Shirasu Porous Glass Membrane Research Articles

Facile Method for Preparing Liposomes by Permeation of Lipid–Alcohol Solutions through Shirasu Porous Glass Membranes

We present a novel and facile approach for preparing monodispersed liposomes simply by permeating lipid–alcohol solutions through Shirasu porous glass (SPG) membranes. This method uses the phenomenon of mixing of two miscible liquids at their interface formed near an SPG membrane surface, which induces spontaneous formation of liposomes. The effects of lipid concentration, pore size of the SPG membrane, and the alcohol used for the lipid solution on the structures and properties of the liposomes are studied. The liposome size is around 120 nm, and the size distribution is narrow, regardless of the lipid concentration, pore size, and alcohol used. However, the alcohol used affects the property of liposomes: An increase in the liposome size is clearly observed in a freezing–thawing treatment when isopropyl alcohol is used as the alcohol, whereas the liposome size is unchanged by the freezing–thawing treatment when ethanol is used.

Preparation of Bovine Serum Albumin (BSA) nanoparticles by desolvation using a membrane contactor: A new tool for large scale production

Albumin nanoparticles are attractive drug delivery systems as they can be prepared under soft conditions and incorporate several kinds of molecules. The aim of this study was to upscale the desolvation process for preparing Bovine Serum Albumin (BSA) nanoparticles using a membrane contactor. At a first step, the BSA nanoparticles were prepared at small scale using a syringe pump. BSA nanoparticles of 139nm in size, with a polydispersity index of 0.046, were obtained at the optimal conditions: pH 8.2, 100mgmL−1 BSA albumin solution (2mL), and 1mLmin−1 flow rate of ethanol addition (8mL). The upscaling with a membrane contactor was achieved by permeating ethanol through the pores of a Shirasu Porous Glass (SPG Technology Co., Japan) membrane and circulating the aqueous phase tangentially to the membrane surface. By increasing the pressure of the ethanol from 1 to 2.7 bars, a progressive decrease in nanoparticle size was obtained with a high nanoparticles yield (around 94–96%). In addition, the flow rate of the circulating phase did not affect the BSA nanoparticle characteristics. At the optimal conditions (pH 8.2, 100mgmL−1 BSA albumin solution, pressure of ethanol 2.7 bars, flow rate of the circulating phase 30.7mLs−1), the BSA nanoparticles showed similar characteristics to those obtained with the syringe pump. Large batches of BSA nanoparticles were prepared up to 10g BSA. The BSA nanoparticles were stable at least during 2months at 4°C, and their characteristics were reproducible. It was then concluded that the membrane contactor technique could be a suitable method for the preparation of albumin nanoparticles at large scale with properties similar to that obtained at small scale.

NIR‐Emitting Quantum Dot‐Encoded Microbeads through Membrane Emulsification for Multiplexed Immunoassays

NIR-emitting CdSeTe/CdS/ZnS core/shell/shell QD-encoded microbeads are combined with common flow cytometry with one laser for multiplexed detection of hepatitis B virus (HBV). A facile one-pot synthetic route is developed to prepare CdSeTe/CdS/ZnS core/shell/shell QDs with high photoluminescence quantum yield and excellent stability in liquid paraffin, and a Shirasu porous glass (SPG) membrane emulsification technique is applied to incorporate the QDs into polystyrene-maleic anhydride (PSMA) microbeads to obtain highly fluorescent QD-encoded microbeads. The relatively wide NIR photoluminescence full width half maximum of the CdSeTe/CdS/ZnS QDs is used to develop a 'single wavelength' encoding method to obtain different optical codes by changing the wavelengh and emission intensity of the QDs incorporated into the microbeads. Moreover, a detection platform combining NIR-emitting CdSeTe/CdS/ZnS QD-encoded microbeads and Beckman Coulter FC 500 flow cytometry with one laser of 488 nm is successfully used to conduct a 2-plex hybridization assay for hepatitis B surface antigen (HBsAg), hepatitis B e antigen (HBeAg), and a 3-plex hybridization assay for hepatitis B surface antibody (HBsAb), hepatitis B e antibody (HBeAb), and hepatitis B core antibody (HBcAb), which suggests the promising application of NIR QD-encoded microbeads for multiplex immunoassays.

