Porous biodegradable microspheres for controlled drug delivery. I. Assessment of processing conditions and solvent removal techniques

Long-Acting Injectable Antipsychotics-A Review on Formulation and In Vitro Dissolution

Long-acting injectable (LAI) neuroleptics constitute an effective therapeutical alternative for individuals suffering from persistent mental illness. These injectable pharmaceuticals help patients manage their condition better and improve long-term outcomes by preventing relapses and improving compliance. This review aims to analyse the current formulation aspects of LAI neuroleptics, with particular emphasis on analysis of drug release profiles as a critical test to guarantee drug quality and relevant therapeutical activity. While there is no officially approved procedure for depot parenteral drug formulations, various dissolution tests which were developed by LAI manufacturers are described. In vitro dissolution tests also possess a critical function in the estimation of the in vivo performance of a drug formulation. For that reason, thorough inspection of the in vitro-in vivo correlation (IVIVC) is also discussed.

Challenges and opportunities in the development of complex generic long-acting injectable drug products

Long-acting injectable (LAI) drug products enable the controlled release of a drug over an extended duration of time to improve the therapeutic effect, safety profile, or administration of an injectable product. The development of generic [505(j)] and differentiated [505(b)(2)] LAI products helps to provide patients and healthcare providers with more treatment options and to reduce overall healthcare costs, including those associated with drug product administration and patient compliance. In this review, we analyze the landscape of LAI products and identify the most common technical challenges that potential generic product entrants face. We focus on five formulation technologies that account for ~90% of approved LAI products, including those eligible for generic product registration over the next five years, to illustrate technology-specific challenges. We then review efforts from the U.S. Food and Drug Administration (FDA) to promote more generic product competition and emphasize the importance of collaboration among government, industry, and academia to advance the knowledge and capabilities of the scientific community. Regulatory bodies, industry, and academia are encouraged to anticipate challenges with emerging innovative LAI technologies and to leverage the experiences built on established technologies to foster generic product development.

Polymeric Microsphere Formulation for Colon Targeted Delivery of 5-Fluorouracil Using Biocompatible Natural Gum Katira

Controlled release delivery system of chemotherapeutic agents at the site of colon endorses modern drug-entrapped delivery tools, which release the entrappedagents at a controlled rate for anextended period providing patient compliance and additional protection from the degradinggastric environment. Thus, the present study was aimed to develop and optimize a novel polymeric microsphere of 5-fluorouracil (5-FU) using natural gum katira to obtain an optimal therapeutic response at the colon. Due course of experimentation, in-vivo safety profile of the gum katira in an animal model was established. Modified solvent extraction/evaporation technique wasemployed to encapsulate 5-FU in the natural polymeric microsphere and was characterized using in-vitro studies to investigate particle size, morphology, encapsulation efficiency and release of the drug from developed formulation. Formulated and optimized polymeric microsphere of 5-FU using gum katira polymer own optimal physicochemical characteristics with a fine spherical particle with size ranged from 210.37±7.50 to 314.45±7.80 µm.Targeted microsphere exhibited good cytotoxicity and also has high drug entrapment efficiency, and satisfactory release pattern of the drug within a time frame of 12 h. Finally, we foresee that the optimized polymeric gum katiramicrosphere of 5-FU could be a promising micro-carrier for efficient colon drug targeting delivery tool with improved chemotherapeutic efficacy against colon cancer.

A numerical model for aggregations formation and magnetic driving of spherical particles based on OpenFOAM®

BACKGROUND AND OBJECTIVE

This work presents a numerical model for the formation of particle aggregations under the influence of a permanent constant magnetic field and their driving process under a gradient magnetic field, suitably created by a Magnetic Resonance Imaging (MRI) device.

METHODS

The model is developed in the OpenFOAM platform and it is successfully compared to the existing experimental and numerical results in terms of aggregates size and their motion in water solutions. Furthermore, several series of simulations are performed for two common types of particles of different diameter in order to verify their aggregation and flow behaviour, under various constant and gradient magnetic fields in the usual MRI working range. Moreover, the numerical model is used to measure the mean length of aggregations, the total time needed to form and their mean velocity under different permanent and gradient magnetic fields.

RESULTS

The present model is found to predict successfully the size, velocity and distribution of aggregates. In addition, our simulations showed that the mean length of aggregations is proportional to the permanent magnetic field magnitude and particle diameter according to the relation : l¯_a=7.5B₀d_i^3/2. The mean velocity of the aggregations is proportional to the magnetic gradient, according to : u¯_a=6.63G˜B₀ and seems to reach a steady condition after a certain period of time. The mean time needed for particles to aggregate is proportional to permanent magnetic field magnitude, scaled by the relationship : t¯_a∝7B₀.

CONCLUSIONS

A numerical model to predict the motion of magnetic particles for medical application is developed. This model is found suitable to predict the formation of aggregations and their motion under the influence of permanent and gradient magnetic fields, respectively, that are produced by an MRI device. The magnitude of the external constant magnetic field is the most important parameter for the aggregations formation and their driving.

