Large Extensibility Research Articles

Overcoming strength-ductility and functional period-degradability tradeoffs: Multifunctional biodegradable polyesters with ionic cluster skeleton and PDMS skin

To overcome the strength-ductility and functional period-degradability tradeoffs of biodegradable polyesters, we proposed a nanophase structure design strategy to construct a soft-hard dual phase in poly(butylene succinate) (PBS) copolymers by simultaneously introducing polydimethylsiloxane (PDMS) and isophthalate-5-sulfonate (SIPM) on PBS macromolecular chains to improve the stiffness, toughness, and multifunctionality. The high-resolution transmission electron microscope (HR-TEM) and energy dispersive X-Ray spectroscopy (EDX) tests indicated that PBS copolymers possessed continuous “ionic cluster skeleton” and “PDMS skin”. The hybrid liquid state theory and self-consistent field approach for copolymers further demonstrated the mechanism of microphase separation for PDMS blocks and SIPM segments. The copolymers showed excellent yield strength of 52 MPa, great impact strength of 171 J/m, large extensibility of 491 %, and long functional period in the acidic environment. The novel stereo nanostructure endowed the materials with advanced multifunctions that can be applied in various applications, such as the biomedical field and flexible electronic devices. Compared with PBS, copolymers possessed excellent in vitro attachment and proliferation of MC3T3-E1 cells. Furthermore, the synergistic effect of the ionic skeleton and PDMS skin improved the ionic conductivity of the materials. The copolymer film was innovatively employed as anion-exchanging separators of supercapacitors with acid-organized electrolytes. It has been testified that this newly designed strategy of a novel stereo nanophase structure was efficient in endowing the biodegradable polyesters with excellent combined properties and multifunctions.

Soft-hard dual nanophases: a facile strategy for polymer strengthening and toughening.

Polymers often face a trade-off between stiffness and extensibility-for example, toughening rigid polymers by incorporating plasticizers or flexible polymers leads to strikingly decreased stiffness. Herein, we circumvent this long-standing tricky dilemma in materials science via constructing soft-hard dual nanophases in polymers. As-fabricated dual-nanophase PLA shows a high yield strength of 69.1 ± 4.4 MPa, a large extensibility of 279.1 ± 25.5%, and a super toughness of 115.2 ± 10.3 MJ m-3, which are 1.2, 48 and 82 times, respectively, those of neat PLA. Combined high stiffness, large ductility, and super toughness are unprecedented for PLA and enable bio-sourced PLA to replace petroleum-based resins such as PP, PET and PC. Besides, soft-hard dual nanophases in polymers are rarely reported due to significant constraints in terms of modifier dispersion/aggregation, interfacial regulation, and processing difficulties. The construction strategy described herein, combining controlled annealing and a well-designed plasticizer, can efficiently construct soft-hard dual nanophases in polymers, which will greatly advance the nanostructure design of polymers. More importantly, the proposed strategy for materials design will be widely applicable to industrial manufacturing in terms of nanophase construction and interfacial optimization due to the simplicity and availability at a large scale. We envision that this work offers an innovative and facile strategy to circumvent the trade-off between stiffness and extensibility and to advance the nanostructure design of high-performance polymers in a manner applicable to industrial manufacturing.

Hierarchically Structured Bioinspired Fibers Shaped by Liquid Droplets

AbstractNature has a remarkable ability to create multifunctional fibers, such as spider silk, by precisely controlling structures across various scales. However, replicating this in high‐speed spun synthetic fibers is challenging due to the absence of life‐specific forces and interactions required for manipulating composition, gradients, and structures. Here, a novel droplet‐coupled pultrusion spinning technique is demonstrated for industrial‐scale production of microfibers with hierarchical structures. Droplets spontaneously form on the surface of high‐speed spun fibers to tailor multiscale hierarchical structures, resulting in a nonlinear viscoelastic core embedded with anharmonic nanosprings consisting of amorphous and crystalline domains and a periodically reinforced nanofiber skin. These structural hierarchies enable unique mechanical property combinations including nonlinear viscoelasticity, large extensibility (613%), record‐high toughness (536 MJ m−3), highly efficient impact energy absorption, vibration damping and wide temperature adaptability (−67.4 to 278.9 °C). Additionally, the structured bioinspired fibers exhibit low‐frequency phononic bandgap and anomalous dispersion of mechanical waves. The droplet‐based approach allows precise control over heterogeneity at multiple scales within the identical components leading to impressive mechanical performance and additional functionalities, and is consider that it could be applied to the design of the next era of hierarchically structured nanocomposites for a wide range of applications.

