range of 5.1 × 10−5 mm3/Nm, followed by normal load with a range of 4.2 × 10−5 mm3/Nm. The effect of the interaction between the normal load and sliding speed is significantly greater than the effect of the sliding time. Finally, the wear mechanism of the worn surface and microstructure of the subsurface under the wear track were discussed in detail. The dominant wear modes are adhesion, abrasion and delamination.

4D Printing of Biocompatible Scaffolds via In Situ Photo-crosslinking from Shape Memory Copolyesters.

The complexity of surgical treatments for large-area soft tissue injuries makes placing large implants into injury sites challenging. Aliphatic polyesters are often used for scaffold preparation in tissue engineering owing to their excellent biodegradability and biocompatibility. Scaffolds with shape-memory effect (SME) can also avoid large-volume trauma during the implantation. However, the complexity and diversity of diseases require more adaptable and precise processing methods. Four-dimensional (4D) printing, a booming smart material additive manufacturing technology, provides a new opportunity for developing shape memory scaffolds. With the aim of personalized or patient-adaptable soft tissues such as blood vessels, we developed a feasible strategy for fabricating scaffolds with fine architectures using 4D printing crosslinkable shape memory linear copolyesters using fused deposition modeling (FDM). To overcome the weak bonding strength of each printed layer during FDM, a catalyst-free photo-crosslinkable functional group derived from biocompatible cinnamic acid was embedded into the linear copolyesters as in situ crosslinking points during FDM printing. Under ultraviolet-assisted irradiation, the resulting 4D scaffold models demonstrated excellent SME, desirable mechanical performance, and good stability in a water environment owing to the chemical bonding between each layer. Moreover, the excellent biocompatibility of the scaffold was evaluated in vitro and in vivo. The developed composite scaffolds could be used for minimally invasive soft tissue repair.

Structural, mechanical, and thermodynamic properties of Ni–Ti intermetallic compounds: First-principle calculation

Intermetallic compounds were applied widely in the fields of automotive and aerospace because of its excellent shape memory effect. In this work, the structural, mechanical, and thermodynamic properties of Ni–Ti intermetallic compounds are studied by first-principle calculation. The results show that Ti, NiTi3, NiTi2, NiTi, Ni4Ti3, Ni3Ti, Ni4Ti, and Ni are stable based on Born stable criterion. On the mechanical aspect, the bulk modulus of Ni–Ti intermetallic compounds increases with the rising electron density. Their ductility is ranked as follows: NiTi3 > Ni4Ti3 > NiTi2 > Ni4Ti > NiTi > Ni3Ti. And when the ratio of Ni and Ti is 3:1, it is the hardest. In addition, the Ni–Ti intermetallic compounds in this work are anisotropy, except NiTi2. On the thermodynamic aspect, the Debye temperature θD, melting point Tm, and minimum thermal conductivity kmin of Ni–Ti intermetallic compounds increase first and then decrease with the rising content of Ni. The θD and kmin of NiTi3 are the minimum among the Ni–Ti ICs mentioned above, and θD of Ni3Ti and kmin of NiTi are both the maximum. The melting point of Ni3Ti is 1940 K, it is the highest temperature.

Mechanical and shape memory properties of NiTi triply periodic minimal surface structures fabricated by laser powder bed fusion