Comparative in vitro release and clinical pharmacokinetics of leuprolide from Luphere 3M Depot, a 3-month release formulation of leuprolide acetate

A 3-month depot formulation of leuprolide acetate (Luphere 3M Depot) with a mean microsphere diameter of 22.3 μm was prepared aseptically by spray-drying glacial acetic acid solution of the drug and polylactic acid, and lyophilization in a d-mannitol solution. The encapsulation efficiency and loading content of the drug in the Luphere 3M Depot were 94.7% and 9.92% (w/w), respectively. The in vitro release of leuprolide from the depot was substantially delayed and the release profile was similar to that of Lucrin Depot (Abbott Korea, Korea). The safety and pharmacokinetics of leuprolide were investigated over a period of 42 days in 20 prostate cancer patients following a subcutaneous injection of Luphere 3M or Lucrin Depot suspensions (leuprolide acetate dose of 11.25 mg) in a multi-center, randomized, single dose, parallel study. Both formulations were well tolerated by the patients and no serious adverse effects were observed during and after the study. No significant differences were observed in the maximum serum concentration (C_max) and area under the curve (AUC_last) of leuprolide between the two formulations. The results suggest comparable safety and efficacy profiles of Luphere 3M Depot and Lucrin Depot in clinical situations.

Review : Biodegradable Microcapsular Drug Delivery Systems: Manufacturing Methodology, Release Control and Targeting Prospects

An overview of the subject of biodegradable microcapsular drug delivery systems is presented from a polymer chemist's viewpoint. Various polymerization and microencapsulation techniques (including emulsion polymerization, interfacial polycondensation, suspension crosslinking, coacer vation/phase separation and solvent evaporation/extraction) suitable for the preparation of biodegradable microcapsules based on proteins, polysaccharides, polyesters, polyamides, or cyanoacrylates are described. Drug release from biodegradable microcapsules is discussed, and examples are presented to illus trate how the rate of drug release can be controlled by adjusting parameters such as microcapsule size, porosity, and crosslinking. Prospects of site-specific chemotherapy by means of passive and active targeting of microcapsular drug carriers are also analyzed.

Formulation and evaluation of controlled release ethylcellulose and polyethylene glycol microspheres containing metoprolol tartrate

Metoprolol tartrate is rapidly absorbed from both gastric and intestinal regions, after oral administration. To retard the release rate of the metoprolol tartrate, microspheres were prepared with varying concentrations of a mixture containing ethylcellulose and polyethylene glycol-6000. The prepared microspheres were evaluated for various physicochemical characteristics and in vitro drug release. The percent yield of microspheres was in the range of 75.2-87.3%. The particle size of microspheres was found to be in the range of 73.2-85.5 μm. Fourier transform-infrared spectral analysis and differential scanning calorimetry concluded the absence of any interaction between the drug and the carriers. The release time profile of metoprolol tartrate from microspheres in 0.1 N hydrochloric acid solution was to the extent of 33.4-60.2%. The complete release of metoprolol tartrate occurred from MPT-3 and MPT-4 in phosphate buffer solution (pH 7.4) within 8 and 7 h, respectively, whereas the incomplete release (72.3%) occurred from MPT-1. Nearly, the complete release (98.5%) of metoprolol occurred from MPT-2 in 10 h. Formulation MPT-2 would be a preferred formulation. The release of metoprolol involves diffusion rate limited (R² = 0.9865) as a mechanism from drug release. The prepared microspheres of metoprolol tartrate eliminate the need for multiple dosing and provide patient compliance.

Impact of surfactant selection on the formulation and characterization of microparticles for pulmonary drug delivery

The effect of suspension stabilizers, internal aqueous phase volume and polymer amount were investigated for the production of protein loaded poly(d,l lactide-co-glycolide) (PLGA) microparticles suitable for pulmonary drug delivery. PLGA microparticles were produced adopting water-in-oil-in-water (W/O/W) solvent evaporation technique and were investigated for surface morphology, particle size, encapsulation efficiency (EE%) and in-vitro release profile. Porous surface morphologies with a narrow size distribution were observed when employing 0.5 ml internal aqueous phase; 23.04 µm (± 0.98), 15.05 µm (± 0.27) and 22.89 µm (±0.41) for PVA, Tween 80 and oleic acid. Porous microparticles exhibited increased size and reduction in EE% with increasing internal aqueous phase, with non-porous microparticles produced when adopting 2.0 ml internal aqueous phase. The selection of stabilizer influences the size of the pores formed thus offers potential for the aerodynamic properties of the microparticles to be manipulated to achieve suitable aerosolization characteristics for pulmonary delivery of proteins.

