Spray Dried Polylactide Microsphere Preparation: Influence of the Technological Parameters

Preparation and Evaluation of Mucus-Penetrating Inhalable Microparticles of Tiotropium Bromide Containing Sodium Glycocholate

This study aimed to prepare mucus-penetrating inhalable microparticles for dry powder inhalers and to evaluate their applicability in an asthma-induced rat model. Microparticles were prepared from water solutions containing tiotropium bromide, L-leucine, and sodium glycocholate (NaGc) as permeation enhancers using the spray drying method. Four formulations (SDL1, SDL2, SDL3, and SDL4) were used, depending on the various NaGc concentrations. Tiotropium microparticles were characterized by standard methods. Additionally, an asthma-induced rat model was used to confirm the effects of the formulations on lung function. Tiotropium microparticles with NaGc resulted in formulations with a more corrugated morphology and smaller particle size distribution than those without NaGc. SDL 1 had a rough surface with irregular morphology, and SDL 2, 3, and 4 had a corrugated morphology. All SDL formulations had an aerodynamic size of <3 µm. The microparticles with a corrugated morphology aerosolized better than SDL1 microparticles. The apparent permeability coefficient (Papp) values of SDL3 and SDL4 were significantly higher than those for raw tiotropium. In an in vivo study using an asthma-induced rat model, the specific airway resistance (Sraw), airway wall thickness, and mean alveolus size recovered to those of the negative control group in the SDL4 formulation.

The Effect of Particle Size and Surface Roughness of Spray-Dried Bosentan Microparticles on Aerodynamic Performance for Dry Powder Inhalation

The purpose of this study was to prepare spray dried bosentan microparticles for dry powder inhaler and to characterize its physicochemical and aerodynamic properties. The microparticles were prepared from ethanol/water solutions containing bosentan using spray dryer. Three types of formulations (SD60, SD80, and SD100) depending on the various ethanol concentrations (60%, 80%, and 100%, respectively) were used. Bosentan microparticle formulations were characterized by scanning electron microscopy, powder X-ray diffraction, laser diffraction particle sizing, differential scanning calorimetry, Fourier-transform infrared spectroscopy, dissolution test, and in vitro aerodynamic performance using Andersen cascade impactor^™ (ACI) system. In addition, particle image velocimetry (PIV) system was used for directly confirming the actual movement of the aerosolized particles. Bosentan microparticles resulted in formulations with various shapes, surface morphology, and particle size distributions. SD100 was a smooth surface with spherical morphology, SD80 was a rough surfaced with spherical morphology and SD60 was a rough surfaced with corrugated morphology. SD100, SD80, and SD60 showed significantly high drug release up to 1 h compared with raw bosentan. The aerodynamic size of SD80 and SD60 was 1.27 µm and SD100 was 6.95 µm. The microparticles with smaller particle size and a rough surface aerosolized better (%FPF: 63.07 ± 2.39 and 68.27 ± 8.99 for SD60 and SD80, respectively) than larger particle size and smooth surface microparticle (%FPF: 22.64 ± 11.50 for SD100).

Ondansetron-loaded biodegradable microspheres as a nasal sustained delivery system: in vitro/in vivo studies

The aim of this study was to prepare ondansetron-loaded biodegradable microspheres as a nasal delivery system. Microspheres were prepared with emulsification/spray-drying technique using poly(d,l-lactide) (PLA) and two different types of poly(d,l-lactide-co-glycolide) (PLGA). The effect of the type of organic solvent (dichloromethane (DCM) or a mixture of DCM and ethyl acetate) on the microsphere characteristics was also examined. The prepared microspheres were evaluated with respect to the morphological properties, particle size, zeta potential, drug loading efficiency, and in vitro drug release. The mean particle size (d(50)) of microsphere formulations was ranged from 11.67-25.54 μm, indicating suitable particle size for nasal administration. All microspheres had low drug loading efficiency in the range of 12.28-21.04%. The results indicated that particle size of microspheres were affected by both type of polymer and organic solvent, however drug loading efficiency of microspheres were affected by only the type of organic solvent used. All microspheres were negatively charged due to the polymers (PLA or PLGA) used. A prolonged in vitro drug release profile was observed for 96 h. Based on in vitro data, the selected microsphere formulation has been applied via nasal route to rats in vivo. Following nasal administration of ondansetron-loaded microsphere to rats, ondansetron plasma levels were within a range of 30-48 ng/mL during 96 h, indicating a sustained drug delivery pattern and relatively a constant plasma drug concentration level. The results suggested that biodegradable microspheres prepared with emulsification/spray-drying technique could be considered to deliver ondansetron via nasal route to obtain a prolonged release.

