Effects of preparation conditions on the monodispersity of albumin microspheres

Passive targeting and lung tolerability of enoxaparin microspheres for a sustained antithrombotic activity in rats

Pulmonary bed can retain microparticles (MP) larger than their capillaries' diameter, hence we offer a promising way for lung passive targeting following intravenous (IV) administration. In this study, enoxaparin (Enox)-albumin microspheres (Enox-Alb MS) were, optimally, developed as lung targeted sustained release MP for IV use. Lung tolerability and targeting efficiency of Enox-Alb MS were tested, and the pharmacokinetic profile following IV administration to albino rats was constructed. In vivo studies confirmed high lung targeting efficiency of Enox-Alb MS with lack of potential tissue toxicity. The anticoagulant activity of the selected Alb MS was significantly sustained for up to 38 h compared to 5 h for the market product. Alb MS are promising delivery carriers for controlled and targeted delivery of Enox to the lungs for prophylaxis and treatment of pulmonary embolism.

Structured microparticles with tailored properties produced by membrane emulsification

This paper provides an overview of membrane emulsification routes for fabrication of structured microparticles with tailored properties for specific applications. Direct (bottom-up) and premix (top-down) membrane emulsification processes are discussed including operational, formulation and membrane factors that control the droplet size and droplet generation regimes. A special emphasis was put on different methods of controlled shear generation on membrane surface, such as cross flow on the membrane surface, swirl flow, forward and backward flow pulsations in the continuous phase and membrane oscillations and rotations. Droplets produced by membrane emulsification can be used for synthesis of particles with versatile morphology (solid and hollow, matrix and core/shell, spherical and non-spherical, porous and coherent, composite and homogeneous), which can be surface functionalised and coated or loaded with macromolecules, nanoparticles, quantum dots, drugs, phase change materials and high molecular weight gases to achieve controlled/targeted drug release and impart special optical, chemical, electrical, acoustic, thermal and magnetic properties. The template emulsions including metal-in-oil, solid-in-oil-in-water, oil-in-oil, multilayer, and Pickering emulsions can be produced with high encapsulation efficiency of encapsulated materials and narrow size distribution and transformed into structured particles using a variety of solidification processes, such as polymerisation (suspension, mini-emulsion, interfacial and in-situ), ionic gelation, chemical crosslinking, melt solidification, internal phase separation, layer-by-layer electrostatic deposition, particle self-assembly, complex coacervation, spray drying, sol-gel processing, and molecular imprinting. Particles fabricated from droplets produced by membrane emulsification include nanoclusters, colloidosomes, carbon aerogel particles, nanoshells, polymeric (molecularly imprinted, hypercrosslinked, Janus and core/shell) particles, solder metal powders and inorganic particles. Membrane emulsification devices operate under constant temperature due to low shear rates on the membrane surface, which range from (1-10)×10(3) s(-1) in a direct process to (1-10)×10(4) s(-1) in a premix process.

Microencapsulated probiotics using emulsification technique coupled with internal or external gelation process

Alginate-chitosan microcapsules containing probiotics (Yeast, Y235) were prepared by emulsification/external gelation and emulsification/internal gelation techniques respectively. The gel beads by external gelation showed asymmetrical structure, but those by internal gelation showed symmetrical structure in morphology. The cell viability was approximately 80% for these two techniques. However, during cell culture process, emulsification/internal gelation microcapsules showed higher cell growth and lower cell leakage. Moreover, the survival rate of entrapped low density cells with culture (ELDCwc) increased obviously than that directly entrapped high density cells (dEHDC) and free cells when keeping in simulated gastrointestinal conditions. It indicated the growth process of cells in microcapsule was important and beneficial to keep enough active probiotics under harmful environment stress. Therefore, the emulsification/internal gelation technique was the preferred method for application in food or biotechnological industries.