Microsponges: A novel strategy for drug delivery system

Microsponges are polymeric delivery systems composed of porous microspheres. They are tiny sponge-like spherical particles with a large porous surface. Moreover, they may enhance stability, reduce side effects and modify drug release favorably. Microsponge technology has many favorable characteristics, which make it a versatile drug delivery vehicle. Microsponge Systems are based on microscopic, polymer-based microspheres that can suspend or entrap a wide variety of substances, and can then be incorporated into a formulated product such as a gel, cream, liquid or powder. The outer surface is typically porous, allowing a sustained flow of substances out of the sphere. Microsponges are porous, polymeric microspheres that are used mostly for topical use and have recently been used for oral administration. Microsponges are designed to deliver a pharmaceutical active ingredient efficiently at the minimum dose and also to enhance stability, reduce side effects, and modify drug release.

Tyrosinase inhibitor-loaded microsponge drug delivery system: new approach for hyperpigmentation disorders

OBJECTIVE

The aim of the present investigation was to design and formulate appropriate form of glabridin, using microsponge drug delivery system.

METHOD

Microsponges were prepared by emulsion solvent evaporation method and characterized by drug loading, infrared spectroscopy and scanning electron microscopy. In vitro diffusion studies of gel formulation were performed using ethanol: phosphate buffer (1:1) mixture as receptor medium. Animal studies were carried out using brownish guinea pigs with UV-induced pigmentation model.

RESULTS

Prepared microsponges were predominantly yellowish, free-flowing and spherical in shape. The infrared spectra revealed the absence of drug polymer interaction. Scanning electron microscopy (SEM) and porosity studies confirmed spherical and porous nature. In vitro release studies data depicted highest correlation with Higuchi treatment. Animal studies also supported the better depigmenting activity as compared to plain gel.

CONCLUSION

Glabridin microsponge-loaded gel could be efficacious in treating various hyperpigmentation disorders.

Structure-Processing-Property Relationship of Poly(Glycolic Acid) for Drug Delivery Systems 1: Synthesis and Catalysis

Till date, market is augmented with a huge number of improved drug delivery systems. The success in this area is basically due to biodegradable polymers. Although conventional systems of drug delivery utilizing the natural and semisynthetic polymers so long but synthetic polymer gains success in the controlled drug delivery area due to better degradation profile and controlled network and functionality. The polyesters are the most studied class group due the susceptible ester linkage in their backbone. The Poly(glycolic Acid) (PGA), Poly(lactic acid) (PLA), and Polylactide-co-glycolide (PLGA) are the best profiled polyesters and are most widely used in marketed products. These polymers, however, still are having drawbacks which failed them to be used in platform technologies like matrix systems, microspheres, and nanospheres in some cases. The common problems arose with these polymers are entrapment inefficiency, inability to degrade and release drugs with required profile, and drug instability in the microenvironment of the polymers. These problems are forcing us to develop new polymers with improved physicochemical properties. The present review gave us an insight in the various structural elements of Poly(glycolic acid), polyester, with in depth study. The first part of the review focuses on the result of studies related to synthetic methodologies and catalysts being utilized to synthesize the polyesters. However the author will also focus on the effect of processing methodologies but due some constraints those are not included in the preview of this part of review.

Key parameters affecting the initial leaky effect of hemoglobin-loaded nanoparticles as blood substitutes

In order to realize long-term carrying/delivering oxygen and minimize the adverse effects of free hemoglobin (Hb) in vivo, Hb is desired to be confined in Hb-loaded nanoparticles (HbP), a novel blood substitute with potential clinical applications, and thus functions as the native red blood cells (RBCs). However, the initial burst release of Hb ("leaky effect") greatly underscores the significance of this work. The study described here wants to disclose the key preparative parameters, including polymer, excipients in the inner aqueous phase and solvent profile, affecting the Hb release behavior (the initial 24 h) from HbP fabricated by commonly used solvent diffusion/evaporation double emulsion technique. The results demonstrate that PEGlytated polymers, regardless of two- or tri-block copolymers show slower release compared with the corresponding non-PEGlytated ones. The higher polymer concentration yields lower initial release. PEG200, added as excipient facilitates Hb burst effect to about 38.4%, almost 17% increase compared to the control ( approximately 21%), whereas, PVA and Poloxamer188, due to amphiphilic nature, can effectively attenuate this leakage to about 13.0 and 5.1%, respectively. The diffusion/extraction rate from oil phase and the subsequent evaporation rate from the aqueous continuous phase of solvents impose different influences on Hb release. To reduce the burst effect, the initial diffusion/extraction rate should be slow, whereas, the concomitant evaporation rate should be as fast as possible. The results obtained here will be guidance's for the future tailored design of more desirable polymersome nanoparticle blood substitutes.

