Synthesis and Self‐Assembly of New Double‐Crystalline Amphiphilic Polyethylene‐block‐Poly[oligo(ethylene glycol) Methyl Ether Methacrylate] Coil‐Brush Diblock Copolymer

We report on the synthesis and self‐assembly of a novel well‐defined coil‐brush diblock copolymer with linear crystalline polyethylene (PE) as the coil block and hydrophilic poly [oligo(ethylene glycol) methyl ether methacrylate] (POEGMA) as rod brush via a combination of chain shuttling ethylene polymerization (CSEP) and atom transfer radical polymerization (ATRP). Initially, bromine end‐terminated PE macroinitiator (PE–Br) was synthesized through the esterification of 2‐bromo‐2‐methylpropionyl bromide with monohydroxyl‐terminated PE (PE–OH) which was prepared by means of CSEP with 2,6‐bis[1‐(2,6‐dimethylphenyl)imino ethyl] pyridine iron (II) dichloride/methylaluminoxane (MAO)/ZnEt₂ and subsequent in situ oxidation with oxygen. The resultant PE‐b‐POEGMA coil‐brush diblock copolymer was synthesized by ATRP of monomethoxy‐capped oligo(ethylene glycol)methacrylate (OEGMA) using PE–Br as macroinitiator. The self‐assembly of the double‐crystalline PE‐b‐POEGMA in aqueous solution was investigated by dynamic light scattering, transmission electron microscopy and cryofield emission scanning electron microscopy. It was found that, in water, a solvent selectively good for the POEGMA brush, PE‐b‐POEGMA chains could self‐assemble to form sandwich‐like micelles with the insoluble and crystallized PE blocks as the interlayer cores and the soluble and swollen POEGMA brush as the outer‐layer shell. The crystallization of both PE and POEGMA blocks in self‐assembled structure formed from aqueous solution was investigated by differential scanning calorimetry.

     

Bacterial and mammalian cell response to poly(3-sulfopropyl methacrylate) brushes loaded with silver halide salts

This study investigates the antibacterial and cytotoxic effect of surfaces with sulphonate brushes containing silver salts. By using the same type of samples for both cytotoxicity and antibacterial studies, these two parameters could be compared in a controlled way. The silver was incorporated into the brush in four different forms to enable release of silver ions at different concentrations and different rates. It was found that although the surfaces displayed very good antibacterial properties in buffer solutions, this effect disappeared in systems with high protein content. Similarly, the silver-containing surfaces displayed cytotoxic effects in the absence of serum proteins but this effect was reduced in the presence of serum. The speciation of silver in the different solutions is discussed. Cytotoxic and antibacterial effects are compared at the different silver concentrations released. The implications of a concentration range where silver could be used to kill bacterial without harmful effects on mammalian cells are also discussed and questioned.     

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.     

Effect of poly(dimethylsiloxane)-block-poly(oligo (ethylene glycol) methacrylate) amphiphilic block copolymers on dermal fibroblast viability and proliferation

Abstract

In this work, well-defined poly(dimethylsiloxane)-b-poly(oligo (ethylene glycol) methacrylate) (PDMS-b-POEGMA) amphiphilic block copolymers were synthesized and their effect on human dermal fibroblast were investigated. Anionic ring opening polymerization (ROP) and atom transfer radical polymerization (ATRP) were used to synthesis the block copolymers. The molecular weight of synthesized copolymers ranged from 1000 to 2300?Da by changing the number of both PDMS and POEGMA units. It was found that the copolymer having low molecular weight decreased the fibroblast viability and proliferation by inducing apoptosis. It was proved by flow cytometry and TUNEL assay that human dermal fibroblast experienced apoptosis after exposure to synthesized amphiphilic copolymers. The results of this work suggest the use of PDMS-b-POEGMA amphiphilic copolymers with low molecular weight for hypertrophic scars remediation.     

Effect of the Hydrophobic Basal Layer of Thermoresponsive Block Co-Polymer Brushes on Thermally-Induced Cell Sheet Harvest

Abstract

Thermoresponsive poly(benzyl methacrylate)-b-poly(N-isopropylacrylamide) (PBzMA-b-PIPAAm) block co-polymer brush surfaces were prepared by surface-initiated two-step reversible addition-fragmentation chain transfer radical (RAFT) polymerization. PBzMA brushes were fabricated on azoinitiator-immobilized glass substrates in the presence of dithiobenzoate (DTB) compound as a RAFT agent. The amount of grafted polymer was regulated by initial monomer concentrations. The second thermoresponsive blocks were added to the RAFT-related DTB groups located at PBzMA termini through the propagation of PIPAAm chains, resulting in formation of PBzMA-b-PIPAAm brushes. Surface characteristics of the block co-polymer brushes and its influence on thermally regulated cellular behavior were investigated using bovine carotid artery endothelial cells (BAECs), compared with PIPAAm brush surfaces. Cell adhesion/detachment behavior on thermoresponsive polymer brush surfaces significantly depended on their individual polymer architectures and chemical compositions of grafted polymers. Low-temperature treatment at 20°C, below the phase-transition temperature of PIPAAm, induced the spontaneous detachment of adhering cells from the PBzMA-b-PIPAAm brush surfaces with a higher rate than that from PIPAAm brush surfaces. In addition, the cell-repellent effect of the hydrophobic basal layer successfully accelerated for harvesting BAEC sheets from the block co-polymer brush surfaces. Unique features of thermoresponsive block co-polymer brush architectures can be applied to control cell-adhesion strength for enhancing cell adhesion or accelerating cell detachment.     