Gastroretentive drug delivery system of acyclovir-loaded alginate mucoadhesive microspheres: formulation and evaluation

In the present study, mucoadhesive alginate microspheres of acyclovir were prepared to prolong the gastric residence time using a simple emulsification phase separation technique. The particle size of drug-loaded formulations was measured by SEM and the particle size distribution was determined using an optical microscope and mastersizer. The release profile of acyclovir from microspheres was examined in simulated gastric fluid (SGF pH 1.2). The particles were found to be discreet and spherical with the maximum particles of an average size (70.60 ± 2.44 µm). The results indicated that the mean particle size of the microspheres increased with an increase in the concentration of polymer and decreased with increase in stirring speed. The entrapment efficiency was found to be in the range of 51.42-80.46%. The concentration of the calcium chloride (% w/v) of 10% and drug-polymer ratio of 1:4 resulted in an increase in the entrapment efficiency and the extent of drug release. The optimized alginate microspheres were found to possess good mucoadhesion (66.42 ± 1.01%). The best fit model with the highest regression coefficient values (R²) was predicted by Peppas model (0.9813). In Gamma scintigraphy analysis, the section of GIT was critically analyzed and much differentiation was present at each time point after oral administration, which revealed that the optimized formulation demonstrated gastroretention in vivo for more than 4 h, which revealed that optimized formulation could be a good choice for gastroretentive systems.

Preparation of uniform-sized multiple emulsions and micro/nano particulates for drug delivery by membrane emulsification

Much attention has in recent years been paid to fine applications of drug delivery systems, such as multiple emulsions, micro/nano solid lipid and polymer particles (spheres or capsules). Precise control of particle size and size distribution is especially important in such fine applications. Membrane emulsification can be used to prepare uniform-sized multiple emulsions and micro/nano particulates for drug delivery. It is a promising technique because of the better control of size and size distribution, the mildness of the process, the low energy consumption, easy operation and simple equipment, and amendable for large scale production. This review describes the state of the art of membrane emulsification in the preparation of monodisperse multiple emulsions and micro/nano particulates for drug delivery in recent years. The principles, influence of process parameters, advantages and disadvantages, and applications in preparing different types of drug delivery systems are reviewed. It can be concluded that the membrane emulsification technique in preparing emulsion/particulate products for drug delivery will further expand in the near future in conjunction with more basic investigations on this technique.

Multiple-channel emulsion chips utilizing pneumatic choppers for biotechnology applications

The formation of micro-scale monodispersed emulsions is crucial for a variety of applications such as cosmetics, food industry and biotechnology. In this study, a new microfluidic chip with a multiple-channel layout for high-throughput emulsions is reported. This chip generated fine-tuned and uniform microdroplets in liquids with a higher throughput for emulsification applications. It employed a combination of multiple hydrodynamic flow focusing and liquid-cutting devices called "active pneumatic choppers." Experimental data indicated that oil-in-water microdroplets with diameters ranging from 6 to 120 microm can be successfully generated with a coefficient of variation less than 3.75%. The size of the droplets can be actively fine-tuned by using two approaches by adjusting relative sheath/sample flow velocity ratios and chopping frequency. Finally, two commonly used biocompatible materials, including collagen and calcium-alginate (Ca-alginate), were used to form microspheres by utilizing the liquid-cutting technique. The developed microfluidic chip is promising in various applications including biotechnology, nano-medicine and cosmetics.

Insulin encapsulation in reinforced alginate microspheres prepared by internal gelation

Insulin-loaded alginate microspheres prepared by emulsification/internal gelation were reinforced by blending with polyanionic additive polymers and/or chitosan-coating in order to increase the protection of insulin at simulated gastric pH and obtain a sustained release at simulated intestinal pH. Polyanionic additive polymers blended with alginate were cellulose acetate phtalate (CAP), Eudragit L100 (EL100), sodium carboxymethylcellulose (CMC), polyphosphate (PP), dextran sulfate (DS) and cellulose sulfate (CS). Chitosan-coating was applied by using a one-stage procedure. The influence of additive polymers and chitosan-coating on the size distribution of microspheres, encapsulation efficiency and release profile of insulin in simulated gastrointestinal pH conditions was studied. The mean diameter of blended microspheres ranged from 65 to 106 microm and encapsulation efficiency of insulin varied from 14 to 100%, reaching a maximum value when CS and DS were incorporated in the alginate matrix. Insulin release, at pH 1.2, was almost prevented by the incorporation of PP, DS and CS. When uncoated microspheres were transferred to pH 6.8, a fast dissolution occurred, independently of the additive polymer blended with alginate, and insulin was completely released. Increasing the additive polymer concentration in the alginate matrix and/or chitosan-coating the blended alginate microspheres did not promote a sustained release of insulin from microspheres at pH 6.8.

