Monodisperse Polymer Research Articles

MALDI In-Source Decay Mass Spectrometry of Polyamidoamine Dendrimers

We report using MALDI-ISD (in-source decay) mass spectrometry (MS) to characterize highly branched synthetic polymers of polyamidoamine (PAMAM) dendrimer. This inherently monodisperse polymer possesses dendritic branches networked by tertiary amines and an amide functionality in each repeating unit. Among various ISD matrices examined, 2,5-DHB was the most efficient, yielding 33 fragments produced by single- or multiple-bond cleavages. Detailed analysis revealed that cleavages at tertiary amine sites (S- and E-type fragments) were the most pronounced, with various other cleavages around amide groups. The fragmentation mechanism appeared to follow the radical-induced dissociation pathway. In addition, the matrix dependence of PAMAM MALDI-ISD differed from that of peptides/proteins. The observed fragments provided rich structural information, which was suitable to characterize dendritic polymers.

Fluorescence-profile pre-definable quantum-dot barcodes in liquid-core microcapsules

Microparticles incorporated with quantum-dot (QD) barcodes for multiplexed bioassays attract a great attention due to their potential applications in drug discovery, gene profiling and clinic diagnostics. However, the existing QD barcodes lack a necessary optical stability to ambient fluids or a repeatability of fluorescent profiles. We developed a new QD barcode by loading an aqueous QD mixture as a liquid core into a monodispersed polymer microcapsule by a microfluidic method to avoid those problems. We found that the QDs in the liquid cores were able to maintain their original characteristics, especially the linear relation between photoluminescence intensity and concentration. In addition, we found that the fluorescent profiles of the QD-loaded liquid cores were the same as those of the QD mixtures before being loaded inside the microcapsules. With these two properties, the QD barcodes can be predefined directly by multiplexing the emission peaks and concentrations of the QDs in the liquid cores. Furthermore, the graphical information from fluorescent images of the microcapsules, such as the sizes and numbers of the QD-loaded liquid cores, offers another dimension for barcoding to increase the coding capacity. We also presented a microfluidic method to manufacture the QD-barcoded microcapsules of size ~30 μm. These pre-definable QD barcodes with stable fluorescent profiles can be used as a platform for various high-throughput screening applications in different bioassay buffers.

Spherical Pseudo‐Inverse Opal Silica with Pomegranate‐Like Polymer Microparticles as Templates

AbstractSpherical silica particles with pseudo‐inverse opal structure are synthesized by using pomegranate‐like polymer microparticles as templates. A micro‐dispersion polymerization occurring in the suspended monomer droplets in the presence of a silica precursor leads to the formation of nearly monodisperse polymer sub‐particles of about 1 µm size, randomly‐packed within a 30–100 µm polymer particle. The polymerization is followed by an acid‐catalyzed reaction that induces formation of silica in the interstices between the sub‐particles within a polymer particle. Spherical PIOS particles are eventually produced by selectively removing the polymer template by pyrolysis. The PIOS particles show large specific surface areas with unique pore geometry and pore size distribution.magnified image

ChemInform Abstract: Recombinant Protein‐Based Polymers for Advanced Drug Delivery

AbstractReview: 95 refs.

Monodispersed Molecularly Imprinted Polymer Beads with Enhanced Atrazine Retention Ability Synthesized with Polymeric Diluents

Molecular imprinting technique was applied for the preparation of polymer beads selected for a triazine herbicide, atrazine. Polystyrene, poly(methyl methacrylate) and poly(ethylene glycol) were examined as polymeric diluents, and the morphology of the resultant molecularly imprinted polymers was investigated by scanning electron microscopy. Among the examined polymeric diluents, styrene was shown to be favorable for obtaining monodispersed spherical polymer with high retention ability for atrazine.

Synthesis and Adsorption Characters of Silica Hollow Spheres

A kind of ordered meso-sized hollow silica spherical material was prepared by hydrothermal route using monodispersed cross-linked polymethyl polymer spheres as template, metacrylate tetraethyl orthosilicate as a silica source. The calcination was empolyed for the removing of template and generation silica hollow spherical materials with meso-sized pores. The adsorption performance of the obtained hollow silica spheres was investigated and the results indicated that the obtained hollow silica spheres had high adsorption capacity for sulfadimethoxine. They were sucessfully used as the dispersive adsorbent for matrix solid phase dispersive extraction sulfadimethoxine from chicken tissue with satisfactory results.