Nasal route: an alternative approach for antiemetic drug delivery

INTRODUCTION

Antiemetic drugs are used in the treatment of nausea and emesis. Development of novel delivery systems for antiemetic drugs, as an alternative to conventional preparations, is important in terms of good patient compliance and improving bioavailability. The nasal route offers unique superiorities, such as fast and high drug absorption, and high patient compliance. Therefore, a considerable amount of research has been carried out on the development of nasal delivery systems for antiemetic drugs.

AREAS COVERED

This review deals with the importance of nasal delivery of antiemetic drugs and the studies performed on this subject. The first part of this review summarizes the properties of the nasal route, its advantages and limitations, parameters affecting drug absorption through nasal mucosa, nasal passage pathways and general approaches to improve nasal transport. The second part reviews the studies conducted on the development of nasal delivery systems.

EXPERT OPINION

Due to its superiorities, the nasal route could be considered as an attractive alternative to oral and parenteral routes. To overcome the barrier properties of the nasal epithelium and to enhance transport of antiemetic drugs, several approaches, including permeation enhancers, in situ gel formulations and micro- and nanoparticulate systems, have been evaluated. The results obtained are promising and indicate that nasal formulations of some antiemetic drugs may enter the market in the near future.

Influence of Formulation Variables on the Morphology of Biodegradable Micropartieles Prepared by Spray Drying

The preparation of microparticles of the biodegradable poly-DL-lactide (PLA) and polylactide-co-glycolide (PLGA) polymers using spray-drying technology was studied. Formulation parameters investigated include polymer type, polymer molecular weight, polymer concentration, and viscosity. Microparticles were characterized using electron microscopy, particle size analysis, and gel permeation chromatography. Kinematic viscosity was determined for each of the sprayed polymer solutions. Polymer molecular weight and polymer concentration were found to be important parameters when preparing PLA and PLGA microparticles using spray-drying technology.

Nanoparticle-coated microparticles: preparation and characterization

The objective of the present work was to design and prepare new nanoparticle-coated drug-loaded inorganic microparticles by spray-drying using diclofenac as drug model. Previous works presented the process to dry drug-loaded polymeric nanoparticles using silicon dioxide as adjuvant, otherwise in the present proposition the drug is associated with the silicon dioxide and unloaded polymeric nanocapsule or nanosphere suspensions were used as organic coating. Eudragit S100 was chosen because of its gastric resistance. The potential application of polymeric colloidal suspensions as nanocoating for microparticles were evaluated in terms of process yields, encapsulation efficiencies, morphologic analyses and in vitro drug release profiles in buffered media (pH 1.2; 5.0 and 7.4). The results showed the technological feasibility of preparing controlled nanoparticle-coated drug-loaded inorganic microparticles. When the diclofenac was employed as a hydrophilic model, in this salt form, the powders prepared in two steps (core previously prepared) showed an adequate gastroresistance by the use of Eudragit S100. The use of diclofenac as a hydrophobic model (acid form) conducted to powders presenting good gastroresistance when the nanocapsules and triacetin were employed.

Spray-drying nanocapsules in presence of colloidal silica as drying auxiliary agent: formulation and process variables optimization using experimental designs

PURPOSE

Spray-drying process was used for the development of dried polymeric nanocapsules. The purpose of this research was to investigate the effects of formulation and process variables on the resulting powder characteristics in order to optimize them.

MATERIALS AND METHODS

Experimental designs were used in order to estimate the influence of formulation parameters (nanocapsules and silica concentrations) and process variables (inlet temperature, spray-flow air, feed flow rate and drying air flow rate) on spray-dried nanocapsules when using silica as drying auxiliary agent. The interactions among the formulation parameters and process variables were also studied. Responses analyzed for computing these effects and interactions were outlet temperature, moisture content, operation yield, particles size, and particulate density. Additional qualitative responses (particles morphology, powder behavior) were also considered.