Porous NiTi lattice structures are widely used in the manufacture of crucial components owing to their excellent shape memory effect, superelasticity, and high damping capacities. However, the specific strength and lightweight characteristics of porous NiTi lattice structures fabricated by conventional technologies are limited by unpredictability. In this work, three types of porous NiTi structures based on triply periodic minimal surface (TPMS) – Diamond, Gyroid, and Primitive – were designed and manufactured by the laser powder bed fusion (LPBF) additive manufacturing process. This work demonstrates LPBF is a feasible and efficient approach to fabricate highly accurate porous NiTi TPMS structures. Moreover, the influence of each of these structures on the mechanical and shape memory properties was investigated. Among the three structures, Gyroid had the smallest volume fraction deviation. Furthermore, the Diamond structure had the largest compressive modulus (782.82 MPa) and ultimate yield strength (163.14 MPa). The Gyroid and Primitive structures exhibit excellent elastic recovery deriving from high values of compressive modulus (662.44 MPa, and 703.29 MPa), and can maintain reliable structural robustness. The Primitive structure exhibited the lowest mechanical properties (37.80 MPa). During the cyclic compression test, Gyroid and Primitive show a smaller unrecovered strain than Diamond. Primitive shows the largest recovered strain during the heating process (6.98%). The higher mechanical flexibility of Primitive structure endows this structure with higher recovery ratio. During the direct compression test, the residual strain exhibits a positive correlation with the loading strain. All three structures exhibit good deformation recovery capability with a strain of 4%. At a strain of 12%, recovered strain during heating became the dominant factor in the recovery of the TPMS structure. Overall, porous NiTi TPMS structures are capable of reversible compressibility composed of rapid elastic recovery and controllable shape memory recovery. The unique performance of porous NiTi TPMS structure fabricated by LPBF renders it a highly efficiency energy-absorbing structure.

Study of Structure and Phase Transformations in Rejuvenated Rapidly Quenched TiNiCu Alloys

Alloys of the quasibinary TiNi-TiCu system manufactured by melt quenching in the form of thin 20–50 μm ribbons have proven to show good potential as materials for the fabrication of micromechanical devices. At high cooling rates (about 106 K/s), this method allows producing high-copper (more than 20 at.%) amorphous alloys which exhibit an excellent shape-memory effect after crystallization. Their properties are known to largely depend on the crystallization conditions and the structure of the initial amorphous material acting as a precursor for the formation of crystal phases. It has been shown recently that the rejuvenation procedure (cryogenic thermocycling) of metallic glasses is one of the most promising methods of improving their properties. In this study, we investigated for the first time the effect of cryogenic thermocycling of rapidly quenched amorphous TiNiCu on the initial state, as well as on structure formation and the phase transformation patterns of subsequent crystallization conducted using various methods. The effect was analyzed utilizing the methods of scanning and transmission electron microscopy, X-ray diffraction analysis, and differential scanning calorimetry. The results show that rejuvenation treatment slightly reduces the glass transition and crystallization onset temperatures and moderately changes the sizes of structural features (grains, martensite plates), the quantity of the martensite phase, and the characteristic temperatures and enthalpy of the martensitic transformation.

A multifunctional hybrid extrinsic–intrinsic self-healing laminated composites

Damage healing in fiber reinforced thermoset polymer composites has been generally divided into intrinsic healing by the polymer itself and extrinsic healing by incorporation of external healing agent. In this study, we propose to use a hybrid extrinsic-intrinsic self-healing strategy to heal delamination in laminated composite induced by low velocity impact. Especially, we propose to use an intrinsic self-healing thermoset vitrimer as an external healing agent, to heal delamination in laminated thermoset polymer composites. To this purpose, we designed and synthesized a new vitrimer, machined it into powders, and strategically sprayed a layer of vitrimer powders at the interface between the laminas during manufacturing. Also, a thermoset shape memory polymer with fire-proof property was used as the matrix. As a result, incorporation of about 3% by volume of vitrimer powders made the laminate exhibit multifunctionalities such as repeated delamination healing, excellent shape memory effect, improved toughness and impact tolerance, and decent fire-proof properties. In particular, the novel vitrimer powder imparted the laminate with first cycle and second cycle delamination healing efficiencies of 98.06% and 85.93%, respectively. The laminate also exhibited high recovery stress of 65.6 MPa. This multifunctional composite laminate has a great potential in various engineering applications, for example, actuators, robotics, deployable structures, and smart fire-proof structures.

