Influence of post-emulsification drying processes on the microencapsulation of human serum albumin

In the present work, methods used to microencapsulate Human Serum Albumin (HSA) in a biodegradable polymer were compared for their effects on the physicochemical characteristics of HSA-loaded microparticles and on the release and integrity of encapsulated HSA. The polymer used was poly(D,L-lactide-co-glycolide) (75:25) (PLGA) (Boehringer Ingelheim, Resomer RG 752, MW 20,900). Microparticles were formulated by (i) w/o/w emulsification and freeze-drying (EFD) or (ii) w/o/w emulsification and spray-drying (ESD). Particle morphology and size were evaluated by scanning electron microscopy and by laser diffraction analysis. Loading, encapsulation efficiency and protein release were determined using a commercial protein assay kit. Protein integrity was evaluated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis. Particles produced by emulsification/spray-drying exhibited greater diversity in shape than those produced by emulsification/freeze-drying. Additionally, protein loading values were significantly higher for particles produced by emulsification/spray-drying rather than particles produced by emulsification/freeze-drying. The structural integrity of encapsulated protein was confirmed for particles produced by both processes. The fraction of HSA released was similar for both formulations. The emulsification/spray-drying technique described appears to be a rapid and efficient method for the preparation of PLGA microparticles loaded with a model protein.     

Optimisation of the microencapsulation of lavender oil by spray drying

Background: Lavender oil consists of around 100 components and is susceptible to volatilisation and degradation reactions.

Aim: Microencapsulate lavender oil by spray drying using a biocompatible polymeric blend of gum acacia and maltodextrin to protect the oil components. Effect of total polymer content, oil loading, gum acacia, and maltodextrin proportions on the size, yield, loading, and encapsulation efficiency of the microparticles was investigated.

Methods: Morphology and oil localisation within microparticles were assessed by confocal laser scanning electron microscope. Structural preservation and compatibility were assessed using Fourier transform infra-red spectroscopy, differential scanning calorimetry, and gas chromatography–mass spectrometry.

Results: Lavender microparticles of size 12.42?±?1.79?µm prepared at 30 w/w% polymer concentration, 16.67 w/w% oil loading, and 25w/w% gum acacia showed maximum oil protection at high loading (12?mg w/w%), and encapsulation efficiency (77.89 w/w%).

Conclusion: Lavender oil was successfully microencapsulated into stable microparticles by spray drying using gum acacia/maltodextrin polymeric blend.     

Integrated optimization of fish oil microencapsulation process by spray drying

An integrated approach through coupling response surface method (RSM) and genetic algorithm (GA) was applied to optimize the spray dryer operational condition for production of fish oil microcapsules. The inlet drying air temperature, aspirator rate, and peristaltic pump rate were independent and encapsulation efficiency (EE) and exergy efficiency were dependent variables. RSM was applied to establish the relationship between the independent and dependent variables followed by integrating the developed models using three mathematical approaches and measure the fitness value of GA. Consequently, the optimal drying condition for microencapsulation of fish oil was: inlet drying air temperature?=?177.23°C, aspirator rate?=?63.93%, and peristaltic pump rate?=?14.04% yielding exergy efficiency of 8.10% and EE of 79.14%. The results of confirmation experiments for selected drying condition proved the capability of utilized approach for determination of sustainable and qualified process in fish oil microencapsulation by spray drying.     

A comparison between spray drying and spray freeze drying for dry powder inhaler formulation of drug-loaded lipid-polymer hybrid nanoparticles

Lipid-polymer hybrid nanoparticles - polymeric nanoparticles enveloped by lipid layers - have emerged as a potent therapeutic nano-carrier alternative to liposomes and polymeric nanoparticles. Herein we perform comparative studies of employing spray drying (SD) and spray freeze drying (SFD) to produce inhalable dry-powder form of drug-loaded lipid-polymer hybrid nanoparticles. Poly(lactic-co-glycolic acid), lecithin, and levofloxacin are employed as the polymer, lipid, and drug models, respectively. The hybrid nanoparticles are transformed into micro-scale nanoparticle aggregates (or nano-aggregates) via SD and SFD, where the effects of (1) different excipients (i.e. mannitol, polyvinyl alcohol (PVA), and leucine), and (2) nanoparticle to excipient ratio on nano-aggregate characteristics (e.g. size, flowability, aqueous reconstitution, aerosolization efficiency) are examined. In both methods, PVA is found more effective than mannitol for aqueous reconstitution, whereas hydrophobic leucineis needed to achieve effective aerosolization as it reduces nano-aggregate agglomeration. Using PVA, both methods are equally capable of producing nano-aggregates having size, density, flowability, yield and reconstitutibility in the range ideal for inhaled delivery. Nevertheless, nano-aggregates produced by SFD are superior to SD in terms of their aerosolization efficiency manifested in the higher emitted dose and fine particle fraction with lower mass median aerodynamic diameter.     

