Mechanically Interlocked Polymers with Dense Mechanical Bonds.

ConspectusMechanically interlocked polymers (MIPs) such as polyrotaxanes and polycatenanes are polymer architectures that incorporate mechanical bonds, which represent a compelling frontier in polymer science. MIPs with cross-linked structures are known as mechanically interlocked networks (MINs) and are widely utilized in materials science. Leveraging the motion of mechanical bonds, MINs hold the potential for achieving a combination of robustness and dynamicity. Currently, the reported MINs predominantly consist of networks with discrete mechanical bonds as cross-linking points, exemplified by well-known slide-ring materials and rotaxane/catenane cross-linked polymers. The motion of these mechanically interlocked cross-linking points facilitates the redistribution of tension throughout the network, effectively preventing stress concentration and thereby enhancing material toughness. In these instances, the impact of mechanical bonds can be likened to the adage "small things can make a big difference", whereby a limited number of mechanical bonds substantially elevate the mechanical performance of conventional polymers. In addition to MINs cross-linked by mechanical bonds, there is another type of MIN in which their principal parts are polymer chains composed of dense mechanical bonds. Within these MINs, mechanical bonds generally serve as repeating units, and their unique properties stem from integrating and amplifying the function of a large amount of mechanical bonds. Consequently, MINs with dense mechanical bonds tend to reflect the intrinsic properties of mechanical interlocked polymers, making their exploration critical for a comprehensive understanding of MIPs. Nevertheless, investigations into MINs featuring dense mechanical bonds remain relatively scarce.This Account presents a comprehensive overview of our investigation and insights into MINs featuring dense mechanical bonds. First, we delve into the synthetic strategies employed to effectively prepare MINs with dense mechanical bonds, while critically evaluating their advantages and limitations. Through meticulous control of the core interlocking step, three distinct strategies have emerged: mechanical interlocking followed by polymerization, supramolecular polymerization followed by mechanical interlocking, and dynamic interlocking. Furthermore, we underscore the structure-property relationships of MINs with dense mechanical bonds. The macroscopic properties of MINs originate from integrating and amplifying countless microscopic motions of mechanical bonds, a phenomenon we define as an integration and amplification mechanism. Our investigation has revealed detailed motion characteristics of mechanical bonds in bulk mechanically interlocked materials, encompassing the quantification of motion activation energy, discrimination of varying motion distances, and elucidation of the recovery process. Additionally, we have elucidated their influence on the mechanical performance of the respective materials. Moreover, we have explored potential applications of MINs, leveraging their exceptional mechanical properties and dynamicity. These applications include enhancing the toughness of conventional polymers, engineering mechanically adaptive and multifunctional aerogels, and mitigating Li protrusion as interfacial layers in lithium-ion batteries. Finally, we offer our personal perspectives on the promises, opportunities, and key challenges in the future development of MINs with dense mechanical bonds, underscoring the potential for transformative advancements in this burgeoning field.

A Crown-Ether-Based Elastomer Bearing Loop Structures with Dissipating Characteristics and Enhanced Mechanical Performance.

Loops are prevalent topological structures in cross-linked polymer networks, resulting from the folding of polymer chains back onto themselves. Traditionally, they have been considered as defects that compromise the mechanical properties of the network, leading to extensive efforts in synthesis to prevent their formation. In this study, we introduce the inclusion of cyclic dibenzo-24-crown-8 (DB24C8) moieties within the polymer network strands to form CCNs, and surprisingly, these loops enhance the mechanical performances of the network, leading to tough elastomers. The toughening effect can be attributed to the unique cyclic structure of DB24C8. The relatively small size and the presence of rigid phenyl rings provide the loops with relatively stable conformations, allowing for substantial energy dissipation upon the application of force. Furthermore, the DB24C8 rings possess a broad range of potential conformations, imparting the materials with exceptional elasticity. The synergistic combination of these two features effectively toughens the materials, resulting in a remarkable 66-fold increase in toughness compared to the control sample of covalent networks. Moreover, the mechanical properties, particularly the recovery performance of the network, can be effectively tuned by introducing guests to bind with DB24C8, such as potassium ions and secondary ammonium salts.

A Stretchable and Tough Graphene Film Enabled by Mechanical Bond.