Temperature‐Responsiveness and Antimicrobial Properties of CNT–PNIPAM Hybrid Brush Films

Temperature‐responsive carbon nanotube (CNT)/poly(N‐isopropylacrylamide) (PNIPAM) hybrid brush films were prepared by combining the layer‐by‐layer and surface‐initiated polymerization (LbL‐SIP) techniques. Atom transfer radical polymerization (ATRP) is employed for the preparation of PNIPAM polymer brushes. Antibacterial activity of the CNT/PNIPAM films are investigated against Exiguobacterium sp. AT1b and Exiguobacterium sibiricum strains. Dead assay results show high microbial inactivation on coated surfaces with CNT films, while very low microbial inactivation is observed in PNIPAM films at all temperatures tested. The CNT–PNIPAM films, on the other hand, have antibacterial properties below 32 °C, which is below the lower critical solution temperature (LCST), but allows biofilm formation above the LCST.     

Synthesis and Characterization of Poly(acrylic acid) Brushes: “Grafting‐Onto” Route

A guideline for the synthesis of poly(acrylic acid) brushes on planar silica surfaces by the “grafting‐onto” approach is described. It is demonstrated that some thermal precautions must be taken to obtain extended brushes. It is also shown that neutron reflectivity is well suited for the characterization of each step of the synthesis, while it is (unfortunately) rarely used for that purpose. The steps are the following: first, the substrates are covered with a self‐assembled monolayer of epoxy‐terminated molecules; then, the poly(tert‐butyl acrylate) brushes are built using preformed and end‐functionalized chains; finally, the deprotection of the ester group is performed using a pyrolysis reaction to convert the poly(tert‐butyl acrylate) brushes into poly(acrylic acid) brushes.     

Neutron reflectometry from poly (ethylene-glycol) brushes binding anti-PEG antibodies: Evidence of ternary adsorption

Neutron reflectometry provides evidence of ternary protein adsorption within polyethylene glycol (PEG) brushes. Anti-PEG Immunoglobulin G antibodies (Abs) binding the methoxy terminated PEG chain segment specifically adsorb onto PEG brushes grafted to lipid monolayers on a solid support. The Abs adsorb at the outer edge of the brush. The thickness and density of the adsorbed Ab layer, as well as its distance from the grafting surface grow with increasing brush density. At high densities most of the protein is excluded from the brush. The results are consistent with an inverted “Y” configuration with the two F_AB segments facing the brush. They suggest that increasing the grafting density favors narrowing of the angle between the F_AB segments as well as overall orientation of the bound Abs perpendicular to the surface.     

Grafting Binary PEG and Fluoropolymer Brushes from Mix‐Biomimic Initiator as “Ambiguous” Surfaces for Antibiofouling

A series of random binary poly(ethylene glycol) and fluoropolymer brushes (POEGMA‐PNCA‐F₁₅) are grafted onto substrates via surface‐initiated polymerizations (atomic transfer radical polymerization and ring opening metathesis polymerization, respectively) from polydopamine based mix‐catecholic initiators. The chemical composition, surface morphology, swellability, and wettability of the as‐prepared surfaces are characterized by X‐ray photoelectron spectra (XPS), atomic force microscopy (AFM), and static water contact angle measurements, respectively. The antifouling properties are evaluated by settlement of spores and diatoms, the results indicate that the as‐prepared amphiphilic surfaces with random hydrophilic and hydrophobic polymer brushes can mitigate biofouling, and the ratio of the hydrophilic and hydrophobic polymer brushes is a key determinant factor in antifouling effect, the optimal ratio (1:1 initiator) of bipolymer brushes on surfaces exhibits good antiadhesion performance against both Chlorella spores and Navicula diatoms.

