Preparation of non-porous microspheres with high entrapment efficiency of proteins by a (water-in-oil)-in-oil emulsion technique

Double emulsion microencapsulation of ionic liquids for carbon capture

Microencapsulation of pristine core liquids in polymer shells has critical applications in thermal energy storage and management, targeted drug delivery, and carbon capture, among others. Herein, we report a novel encapsulation approach based on a double emulsion soft-template to produce microcapsules comprised of an ionic liquid (IL) core in a degradable polymer shell. We demonstrate the production of [IL-in-oil1]-in-oil2 (IL/O1/O2) double emulsions, in which the oil interphase (O1) contains a CO2-derived polycarbonate bearing vinyl pendant groups, tetrathiol small molecule crosslinker, and photoinitiator; upon irradiation of the double emulsion under low shear, thiol-ene crosslinking of the loaded species results in the formation of a robust shell around the pure IL droplets. The core-shell structures have enhanced physisorption for CO2 uptake compared to the bulk IL, which is consistent with the combined capacity of the IL/shell alone and demonstrates more rapid uptake due to an enhanced gas-liquid interface. This approach to microencapsulation of functional liquids offers researchers a distinct route to fabricate composite architectures with a pristine core for applications in separations, transport of cargo, and gas uptake.

A novel thermoresponsive nano carrier matrix of hyaluronic acid, methotrexate and chitosan to target the cluster of differentiation 44 receptors in tumors

Major challenges in current cancer chemotherapy include drug resistance, low efficacy and non-selectivity, resulting in undesirable side effects. In this study, we demonstrate a solution to these challenges that involves a dual targeting approach for tumors that overexpress CD44 receptors. The approach employs a nano-formulation (tHAC-MTX nano assembly), fabricated from hyaluronic acid (HA), the natural ligand for CD44, conjugated with methotrexate (MTX) and complexed with the thermoresponsive polymer 6-O-carboxymethylchitosan (6-OCMC) graft poly(N-isopropylacrylamide) [6-OCMC-g-PNIPAAm]. The thermoresponsive component was designed to have a lower critical solution temperature of 39 °C (the temperature of tumor tissues). In-vitro drug release studies reveal faster release of the drug at the higher temperatures of the tumor tissue likely due to the conformation changes in the thermoresponsive component of the nano assembly. Drug release was also enhanced in the presence of hyaluronidase enzyme. Higher cellular uptake and greater cytotoxicity of the nanoparticles were demonstrated in cancer cells that overexpress CD44 receptors suggesting a receptor binding and cellular uptake mechanism. Such nano-assemblies which incorporate multiple targeting mechanisms have the potential to improve efficacy and decrease side effects of cancer chemotherapy.

A keratin-based microparticle for cell delivery

Keratin-based biomaterials represent an attractive opportunity in the fields of wound healing and tissue regeneration, not only for their chemical and physical properties, but also for their ability to act as a delivery system for a variety of payloads. Importantly, keratins are the only natural biomaterial that is not targeted by specific tissue turnover-related enzymes, giving it potential stability advantages and greater control over degradation after implantation. However, in-situ polymerization chemistry in some keratin systems are not compatible with cells, and incorporation within constructs such as hydrogels may lead to hypoxia and cell death. To address these challenges, we envisioned a pre-formed keratin microparticle on which cells could be seeded, while other payloads (e.g. drugs, growth factors or other biologic compounds) could be contained within, although studies investigating the potential partitioning between phases during emulsion polymerization would need to be conducted. This study employs well-established water-in-oil emulsion procedures as well as a suspension culture method to load keratin-based microparticles with bone marrow-derived mesenchymal stem cells. Fabricated microparticles were characterized for size, porosity and surface structure and further analyzed to investigate their ability to form gels upon hydration. The suspension culture technique was validated based on the ability for loaded cells to maintain their viability and express actin and vinculin proteins, which are key indicators of cell attachment and growth. Maintenance of expression of markers associated with cell plasticity was also investigated. As a comparative model, a collagen-coated microparticle (Sigma) of similar size was used. Results showed that an oxidized form of keratin ("keratose" or "KOS") formed unique microparticle structures of various size that appeared to contain a fibrous sub-structure. Cell adhesion and viability was greater on keratin microparticles compared to collagen-coated microparticles, while marker expression was retained on both.

Particle Stabilization of Oil-Fluorocarbon Interfaces and Effects on Multiphase Oil-in-Water Complex Emulsion Morphology and Reconfigurability

Stabilization of oil-oil interfaces is important for nonaqueous emulsions as well as for multiphase oil-in-water emulsions, with relevance to a variety of fields ranging from emulsion polymerization to sensors and optics. Here, we focus on examining the ability of functionalized silica particles to stabilize interfaces between fluorinated oils and other immiscible oils (such as hydrocarbons and silicones) in nonaqueous emulsions and also on the particles' ability to affect the morphology and reconfigurability of complex, biphasic oil-in-water emulsions. We compare the effectiveness of fluorophilic, lipophilic, and bifunctional fluorophilic-lipophilic coated nanoparticles to stabilize these oil-oil interfaces. Sequential bulk emulsification steps by vortex mixing, or emulsification by microfluidics, can be used to create complex droplets in which particles stabilize the oil-oil interfaces and surfactants stabilize the oil-water interfaces. We examine the influence of particles adsorbed at the internal oil-oil interface in complex droplets to hinder the reconfiguration of these complex emulsions upon addition of aqueous surfactants, creating "metastable" droplets that resist changes in morphology. Such metastable droplets can be triggered to reconfigure when heated above their upper critical solution temperature. Thus, not only do these bifunctional silica particles enable the stabilization of a broad array of oil-fluorocarbon nonaqueous emulsions, but the ability to address the oil-oil interface within complex O/O/W droplets expands the diversity of oil chemical choices available and the accessibility of droplet morphologies and sensitivity.

