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Architectural, compositional, and mechanical gradients are present in many interfacial tissues in the body. Yet desired for regeneration, the recreation of these complex natural gradients in porous scaffolds remains a challenging task. Additive manufacturing (AM) has been highlighted as a technology to fabricate constructs to regenerate interfacial tissues. Integration of different types of gradients, which can be physical, mechanical, and/or biochemical, shows promise to control cell fate and the regeneration process in a spatial controlled manner. One of the most studied tissue interfaces is the osteochondral unit which connects cartilage to bone. This tissue is often damaged because of trauma or ageing, leading to osteoarthritis; a degenerative disease and a major cause of disability worldwide. Therefore, in view of osteochondral (OC) regeneration, a state‐of‐the‐art overview of current approaches is presented to manufacture gradient scaffolds prepared by AM techniques. The focus is on thermoplastic, hydrogel, and hybrid scaffolds comprising gradients that induce biomimicry by their physical and biological properties. The effect of these different systems on OC tissue formation in‐vitro and in‐vivo is addressed. Finally, an outlook on current trends of dynamic materials is provided, including proposals on how these materials could improve the mimicry of scaffolds applied for OC regeneration. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Adhesives have been widely used to splice and repair materials to meet practical needs of humanity for thousands of years. However, developing robust adhesives with balanced adhesive and cohesive properties still remains a challenging task. Herein, we report the design and preparation of a robust mechanically interlocked [an]daisy chain network (DCMIN) adhesive by orthogonal integration of mechanical bonds and 2‐ureido‐4[1H]‐pyrimidone (UPy) H‐bonding in a single system. Specifically, the UPy moiety plays a dual role: it allows the formation of a cross‐linked network and engages in multivalent interactions with the substrate for strong interfacial bonding. The mechanically interlocked [an]daisy chain, serving as the polymeric backbone of the adhesive, is able to effectively alleviate applied stress and uphold network integrity through synergistic intramolecular motions, and thus significantly improves the cohesive performance. Comparative analysis with the control made of the same quadruple H‐bonding network but with non‐interlocked [an]daisy chain backbones demonstrates that our DCMIN possesses superior adhesion properties over a wide temperature range. These findings not only contribute to a deep understanding of the structure‐property relationship between microscopic mechanical bond motions and macroscopic adhesive properties but also provide a valuable guide for optimizing design principles of robust adhesives. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Mechanical bonds have been utilized as promising motifs to construct mechanically interlocked aerogels (MIAs) with mechanical adaptivity and multifunctionality. However, fabricating such aerogels with not only precise chemical structures but also dynamic features remains challenging. Herein, we present MIAs carrying dense [2]rotaxane units, which bestow both the stability and flexibility of the aerogel network. Owing to the stable chemical structure of a [2]rotaxane, MIAs possessing a precise and full‐scale mechanically interlocked network could be fabricated with the aid of diverse solvents. In addition, the dynamic nature of the [2]rotaxane resulted in morphologies and mechanical performances of the MIAs that can be dramatically modulated under chemical stimuli. We hope that the structure–property relationship in MIAs will facilitate the development of mechanically interlocked materials and provide novel opportunities toward constructing smart materials with multifunctionalities. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The transient self‐assembly of molecules under the direction of a consumable fuel source is fundamental to biological processes such as cellular organization and motility. Such biomolecular assemblies exist in an out‐of‐equilibrium state, requiring continuous consumption of high energy molecules. At the same time, the creation of bioinspired supramolecular hydrogels has traditionally focused on associations occurring at the thermodynamic equilibrium state. Here, hydrogels are prepared from cucurbit[7]uril host–guest supramolecular interactions through transient physical crosslinking driven by the consumption of a reactive chemical fuel. Upon action from this fuel, the affinity and dynamics of CB[7]–guest recognition are altered. In this way, the lifetime of transient hydrogel formation and the dynamic modulus obtained are governed by fuel consumption, rather than being directed by equilibrium complex formation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Dynamic materials (DMs) or dynamers have potential applications across a broad range of material science challenges. These applications include sustainable materials as a part of the circular plastics economy, advanced materials with tailored high stress properties and biomedical agents. DMs are comprised of polymers that crosslinked through reversible covalent and noncovalent linking groups. This group provides reversible bonds, which impart properties such as (re)healing, adaptability, toughness into a material. The nature of the linker dictates the dynamer's stability and dynamic properties, although for many applications one linker alone cannot give materials with complex multiresponsive functions. The combination of multiple dynamic linkers can introduce complementary functionalities into a single material. This combination of linkers enhances the collective material properties by matching their strengths and offsetting the weaknesses, or by selecting linkers for specific functions, such as one linker for rapid exchange and the other to respond to external stimuli. This contribution highlights the possibilities and unique features of materials containing multiple dynamic linkers, reviewing both fundamental discoveries of materials possessing multiple dynamic bonds and applications facilitated by the presence of multiple linking group chemistry. [ABSTRACT FROM AUTHOR]

