Facile Fabrication of Chemically Grafted Graphene Oxide–Poly(glycidyl methacrylate) Composite Microspheres and Their Electrorheology

This paper reports a facile approach for fabricating core‐shell structured graphene oxide (GO)‐wrapped amine‐modified poly(glycidyl methacrylate) (ami‐PGMA) microspheres. The resulting core‐shell structure is confirmed by scanning electron micsroscopy (SEM) and transmission electron microscopy (TEM), whereas the coexistence of GO and PGMA is confirmed by FTIR spectroscopy. The thermal stability of the ami‐PGMA/GO microspheres is enhanced compared with that of pure PGMA microspheres. The novel ami‐PGMA/GO composite microsphere‐based electrorheological (ER) fluid shows typical ER characterization, using a rotational rheometer under an applied electric field. The dielectric analysis results along with the relaxation time and achievable polarizability of the fluid are correlated with the ER performance using a LCR meter.

     

Poly(ethylene glycol)-containing Hydrogels for Oral Protein Delivery Applications

Novel pH-sensitive hydrogels were developed as suitable candidates for carriers in bioMEMS devices as well as for oral delivery of therapeutic peptides and proteins due to their ability to respond to environmental pH change. Macromonomers containing various PEG molecular weights were synthesized and used to prepare P(MAA-g-EG) hydrogels were by photopolymerization. P(MAA-g-EG) hydrogels showed a drastic change of the equilibrium swelling ratio between pH 2.2 and 7.0. At pH 7.0, hydrogels with PEGMA2000 exhibited higher swelling ratio than hydrogels with PEGMA1000. For both hydrogels with PEGMA1000 and PEGMA2000, the swelling mechanism became more relaxation-controled as the environmental pH changed from 2.2 to 7.0 due to the ionization of the functional groups in polymer networks at high pH. In vitro release studies of insulin were conducted. P(MAA-g-EG) hydrogels exhibited drastic increase of insulin release as the pH of the medium was changed from acidic to basic. Insulin release from P(MAA-g-EG) hydrogels with PEGMA2000 was slower than from hydrogels with PEGMA1000 at both low and high pH. These results were used to design and improve protein release behavior from these carriers.     

Poly(ethylene glycol) methacrylate hydrolyzable microspheres for transient vascular embolization

Poly(ethylene glycol) methacrylate (PEGMA) hydrolyzable microspheres intended for biomedical applications were readily prepared from poly(lactide-co-glycolide) (PLGA)–poly(ethylene glycol) (PEG)–PLGA crosslinker and PEGMA as a monomer using a suspension polymerization process. Additional co-monomers, methacrylic acid and 2-methylene-1,3-dioxepane (MDO), were incorporated into the initial formulation to improve the properties of the microspheres. All synthesized microspheres were spherical in shape, calibrated in the 300–500 μm range, swelled in phosphate-buffered saline (PBS) and easily injectable through a microcatheter. Hydrolytic degradation experiments performed in PBS at 37 °C showed that all of the formulations tested were totally degraded in less than 2 days. The resulting degradation products were a mixture of low-molecular-weight compounds (PEG, lactic and glycolic acids) and water-soluble polymethacrylate chains having molecular weights below the threshold for renal filtration of 50 kg mol⁻¹ for the microspheres containing MDO. Both the microspheres and the degradation products were determined to exhibit minimal cytotoxicity against L929 fibroblasts. Additionally, in vivo implantation in a subcutaneous rabbit model supported the in vitro results of a rapid degradation rate of microspheres and provided only a mild and transient inflammatory reaction comparable to that of the control group.     

AGET ATRP of Poly[poly(ethylene glycol) methyl ether methacrylate] Catalyzed by Hydrophobic Iron(III)–Porphyrins

Commercially available hydrophobic porphyrins are investigated as an environmentally friendly catalytic system for iron‐mediated atom transfer radical polymerization (ATRP) of poly(ethylene glycol) monomethyl ether methacrylate (PEGMA). Polymerizations in organic solvent are optimized using activators generated by electron transfer (AGET ATRP), based on iron(III)–porphyrin complexes, and tin(II) 2‐ethyl hexanoate or ascorbic acid as a reducing agent. Copper‐free PPEGMA macromolecules are obtained with high conversion, controlled molecular weight, and polydispersity index compared with standard copper‐based ATRP. The facile preparation and availability of the catalyst, together with its expected low toxicity, represent clear advantages for the synthesis of PPEGMA‐based materials for biomedical use.

