State-of-the-Art Polyurea Coatings: Synthesis Aspects, Structure-Properties Relationship, and Nanocomposites for Ballistic Protection Applications

This review presents polyurea (PU) synthesis, the structure-properties relationship, and characterization aspects for ballistic protection applications. The synthesis of polyurea entails step-growth polymerization through the reaction of an isocyanate monomer/prepolymer and a polyamine, each component possessing a functionality of at least two. A wide range of excellent properties such as durability and high resistance against atmospheric, chemical, and biological factors has made this polymer an outstanding option for ballistic applications. Polyureas are an extraordinary case because they contain both rigid segments, which are due to the diisocyanates used and the hydrogen points formed, and a flexible zone, which is due to the chemical structure of the polyamines. These characteristics motivate their application in ballistic protection systems. Polyurea-based coatings have also demonstrated their abilities as candidates for impulsive loading applications, affording a better response of the nanocomposite-coated metal sheet at the action of a shock wave or at the impact of a projectile, by suffering lower deformations than neat metallic plates.

Co-solvent polarity tuned thermochromic nanotubes of cyclic dipeptide-polydiacetylene supramolecular system

The cooperative non-covalent interactions arising from structurally integrated multiple molecules have emerged as a powerful tool for the creation of functional supramolecular structures. Herein, we constructed cyclic dipeptide (CDP)–polydiacetylene (PDA) conjugate (CDP–DA) by introducing cyclo(l-Phe-l-Lys) to the linear 10,12-pentacosadiynoic acid. Owing to extensive hydrogen bonding characteristics, together with structural chirality of cyclo(l-Phe-l-Lys) and strong π–π stacking diacetylenic template, CDP–DA generated supramolecular nanotubes. The structural visualization using scanning and transmission electron microscopy revealed chloroform/methanol co-solvent polarity tuned morphological transformation of intrinsic lamellar assemblies into nanotubes comprising single-wall and multi-wall structure. The mechanistic understanding by X-ray diffraction patterns confirms bilayer organization in lamellar structure, which forms nanotubes via a gradual lamellar curling-to-scrolling process. The supramolecular CDP–DA nanotubes are transformed into the rigid covalently cross-linked blue-phase polydiacetylene (CDP–PDA) by UV irradiation. Very interestingly, the blue-phase nanotubes display reversible thermochromic changing temperature up to 150 °C with excellent repeatability over a dozen thermal cycles. This work provides an efficient strategy for precise morphological control and aiding the perspective for development in nanostructures for functional devices.

Co-solvent controlled fabrication of thermo-responsive chromogenic nanotubes of a cyclic dipeptide–polydiacetylene supramolecular system.

Self-healing and reprocessable bromo butylrubber based on combined ionic cluster formation and hydrogen bonding

The properties of modified bromobutyl rubber are strongly influenced by competing interactions via hydrogen bridges and ionic cluster formation. Dynamic network formation enables self-healing and reprocessability of the material.

Functional materials with self-healing properties: a review

Self-healing materials (SHMs) have been a research hot topic in recent years owing to their greatly improved longevity and safety in practical applications. Recently, research on SHMs has gradually expanded from structural materials to functional materials. Functional materials with self-healing properties (FMSH) require simultaneous repairing not only of the mechanical properties but of the functionalities from damaged cracks or wounds. It is more challenging to introduce both self-healing properties and a particular functionality to materials owing to the difficulties of preparing the materials and their more complex healing mechanism. Herein, we summarize the recent progress that has been made in FMSH, put forward insights from the perspectives of material preparation and healing mechanisms and highlight future developments for FMSH.

Reversible Self-Healing Carbon-Based Nanocomposites for Structural Applications

Reversible Hydrogen Bonds (RHB) have been explored to confer self-healing function to multifunctional nanocomposites. This study has been carried out through a sequence of different steps. Hydrogen bonding moieties, with the intrinsic ability to simultaneously perform the functions of both hydrogen donors and acceptors, have been covalently attached to the walls of carbon nanotubes. The epoxy matrix has been modified to adapt the formulation for hosting self-healing mechanisms. It has been toughened with different percentages of rubber phase covalently linked to the epoxy precursor. The most performant matrix, from the mechanical point of view, has been chosen for the incorporation of MWCNTs. Self-healing performance and electrical conductivities have been studied. The comparison of data related to the properties of nanocomposites containing incorporated functionalized and nonfunctionalized MWCNTs has been performed. The values of the electrical conductivity of the self-healing nanocomposites, containing 2.0% by weight of functionalized multiwalled carbon nanotubes (MWCNTs), range between 6.76 × 10-3 S/m and 3.77 × 10-2 S/m, depending on the nature of the functional group. Curing degrees, glass transition temperatures, and storage moduli of the formulated multifunctional nanocomposites prove their potential for application as functional structural materials.