Multi-physics modeling for laser powder bed fusion process of NiTi shape memory alloy

Due to its excellent shape memory effect and super elasticity, NiTi Shape Memory Alloy (NiTi SMA) has broad application prospects in aerospace, ship, biomedicine and other fields. Laser powder bed fusion (L-PFB) has proven to be a feasible way to fabricate NiTi with a complex and precise structure. In this study, a 3D transient multi-physics model based on the computational fluid dynamics (CFD) model is proposed, which incorporates the effects of convective heat transfer and radiation heat transfer on the forming quality of parts and mechanical models such as thermal buoyancy. The temperature field and stress field distribution during the L-PBF forming process of NiTi alloy were studied by using this multi-physics model. Furthermore, the influence of different process parameters on the shape of the molten pool was analyzed, and a nonlinear regression equation was proposed to predict the size of the molten pool. The proposed model is verified by experimental results with a prediction error of 3 %−8 %. Both numerical and experimental results demonstrate that under the process parameters of P= 125 W and V= 500 mm/s, the shape of the molten pool is stable and the NiTi single track is continuous. This work illustrates the reliability of the established simulation method and provides a timesaving approach to optimize the L-PFB process parameters of nickel-titanium alloy.

Pulsed laser micro drilling act on Perspex intended for microfluidic devices

An amorphous material with excellent shape memory effect (SME) like Perspex is a versatile material with broad applications in the bio-related field. Moreover, its extravagant properties like biological behavior, antimicrobial capacity, and porosity make it a choice for ophthalmologic devices, drug delivery, and microfluidic-based chromatography. However, its brittleness property and the formation of brittle-ductile transition make it a complex and delicate material for machining processes. A laser beam is an idiosyncratic tool used in engineering to biomedical fields. Compared to other lasers, the CO2 laser has a longer wavelength of 10.6 µm, which makes it the best choice for processing transparent material like Perspex. In this research CO2 laser micro-drilling (CLMD) act has been performed to design micro-holes on Perspex by tailoring the scan tracks of the laser. The movement of scanning tracks was controlled, and the beam functionalities' process windows were handled through adequate parametric settings like scan mode, machining speed, power, and pulsed frequency. The selection of optimal control factors is crucial for the adequate dimensional characteristics of holes, such as circularity and conicity. In continuation, multi-response optimization using RSM was employed to acquire the desired values of CLMD responses. Thus, the current CLMD approach may emanate its proprietary in fabricating micro-holes designed for a microfluidic device as an integrated inlet–outlet connector for fluidic manipulation. The findings of this research may be a worthy contribution to the biomedical field, as the designed holes by the current process on Perspex have not yet been addressed in any articles.

Weavable phase change fibers with wide thermal management temperature range, reversible thermochromic and triple shape memory functions towards human thermal management

Developing multifunctional phase change materials that could be employed in human thermal management is of great significance for enhancing personal comfort. However, limited thermal management temperature range, strong rigidity and lack of effective visual thermal management approach still hinder their extensive application. In this work, flexible phase change fibers (PCFs) were fabricated by encapsulating the phase change mixtures blended with paraffin wax (PW, Tm = 62.0 °C), nonadecane (NO, Tm = 31.9 °C), and thermochromic agent (TA) into polydimethylsiloxane (PDMS) hollow tubes via a vacuum injection method. PW/NO/PDMS PCFs possessed dual phase change temperature regions around 31.9 °C and 62.0 °C, which broadened the thermal management temperature range. TA realized the visualization of the phase transition of NO and PW via the red-yellow-green color evolution. Combined the dual phase transitions of PW/NO with the elastic PDMS tube, the PCFs exhibited excellent triple shape memory effects. Fabrics woven with PCFs can provide intelligent thermal management functions to keep the temperature constant and improve comfort of humans in hot/cold situations. Therefore, this study provides a facile strategy for fabricating weavable PCFs with wide thermal management temperature range, thermochromic and triple shape memory properties, which have great potential in intelligent thermal management for humans.