Flurbiprofen-loaded nanoparticles prepared with polyvinylpyrrolidone using Shirasu porous glass membranes and a spray-drying technique: nano-sized formation and improved bioavailability

A unique flurbiprofen-loaded nanoemulsion was listed earlier using a Shirasu porous glass (SPG) membrane emulsification technique, which gave constant emulsion droplets with a thin size distribution. In this study, a flurbiprofen-loaded nanoemulsion was developed further into a solid form using polyvinylpyrrolidone (PVP) as a carrier by a spray-drying technique. The flurbiprofen-loaded nanoparticles with a weight ratio of flurbiprofen/PVP/surfactant mixture of 1/8/2 were connected with about 130 000-fold enhanced drug solubility and had a mean size of about 70 nm. In these nanoparticles, flurbiprofen was found in an altered amorphous state. Additionally, the nanoparticles gave significantly shorter Tmax, and greater AUC and Cmax compared to the commercially available product. Specially, the AUC of the drug from the nanoparticles was about 10-fold greater compared to the commercially available product. Therefore, these flurbiprofen-loaded nanoparticles can be convenient for distributing a poorly water-soluble flurbiprofen with improved bioavailability using uniform nano-sized particles.

Microencapsulation of menthol by crosslinked chitosan via porous glass membrane emulsification technique and their controlled release properties

Chitosan-encapsulated menthol microcapsules were successfully prepared in an oil-in-water (o/w) emulsion using the Shirasu Porous Glass (SPG) membrane emulsification technique and high-speed dispersion technique for preparing a mixed o/w emulsion. The size of the menthol-loaded chitosan microcapsules was strongly depended on the average pore size of the SPG membrane and the amount of menthol loading in the dispersed phase. The membrane pore size of 5.2 µm was suitable for a viscous dispersed phase containing light mineral oil. The average diameter of emulsion droplets of 28.3 µm was obtained. Increasing the menthol loading in the dispersion phase from 5% to 10% w/w of chitosan decreased the emulsion droplet size with a broad size distribution. The crosslinked microcapsule size and size distribution of mixed emulsion droplets decreased with the increasing crosslinking time. The menthol release was a diffusion control which depended on the proportion of amino group in chitosan-to-tripolyphosphate molar ratio and crosslinking time. This work also demonstrated that hydrophilicity/hydrophobicity of the continuous phase and dispersion phase controlled SPG membrane emulsification efficiency and quality of the resulting emulsion droplets.

Silymarin-loaded solid nanoparticles provide excellent hepatic protection: physicochemical characterization and in vivo evaluation