Self-Assembled pH-Responsive Polymeric Micelles for Highly Efficient, Noncytotoxic Delivery of Doxorubicin Chemotherapy To Inhibit Macrophage Activation: In Vitro Investigation

Self-assembled pH-responsive polymeric micelles, a combination of hydrophilic poly(ethylene glycol) segments and hydrogen bonding interactions within a biocompatible polyurethane substrate, can spontaneously self-assemble into highly controlled, nanosized micelles in aqueous solution. These newly developed micelles exhibit excellent pH-responsive behavior and biocompatibility, highly controlled drug (doxorubicin; DOX) release behavior, and high drug encapsulation stability in different aqueous environments, making the micelles highly attractive potential candidates for safer, more effective drug delivery in applications such as cancer chemotherapy. In addition, in vitro cell studies revealed the drug-loaded micelles possessed excellent drug entrapment stability and low cytotoxicity toward macrophages under normal physiological conditions (pH 7.4, 37 °C). When the pH of the culture media was reduced to 6.0 to mimic the acidic tumor microenvironment, the drug-loaded micelles triggered rapid release of DOX within the cells, which induced potent antiproliferative and cytotoxic effects in vitro. Importantly, fluorescent imaging and flow cytometric analyses confirmed the DOX-loaded micelles were efficiently delivered into the cytoplasm of the cells via endocytosis and then subsequently gradually translocated into the nucleus. Therefore, these multifunctional micelles could serve as delivery vehicles for precise, effective, controlled drug release to prevent accumulation and activation of tumor-promoting tumor-associated macrophages in cancer tissues. Thus, this unique system may offer a potential route toward the practical realization of next-generation pH-responsive therapeutic delivery systems.

Preparation of a photo- and thermo-responsive topological gel from anthracene-modified polyrotaxanes

A topological gel was formed from anthracene-modified polyrotaxanes (An-PRs) under UV irradiation, and the gel can turn back to a sol under thermal treatment due to the dimerization between the anthracene units and the dissociation of the formed dimer.

Self-assembled supramolecular polymers with tailorable properties that enhance cell attachment and proliferation

Self-assembled supramolecular scaffolds, a combination of noncovalent interactions within a biocompatible polymer substrate, can be used for efficient construction of highly-controlled self-organizing hierarchical structures; these newly-developed biomaterials exhibit excellent mechanical properties, tunable surface hydrophilicity, low cytotoxicity and high biodegradability, making them highly attractive for tissue engineering and regenerative medicine applications. Herein, we demonstrate a novel supramolecular poly(ε-caprolactone) (PCL) containing self-complementary sextuple hydrogen-bonded uracil-diamidopyridine (U-DPy) moieties, which undergoes spontaneous self-assembly to form supramolecular polymer networks. Inclusion of various U-DPy contents enhanced the mechanical strength and viscosities of the resulting materials by up to two orders of magnitude compared to control PCL. Surface wettability and morphological studies confirmed physically-crosslinked films can be readily tailored to provide the desired surface properties. Cell viability assays indicated the excellent in vitro biocompatibility of U-DPy-functionalized substrates and indicate the potential of these materials for various biomedical applications. More importantly, mouse fibroblast NIH/3T3 cells cultured on these substrates displayed a more elongated cell morphology and had substantially higher cell densities than cells seeded on control PCL substrate, which indicates that introduction of U-DPy moieties into polymer matrixes could be used to create tissue culture surfaces that enhance cell attachment and proliferation. This new system is suggested as a potential route towards the practical realization of next-generation tissue-engineering scaffolds.

STATEMENT OF SIGNIFICANCE

In this study, we report a significant breakthrough in development of self-assembled supramolecular polymers to form well-defined scaffolds through self-complementary hydrogen-bonding interactions. These newly developed materials exhibited extremely good mechanical properties, fine-tunable hydrophilic characteristics and excellent biocompatibility due to hydrogen-bond-induced physical cross-linking. Importantly, cell adhesion and proliferation assays indicated that these substrates efficiently promoted the growth of mouse embryonic fibroblasts NIH/3T3 cells in vitro. Thus, this finding provides a simple and effective route for the development of next-generation tissue-engineering scaffolds that have improved mechanical properties, increased surface hydrophilicity and can enhance the growth and biological activity of adherent cells.

Supramolecular core-shell nanoparticles for photoconductive device applications

We report a breakthrough discovery involving supramolecular-based strategies to construct novel core-shell heterojunction nanoparticles with hydrophilic adenine-functionalized polythiophene (PAT) as the core and hydrophobic phenyl-C61-butyric acid methyl ester (PCBM) as the shell, which enables the conception of new functional supramolecular assemblies for constructing functional nanomaterials for applications in optoelectronic devices. The generated nanoparticles exhibit uniform spherical shape, well-controlled tuning of particle size with narrow size distributions, and excellent electrochemical stability in solution and the solid state owing to highly efficient energy transfer from PAT to PCBM. When the PAT/PCBM nanoparticles were fabricated into a photoconducting layer in an electronic device, the resulting device showed excellent electric conduction characteristics, including an electrically-tunable voltage-controlled switch, and high short-circuit current and open-circuit voltage. These observations demonstrate how the self-assembly of PAT/PCBM into specific nanostructures may help to promote efficient charge generation and transport processes, suggesting potential for a wide variety of applications as a promising candidate material for bulk heterojunction polymer devices.

Ureido cytosine and cytosine-containing acrylic copolymers

Ureido-cytosine pendant groups contributed to random acrylic copolymers with enhanced thermomechanical performance, well-defined morphologies, and reduced water uptake.

Supramolecular assembly-mediated lithium ion transport in nanostructured solid electrolytes

Supramolecular solid polymer electrolytes provide mechanical integrity and well-defined ion-conducting paths for rapid ion transport that can be applied in high-performance lithium-ion batteries.