RESULTS

Nanocapsules and silica concentrations were the main factors influencing the yield, particulate density and particle size. In addition, they were concerned for the only significant interactions occurring among two different variables. None of the studied variables had major effect on the moisture content while the interaction between nanocapsules and silica in the feed was of first interest and determinant for both the qualitative and quantitative responses. The particles morphology depended on the feed formulation but was unaffected by the process conditions.

CONCLUSION

This study demonstrated that drying nanocapsules using silica as auxiliary agent by spray drying process enables the obtaining of dried micronic particle size. The optimization of the process and the formulation variables resulted in a considerable improvement of product yield while minimizing the moisture content.

Spray-dried microparticles containing polymeric nanocapsules: Formulation aspects, liquid phase interactions and particles characteristics

Up to now, the full potential of polymer-based nanoparticles is not yet exploited because of a lack of stability when conserved in aqueous medium. The present paper reports the water elimination from nanocapsules (NC) dispersions by means of the spray-drying technique with the aim to achieve dried solid forms of interest using colloidal silicon dioxide as drying auxiliary. The influence of formulation parameters on the suspension behaviour and on the powders characteristics was also evaluated. Our findings demonstrated that the mixing protocol, the concentrations of both NC and silica are crucial parameters that affect the feed behaviour and the spray-dried particles characteristics. Interactions occurring in the feed are directed by hydrogen bounds and were more sensitive to the silica concentration than that of NC as evidenced by rheological measurements. The NC are entrapped within solid dried matrixes following their interaction with silica particles in the feed. SEM analyses of the obtained powders showed spherical separated microparticles formed by the association of NC and silica when they are mixed at adequate concentrations in the feed before spray-drying. On the other hand, fused agglomerated particles presenting NC at their surface, characterised by irregular shapes and a strong adhesiveness were prepared when the silica concentration was not sufficient. The surface composition of the spray-dried powders was investigated using the ESCA technique and revealed the NC exclusion from the surface to obtain powders suitable for further handling.

Etanidazole-loaded microspheres fabricated by spray-drying different poly(lactide/glycolide) polymers: effects on microsphere properties

In this work, a spraying technique was used to encapsulate etanidazole (a hypoxic radiosensitizer) into different poly(lactide/glycolide) polymers. The properties of the obtained microspheres, especially the particle size and distribution, morphology and release rate were investigated. Unexpectedly, poly(L-lactide) (PLLA) shows a fast release rate, comparable to PLGA 50: 50, due to the dissociation of the microspheres although the release rate of the spray-dried microspheres of other polymers decreases with increasing lactide ratio. It is also interesting to note that, contrary to the viscosity sequence of the polymer solutions, the particle size of the microspheres decreases in the order PLGA 50: 50, PLGA 65: 35, PLGA 85: 15 and PDLA. The morphology of microspheres can be affected by polymer properties (e.g. lactide/glycolide ratio, molecular weight, crystallinity and Tg) and fabrication conditions (e.g. solvent and polymer concentration to be sprayed). Although most of the microspheres fabricated by EA have a donghnut-like shape with smooth surface, it is possible to obtain spherical particles by choosing proper polymer type and polymer concentration. A further examination of the mechanisms of the atomization process and the solvent evaporation process reveals their respective effect on droplet formation and particle formation, both of which are essential for the spray-drying technique. It is found that polymer phase transition (affected by the polymer solubility) and its subsequent solvent evaporation processes can finally determine the morphology and the particle size of the spray-dried particles made from different polymers. In essence, the lactide/glycolide ratio of the polymers plays a more important role in affecting the properties of the spray-dried microspheres.

Gelatin microparticles containing propolis obtained by spray-drying technique: preparation and characterization

Gelatin microparticles containing propolis extractive solution (PES) were prepared by spray-drying technique. The optimization of the spray-drying operating conditions and the proportions of gelatin and mannitol were investigated. Regular particle morphology was obtained when mannitol was used, whereas mannitol absence produced a substantial number of coalesced and agglomerated microparticles. Microparticles had a mean diameter of 2.70 microm without mannitol and 2.50 microm with mannitol. The entrapment efficiency for propolis of the microparticles was upto 41% without mannitol and 39% with mannitol. The microencapsulation by spray-drying technique maintained the activity of propolis against Staphylococcus aureus. These gelatin microparticles containing propolis would be useful for developing intermediary or eventual propolis dosage form without the PES' strong and unpleasant taste, aromatic odour, and presence of ethanol.