BackgroundThe purpose of this study was to develop a novel silymarin-loaded solid nanoparticle system with enhanced oral bioavailability and an ability to provide excellent hepatic protection for poorly water-soluble drugs using Shirasu porous glass (SPG) membrane emulsification and a spray-drying technique.MethodsA silymarin-loaded liquid nanoemulsion was formulated by applying the SPG membrane emulsification technique. This was further converted into solid state nanosized particles by the spray-drying technique. The physicochemical characteristics of these nanoparticles were determined by scanning electron microscopy, differential scanning calorimetry, and powder X-ray diffraction. Their dissolution, bioavailability, and hepatoprotective activity in rats were assessed by comparison with a commercially available silymarin-loaded product.ResultsFormulation of a silymarin-loaded nanoemulsion, comprising silymarin, castor oil, polyvinylpyrrolidone, Transcutol HP, Tween 80, and water at a weight ratio of 5/3/3/1.25/1.25/100 was accomplished using an SPG membrane emulsification technique at an agitator speed of 700 rpm, a feed pressure of 15 kPa, and a continuous phase temperature of 25°C. This resulted in generation of comparatively uniform emulsion globules with a narrow size distribution. Moreover, the silymarin-loaded solid nanoparticles, containing silymarin/castor oil/polyvinylpyrrolidone/Transcutol HP/Tween 80 at a weight ratio of 5/3/3/1.25/1.25, improved about 1,300-fold drug solubility and retained a mean size of about 210 nm. Silymarin was located in unaltered crystalline form in the nanoparticles. The drug dissolved rapidly from the nanoparticles, reaching nearly 80% within 15 minutes, indicating three-fold better dissolution than that of the commercial product. Further, the nanoparticles showed a considerably shorter time to peak concentration, a greater area under the concentration-time curve, and a higher maximum concentration of silymarin compared with the commercial product (P < 0.05). In particular, the area under the concentration-time curve of the drug provided by the nanoparticles was approximately 1.3-fold greater than that of the commercial product. In addition, the silymarin-loaded nanoparticles significantly reduced carbon tetrachloride-induced hepatotoxicity, indicating improved bioactivity compared with silymarin powder and the commercial product.ConclusionSilymarin-loaded nanoparticles developed using SPG membrane emulsification and spray-drying techniques could be a useful system for delivery of poorly water-soluble silymarin while affording excellent hepatic protection.

Preparation of Uniform-Sized Poly[methacryloxypropyl Tris(trimethylsiloxy)silane] Microspheres via Shirasu Porous Glass Membrane Emulsification Technique

Preparation of Uniform-Sized Poly[methacryloxypropyl Tris(trimethylsiloxy)silane] Microspheres via Shirasu Porous Glass Membrane Emulsification Technique

Successful application of Shirasu porous glass (SPG) membrane system for microbubble aeration in a biofilm reactor treating synthetic wastewater

Microbubble aeration is supposed to be able to provide potential advantage for aerobic biological wastewater treatment due to enhancement of oxygen mass transfer. Then SPG membrane microbubble generation system was used to aerate a biofilm reactor treating a synthetic wastewater. Successfully long-term operation of the experimental system demonstrated the application feasibility of microbubble aeration in aerobic biological wastewater treatment. The air permeation of SPG membrane depended on its surface property and pore size, rather than membrane fouling which influenced microbubble generation and subsequent oxygen transfer. Stable and efficient COD removal was achieved but the ammonia removal became inefficient at high organic loading rate due to DO limitation. The suitable SPG membrane area-based COD removal capacity should be controlled around 6.69kgCOD/(m2d), considering the stable DO concentration and efficient contaminant removal. Microbubble floatation also provided contribution to suspending and colloidal contaminant removal. The oxygen utilization was estimated as high as almost close to 100% under certain conditions based on contaminant removal, but the energy consumption of this microbubble aeration system was also very high. To use hydrophobic SPG membranes and increase their air supply capacity could contribute to energy-saving.

Non-encapsulated thermo-liquid crystals for digital particle tracking thermography/velocimetry in microfluidics

The ever accelerating state of technology has powered an increasing interest in heat transfer solutions and process engineering innovations in the microfluidics domain. In order to carry out such developments, reliable heat transfer diagnostic techniques are necessary. Thermo-liquid crystal (TLC) thermography, in combination with particle image velocimetry, has been a widely accepted and commonly used technique for the simultaneous measurement and characterization of temperature and velocity fields in macroscopic fluid flows for several decades. However, low seeding density, volume illumination, and low TLC particle image quality at high magnifications present unsurpassed challenges to its application to three-dimensional flows with microscopic dimensions. In this work, a measurement technique to evaluate the color response of individual non-encapsulated TLC particles is presented. A Shirasu porous glass membrane emulsification approach was used to produce the non-encapsulated TLC particles with a narrow size distribution and a multi-variable calibration procedure, making use of all three RGB and HSI color components, as well as the proper orthogonally decomposed RGB components, was used to achieve unprecedented low uncertainty levels in the temperature estimation of individual particles, opening the door to simultaneous temperature and velocity tracking using 3D velocimetry techniques.