Matrine- and oxymatrine-imprinted monodisperse polymers prepared by precipitation polymerization and their applications for the selective extraction of matrine-type alkaloids from Sophora flavescens Aiton

Matrine (MT)- and oxymatrine (OMT)-imprinted monodisperse polymers have been prepared by precipitation polymerization. The prepared molecularly imprinted polymers (MIPs) for MT and OMT, MIPMT and MIPOMT, were monodispersed microspheres of 3.3 and 3.9μm in diameter, respectively. Binding experiments and Scatchard analyses revealed that two classes of binding sites were formed on MIPMT and MIPOMT. In addition to shape recognition, ionic and hydrophobic interactions seemed to affect the retention and recognition of MT and OMT on MIPMT and MIPOMT, respectively, in low acetonitrile content, and ionic and hydrophilic interactions affected these properties in high acetonitrile content. MIPMT was used to selectively extract MT and sophocarpine (13,14-dehydromatrine) from Sophora flavescens root, while MIPOMT was used to extract OMT and oxysophocarpine (13,14-dehydrooxymatrine).

Density-dependent separation of encapsulated cells in a microfluidic channel by using a standing surface acoustic wave

This study presents a method for density-based separation of monodisperse encapsulated cells using a standing surface acoustic wave (SSAW) in a microchannel. Even though monodisperse polymer beads can be generated by the state-of-the-art technology in microfluidics, the quantity of encapsulated cells cannot be controlled precisely. In the present study, mono-disperse alginate beads in a laminar flow can be separated based on their density using acoustophoresis. A mixture of beads of equal sizes but dissimilar densities was hydrodynamically focused at the entrance and then actively driven toward the sidewalls by a SSAW. The lateral displacement of a bead is proportional to the density of the bead, i.e., the number of encapsulated cells in an alginate bead. Under optimized conditions, the recovery rate of a target bead group (large-cell-quantity alginate beads) reached up to 97% at a rate of 2300 beads per minute. A cell viability test also confirmed that the encapsulated cells were hardly damaged by the acoustic force. Moreover, cell-encapsulating beads that were cultured for 1 day were separated in a similar manner. In conclusion, this study demonstrated that a SSAW can successfully separate monodisperse particles by their density. With the present technique for separating cell-encapsulating beads, the current cell engineering technology can be significantly advanced.

Core–shell polymerization for monodispersed hollow polymer spheres embedded with magnetic nanoparticles

Monodispersed hollow polymers embedded with Fe3O4 nanoparticles were prepared by core–shell polymerization applied to both the hydrophobic surface and hydrophilic surface of the magnetic nanoparticles. The void size and polymer shell thickness of these hollow polymers can be easily tuned over a wide range. The final magnetic hollow polymers were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), thermogravimetric analysis (TGA) and magnetic force microscopy (MFM) and confirmed to form capsules embedded with magnetic nanoparticles. These magnetic hollow polymers were stably dispersed in an aqueous phase and were intrinsically superparamagnetic because of the presence of magnetic nanoparticles.

Effect of molecular weight of amine end-modified poly(β-amino ester)s on gene delivery efficiency and toxicity

Amine end-modified poly(β-amino ester)s (PBAEs) have generated interest as efficient, biodegradable polymeric carriers for plasmid DNA (pDNA). For cationic, non-degradable polymers, such as polyethylenimine (PEI), the polymer molecular weight (MW) and molecular weight distribution (MWD) significantly affect transfection activity and cytotoxicity. The effect of MW on DNA transfection activity for PBAEs has been less well studied. We applied two strategies to obtain amine end-modified PBAEs varying in MW. In one approach, we synthesized four amine end-modified PBAEs with each at 15 different monomer molar ratios, and observed that polymers of intermediate length mediated optimal DNA transfection in HeLa cells. Biophysical characterization of these feed ratio variants suggested that optimal performance was related to higher DNA complexation efficiency and smaller nanoparticle size, but not to nanoparticle charge. In a second approach, we used preparative size exclusion chromatography (SEC) to obtain well-defined, monodisperse polymer fractions. We observed that the transfection activities of size-fractionated PBAEs generally increased with MW, a trend that was weakly associated with an increase in DNA binding efficiency. Furthermore, this approach allowed for the isolation of polymer fractions with greater transfection potency than the starting material. For researchers working with gene delivery polymers synthesized by step-growth polymerization, our data highlight the potentially broad utility of preparative SEC to isolate monodisperse polymers with improved properties. Overall, these results help to elucidate the influence of polymer MWD on nucleic acid delivery and provide insight toward the rational design of next-generation materials for gene therapy.

Crosslinked monodisperse particles containing luminophore groups in shells for molecular recognition of lower alcohols

The molecular imprinting technique is used for the synthesis of monodisperse polymer particles via the seed emulsion copolymerization of methyl methacrylate, ethylene glycol dimethacrylate, and comonomers based on Nile Red. The introduction of lower alcohol templates into the reaction mixture and their removal after the synthesis lead to the formation of molecular-recognition sites in the shell that contain luminophore groups and give an optical response to the presence of methanol and ethanol in the gas phase. The particles are investigated via electron microscopy and dynamic light scattering, and their specific surface area is determined through the BET method. The kinetics of a change in the luminescence of thin films based on the particles in vapors of lower alcohols is investigated.