Nature has engineered delicate synergistic covalent and supramolecular polymers (CSPs) to achieve advanced life functions, such as the thin filaments that assist in muscle contraction. Constructing artificial synergistic CSP materials with bioinspired mechanically adaptive features, however, represents a challenging goal. Here, we report an artificial CSP system to illustrate the integration of a covalent polymer (CP) and a supramolecular polymer (SP) in a synergistic fashion, along with the emergence of notable mechanical and dynamic properties which are unattainable when the two polymers are formed individually. The synergistic effect relies on the peculiar network structures of the SP and CPs, which endow the resultant CSPs with overall improved mechanical performance in terms of the stiffness, strength, stretchability, toughness, and elastic recovery. Moreover, the dynamic properties of the SP, including self‐healing, stimuli‐responsiveness, and reprocessing, are also retained in the CSPs, thus leading to their application as programmable and tunable materials. [ABSTRACT FROM AUTHOR]

Exploring dynamic bonds and their applications in fabricating dynamic materials has received great attention. A photoinduced [2]rotaxane‐based dynamic mechanical bond (DMB) features visible‐light‐triggered dynamic bonding behavior that is essentially distinguished from conventional dynamic chemical bonds. In this DMB, a photoisomerizable ortho‐fluoroazobenzene unit is introduced as a steric‐controllable stopper, the visible‐light‐induced dynamic wagging movement of which enables the photoregulated threading of the macrocycle. This allows reversible in situ de‐/reforming of the mechanical bond without involving dynamic chemical linkage. The DMB‐cross‐linked polymeric gel shows interesting photoinduced degradation behavior upon visible light irradiation. Benefiting from the distinctive dual dynamic nature of reversible bonding behavior and mechanical interlocked structure, this DMB is expected to serve as a new type of dynamic bond that can be applied in designing dynamic soft materials. [ABSTRACT FROM AUTHOR]

Dynamic assembly of macromolecules in biological systems is one of the fundamental processes that facilitates life. Although such assembly most commonly uses noncovalent interactions, a set of dynamic reactions involving reversible covalent bonding is actively being exploited for the design of functional materials, bottom‐up assembly, and molecular machines. This Minireview highlights recent implementations and advancements in the area of tunable orthogonal reversible covalent (TORC) bonds for these purposes, and provides an outlook for their expansion, including the development of synthetically encoded polynucleotide mimics. TORC about: The utilization of tunable orthogonal reversible covalent (TORC) bonds is highlighted in this Minireview. The focus lies in the variety of different applications that are possible, including controlling molecular assembly, operating complex molecular machines, and designing dynamic, self‐healable polymer networks. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogels are commonly used as engineered extracellular matrix (ECM) mimics in applications ranging from tissue engineering to in vitro disease models. Ideal mechanisms used to crosslink ECM‐mimicking hydrogels do not interfere with the biology of the system. However, most common hydrogel crosslinking chemistries exhibit some form of crossreactivity. The field of bioorthogonal chemistry has arisen to address the need for highly specific and robust reactions in biological contexts. Accordingly, bioorthogonal crosslinking strategies are incorporated into hydrogel design, allowing for gentle and efficient encapsulation of cells in various hydrogel materials. Furthermore, the selective nature of bioorthogonal chemistries can permit dynamic modification of hydrogel materials in the presence of live cells and other biomolecules to alter matrix mechanical properties and biochemistry on demand. This review provides an overview of bioorthogonal strategies used to prepare cell‐encapsulating hydrogels and highlights the potential applications of bioorthogonal chemistries in the design of dynamic engineered ECMs. [ABSTRACT FROM AUTHOR]