Structural engineering of porous biochar loaded with ferromagnetic/anti-ferromagnetic NiCo2O4/CoO for excellent electromagnetic dissipation with flexible and self-cleaning properties

Design of multi-functional microwave absorption materials with strong dissipation ability is a practical approach to address the current issue of electromagnetic radiation pollution. Herein, based on the exchange bias interaction between ferromagnetic and anti-ferromagnetic interfaces, a series of absorbers composed of the porous biochar loaded with ferromagnetic/anti-ferromagnetic NiCo2O4/CoO were successfully prepared via a fairly simple process of one-step calcination. By regulating the calcination temperature, the pore size and porosity of porous carbon, morphology of loaded NPs as well as the electromagnetic response property and impedance matching characteristic in such composites can be modulated. The porous biochar/NiCo2O4/CoO composite prepared under 350 °C possesses a remarkable electromagnetic absorption reflection loss (RL) of –48.41 dB at 9.12 GHz with 2.5 mm thickness, and the effective absorption bandwidth (EAB) of 4.32 GHz with 2.2 mm thickness is located at X band, this is owing to the strong coupling effect of multiple dielectric polarizations, magnetic resonances, and eddy current consumption under matched impedance. In addition, the microwave absorbing patch prepared with this composite exhibits a well-hydrophobic property for self-cleaning function, and the large extensibility with substantial breaking strength endows its practical usage as a flexible absorber.

Design of a class of reconfigurable hybrid mechanisms for large complex curved surface machining based on topological graph theory

A design method for hybrid mechanism configuration synthesis based on topological graph theory is proposed to address the challenge of machining large and complex curved surfaces in the aerospace domain. The method leads to the generation of a new class of reconfigurable large extension hybrid mechanisms. Firstly, the spatial mechanism topological graph (SMTG) is obtained by evolving the structure of chemical molecules, which is used to express the spatial mechanism topological relationships. Then, combining graph theory methods with the SMTG, the topological relationships between motion modules of the hybrid mechanism are expressed, and the mechanisms of each motion module are designed. Finally, mechanisms of different functional modules are topologically connected and combined using the proposed topological connection relationship for the motion modules of hybrid mechanisms, thus resulting in a class of reconfigurable hybrid mechanisms (RHMs) with large extensibility. The RHMs exhibit strong structural stability, a large working space, and a small volume of occupation. It can be installed on the ends of industrial robots or in large guideways in the future to achieve high-precision machining of large complex curved structures.

Modeling fracture in polymeric material using phase field method based on critical stretch criterion

In this work, the phase field method (PFM) is applied for modeling fracture in the polymeric type of materials. Considering the large extensibility of polymer chains before fracture, a crack initiation criteria based on a critical stretch value is proposed. The tensile stretches in the material contribute to the active strain energy, which is responsible for driving fracture. Additive decomposition of strain energy into active and passive parts is adopted based on the critical stretch value of polymer chains in a phase-field setting. This critical value is determined by assuming an equivalent uniaxial tensile state of stress in front of the crack tip at the onset of fracture. The stretch of individual polymeric chains is determined by using a polymer network model. The critical fracture toughness of the polymer is kept constant up to the onset of fracture and a gradually reducing value of it is adopted in front of the crack tip beyond the critical stretch. A hybrid phase-field formulation with a staggered solver is used owing to its numerical efficiency and robustness. The effectiveness and applicability of the present model are demonstrated through various numerical examples.

Hysteresis-free and high sensitivity strain sensing of ionically conductive hydrogels.