The pursuit of fabricating high-performance graphene films has aroused considerable attention due to their potential for practical applications. However, developing both stretchable and tough graphene films remains a formidable challenge. To address this issue, we herein introduce mechanical bond to comprehensively improve the mechanical properties of graphene films, utilizing [2]rotaxane as the bridging unit. Under external force, the [2]rotaxane cross-link undergoes intramolecular motion, releasing hidden chain and increasing the interlayer slip distance between graphene nanosheets. Compared with graphene films without [2]rotaxane cross-linking, the presence of mechanical bond not only boosted the strength of graphene films (247.3 vs 74.8 MPa) but also markedly promoted the tensile strain (23.6 vs 10.2 %) and toughness (23.9 vs 4.0 MJ/m3). Notably, the achieved tensile strain sets a record high and the toughness surpasses most reported results, rendering the graphene films suitable for applications as flexible electrodes. Even when the films were stretched within a 20 % strain and repeatedly bent vertically, the light-emitting diodes maintained an on-state with little changes in brightness. Additionally, the film electrodes effectively actuated mechanical joints, enabling uninterrupted grasping movements. Therefore, the study holds promise for expanding the application of graphene films and simultaneously inspiring the development of other high-performance two-dimensional films.

Mechanically Interlocked Polyrotaxane Networks with Collective Motions of Multiple Main-Chain Mechanical Bonds.

Type I main-chain polyrotaxanes (PRs) with multiple wheels threaded onto the axle are widely employed to design slide-ring materials. However, Type II main-chain PRs with axles threading into the macrocycles on the polymer backbones have rarely been studied, although they feature special topological structures and dynamic characteristics. Herein, we report the design and preparation of Type II main-chain PR-based mechanically interlocked networks (PRMINs), based on which the relationship between microscopic motion of mechanical bonds on the PRs and macroscopic mechanical performance of materials has been revealed. The representative PRMIN-2 exhibits a robust feature in tensile tests with high stretchability (1680%) and toughness (47.5 MJ/m3). Moreover, it also has good puncture performance with puncture energy of 22.0 mJ. Detailed rheological measurements and coarse-grained molecular dynamics (CGMD) simulation reveal that the embedded multiple [2]rotaxane mechanical bonds on the PR backbones of PRMINs could undergo a synergistic long-range sliding motion under external force, with the introduction of collective dangling chains into the network. As a result, the synchronized motions of coherent PR chains can be readily activated to accommodate network deformation and efficiently dissipate energy, thereby leading to enhanced mechanical performances of PRMINs.

Assembly and Utility of a Drawstring-Mimetic Supramolecular Complex.

Inspired by the drawstring structure in daily life, here we report the development of a drawstring-mimetic supramolecular complex at the molecular scale. This complex consists of a rigid figure-of-eight macrocyclic host molecule and a flexible linear guest molecule which could interact through three-point non-covalent binding to form a highly selective and efficient host-guest assembly. The complex not only resembles the drawstring structure, but also mimics the properties of a drawstring with regard to deformations under external forces. The supramolecular drawstring can be utilized as an interlocked crosslinker for poly(methyl acrylate), and the corresponding polymer samples exhibit comprehensive enhancement of macroscopic mechanical performance including stiffness, strength, and toughness.

Insights into the Correlation of Microscopic Motions of [c2]Daisy Chains with Macroscopic Mechanical Performance for Mechanically Interlocked Networks.

Mimicking filament sliding in sarcomeres using artificial molecular muscles such as [c2]daisy chains has aroused increasing interest in developing advanced polymeric materials. Although few bistable [c2]daisy chain-based mechanically interlocked polymers (MIPs) with stimuli-responsive behaviors have been constructed, it remains a significant challenge to establish the relationship between microscopic responsiveness of [c2]daisy chains and macroscopic mechanical properties of the corresponding MIPs. Herein, we report two mechanically interlocked networks (MINs) consisting of dense [c2]daisy chains with individual extension (MIN-1) or contraction (MIN-2) conformations decoupled from a bistable precursor, which serve as model systems to address the challenge. Upon external force, the extended [c2]daisy chains in MIN-1 mainly undergo elastic deformation, which is able to assure the strength, elasticity, and creep resistance of the corresponding material. For the contracted [c2]daisy chains, long-range sliding motion occurs along with the release of latent alkyl chains between the two DB24C8 wheels, and accumulating lots of such microscopic motions endows MIN-2 with enhanced ductility and ability of energy dissipation. Therefore, by decoupling a bistable [c2]daisy chain into individual extended and contracted ones, we directly correlate the microscopic motion of [c2]daisy chains with macroscopic mechanical properties of MINs.

