wileyonlinelibrary.comstiffness. Due to their molecular architecture, thermosets cannot be reshaped, processed, or recycled after full curing. In contrast, thermoplastics can fl ow upon heating, enabling multiple and easy processing, such as by extrusion, [ 3 ] as well as recycling in many cases. [ 4 ] Designing polymer systems that combine the benefi ts of traditional thermosets with the "plastic" properties to facilitate processing is therefore a challenge that has recently attracted great interest.A way to make the combination of these properties is offered by the introduction of exchangeable chemical bonds into a polymer network, leading to dynamic cross-links. These bonds should be able to rearrange themselves in a reversible manner, providing on a molecular level a mechanism for macroscopic fl ow without risking structural damage. Polymer networks containing such exchangeable bonds, also known as covalent adaptable networks or CANs, [ 5 ] may be further classifi ed into those relying on respectively dissociative and associative exchange reactions. [ 6 ] The most common "dissociative" group of CANs relies on a reversible covalent bond formation between two groups attached to the polymer chains. By triggering the reversed bond forming step (bond dissociation), the material can achieve topology rearrangements (stress relaxation and fl ow), simply because of a decrease in connectivity during the temporary depolymerization, resulting in a strong and sudden viscosity drop and a loss of dimensional stability. Such systems will always present a sol/ gel transition and can thus be solubilized in the presence of solvent. A representative example of a thermally triggered dissociative CAN relies on the well-known reversible Diels-Alder reaction between furans and maleimides. [ 7 ] A less common type of CAN makes use of associative bond exchanges between polymer chains, [ 8 ] in which the original cross-links between polymer chains are only broken once a bond to another (part of the) polymer chain has been formed. As a result, such systems can change their topology with no loss of connectivity during the dynamic reorganization process, making such networks effectively permanent and insoluble, even at (very) high temperatures. Interestingly, as with all chemical reactions, the rate of this associative exchange increases with the temperature, leading to an Arrhenius-like viscosity dependence, rather than a sudden and marked viscosity drop at the sol/gel transition. Thermally triggered associative CANs have been coined vitrimers, [ 9 ] because of their unique combination of insolubility and gradual thermal viscosity behavior, Vitrimers are a new class of polymeric materials with very attractive properties, since they can be reworked to any shape while being at the same time permanently cross-linked. As an alternative to the use of transesterifi cation chemistry, we explore catalyst-free transamination of vinylogous urethanes as an exchange reaction for vitrimers. First, a kinetic study on model compounds reveals the occu...

Furan-based thermoset polyurethanes have been prepared in a one-pot fashion with the ability to selfmend under mild temperature conditions, by making use of a Diels−Alder shape-memory assisted self-healing (DASMASH) approach. For this, thermoreversible covalent bonds, obtained by Diels−Alder chemistry, are introduced as cross-linkers into a polycaprolactone (PCL) containing polyurethane material. It is demonstrated that, after introduction of a crack into the PUthermoset, Diels−Alder bonds preferentially break, regenerating free furan/maleimide functional groups, while the shape memory effect favors the crack closure at temperatures above the melting point of PCL, simultaneously resulting in a reformation of the reversible cross-links. The reversibility and shape memory ability of the materials were optimized and studied by FTIR, 1 H NMR and tensile measurements. Different compositions were used to properly understand the role and influence of each component. The polyurethane materials healed at 50°C after mechanical damage induced by either the application of a large tensile deformation or by performing controlled macro/micro scratches with a depth sensing indenter. Online FT-IR monitoring provided a kinetic description of the system reversibility for numerous cycles. Furthermore, mechanical recovery with complete disappearance of the microscratches was accomplished after multiple cycles of large tensile deformation. The results were not only confirmed by an optical inspection and scanning electron microscopy, but also with confocal microscopic mapping, by comparison of the cross-section profiles of the microscratches before and after healing.

Electrospun nanocomposite matrices based on poly(ε-caprolactone) (PCL), nano-hydroxyapatite (nHAp) and amoxicillin (AMX) were designed and investigated for dental applications. nHAp provides good biocompatibility, bioactivity, osteoconductivity, and osteoinductivity properties, and AMX, as antibiotic model, controls and/or reduces bacterial contamination of periodontal defects while enhancing tissue regeneration. A series of polymeric nanocomposites was obtained by varying both the antibiotic and nHAp contents. Fibrous membranes of different compositions were obtained by electrospinning technique, and morphological, thermal, mechanical and surface properties were characterized. The incorporation of AMX seemed to alter the nHAp distribution within the microfibrous matrix. The interaction between AMX and nHAp affected the mechanical performance and modulated the antibiotic release behavior. AMX release profiles presented a burst release that depended on nHAp content, followed by a slow release stage where the drug content (85-100%) was released in 3 weeks. The antimicrobial activity of the AMX-loaded membranes was tested with four bacterial strains depended on both the drug and nHAp contents. Extensive mineralization in simulated body fluid (SBF) was evidenced by SEM/EDX analysis after 21 days. The studied electrospun nanocomposite amoxicillin-loaded membranes could be a promising fibrous-based antibiotic carrier system for dental and tissue engineering applications. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 966-976, 2017.

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A smart catalyst that can be activated by UV-light was prepared by encapsulating Metal-Organic-Framework (MOF) particles in microcapsules with a photocleavable polyurea shell. Addition of palmitic acid as a modulator during the synthesis of the Fe-terephthalate MOF MIL-88B(Fe) yields MOF particles with a hydrophobic surface. These particles can be successfully encapsulated via interfacial polymerization, as proven by a combination of PXRD, SEM and EDX techniques. By the incorporation of photolabile groups in the polymer shell, UV light can be employed to trigger degradation of the capsules, releasing the catalytic load. Catalyst activation triggered by UV light was monitored by recording the rates for catalytic tetramethylbenzidine (TMB) oxidation with H 2 O 2 . The reactivity could be controlled by tuning irradiation time, UV intensity or MOF loading. The activity of the capsules was up to 90 times higher after irradiation.

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Adipose-derived mesenchymal stem cells (ASCs) accelerate the osteointegration of bone grafts and improve the efficiency in the formation of uniform bone tissue, providing a practical and clinically attractive approach in bone tissue regeneration. In this work, the effect of nanofibrous biomimetic matrices composed of poly(ε-caprolactone) (PCL), nanometric hydroxyapatite (nHA) particles and 14-3-3 protein isoform epsilon on the initial stages of human ASCs (hASCs) osteogenic differentiation was investigated. The cells were characterized by flow cytometry and induction to differentiation to adipogenic and osteogenic lineages. The isolated hASCs were induced to differentiate to osteoblasts over all scaffolds, and adhesion and viability of the hASCs were found to be similar. However, the activity of alkaline phosphatase (ALP) as early osteogenic marker in the PCL-nHA/protein scaffold was four times higher than in PCL-nHA and more than five times than the measured in neat PCL.