Synthesis, Characterization and Thermal Properties of Poly(ethylene oxide), PEO, Polymacromonomers via Anionic and Ring Opening Metathesis Polymerization

Innovative Functional Biomaterials as Therapeutic Wound Dressings for Chronic Diabetic Foot Ulcers

The imbalance of local and systemic factors in individuals with diabetes mellitus (DM) delays, or even interrupts, the highly complex and dynamic process of wound healing, leading to diabetic foot ulceration (DFU) in 15 to 25% of cases. DFU is the leading cause of non-traumatic amputations worldwide, posing a huge threat to the well-being of individuals with DM and the healthcare system. Moreover, despite all the latest efforts, the efficient management of DFUs still remains a clinical challenge, with limited success rates in treating severe infections. Biomaterial-based wound dressings have emerged as a therapeutic strategy with rising potential to handle the tricky macro and micro wound environments of individuals with DM. Indeed, biomaterials have long been related to unique versatility, biocompatibility, biodegradability, hydrophilicity, and wound healing properties, features that make them ideal candidates for therapeutic applications. Furthermore, biomaterials may be used as a local depot of biomolecules with anti-inflammatory, pro-angiogenic, and antimicrobial properties, further promoting adequate wound healing. Accordingly, this review aims to unravel the multiple functional properties of biomaterials as promising wound dressings for chronic wound healing, and to examine how these are currently being evaluated in research and clinical settings as cutting-edge wound dressings for DFU management.

Solvent-Free Direct PEGylation of Collagen Fibers

The addition of poly(ethylene glycol) (PEG) to biomolecules and biomaterials is a well-established approach to modify their properties for therapeutic applications. For biomaterials, the approach is typically to blend or electrospray the synthetic polymer with the biomaterial. Effective surface modification approaches such as surface-initiated polymer brushes are challenging since the harsh solvents required for brush synthesis may destroy the biomaterial. Herein, we describe the PEGylation of collagen fibers by surface-initiated PEG brushes using a living anionic grafting-from mechanism. This brush synthesis is done in the absence of solvents to minimize the degradation of the native collagen structure. We quantify the effect the brush synthesis has on the native structure of the collagen fiber using differential scanning calorimetry (DSC) and find that even at long reaction times a significant fraction of the native structure remains. Dynamic mechanical analysis indicates the collagen undergoes only modest structural degradation, while adhesion studies find a significant improvement of antifouling properties. Further, our approach opens the way for further chemistry, as the growing polymer chain is a potassium alkoxy group that can be functionalized by termination or by subsequent reaction by a wide variety of molecules.

Synthesis and characterization of poly(ethylene glycol) bottlebrush networks via ring-opening metathesis polymerization

Herein it is reported how the overlap concentration (C*) can be used to overcome crosslinking due to diol impurities in commercial PEG, allowing for the synthesize of bottlebrush polymers with good control over molecular weight. Additionally, PEG-based bottlebrush networks are synthesized via ROMP, attaining high conversions with minimal sol fractions (<2%). The crystallinity and mechanical properties of these networks are then further altered by solvent swelling with phosphate buffer solution (PBS) and 1-ethyl-3-methylimidazolium ethyl sulfate/DCM cosolvents. The syntheses reported here highlight the potential of the bottlebrush network architecture for use in the rational design of new materials.

Chitosan/PEO nanofibers containing Calendula officinalis extract: Preparation, characterization, in vitro and in vivo evaluation for wound healing applications