The homogenization of kinetic laminates in the framework of time-dependent linearized elasticity is studied from a variational point of view through the Γ-convergence of the associated energies. The characterization of the effective coefficients is achieved by means of a finite dimensional minimization problem. [ABSTRACT FROM AUTHOR]

A multistimuli-responsive transient supramolecular polymerization of β-sheet-encoded dendritic peptide monomers in water is presented. The amphiphiles, which contain glutamic acid and methionine, undergo a glucose oxidase catalyzed, glucose-fueled transient hydrogelation in response to an interplay of pH and oxidation stimuli, promoted by the production of reactive oxygen species (ROS). Adjusting the enzyme and glucose concentration allows tuning of the assembly and the disassembly rates of the supramolecular polymers, which dictate the stiffness and transient stability of the hydrogels. The incorporation of triethylene glycol chains introduces thermoresponsive properties to the materials. We further show that repair enzymes are able to reverse the oxidative damage in the methionine-based thioether side chains. Since ROS play an important role in signal transduction cascades, our strategy offers great potential for applications of these dynamic biomaterials in redox microenvironments. [ABSTRACT FROM AUTHOR]

The temporary nature of this fuel-directed change in the interacting molecules causes the gels that are formed from this fuel to have a limited lifetime, autonomously converting back to their original pre-gel state over time without additional user input. Inside Back Cover: Transient and Dissipative Host-Guest Hydrogels Regulated by Consumption of a Reactive Chemical Fuel (Angew. Keywords: Chemical Fuel; Dynamic Materials; Non-Equilibrium; Rheology; Soft Matter EN Chemical Fuel Dynamic Materials Non-Equilibrium Rheology Soft Matter 1 1 1 03/02/23 20230306 NES 230306 B A new route to prepare hydrogels b relies on consumption of a chemical fuel to transiently drive network crosslinking by host-guest motifs, thereby prompting hydrogelation. [Extracted from the article]

The temporary nature of this fuel-directed change in the interacting molecules causes the gels that are formed from this fuel to have a limited lifetime, autonomously converting back to their original pre-gel state over time without additional user input. Keywords: Chemical Fuel; Dynamic Materials; Non-Equilibrium; Rheology; Soft Matter EN Chemical Fuel Dynamic Materials Non-Equilibrium Rheology Soft Matter 1 1 1 03/02/23 20230306 NES 230306 B A new route to prepare hydrogels b relies on consumption of a chemical fuel to transiently drive network crosslinking by host-guest motifs, thereby prompting hydrogelation. Chemical Fuel, Dynamic Materials, Non-Equilibrium, Rheology, Soft Matter. [Extracted from the article]

Localized inclusions of liquids provide solid materials with many functions, such as self-healing, secretion, and tunable mechanical properties, in a spatially controlled mode. However, a strategy to control the distribution of liquid droplets in solid matrices directly obtained from a homogeneous solution has not been reported thus far. Herein, we describe an approach to selectively localize liquid droplets in a supramolecular gel directly obtained from its solution by using evaporative lithography. In this process, the formation of droplet-embedded domains occurs in regions of free evaporation where the non-volatile liquid is concentrated and undergoes a phase separation to create liquid droplets prior to gelation, while a homogeneous gel matrix is formed in the regions of hindered evaporation. The different regions of a coating with droplet embedment patterns display different secretion abilities, enabling the control of the directional movement of water droplets. [ABSTRACT FROM AUTHOR]

Chemical systems that remain kinetically dormant until activated have numerous applications in materials science. Herein we present a method for the control of gelation that exploits an inbuilt switch: the increase in pH after an induction period in the urease-catalyzed hydrolysis of urea was used to trigger the base-catalyzed Michael addition of a water-soluble trithiol to a polyethylene glycol diacrylate. The time to gelation (minutes to hours) was either preset through the initial concentrations or the reaction was initiated locally by a base, thus resulting in polymerization fronts that converted the mixture from a liquid into a gel (ca. 0.1 mm min−1). The rate of hydrolytic degradation of the hydrogel depended on the initial concentrations, thus resulting in a gel lifetime of hours to months. In this way, temporal programming of gelation was possible under mild conditions by using the output of an autocatalytic enzyme reaction to drive both the polymerization and subsequent degradation of a hydrogel. [ABSTRACT FROM AUTHOR]