In-vitro and in-vivo evaluation of polymeric microsphere formulation for colon targeted delivery of 5-fluorouracil using biocompatible natural gum katira

The aim was to develop oral site-specific rate-controlled anticancer drug delivery to pacify systemic side-effects and offer effective and safe therapy for colon cancer with compressed dose and duration of treatment. The double emulsion solvent evaporation method was employed. To check functionality, DAPI-staining and in-vivo anticancer study of Ehrlich Ascites Carcinoma bearing mice was tested. Histopathology of liver and kidney and Cell morphology of EAC cell was also performed. Formulated and optimized polymeric microsphere of 5-FU showed excellent physicochemical features. In-vitro, DAPI results pointed drug-treated groups displayed the prominent feature of apoptosis. The percentage of apoptotic of entrapped drug played in a dose-dependent manner. Significant decreases in EAC liquid tumors and increased life span of treated mice were observed. Rate of variation of cell morphology was more in 5-FU loaded microsphere than 5-FU injection. Hematological and biochemical parameter's and Histopathology of liver and kidney resulted that due to control released formulation have slow release rate, that gives less trace on liver and kidney function. Finally, we foresee that polymeric microsphere of 5-FU applying natural gum katira could be an assuring micro-carrier for active colon targeting delivery tool with augmented chemotherapeutic efficacy and lowering side effect against colon cancer.

Improved Stability of Rifampicin in the Presence of Gastric-Resistant Isoniazid Microspheres in Acidic Media

The degradation of rifampicin (RIF) in an acidic medium to form 3-formyl rifamycin SV, a poorly absorbed compound, is accelerated in the presence of isoniazid, contributing to the poor bioavailability of rifampicin. This manuscript presents a novel approach in which isoniazid is formulated into gastric-resistant sustained-release microspheres and RIF into microporous floating sustained-release microspheres to reduce the potential for interaction between RIF and isoniazid (INH) in an acidic environment. Hydroxypropyl methylcellulose acetate succinate and Eudragit^® L100 polymers were used for the manufacture of isoniazid-loaded gastric-resistant sustained-release microspheres using an o/o solvent emulsification evaporation approach. Microporous floating sustained-release microspheres for the delivery of rifampicin in the stomach were manufactured using emulsification and a diffusion/evaporation process. The design of experiments was used to evaluate the impact of input variables on predefined responses or quality attributes of the microspheres. The percent degradation of rifampicin following 12 h dissolution testing in 0.1 M HCl pH 1.2 in the presence of isoniazid gastric-resistant sustained-release microspheres was only 4.44%. These results indicate that the degradation of rifampicin in the presence of isoniazid in acidic media can be reduced by encapsulation of both active pharmaceutical ingredients to ensure release in different segments of the gastrointestinal tract, potentially improving the bioavailability of rifampicin.

Application of sodium alginate extracted from a Tunisian brown algae Padina pavonica for essential oil encapsulation: Microspheres preparation, characterization and in vitro release study

In recent years, there has been considerable interest in essential oils encapsulation and in developing biodegradable microparticles. The aim of this present work was to prepare clove essential oil loaded microspheres, by a modified emulsification method, using sodium alginate extracted from a Tunisian Brown seaweed Algae Padina pavonica as biopolymer. The obtained microparticles were characterized by FT-IR, DSC and SEM. Loading capacity yield, encapsulation efficiency (%EE) and in vitro release of the essential oil were also investigated. Sodium alginate microspheres were successfully prepared as confirmed by physico-chemical characterizations. %yield of microspheres and %EE of essential oil were 72.73% and 24.77% ± 7.47%, respectively. SEM showed pseudospherical microspheres with rough surface ranging, in size, from 1500 μm to 3000 μm. In vitro dissolution study indicates a controlled released of the essential oil which follows, mainly, classical Fickian diffusion. Thus, this present work highlighted the potential of this polysaccharide as a biopolymer to formulate polymeric microspheres.