Micromachined Microsieves With High Aspect Ratio Features

Micromachined microsieves fabricated entirely by dry etch processes with pore diameters ranging from 3 to 5 μm are reported. Two microsieve architectures are explored: 2.1 and 5.3 μm thin dielectric layer membranes supported by high aspect ratio rib features (10:1), and 50 μm thick silicon membranes from silicon-on-insulator wafers with no supporting ribs and high aspect ratio pore features (16:1). The flow throughput of each design is evaluated experimentally and theoretically, and the expected relative robustness is assessed and compared to typical microsieve structures reported in the literature. The experimental and theoretical work suggests that both structures have the potential for higher robustness than the typical micromachined microsieve architectures, with reduced but still reasonable flow throughputs in the range of 105 to 106 L/m2-hr-bar, depending on the microsieve porosity. Both microsieve architectures are shown to block monodisperse polymer beads 3 μm in diameter.

A device for the fabrication of multifunctional particles from microbubble suspensions

A novel V-junction microfluidic (VJM) device has been used to generate several types of particles from the break-up of bubbles. The flow rates of selected solutions and the gas pressure were adjusted in order to successfully generate monodisperse polymer coated microbubbles, which serve as a platform for particle generation. Uniform particles in both the nano and micro size ranges with different shapes were spontaneously generated from bubbles and have the potential to be used in several advanced technological applications.

Polydispersity-Driven Block Copolymer Amphiphile Self-Assembly into Prolate-Spheroid Micelles.

The aqueous self-assembly behavior of polydisperse poly(ethylene oxide-b-1,4-butadiene-b-ethylene oxide) (OBO) macromolecular triblock amphiphiles is examined to discern the implications of continuous polydispersity in the hydrophobic block on the resulting aqueous micellar morphologies of otherwise monodisperse polymer surfactants. The chain length polydispersity and implicit composition polydispersity of these samples furnishes a distribution of preferred interfacial curvatures, resulting in dilute aqueous block copolymer dispersions exhibiting coexisting spherical and rod-like micelles with vesicles in a single sample with a O weight fraction, wO, of 0.18. At higher wO = 0.51-0.68, the peak in the interfacial curvature distribution shifts and we observe the formation of only American football-shaped micelles. We rationalize the formation of these anisotropically shaped aggregates based on the intrinsic distribution of preferred curvatures adopted by the polydisperse copolymer amphiphiles and on the relief of core block chain stretching by chain-length-dependent intramicellar segregation.

Fabrication of Colloidal Clusters of Polymer Microspheres and Nonspherical Hollow Micro-particles from Pickering Emulsions

We have introduced the Pickering emulsion systems to generate novel confining geometries for the selforganization of monodisperse polymer microspheres using nanoparticle-stabilized emulsion droplets encapsulating the building block particles. Then, through the slow evaporation of emulsion phases by heating, these microspheres were packed into regular polyhedral colloidal clusters covered with nanoparticle-stabilizers made of silica. Furthermore, polymer composite colloidal clusters were burnt out leaving nonspherical hollow micro-particles, in which the configurations of the cluster structure were preserved during calcination. The selfassembled porous architectures in this study will be potentially useful in various applications such as novel building block particles or supporting materials for catalysis or gas adsorption.

Electrically conductive polymeric photonic crystals

Electrically conductive polymeric 3D photonic crystals are prepared by the shear ordering of composites consisting of monodisperse core-shell polymer spheres and single-walled carbon nanotubes (SWNTs). Strong iridescent colour indicates that the highly ordered opaline structures are not disrupted by the presence of the conductive nanotube networks. Thermal annealing leads to a significant increase in the overall electrical conductivity of thin-film samples yielding DC conductivities of 10−4 S cm−1, with percolation thresholds of less than 0.4 wt% of SWNT. Such composites with open networks of carbon nanotubes held apart by lattices of hard spheres, give combined conductive properties and structural colour effects, within a tuneable viscoelastic medium, with many potential functional applications.

Recombinant protein-based polymers for advanced drug delivery

Advances in recombinant techniques have led to the development of genetically engineered polymers with exquisite control over monomer sequence and polymer length. The ability to study how precise structures correlate with function has provided opportunities for the utility of these polymers in drug delivery. Chemically derived and developed methods of synthesis have yielded many useful polymers for drug delivery to-date, including those currently used in patients. However they have drawbacks, including limitations involved in statistical characterization of conventional polymer synthetic techniques. Encoding at the genetic level and production of such recombinant polymers in organisms allow for precise order and accuracy of amino acid residues and production of monodisperse polymers with specific function and physicochemical properties. Research into elastin-like, silk-like, and silk-elastinlike protein polymers for example has led to the development of delivery systems based on natural motifs of structural proteins to take advantage of their physicochemical properties. Additionally, protein based polymers on other natural motifs and de novo designs are starting to produce promising constructs for drug and gene delivery applications where precise control over structure promises correlation with function and guides the development of new and improved constructs. Clinical applications based on recombinant polymers for delivery of bioactive agents have not been realized at this point. However lessons learned from fundamental research with these polymers can be used to guide design of safe and effective systems for use in the clinic. This tutorial review summarizes progress made in the design and utility of recombinant polymers in drug and gene delivery and discusses challenges and future directions of such polymers for this purpose.

