The replacement of halogen-free flame retardants, driven by health concerns, has sparked a large demand for new “green” flame-retardant alternatives. Inspired by the natural flame-retardant properties of Cladophora sp. algae coated with silica diatoms, a silica sol–gel method has been employed to improve the fire resistance of common, open-cell polyurethane (PU) foams. The Stöber process with components 2-propanol, water, tetraethyl orthosilicate (TEOS), and ammonium hydroxide was employed for silica nanoparticle synthesis on the inside walls and struts of PU foam. Upon ignition, the treated foams briefly burn, followed by formation of a propagating char front that leads to self-extinguishment. Most importantly, the coating of silica nanoparticles prevents dripping of flaming residues seen in common untreated PU foams. Microcomputerized tomography of silica-treated foam after burning reveals that char formation is confined to the outer edges of the bulk foam. Via cone calorimetry, the peak heat release rate of a 0.5 M TEOS foam was reported as dropping from 560 to 262 kW/m2, relative to untreated foam. These results, coupled with the ease of application of the silica coatings, suggest a viable and scalable approach to the mitigation of burning of common open-cell PU foams.

Poly(acrylic acid) gels synthesized via free-radical polymerization of acrylic acid and high molarities of salt show properties quite different from such gels synthesized without salt. Enhanced properties include increased extensibility and modulus.

This manuscript is dedicated to Professor Mitsuo Sawamoto's outstanding achievements in polymer chemistry and recognizes his recent retirement from 40 years of exceptional service to Kyoto University. ABSTRACT: Self-assembly of amphiphilic ABA random triblock copolymers in water serves as a novel approach to create unique structure micelles connected with flexible linkages. The ABA triblock copolymers consist of amphiphilic random copolymers bearing hydrophilic poly(ethylene glycol) and hydrophobic dodecyl pendants as the A segments and a hydrophilic poly(ethylene oxide) (PEO) as the middle B segment. The A block is varied in dodecyl methacrylate content of 20%-50% and degree of polymerization (DP) of 100-200. By controlling the composition and DP of the A block, various architectures can be tailor-made as micelles in water: PEO-linked double core unimer micelles, PEOlooped unimer or dimer micelles, and multichain micelles. Those PEO-linked or looped micelles further exhibit thermoresponsive solubility in water.

Polyelectrolyte gels are ionizable, crosslinked polymer networks swollen in a solvent. These materials are prevalent in biological and synthetic applications ranging from the extracellular matrix to personal care products because they swell and deswell according to changes in the solution environment and internal structure. These environmental and internal factors include temperature, solvent, salt, pH, polymer volume fraction, and crosslink density. In order to predict useful properties like swelling and modulus, 70+ years of effort have been taken to understand the thermodynamic driving forces that affect polyelectrolyte gels. Here, we consider the current thermodynamic model of polyelectrolyte gel behavior, which includes balancing the mixing, electrostatic, Donnan, and elastic osmotic pressures, and we present current experimental results in the context of this model. Since the internal free energy of polyelectrolyte gels results in structural and modulus changes, we also review how thermodynamics are linked to rheological and scattering studies. Due to the complex nature of polyelectrolyte gels, the influence of the solution environment on gel behavior and structure has been investigated; however, the current findings are convoluted with multiple equilibrium states and there is a need for greater understanding of the influence of counterion condensation, interfaces, and inhomogeneities. By describing the current state of the thermodynamic model for polyelectrolyte behavior, we emphasize the complexity and tunability of polyelectrolyte gels for future applications. We propose the future direction of polyelectrolyte gel research to focus on gels at interfaces, in human biology, and on gel inhomogeneities. However, these future directions require an understanding of polyelectrolyte gel mechanical properties, structure, and complex nature that can be understood using the current thermodynamic model.

Electrical excitability of cells, tissues and organs is a fundamental phenomenon in biology and physiology. Signatures of excitability include transient currents resulting from a constant or varying voltage gradient across compartments. Interestingly, such signatures can be observed with non-biologically-derived, macromolecular systems. Initial key literature, dating to roughly the late 1960’s into the early 1990’s, is reviewed here. We suggest that excitability in response to electrical stimulation is a material phenomenon that is exploited by living organisms, but that is not exclusive to living systems. Furthermore, given the ubiquity of biological hydrogels, we also speculate that excitability in protocells of primordial organisms might have shared some of the same molecular mechanisms seen in non-biological macromolecular systems, and that vestigial traces of such mechanisms may still play important roles in modern organisms’ biological hydrogels. Finally, we also speculate that bio-mimicking excitability of synthetic macromolecular systems might have practical biomedical applications.

Polyelectrolytes are ubiquitous in biology, from the polynucleotide chain in our DNA, the hyaluronic acid in the vitreous body of the eye (Gao et al., Int J Ophthalmol, 8, 437-440, 2015) to the myosin and actin fibrils that make up our muscles. While synthetic polyelectrolytes are well studied, their correlation to biological polyelectrolytes is just beginning. This review will examine the polyelectrolytes that make up fundamental cell biology from a macromolecular perspective and the implications polyelectrolyte theory has on biological function.

Poly(acrylic acid) (PAA) bulk gels and threads, typically derived via free-radical polymerization, are of interest as anionic polyelectrolyte mimics of cellular cytosol and as models for early protocells. The thread dimensions have been limited by the diameters of readily-available glass or plastic capillaries, and threads with diameters of less than 50 µm have been difficult to achieve. Here, we report a useful approach for achieving crosslinked, partially neutralized PAA, namely poly(acrylate), gel threads with diameters of a few microns when dry. This technique utilizes coaxial electrospinning to effectively produce capillaries (shells) of polystyrene loaded with a gel-forming precursor mixture composed of 3 M acrylic acid, methylene-bisacrylamide, potassium persulfate and 2.2 M NaOH in the core, followed by thermally-induced polymerization and then the removal of the polystyrene shell. Relatively long (up to 5 mm), continuous PAA threads with thicknesses of 5–15 µm are readily obtained, along with a multitude of PAA gel particles, which result from the occasional break-up of the fluid core prior to gel formation during the electrospinning process. The threads and beads are of the sizes of interest to model ancient protocells, certain functional aspects of excitable cells, such as myocytes and neurons, and various membraneless organelles.

Cyclodextrins are a class of molecules which inclusion complexes with small hydrophobic drugs, and has historically been used to improve solubility and bioavailability of labile drugs in pharmaceutical applications. More recently, polymerized cyclodextrin has been applied in various applications as implantable drug delivery depots and as medical device coatings (e.g. polymeric hernia meshes) due to their ability to sustain and control drug delivery as well as prevent biofouling. Cyclodextrin polymers as coatings for metal medical devices, like screws or stents, is less explored; due to the high mechanical property mismatch between polymers and metals, a polymer coating is liable to delaminate easily, especially during device deformation. Novel methods for facilitating attachment to metal substrates have been explored, but coating longevity is still an issue, and these methods typically require the use of multiple reagents and complex methods. We report here the development and characterization of a cyclodextrin polymer with a chelator-based crosslinker with respect to appearance, chemistry, drug release profiles, erosion, pH-dependence. We found that increasing the crosslinking ratio (crosslinker:cyclodextrin) slowed down degradation and decreased drug loading as well. Drug release of the anti-restenotic drug sirolimus proceeded for over 4 weeks. The ability of the polymer to stably coat metal stents was verified, and the coating procedure is a simple, single step protocol.