Enhancement of Transdermal Delivery of Haloperidol via Spanlastic Dispersions: Entrapment Efficiency vs. Particle Size

Haloperidol (Hal) is a well-known typical antipsychotic. Hepatic first pass metabolism leads to its limited oral bioavailability. This study aimed at enhancing transdermal delivery of Hal via spanlastic formulae. Hal-loaded spanlastics of Span®60 and an edge activator (EA) were successfully prepared by ethanol injection method according to a 3¹.4¹ full factorial design. In this design, independent variables were X₁, EA type, and X₂, Span®60 to EA ratio. Y₁, percentage entrapment efficiency (EE%); Y₂, particle size (PS); Y₃, deformability index (DI); and Y₄, percentage drug released after 4h (Q4h), were chosen as dependent variables. The Fourier-transform infrared spectral analysis showed no considerable chemical interaction between Hal and the used excipients. Both factors affected significantly all the responses except DI. Desirability of each prepared formula was calculated based on maximizing EE% and Q4h and minimizing PS. Formula F6, with X₁, Tween®80, and X₂, 8:2, had the highest desirability value followed by F7, with X₁, Tween®80, and X₂, 6:4, and both were chosen as selected formulae (SF) for further investigation. F6 (having more entrapped Hal), F7 (of smaller PS), and Hal solution in propylene glycol were subjected to ex vivo permeation test through newborn rat skin. Both formulae showed marked enhancement in drug permeation compared with drug solution. The significantly higher Q_36h and J_36h of F7 from F6 may indicate that the smaller particle size aided more than higher entrapment in achieving a higher permeation for Hal of 3.5±0.2μg/cm².h. These results are promising for further investigation of this formula.

Iron Encapsulation in Water-in-Oil Emulsions: Effect of Ferrous Sulfate Concentration and Fat Crystal Formation on Oxidative Stability

Iron deficiency is a major global human health concern. Encapsulation of iron in functional food products may help to solve this problem. However, iron is highly reactive and may promote rapid lipid oxidation in fatty foods. In this study, the effect of ferrous sulfate (0.1 to 0.5 wt%) and rice bran stearin (0 or 30 wt%) on the physical properties, oxidative stability, and encapsulation efficiency of 20 wt% water-in-oil (W/O) emulsions stabilized with polyglycerol polyricinoleate was investigated. In the presence of rice bran stearin crystals in the continuous oil phase, W/O emulsions had smaller mean droplet diameters (d ∼ 250 nm) and better physical stability than its absence (d ∼ 330 nm). An increase in the ferrous sulfate concentration in the water droplets led to a decrease in the oxidative stability of the W/O emulsions. However, the presence of rice bran stearin significantly (P ≤ 0.05) improved their oxidative stability. Moreover, addition of rice bran stearin also significantly (P ≤ 0.05) improved the encapsulation efficiency and delayed ferrous sulfate release from the W/O emulsions. The impact of pH and ionic strength on the encapsulation efficiency of the W/O emulsion was also investigated. Ionic strength affected the encapsulation efficiency much more than pH. The W/O emulsions created in the present study may be useful for the encapsulation and delivery of iron and other water-soluble nutrients into food products.

PRACTICAL APPLICATION

Water-in-oil (W/O) emulsions may be used to encapsulate, protect, and deliver water-soluble bioactive compounds or nutrients into food products. In this study, W/O emulsions stabilized using an oil-soluble surfactant (polyglycerol polyricinoleate, PGPR) and fat crystal network (rice bran stearin) were shown to be useful for encapsulation and delivery of iron into foods. This strategy may be a promising approach to reduce iron deficiency, a major nutritional deficiency for people with inadequate food supplies.

Fast and Environmentally Friendly Microfluidic Technique for the Fabrication of Polymer Microspheres

This paper reports on a novel microfluidic technique for the fabrication of microspheres of synthetic polymers including poly(vinyl chloride) (PVC), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), poly(lactic acid) (PLA), and polystyrene (PS). The polymers are dissolved in tetrahydrofuran (THF) and the method is based on the diminished solubility of THF in a 20% (w/v) NaCl solution which allows the formation of droplets of the polymer solution. These polymer solution droplets are generated in a microfluidic system and their desolvation is accomplished within seconds by allowing the droplets to rise by buoyancy through a NaCl solution with a concentration lower than 15%. The size and morphology of the resultant polymer microspheres have been investigated by optical and scanning electron microscopy. Apart from the elimination of the use of highly toxic solvents as in conventional methods for manufacturing of polymer microspheres, the newly developed technique has the advantages of providing faster desolvation of the polymer solution droplets and a higher yield of microspheres compared to emulsification-based techniques.

Photothermal triggered protein release from an injectable polycaprolactone-based microspherical depot

Visible light mediated controlled release of biologically active enzymes was confirmed by released horseradish peroxidase's ability to ameliorate H₂O₂ cytotoxicity in vitro.

Study of Effect of Different Factors in Formulation of Micro and Nanospheres with Solvent Evaporation Technique

Background:

There are various methods of formulation of micro and nanospheres such as solvent evaporation, solvent removal, polymerization, hot-melt encapsulation, coacervation, phase/wet inversion, spray drying, spray congealing etc. Amongst these all, solvent evaporation is one of the most widely used, researched, easy, accessible methods and for which many patents have been applied. It is thus imperative to understand the basics of effect of formulation variables and design of solvent evaporation method which will be covered in this review article.

Objective:

To discuss the various formulation factors while designing the robust micro and nanospherical systems with better morphology, entrapment and release of the drugs.

Method:

Systematic analysis of the relevant literature, bibliographies, and interactions with investigators.

Results:

From the investigation of different literatures, it was found that various factors of solvent evaporation technique may be controlled in order to design the micro and nanospheres of suitable morphology, entrapment and release characters.

