A Mortise-and-Tenon Joint Inspired Mechanically Interlocked Network
TL;DR: In this article, a mechanically interlocked network (MIN) inspired by a mortise-and-tenon joint inspired mechanically interlocking network is presented. But the model is based on a rotaxane crosslink.
Abstract: 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.
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TL;DR: In this article , a theranostic metallacycle (M) is developed for imaging-guided cancer radio-chemotherapy using perylene bisimide fluorophore (PPy) and tetraphenylethylene-based di-Pt(II) organometallic precursor (TPE)-Pt) as building blocks.
Abstract: To promote the clinical theranostic performances of platinum-based anticancer drugs, imaging capability is urgently desired, and their chemotherapeutic efficacy needs to be upgraded. Herein, a theranostic metallacycle (M) is developed for imaging-guided cancer radio-chemotherapy using perylene bisimide fluorophore (PPy) and tetraphenylethylene-based di-Pt(II) organometallic precursor (TPE-Pt) as building blocks. The formation of this discrete supramolecular coordination complex facilitates the encapsulation of M by a glutathione (GSH)-responsive amphiphilic block copolymer to prepare M-loaded nanoparticles (MNPs). TPE-Pt acts as a chemotherapeutic drug and also an excellent radiosensitizer, thus incorporating radiotherapy into the nanomedicine to accelerate the therapeutic efficacy and overcome drug resistance. The NIR-emission of PPy is employed to detect the intracellular delivery and tissue distribution of MNPs in real time. In vitro and in vivo investigations demonstrate the excellent anticancer efficacy combining chemotherapy and radiotherapy; the administration of this nanomedicine effectively inhibits the tumor growth and greatly extends the survival rate of cisplatin-resistant A2780CIS-tumor-bearing mice. Guided by in vivo fluorescence imaging, radio-chemotherapy is precisely carried out, which facilitates boosting of the therapeutic outcomes and minimizing undesired side effects. The success of this theranostic system brings new hope to supramolecular nanomedicines for their potential clinical translations.
51 citations
TL;DR: In this article , a cross-linker for mechanically interlocked networks is presented, in which multiple crown ethers are threaded on a hexagonal metallacyclic framework to furnish a crosslinker with delicate interlocked structures.
Abstract: Molecular necklaces have attracted much research attention due to their unique topological structures. Although numerous molecular necklaces with exquisite structures have been constructed, it remains a major challenge to exploit the functions and applications associated with their fascinating architectural and dynamic characteristics. Herein, we report a class of mechanically interlocked networks (MINs) cross-linked by a molecular necklace, in which multiple crown ethers are threaded on a hexagonal metallacyclic framework to furnish a cross-linker with delicate interlocked structures. The molecular necklace cross-linker possesses multiple peculiar advantages: multivalent interactions and rigid metallacycle framework guarantee robust features of MINs while the motion and dissociation of the interlocked structures bring in notable mechanical adaptivity. Moreover, the MINs could respond to the stimuli of K+ and Br-, which lead to the dethreading of crown ether and even the complete decomposition of molecular necklace, respectively, showing abundant active properties. These findings demonstrate the untapped potential of molecular necklaces as cross-linkers and open the door to extend their advanced applications in intelligent supramolecular materials.
30 citations
TL;DR: In this article , the authors outline the synthetic strategies, structure-property relationships, and application explorations of various polyrotaxanes, including linear poly-rotaxane, poly-poly-axane networks, and rotaxane dendrimers.
Abstract: The nature of mechanically interlocked molecules (MIMs) has continued to encourage researchers to design and construct a variety of high-performance materials. Introducing mechanically interlocked structures into polymers has led to novel polymeric materials, called mechanically interlocked polymers (MIPs). Rotaxane-based MIPs are an important class, where the mechanically interlocked characteristic retains a high degree of structural freedom and mobility of their components, such as the rotation and sliding motions of rotaxane units. Therefore, these MIP materials are known to possess a unique set of properties, including mechanical robustness, adaptability and responsiveness, which endow them with potential applications in many emerging fields, such as protective materials, intelligent actuators, and mechanisorption. In this review, we outline the synthetic strategies, structure-property relationships, and application explorations of various polyrotaxanes, including linear polyrotaxanes, polyrotaxane networks, and rotaxane dendrimers.