Porous PLGA microparticles: AI-700, an intravenously administered ultrasound contrast agent for use in echocardiography

The production and characterization of AI-700, an intravenously administered ultrasound contrast agent under investigation for myocardial perfusion echocardiography, are described. The product consists of small, porous microparticles filled with decafluorobutane gas, and formulated as a dry powder. Small scale spray drying studies demonstrated that porous PLGA microparticles could be produced with varying porosity using ammonium bicarbonate as a volatile pore-forming agent. The porous microparticles of AI-700 were created aseptically by spray drying a water-in-oil emulsion containing poly-d,l-lactide-co-glycolide, 1,2-diarachidoyl-sn-glycero-3-phosphocholine, and ammonium bicarbonate using a two-chamber spray dryer. The porous microparticles were further formulated into a dry powder drug product (AI-700) containing decafluorobutane gas and excipients. The dry powder was reconstituted with sterile water prior to evaluation. Microscopy demonstrated that the microparticles were sphere-shaped and internally porous. The microparticles were appropriately sized for intravenous administration, having an average diameter of 2.3 mum. Zeta-potential analysis demonstrated that the microparticles would be expected to be stable post-reconstitution. The microparticles retained encapsulated gas post-reconstitution, had high acoustic potency that was stable over time and were physically stable upon exposure to high-power ultrasound, as used clinically. AI-700 has the characteristics desirable for an intravenously administered ultrasound contrast agent for myocardial perfusion echocardiography.

Effect of preparation temperature in solvent evaporation process on Eudragit RS microsphere properties

Eudragit RS 100 microspheres containing ketoprofen as a model drug were prepared by the solvent evaporation method using an acetone/liquid paraffin solvent system. The influence of various preparation temperatures: 10, 25, 35, and 40 degrees C, on particle size and morphology, drug content and release kinetics, and drug crystal state was evaluated. With increasing temperature, microsphere average size was found to increase and particle size distribution to widen significantly. At 10 degrees C particles of irregular shape are formed, whereas higher temperatures gradually improve the sphericity of microspheres. As can be seen from SEM photographs, particle surface roughness decreases as preparation temperature increases. It was found that temperature had no effect either on ketoprofen microencapsulation efficiency or on its crystal state, but it does influence emulsion-stabilizer incorporation. Ketoprofen forms solid solution in Eudragit matrix and maintains amorphous state for significant period of time. Drug release rates from microspheres correlated with microspheres' surface roughness and to a lesser extent with particle size.

Drying of poloxamer hydrogel films

The drying of hydrogel films formed by Poloxamer 407 poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) amphiphilic block copolymer was investigated at various air relative humidity (RH) conditions ranging from 11 to 97%. Initially, the amount of water lost increased linearly with the drying time. After this linear region (stage I), a nonlinear behavior was observed (stage II). The drying rate increased with decreasing RH, thus greatly shortening the drying time. A decrease of the film thickness also shortened the drying time; however, the drying mechanism did not change. Three models for one-dimensional water diffusion were used to fit the experimental results at different RH conditions and film thicknesses. Model 1 assumes semi-infinite medium and constant diffusion coefficient, and fits very well the data in stage I of the drying process. The fitted water diffusion coefficient (D) is 5 x 10(-10) m(2)/s, whereas the effects of the RH are captured by a proportionality constant (alpha) that appears in the boundary condition. Model 2 considers a finite (constant) film thickness and captures the experimental observations over the whole drying period for the same D and alpha as in Model 1. The analytical solutions available for Models 1 and 2, used together with the experimentally derived model parameters D and alpha, allow for easy estimation of drying time and water loss from Poloxamer hydrogel films of various compositions and thicknesses and at different relative humidities. Numerical solutions for water diffusion under conditions of decreasing film thickness and diffusion coefficient being a function of concentration are also presented (Model 3). It becomes apparent from the fit of the data to the different models that the drying rate is more sensitive to the boundary condition at the film-air interface (represented by alpha) than to the diffusion in the film. It is notable that the alpha values obtained from the fits of the Poloxamer hydrogel drying rate are comparable to those obtained from drying of water films under the same experimental conditions.

Encapsulation of water-insoluble drug by a cross-linking technique: effect of process and formulation variables on encapsulation efficiency, particle size, and in vitro dissolution rate

Ibuprofen-gelatin micropellets were prepared by the cross-linking technique using formaldehyde. Spherical micropellets having an entrapment efficiency of 65% to 85% were obtained. The effect of core to coat ratio, speed of agitation, temperature, and volume of oil phase was studied with respect to entrapment efficiency, micropellet size, and surface characteristics. Fourier transform infrared spectroscopy and differential scanning calorimetric analysis confirmed the absence of any drug-polymer interaction. X-ray diffraction patterns showed that there is a decrease in crystallinity of the drug. The micromeritic properties of micropellets were found to be slightly changed by changing various processing parameters to give micropellets of good flow property. The in vitro release profile could be altered significantly by changing various processing parameters to give a controlled release of drug from the micropellets. The stability studies of the drug-loaded micropellets showed that the drug was stable at storage conditions of room temperature, 37 degrees C, 25 degrees/60% relative humidity (RH) and 45 degrees/60% RH, for 12 weeks.