Conclusion:

Various factors like type of polymer used, weight, viscosity, hydrophilicity, concentration, polymer ratio, stirring speed, emulsifier concentration, concentration of cross-linking agents, type of solvent used, rate of addition of solvent etc. Affect the yield, morphology, release and entrapment of the drug inside the system. Hence, these factors play crucial role in the design of a robust micro and nanospherical system.

Thermostabilization of inactivated polio vaccine in PLGA-based microspheres for pulsatile release

Vaccines are a critical clinical tool in preventing illness and death due to infectious diseases and are regularly administered to children and adults across the globe. In order to obtain full protection from many vaccines, an individual needs to receive multiple doses over the course of months. However, vaccine administration in developing countries is limited by the difficulty in consistently delivering a second or third dose, and some vaccines, including the inactivated polio vaccine (IPV), must be injected more than once for efficacy. In addition, IPV does not remain stable over time at elevated temperatures, such as those it would encounter over time in the body if it were to be injected as a single-administration vaccine. In this manuscript, we describe microspheres composed of poly(lactic-co-glycolic acid) (PLGA) that can encapsulate IPV along with stabilizing excipients and release immunogenic IPV over the course of several weeks. Additionally, pH-sensitive, cationic dopants such as Eudragit E polymer caused clinically relevant amounts of stable IPV release upon degradation of the PLGA matrix. Specifically, IPV was released in two separate bursts, mimicking the delivery of two boluses approximately one month apart. In one of our top formulations, 1.4, 1.1, and 1.2 doses of the IPV serotype 1, 2, and 3, respectively, were released within the first few days from 50mg of particles. During the delayed, second burst, 0.5, 0.8, and 0.6 doses of each serotype, respectively, were released; thus, 50mg of these particles released approximately two clinical doses spaced a month apart. Immunization of rats with the leading microsphere formulation showed more robust and long-lasting humoral immune response compared to a single bolus injection and was statistically non-inferior from two bolus injections spaced 1 month apart. By minimizing the number of administrations of a vaccine, such as IPV, this technology can serve as a tool to aid in the eradication of polio and other infectious diseases for the improvement of global health.

Maximizing the encapsulation efficiency and the bioavailability of controlled-release cetirizine microspheres using Draper-Lin small composite design

This study was aimed at developing a controlled-release cetirizine hydrochloride (CTZ)-loaded polymethacrylate microsphere by optimization technique using software-based response surface methodology. The emulsion solvent evaporation method was utilized in the preparation of microspheres. Four process variables were selected, namely, Eudragit RLPO loading percentage in total polymer, the emulsifier hydrophilic lipophilic balance (HLB), the antitacking percentage, and the dispersed phase volume. The desired responses were particle size, angle of repose, production yield, encapsulation efficiency, loading capacity, initial drug release, and the time for 85% of drug release from the microspheres. Optimization was carried out by fitting the experimental data to the software program (Statgraphics Centurion XV). Moreover, 18 batches were subjected to various characterization tests required for the production of dosage form. The pharmacokinetic parameters were evaluated after the oral administration of 10 mg CTZ in both optimized formulation and commercial product on healthy human volunteers using a double-blind, randomized, cross-over design. The optimized formulation showed satisfactory yield (84.43%) and drug encapsulation efficiency (87.1%). Microspheres were of spherical shape, smooth surface, and good flowability with an average size of 142.3 μm. The developed optimized batch of microspheres ensured 28.87% initial release after 2 hours, and the release of CTZ extended for >12 hours. In addition, the relative bioavailability of the optimized formulation was 165.5% with respect to the marketed CTZ tablets indicating a significant enhancement of CTZ bioavailability. Thus, there is an expectation to decrease the administered dose and the frequency of administration, and subsequently minimize the adverse effects that are faced by the patient during the treatment.

Controlled release of dutasteride from biodegradable microspheres: in vitro and in vivo studies

The aim of the present work was to study the in vitro/in vivo characteristics of dutasteride loaded biodegradable microspheres designed for sustained release of dutasteride over four weeks. An O/W emulsion-solvent evaporation method was used to incorporate dutasteride, which is of interest in the treatment of benign prostatic hyperplasia (BPH), into poly(lactide-co-glycolide) (PLGA). A response surface method (RSM) with central composite design (CCD) was employed to optimize the formulation variables. A prolonged in vitro drug release profile was observed, with a complete release of the entrapped drug within 28 days. The pharmacokinetics study showed sustained plasma drug concentration-time profile of dutasteride loaded microspheres after subcutaneous injection into rats. The in vitro drug release in rats correlated well with the in vivo pharmacokinetics profile. The pharmacodynamics evaluated by determination of the BPH inhibition in the rat models also showed a prolonged pharmacological response. These results suggest the potential use of dutasteride loaded biodegradable microspheres for the management of BPH over long periods.

Injectable controlled release depots for large molecules

Biodegradable, injectable depot formulations for long-term controlled drug release have improved therapy for a number of drug molecules and led to over a dozen highly successful pharmaceutical products. Until now, success has been limited to several small molecules and peptides, although remarkable improvements have been accomplished in some of these cases. For example, twice-a-year depot injections with leuprolide are available compared to the once-a-day injection of the solution dosage form. Injectable depots are typically prepared by encapsulation of the drug in poly(lactic-co-glycolic acid) (PLGA), a polymer that is used in children every day as a resorbable suture material, and therefore, highly biocompatible. PLGAs remain today as one of the few "real world" biodegradable synthetic biomaterials used in US FDA-approved parenteral long-acting-release (LAR) products. Despite their success, there remain critical barriers to the more widespread use of PLGA LARproducts, particularly for delivery of more peptides and other large molecular drugs, namely proteins. In this review, we describe key concepts in the development of injectable PLGA controlled-release depots for peptides and proteins, and then use this information to identify key issues impeding greater widespread use of PLGA depots for this class of drugs. Finally, we examine important approaches, particularly those developed in our research laboratory, toward overcoming these barriers to advance commercial LAR development.