Nano-structure construction of porous membranes by depositing nanoparticles for enhanced surface wettability

Two-dimensional nano-structures are successfully constructed on the pore surfaces of porous membranes by depositing nanoparticles for enhanced surface wettability in this study, in order to obtain improved oil–water separation performance of membranes. Shirasu porous glass (SPG) membranes are used as the substrate membranes, and the two-dimensional nano-structures are constructed by depositing SiO2 nanoparticles onto the membrane pore surfaces, with which the smooth membrane surfaces turn into nano-structured concavo-convex rough surfaces. Chlorotrimethylsilane (CTMS) are grafted on the nano-structured membranes to achieve the membrane surface hydrophobicity and oleophilicity, while perfluorinated surfactants (f-PEG) are grafted on the membranes to achieve the surface hydrophilicity and oleophobicity. The formation and microstructures of the prepared membranes are investigated by employing scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS), and the relationship between the two-dimensional nano-structures and the surface wettability is explored by measuring the water/oil contact angle of membranes. The results show that, the SiO2 nanoparticles are uniformly and compactly deposited on the membrane pore surfaces, and the nano-structured architectures on the membrane surfaces could efficiently enhance the surface wettability of both CTMS-grafted and f-PEG-grafted membranes. Both CTMS-grafted and f-PEG-grafted nano-structured SPG membranes exhibit satisfactory performance of oil–water separation including separation of O/W emulsions. The results provide valuable guidance for designing and fabricating efficient membranes for oil–water separation.

Effect of microbubble and its generation process on mixed liquor properties of activated sludge using Shirasu porous glass (SPG) membrane system

Microbubble aeration is supposed to be able to provide potential advantage for aerobic biological wastewater treatment due to enhancement of oxygen mass transfer. On the other hand, microbubble and its generation methods might affect mixed liquor properties of activated sludge. Then SPG membrane microbubble generation system was used to investigate variation of mixed liquor properties of activated sludge in microbubble aeration. The results indicated that sludge floatation happened in microbubble aeration due to attachment of microbubbles to sludge flocs, resulting in a decrease in mixed liquor suspended solid (MLSS) concentration and poor sludge settleability. The strong shear stress caused by liquid circulation pump during microbubble generation led to sludge broken, resulting in decreased sludge floc size and sludge organics release, such as extracellular polymers (EPS). The organics release from broken sludge flocs was the main reason for increased both supernatant organic content (especially organic colloids) and consequent supernatant turbidity. The re-flocculation ability of broken sludge flocs also depended on sludge EPS release. In addition, the viscosity of mixed liquor increased along with sludge broken and increased supernatant organic content but the surface tension of mixed liquor remained constant. These results displayed the possible problems to apply microbubble aeration in aerobic wastewater treatment processes based on activated sludge.

Fouling and structural changes of Shirasu porous glass (SPG) membrane used in aerobic wastewater treatment process for microbubble aeration

In the present study a hydrophilic SPG membrane was used for microbubble generation to aerate a pilot-scale biofilm reactor treating synthetic municipal wastewater. The external fouling of SPG membrane was observed and identified during continuous operation of the bioreactor. Then the SPG membrane was cleaned offline by ultrasonic, thermal and acid treatment to remove fouling layer, organic and inorganic foulants on the membrane surface. The structural changes of SPG membrane were investigated after fouling and offline cleaning, using scanning electron microscopy (SEM), mercury and gas adsorption porosimetry, X-ray Diffraction (XRD), and Infrared (IR) absorption. SEM tests clearly demonstrated that these offline cleaning methods were effective to clear membrane external fouling. There was no obvious change in membrane pore size distribution after SPG membrane fouling and offline cleaning, but the membrane porosity and pore surface area increased slightly. XRD and IR analysis also showed that rare inorganic or organic foulants deposited on the pore surface inside the membrane. Therefore, the external fouling was identified as the main mechanism of SPG membrane fouling used in aerobic wastewater treatment process. The microbubble generation and oxygen mass transfer deteriorated due to external fouling of SPG membrane, which recovered after membrane offline cleaning.