     

Films of Highly Disperse Electrodeposited Poly(N‐vinylcarbazole)–Graphene Oxide Nanocomposites

The electrodeposition of polymer nanocomposite thin films of PVK–GO is demonstrated. Highly exfoliated and stable graphene oxide (GO) solutions are prepared by incorporating poly(N‐vinylcarbazole) (PVK) through mixing. Enhanced stability up to 30 d is observed in both aqueous and organic solvents. TGA, XRD, FTIR, and UV‐vis measurements confirm nanocomposite formation. CV enables electrodeposition of the films. The presence of GO on the PVK–GO surface is confirmed by the appearance of the C=O and OH stretching vibrations, attributed to the carboxylic and hydroxyl groups of GO. AFM measurements show homogeneous and well‐defined film morphology.     

Control of Mammalian Cell and Bacteria Adhesion on Substrates Micropatterned with Poly(ethylene glycol) Hydrogels

A simple method for controlling the spatial positioning of mammalian cells and bacteria on substrates using patterned poly(ethylene glycol) (PEG) hydrogel microstructures is described. These microstructures were fabricated using photolithography on silicon, glass or poly (dimethylsiloxane) (PDMS) surfaces modified with a 3-(trichlorosilyl) propyl methacrylate (TPM) monolayer. During the photogelation reaction, the resulting hydrogel microstructures were covalently bound to the substrate via the TPM monolayer and did not detached from the substrate upon hydration. For mammalian cell patterning, microwell arrays of different dimensions were fabricated. These microwells were composed of hydrophilic PEG hydrogel walls surrounding hydrophobic TPM floors inside the microwells. Murine 3T3 fibroblasts and transformed hepatocytes were shown to selectively adhere to the TPM monolayer inside the microwells, maintaining their viability, while adherent cells were not present on the hydrogel walls. The number of cells inside one microwell could be controled by changing the lateral dimension of the microwells, thus allowing only a single cell per microwell if desired. In the case of 30×30 m microwells, as many as 400 microwells were fabricated in 1 mm². In addition, PEG hydrogel microstructures were also shown to effectively resist the adhesion of bacteria such as Escherichia coli.     

Linear Terpyridine‐Ruthenium(II) Poly(ethylene glycol) Coordination Polymers

In the present contribution, we synthesized linear coordination polymers based on oligo(ethylene glycol)s as well as poly(ethylene glycol)s and terpyridine ruthenium(II) complexes. The reaction conditions, e.g., solvent, concentration, were varied to obtain well‐soluble, high molecular weight polymers. The resulting compounds were characterized by UV‐vis and NMR spectroscopy. The viscosity of the materials was also investigated with and without salt addition. Finally, the polymers were characterized with DSC and AFM. AFM revealed a lamellar morphology.

     

Phase Separation in Poly(9,9‐dioctylfluorene)/Poly(methyl methacrylate) Blends

Binary blends of the conjugated polymer poly(9,9‐dioctylfluorene) (PFO) and the insulating polymer poly(methyl methacrylate) (PMMA) phase‐separated and exhibited optical and electrical activity in light‐emitting‐diodes. The phase‐separated PFO columns were uniformly packed and situated directly on a transparent hole‐injecting contact. The length scales of lateral topographical features can be adjusted discretionarily by controlling the blend concentration and compositional ratio. The mechanism leading to the formation of lateral structures was investigated by comparing with the vertical segregation in polar conjugated polymer poly(9,9‐bis(6‐diethoxylphosphorylhexyl)fluorene) (PF‐EP) blends with PMMA, which suggested that kinetics rather than interfacial free energy acted. In such lateral phase‐separated structures, the phase‐separated PFO domains were the optically and electrically active phase. This highlighted the potential opportunity as nanoscale light source for organic optoelectronic device applications with well‐controllable properties.