Switchable self-assemblies respond to external stimuli with a transition between near-equilibrium states. Although being a key to present-day advanced materials, these systems respond rather passively, and do not display autonomous dynamics. For autonomous behavior, approaches must be found to orchestrate the time domain of self-assemblies, which would lead to new generations of dynamic and self-regulating materials. Herein, we demonstrate catalytic control of the time domain of pH-responsive peptide hydrogelators in a closed system. We program transient acidic pH states by combining a fast acidic activator with the slow, enzymatic, feedback-driven generation of a base (dormant deactivator). This transient state can be programmed over orders of magnitude in time. It is coupled to dipeptides to create autonomously self-regulating, dynamic gels with programmed lifetimes, which are used for fluidic guidance, burst release, and self-erasing rapid prototyping. [ABSTRACT FROM AUTHOR]

Dynamic materials have been widely studied for regulation of cell adhesion that is important to a variety of biological and biomedical applications. These materials can undergo changes mainly through one of the two mechanisms: ligand release in response to chemical, physical, or biological stimuli, and ligand burial in response to mechanical stretching or the change of electrical potential. This study demonstrates an encrypted ligand and anew hydrogel that are capable of inducing and inhibiting cell adhesion, which is controlled by molecular reconfiguration. The ligand initially exhibits an inert state; it can be reconfigured into active and inert states by using unblocking and recovering molecules in physiological conditions. Since molecular reconfiguration does not require the release of the ligand from the hydrogels, inhibiting and inducing cell adhesion on the hydrogels can be repeated for multiple cycles. [ABSTRACT FROM AUTHOR]

Chemistry, pure and applied, is a science and an industry. By its power over the expressions of matter, it also displays the creativity of art. It has expanded from molecular to supramolecular chemistry and then, by way of constitutional dynamic chemistry, towards adaptive chemistry. Constitutional dynamics allow for adaptation, through component exchange and selection in response to physical stimuli (e.g. light, photoselection), to chemical effectors (e.g. metal ions, metalloselection) or to environmental effects (e.g. phase change) in equilibrium or out-of-equilibrium conditions, towards the generation of the best-adapted/fittest constituent(s) in a dynamic set. Such dynamic systems can be represented by two-dimensional or three-dimensional dynamic networks that define the agonistic and antagonistic relationships between the different constituents linked through component exchange. The introduction of constitutional dynamics into materials science opens perspectives towards adaptive materials and technologies, presenting attractive behavioral features (such as self-healing). In particular, dynamic polymers may undergo modification of their properties (mechanical, optical, etc.) through component exchange and recombination in response to physical or chemical agents. Constitutional adaptive materials open towards a systems materials science and offer numerous opportunities for soft-matter technologies. [ABSTRACT FROM AUTHOR]

The concept of self-healing has created a paradigm shift in the development of a new kind of responsive polymeric materials, which have traditionally been used in a passive role. Inspired by nature, the advancements made in this nascent field of research have given materials the ability of not only sensing damage but also responding and mending themselves in an appropriate manner. Self-healing in polymers can be autonomous, without the need for human intervention, or nonautonomous, requiring some form of external stimulus. The latter type involves the incorporation of dynamic bonds within the polymeric system, giving the ability to heal multiple times. This minireview discusses some of the prominent self-healing polymeric systems that harness different dynamic bond chemistries, with the aim of highlighting the potential of dynamic bonds to prepare such advanced materials. [ABSTRACT FROM AUTHOR]

The concept of dynamic materials (DM) was introduced in the earlier work [1, 2, 9] and developed there for the case of non-colliding characteristics. The present paper extends this concept toward the case when the characteristics collide. The extension is formulated for a linear continuity equation in 1D with a no takeover condition applied to the moving masses. This implies the formation of clots with the preservation of both mass and momentum, which makes the approach resemble the method of “sticky particles” known in pressureless gas dynamics. The extension introduces non-linearity into the transportation problem that was originally missing, thus placing it closer to a non-linear conservation law. [ABSTRACT FROM AUTHOR]

The autonomous self‐regulation of a pH‐responsive peptide hydrogelator by internal biocatalytic feedback is reported by A. Walther and co‐workers in their Communication on page 13258 ff. The resulting dynamic hydrogels have a programmed lifetime and are suitable for applications in transient rapid prototyping and fluidic guidance. [ABSTRACT FROM AUTHOR]