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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]

Abstract: We consider propagation of waves through a spatio-temporal doubly periodic material structure with rectangular microgeometry in one spatial dimension and time. Both spatial and temporal periods in this dynamic material are assumed to be the same order of magnitude. Mathematically the problem is governed by a standard wave equation with variable coefficients. We consider a checkerboard microgeometry where variables cannot be separated. The rectangles in a space–time checkerboard are assumed filled with materials differing in the values of phase velocities but having equal wave impedance . The difference between dynamic materials and classical static composites is that in the former case the design variables will also be time dependent. Within certain parameter ranges, the formation of distinct and stable limiting characteristic paths, i.e., limit cycles, was observed in [K.A. Lurie, S.L. Weekes, Wave propagation and energy exchange in a spatio-temporal material composite with rectangular microstructure, J. Math. Anal. Appl. 314 (2006) 286–310]; such paths attract neighboring characteristics after a few time periods. The average speed of propagation along the limit cycles remains the same throughout certain ranges of structural parameters, and this was called in [K.A. Lurie, S.L. Weekes, Wave propagation and energy exchange in a spatio-temporal material composite with rectangular microstructure, J. Math. Anal. Appl. 314 (2006) 286–310] a plateau effect. Based on numerical evidence, it was conjectured in [K.A. Lurie, S.L. Weekes, Wave propagation and energy exchange in a spatio-temporal material composite with rectangular microstructure, J. Math. Anal. Appl. 314 (2006) 286–310] that a checkerboard structure is on a plateau if and only if it yields stable limit cycles and that there may be energy concentrations over certain time intervals depending on material parameters. In the present work we give a more detailed analytic characterization of these phenomena and provide a set of sufficient conditions for the energy concentration that was predicted numerically in [K.A. Lurie, S.L. Weekes, Wave propagation and energy exchange in a spatio-temporal material composite with rectangular microstructure, J. Math. Anal. Appl. 314 (2006) 286–310]. [Copyright &y& Elsevier]

Abstract: A space–time extension of the topology optimization method is presented. The formulation, with design variables in both the spatial and temporal domains, is used to create structures with an optimized distribution of material properties that can vary in time. The method is outlined for one-dimensional transient wave propagation in an elastic rod with time dependent Young’s modulus. By two simulation examples it is demonstrated how dynamic structures can display rich dynamic behavior such as wavenumber/frequency shifts and lack of energy conservation. The optimization method’s potential for creating structures with novel dynamic behavior is illustrated by a simple example; it is shown that an elastic rod in which the optimized stiffness distribution is allowed to vary in time can be much more efficient in prohibiting wave propagation compared to a static bandgap structure. Optimized designs in form of spatio-temporal laminates and checkerboards are generated and discussed. The example lays the foundation for creating designs with more advanced functionalities in future work. [Copyright &y& Elsevier]

Abstract: Dynamers may be defined as constitutional dynamic polymers, i.e. polymeric entities whose monomeric components are linked through reversible connections and have therefore the capacity to modify their constitution by exchange and reshuffling of their components. They may be either of molecular or supramolecular nature depending on whether the connections are reversible covalent bonds or non-covalent interactions. They are formed, respectively, either by polycondensation with functional recognition or by polyassociation with interactional recognition between the connecting subunits. Both types are illustrated by specific examples implementing hydrogen bonding on one hand and acylhydrazone formation on the other. The dynamic properties confer to dynamers the ability to undergo adaptation and driven evolution under the effect of external chemical or physical triggers. Dynamers thus are constitutional dynamic materials resulting from the application of the principles of constitutional dynamic chemistry to polymer science. [Copyright &y& Elsevier]

Component exchange in reversible polymers allows the generation of dynamic constitutional diversity. The polycoridensation of dihydrazides with dialdehydes generates polyacylhydrazones, to which the acylhydrazone functionality formed confers both hydrogen-bonding and reversibility features through the amide and imine groups, respectively. Polyacylhydrazones are thus dynamic polyamides. They are able to reversibly exchange either one or both of their repeating monomer units in the presence of different monomers, thus presenting constitutional dynamic diversity. The polymers subjected to monomer exchange/interchange may be brought to exhibit physical properties vastly different from those of the original polymer. The principle may be extended to other important classes of polymers, giving access, for instance, to dynamic polyureas or polycarbamates. These reversible polymers are therefore able to incorporate, decorporate, or reshuffle their constituting monomers, namely in response to environmental physical or chemical factors, an adaptability feature central to constitutional dynamic chemistry. [ABSTRACT FROM AUTHOR]