Hydrogels are promising materials for soft and implantable strain sensors owing to their large compliance (E<100 kPa) and significant extensibility (εmax >500%) compared to other polymer networks. Further, hydrogels can be functionalized to seamlessly integrate with many types of tissues. However, most current methods attempt to imbue additional electronic functionality to structural hydrogel materials by incorporating fillers with orthogonal properties such as electronic or mixed ionic conduction. Although composite strategies may improve performance or facilitate heterogeneous integration with downstream hardware, composites complicate the path for regulatory approval and may compromise the otherwise compelling properties of the underlying structural material. Here we report hydrogel strain sensors composed of genipin-crosslinked gelatin and dopamine-functionalized poly(ethylene glycol) for in vivo monitoring of cardiac function. By measuring their impedance only in their resistive regime (>10 kHz), hysteresis is reduced and the resulting gauge factor is increased by ~50x to 1.02±0.05 and 1.46±0.05 from approximately 0.03-0.05 for PEG-Dopa and genipin-crosslinked gelatin respectively. Adhesion and in vivo biocompatibility are studied to support implementation of strain sensors for monitoring cardiac output in porcine models. Impedance-based strain sensing in the kilohertz regime simplifies the piezoresistive behavior of these materials and expands the range of hydrogel-based strain sensors.

Neurotransmitter uptake of synaptic vesicles studied by X-ray diffraction

The size, polydispersity, and electron density profile of synaptic vesicles (SVs) can be studied by small-angle X-ray scattering (SAXS), i.e. by X-ray diffraction from purified SV suspensions in solution. Here we show that size and shape transformations, as they appear in the functional context of these important synaptic organelles, can also be monitored by SAXS. In particular, we have investigated the active uptake of neurotransmitters, and find a mean vesicle radius increase of about 12% after the uptake of glutamate, which indicates an unusually large extensibility of the vesicle surface, likely to be accompanied by conformational changes of membrane proteins and rearrangements of the bilayer. Changes in the electron density profile (EDP) give first indications for such a rearrangement. Details of the protein structure are screened, however, by SVs polydispersity. To overcome the limitations of large ensemble averages and heterogeneous structures, we therefore propose serial X-ray diffraction by single free electron laser pulses. Using simulated data for realistic parameters, we show that this is in principle feasible, and that even spatial distances between vesicle proteins could be assessed by this approach.

Highly stretchable, self-healing and conductive silk fibroin-based double network gels via a sonication-induced and self-emulsifying green procedure.

Regenerated silk fibroin (RSF)-based hydrogels are promising biomedical materials due to their biocompatibility and biodegradability. However, the weak mechanical properties and lack of functionality limit their practical applications. Here, we developed a tough and conductive RSF-based double network (DN) gel, consisting of a sonication-induced β-sheet physically crosslinked RSF/S gel as the first network and a hydrophobically associated polyacrylamide/stearyl methacrylate (PAAm/C18) gel as the second network. In particular, the cross-linking points of the second network were micelles formed by emulsifying the hydrophobic monomer (C18M) with a natural SF- capryl glucoside co-surfactant. The reversible dynamic bonds in the DN provided good self-healing ability and an effective dissipative energy mechanism for the DN hydrogel, while the addition of calcium ions improved the self-healing ability and electrical conductivity of the hydrogel. Under optimal conditions, the RSF/S-PAAm/C18 DN gels exhibited large extensibility (1400%), high tensile strength (0.3 MPa), satisfactory self-healing capability (90%) and electrical conductivity (0.12 S·m−1). The full physically interacted DN hydrogels are expected to be applied in various fields such as tissue engineering, biosensors and artificial electronic skin.

High Energy Density Shape Memory Polymers Using Strain-Induced Supramolecular Nanostructures.

Shape memory polymers are promising materials in many emerging applications due to their large extensibility and excellent shape recovery. However, practical application of these polymers is limited by their poor energy densities (up to ∼1 MJ/m3). Here, we report an approach to achieve a high energy density, one-way shape memory polymer based on the formation of strain-induced supramolecular nanostructures. As polymer chains align during strain, strong directional dynamic bonds form, creating stable supramolecular nanostructures and trapping stretched chains in a highly elongated state. Upon heating, the dynamic bonds break, and stretched chains contract to their initial disordered state. This mechanism stores large amounts of entropic energy (as high as 19.6 MJ/m3 or 17.9 J/g), almost six times higher than the best previously reported shape memory polymers while maintaining near 100% shape recovery and fixity. The reported phenomenon of strain-induced supramolecular structures offers a new approach toward achieving high energy density shape memory polymers.

