Electrohydrodynamic atomization for biodegradable polymeric particle production

Electrohydrodynamic atomization (EHDA) has many applications such as electrospray ionization in mass spectroscopy, electrospray deposition of thin films, pharmaceutical productions, and polymeric particle fabrications for drug encapsulation. In the present study, EHDA was employed to produce biodegradable polymeric micro- and nanoparticles. The effects of processing parameters such as polymer concentration, flow rate, surfactants, organic salt, and setup configurations on the size and morphology of polymeric particles were investigated systematically. By changing the various processing parameters, controllable particle shape and size can be achieved. PLGA nanoparticles with size of around 250 nm can be obtained by using organic salts to increase the conductivity of the spraying solution even at a relatively high flow rate. A higher flow rate has the advantage of producing a stable cone spray and can be easily reproduced. Solid and porous particles can be fabricated using different experimental setups to control the organic solvent evaporation rate. Also, paclitaxel, a model antineoplastic drug, was encapsulated in polymeric particles which can be employed for controlled release applications. In short, EHDA is a promising technique to fabricate polymeric micro- or nanoparticles which can be used in drug delivery systems.     

Electrohydrodynamic atomization: an approach to growing continuous self-supporting polymeric fibers

The investigation presented in this paper illustrates a technique for growing in-situ polymerized networks, forming scaffold-like structures usually formed by means of electrospinning. The technique of jet atomization employing electrohydrodynamics is a manifestation of electrospinning. However, we show for the first time that using this technique where individual droplets are generated, a continuous self-supporting submicrometer web-like structure can be grown whereby fragments of the structure are delivered in the droplets and polymerize on the surface of the growing structure via polycondensation. The development of these growing fibers into web structures is a direct result of the processing route together with the excellent tailor-made cross-linking nature of the resin. An operational map is generated to identify a parametric space in which the stable cone-jet mode of electrohydrodynamic atomization prevails for generating the finest droplets. A statistical analysis on the formed fibers for a given time and electrospray condition is presented together with optical micrographs of the structure, which concludes the discussion in this paper.     

Preferential deposition of cyanometallate coordination polymer nanoplates through evaporation of droplets

We reported a room-temperature method to deposit self-adhesive coordination polymers nanoplates on glass slides preferentially.     

The effect of a polymeric additive on the evaporation of organic aerocolloidal droplets

 The evaporation of single triethyl phosphate (TEP) micro-droplets containing a high molecular weight polymer, poly(methyl methacrylate) (PMAA), was inves-tigated using an electrodynamic trap and light scattering measurements to explore the suppression of evaporation by the additive. Pure-component evaporation rates were measured to determine the vapor pressure over a range of temperatures, and the polymer was found to significantly decrease the evaporation rate. A numerical solution of the problem of simultaneous solvent evaporation and polymer diffusion within the droplet indicated a rapid build-up of PMMA at the surface of the drop, but vapor/liquid thermodynamic considerations alone do not account for the observed reduction in the evaporation rate for the droplets containing PMMA. After significant evaporation of TEP occurred, the ultra-low evaporation rate was measured using changes in the Raman spectra associated with morphology-dependent resonances. The evaporation in this regime appears to be controlled by the rate of solvent molecules diffusing through the polymer matrix. Received: 17 June 1997 Accepted: 24 October 1997     

Surface deposition and imaging of large Ag clusters formed in He droplets

The utility of a continuous beam of He droplets for the assembly and surface deposition of Ag(N) clusters, ~ 300-6000, is studied with transmission electron microscopy. Images of the clusters on amorphous carbon substrates obtained at short deposition times have provided for a measure of the size distribution of the metal clusters. The average sizes of the deposited clusters are in good agreement with an energy balance based estimate of Ag(N) cluster growth in He droplets. Measurements of the deposition rate indicate that upon impact with the surface the He-embedded cluster is attached with high probability. The stability of the deposited clusters on the substrate is discussed.     