A temporal laminate is a material whose parameters are homogeneous in space but vary periodically and discontinuously in time. In this article, we consider wave propagation through a temporal laminate where the period of the disturbance moving through the media is large relative to ϵ the period of the lamination. It is worth noting that the constituent materials and the mixing coefficient can be chosen so that the effective speed in a temporal laminate is greater than the individual phase speeds. We show that the analytic problem admits stable long wave modes, but shorter wave modes grow as they pass through the laminate layers. Computing wave motion through this composite medium using the standard upwind, finite-difference method under the CFL condition for numerical wave propagation in the individual media will produce growing short wave modes. Numerical results are degraded since accuracy is quickly lost due to the growth of short waves which enter into the computation through truncation and round-off error. A new CFL constraint is derived for a finite-difference numerical scheme which will allow us to compute the stable long wave motion. Numerical results are given for the direct numerical simulation of the homogenization problem (ϵ→0). [Copyright &y& Elsevier]

Mechanically interlocked polymers (MIPs) are promising candidates for the construction of elastomeric materials with desirable mechanical performance on account of their abilities to undergo inherent rotational and translational mechanical movements at the molecular level. However, the investigations on their mechanical properties are lagging far behind their structural fabrication, especially for linear polyrotaxanes in bulk. Herein, we report stretchable poly[2]rotaxane elastomers (PREs) which integrate numerous mechanical bonds in the polymeric backbone to boost macroscopic mechanical properties. Specifically, we have synthesized a hydroxy-functionalized [2]rotaxane that subsequently participates in the condensation polymerization with diisocyanate to form PREs. Benefitting from the peculiar structural and dynamic characteristics of the poly[2]rotaxane, the representative PRE exhibits favorable mechanical performance in terms of stretchability (∼1200%), Young's modulus (24.6 MPa), and toughness (49.5 MJ/m 3 ). Moreover, we present our poly[2]rotaxanes as model systems to understand the relationship between mechanical bonds and macroscopic mechanical properties. It is concluded that the mechanical properties of our PREs are mainly determined by the unique topological architectures which possess a consecutive energy dissipation pathway including the dissociation of host-guest interaction and consequential sliding motion of the wheel along the axle in the [2]rotaxane motif., Competing Interests: The authors declare that they have no conflicts of interest in this work., (© 2022 The Authors. Publishing Services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd.)

Developing photopolymerizable polymeric materials offers many opportunities to process materials in a remote and controllable manner. However, most photopolymerizable technologies require the external introduction of photoabsorbing units, whereas designing intrinsically photopolymerizable polymers is still highly challenging. Here, we report that a natural small-molecule disulfide, thioctic acid, can be directly transformed into a poly(disulfides) network under the irradiation of visible light without any external additives. The resulting polymer network exhibits optical transparency, mechanical stretchability and toughness, ambient self-healing ability, and especially strong adhesive ability to different surfaces. The dynamic covalent backbones of the poly(disulfides) endow the depolymerization ability to recycle the material in a closed-loop manner. We foresee that this facile and robust photopolymerization system is of great promise toward low-cost and high-performance photocuring coatings and adhesives.

We consider the problem of wave propagation through one-dimensional dynamic laminates when the wavelength of the disturbance is large relative to the scale of the microstructure. Dynamic materials are heterogeneous formations assembled from materials which are distributed on a microscale in space and in time. Using the techniques of Floquet analysis and asymptotic expansions, we uncover the dispersive effects of the effective medium. [Copyright &y& Elsevier]

Magnetically actuated micro/nanoscale pillars have attracted significant research interest recently because of their dynamic properties. These structures can be used for various applications, such as dry adhesion, cell manipulation, and sensors or actuators in microfluidics. Magnetically actuated structures can be fabricated by mixing magnetic particles and polymers to yield a favorable combination of magnetic permeability and mechanical compliance. However, the pillar density of demonstrated structures is relatively low, which limits the potential applications in active surface manipulation of microscale objects. Here, we demonstrate active periodic nanostructures with a pillar density of 0.25 pillar/μm 2 , which is the highest density for magnetically actuated pillars so far. Having a structure period of 2 μm, diameter of 600 nm, and high aspect ratio of up to 11, this structure can be magnetically actuated with a displacement of up to 200 nm. The behaviors of the pillars under various cyclic actuation modes have been characterized, demonstrating that the actuation can be well controlled. This work can find potential applications in particle manipulation and tunable photonic elements.