Covalent Hybrid Elastomers Based on Anisotropic Magnetic Nanoparticles and Elastic Polymers

Particle-filled elastomers are ubiquitous composite materials with applications ranging from durable materials, such as tires, to smart actuators and sensor materials. By employing magnetic nanoparticles as multifunctional, inorganic cross-linkers, PDMS-based hybrid elastomers with a novel unique architecture and a defined type of particle-matrix interaction are obtained—a direct covalent coupling between magnetic and elastic properties. The resulting particle-cross-linked elastomers possess application potential due to their defined magnetomechanical coupling and their large extensibility. As the filler phase, spindle-shaped hematite nanoparticles with a silica shell are used, and the swelling, thermal, magnetic, and mechanical properties of the resulting particle-cross-linked elastomers are systematically evaluated and compared to the properties of analogous yet conventionally cross-linked particle-filled elastomers of a similar composition. Some unique features are found for the hybrid elastomers, such as a large strain at break of up to εB ≈ 1700%, that are attributed to the exceptional architecture, combining a well-integrated network of long polymer chains that are interconnected by network nodes with a high cross-linker functionality formed by the anisotropic magnetic nanoparticles.

Super flexible, fatigue resistant, self-healing PVA/xylan/borax hydrogel with dual-crosslinked network

The high mechanical strength and self-healing properties of hydrogels are the focus of tissue engineering and biomedical research. Furthermore, the incompatibility between hydrogel toughness and self-healing has not been resolved. It is noteworthy that the double network (DN) hydrogels show great promise as a viable method for producing self-healing hydrogels with the above properties. The Xylan/PVA/Borax DN hydrogel was prepared by the one-pot method, shows various excellent performances, including strong strength (ca. 81 kPa), high toughness (ca.1652.42 kJ/m3), good self-recovery (ca. 79% recovery), and excellent self-healing properties (self-healing efficiency reached to 85.8% for 30 s). This study proposes a strategy to design high strength, high toughness, large extensibility, and self-healing properties hydrogels based on xylan.

QubiC: An Open-Source FPGA-Based Control and Measurement System for Superconducting Quantum Information Processors

As quantum information processors grow in quantum bit (qubit) count and functionality, the control and measurement system becomes a limiting factor to large scale extensibility. To tackle this challenge and keep pace with rapidly evolving classical control requirements, full control stack access is essential to system level optimization. We design a modular FPGA (field-programmable gate array) based system called QubiC to control and measure a superconducting quantum processing unit. The system includes room temperature electronics hardware, FPGA gateware, and engineering software. A prototype hardware module is assembled from several commercial off-the-shelf evaluation boards and in-house developed circuit boards. Gateware and software are designed to implement basic qubit control and measurement protocols. System functionality and performance are demonstrated by performing qubit chip characterization, gate optimization, and randomized benchmarking sequences on a superconducting quantum processor operating at the Advanced Quantum Testbed at Lawrence Berkeley National Laboratory. The single-qubit and two-qubit process fidelities are measured to be 0.99800.0001 and 0.9480.004 by randomized benchmarking. With fast circuit sequence loading capability, the QubiC performs randomized compiling experiments efficiently and improves the feasibility of executing more complex algorithms.

Understanding the Continuous Dynamic Mechanical Behavior of Animal Silk

Animal silks offer the combined advantages of high strength, high elastic modulus, and large extensibility and are often used as a powerful example of the biological material design paradigm to guide synthetic polymer designs. Although much is known about quasistatic mechanical properties of animal silks, their behavior under dynamic loading conditions has not been extensively explored. In this study, we used continuous dynamic analysis (CDA), which combines dynamic mechanical analysis and the quasistatic tensile test to quantitatively measure the viscoelastic properties of silk as a continuous function of strain. CDA observations indicate that instead of the simple linear-elastic response detected in quasistatic tensile measurements, a different structure-mechanic response occurs before the yield point. Furthermore, a structure-mechanic model based on viscoelastic theory was established to understand the contribution of secondary structures to the continuous dynamic mechanical behavior of silk. The secondary structures of silks and polymers are highly similar; therefore, the structure-property relationship uncovered in this study can directly guide the design of high-performance polymers, in particular, polymer fibers with desired dynamic mechanical characteristics.