Influence of polymeric additives on biomimetic silica deposition on patterned microstructures

Microstructured polymer films prepared by photochemical grafting of different polymers were used as restricted reaction areas in silica deposition experiments. Linear and branched poly(alkyleneimines) and poly(allylamine hydrochloride) in pure aqueous or phosphate-containing solutions were used as additives to silica precursor solutions. The silica deposits obtained by spin-coating these solutions onto microstructured polymer films were investigated by scanning electron microscopy and atomic force microscopy. Experiments with poly(alkylene imines) in the silica precursor solution show the deposition of smooth and granular silica structures that closely mimic the natural patterns. The structure formation can be explained by physicochemical processes. Hypotheses that have been made for the natural silification processes can be evaluated on this basis.     

Chemical changes of polymeric surfaces after modification with multi-source cluster deposition

A new process for surface modification of polymers with multi-source cluster deposition apparatus has been reported in our previous work. The apparatus simultaneously supplies reactant of ammonium sulfamate and activator of energetic Ar(+) ion. In this work chemical changes are analyzed on the basis of XPS spectra and the relations of contact angle and platelet adhesion with chemical changes are discussed. Polymer film, setting on a turning holder, was irradiated by Ar(+) ions during bombardment with ammonium sulfamate clusters. The Ar(+) ion source served for activation of polymer surface and a cluster ion source supplied ammonium sulfamate molecules to react with activated surface. After thorough washing with deionized sterile water, the modified surfaces were evaluated in terms of contact angle of water, elemental composition and binding state on XPS and platelet adhesion with platelet rich plasma (PRP). The modification of polysulfone decreased the contact angle of water on surfaces from 82.6 down to 34.5 degrees. The adhesion number of platelets were decreased to one-tenth of the original surface. Ammonium, amine, sulfate and thiophene combinations were formed on the modified surfaces. The primary studies showed successful modification of polysulfone with ammonium sulfamate by assistance of Ar(+) ion irradiation. The polar groups like N-sulfate were formed on surfaces and contribute to the decrease of surface contact angle and adhesion number of platelets. Since the same process can also be applied to other polymeric materials with various substrates, combining with the features of no solvent and no topographic changes, this method might be developed in a promising way for modification of polymers.     

Surface modification of droplet polymeric microfluidic devices for the stable and continuous generation of aqueous droplets

Droplet microfluidics performed in poly(methyl methacrylate) (PMMA) microfluidic devices resulted in significant wall wetting by water droplets formed in a liquid-liquid segmented flow when using a hydrophobic carrier fluid such as perfluorotripropylamine (FC-3283). This wall wetting led to water droplets with nonuniform sizes that were often trapped on the wall surfaces, leading to unstable and poorly controlled liquid-liquid segmented flow. To circumvent this problem, we developed a two-step procedure to hydrophobically modify the surfaces of PMMA and other thermoplastic materials commonly used to make microfluidic devices. The surface-modification route involved the introduction of hydroxyl groups by oxygen plasma treatment of the polymer surface followed by a solution-phase reaction with heptadecafluoro-1,1,2,2-tetrahydrodecyl trichlorosilane dissolved in fluorocarbon solvent FC-3283. This procedure was found to be useful for the modification of PMMA and other thermoplastic surfaces, including polycyclic olefin copolymer (COC) and polycarbonate (PC). Angle-resolved X-ray photoelectron spectroscopy indicated that the fluorination of these polymers took place with high surface selectivity. This procedure was used to modify the surface of a PMMA droplet microfluidic device (DMFD) and was shown to be useful in reducing the wetting problem during the generation of aqueous droplets in a perfluorotripropylamine (FC-3283) carrier fluid and could generate stable segmented flows for hours of operation. In the case of PMMA DMFD, oxygen plasma treatment was carried out after the PMMA cover plate was thermally fusion bonded to the PMMA microfluidic chip. Because the appended chemistry to the channel wall created a hydrophobic surface, it will accommodate the use of other carrier fluids that are hydrophobic as well, such as hexadecane or mineral oils.     

Facile electrochemical fabrication of polymeric templates for spatially selective deposition of metals

Here, we report on a simple and general approach to fabricate polymeric (poly(2-methoxyaniline)) templates for deposition of silver in the form of micro islands on the electrode surface. The method is based on the application of electrochemically generated hydrogen microbubbles to locally block polymerization of monomers on the surface. This yields micrometer-sized holes within the forming polymeric film, which act as gate sites enabling further selective deposition of the metal on the surface.     