Fabrication of a uniformly sized fenofibrate microemulsion by membrane emulsification

Fenofibrate-loaded microemulsions composed of Labrafil M 1944 CS, Capryol PGMC and fenofibrate as the dispersed phase and Labrasol in demineralised water as the continuous phase were prepared by utilising a Shirasu-porous-glass (SPG) membrane emulsification technique. The process parameters were optimised by adjusting the feed pressure (15–45 kPa), agitator speed (250–800 rpm) and temperature of the continuous phase (25–45°C). As a result, narrowly distributed microemulsions were obtained via SPG membrane emulsification at an agitator speed of 250 rpm, a feed pressure of 30 kPa and a continuous phase temperature of 25°C. Furthermore, TEM images clearly showed that the microemulsion prepared by SPG membrane emulsification had a uniform, spherical morphology with a narrow size distribution. Our results indicated that the SPG membrane emulsification technique is highly efficient for the preparation of narrowly distributed microemulsions with relatively smaller particle sizes compared with the common stirring method.

Enhanced solubility and oral bioavailability of itraconazole by combining membrane emulsification and spray drying technique

The objective of the present study was to enhance solubility and bioavailability of itraconazole by a combined use of membrane emulsification and spray drying solidification technique. A shirasu-porous-glass (SPG) membrane with a mean pore size of 2.5μm was used to produce monodispersed microemulsions of itraconazole consisting of methylene chloride as the dispersed phase, a mixture of Transcutol HP and Span 20 as a stabilizer, and dextran as solid carrier dissolved in water as the continuous phase. The dispersed phase permeated through the SPG membrane into the continuous phase at an agitator speed of 150rpm, a feed pressure of 15kPa and a continuous phase temperature of 25°C and the resultant emulsion was solidified using spray-drying technique. Solid state characterizations of the solid emulsion showed that the crystal state of itraconazole in solid emulsion was converted from crystalline to amorphous form. The solid emulsion of itraconazole displayed a significant increase in the dissolution rate than that of pure itraconazole. Furthermore, the solid emulsion after oral administration gave about eight-fold higher AUC and about ten-fold higher Cmax in rats than pure itraconazole powder (p<0.05), indicating this formulation greatly improved the oral bioavailability of drug in rats. Thus, these results demonstrated that the SPG membrane emulsification system combined with spray-drying technique could be used as a promising technique to develop solid formulation of itraconazole with enhanced solubility and bioavailability.

Preparation strategies of thermo-sensitive P(NIPAM-co-AA) microspheres with narrow size distribution

Stimuli-responsive polymer microspheres have attracted great attention due to their applications in drug delivery system which can offer considerable versatility for encapsulation and triggered release. In this article, thermo-sensitive poly (N-isopropyl acrylamide-co-acrylic acid) [P(NIPAM-co-AA)] microspheres with narrow size distribution were successfully prepared using a new technique-premix membrane emulsification technique combined with low temperature polymerization. Coarse W/O (water in oil) emulsion with broad size distribution was repeatedly pressed through Shirasu Porous Glass (SPG) membrane under nitrogen gas pressure to form the fine emulsion with narrow size distribution. In order to avoid phase transition triggered aggregation of thermo-sensitive P(NIPAM-co-AA) microspheres during polymerization, N, N, N' N'-tetramethylethylene-diamine (TEMED) was introduced to polymerization system by adding it into W/O emulsion to initiate polymerization at low temperature. The morphology and size distribution were investigated by confocal laser scanning microscopy (CLSM) and zeta potential analyzer. Rhodamine 123 was screened out from several dyes to label P(NIPAM-co-AA) microspheres in order to characterize them by CLSM. Effects of trans-membrane pressure, number of cross membrane passes and stirring rate during polymerization on size distribution of the microspheres were investigated in detail. The optimized preparation conditions were determined as follows: trans-membrane pressure was 250 kPa and trans-membrane passes were three times when using a membrane of 5.2 mu m pore size. The obtained microspheres were around 5.11 with the polydispersity index of 0.0312. Good linear relationship (Y = 0.89X + 0.62, R-2 = 0.999) between the membrane pore size (X) and the mean diameter of the microspheres (Y) was observed. This research would also shed light on preparation of other thermo-sensitive microspheres with narrow size distribution, which would have extensive applications in drug delivery system (DDS). (C) 2012 Elsevier B.V. All rights reserved.