Oligo[2]catenane That Is Robust at Both the Microscopic and Macroscopic Scales.

Polycatenanes are extremely attractive topological architectures on account of their high degrees of conformational freedom and multiple motion patterns of the mechanically interlocked macrocycles. However, exploitation of these peculiar structural and dynamic characteristics to develop robust catenane materials is still a challenging goal. Herein, we synthesize an oligo[2]catenane that showcases mechanically robust properties at both the microscopic and macroscopic scales. The key feature of the structural design is controlling the force-bearing points on the metal-coordinated core of the [2]catenane moiety that is able to maximize the energy dissipation of the oligo[2]catenane via dissociation of metal-coordination bonds and then activation of sequential intramolecular motions of circumrotation, translation, and elongation under an external force. As such, at the microscopic level, the single-molecule force spectroscopy measurement exhibits that the force to rupture dynamic bonds in the oligo[2]catenane reaches a record high of 588 ± 233 pN. At the macroscopic level, our oligo[2]catenane manifests itself as the toughest catenane material ever reported (15.2 vs 2.43 MJ/m3). These fundamental findings not only deepen the understanding of the structure-property relationship of poly[2]catenanes with a full set of dynamic features but also provide a guiding principle to fabricate high-performance mechanically interlocked catenane materials.

Self-Healable, Malleable, Ecofriendly Recyclable and Robust Polyimine Thermosets Derived from Trifluoromethyl Diphenoxybenzene Backbones.

Dynamic covalent chemistry opens up great opportunities for a sustainable society by producing reprocessable networks of polymers and even thermosets. However, achieving the closed-loop recycling of polymers with high performance remains a grand challenge. The introduction of aromatic monomers and fluorine into covalent adaptable networks is an attractive method to tackle this challenge. Therefore, we present a facile and universal strategy to focus on the design and applications of polyimine vitrimers containing trifluoromethyl diphenoxybenzene backbones in applications of dynamic covalent polymers. In this study, fluorine-containing polyimine vitrimer networks (FPIVs) were fabricated, and the results revealed that the FPIVs not only exhibited good self-healability, malleability and processability without the aid of any catalyst, but also possessed decent mechanical strength, superior toughness and thermal stability. We hope that this work could provide a novel pathway for the design of high-performance polyimine vitrimers by recycling of plastic wastes.

Application of three-dimensional multi-imaging combination in brachytherapy of cervical cancer.

BACKGROUND: Three-dimensional (3D) imaging has an important role in brachytherapy and the treatment of cervical cancer. The main imaging methods used in the cervical cancer brachytherapy include magnetic resonance imaging (MRI), computer tomography (CT), ultrasound (US), and positron emission tomography (PET). However, single-imaging methods have certain limitations compared to multi-imaging. The application of multi-imaging can make up for the shortcomings and provide a more suitable imaging selection for brachytherapy. PURPOSE: This review details the situation and scope of existing multi-imaging combination methods in cervical cancer brachytherapy and provides a reference for medical institutions. MATERIALS AND METHODS: Searched the literature related to application of three-dimensional multi-imaging combination in brachytherapy of cervical cancer in PubMed/Medline and Web of Science electronic databases. Summarized the existing combined imaging methods and the application of each method in cervical cancer brachytherapy. CONCLUSION: The current imaging combination methods mainly include MRI/CT, US/CT, MRI/US, and MRI/PET. The combination of two imaging tools can be used for applicator implantation guidance, applicator reconstruction, target and organs at risk (OAR) contouring, dose optimization, prognosis evaluation, etc., which provides a more suitable imaging choice for brachytherapy.

Insights into the Correlation of Cross-linking Modes with Mechanical Properties for Dynamic Polymeric Networks.