23 citations
TL;DR: In this article, a spider silk-inspired hydrogen-bond cross-linking has been shown to enable polymers, e.g., polyvinyl alcohol (PVA), to achieve high strength in combination with large ductility.
Abstract: Spider silk-inspired hydrogen-bond (H-bond) cross-linking has recently been shown to enable polymers, e.g., poly(vinyl alcohol) (PVA), to achieve high strength in combination with large ductility a...
19 citations
TL;DR: In this article , a review of the strategies used to prepare self-healing and self-restoring materials utilizing reversible and movable crosslinks is presented, where reversible crosslinks exploit many kinds of dynamic covalent bonds and noncovalent bond, such as hydrogen bonds, metal coordination bonds, ionic interactions, π-π stacking, van der Waals forces, and hydrophobic interactions.
Abstract: Abstract Self-healing materials have attracted attention due to their ability to regain their structure and function after damage. In recent years, significant progress has been made in achieving various functions through supramolecular chemistry. This review describes an overview of the strategies used to prepare self-healing and self-restoring materials utilizing reversible and movable crosslinks. Reversible crosslinks, consisting of noncovalent bonds, can reversibly undergo repeated cleavage and reformation. Therefore, self-healing can be achieved by effectively regenerating reversible crosslinks between polymeric chains. Reversible crosslinks exploit many kinds of dynamic covalent bonds and noncovalent bonds, such as hydrogen bonds, metal coordination bonds, ionic interactions, π–π stacking, van der Waals forces, and hydrophobic interactions. Movable crosslinks exhibit self-restoring properties. Self-restoring materials can regain their original shape and mechanical properties after a cycle of loading and unloading external stress. Movable crosslinks consist of polymer chains that penetrate macrocyclic units and have self-restoring properties due to their sliding motion along the polymeric chains. In addition, multiple reversible cross-links produce synergistic effects to simultaneously achieve high toughness and effective self-healing. We believe that self-healing and self-restoring materials will play a substantial role in realizing a sustainable society.
19 citations
References
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TL;DR: The synthesis of hydrogels from polymers forming ionically and covalently crosslinked networks is reported, finding that these gels’ toughness is attributed to the synergy of two mechanisms: crack bridging by the network of covalent crosslinks, and hysteresis by unzipping thenetwork of ionic crosslinks.
Abstract: Hydrogels with improved mechanical properties, made by combining polymer networks with ionic and covalent crosslinks, should expand the scope of applications, and may serve as model systems to explore mechanisms of deformation and energy dissipation. Hydrogels are used in flexible contact lenses, as scaffolds for tissue engineering and in drug delivery. Their poor mechanical properties have so far limited the scope of their applications, but new strong and stretchy materials reported here could take hydrogels into uncharted territories. The new system involves a double-network gel, with one network forming ionic crosslinks and the other forming covalent crosslinks. The fracture energy of these materials is very high: they can stretch to beyond 17 times their own length even when containing defects that usually initiate crack formation in hydrogels. The materials' toughness is attributed to crack bridging by the covalent network accompanied by energy dissipation through unzipping of the ionic crosslinks in the second network. Hydrogels are used as scaffolds for tissue engineering1, vehicles for drug delivery2, actuators for optics and fluidics3, and model extracellular matrices for biological studies4. The scope of hydrogel applications, however, is often severely limited by their mechanical behaviour5. Most hydrogels do not exhibit high stretchability; for example, an alginate hydrogel ruptures when stretched to about 1.2 times its original length. Some synthetic elastic hydrogels6,7 have achieved stretches in the range 10–20, but these values are markedly reduced in samples containing notches. Most hydrogels are brittle, with fracture energies of about 10 J m−2 (ref. 8), as compared with ∼1,000 J m−2 for cartilage9 and ∼10,000 J m−2 for natural rubbers10. Intense efforts are devoted to synthesizing hydrogels with improved mechanical properties11,12,13,14,15,16,17,18; certain synthetic gels have reached fracture energies of 100–1,000 J m−2 (refs 11, 14, 17). Here we report the synthesis of hydrogels from polymers forming ionically and covalently crosslinked networks. Although such gels contain ∼90% water, they can be stretched beyond 20 times their initial length, and have fracture energies of ∼9,000 J m−2. Even for samples containing notches, a stretch of 17 is demonstrated. We attribute the gels’ toughness to the synergy of two mechanisms: crack bridging by the network of covalent crosslinks, and hysteresis by unzipping the network of ionic crosslinks. Furthermore, the network of covalent crosslinks preserves the memory of the initial state, so that much of the large deformation is removed on unloading. The unzipped ionic crosslinks cause internal damage, which heals by re-zipping. These gels may serve as model systems to explore mechanisms of deformation and energy dissipation, and expand the scope of hydrogel applications.