Production of uniform droplets using membrane, microchannel and microfluidic emulsification devices

This review provides an overview of major microengineering emulsification techniques for production of monodispersed droplets. The main emphasis has been put on membrane emulsification using Shirasu Porous Glass and microsieve membrane, microchannel emulsification using grooved-type and straight-through microchannel plates, microfluidic junctions and flow focusing microfluidic devices. Microfabrication methods for production of planar and 3D poly(dimethylsiloxane) devices, glass capillary microfluidic devices and single-crystal silicon microchannel array devices have been described including soft lithography, glass capillary pulling and microforging, hot embossing, anisotropic wet etching and deep reactive ion etching. In addition, fabrication methods for SPG and microseive membranes have been outlined, such as spinodal decomposition, reactive ion etching and ultraviolet LIGA (Lithography, Electroplating, and Moulding) process. The most widespread application of micromachined emulsification devices is in the synthesis of monodispersed particles and vesicles, such as polymeric particles, microgels, solid lipid particles, Janus particles, and functional vesicles (liposomes, polymersomes and colloidosomes). Glass capillary microfluidic devices are very suitable for production of core/shell drops of controllable shell thickness and multiple emulsions containing a controlled number of inner droplets and/or inner droplets of two or more distinct phases. Microchannel emulsification is a very promising technique for production of monodispersed droplets with droplet throughputs of up to 100 l h−1.

Size-controlled and monodisperse enzyme-encapsulated chitosan microspheres developed by the SPG membrane emulsification technique

Lysozyme-encapsulated chitosan microspheres with micron-size diameters were successfully prepared for the first time by employing the Shirasu porous glass (SPG) membrane emulsification technique followed by cross-linking with glutaraldehyde, and the relationships between the preparation conditions and characteristics of the microspheres were studied in detail. This preparation method provided size-controllability and monodispersity of the microspheres, owing to the sharpness of the pore sizes of the SPG membranes. It was also possible to predict the average diameters of the enzyme-encapsulated microspheres using no fitting parameters, on the basis that each microsphere is prepared in an emulsion containing chitosan and lysozyme, without any collisions or aggregation occurring. X-ray photoelectron spectroscopy measurements indicated that the amount of encapsulated lysozyme was controlled by the concentrations of chitosan and lysozymes in the dispersion phase used for preparing the emulsions from which the enzyme-encapsulated microspheres are formed. Finally, the apparent activity of the encapsulated lysozymes was measured by the viscosimetric method, using ethyleneglycolchitin. Results showed that about half of the activity of the encapsulated lysozymes was maintained during the preparation procedure when employing the SPG membrane emulsification technique.

Fabrication of nano-scale liposomes containing doxorubicin using Shirasu porous glass membrane

Nano-scale liposomes were successfully produced using a Shirasu porous glass (SPG) membrane emulsification technique. Primary liposomes prepared by a film-hydration method were treated using SPG membranes with different pore sizes (2.0, 1.0, 0.7, 0.5, and 0.2 μm) for control over the liposome size. The liposome sizes were evaluated using a dynamic light scattering method and their morphologies were observed by optical microscopy and transmission electron microscopy. As the passage number of liposomes through SPG membrane increased, the size and its distribution of the liposomes gradually decreased. A smaller pore size of the SPG membrane and a higher applied pressure resulted in liposomes with a smaller size. After the preparation of nano-scale liposomes containing ammonium sulfate (AS), doxorubicin (DOX) was encapsulated in the liposomes by a remote loading method, where AS served as a precipitant for DOX. The encapsulation efficiency of the DOX was maximized up to 94% when the concentrations of AS and DOX were 250 and 0.045 mM, respectively. We have obtained the release profiles of the liposomes with different sizes. As shown below, liposomes with smaller size exhibited a faster release profile of drug due to the large surface area. These nano-scale liposomes encapsulating an anti-cancer drug can potentially be employed as drug delivery vehicles for intravenous injection.