     

Poly(hydroxyl propyl methacrylate)‐b‐Poly(oligo ethylene glycol methacrylate) Thermoresponsive Block Copolymers by RAFT Polymerization

Thermoresponsive amphiphilic poly(hydroxyl propyl methacrylate)‐b‐poly(oligo ethylene glycol methacrylate) block copolymers (PHPMA‐b‐POEGMA) are synthesized by RAFT polymerization, with different compositions and molecular weights. The copolymers are molecularly characterized by size‐exclusion chromophotography, and ¹H NMR spectroscopy. Dynamic light scattering (DLS) and static light scattering (SLS) experiments in aqueous solutions show that the copolymers respond to temperature variations via formation of self‐organized nanoscale aggregates. Aggregate structural characteristics depend on copolymer composition, molecular weight, and ionic strength of the solution. Fluorescence spectroscopy experiments confirm the presence of less hydrophilic domains within the aggregates at higher temperatures. The thermoresponsive behavior of the PHPMA‐b‐POEGMA block copolymers is attributed to the particular solubility characteristics of the hydrophilic, water insoluble PHPMA block that are modulated by the presence of the water soluble POEGMA block.     

Thermoresponsive UCST‐Type Behavior of Interpolymer Complexes of Poly(ethylene glycol) and Poly(poly(ethylene glycol) methacrylate) Brushes with Poly(acrylic acid) in Isopropanol

Upper critical solution temperature (UCST)‐type thermoresponsive behavior of poly(ethylene glycol)–poly(acrylic acid) (PEG–PAA) and poly(poly(ethylene glycol) methacrylate)–poly(acrylic acid) (PPEGMA–PAA) interpolymer complexes has been observed in isopropanol. For these investigations, PPEGMA and PAA with various average molecular weights have been synthesized by atom transfer radical polymerization. It has been found that both the PEG and PPEGMA have lower cloud point temperatures (T _cp) than its mixed polymer solutions with PAA, whereas PAA does not show such behavior in the investigated temperature range. These findings indicate the reversible formation of interpolymer complexes with variable structure and composition in the solutions of the polymer mixtures in isopropanol. Increasing the ethylene glycol/acrylic acid molar ratio or the molecular weight of either the PAA or the H‐acceptor PEG component of the interpolymer complexes increases the UCST‐type cloud point temperatures of these interpolymer systems. The polymer–polymer interactions by hydrogen bonds between PAA and PEG or PPEGMA and the correlations between T _cp and structural parameters of the components revealed in the course of these investigations may be utilized for exploring well‐defined UCST‐type material systems for various applications.

     

Electrically Conductive Graphene/Poly(methyl methacrylate) Composites with Ultra‐Low Percolation Threshold by Electrostatic Self‐Assembly in Aqueous Medium

Thermally reduced graphene modified with cationic ammonium ions (AAG)—affording a stable dispersion in water—self‐assembles well by electrostatic interaction on the surface of anionic poly(methyl methacrylate) (PMMA) particles of various sizes, by simple mixing in water. An interconnected 3D electrically conductive network of AAG is effectively generated in the composite when the self‐assembled composite is compression molded. The AAG network becomes wide‐meshed and electrical conduction is improved when the PMMA particle size increases, exhibiting a percolation threshold of electrical conductivity as low as 0.06 vol%. In contrast, the protection of PMMA from oxidation by air is more effective when the network is fine‐meshed.

     

Photocrosslinked Chitosan Hydrogels Reinforced with Chitosan‐Derived Nano‐Graphene Oxide

Chitosan and chitosan‐derived nano‐graphene oxide carbon dots are successfully methacrylated and utilized for the fabrication of photocurable hydrogels. The addition of the nano‐graphene oxide (nGO) does not significantly delay the polymer network build‐up, but significantly reduces the storage modulus of the crosslinked network, with important detrimental effects on the mechanical performance. By replacing nGO with methacrylated M‐nGO, the mechanical performance of the crosslinked polymer network is improved with an increase of the storage modulus as a function of increasing the M‐nGO content in the photocurable formulation.     

Poly(methyl methacrylate)/Graphene Microparticles Having a Core/Shell Structure Prepared with Carboxylated Graphene as a Pickering Stabilizer

Two kinds of carboxylated thermally reduced graphenes (carboxylated TRGs) with different lateral sizes are examined as a Pickering stabilizer in the suspension polymerization of methyl methacrylate. The size and the shape of the prepared composite particles are irregular due to agglomeration, more evidently when the larger carboxylated TRG is used. In addition, carboxylated TRG is distributed not only on the surface but also inside the composite particles. It indicates that the carboxylated TRG alone is not a stable Pickering agent. However, a very small dosage of acrylic acid remedies all these issues because acrylic acid interacts with carboxylated TRG and synergizes the stabilizing effect. The compression molded composite of the core/shell poly(methyl methacrylate)/carboxylated TRG particles exhibits a very low percolation threshold of electrical conductivity of 0.03 vol%. It demonstrates that the carboxylated TRG shells of the composite particles effectively form a segregated conductive network throughout the composite.