Carbamazepine/betaCD/HPMC solid dispersions. I. Influence of the spray-drying process and betaCD/HPMC on the drug dissolution profile

The aim of this study was to compare carbamazepine (CBZ) solid dispersions prepared by spray-drying of aqueous dispersions with the corresponding physical mixtures. The influence of the association of beta-cyclodextrin (betaCD) and hydroxypropyl methylcellulose (HPMC) on the CBZ dissolution profile of the preparations was investigated. Results demonstrated that CBZ release from solid dispersions is dependent on the ratio of betaCD and HPMC. The spray-drying process confers better homogeneity to CBZ polymeric dispersions than the physical mixture process. In summary, we demonstrated the feasibility of obtaining a homogeneous polymeric solid dispersion of CBZ from an aqueous media by spray-drying and a clear influence of the betaCD:HPMC ratio on the release profile of CBZ.

Mucoadhesive microspheres containing gentamicin sulfate for nasal administration: preparation and in vitro characterization

In this study, suitable microsphere formulations were designed in order to provide the absorption of a high polar drug through nasal mucosa. For this purpose, gentamicin sulfate (GS) was chosen as a model drug and used at different drug/polymer ratios in the microsphere formulations. The microspheres were prepared by spray drying technique. Hydroxypropyl methylcellulose was used as a mucoadhesive polymer in the formulations to increase the residence time of the microspheres on the mucosa. Sodium cholate was added into the formulations for increasing the absorption of GS through nasal mucosa. The in vitro characteristics of the microspheres were determined. The microspheres were evaluated with respect to the particle size, production yield, encapsulation efficiency, shape and surface properties, drug-polymer interaction, mucoadhesive property, in vitro drug release and suitability for nasal drug delivery.

Preparation and in vitro evaluation of pyridostigmine bromide microparticles

Pyridostigmine bromide (PB) is an anticholinesterase agent whose aqueous solubility is high and which has a short elimination half-life. Its dosage rate in the treatment of myastenia gravis is frequent due to the short half-life and it exhibits side effects. Microparticles designed to deliver a pharmaceutical active ingredient efficiently at the minimum dose and also to enhance stability, reduce side effects and modify drug release were prepared in this study using an acrylic polymer (Eudragit) as the vehicle by the spray-drying technique. The drug was either dissolved or dispersed in the polymeric solution and following the preparation of microparticles using different ratios of ingredients, characterization studies including the determination of shape, particle size distribution, amount loaded, release and stability of PB were performed. The results obtained were compared to those of pure PB. Drug release from microparticles could be modified and was found to depend on the shapes of the microparticles. In vitro evaluation results indicate that the frequent dosage and side effects of pure PB may be reduced with the formulation of microparticles.

Spray-dryed bupivacaine-loaded microspheres: in vitro evaluation and biopharmaceutics of bupivacaine following brachial plexus administration in sheep

Microspheres could be used as a drug delivery system to prolong the duration of action of bupivacaine and to reduce its systemic absorption leading to high plasma concentrations related to central nervous and cardiovascular toxicity. Bupivacaine-loaded microspheres were made by spray-drying using polylactide-co-glycolide polymers from different sources and with different bupivacaine-polymer ratio. The characterization of microspheres concerned the shape and size, the bupivacaine drug-content (DC) and the cumulative release profiles. We evaluated in sheep the bupivacaine pharmacokinetics: (i) after short intravenous infusion of 75 mg bupivacaine solution; and (ii) following brachial nerve plexus injections of 75 mg bupivacaine solution alone, with the addition of 75 microg epinephrine, with the addition of 150 microg epinephrine and of bupivacaine (750 mg)-loaded microspheres. Release profiles showed a biphasic pattern whatever the DC. After i.v. infusion the mean clearance value was 1.53+/-0.53 l/min and the mean elimination half-life was 120.5+/-73.1 min. Following brachial plexus nerve injection, bupivacaine C(max) were lower than 100 ng/ml following either solution or microspheres administration. Ninety percent of the 75 mg bupivacaine given as a solution were absorbed in 5.8+/-1.0 h (bupivacaine alone) compared to 24.6+/-1.2 h following microsphere administration.