3,856 citations
TL;DR: It is reported that polyampholytes, polymers bearing randomly dispersed cationic and anionic repeat groups, form tough and viscoelastic hydrogels with multiple mechanical properties.
Abstract: Hydrogels attract great attention as biomaterials as a result of their soft and wet nature, similar to that of biological tissues. Recent inventions of several tough hydrogels show their potential as structural biomaterials, such as cartilage. Any given application, however, requires a combination of mechanical properties including stiffness, strength, toughness, damping, fatigue resistance and self-healing, along with biocompatibility. This combination is rarely realized. Here, we report that polyampholytes, polymers bearing randomly dispersed cationic and anionic repeat groups, form tough and viscoelastic hydrogels with multiple mechanical properties. The randomness makes ionic bonds of a wide distribution of strength. The strong bonds serve as permanent crosslinks, imparting elasticity, whereas the weak bonds reversibly break and re-form, dissipating energy. These physical hydrogels of supramolecular structure can be tuned to change multiple mechanical properties over wide ranges by using diverse ionic combinations. This polyampholyte approach is synthetically simple and dramatically increases the choice of tough hydrogels for applications.
1,496 citations
952 citations
TL;DR: Two supramolecular gels are stimuli-responsive materials that respond to changes of the pH value and are also self-healing materials, as can be seen by eye and as evidenced by rheological data.
Abstract: Automatic repair: a polymer with pendent dibenzo[24]crown-8 units (purple in picture) was cross-linked by two bisammonium salts (green) to form two supramolecular gels based on host-guest interactions. These two gels are stimuli-responsive materials that respond to changes of the pH value and are also self-healing materials, as can be seen by eye and as evidenced by rheological data.
664 citations
TL;DR: In this paper, the authors highlight that most of the necessary elements for the development of more complex synthetic matter are available today using modern strategies, such as controlled radical polymerizations, supramolecular polymerizations or stepwise synthesis, polymers with precisely controlled molecular structures can be synthesized.
Abstract: Complex chemical systems, such as living biological matter, are highly organized structures based on discrete molecules in constant dynamic interactions. These natural materials can evolve and adapt to their environment. By contrast, man-made materials exhibit simpler properties. In this Review, we highlight that most of the necessary elements for the development of more complex synthetic matter are available today. Using modern strategies, such as controlled radical polymerizations, supramolecular polymerizations or stepwise synthesis, polymers with precisely controlled molecular structures can be synthesized. Moreover, such tailored polymers can be folded or self-assembled into defined nanoscale morphologies. These self-organized macromolecular objects can be at thermal equilibrium or can be driven out of equilibrium. Recently, in the latter case, interesting dynamic materials have been developed. However, this is just a start, and more complex adaptive materials are anticipated. The polymer materials of the twenty-first century will be complex chemical systems that can respond and adapt to their environment. Such materials can be attained by synthesizing precision macromolecules with controlled architectures, and by mastering polymer interactions and self-organization.
649 citations