Simultaneously introducing covalent and supramolecular cross-links into one system to construct dually cross-linked networks, has been proved an effective approach to prepare high-performance materials. However, so far, features and advantages of dually cross-linked networks compared with those possessing individual covalent or supramolecular cross-linking points are rarely investigated. Herein, on the basis of comparison between supramolecular polymer network (SPN), covalent polymer network (CPN) and dually cross-linked polymer network (DPN), we reveal that the dual cross-linking strategy can endow the DPN with integrated advantages of CPN and SPN. Benefiting from the energy dissipative ability along with the dissociation of host-guest complexes, the DPN shows excellent toughness and ductility similar to the SPN. Meanwhile, the elasticity of covalent cross-links in the DPN could rise the structural stability to a level comparable to the CPN, exhibiting quick deformation recovery capacity. Moreover, the DPN has the strongest breaking stress and puncture resistance among the three, proving the unique property advantages of dual cross-linking method. These findings gained from our study further deepen the understanding of dynamic polymeric networks and facilitate the preparation of high-performance elastomeric materials.

Highly Strong and Tough Supramolecular Polymer Networks Enabled by Cryptand-Based Host-Guest Recognition.

Supramolecular polymer networks (SPNs) demonstrate great potential in the development of smart materials owing to their attractive dynamic properties. However, as they suffer from the inherent weak bonding of most noncovalent cross-links, it remains a significant challenge to construct SPNs with outstanding mechanical performance. Herein, we exploit the cryptand/paraquat host-guest recognition motifs as cross-links to prepare a class of highly strong and tough SPNs. Unlike those supramolecular cross-links with relatively weak binding abilities, the cryptand-based host-guest interactions have a high association constant and steady complexing structure, which effectively stabilizes the network and resists mechanical deformation under external force. Such favorable structural stability endows our SPNs with greatly enhanced mechanical performance, compared with the control-1 cross-linked by the weakly complexed crown ether/secondary ammonium salt motif (tensile strength: 21.1±0.5 vs 2.8±0.1 MPa; Young's modulus: 102.6±4.8 vs 2.1±0.3 MPa; toughness: 90.4±2.0 vs 10.8±0.6 MJ m-3 ). Moreover, our SPNs also retain abundant dynamic properties including good abilities in energy dissipation, reprocessability, and stimuli-responsiveness. These findings provide novel insights into the preparation of SPNs with enhanced mechanical properties, and promote the development of high-performance intelligent supramolecular materials.

Mechanically Interlocked Vitrimers.

Mechanically interlocked networks (MINs) have emerged as an encouraging platform for the development of mechanically robust yet adaptive materials. However, the difficulty in reversibly breaking the mechanical bonds poses a real challenge to MINs as customizable and sustainable materials. Herein, we couple the vitrimer chemistry with mechanically interlocked structures to generate a new class of MINs─referred to as mechanically interlocked vitrimers (MIVs)─to address the challenge. Specifically, we have prepared the acetoacetate-decorated [2]rotaxane that undergoes catalyst-free condensation reaction with two commercially available multiamine monomers to furnish MIVs. Compared with the control whose wheels are nonslidable under applied force, our MIVs with slidable mechanically interlocked motifs showcase enhanced mechanical performance including Young's modulus (18.5 ± 0.9 vs 1.0 ± 0.1 MPa), toughness (3.7 ± 0.1 vs 0.9 ± 0.1 MJ/m3), and damping capacity (98% vs 72%). The structural basis behind unique property profiles is demonstrated to be the force-induced host-guest dissociation and consequential intramolecular sliding of the wheels along the axles. The peculiar behaviors represent a consecutive energy dissipation mechanism, which provides a complement to other pathways that mainly depend on the breaking of sacrificial bonds. Moreover, by virtue of the vitrimer chemistry of vinylogous urethanes, we impart reprocessability and chemical recyclability to the MINs, thereby empowering the reconfiguration of the networks without breaking of the mechanical bonds. Finally, it is disclosed that the intramolecular motions of [2]rotaxanes could accelerate the dynamic exchange of the vinylogous urethane bonds via loosening the network, suggestive of a synergistic effect between the dual dynamic entities.

Mechanically Interlocked Aerogels with Densely Rotaxanated Backbones.