Alginate microspheres prepared by internal gelation: Development and effect on insulin stability

Recombinant human insulin was encapsulated within alginate microspheres by the emulsification/internal gelation technique with the objective of preserving protein stability during encapsulation procedure. The influence of process and formulation parameters was evaluated on the morphology and encapsulation efficiency of insulin. The in vitro release of insulin from microspheres was studied under simulated gastrointestinal conditions and the in vivo activity of protein after processing was assessed by subcutaneous administration of extracted insulin from microspheres to streptozotocin-induced diabetic rats. Microspheres mean diameter, ranging from 21 to 287 microm, decreased with the internal phase ratio, emulsifier concentration, mixer rotational speed and increased with alginate concentration. Insulin encapsulation efficiency, near 75%, was not affected by emulsifier concentration, mixer rotational speed and zinc/insulin hexamer molar ratio but decreased either by increasing internal phase ratio and calcium/alginate mass ratio or by decreasing acid/calcium molar ratio and alginate concentration. A high insulin release, above 75%, was obtained at pH 1.2 and under simulated intestinal pH a complete dissolution of microspheres occurred. Extracted insulin from microspheres decreased hyperglycemia of diabetic rats proving to be bioactive and showing that encapsulation in alginate microspheres using the emulsification/internal gelation is an appropriate method for protein encapsulation.

Microemulsion and diafiltration approaches: An attempt to maximize the global yield of DNA-loaded nanospheres

The yield of DNA-loaded nanospheres in its widest definition includes encapsulation efficiency and the integrity of the loaded molecules plus the production yield of fabricated nanospheres. The former aspect could be considerably improved by adopting the microemulsion concept to enhance the stability of the primary emulsion during the preparation of nanospheres by the double emulsion solvent-removal method. The droplet size of the mentioned emulsion was monitored by means of photon electron correlation spectroscopy and could serve as an index for emulsion fineness and stability. DNA stability as a function of applied mechanical stress was monitored by horizontal agarose gel electrophoresis. The impact of the primary emulsion on nanosphere porosity was assessed as well. Regarding the second aspect of the global yield of nanospheres, i.e. production yield, a modified diafiltration technique was adopted for the washing and recovery processes in comparison with the traditional and for the conservation of particle size characteristics of the recovered nanospheres.

Recent developments in manufacturing emulsions and particulate products using membranes

Membrane emulsification (ME) is a relatively new technique for the highly controlled production of particulates. This review focuses on the recent developments in this area, ranging from the production of simple oil-in-water (O/W) or water-in-oil (W/O) emulsions to multiple emulsions of different types, solid-in-oil-in-water (S/O/W) dispersions, coherent solids (silica particles, solid lipid microspheres, solder metal powder) and structured solids (solid lipid microcarriers, gel microbeads, polymeric microspheres, core-shell microcapsules and hollow polymeric microparticles). Other emerging technologies that extend the capabilities into different membrane materials and operation methods (such as rotating membranes, repeated membrane extrusion of coarsely pre-emulsified feeds) are introduced. The results of experimental work carried out by cited researchers in the field together with those of the current authors are presented in a tabular form in a rigorous and systematic manner. These demonstrate a wide range of products that can be manufactured using different membrane approaches. Opportunities for creation of new and novel entities are highlighted for low throughput applications (medical diagnostics, healthcare) and for large-scale productions (consumer and personal products).

Sustained release and biological availability of dalarelin from the biodegradable coacervate microcapsules

A complex coacervation method was used to prepare microcapsules containing 74.8 +/- 1.5% of the 125I labelled dalarelin incorporated in the gelatine-algin coating. Microcapsules (62 +/- 1.7%) formed, did not exceed a size of 108 microm. The high content of the small size allowed this formulation to be administered by intramuscular injection to rats. It was found that the 125I labelled dalarelin in the form of microcapsules had better bioavailability and was active longer in the rat when compared with the 125I labelled dalarelin solution injections. Dalarelin administered in the microcapsular form was characterised by a higher biological availability. The degree of relative biological availability was calculated as 123% for the dalarelin in the microcapsular form.