     

Green synthesis of tea Ag nanocomposite hydrogels via mint leaf extraction for effective antibacterial activity

In this report, we investigated the swelling behavior and antibacterial property of nanosilver composite hydrogels made from tea with polyacrylamide via a free-radical polymerization and green process technique. This is probably for the first time; tea-based nano silver composite hydrogels were developed. The composite hydrogels comprise embedded nano silver particles in the tea hydrogel matrix via a green process with mint leaf extract. The size of the nano silver particles in the hydrogel matrix was found to be < 10 nm. The nano silver composite hydrogels formed and their blank hydrogels from the mint leaf were characterized by using ultraviolet-visible spectroscopy, scanning electron microscopy with energy dispersive spectroscopy, transmission electron microscopy, thermogravimetric analysis and X-ray diffraction studies. The nano silver composite hydrogels developed exhibit eminent antibacterial activity against Escherichia coli and Staphylococcus aureus. This clearly indicates that the nano silver composite hydrogels are potential candidates for antimicrobial applications.     

Preparation of a novel antibacterial chitosan-poly(ethylene glycol) cryogel/silver nanoparticles composites

Cryogel was synthesized through cryogelation of methacrylated carboxymethyl chitosan (mCMC) and poly(ethylene glycol) diacrylate (PEGDA) precursors by photopolymerization. Due to its excellent properties, such as fast swelling behavior, inter-connective porous structure, high water absorbing capacity, especially the presence of abundant carboxylmethyl groups on its backbone, the cryogel not only favored the absorption of silver ions but also was proved to be a good matrix for the incorporation of silver nanoparticles (AgNPs) by in situ chemical reduction. The structure, morphology, and swelling behavior of the cryogel and cryogel/AgNPs composite were characterized. And the results of inhibition zone test and antibacterial inhibition ratio indicated the cryogel/AgNPs composite exhibited prominent and durable antibacterial activity against Gram-negative E. coli and could be utilized as potential antibacterial materials.     

Synthesis and Characterization of Polymer Brushes on Micromechanical Cantilevers

Summary: A technique to cover microelectromechanical systems (MEMS), such as micromechanical cantilever (MC) sensors, with a covalently bound brush layer has been developed. The polymer layer was grown using a “grafting‐from” synthesis of polymer brushes under mild conditions, by surface‐initiated atom transfer radical polymerization. Atomic force microscopy (AFM) and ellipsometry have revealed a uniform thickness of about 12 nm from which a grafting density of polymer brushes of 0.19 chains · nm^?2 was estimated. The coating with polymer brushes can be realized on a selected surface. It was shown that a single‐sided brush layer swells reversibly in toluene, resulting in a bending of the micromechanical cantilever.

Schematic representation of the PMMA brush synthesis on the MC surface, by surface‐initiated ATRP.     

Neutron reflectivity study of the swollen structure of polyzwitterion and polyeletrolyte brushes in aqueous solution

The swollen brush structures of polycation and zwitterionic polymer brushes, such as poly(2-methacryloyloxyethyltrimethylammonium chloride) (PMTAC), poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), and poly[3-(N-2-methacryloyloxyethyl-N,N-dimethyl)ammonatopropanesulfonate] (PMAPS), in aqueous solutions of various ionic strengths were characterized by neutron reflectivity (NR) measurements. A series of the polyelectrolyte brushes were prepared by surface-initiated controlled radical polymerization on silicon substrates. A high-graft-density PMTAC brush in salt-free water (D₂O) adopted a two-region step-like structure consisting of a shrunk region near the Si substrate surface and a diffuse brush region with a relatively stretched chain structure at the solution interface. The diffuse region of PMTAC was reduced with increase in salt (NaCl) concentration. The PMAPS brush in D₂O formed a collapsed structure due to the strong molecular interaction between betaine groups, while significant increase in the swollen thickness was observed in salt aqueous solution. In contrast, no change was observed in the depth profile of the swollen PMPC brush in D₂O with various salt concentrations. The unique solution behaviors of zwitterionic polymer brushes were described.     

The Distribution of Immobilized Platinum and Palladium Nanoparticles within Poly(2‐vinylpyridine) Brushes

Novel catalytic surfaces can be prepared by in situ synthesis of metal nanoparticles (NPs) inside polymer brush systems. To gain more control over the properties of these nanocatalysts, it is important to quantify their distribution inside the polymer brush and understand their formation process better. Here, measurements of the distributions of Pt and Pd NPs within poly(2‐vinylpyridine) (P2VP) brushes are reported. The amount of surface accumulation and the extent of penetration of the two metal NPs into the brush layer are determined using X‐ray reflectivity measurements. Quantitative analysis of the data reveals a significant difference between the distributions of the two NP species. Pd NPs exhibit higher accumulation at the surface and larger penetration depth within the brush. This difference in behavior is attributed to the different adsorption mechanisms exhibited by the two metal ions. Whereas Pt ions adsorb to the polymer brush via ionic bonds, Pd ions form complex coordination bonds. The different distributions of the NPs within the polymer brush are related to the previously investigated catalytic activity of these systems. The reported unusually high specific activity of Pt hybrid brushes, as compared with Pd ones, can now be explained by buried Pd NPs that do not take part in the catalytic reaction.