Two-stage optimization process for formulation of chitosan microspheres

The objective of the present study was to optimize the concentration of a chitosan solution, stirring speed, and concentration of drugs having different aqueous solubility for the formulation of chitosan microspheres. Chitosan microspheres (unloaded and drug loaded) were prepared by the chemical denaturation method and were subjected to measurement of morphology, mean particle size, particle size distribution, percentage drug entrapment (PDE), drug loading, and drug release (in vitro). Morphology of the microspheres was dependent on the level of independent process parameters. While mean particle size of unloaded microspheres was found to undergo significant change with each increase in concentration of chitosan solution, the stirring rate was found to have a significant effect only at the lower level (ie, 2000 to 3000 rpm). Of importance, spherical unloaded microspheres were also obtained with a chitosan solution of concentration less than 1 mg/mL. Segregated unloaded microspheres with particle size in the range of 7 to 15 microm and mean particle size of 12.68 microm were obtained in the batch prepared by using a chitosan solution of 2 mg/mL concentration and stirring speed of 3000 rpm. The highest drug load ( microg drug/mg microspheres) was 50.63 and 13.84 for microspheres containing 5-fluorouracil and methotrexate, respectively. While the release of 5-fluorouracil followed Higuchi's square-root model, methotrexate released more slowly with a combination of first-order kinetics and Higuchi's square-root model. The formation of chitosan microspheres is helped by the use of differential stirring. While an increase in the concentration of water-soluble drug may help to increase PDE and drug load over a large concentration range, the effect is limited in case of water-insoluble drugs.

Microsphere design for the colonic delivery of 5-fluorouracil

The treatment of colon cancer has been aimed by approaches of oral drug administration. 5-Fluorouracil is the standard treatment still nowadays and would be a candidate to be delivered orally to the colon. A pH-sensitive polymer Eudragit P-4135F was used to prepare microspheres by a simple oil/water emulsification process. Process parameters were analyzed in order to optimize the drug loading and release profiles. In further attempts mixtures with Eudragit RS100 were prepared to prolong drug release. Scanning electron microscopy and confocal laser scanning microscopy permitted a structural analysis. The solvent extraction was preferable over solvent evaporation with a view to the encapsulation rate (extraction: 37%; evaporation: 19%) due to the hydrophilic character of the drug while release pattern were nearly unchanged. Eudragit P-4135F, pure or in mixture, was found to retain drug release at pH 6.8 lower than 35% within 6 h. At pH 7.4, nearly immediate release (within 30 min) was observed for pure P-4135F, while mixtures enabled to prolong the release slightly. Analysis of the morphology led to an inhomogeneous polymer distribution of P-4135F and RS100 throughout the particle core. A capsule-like structure was concluded which allowed only slight changes of the release kinetics by the addition of RS100. However, the formulation proved its applicability in-vitro as a promising device for pH-dependent colon delivery of 5-fluorouracil.

Poly(D,L-lactide-co-glycolide) microspheres containing 5-fluorouracil: optimization of process parameters

The objective of this research was to optimize the processing parameters for poly(D,L-lactide-co-glycolide) (PLGA) microspheres of 5-fluorouracil (5-FU) and to mathematically relate the process parameters and properties of microspheres. Microspheres were prepared by a water-in-oil-in-water emulsion solvent evaporation technique. A 3(2) factorial design was employed to study the effect of the volume of the internal phase of the primary emulsion and the volume of the external phase of the secondary emulsion on yield, particle size, and encapsulation efficiency of microspheres. An increase in the volume of the internal phase of the primary emulsion resulted in a decrease in yield and encapsulation efficiency and an increase in particle size of microspheres. When the volume of the external phase of the secondary emulsion was increased, a decrease in yield, particle size, and encapsulation efficiency was observed. Microspheres with good batch-to-batch reproducibility could be produced. Scanning electron microscopic study indicated that microspheres existed as aggregates.

Assessment of biodegradable controlled release rod systems for pain relief applications

Control of chronic, severe pain is a difficult and important clinical problem for most patients, especially those with cancer. Although current applications are insufficient for a satisfactory solution to this problem, the rate of disease incidence is increasing worldwide, thus making the problem more apparent. Based on this fact, this study was designed with the ultimate goal of formulating a controlled release system of pain relievers, mainly opioids, for the local treatment of pain to achieve satisfactory, fast, and less side effect-related relief and to provide a better life status for chronic pain patients. Two copolymers of a biodegradable polymer poly(L-lactide-co-glycolide) (PLGA) were used to prepare an implantable rod type drug release system containing either an analgesic or anesthetic type of pain reliever. In vitro drug release kinetics of these systems were studied. It was observed that release from PLGA 85 : 15 was more zero-order than it was from PLGA 50 : 50. A zero-order release rate was obtained for codeine, hydromorphone, and bupivacaine from PLGA (85 : 15) rods. They, however, were released from PLGA (50 : 50) rods with Higuchi kinetics. The drug solubility was also influential on release rate, as shown by the zero-order morphine release from PLGA (50 : 50) rods. Scanning electron micrographs (SEMs) of the monolithic rods revealed erosion of the rods and the removal of drug crystals from the rod structure.