Growth of Escherichia coli under extremely low-frequency electromagnetic fields

The inflence of extremely low-frequency (ELF) electromagnetic fields on Escherichia coli cultures in submerse fermentation was studied. The fermentation processes were carried out recycling the culture medium externally through a stainless steel tube inserted in a magnetic field generator (solenoid). The exposure time and electromagnetic induction were varied in a range of 1 to 12 h and 0.010 to 0.10 T, respectively, according to a Box-Wilson Central Composite Designs of face centered with five central points. Growth of E. coli could be altered (stimulated or inhibited) under magnetic fieldinduced effects. E. coli culturesexposed at 0.1 T during 6.5 h exhibited changes in its viability compared to unexposed cells, which was 100 times higher than the control. The magnetic field generator associated with the cellular suspension recycle is a new way of magnetic treatment in fermentation processes and could be appropriate to industrial scale up.     

Photoinitiated chemical vapor deposition of polymeric thin films using a volatile photoinitiator

Photoinitiated chemical vapor deposition (piCVD) is an evolutionary CVD technique for depositing polymeric thin films in one step without using any solvents. The technique requires no pre- or post-treatment and uses a volatile photoinitiator to initiate free-radical polymerization of gaseous monomers under UV irradiation. Glycidyl methacrylate (GMA) was used as a test monomer for its ability to undergo free-radical polymerization, and 2,2'-azobis(2-methylpropane) (ABMP) was used as the photoinitiator, as it is known to produce radicals when excited by photons. GMA and ABMP vapors were fed into a vacuum chamber in which film growth was observed on a substrate exposed to UV irradiation. The resulting poly(glycidyl methacrylate) (PGMA) thin films were comprised of linear chains and had high structural resemblance to conventionally polymerized PGMA, as shown by the high solubility in tetrahydrofuran and the infrared and X-ray photoelectron spectroscopy measurements. The introduction of ABMP into the vacuum chamber significantly increased growth rates. The maximum growth rate achieved was approximately 140 nm/min and represents a 7-fold enhancement over the case without ABMP. The molecular weight was found to increase with increasing monomer-to-initiator (M/I) feed ratio, and the polydispersity indexes (PDIs) of the samples were between 1.8 and 2.2, lower than the values obtained in conventional batch polymerization but in agreement with the theoretical expressions developed for low-conversion solution-phase polymerization, which are applicable to continuous processes such as piCVD. Molecular-weight distributions can be narrowed by filtering out wavelengths shorter than 300 nm, which induce branching and/or cross-linking. The strong dependence of the molecular weight on the M/I ratio, the rate enhancement due to the use of a radical photoinitiator, the good agreement between the experimental, and the theoretical PDIs provide evidence of a free-radical mechanism in piCVD. The clear films obtained in this work had number-average molecular weights between 12 500 and 97 000 g/mol. The similarities in growth conditions, growth rates, and molecular weights between the initiated CVD, a previously reported thermal process able to synthesize a wide range of polymers, and the piCVD of PGMA suggest that piCVD can also be used to produce those polymers and potentially others whose monomers undergo free-radical mechanisms. This paper serves as an introduction to the technique by demonstrating piCVD's ability in synthesizing high-molecular-weight PGMA thin films with narrow molecular-weight distributions from vapors of GMA and ABMP in a single, dry step under UV irradiation.     

Electrohydrodynamic ionization mass spectrometry of sulfonates

Electrohydrodynamic ionization mass spectrometry has been applied to the analysis of 2-naphthol-3,6-disulfonic acid, disodium salt and 4,5-dihydroxy-2,7-naphthalenedisulfonic acid, disodium salt. The negative ion mass spectra indicate ions characteristic of the sample and no fragment ions are observed. Degrees of dissociation of the sulfonates and the ion-solvent interactions are reflected in the negative ion spectra.     

Reactions under mixing in viscous polymeric media

Mixing of viscous liquids is of common occurence in polymer technology. We consider the effects of mixing on the simplest bimolecular reaction A+B→O. Under mixing often lamellar arrays of striations of the A and B reactants are formed. The structure of these arrays and the thinning of the striations during mixing determine the kinetics of the reaction. We consider both a premixed situation (where the reaction is diffusion-controlled) and also a situation where mixing and reaction take place simultaneously.     