Wound healing is a complex pathophysiological process, highlighting the importance of effective and thorough wound care along with the prevention of wound infection, a major barrier that can slow down or even disrupt the healing process. To date, there are plenty of herbal plants well known and historically supernatural, showing profound wound healing effects. Application of such herbal extracts/ingredients in electrospun nanofiber platforms has shown promising outcomes in improving wound healing process. Based on these facts, we loaded Calendula officinalis extract (CO) in chitosan/polyethylene oxide scaffolds (CS/PEO) by electrospinning. Using SEM, morphology of electrospun scaffolds showed a narrow range of fiber diameter, around 143--252 nm, with uniform and bead-free appearance. FT-IR spectroscopy confirmed the presence of CO extract in nanofibrous scaffolds. Of importance, incorporation of CO extract improved mechanical properties of CS/PEO nanofibers. A 1602 cP reduction in viscosity and a 0.892 ms/cm increase in the conductivity of the solution was observed after addition of the CO extract. CO extract showed strong antibacterial properties with 96% and 94% reduction in Gram positive and Gram negative bacteria, respectively. In vitro studies with fibroblast cells confirmed enhanced proliferation, growth and attachment of the cells. The in vivo and histological analysis of rat wounds, revealed excellent wound healing ability of CS/PEO/CO dressings (87.5 % wound closure after 14 days) via improving collagen synthesis, re-epithelization and remodeling of the tissue. In sum, our findings show that CS/PEO/CO scaffolds can be used as a promising dressing for the treatment of skin wounds.

Precise Synthesis and Thin Film Self-Assembly of PLLA-b-PS Bottlebrush Block Copolymers

The ability of bottlebrush block copolymers (BBCPs) to self-assemble into ordered large periodic structures could greatly expand the scope of photonic and membrane technologies. In this paper, we describe a two-step synthesis of poly(l-lactide)-b-polystyrene (PLLA-b-PS) BBCPs and their rapid thin-film self-assembly. PLLA chains were grown from exo-5-norbornene-2-methanol via ring-opening polymerization (ROP) of l-lactide to produce norbornene-terminated PLLA. Norbonene-terminated PS was prepared using anionic polymerization followed by a termination reaction with exo-5-norbornene-2-carbonyl chloride. PLLA-b-PS BBCPs were prepared from these two norbornenyl macromonomers by a one-pot sequential ring opening metathesis polymerization (ROMP). PLLA-b-PS BBCPs thin-films exhibited cylindrical and lamellar morphologies depending on the relative block volume fractions, with domain sizes of 46-58 nm and periodicities of 70-102 nm. Additionally, nanoporous templates were produced by the selective etching of PLLA blocks from ordered structures. The findings described in this work provide further insight into the controlled synthesis of BBCPs leading to various possible morphologies for applications requiring large periodicities. Moreover, the rapid thin film patterning strategy demonstrated (>5 min) highlights the advantages of using PLLA-b-PS BBCP materials beyond their linear BCP analogues in terms of both dimensions achievable and reduced processing time.

Recent Advances in Fiber-Hydrogel Composites for Wound Healing and Drug Delivery Systems

In the last decades, much research has been done to fasten wound healing and target-direct drug delivery. Hydrogel-based scaffolds have been a recurrent solution in both cases, with some reaching already the market, even though their mechanical stability remains a challenge. To overcome this limitation, reinforcement of hydrogels with fibers has been explored. The structural resemblance of fiber-hydrogel composites to natural tissues has been a driving force for the optimization and exploration of these systems in biomedicine. Indeed, the combination of hydrogel-forming techniques and fiber spinning approaches has been crucial in the development of scaffolding systems with improved mechanical strength and medicinal properties. In this review, a comprehensive overview of the recently developed fiber-hydrogel composite strategies for wound healing and drug delivery is provided. The methodologies employed in fiber and hydrogel formation are also highlighted, together with the most compatible polymer combinations, as well as drug incorporation approaches creating stimuli-sensitive and triggered drug release towards an enhanced host response.

Trends in Polymers 2017/2018: Polymer Synthesis

Polymer synthesis is a substantial area in polymer science and marks the starting point for all sorts of polymer materials that have a plethora of applications in everyday life but also in academic research [...].

Macromolecular Brushes Based on Poly(L-Lactide) and Poly(ε-Caprolactone) Single and Double Macromonomers via ROMP. Synthesis, Characterization and Thermal Properties

Single and double poly(L-lactide) (PLLA) and poly(ε-caprolactone) (PCL) macromonomers having a norbornenyl polymerizable group were prepared by conventional Ring Opening Polymerization (ROP). These macromonomers were further subjected to ring opening metathesis polymerization (ROMP) reactions in order to produce double polymer brushes consisting of PLLA or PCL side chains on a polynorbornene (PNBE) backbone. Statistical or block ring opening metathesis copolymerization of the PLLA and PCL macromonomers afforded the corresponding random and block double brushes. Sequential ROMP of the single PLLA, PCL and PLLA macromonomers resulted in the synthesis of the corresponding triblock copolymer brush. The molecular characteristics of the macromolecular brushes were obtained by 1H-NMR spectroscopy and Size Exclusion Chromatography. The thermal properties of the samples were studied by thermogravimetric analysis, TGA, Differential Thermogravimetry, DTG and Differential Scanning Calorimetry, DSC.