Release mechanisms from gentamicin loaded poly(lactic-co-glycolic acid) (PLGA) microparticles

To provide local gentamicin delivery for 1 week based on a biodegradable system, poly(lactic-co-glycolic acid) (PLGA) microparticles were developed utilizing a 50/50 blend of Resomer RG 502H, an uncapped variety of 13.5 kD, and Resomer RG 503, an endcapped polymer of 36.2 kD. The liberation mechanism was investigated by analysis of morphological changes and thermal analysis focusing on the polymer glass transition temperature (T(g)) and the mechanical properties. The release of gentamicin was related to a structural breakdown of the particles reaching a critical molecular weight. A T(g) of < 37 degrees C in the hydrated state was not indicative of collapse and agglomeration of the particles because the mechanical strength of the polymer structures in the rubbery state may still render sufficient support. As the gap between incubation temperature and T(g) widened, the mechanical stability of the PLGA microparticles decreased and became decisive. Particles prepared with RG 502H show a lower ability to bear mechanical stress than RG 503 and 50/50 RG 502H/RG 503 microparticles.

Preparation, characterization and in vivo evaluation of 120-day poly(D,L-lactide) leuprolide microspheres

A 120-day poly(D,L-lactide) (PLA) microsphere delivery system for a luteinizing hormone-releasing hormone (LHRH) analogue, leuprolide, was prepared and evaluated. Leuprolide microspheres were prepared with PLA (m.w. 11000 Da) by a dispersion/solvent extraction-evaporation method and characterized for drug load by HPLC, particle size by laser diffractometry and surface morphology by scanning electron microscopy. In vitro peptide release and polymer degradation were studied using a modified dialysis method. Serum peptide and testosterone levels were analyzed after subcutaneous administration using a rat model. Spherical microspheres with a mean diameter of 52 microm containing 13.4% peptide released 10% of the peptide within 24 h, followed by a linear release for 150 days. Serum leuprolide levels increased immediately after administration of the microspheres to 45.6 ng/ml, but then fell to 4.3 ng/ml at 15 days and approximately 2.0 ng/ml at 30 days where they remained for 120 days. The testosterone levels increased initially to 15 ng/ml and then decreased to below 0.5 ng/ml by day 4 where they remained for 120 days. In conclusion, a 120-day microsphere formulation of leuprolide was developed with excellent controlled peptide release characteristics and in vivo efficacy.

Ethyl cellulose polymer microspheres for controlled release of norfluazon

The pesticide norfluazon has been microencapsulated using ethyl cellulose to develop controlled-release formulations that decrease its mobility through the soil and protect it from photodegradation. Ethyl cellulose microspheres loaded with norfluazon were prepared by the solvent-evaporation method. To obtain the microspheres, certain conditions (pesticide/polymer ratio, percentage of emulsifying agent and solvent) were varied. The shape and size of the microspheres obtained were studied by scanning electron microscopy. Other parameters, such as solids recovery, encapsulation efficiency and pesticide loading, were also studied. The release rate of norfluazon from the different microspheres was slower than that of pure norfluazon. In particular, microspheres obtained with o-xylene, which provided the largest diameter, retarded the initial release of the pesticide relative to microspheres obtained with chloroform, or to pure norfluazon. Moreover, the studies showed that the pesticide/polymer ratio controlled the release of norfluazon, which was slower when this ratio was low. Release rates conformed to a generalised kinetic equation for a diffusion-controlled release mechanism, and the time taken for 50% of the active ingredient to be released into water, t50, was calculated.

Effects of the rate of solvent evaporation on the characteristics of drug loaded PLLA and PDLLA microspheres

We investigated the effects of the rate of solvent removal by varying ambient pressure at a fixed temperature on the morphology, particle sizes, drug encapsulation efficiency and releases pattern of lidocaine loaded poly-L-lactatide (PLLA) and poly-D,L-lactatide (PDLLA) microspheres, prepared with O/W emulsion-solvent evaporation process. Prepared in the fast rate of solvent evaporation (FRSE) process by reducing ambient pressure, smoothly morphological surface of drug loaded PLLA and PDLLA microspheres was observed. While in the normal rate of solvent evaporation (NRSE) process, roughness or pinhole surface was only found at drug loaded PLLA microspheres. Fabricated in the FRSE process, both PLLA and PDLLA microspheres showed smaller particle sizes and lower drug encapsulation efficiencies than those prepared in NRSE process. In regard to two materials, PLLA microspheres had higher drug encapsulation efficiencies than PDLLA ones for both processes. Although initial burst releases of drug were observed for both PLLA and PDLLA microspheres prepared in whatever solvent removal process, drug release for PLLA microspheres was slightly less than that for PDLLA ones in the earlier stage of drug release. However, in the subsequent stage of drug release, there was no difference between two materials. In corporation with different crystalline characteristics of PLA polymer and its derivatives, FRSE process by reducing ambient pressure could be further applied to produce different characteristics of microspheres for drug delivery.