     

Flexibility Improvement of Poly(L‐lactide) by Reactive Blending With Poly(ether urethane) Containing Poly(ethylene glycol) Blocks

Poly(L ‐lactide) (PLLA) is melt blended with poly(ether urethane) (PEU) based on poly(ethylene glycol) blocks via a chain‐extension reaction by diisocyanate as a chain extender to improve its flexibility without sacrificing comprehensive performance. The elongation at break of the blends with triphenyl phosphate (TPP) as a reactive blending additive is much higher than that without TPP by physical blending. When 10 wt% PEU is blended, the former elongation reaches to 298%, while the latter one is only approximately 20%. The reactive blending forms a PLLA–PEU block copolymer, thus improving their compatibility. When the weight‐average molecular weight (M _w) of PEUs is 18–90 kg mol^?1, the effect of M _w is very little on tensile properties of blends. The rheological properties of the blends are modified through the content and molecular weight of PEU. The complex viscosity (η*) of PLLA/PEU blends increases with increasing M _w of PEU. The η* of the PLLA blend containing 5 wt% PEU in M _w 73 kg mol^?1 is higher than that of neat PLLA. The water absorption of the PLLA/PEU blends enhances because of the hydrophilicity of PEUs versus neat PLLA.

     

Crosslinking Density Influences Chondrocyte Metabolism in Dynamically Loaded Photocrosslinked Poly(ethylene glycol) Hydrogels

In approaches to tissue engineer articular cartilage, an important consideration for in situ forming cell carriers is the impact of mechanical loading on the cell composite structure and function. Photopolymerized hydrogel scaffolds based on poly(ethylene glycol) (PEG) may be synthesized with a range of crosslinking densities and corresponding macroscopic properties. This study tests the hypothesis that changes in the hydrogel crosslinking density influences the metabolic response of encapsulated chondrocytes to an applied load. PEG hydrogels were formulated with two crosslinking densities that resulted in gel compressive moduli ranging from 60 to 670 kPa. When chondrocytes were encapsulated in these PEG gels, an increase in crosslinking density resulted in an inhibition in cell proliferation and proteoglycan synthesis. Moreover, when the gels were dynamically loaded for 48 h in unconfined compression with compressive strains oscillating from 0 to 15% at a frequency of 1 Hz, cell proliferation and proteoglycan synthesis were affected in a crosslinking-density-dependent manner. Cell proliferation was inhibited in both crosslinked gels, but was greater in the highly crosslinked gel. In contrast, dynamic loading did not influence proteoglycan synthesis in the loosely crosslinked gel, but a marked decrease in proteoglycan production was observed in the highly crosslinked gel. In summary, changes in PEG hydrogel properties greatly affect how chondrocytes respond to an applied dynamic load.     

Poly(acrylamide‐co‐itaconic acid) and Semi‐IPNS with Poly(ethylene glycol): Preparation and Characterization

Summary: A pH‐responsive poly(acrylamide‐co‐itaconic acid) (PAAm/IA) hydrogel and semi‐interpenetrating networks (semi‐IPNs) with 5, 10 and 15 wt.‐% of poly(ethylene glycol) (PAAm/IA/PEG), were synthesized. Their swelling behavior was studied in the pH range from 1.76 to 7.81, as well as their oscillatory swelling behavior at pH = 7.81 and pH = 1.7. Throughout these studies, the gels maintained their mechanical strengths and shape. The shear storage (G′) and loss (G″) moduli, obtained as a function of frequency, for the gels as formed and at equilibrium swelling were higher for the semi‐IPNs than for the copolymer hydrogel. The shear storage moduli of copolymer hydrogel and semi‐IPNs as formed were independent of frequency over the whole experimental range, whereas the values for the gels at equilibrium swelling decreased with increasing degree of swelling, i.e., the PAAm/IA hydrogel which exhibited the largest swelling had the lowest G′ value. The G′ and G″ values also depended on the content of PEG.

Diffusion exponent vs. pH for PAAm, copolymer hydrogel PAAm/IA and semi‐IPN with PEG.     