Statistical Copolymers of n-Butyl Vinyl Ether and 2-Chloroethyl Vinyl Ether via Metallocene-Mediated Cationic Polymerization. A Scaffold for the Synthesis of Graft Copolymers

The cationic statistical copolymerization of n-butyl (be) and 2-chloroethyl vinyl ether (CEVE), is efficiently conducted using bis(η⁵-cyclopentadienyl)dimethyl zirconium (Cp₂ZrMe₂) in combination with tetrakis(pentafluorophenyl)borate dimethylanilinum salt [B(C₆F₅)₄]^–[Me₂NHPh]⁺, as an initiation system. The reactivity ratios are calculated using both linear graphical and non-linear methods. Structural parameters of the copolymers are obtained by calculating the dyad sequence fractions and the mean sequence length, which are derived using the monomer reactivity ratios. The glass transition temperatures (T_g) of the copolymers are measured by Differential Scanning Calorimetry (DSC), and the results are compared with predictions based on several theoretical models. The statistical copolymers are further employed as scaffolds for the synthesis of graft copolymers having poly(vinyl ether)s as a backbone and either poly(ε-caprolactone) (PCL) or poly(l-lactide) (PLLA) as side chains. Both the grafting “onto” and the grafting “from” methodologies are employed. The reaction sequence is monitored by Size Exclusion Chromatography (SEC), NMR and IR spectroscopies. The advantages and limitations of each approach are thoroughly examined.

Advanced Nanoclay-Based Nanocomposite Solid Polymer Electrolyte for Lithium Iron Phosphate Batteries

High-performance solid polymer electrolytes (SPEs) have long been desired for the next generation of lithium batteries. One of the most promising ways to improve the morphological and electrochemical properties of SPEs is the addition of fillers with specific nanostructures. However, the production of such fillers is generally expensive and requires complicated preparation procedures. Halloysite nanotubes (HNTs), with their tubular structure, resemble carbon nanotubes in terms of geometric features and can be obtained at a relatively low cost. Previously, we reported that the HNT poly(ethylene oxide) composite SPE possesses excellent electrochemical and mechanical properties and outstanding cycling performance for all-solid-state lithium sulfur batteries. However, the HNT/SPE was not effective for lithium iron phosphate (LFP) batteries. The compatibility between the electrodes and the electrolyte sharply decreased, and no decent cycling performance was achieved. Therefore, a modification was studied which involves a minor addition of LFP during the preparation procedure. With this modification, good ionic conductivity (9.23 × 10^-5 S cm^-1 at 25 °C) is achieved, and compatibility between the electrodes and the electrolyte is enhanced. At the same time, an electrochemical stability window of 5.14 V and lithium-ion transference number of 0.46 are found. All-solid-state LFP batteries possessing excellent cycling performance are further demonstrated.

Grubbs' and Schrock's Catalysts, Ring Opening Metathesis Polymerization and Molecular Brushes-Synthesis, Characterization, Properties and Applications

In this review, molecular brushes and other macromolecular architectures bearing a bottlebrush segment where the main chain is synthesized by ring opening metathesis polymerization (ROMP) mediated by Mo or Ru metal complexes are considered. A brief review of metathesis and ROMP is presented in order to understand the problems and the solutions provided through the years. The synthetic strategies towards bottlebrush copolymers are demonstrated and each one discussed separately. The initiators/catalysts for the synthesis of the backbone with ROMP are discussed. Syntheses of molecular brushes are presented. The most interesting properties of the bottlebrushes are detailed. Finally, the applications studied by different groups are presented.

Recent development of brush polymers via polymerization of poly(ethylene glycol)-based macromonomers

Polymerization of poly(ethylene glycol)-based macromonomers is a facile and versatile synthetic method to generate well-defined brush polymers.