Surface microarchitectural design in biomedical applications: in vivo analysis of tissue ingrowth in excimer laser-directed micropored scaffold for cardiovascular tissue engineering

A micropatterned microporous segmented polyurethane film (20 x 12 mm in size, 30 micrometer thick) with four regions was prepared by excimer laser microprocessing to provide an in vivo model of transmural tissue ingrowth in an open cell-structured scaffold specially designed for cardiovascular tissue engineering. Three microporous regions had the same circular micropores (30 micrometer diameter) but different pore density arrangements (percentage of total pore area against unit area was 0.3%, 1.1%, and 4.5%), and the other region remained nonporous. The covered stent, prepared by wrapping the regionally different density-microporous film on an expandable metallic stent (approximately 3.1 mm in diameter), was delivered to the luminal surface of canine common carotid arteries and placed after expansion of the stent to a diameter of approximately 8 mm using a balloon catheter. At 4 weeks of implantation, all the covered stents (n = 10) were patent. The luminal surfaces of the covered stents were almost confluently endothelialized both in nonporous and microporous regions. Histological examination showed that the neointimal wall was formed by tissue ingrowth from host through micropores (transmural) and anastomotic sites. Thrombus formation occurred frequently in the lowest density porous region and nonporous region. With an increase in pore density, the thickness of the neointimal wall decreased. This study demonstrated how the micropore density of implanted devices influences tissue ingrowth in arterial implantation.

Respirable PLGA microspheres containing rifampicin for the treatment of tuberculosis: manufacture and characterization

PURPOSE

Particles with aerodynamic diameters of 1-5 microm deposit in the periphery of the lungs and are phagocytized by alveolar macrophages, the primary site of Mycobacterium tuberculosis infection. Aerosols of biodegradable polymeric microspheres containing antitubercular agents may be delivered to the lungs to improve the treatment of tuberculosis.

METHODS

Poly(lactide-co-glycolide) (PLGA) microspheres containing rifampicin were prepared using solvent evaporation and spray drying methods. The solvent evaporation process was optimized using factorial experimental design and surface response methodology. The morphology, particle size, drug loading, and dissolution of microspheres was evaluated.

RESULTS

The spray dried rifampicin loaded PLGA microparticles were shriveled, unlike the spherical particles produced by solvent evaporation. Drug loadings of 20% and 30% were achieved for solvent evaporation and spray dried products, respectively. The particles prepared by solvent evaporation and spray drying had 3.45 microm and 2.76 microm median diameters by volume, respectively.

CONCLUSIONS

Respirable rifampicin loaded PLGA microspheres were produced by both solvent evaporation and spray drying methods. These particles are being evaluated in an animal model of tuberculosis.

Kinetics of a model nucleoside (guanosine) release from biodegradable poly(DL-lactide-co-glycolide) microspheres: a delivery system for long-term intraocular delivery

The objective of this study was to prepare poly(DL-lactide-co-glycolide) (PLGA) microspheres containing guanosine as a model drug for intraocular administration. Microspheres were prepared by solvent evaporation technique using o/w emulsion system. The influence of composition and molecular weight of PLGA, drug loading efficiency, microsphere size, and in vitro and in vivo release rates were determined. Differential scanning calorimetry (DSC) and FTIR studies were conducted to examine the guanosine-polymer interaction. In vitro release studies indicated that the permeant release from microspheres exhibits an initial burst followed by slow first-order kinetics. Ascending molecular weights of the polymers generated progressively slower release rates. Three different sizes of microspheres were prepared. The release continued for 7 days with a maximum of 70% of the content released within that time period. DSC and FTIR studies showed no polymer-guanosine interaction. A novel microdialysis technique was used to examine the initial release kinetics from microspheres in isolated vitreous humor. This technique was also employed to observe in vivo intravitreal release in albino rabbits. A good correlation exists between in vitro and in vivo release rates from both 75 and 140 kDa PLGA microspheres. Guanosine-loaded microspheres could be prepared for once-a-week intravitreal injection with minimum required concentration maintained throughout the dosing interval. Because the structural and solubility characteristics of guanosine are similar to those of acyclovir and ganciclovir (two acycloguanosine analogues effective against herpes simplex virus [HSV-1] and cytomegalovirus [CMV], respectively), similar biodegradable polymer-based microsphere technology can be employed for the long-term intraocular delivery of these two drugs.

Diclofenac sodium incorporated PLGA (50:50) microspheres: formulation considerations and in vitro/in vivo evaluation

Recently, considerable interest has been focused on the use of biodegradable polymers for specialized applications such as controlled release of drug formulations; meanwhile, microsphere drug-delivery systems using various kinds of biodegradable polymers have been studied extensively during the past two decades. Poly (lactide-co-glycolide) (PLGA) polymers have been proven to be excellent drug carriers for microparticulate systems due to their advantages, e.g. biocompatibility and regulatory approval. The administration of nonsteroidal anti-inflammatory drugs (NSAIDs) into the intra-articular cavity in patients with chronic inflammatory disease is complicated due to the short duration of effect. In the present study, controlled-release parenteral formulations of diclofenac sodium (DS), a commonly used NSAID, were prepared for intra-articular administration, and evaluated in vitro for particle size, yield, drug loading, surface morphology and release characteristics. For in vivo studies, Technetium-99m labelled polyclonal human immunogammaglobulin (99m Tc-HIG) was used as the radiopharmaceutical to demonstrate arthritic lesions by gamma scintigraphy. Evaluation of arthritic lesions post-therapy in rabbits showed no significant difference in the group treated with PLGA (50:50) (mw 34000) DS microspheres compared to control groups.