Fabrication, characterization and in vitro release of paclitaxel (Taxol) loaded poly (lactic-co-glycolic acid) microspheres prepared by spray drying technique with lipid/cholesterol emulsifiers

Spray dry technique was applied to produce paclitaxel loaded microspheres of biodegradable poly (lactic-co-glycolic acid) (PLGA) as an alternative delivery system. Various emulsifiers such as L-alpha-dipalmitoyl-phosphatidylcholine (DPPC), cholesterol, polyvinyl alcohol (PVA), gelatin were incorporated in order to achieve high encapsulating efficiency of paclitaxel in the microspheres and desired properties for a sustained release. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) showed that the surface of the microspheres with high ratio of lipid was spherical and smooth. Those made with other emulsifiers had rougher surface with pores. Incorporation of lipid, cholesterol or gelatin can significantly increase the drug content in the microspheres. The differential scanning calorimetry (DSC) result indicated that the paclitaxel trapped in the microspheres existed in an amorphous or disordered-crystalline status in the polymer matrix. The zeta potential of the microspheres was negative in general and was strongly influenced by the type of the emulsifiers used in fabrication. The system formulated with cholesterol was most stable. The release profiles of various formulations with PVA, gelatin as well as low ratio of DPPC showed almost zero-order release kinetics in the first 3 weeks after an initial burst less than 5% in the first day. The release rate then gradually decreased. The microspheres fabricated with high ratio of DPPC exhibited large initial burst. When cholesterol was combined together with DPPC as an emulsifier, the release became faster.

Preparation and characterization of spray-dried oxidized cellulose microparticles

The goal of this study was to investigate the feasibility of spray drying to produce microparticles of oxidized cellulose (OC), a biocompatible and bioresorbable polymer. OCs containing 7, 13, and 20 wt% carboxylic groups were converted into stable aqueous dispersions and then spray dried using a Yamoto G-32 spray dryer equipped with a standard fluid nozzle with an orifice of 406 microm. The following operating conditions were investigated: inlet temperature 140, 170, and 190 degrees C; feed rate 3, 6, and 9 mL/min; and atomization airpressure 0.5, 1, and 1.5 kg f/cm2. The amounts of OC used in feed were 1, 2.5, and 5%. OC microparticles produced under these conditions were shrunken spheres, ranging in size between 0.98+/-0.47 and 2.05+/-0.98 microm. The different operating conditions used had no significant effect on the size and shape of particles. The use of a water-soluble plasticizer (glycerin, polyethylene glycol 400, or polyethylene glycol 6000) in the dispersion yielded microparticles with a good sphericity and a smooth surface morphology, whereas no change in the shape or size of microparticles was noted with water-insoluble plasticizers, Triacetin and dibutyl phthalate. Powder X-ray diffraction and Fourier transform infrared spectral analyses of spray-dried microparticles showed no change in the solid-state structure of OC. In conclusion, results show that OC can be converted into stable aqueous dispersions and used to produce microparticles by spray drying.

Spray-drying as a method for microparticulate controlled release systems preparation: advantages and limits. I. Water-soluble drugs

Spray-drying was used for the preparation of paracetamol/eudragit RS or RL or ethylcellulose microspheres to verify the possibility of their use in controlled-release solid-dosage forms formulation and try to determine advantages and limits of the technique of such use. Microspheres were first characterized by scanning electron microscopy, differential scanning calorimetry, x-ray diffractometry, and in vitro dissolution studies and then used for the preparation of tablets. During this step, the compressibility of the spray-dried powders was also evaluated. In vitro dissolution studies were performed also on the tablets and their release control was accessed. Although powders were unable to slow down drug release, tablets obtained from microsphere compression showed a good capability of controlling paracetamol release when eudragit RS or ethylcellulose was used, even at low polymer amounts.