Mechanically interlocked molecules are considered promising candidates for the construction of self-adaptive materials by virtue of their fascinating structural and dynamic features. However, it is still a great challenge to fabricate such materials with higher complexity and richer functionality. Herein, we propose the concept of mechanically interlocked aerogels (MIAs) in which the three-dimensional (3D) porous frameworks are made of dense mechanically interlocked modules, thereby enabling the integration of mechanical adaptivity and multifunctionality in a single entity. The lightweight MIA monoliths possess a good appearance and hierarchical meso- and submicron-pores. Profiting from the combination of dynamic mechanical bonds and porous skeletons of aerogels, our MIAs are not only mechanically robust (average Young's modulus = 5.80 GPa and specific modulus = 130.5 kN·m/kg) but also showcase favorable mechanical adaptivity and responsiveness under external stimuli. Taking advantage of the above integrative merits, we demonstrate the multifunctionality of our MIAs in terms of iodine uptake, thermal insulation, and selective adsorption of organic dyes. Our work opens the door to designing intelligent aerogels with delicate topological chemical structures while facilitating the development of mechanically interlocked materials.

Anisotropic Thermal Expansion and Electronic Structure of LiInSe2.

Optical quality cm-sized LiInSe2 crystals were grown using the Bridgman-Stockbarger method, starting from pure element reagents, under the conditions of a low temperature gradient of 5-6 degrees/cm and a slight melt overheating. The phase purity of the grown crystal was verified by the powder XRD analysis. The thermophysical characteristics of LiInSe2 were determined by the XRD measurements in the temperature range of 303-703 K and strong anisotropy of the thermal expansion coefficients was established. The following values of thermal expansion coefficients were determined in LiInSe2: αa = 8.1 (1), αb = 16.1 (2) and αc = 5.64 (6) MK-1. The electronic structure of LiInSe2 was measured by X-ray photoelectron spectroscopy. The band structure of LiInSe2 was calculated by ab initio methods.

Robust and Dynamic Polymer Networks Enabled by Woven Crosslinks.

Crosslinking plays a crucial role in determining mechanical properties of polymer materials. Although various crosslinks based on covalent or noncovalent bonds have been adopted, it remains an enormous challenge to develop a crosslink which could endow corresponding polymer network with robust yet dynamic properties. Herein, we report a crosslink simultaneously having dynamic property and woven geometry, and the polymer network with woven crosslinks (WPN) could integrate the merits of covalent polymer network (CPN) and supramolecular polymer network (SPN). In specific, the WPN not only exhibits comparable stiffness, strength, elastic recovery, and anti-fatigue property to those of CPN, but also possesses decent mechanical adaptivity and ductility, similar to those of SPN. Particularly, its toughness and puncture resistance are much superior to those of the others. Besides, the dynamicity of woven crosslink also imparts good performances of self-healing and processability to WPN.

Muscle-Mimetic Synergistic Covalent and Supramolecular Polymers: Phototriggered Formation Leads to Mechanical Performance Boost.

A thin filament stimulated by Ca2+ to combine with myosin is the structural basis to achieve filament sliding and muscle contraction. Though a large variety of artificial materials has been developed by mimicking muscle, the on-demand combination of the actin filament and myosin has never been precisely reproduced in polymeric systems. Herein, we show that both the combination process and the combined structure of actin filament and myosin have been mimicked to construct synergistic covalent and supramolecular polymers (CSPs). Specifically, photoirradiation as a stimulus induces the independently formed covalent polymers (CPs) and supramolecular polymers (SPs) to interact with each other through activated quadruple H-bonding. The resultant CSPs possess a unique network structure which not only facilitates the synergistic effect of CPs and SPs to afford stiff, strong, yet tough materials but also provides efficient pathways to dissipate energy with the damping capacity of the representative material being higher than 95%. Furthermore, muscle functions, for example, by becoming stiff during contraction and self-growth by training, are imitated well in our system via in situ phototriggered formation of CSP in the solid state. We hope that the fundamental understanding gained from this work will promote the development of synergistic CSP systems with emergent functions and applications by mimicking the principle of muscle movements.

Biomimetic Impact Protective Supramolecular Polymeric Materials Enabled by Quadruple H-Bonding.

Nature has been inspiring scientists to fabricate impact protective materials for applications in various aspects. However, it is still challenging to integrate flexible, stiffness-changeable, and protective properties into a single polymer, although these merits are of great interest in many burgeoning areas. Herein, we report an impact-protective supramolecular polymeric material (SPM) with unique impact-hardening and reversible stiffness-switching characteristics by mimicking sea cucumber dermis. The emergence of softness-stiffness switchability and subsequent protective properties relies on the dynamic aggregation of the nanoscale hard segments in soft transient polymeric networks modulated by quadruple H-bonding. As such, we demonstrate that our SPM could efficiently reduce the impact force and increase the buffer time of the impact. Importantly, we elucidate the underlying mechanism behind the impact hardening and energy dissipation in our SPM. Based on these findings, we fabricate impact- and puncture-resistant demos to show the potential of our SPM for protective applications.