Wafer-Level Bonding using Anisotropic Conductive Adhesive for 3D MEMS Applications

As opposed to planar ICs, micro-electro mechanical systems (MEMS) are three dimensional structures with movable parts, membranes and cavities. Fragile movable structures are generally encapsulated inside a cavity by bonding a cap wafer to a MEMS device wafer. The use of through silicon vias (TSVs) in MEMS allows a significant miniaturization of the devices. TSVs through the cap wafer require an electrical connection between the TSVs and bond pads on the device wafer. This paper presents a novel bonding method that allows to do this in a simple and cost-effective way. We demonstrate the use of Benzocyclobutene (BCB) containing metal coated monodisperse polymer spheres (MPS) as an anisotropic conductive adhesive (ACA) for wafer-to-wafer bonding. The technology is demonstrated by bonding glass cap wafers with cavities and a patterned metallization to silicon wafers with a patterned metallization. The ACA is spray-coated onto the cap wafer and the bonding is performed in vacuum at 250 °C for 60 minutes with 300 mbar pressure applied. The electrical performance is evaluated using daisy-chain and kelvin structures, and the bond strength is verified by shear testing. Variations in bond frame size, contact area and minimum distance between conductor lines are investigated. Four wafers with a total of 880 dies are electrically tested. An average resistance of34 ±14mΩ is obtained for a contact area of 300 × 300 μm2 and 78 ±55 mΩ for 200 x 200 μm2. Daisy chains with 16 contact areas have a yield of 98 % for a 300 × 300 μm2 contact area and 95 % for 200 x 200 μm2. The technology is expected to be scalable to smaller contact areas by increasing the amount of MPS in the BCB. An average bond shear strength of 36 ± 9MPa is measured.

Four degree of freedom liquid dispenser for direct write capillary self-assembly with sub-nanoliter precision

Capillary forces provide a ubiquitous means of organizing micro- and nanoscale structures on substrates. In order to investigate the mechanism of capillary self-assembly and to fabricate complex ordered structures, precise control of the meniscus shape is needed. We present a precision instrument that enables deposition of liquid droplets spanning from 2 nl to 300 μl, in concert with mechanical manipulation of the liquid-substrate interface with four degrees of freedom. The substrate has sub-100 nm positioning resolution in three axes of translation, and its temperature is controlled using thermoelectric modules. The capillary tip can rotate about the vertical axis while simultaneously dispensing liquid onto the substrate. Liquid is displaced using a custom bidirectional diaphragm pump, in which an elastic membrane is hydraulically actuated by a stainless steel syringe. The syringe is driven by a piezoelectric actuator, enabling nanoliter volume and rate control. A quantitative model of the liquid dispenser is verified experimentally, and suggests that compressibility in the hydraulic line deamplifies the syringe stroke, enabling sub-nanoliter resolution control of liquid displacement at the capillary tip. We use this system to contact-print water and oil droplets by mechanical manipulation of a liquid bridge between the capillary and the substrate. Finally, we study the effect of droplet volume and substrate temperature on the evaporative self-assembly of monodisperse polymer microspheres from sessile droplets, and demonstrate the formation of 3D chiral assemblies of micro-rods by rotation of the capillary tip during evaporative assembly.

GPU implementations of the bond fluctuation model

We present two parallel implementations of the bond fluctuation model on graphics processors that outperform by a factor of up to 50 times an equivalent implementation on single CPU processor. The first algorithm is a parallelized version of an accelerated MC method published earlier in [S. Nedelcu, J.-U. Sommer, Single chain dynamics in polymer networks: a Monte Carlo study, J. Chem. Phys. 130 (2009) 204902]. In this first algorithm we use the parallel domain decomposition technique to avoid monomer collisions. In contrast, in the second algorithm we associate each monomer with a parallel process, where all monomers in the system are attempted to move simultaneously. In both cases, only monomer moves that result in allowed bonds and preserve lattice occupancy are accepted. To validate the correctness of the GPU algorithms we simulated monodisperse polymer melts at monomer number density 0.5 and compared static and dynamical properties with standard CPU implementations. We found good agreement between the CPU and the GPU results, which demonstrates the equivalence of the serial and parallel implementations. The influence of higher monomer number density is discussed.