     

Random Poly(methyl methacrylate‐co‐styrene) Brushes by ATRP to Create Neutral Surfaces for Block Copolymer Self‐Assembly

Random copolymer brushes of styrene and methyl methacrylate (MMA) on silicon wafers by atom transfer radical polymerization (ATRP) are synthesized using CuCl/CuCl₂/HMTETA. It is found that with increasing amount of styrene the thickness of the brush layer could no longer be well controlled by the amount of free (sacrificial) initiator in the reaction. At constant concentration of free initiator a constant thickness is obtained for various ratios of MMA to styrene. Within 30–70% MMA in the monomer feed the composition of the free polymer corresponds well to the monomer feed ratio, displaying a water contact angle in agreement with the theoretical value for a random copolymer. These copolymers are shown to create a neutral surface directing spin‐coated poly(styrene‐b‐MMA) into a perpendicular lamellae orientation.     

Thermo‐Induced Double Phase Transition Behavior of Physically Cross‐Linked Hydrogels Based on Oligo(ethylene glycol) methacrylates

Double thermosensitive clay/P(MEO₂MA‐co‐POEGMA) nanocomposite (NC) hydrogels are prepared by in situ free radical polymerization of 2‐(2‐methoxyethoxy) ethyl methacrylate (MEO₂MA) and oligo(ethylene glycol) methacrylate (OEGMA) in the presence of physical cross‐linker clay. The temperature‐induced phase transition behavior of NC hydrogels is investigated by turbidity, temperature dependent nuclear magnetic resonance, and variable temperature Fourier transform infrared spectroscopy. 2D infrared analysis is employed to study the sequential order of changes of all groups in NC hydrogels during the heating and cooling process. The obtained novel clay/P(MEO₂MA‐co‐POEGMA) NC hydrogels exhibit an unusual thermally induced multistep aggregation process and successively undergo three consecutive microstructural changes: “loose clay/polymer microaggregation ? homogeneous network structure ? dense clay/polymer macroaggregation.” Dynamic light scattering and transmission electron microscopy measurements show similar results of the NC nanogel at the same temperature regions, confirming the three consecutive microstructural changes. This new generation of thermosensitive hydrogel offers promising potential for applications as smart devices, biomedical materials, and drug carriers.

     

An environmentally benign dual action antimicrobial: quaternized chitosan/sodium alga acid multilayer films and silver nanoparticles decorated on magnetic nanoparticles

There is an urgent need to develop a puissant and environmentally benign antibacterial composite that act via multiple mechanisms to make response to the potentially daunting complexity of the microbial population and microbial antibiotic resistance. In this work, a facile and green approach, layer-by-layer self-assembly technology was applied to assemble polycation quaternized chitosan (QAC) and polyanion sodium alga acid onto magnetic nanoparticles (MNPs). Then silver nanoparticles (AgNPs) with stable and narrow-sized distribution in the range of 25–35 nm were immobilized on the surface of MNPs with L-ascorbic acid as reducing agent and organic multilayers as stabilizer. Through above modification on MNPs, we expected to achieve a green dual antibacterial and recyclable composite via the combined antibacterial action of QAC and AgNPs. Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, transmission electron microscopy, zeta potentials, and dynamic light scattering were employed to confirm the success of the surface functionalization. Silver ion release process was detected by inductively coupled plasma mass spectrometry. Furthermore, the antibacterial properties of the biomaterials against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus were studied. The modified MNPs exhibited rapid, efficient, and long-lasting biocidal abilities against E. coli and S. aureus. The magnetic antibacterial composite still showed excellent antibacterial efficiency during five exposure/collection/recycle procedures.     

Hollow S-nitrosothiols nanoparticle with polymeric brushes for nitric oxide (NO)-releasing as tumor targeted chemotherapy

A kind of tumor targeting nitric oxide donor nanoparticle with brushes is described in this paper. The poly(4-vinylphenylboronic acid) polymeric brush, which shows glucose and pH dual responsiveness, endows the ability of hollow S-nitrosothiols nanoparticle to accurate recognition and binding with the sialic acid over-expressed type tumor cells, such as HepG2 and MCF-7 cells. In vitro experiments, including cells capture and release experiments, confocal fluorescence microscope characterization, cytotoxicity assay with different cells, demonstrate the selective recognition and the controlled NO release to kill tumor cells for these S-nitrosothiols nanoparticles. Low concentration of the released NO from the S-nitrosothiols nanoparticles in the transmission would participate physiological activity and avoid serious side effects because the endogenous nature and the physiological necessity to regulate normal biological functions. To the best of our knowledge, this is the first report about polymer nanoparticles as NO donors with functional brushes to selectively identify tumor cells and release NO in a controlled manner.