Development of spray-dried acetaminophen microparticles using experimental designs

Experimental factorial designs were built to investigate the effects of five parameters on production yields and moisture contents of spray-dried products. These factors concerned both the solution feed (drug concentration, colloidal silica concentration and polymer/drug ratio) and the spray dryer (inlet temperature and feed rate). Three formulations containing cellulose derivatives and acetaminophen were tested. The aim of the study was to optimize the operating conditions to maximize production yields while minimizing moisture contents. First screening experiments consisting of fractional factorial designs revealed the most significant factors to be inlet temperature, feed rate and their interaction for both formulations containing sodium carboxymethylcellulose and feed rate and colloidal silica concentration for the formulation containing microcrystalline cellulose. Then, the optimal operating conditions were estimated by response surface methodology. Central rotational composite designs showed quadratic models were adequate. New assays were carried out using these last conditions to evaluate both the repeatability and reproducibility of the spray-drying technique. Yields above 80% and moisture content of approximately 1% were reached. The characterization of microparticles revealed the poor flowability of the spray-dried products due to significant cohesiveness and very small size (less than 55 microm).

Influence of various technological parameters on the preparation of spray-dried poly(epsilon-caprolactone) microparticles containing a model antigen

This work evaluates the efficacy of the spray-drying technique to prepare poly(epsilon-caprolactone) (PCL) microparticles containing an entrapped model antigen (bovine albumin, BSA). The presence of a stabiliser was found to be an important parameter when preparing PCL microparticles containing a hydrophilic antigen. The effect of various technological parameters (concentration of the polymer and protein solutions, organic/aqueous phases ratio, nature of solvents and emulsion parameters such as duration and speed of agitation) on microparticle morphology and size, BSA entrapment and encapsulation efficiency was studied. Microparticles were characterized by a mean size from 9.56+/-0.25 to 24.31+/-2.87 microm and a BSA entrapment from 0.80+/-0.02 to 24.21+/-0.23% (w/w). SDS-PAGE electrophoresis and isoelectric focusing (IEF) confirmed the conservation of the physicochemical characteristics of the BSA entrapped within PCL microparticles produced by spray-drying. Together, these results showed that spray-drying is an efficient technique to overcome the key obstacle that represents the scaling-up of the manufacturing process to produce sufficient quantities of vaccine for clinical trials and, ultimately, commercialization.

Parameters influencing the antigen release from spray-dried poly(DL-lactide) microparticles

Microparticles were produced by spray-drying from a high molecular weight polylactide (PLA R207) for the development of long-lasting controlled release systems of vaccines, which may be designed to obviate the need for booster doses. The current investigation considered the effect of both technological parameters (inlet air temperature and spray rate of feed) and polymeric solutions (polymer concentration and nature of organic solvents) on characteristics of microparticles (morphology, size and antigen loading) containing a water-soluble model antigen (bovine serum albumin, BSA). Following parameters chosen, microparticles were characterized by a mean size from 3.08 +/- 0.06 to 9.43 +/- 0.26 microm and a BSA loading from 2.45 +/- 0.13 to 18.20 +/- 2.25% (w/w). The BSA release rate from microparticles varied from 11.17 +/- 2.20 to 92.60 +/- 3.46% in 24 h. The modification of the inlet temperature, the spray-rate of feed or the use of a mixture of dichloromethane/chloroform (DCM/CFM) instead of DCM alone resulted in the modification of the BSA burst release. This burst release was followed by a BSA release rate slower for microparticles with a low BSA loading. Moreover, the increase of the R207 concentration resulted in a decrease of the BSA release rate while the burst release was not modified. SDS-PAGE electrophoresis and isoelectric focusing analyses of the BSA released from microparticles confirmed the preservation of its physicochemical characteristics. Together, results showed that the spray-dried microparticles loaded with hydrophilic antigen could be used as a potential delivery system for the long-lasting controlled release of vaccines.

Preparation and characterization of spray-dried polymeric nanocapsules

Recently, much interest has been generated by colloidal drug delivery systems such as nanocapsules because of the possibilities for controlled release, increased drug efficacy, and reduced toxicity after parenteral administration. Nanocapsules of poly-epsilon-caprolactone and Eudragit S90 were prepared. However, these systems present physicochemical instability. To dry these nanocapsule suspensions with the view of obtaining a solid form, the spray-drying process was used. Spray-dried powders of nanocapsules of poly-sigma-caprolactone and Eudragit S90 were prepared by atomization in a Büchi 190 Mini-spray dryer using colloidal silicon dioxide as a technological carrier. The morphological analysis of the surface at the powders showed that nanocapsules remain intact, and no change in particle size was detected after the spray-drying process. These results suggest that this method can be an interesting alternative to dry nanocapsule suspensions.