Effect of Long- and Short-Range Disorder on the Oxygen Ionic Conductivity of Tm2(Ti2-xTmx)O7-x/2 "Stuffed" Pyrochlores.

The long-range average and short-range local structures in the Tm2(Ti2-xTmx)O7-x/2 (x = 0.00-0.67) series were studied using a combination of diffraction and spectroscopic techniques. The long-range average structure, established from synchrotron X-ray and neutron powder diffraction data, shows the development of multiphase regions from x = 0.134 and the formation of antisite cation disorder from x = 0.402. The crystal field splitting of the Ti4+ ions, as derived from the Ti L3-edge X-ray absorption near-edge structure (XANES) spectroscopy, decreases gradually from 2.17 to 1.92 eV with increasing Tm3+ content (x), reflecting the increase in coordination number from 6 to predominantly 7. This is consistent with a gradual evolution of the short-range local disorder from x = 0.00 to 0.67. These results suggest that local disorder develops gradually throughout the entire composition range, whereas changes in the long-range disorder occur more suddenly. Electrochemical impedance spectroscopic results show an increase in oxygen ionic conductivity at 1000 °C, by a factor of 4 upon doping at x = 0.268. This suggests that inducing small amounts of disorder into the pyrochlore structure, by stuffing, may lead to applications of this material as a solid electrolyte in solid-oxide fuel cells.

Tilting and Distortion in Rutile-Related Mixed Metal Ternary Uranium Oxides: A Structural, Spectroscopic, and Theoretical Investigation.

A systematic investigation examining the origins of structural distortions in rutile-related ternary uranium AUO4 oxides using a combination of high-resolution structural and spectroscopic measurements supported by ab initio calculations is presented. The structures of ß-CdUO4, MnUO4, CoUO4, and MgUO4 are determined at high precision by using a combination of neutron powder diffraction (NPD) and synchrotron X-ray powder diffraction (S-XRD) or single crystal X-ray diffraction. The structure of ß-CdUO4 is best described by space group Cmmm whereas MnUO4, CoUO4, and MgUO4 are described by the lower symmetry Ibmm space group and are isostructural with the previously reported ß-NiUO4 [Murphy et al. Inorg. Chem. 2018, 57, 13847]. X-ray absorption spectroscopy (XAS) analysis shows all five oxides contain hexavalent uranium. The difference in space group can be understood on the basis of size mismatch between the A2+ and U6+ cations whereby unsatisfactory matching results in structural distortions manifested through tilting of the AO6 polyhedra, leading to a change in symmetry from Cmmm to Ibmm. Such tilts are absent in the Cmmm structure. Heating the Ibmm AUO4 oxides results in reduction of the tilt angle. This is demonstrated for MnUO4 where in situ S-XRD measurements reveal a second-order phase transition to Cmmm near T = 200 °C. Based on the extrapolation of variable temperature in situ S-XRD data, CoUO4 is predicted to undergo a continuous phase transition to Cmmm at ∼1475 °C. Comparison of the measured and computed data highlights inadequacies in the DFT+U approach, and the conducted analysis should guide future improvements in computational methods. The results of this investigation are discussed in the context of the wider AUO4 family of oxides.

A Mortise-and-Tenon Joint Inspired Mechanically Interlocked Network.

Mortise-and-tenon joints have been widely used for thousands of years in wooden architectures in virtue of their artistic and functional performance. However, imitation of similar structural and mechanical design philosophy to construct mechanically adaptive materials at the molecular level is a challenge. Herein, we report a mortise-and-tenon joint inspired mechanically interlocked network (MIN), in which the [2]rotaxane crosslink not only mimics the joint in structure, but also reproduces its function in modifying mechanical properties of the MIN. Benefiting from the hierarchical energy dissipative ability along with the controllable intramolecular movement of the mechanically interlocked crosslink, the resultant MIN simultaneously exhibits notable mechanical adaptivity and structural stability in a single system, as manifested by decent stiffness, strength, toughness, and deformation recovery capacity.