The Aggregation Behavior of Poly(ethylene oxide)‐Poly(methyl methacrylate) Diblock Copolymers in Organic Solvents

Poly(ethylene oxide)‐poly(methyl methacrylate) and poly(ethylene oxide)‐poly(deuteromethyl methacrylate) block copolymers have been prepared by group transfer polymerization of methyl methacrylate (MMA) and deuteromethyl methacrylate (MMA‐d₈), respectively, using macroinitiators containing poly(ethylene oxide) (PEO). Static and dynamic light scattering and surface tension measurements were used to study the aggregation behavior of PEO‐PMMA diblock copolymers in the solvents tetrahydrofuran (THF), acetone, chloroform, N,N‐dimethylformamide (DMF), 1,4‐dioxane and 2,2,2‐trifluoroethanol. The polymer chains are monomolecularly dissolved in 1,4‐dioxane, but in the other solvents, they form large aggregates. Solutions of partially deuterated and undeuterated PEO‐PMMA block copolymers in THF have been studied by small‐angle neutron scattering (SANS). Generally, large structures were found, which cannot be considered as micelles, but rather fluctuating structures. However, ¹H NMR measurements have shown that the block copolymers form polymolecular micelles in THF solution, but only when large amounts of water are present. The micelles consist of a PMMA core and a PEO shell.     

Role of Thermo-responsiveness and Poly(ethylene glycol) Diacrylate Cross-link Density on Protein Release from Poly(N-isopropylacrylamide) Hydrogels

Thermo-responsive hydrogels have shown promise as injectable materials for local drug delivery. However, the phase-induced changes in polymer properties of N-isopropylacrylamide (NIPAAm) can pose additional challenges for achieving controlled protein release. In this work, thermo-responsive hydrogels derived from NIPAAm and cross-linked with poly(ethylene glycol) diacrylate (PEG-DA) were synthesized via free radical polymerization. The volume phase transition temperature (VPTT) of the hydrogels ranged from 32.9°C to 35.9°C. Below the VPTT, swelling ratios of the hydrogels decreased with cross-linker concentration, and showed a sharp drop (at least 4-fold) upon phase change. Protein encapsulation efficiency was high (84–90%) and decreased with cross-linker concentration. Release of bovine serum albumin, a model protein, at body temperature was significantly higher than at room temperature (67% at 37°C compared to 44% at 23°C after 48 h). The release kinetics of proteins from the hydrogels were initially expected to be a function of cross-link density. However, at the hydrogel compositions explored in this work, protein release did not change significantly with cross-linker mol fraction. The thermo-responsive hydrogels offer a promising platform for the localized delivery of proteins.     

Degradation of Poly(methyl methacrylate) Model Compounds Under Extreme Environmental Conditions

There is a significant knowledge gap in the degradation of poly(methyl methacrylate) (pMMA) under conditions experienced by surface coatings in the harsh Australian environment. In the current study pMMA model compounds were exposed to 95 °C temperatures and high UV radiation (1 kW · m^?2), separately as well as in combination. Contrary to the findings of previous studies, degradation proceeds in these conditions via a non‐radical cyclic mechanism. The mechanism was further confirmed by synthesis and degradation of ethylene‐oxide‐terminated pMMA, an intermediate product in the cycle. Electrospray ionisation mass spectrometry analysis of thermally degraded samples after 155 weeks shows degradation consistent with the proposed cycle in vinyl‐terminated pMMA, while saturated pMMA was shown to be stable after the same period. Saturation delayed the UV‐induced degradation, yet these compounds still displayed some slight degradation after 52 weeks, confirming the terminal vinyl bond in pMMA as a weak point. Combined UV and thermal radiation after 56 weeks showed degradation of both pMMA samples, with the vinyl‐terminated sample also exhibiting crosslinking. The combination of thermal and UV radiation also caused acceleration of degradation, shown by a comparison of the polymer samples after ≈60 weeks.

     

Competition Between Motion Constraint and Aggregation of Macromolecular Chains in Poly(vinyl methyl ether)/Poly(ethylene oxide) Aqueous Solution During Phase Transition

Resonance light scattering (RLS) technique was applied to study macromolecular entanglements in highly dilute poly(vinyl methyl ether) (PVME)/poly(ethylene oxide) (PEO) solution during phase transition process. Temperature dependences of RLS intensities of PVME, PEO and PVME/PEO solutions were recorded. In addition, simulated temperature dependence of RLS intensity of PVME/PEO solution was drawn supposing there was no interaction between PEO and PVME. Comparison between the measured with the simulated results indicated that there were obvious differences in RLS intensities and transition temperatures. The present work proved the existence of entanglements during phase separation in highly dilute solution. Moreover, a model was proposed to describe the entanglement behavior.