Ultrasonic atomization for spray drying: a versatile technique for the preparation of protein loaded biodegradable microspheres

Bovine serum albumin (BDA) loaded microspheres with a spherical shape and smooth surface structure were successfully prepared from poly(lactide-co-glycolide) using an ultrasonic nozzle installed in a Niro laboratory spray dryer. Process and formulation parameters were investigated with respect to their influence on microsphere characteristics, such as particle size, loading capacity, and release properties. Preparation of microspheres in yields of more than 50% was achieved using an ultrasonic atomizer connected to a stream of carrier air. Microsphere characteristics could be modified by changing several technological parameters. An increased polymer concentration of the feed generated larger particles with a significantly reduced initial release of the protein. Moreover, microspheres with a smooth surface structure were obtained from the organic polymer solution with the highest viscosity. Microparticles with a low BSA loading showed a large central cavity surrounded by a thin polymer layer in scanning electron microspheres. A high protein loading led to an enlargement of the shell layer, or even to dense particles without any cavities. A continuous in vitro release pattern of BSA was obtained from the particles with low protein loading. Glass transition temperatures (Tg) of the microspheres before and after lyophilization did not differ from those of the BSA loaded particles prepared by spray drying with a rotary atomizer. Analysis of the polymer by gel permeation chromatography indicated that ultrasonication had no effect on polymer molecular weight. Molecular weight and polydispersity of the pure polymer, placebo microspheres prepared by spray drying, and placebo microspheres prepared using the ultrasonic nozzle were in the same range. In conclusion, ultrasonic atomization represents a versatile and reliable technique for the production of protein loaded biodegradable microspheres without inducing a degradation of the polymer matrix. Particle characteristics can be modified by adjusting formulation parameters and atomization conditions in a simple manner.

Modulation of rifampicin release from spray-dried microspheres using combinations of poly-(DL-lactide)

Microspheres containing 20% w/w rifampicin (RIF) with smooth morphology have been readily prepared from combinations of low, R104 (Mw, 2000) and moderate, R202H (Mw, 9000), molecular weight poly(D,L-lactide) (PDLLA) as a means to modulate drug release from either polymer when used alone. These have been characterized with respect to their drug loading, granulometry, in vitro drug release and thermal behaviour. Particle size distributions were Gaussian, whereby mean microsphere diameter was found to increase from 2.11 to 2.98 microns as the proportion of more viscous R202H increased, whilst > 95% of particles were < 10 microns, irrespective of the polymer blend used. Use of a reduced inlet temperature for spray-drying gave uncharacteristically high production yields in the range of 55.8-80.7% for the process. Encapsulation efficiencies were quantitative with the weight proportion of drug co-dissolved (p < 0.05), yielding microspheres of high and predictable RIF loading. In vitro drug release revealed a dramatic shift in release profile between 40 and 60% R104. Closer examination in this range showed the predicted pattern of increased release rate as the fraction of more hydrophilic R104 increased. However, disproportionate differences were evident between 44 and 48% R104. From the apparent temperature dependent drug release, the criticality of matrix composition was attributed to the coincidence of matrix softening with the dissolution medium temperature and consequent hydration, which, at a finite composition, resulted in a controlled auto-hydration mechanism. Dramatic dependence of release rate with dissolution methodology was accountable to the fact that drug release was considerably quicker where microspheres remained suspended and individualized with the USP paddle method as opposed to aggregated with the shaking bath methodology. In conclusion, the utility of blending racemic PDLLA to modulate drug release and the convenience of spray-drying as a technique to produce microspheres of predictable character have been demonstrated. The temperature-dependent release exhibited may have application in the site-specific delivery of drugs where local increased biochemical activity promotes drug release in response to an increased pharmacological need.