Nanoliter deposition unit for pipetting droplets of small volumes for Total Reflection X-ray Fluorescence applications

A nanoliter droplet deposition unit was developed and characterized for application of sample preparation in TXRF. The droplets produced on quartz reflectors as well as on wafers show a good reproducibility, also the accuracy of the pipetted volume could be proved by a quantitative TXRF analysis using an external standard. The samples were found to be independent of rotation of the sample carrier. Angle scans showed droplet residue behavior, and the fluorescence signal is relatively invariant of the angle of incidence below the critical angle, which is useful for producing standards for external calibration for semiconductor surface contamination measurements by TXRF. Further it could be demonstrated that the nanoliter deposition unit is perfectly able to produce patterns of samples for applications like the quantification of aerosols collected by impactors.     

Electrohydrodynamic generation of monodisperse submicron aerosols

Generation of aerosols by electrostatic spraying of liquids from the tip of a needle placed into a capillary has been studied at a voltage lower than that corresponding to the corona ignition in the regime of the formation of single monodisperse droplets. The peculiarities of the jet-type motion of low-volatile liquid droplets with submicron sizes have been considered.     

A study of the deposition of polymeric material onto surfaces from fluorocarbon RF plasmas

A series of fluorocarbon gases, viz., CF₄, C₂F₆, C₃F₈, and CHF₃, have been compared for their relative tendencies to deposit polymeric material onto various surfaces, including Si and SiO₂, under RF plasma conditions. The plasmas were examined by optical emission spectroscopy. C₃F₈ and CHF₃ were found to produce the highest yields of polymers, although these exhibited significant differences in structure (as shown by XPS and IR) and differences in thermal stability, both of which could be minimized by replacing the C₃F₈ gas with a C₃F₈/H₂ mixture. The polymers produced from CHF₃ under the conditions of the present study were found to accumulate preferentially onto Si rather than SiO₂, as verified by the technique of Rutherford backscattering spectrometry.     

Iodine-starch clathrate complexes under the impact of a low-frequency acoustic field

The results from research on the kinetics of destruction of clathrate complexes (amyloidine, amylopectoiodine and iodinol) in low-frequency acoustic waves from 5 to 25 Hz are presented. Features of the transfer of energy from low-frequency acoustic oscillations are determined. The ability of systems containing biologically active clathrate structures to interact in resonance with external acoustic stimuli according to the energy state of the active part of iodine-containing compexes is confirmed. In the first approximation, such compounds can be regarded as model biochemical systems.     

Confinement and deposition of solution droplets on solvophilic surfaces using a flat high surface energy guide

A method of depositing small amounts of solution on flat micron scale surface areas on a hydrophilic substrate or die was developed. This method utilizes the capillarity of a flat, high surface free energy guide. Interfacial forces confine the solution between the guide and the substrate surface. The liquid follows the movement of the guide along the surface and can be moved to the desired area. The thermodynamic background of the method is given and its application to coat one arm of a gold plasmonic Mach-Zehnder interferometer with bovine serum albumin is described. This method, which is related to but different from microcontact printing and dip-pen microlithography, can be utilized in the manufacturing of biosensors and other lab-on-a-chip structures, and is particularly suitable to development stage devices.     

Microdroplet deposition under a liquid medium

An experimental and numerical study of the factors affecting the reproducibility of microdroplet depositions performed under a liquid medium is presented. In the deposition procedure, sample solution is dispensed from the end of a capillary by the aid of a pressure pulse onto a substrate with pillar-shaped sample anchors. The deposition was modeled using the convective Cahn-Hilliard equation coupled with the Navier-Stokes equations with added surface tension and gravity forces. To avoid a severe time-step restriction imposed by the fourth-order Cahn-Hilliard equation, a semi-implicit scheme was developed. An axisymmetric model was used, and an adaptive finite element method was implemented. In both the experimental and numerical study it was shown that the deposited volume mainly depends on the capillary-substrate distance and the anchor surface wettability. A critical equilibrium contact angle has been identified below which reproducible depositions are facilitated.