Fabrication strategy for amphiphilic microcapsules with narrow size distribution by premix membrane emulsification

Amphiphilic co-polymer, which can maintain the stability of proteins and increase the protein loading efficiency, is considered as an exploring-worthy biodegrade polymer for drug delivery. However, amphiphilic microcapsules prepared by conventional methods, such like mechanical stirring and spray-drying methods, exhibit broad size distributions due to its hydrophilic sequences, leading to poor reproducibility. In this study, we employed poly(monomethoxypoly ethylene glycol-co-D,L-lactide) (mPEG-PLA, PELA), one of common amphiphilic polymers, as model to focus on investigating the process parameters and mechanisms to prepare PELA microcapsules with narrow size distribution and regular sphericity by combining premix membrane emulsification and double emulsion technique. The coarse double emulsion with broad size distribution was repeatedly pressed through Shirasu Porous Glass (SPG) membrane with relatively high pressure to form the fine emulsion with narrow size distribution. Then, the microcapsules with narrow size distribution can be obtained by solvent extraction method. It was found that it was more difficult to obtain PELA microcapsules with narrow size distribution and smooth surface due to its amphiphilic property, compared with the cases of PLA and PLGA. The smooth surface morphology was found to be related to several factors including internal water phase with less volume, slower stirring rate during solidification and using ethyl acetate as oil phase. It was also found that mass ratio of hydrophilic mPEG, stabilizer PVA concentration in external water phase and transmembrane pressure played important role on the distribution of microcapsules size. The suitable preparation conditions were determined as follows: for the membrane with pore size of 2.8 μm, the mass ratio of PLA/mPEG was 19:1, volume ratio of W(1)/O was 1:10 and O/W(2) was 1:5, PVA concentration (w/v) was 1.0%, magnetic stirring rate during solidification was 60 rpm and 300 kPa was chosen as transmembrane pressure. There was a linear relationship between the diameter of microcapsules and the pore size of the membranes. Finally, by manipulating the process parameters, PELA microcapsules with narrow size distributions (coefficient of variation was less than 15%), smooth morphology and various sizes, were obtained. Most importantly, the key factors affecting fabrication have been revealed and mechanisms were illustrated in detail, which would shed light on the research of amphiphilic polymer formulation.

Effect of acrylic acid weight percentage on the pore size in poly(N-Isopropyl acrylamide- co-acrylic acid) microspheres

In this article, a simple way to control pore size in monodispersed poly(N-Isopropyl acrylamide- co-acrylic acid) [P(NIPAM- co-AAc)] microspheres just by changing the acrylic acid wt.% in the formula was developed. The monodispersed P(NIPAM- co-AAc) microspheres with functionalized carboxyl groups were successfully prepared by Shirasu porous glass (SPG) membrane emulsification technique at room temperature. The microspheres were dried by supercritical drying (SCD), lyophilization and vacuum drying, separately. It was observed that SCD was an effective drying method to maintain the morphologies of the microspheres. Scanning electron microscopy (SEM), confocal laser scanning microscope (CLSM), and porosity analyzer results showed that the P(NIPAM- co-AAc) microspheres contained abundant slit-like mesoporous structure with pore size from 2 nm to 50 nm. The increase of AAc wt.% would increase the percentage of mesopores and micropores in the microspheres. P(NIPAM- co-AAc) microspheres with specific pore size can be obtained by simply changing the acrylic acid wt.% in the formula. Such temperature-/pH-ensitive microspheres with controllable pore size were expected to meet various requirements in different bioapplications, such as drug delivery and enzyme immobilization.