Growth Kinetics of Monodisperse Polystyrene Microspheres Prepared by Dispersion Polymerization

Dispersion polymerization has been widely applied to the synthesis of monodisperse micron-sized polymer colloidal spheres. Many efforts have been devoted to studying the influence of initial conditions on the size and uniformity of the resultant microspheres, aiming to synthesize micron-size monodisperse colloidal spheres. However, the inner contradiction between the size and the size distribution of colloidal spheres hinders the realization of this goal. In this work, we drew our attention from the initial conditions to the growth stage of dispersion polymerization. We tracked the size evolution of colloidal sphere during the dispersion polymerization, through which we established a kinetic model that described the relationship between the monomer concentration and the reaction time. The model may provide a guideline to prepare large polymer colloidal spheres with good monodispersity by continuous monomer feeding during the growth stage to maintain the concentration of monomer at a constant value in a dispersion polymerization process.

Preparation and evaluation of polymeric microparticulates for improving cellular uptake of gemcitabine

BACKGROUND

Gemcitabine must be administered at high doses to elicit the required therapeutic response because of its very short plasma half-life due to rapid metabolism. These high doses can have severe adverse effects.

METHODS

In this study, polymeric microparticulate systems of gemcitabine were prepared using chitosan as a mucoadhesive polymer and Eudragit L100-55 as an enteric copolymer. The physicochemical and biopharmaceutical properties of the resulting systems were then evaluated.

RESULTS

There was no endothermic peak for gemcitabine in any of the polymeric gemcitabine microparticulate systems, suggesting that gemcitabine was bound to chitosan and Eudragit L100-55 and its crystallinity was changed into an amorphous form. The polymeric gemcitabine microparticulate system showed more than 80% release of gemcitabine in 30 minutes in simulated intestinal fluid. When mucin particles were incubated with gemcitabine polymeric microparticulates, the zeta potential of the mucin particles was increased to 1.57 mV, indicating that the polymeric gemcitabine microparticulates were attached to the mucin particles. Furthermore, the F53 polymeric gemcitabine microparticulates having 150 mg of chitosan showed a 3.8-fold increased uptake of gemcitabine into Caco-2 cells over 72 hours compared with gemcitabine solution alone.

CONCLUSION

Overall, these results suggest that polymeric gemcitabine microparticulate systems could be used as carriers to help oral absorption of gemcitabine.

Anti-VEGFR2-conjugated PLGA microspheres as an x-ray phase contrast agent for assessing the VEGFR2 expression

The primary goal of this study was to evaluate the feasibility of using anti-vascular endothelial growth factor receptor 2 (VEGFR2)-conjugated poly(lactic-co-glycolic acid) (PLGA) microspheres as an x-ray phase contrast agent to assess the VEGFR2 expression in cell cultures. The cell lines, mouse LLC (Lewis lung carcinoma) and HUVEC (human umbilical vein endothelial cell), were selected for cell adhesion studies. The bound PLGA microspheres were found to better adhere to LLC cells or HUVECs than unbound ones. Absorption and phase contrast images of PLGA microspheres were acquired and compared in vitro. Phase contrast imaging (PCI) greatly improves the detection of the microspheres as compared to absorption contrast imaging. The cells incubated with PLGA microspheres were imaged by PCI, which provided clear 3D visualization of the beads, indicating the feasibility of using PLGA microspheres as a contrast agent for phase contrast CT. In addition, the microspheres could be clearly distinguished from the wall of the vessel on phase contrast CT images. Therefore, the approach holds promise for assessing the VEGFR2 expression on endothelial cells of tumor-associated vessels. We conclude that PLGA microsphere-based PCI of the VEGFR2 expression might be a novel, promising biomarker for future studies of tumor angiogenesis.

Floating microspheres: a review

Gastric emptying is a complex process, one that is highly variable and that makes in vivo performance of drug delivery systems uncertain. A controlled drug delivery system with prolonged residence time in the stomach can be of great practical importance for drugs with an absorption window in the upper small intestine. The main limitations are attributed to the inter- and intra-subject variability of gastro-intestinal (GI) transit time and to the non-uniformity of drug absorption throughout the alimentary canal. Floating or hydrodynamically controlled drug delivery systems are useful in such applications. Various gastroretentive dosage forms are available, including tablets, capsules, pills, laminated films, floating microspheres, granules and powders. Floating microspheres have been gaining attention due to the uniform distribution of these multiple-unit dosage forms in the stomach, which results in more reproducible drug absorption and reduced risk of local irritation. Such systems have more advantages over the single-unit dosage forms. The present review briefly addresses the physiology of the gastric emptying process with respect to floating drug delivery systems. The purpose of this review is to bring together the recent literature with respect to the method of preparation, and various parameters affecting the performance and characterization of floating microspheres.