Tough Hybrid Hydrogels Adapted to the Undergraduate Laboratory

Polymer materials are indispensable in our daily lives. This makes polymer technology of critical importance in higher education. In particular, hands-on experiment-based practicals/laboratories with a focus on polymer science are of tremendous value in the undergraduate curriculum. Along these lines, hydrogels are highly cross-linked polymer networks which show some unique properties such as water absorbance and large extensibility, making them particularly well-suited in various biomedical applications. The properties of hydrogels can be systematically varied via changes in composition. In this practical laboratory, we use hybrid hydrogel formulations containing alginate and polyacrylamide to explore the consequences of compositional changes on mechanical behavior. Mechanical properties are determined using a simplified tensile test that is amenable to large groups of students using standard laboratory equipment. We used marbles to induce an extensional force and a ruler to measure the elongation of the gel as a function of the attached weight. Hereby, stress–strain curves can be obtained, and students are able to compare the difference between single and double network hydrogels as well as quantify the influence of network composition. This practical combines the use of chemical synthesis (i.e., reactant calculations) with practical skills which makes it interesting to use in a third year chemical/biomedical course. Furthermore, students can learn how to deal with chemicals and gain insight in polymer chemistry and its wide applicability, making it particularly well-suited for students coming from outside the traditional chemical science background.

Intrinsic-to-extrinsic transition in fracture toughness through structural design: A lesson from nature

Catastrophic failure of materials and structures due to unstable crack growth could be prevented if fracture toughness could be enhanced at will through structural design, but how can this be possible if fracture toughness is a material constant related to energy dissipation in the vicinity of a propagating crack tip. Here we draw inspiration from the deformation behavior of biomolecules in load bearing biological materials, which have been evolved with a large extensibility and a high breaking strength beyond their elastic limit, and introduce an effective biomimetic strategy to enhance fracture toughness of a structure through an intrinsic to extrinsic (ITE) transition. In the ITE transition, toughness starts as an intrinsic parameter at the basic material level, but by designing a protein-like effective stress–strain behavior the toughness at the system level becomes an extrinsic parameter that increases with the system size without bound. This phenomenon is demonstrated through a combination of numerical simulations, analytic modeling and experiments, and leads to a biomimetic strategy which can be broadly adopted to enhance fracture toughness in engineering systems.

Revealing the molecular origins of fibrin's elastomeric properties by in situ X-ray scattering

Fibrin is an elastomeric protein forming highly extensible fiber networks that provide the scaffold of blood clots. Here we reveal the molecular mechanisms that explain the large extensibility of fibrin networks by performing in situ small angle X-ray scattering measurements while applying a shear deformation. We simultaneously measure shear-induced alignment of the fibers and changes in their axially ordered molecular packing structure. We show that fibrin networks exhibit distinct structural responses that set in consecutively as the shear strain is increased. They exhibit an entropic response at small strains (<5%), followed by progressive fiber alignment (>25% strain) and finally changes in the fiber packing structure at high strain (>100%). Stretching reduces the fiber packing order and slightly increases the axial periodicity, indicative of molecular unfolding. However, the axial periodicity changes only by 0.7%, much less than the 80% length increase of the fibers, suggesting that fiber elongation mainly stems from uncoiling of the natively disordered αC-peptide linkers that laterally bond the molecules. Upon removal of the load, the network structure returns to the original isotropic state, but the fiber structure becomes more ordered and adopts a smaller packing periodicity compared to the original state. We conclude that the hierarchical packing structure of fibrin fibers, with built-in disorder, makes the fibers extensible and allows for mechanical annealing. Our results provide a basis for interpreting the molecular basis of haemostatic and thrombotic disorders associated with clotting and provide inspiration to design resilient bio-mimicking materials. Statement of SignificanceFibrin provides structural integrity to blood clots and is also widely used as a scaffold for tissue engineering. To fulfill their biological functions, fibrin networks have to be simultaneously compliant like skin and resilient against rupture. Here, we unravel the structural origin underlying this remarkable mechanical behaviour. To this end, we performed in situ measurements of fibrin structure across multiple length scales by combining X-ray scattering with shear rheology. Our findings show that fibrin sustains large strains by undergoing a sequence of structural changes on different scales with increasing strain levels. This demonstrates new mechanistic aspects of an important biomaterial's structure and its mechanical function, and serves as an example in the design of biomimicking materials.