Spacecraft are expected to traverse enormous distances over long periods of time without an opportunity for maintenance, re-fueling, or repair, and, for interplanetary probes, no on-board crew to actively control the spacecraft configuration or flight path. Nevertheless, space technology has reached the stage when mining of space resources, space travel, and even colonization of other celestial bodies such as Mars and the Moon are being seriously considered. These ambitious aims call for spacecraft capable of self-controlled, self-adapting, and self-healing behavior. It is a tough challenge to address using traditional materials and approaches for their assembly. True interplanetary advances may only be attained using novel self-assembled and self-healing materials, which would allow for realization of next-generation spacecraft, where the concepts of adaptation and healing are at the core of every level of spacecraft design. Herein, recent achievements are captured and future directions in materials-driven development of space technology outlined., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Materials can be engineered to deliver specific biological cues that control stem cell growth and differentiation. However, current materials are still limited for stem cell engineering as stem cells are regulated by a complex biological milieu that requires spatiotemporal control. Here a new approach of using materials that incorporate designed bacteria as units that can be engineered to control human mesenchymal stem cells (hMSCs), in a highly dynamic-temporal manner, is presented. Engineered Lactococcus lactis spontaneously colonizes a variety of material surfaces (e.g., polymers, metals, and ceramics) and is able to maintain growth and induce differentiation of hMSCs in 2D/3D surfaces and hydrogels. Controlled, dynamic, expression of fibronectin fragments supports stem cell growth, whereas inducible-temporal regulation of secreted bone morphogenetic protein-2 drives osteogenesis in an on-demand manner. This approach enables stem cell technologies using material systems that host symbiotic interactions between eukaryotic and prokaryotic cells., (© 2018 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Dynamic metal-organic frameworks (MOFs) that respond to external stimuli have recently attracted great attention. However, the subtle control of dynamic processes as well as the illustration of the underlying mechanism, which is crucial for the targeted construction and modulation purpose, is extremely challenging. Herein, we report the achievement of simultaneous kinetic and thermodynamic modulation of the structure transformation processes of a family of cobalt(II)-organic frameworks, through the rational combination of coligand replacement, solvent molecule substitution, and ligand-based solid solution strategies. On the basis of the systematic investigation of the structural transformation behaviors, the underlying response mechanism and principles for modulation were illustrated. It is expected that this work can provide valuable hints for the study and further development of dynamic materials.

Soft photonic materials are important for sensors, displays, or energy management and have become switchable under static equilibrium conditions by integration of responsive polymer features. The next step is to equip such materials with the ability for autonomously dynamic and self-regulating behavior, which would advance their functionality and application possibilities to new levels. Here, this study shows the system integration of a nonlinear, biocatalytic pH-feedback system with a pH-responsive block copolymer photonic gel, and demonstrates autonomous transient memories, remotely controlled signal propagation, and sensing. This study utilizes an enzymatic switch to program the lifetime of the reflective state of a photonic gel, and induces propagation of pH-waves extinguishable by illumination with UV-light. The described combination of nonlinear chemistry and responsive photonic gels opens pathways toward out-of-equilibrium photonic devices with active and autonomous behavior useful for sensing, computation, and communication., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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]

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 a new 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., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Control over structural transformations in supramolecular entities by external stimuli is critical for the development of adaptable and functional soft materials. Herein, we have designed and synthesized a dipyridyl donor containing a central Z-configured stiff-stilbene unit that self-assembles in the presence of two 180° di-Pt(II) acceptors to produce size-controllable discrete organoplatinum(II) metallacycles with high efficiency by means of the directional-bonding approach. These discrete metallacycles undergo transformation into extended metallosupramolecular polymers upon the conformational switching of the dipyridyl ligand from Z-configured (0°) to E-configured (180°) when photoirradiated. This transformation is accompanied by interesting morphological changes at nanoscopic length scales. The discrete metallacycles aggregate to spherical nanoparticles that evolve into long nanofibers upon polymer formation. These fibers can be reversibly converted to cyclic oligomers by changing the wavelength of irradiation, which reintroduces Z-configured building blocks owing to the reversible nature of stiff-stilbene photoisomerization. The design strategy defined here represents a novel self-assembly pathway to deliver advanced supramolecular assemblies by means of photocontrol.

Presented here is a cytocompatible covalently adaptable hydrogel uniquely capable of mimicking the complex biophysical properties of native tissue and enabling natural cell functions without matrix degradation. Demonstrated is both the ability to control elastic modulus and stress relaxation time constants by more than an order of magnitude while predicting these values based on fundamental theoretical understanding and the simulation of muscle tissue and the encapsulation of myoblasts., (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)