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[Display omitted] • Simple building blocks enable orthogonal solvent-free coupling of DCBs. • Poly(TABA) shows relatively high mechanical robustness (E = 1.1 GPa, σ t = 30 MPa). • Rheological kinetic analysis reveals intrinsic temperature range of bond exchange. • A fluorescent and shape-memorable dual-encryption material is constructed by design. • Multi-ways (decrosslinking and depolymerization) employed to recycle this material. Replacing the "inert" chemical bonds in traditional materials with dynamic bonds brings opportunities in designing renewable materials that repair, reprocess and recycle. Despite the many efforts made in covalent adaptable networks by elaborating a single type of dynamic covalent chemistry, the fabrication of double dynamic covalent polymeric networks, especially using simple small-molecule building blocks, still remains challenging. Here we report the solvent-free construction of a thermosetting material by combining 1,2-dithiolane-based reversible polymerization and dynamic covalent boroxine chemistry as crosslinkers. The resulting materials exhibit tunable mechanical properties, mechanical reprocessability, shape memory ability and closed-loop chemical recyclability. Quantitative kinetic analysis reveals the temperature-dependent apparent activation energy for the bond exchange of the resulting network as a result of the simultaneous integration of the two dynamic covalent bonds. Meanwhile, the boroxine units also act as a luminescent center to enable an emissive "organic glass" that can be used as a dual encryption material taking advantage of the reprogrammable shape-memory behavior of the dynamic network. Benefitting from the simple design, tunable variables and multi-functions, we envision that this double dynamic chemistry offers a robust scaffold and great chemical spaces for the design of dynamic polymeric materials. [ABSTRACT FROM AUTHOR]

The paper reports new chitosan-based nanofibers, designed to address the healing of burn wounds. To this aim, mesoporous chitosan fiber mats were prepared by electrospinning using poly(ethylene oxide) as sacrificial additive, followed by loading with norfloxacin and coating with an antifungal agent via dynamic imine bonds. Dynamic vapor sorption experiment proved intra-fiber mesopores around 2.7 nm, and UV–vis, FTIR, and NMR spectroscopy confirmed the norfloxacin embedding and the imination reaction. SEM, AFM and POM techniques displayed semicrystalline nanofibers with average diameter around 170 nm entangled into a non-woven mat. Their mesoporous nature favored a rapid adsorption of fluids up to 17 g/g, and a biodegradation rate fitting the wound healing rate, i.e. up to 30 % mass loss in media of pH characteristic to wound exudate and total degradation in that characteristic to normal dermis. The composite fibers released the NFX and 2FPBA in a controlled manner, and showed antimicrobial activity against gram positive, gram negative and fungal strains. They had no cytotoxic effect on normal human dermal fibroblasts, and showed biocompatibility on experimental rats. The investigation of wound healing ability on second/third-degree burn model in rats revealed wound closure and total restoration of the fully functional dermis and epidermis. [Display omitted] [ABSTRACT FROM AUTHOR]

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]

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]