Bovine serum albumin loaded poly(lactide-co-glycolide) microspheres: the influence of polymer purity on particle characteristics

To study the influence of polymer purity on microsphere characteristics, bovine serum albumin (BSA) loaded biodegradable microspheres were prepared by spray drying using two samples of poly(lactide-co-glycolide), PLG, (50:50, mwt = 35 and 69 kDa). Polymer properties were varied by DL-lactide and glycolide addition or by ultrafiltration. While the effective drug loading was not affected by polymer purity, Tg was decreased with increasing monomer and oligomer content. The removal of these low molecular weight substances by ultrafiltration led to a narrower molecular weight distribution compared to the untreated PLG. Concerning the polymer with the higher molecular weight, microsphere morphology was also strongly affected by polymer composition. In contrast to the non-modified PLG, monomer addition yielded particles with a much smoother surface structure. Moreover, in vitro cytotoxicity of the microspheres prepared from the polymer pretreated by ultrafiltration was significantly reduced, whereas monomer addition caused a dramatic decrease of cells surviving contact with the microsphere extract. The in vivo degradation rate of the ultrafiltered microspheres was decreased and as a result, protein release at later times was slowed down. Furthermore, depending on the effective drug loading level, monomer addition resulted in a decrease in the initial protein burst. It can be concluded that the effect of low molecular weight impurities in a polymer on microsphere characteristics and on cytotoxicity cannot be ignored. Their elimination is possible by ultrafiltration.

Recombinant human erythropoietin (rhEPO) loaded poly(lactide-co-glycolide) microspheres: influence of the encapsulation technique and polymer purity on microsphere characteristics

Recombinant human erythropoietin (EPO) and fluorescein isothiocyanate-labelled dextran (FITC-dextran) loaded biodegradable microspheres were prepared from poly(lactide-co-glycolide) (PLG) by a modified spray-drying technique. This microencapsulation method was compared with the water-in-oil-in-water (w/o/w) double-emulsion method. As expected, microsphere morphology, particle size and particle size distribution strongly depended on the production process. The spray-drying method was found to have a number of advantages compared to the w/o/w double-emulsion technique. The content of residual dichloromethane (DCM) in the final product was significantly lower in case of the microspheres prepared by spray-drying. Concerning EPO loaded microspheres, spray-drying yielded higher encapsulation efficiencies. Although the microspheres obtained by spray-drying are subjected to intensive mechanical and thermal stress during the preparation, the amount of aggregates of EPO in PLG microspheres were not increased compared to the w/o/w technique. Depending on the manufacturing method, addition of cyclic DL-lactide dimers (referred to as monomers in the following) affected the in vitro release profiles of EPO and FITC-dextran from PLG microspheres. Using differential scanning calorimetry it was shown that these low molecular weight substances only seem to be present inside the microspheres produced by spray-drying. DL-Lactide significantly reduced the initial burst release of both EPO and FITC-dextran. While the following release period of EPO was not affected by the DL-lactide content, a more linear FITC-dextran release pattern could be achieved. It can be concluded that the spray-drying technique provides a number of advantages compared to the w/o/w method. The modulation of protein release using low molecular weight additives is of particular interest for parenteral depot systems.

PDLLA microspheres containing steroids: spray-drying, o/w and w/o/w emulsifications as preparation methods

Hydrocortisone and its more soluble ester, hydrocortisone 21-acetate, have been incorporated into poly(D,L-lactic) acid (PDLLA) microspheres using single, double emulsion/solvent evaporation and by spray-drying techniques. This paper describes the characterization of the microparticles obtained (morphology, particle size distribution, drug content, yield of production, in vitro drug release behaviour) and a comparison of the results (drug loading, drug release, size of the microspheres) obtained from the different techniques used. These results demonstrate that by using a relatively more soluble ester of an insoluble steroid, hydrocortisone, the drug content within the microspheres can be increased, together with a high efficiency of loading, irrespective of the technique employed. In the case of hydrocortisone, spray-drying produces the highest loading and encapsulation efficiency compared to both single and double emulsion methods for microspheres of similar size (about 2-4 microns) and suitable for lung delivery, but with lower yields (about 55% versus about 33%).

Cellulose acetate trimellitate ethylcellulose blends for non-steroidal anti-inflammatory drug (NSAID) microspheres

Ketoprofen (Ket), a non-steroidal anti-inflammatory drug, has been incorporated into polymeric micromatrices (microspheres) prepared by a spray drying process and made of cellulose acetate trimellitate (CAT)/ethylcellulose (EC) blends. Drug loaded microspheres were obtained by spray-drying organic solutions of the two polymers and the drug. Characterization of the microparticles (morphology, particle size distribution, drug content, yield of production, surface properties, solvent residues) was carried out and in-vitro release behaviour measured. The release rate of the drug diminished as the proportion of EC was raised.