Polímeros sintéticos biodegradáveis: matérias-primas e métodos de produção de micropartículas para uso em drug delivery e liberação controlada

Micropartículas produzidas a partir de polímeros sintéticos têm sido amplamente utilizadas na área farmacêutica para encapsulação de princípios ativos. Essas micropartículas apresentam as vantagens de proteção do princípio ativo, mucoadesão e gastrorresistência, melhor biodisponibilidade e maior adesão do paciente ao tratamento. Além disso, utiliza menores quantidade de princípio ativo para obtenção do efeito terapêutico proporcionando diminuição dos efeitos adversos locais, sistêmicos e menor toxidade. Os polímeros sintéticos empregados na produção das micropartículas são classificados biodegradáveis ou não biodegradáveis, sendo os biodegradáveis mais utilizados por não necessitam ser removidos cirurgicamente após o término de sua ação. A produção das micropartículas poliméricas sintéticas para encapsulação tanto de ativos hidrofílicos quanto hidrofóbicos pode ser emulsificação por extração e/ou evaporação do solvente; coacervação; métodos mecânicos e estão revisados neste artigo evidenciando as vantagens, desvantagens e viabilidade de cada metodologia. A escolha da metodologia e do polímero sintético a serem empregados na produção desse sistema dependem da aplicação terapêutica requerida, bem como a simplicidade, reprodutibilidade e factibilidade do aumento de escala da produção.

In vitro and in vivo evaluation of hydroxyzine hydrochloride microsponges for topical delivery

Hydroxyzine HCl is used in oral formulations for the treatment of urticaria and atopic dermatitis. Dizziness, blurred vision, and anticholinergic responses, represent the most common side effects. It has been shown that controlled release of the drug from a delivery system to the skin could reduce the side effects while reducing percutaneous absorption. Therefore, the aim of the present study was to produce an effective drug-loaded dosage form that is able to control the release of hydroxyzine hydrochloride into the skin. The Microsponge Delivery System is a unique technology for the controlled release of topical agents, and it consists of porous polymeric microspheres, typically 10-50 μm in diameter, loaded with active agents. Eudragit RS-100 microsponges of the drug were prepared by the oil in an oil emulsion solvent diffusion method using acetone as dispersing solvent and liquid paraffin as the continuous medium. Magnesium stearate was added to the dispersed phase to prevent flocculation of Eudragit RS-100 microsponges. Pore inducers such as sucrose and pregelatinized starch were used to enhance the rate of drug release. Microsponges of nearly 98% encapsulation efficiency and 60-70% porosity were produced. The pharmacodynamic effect of the chosen preparation was tested on the shaved back of histamine-sensitized rabbits. Histopathological studies were driven for the detection of the healing of inflamed tissues.

Design and evaluation of niacin microspheres

Present study aims to prepare and evaluate niacin microspheres. Niacin-ethyl cellulose microspheres were prepared by water-in-oil-in-oil double emulsion solvent diffusion method. Spherical, free flowing microspheres having an entrapment efficiency of 72% were obtained. The effect of polymer-drug ratio, surfactant concentration for secondary emulsion process and stirring speed of emulsification process were evaluated with respect to entrapment efficiency, in vitro drug release behavior and particle size. FT-IR and DSC analyses confirmed the absence of drug-polymer interaction. The in vitro release profile could be altered significantly by changing various processing and formulation parameters to give a controlled release of drug from the microspheres. The percentage yield was 85%, particle size range was 405 to 560 μm. The drug release was controlled for 10 h. The in vitro release profiles from optimized formulations were applied on various kinetic models. The best fit with the highest correlation coefficient was observed in Higuchi model, indicating diffusion controlled principle. The in vitro release profiles of optimized formulation was studied and compared with commercially available niacin extended release formulation.

Preparation, in vitro and in vivo evaluation of algino-pectinate bioadhesive microspheres: An investigation of the effects of polymers using multiple comparison analysis

Ionotropic gelation was used to entrap aceclofenac into algino-pectinate bioadhesive microspheres as a potential drug carrier for the oral delivery of this anti-inflammatory drug. Microspheres were investigated in vitro for possible sustained drug release and their use in vivo as a gastroprotective system for aceclofenac. Polymer concentration and polymer/drug ratio were analyzed for their influence on microsphere properties. The microspheres exhibited good bioadhesive property and showed high drug entrapment efficiency. Drug release profiles exhibited faster release of aceclofenac from alginate microspheres whereas algino-pectinate microspheres showed prolonged release. Dunnet's multiple comparison analysis suggested a significant difference in percent inhibition of paw edema when the optimized formulation was compared to pure drug. It was concluded that the algino-pectinate bioadhesive formulations exhibit promising properties of a sustained release form for aceclofenac and that they provide distinct tissue protection in the stomach.