Strain softening and stiffening responses of spider silk fibers probed using a Micro-Extension Rheometer

Spider silk possesses unique mechanical properties like large extensibility, high tensile strength, super-contractility, etc. Understanding these mechanical responses requires characterization of the rheological properties of silk beyond the simple force-extension relations which are widely reported. Here we study the linear and non-linear viscoelastic properties of dragline silk obtained from social spider Stegodyphus sarasinorum using a Micro-Extension Rheometer that we have developed. Unlike continuous extension data, our technique allows for the probing of the viscoelastic response by applying small perturbations about sequentially increasing steady-state strain values. In addition, we extend our analysis to obtain the characteristic stress relaxation times and the frequency responses of the viscous and elastic moduli. Using these methods, we show that in a small strain regime (0-4%) dragline silk of social spiders shows a strain softening response followed by a strain stiffening response at higher strains (>4%). The stress relaxation time, on the other hand, increases monotonically with increasing strain for the entire range. We also show that the silk stiffens while ageing within the typical lifetime of a web. Our results demand the inclusion of the kinetics of domain unfolding and refolding in the existing models to account for the relaxation time behavior.

Mechanically tough and highly stretchable poly(acrylic acid) hydrogel cross-linked by 2D graphene oxide.

The mechanical performances of hydrogels are greatly influenced by the functionality of cross-linkers and their covalent and non-covalent interactions with the polymer chains. Conventional chemical cross-linkers fail to meet the demand of large toughness and high extensibility for their immediate applications as artificial tissues like ligaments, blood vessels, and cardiac muscles in human or animal bodies. Herein, we synthesized a new graphene oxide-based two-dimensional (2D) cross-linker (GOBC) and exploited the functionality of the cross-linker for the enhancement of toughness and stretchability of a poly(acrylic acid) (PAA) hydrogel. The 2D nanosheets of GO were modified in such a way that they could provide multifunctional sites for both physical and chemical bonding with the polymer chains. Carboxylic acid groups at the surfaces of the GO sheets were coupled with the acrylate functional groups for covalent cross-linking, while the other oxygen-containing functional groups are responsible for physical cross-linking with polymers. The GOBC had been successfully incorporated into the PAA hydrogel and the mechanical properties of the GOBC cross-linked PAA hydrogel (PAA-GOBC) were investigated at various compositions of cross-linker. Seven times enhancement in both toughness and elongation at break has been achieved without compromising on the modulus for the as-synthesized PAA-GOBC compared to the conventional N,N′-methylenebis(acrylamide) (MBA) cross-linked PAA hydrogel. This facile and efficient way of GO modification is expected to lead the development of a high-performance nanocomposite for cutting-edge applications in biomedical engineering.

Synthesis of strong and highly stretchable, electrically conductive hydrogel with multiple stimuli responsive shape memory behavior

A highly tough and conductive hydrogel with good shape memory behavior was facilely prepared via constructing the catechol-Fe3+ interactions in the poly(vinyl alcohol) (PVA) hydrogel matrix. The hydrophobic 5,5,6,6-tetrahydroxy-3,3,3,3-tetramethyl-1,1-spirobisindane (TTSBI) was introduced to provide the catechol ligands for Fe3+. The fabricated TTSBI-2@Fe3+-12 nanocomposite hydrogel performed great toughness (9.23 MJ/m3), large tensile strength (3.25 MPa) and high extensibility (752%). The distinguished mechanical performance of the composite hydrogel was contributed by the synergy of nanophase separation structure formed by TTSBI in PVA matrix, strong hydrogen bonding interaction between PVA and TTSBI, and metal coordination interaction of catechol-Fe3+. The introduced Fe3+ also imparted good conductivity to the hydrogel. Moreover, the mechanical and conductive properties of the composite hydrogel could be flexibly regulated by the pH value. The conductive hydrogel showed excellent sensitivity to stretching, bending, twist, and compression. In addition, the hydrogel exhibited multiple-stimuli responsive shape memory behaviors. This work offers a hierarchical self-assembly strategy to fabricate functional hydrogel with tailored mechanical, conductive properties and shape memory behavior for a series of promising applications such as flexible wearable electronics and intelligent actuators.