Recombinant human bone morphogenetic protein-2 binding and incorporation in PLGA microsphere delivery systems

The objective of this research was to determine the binding capacity and kinetics, and total incorporation of recombinant human bone morphogenetic protein-2 (rhBMP-2) in microspheres made from hydrophilic and hydrophobic poly(lactide-co-glycolide) (PLGA). Polymers were characterized by molecular weight, polydispersity, and acid number. Microspheres were produced via a water-in-oil-in-water double emulsion system and characterized for bulk density, size, specific surface area, and porosity. Protein concentrations were determined by reversed phase HPLC. Protein was loaded by soaking microspheres in a buffered solution, pH 4.5, of rhBMP-2, decanting excess liquid, and vacuum drying the wetted particles. Total loading and binding were determined by comparing protein concentration remaining to non-microsphere containing samples. Polymer acid number was the dominant polymer feature affecting the binding. Higher acid values correlated with increased rhBMP-2 binding. The amount of non-bound incorporated rhBMP-2 linearly correlated with the concentration of protein used in binding. High rhBMP-2 concentrations inhibit binding to PLGA microspheres. Binding was also inhibited by increased lactide content in the PLGA polymer. The polymer characteristics controlling rhBMP-2 binding to PLGA microspheres are acid value foremost followed by molecular weight and lactide/glycolide ratio. The total amount of rhBMP-2 incorporated depends on the bound amount and on the amount of free protein present.

Effect of protective colloids on the induction of polymorphic changes in indomethacin agglomerates after solvent evaporation from o/w emulsions

Indomethacin (IMC) agglomerates were prepared by the solvent evaporation process from o/w emulsions containing different protective colloids in the external aqueous solution. The types of protective colloids inducing the polymorphic transformation of IMC in the agglomerates without wall material were investigated. The composition and its polymorphs were evaluated from the X-ray diffraction patterns, IR spectra and DSC thermograms. The results indicate that when pectin, beta-cyclodextrin, sodium alginate or sodium dodecyl supphase acted as a protective colloid, the respective IMC agglomerates consisted only of the alpha form of IMC. When gelatin or hydroxypropyl methylcellulose was used as a protective colloid, the amorphous, alpha and gamma forms as well as methylene chloride solvates of IMC were found in the IMC agglomerates. There was only methylene chloride solvate of IMC with a small amount of amorphous form in the IMC agglomerates prepared from albumin as a protective colloid, while IMC agglomerates prepared from methylcellulose, polyvinyl alcohol or biosoluble polymer consisted of the mixture of amorphous and alpha forms, and methylene chloride solvate of IMC. When polyvinyl pyrrolidone was applied to act as a protective colloid, the mixture of methylene chloride solvate and gamma form of IMC with less quantity of amorphous form was found in its IMC agglomerates. This strongly suggests that the composition of IMC agglomerates prepared from the solvent evaporation process was significantly influenced by the type of protective colloids used.

Effect of polytyrosine on the hydrophobicity of hydroxyethyl starch microspheres

The polypeptide, poly-l-tyrosine (PTYR) was incorporated into hydroxyethyl starch (HES) microspheres to modify the surface hydrophobicity in order to allow subsequent radioiodination and assessment of uptake into the intestinal mucosa following oral administration. The HES microspheres were prepared by a crosslinking polymerization process and characterized for particle size, peptide content and surface morphology. The hydrophobicity of the characterized microspheres was assessed by two techniques-water uptake (swelling) of the microspheres and contact angle measurement using the sessile drop method. Spherical microspheres containing PTYR were prepared with a greater than 80% loading efficiency in the 1-10 microns size range. The surface morphology suggested localization of the PTYR at the surface proportionate to the loading. The percent water uptake of the blank HES microspheres was 87%, whereas that of the 5, 10 and 20% PTYR/HES microspheres was 84%, 61% and 55%, respectively. HES/PTYR was polymerized as films to facilitate contact angle measurement. A monotonical increase in the contact angle was observed as the concentration of the PTYR was increased to 20%. Contact angle of pure HES (0% PTYR) films was 16 degrees and for the PTYR-containing films was 29 degrees for 5% PTYR, 39 degrees for 10% and 57 degrees for 20%. The hydrophobicity of the HES microsphere system could be increased by the incorporation of polytyrosine thereby paving the way to radioiodinate the microspheres and perform uptake studies in an animal model.