Alendronate-loaded microparticles for improvement of intestinal cellular absorption

This study examined a novel alendronate formulation that was developed to overcome the shortcomings of alendronate, such as its low bioavailability and gastric adverse effects. Alendronate microparticles were prepared using mucoadhesive polymers such as chitosan for improving the intestinal cellular absorption of alendronate and also using a gastric-resistant polymer such as Eudragit L100-55 for reducing the gastric inflammation of alendronate. Alendronate microparticles including chitosan showed a threefold increase in alendronate uptake (6.92 ± 0.27%) in Caco-2 cells when compared with the uptake of alendronate solution (2.38 ± 0.27%) into Caco-2 cells. Most interestingly, alendronate microparticles including chitosan showed 2.80 x 10⁻⁶ cm/s of an apparent permeability coefficient across Caco-2 cells and caused a significant 42.4% enhancement compared with that of alendronate solution across Caco-2 cells. The morphology of the Caco-2 cells treated with alendronate microparticles including chitosan was similar to that of the untreated cells and alendronate microparticles exhibited a negative effect to propodium iodide with some annexin-V fluorescence isothiocyante positive effect. It was proposed that the novel alendronate microparticles could possess the potential of an increased intestinal absorption and fewer adverse effects of alendronate.

Ethyl cellulose microcapsules for protecting and controlled release of folic acid

Ethyl cellulose microcapsules were developed for use as a drug-delivery device for protecting folic acid from release and degradation in the undesirable environmental conditions of the stomach, whilst allowing its release in the intestinal tract to make it available for absorption. The controlled release folic acid-loaded ethyl cellulose microcapsules were prepared by oil-in-oil emulsion solvent evaporation using a mixed solvent system, consisting of a 9:1 (v/v) ratio of acetone:methanol and light liquid paraffin as the dispersed and continuous phase. Span 80 was used as the surfactant to stabilize the emulsion. Scanning electron microscopy revealed that the microcapsules had a spherical shape. However, the particulate properties and in vitro release profile depended on the concentrations of the ethyl cellulose, Span 80 emulsifier, sucrose (pore inducer), and folic acid. The average diameter of the microcapsules increased from 300 to 448 microm, whilst the folic acid release rate decreased from 52% to 40%, as the ethyl cellulose concentration was increased from 2.5% to 7.5% (w/v). Increasing the Span 80 concentration from 1% to 4% (v/v) decreased the average diameter of microcapsules from 300 to 141 microm and increased the folic acid release rate from 52% to 79%. The addition of 2.5-7.5% (w/v) of sucrose improved the folic acid release from the microcapsules. The entrapment efficiency was improved from 64% to 88% when the initial folic acid concentration was increased from 1 to 3 mg/ml.

Microspheres made by w/o/o emulsion method with reduced initial burst for long-term delivery of endostar, a novel recombinant human endostatin

The purpose of this work is to design biodegradable Poly(lactide-co-glycolide) (PLGA) microspheres with low initial burst for sustained delivery of Endostar (a novel recombinant human endostatin) and investigate effects of PLGA molecular weight and composition on the release behavior of Endostar microspheres. Endostar microspheres were prepared by using novel w/o/o multiple emulsification-evaporation technique. Effects of polymer molecular weight and copolymer composition on particle properties and release behavior (in vitro and in vivo) have been reported. Drug release in vitro decreased with increase in molecular weight and lactide content of PLGA. Zero order release and low initial burst were obtained with all microsphere formulations. The in vivo performance of Endostar microspheres were also found to be dependent on the polymer molecular weight and copolymer composition. Together, these results suggest that the initial burst release can be reduced by w/o/o emulsion method and the release of Endostar can be changed significantly by varying the polymer molecular weight and copolymer composition.

Multiunit floating drug delivery system of rosiglitazone maleate: development, characterization, statistical optimization of drug release and in vivo evaluation

A multiunit floating drug delivery system of rosiglitazone maleate has been developed by encapsulating the drug into Eudragit RS100 through nonaqueous emulsification/solvent evaporation method. The in vitro performances of microspheres were evaluated by yield (%), particle size analysis, drug entrapment efficiency, in vitro floating behavior, surface topography, drug-polymer compatibility, crystallinity of the drug in the microspheres, and drug release studies. In vitro release was optimized by a {3, 3} simplex lattice mixture design to achieve predetermined target release. The in vivo performance of the optimized formulation was evaluated in streptozotocin-induced diabetic rats. The results showed that floating microspheres could be successfully prepared with good yields (69-75%), high entrapment (78-97%), narrow size distribution, and desired target release with the help of statistical design of experiments from very small number of formulations. In vivo evaluation in albino rats suggested that floating microspheres of rosiglitazone could be a promising approach for better glycemic control.

Formulation and performance characterization of radio-sterilized "progestin-only" microparticles intended for contraception

The aim of this study was to formulate and characterize a microparticulate system of progestin-only contraceptive. Another objective was to evaluate the effect of gamma radio-sterilization on in vitro and in vivo drug release characteristics. Levonorgestrel (LNG) microspheres were fabricated using poly(lactide-co-glycolide) (PLGA) by a novel solvent evaporation technique. The formulation was optimized for drug/polymer ratio, emulsifier concentration, and process variables like speed of agitation and evaporation method. The drug to polymer ratio of 1:5 gave the optimum encapsulation efficiency. Speed of agitation influenced the spherical shape of the microparticles, lower speeds yielding less spherical particles. The speed did not have a significant influence on the drug payloads. A combination of stabilizers viz. methyl cellulose and poly vinyl alcohol with in-water solvent evaporation technique yielded microparticles without any free drug crystals on the surface. This aspect significantly eliminated the in vitro dissolution "burst effect". The residual solvent content was well within the regulatory limits. The microparticles passed the test for sterility and absence of pyrogens. In vitro dissolution conducted on the product before and after gamma radiation sterilization at 2.5 Mrad indicated no significant difference in the drug release patterns. The drug release followed zero-order kinetics in both static and agitation conditions of dissolution testing. The in vivo studies conducted in rabbits exhibited LNG release up to 1 month duration with drug levels maintained within the effective therapeutic window.

Fabrication, characterization and in vivo studies of biodegradable gamma sterilized injectable microparticles for contraception

A Levonorgestrel-loaded microparticulate system was developed with gelatin and bovine serum albumin using triple emulsion technique coupled with chemical cross-linking thermal rigidization method. The formulation was optimized for various formulation variables and process parameters. The microparticulate system was characterized by scanning electron microscopy, encapsulation efficiency, moisture content, IR, DSC, XRD, residual solvent content and evaluated for sterility, abnormal toxicity and absence of pyrogens. Microparticles were sterilized by gamma irradiation at 2.5 Mrad. The system was injected intramuscularly in rabbits and drug blood levels estimated using radioimmunoassay technique. An optimized drug to polymer ratio of 0.4:0.75 w/w gave drug encapsulation efficiency of about 40%. The in vitro drug release followed Higuchi square root kinetics. In in vivo studies the AUC0-t was found to be 12849.25 pg/mL.day(-1) with mean residence time calculated to be about 16 days and Kel of 0.02 day(-1). Levonorgestrel (LNG) levels were maintained between 200 and 400 pg/mL. The pharmacokinetic results indicate that LNG is released from the injectable microparticles for a period of one-month duration.

Sustained delivery of endostatin improves the efficacy of therapy in Lewis lung cancer model

The purpose of this work was to develop an effective delivery system for antiangiogenic therapy. Endostatin was microencapsulated into poly(lactic-co-glycolic acid) (PLGA) microspheres by using a w/o/o multiple emulsification-evaporation technique. Endostatin microspheres showed the encapsulation efficiency 100% with mean particle size about 25 microm. Endostatin released in vitro from PLGA microspheres were biologically active and significantly inhibited the migration of endothelial cells. In rats, endostatin microspheres produced a sustained release process in which the steady-state concentration was reached from day 5 to day 27 with the steady-state levels of endostatin between 174.8+/-33.3 and 351.3+/-126.3 ng/ml. In Lewis lung cancer model, a dose of 10 mg/kg endostatin microspheres was just as effective in suppressing tumor growth as a dose of 2 mg/kg/day free endostatin for 35 days (total dose 70 mg/kg). These results indicated PLGA microspheres further reduced the amount of endostatin needed to achieve significant tumor inhibition in mice when compared with systemic administration.

Characteristics of felodipine-located poly(ε-caprolactone) microspheres

Felodipine-loaded poly (epsilon-caprolactone) (PCL) microspheres were prepared by two methods, the conventional emulsion solvent evapouration method and the quenching method. The aim of this work was to investigate the effects of process parameters such as emulsion type, drug loading, molecular-weight of the polymer, types of emulsion stabilizer and dispersed phase solvents, as well as preparation methods. The results show that, when conventional emulsion solvent evapouration method was used, the o/w-method produced smaller mean size and higher encapsulation efficiency compared with the o/o-method. The encapsulation efficiencies increased with an increase in the molecular weight and a decrease in crystallinity of PCL. The size of microspheres varied with the type of emulsion stabilizer used, smaller microspheres with PVA and narrow size distribution with Pol 237. The water solubility of the dispersed phase solvent was one of the critical factors in controlling the encapsulation efficiency and microsphere mean size. When water-soluble solvents such as acetonitrile and ethyl formate were used, the encapsulation efficiencies decreased due to higher evapouration rate. When quenching methods were used, in contrast to the conventional emulsion solvent evapouration method, very narrowly size-distributed but bigger microspheres were obtained.

Microencapsulation by solvent evaporation: state of the art for process engineering approaches

Microencapsulation by solvent evaporation technique is widely used in pharmaceutical industries. It facilitates a controlled release of a drug, which has many clinical benefits. Water insoluble polymers are used as encapsulation matrix using this technique. Biodegradable polymer PLGA (poly(lactic-co-glycolic acid)) is frequently used as encapsulation material. Different kinds of drugs have been successfully encapsulation: for example hydrophobic drugs such as cisplatin, lidocaine, naltrexone and progesterone; and hydrophilic drugs such as insulin, proteins, peptide and vaccine. The choice of encapsulation materials and the testing of the release of drug have been intensively investigated. However process-engineering aspects of this technique remain poorly reported. To succeed in the controlled manufacturing of microspheres, it is important to investigate the latter. This article reviews the current state of the art concerning this technique by focusing on the influence of the physical properties of materials and operating conditions on the microspheres obtained. Based on the existing results and authors' reflection, it gives rise to reasoning and suggested choices of materials and process conditions. A part of this paper is also dedicated to numerical models on the solvent evaporation and the solidification of microspheres. This review reveals also the surprising lack of knowledge on certain aspects, such as the mechanism of formation of pores in the microspheres and the experimental study on the solidification of microspheres.