Dissolution characteristics of composite particles using a spray freeze drying

A spray freeze drying (SFD) method, using a spray nozzle, liquid N(2) and a lyophilizer, was developed to prepare composite particles of a poorly water-soluble drug. The resultant particles were found to have a porous structure. The purpose of the present research was to prepare a sustained release formulation using the SFD technique. Tolbutamide (TBM)and Eudragit S were used as model drugs and pH-dependent carrier, respectively. Eudragit S is a polymer that is soluble at or above pH 7.0. Morphological evaluation of the composite particles revealed that they had a porous structure with a significantly larger specific surface area than bulk TBM. The physicochemical properties of the particles were found to be dependent on the drug to carrier ratio, with the crystallinity of the TBM decreasing as the proportion of Eudragit S increased. Dissolution tests in solutions of pH 1.2 and pH 6.8 showed that the release profiles of TBM from the SFD composite particles were improved compared to bulk TBM, through the use of the pH-dependent carrier. On the other hand, following compression of the composite particles, sustained release was observed in a solution of pH 6.8, whereas almost no dissolution occurred in a solution of pH 1.2.     

Constant size, variable density aerosol particles by ultrasonic spray freeze drying

This work provides a new understanding of critical process parameters involved in the production of inhalation aerosol particles by ultrasonic spray freeze drying to enable precise control over particle size and aerodynamic properties. A series of highly porous mannitol, lysozyme, and bovine serum albumin (BSA) particles were produced, varying only the solute concentration in the liquid feed, c(s), from 1 to 5 wt%. The particle sizes of mannitol, BSA, and lysozyme powders were independent of solute concentration, and depend only on the drop size produced by atomization. Both mannitol and lysozyme formulations showed a linear relationship between the computed Fine Particle Fraction (FPF) and the square root of c(s), which is proportional to the particle density, ρ, given a constant particle size d(g). The FPF decreased with increasing c(s) from 57.0% to 16.6% for mannitol and 44.5% to 17.2% for lysozyme. Due to cohesion, the BSA powder FPF measured by cascade impaction was less than 10% and independent of c(s). Ultrasonic spray freeze drying enables separate control over particle size, d(g), and aerodynamic size, d(a) which has allowed us to make the first experimental demonstration of the widely accepted rule d(a)=d(g)(ρ/ρ(o))(1/2) with particles of constant d(g), but variable density, ρ (ρ(o) is unit density).     

Comparison of process parameters for microencapsulation of plasmid DNA in poly(D,L-lactic-co-glycolic) acid microspheres

Poly(D,L-lactic-co-glycolic) acid (PLGA) microspheres containing plasmid DNA encoding the firefly luciferase gene were prepared using the water-in-oil-in-water (w/o/w) double emulsion and solvent evaporation method. In this study, we investigated the effects of three process parameters on DNA microencapsulation: (1) emulsification method used to generate the primary emulsion, (2) water/oil ratio during formation of the first emulsion, and (3) surfactant concentration used in the preparation of the second emulsion. The resulting formulations were also analyzed for microsphere size, encapsulation efficiency, and kinetics of DNA release. We found that although each process alteration resulted in encapsulation of biologically active, structurally intact DNA, the surfactant and water/oil ratio significantly affected the size, release kinetics and encapsulation efficiency of plasmid DNA.     

Protein spray freeze drying. 2. Effect of formulation variables on particle size and stability

Spray freeze drying produces protein particles suitable for microencapsulation into polymeric microspheres intended for sustained release. Accessibility of encapsulated protein particles to the microsphere surface increases as the protein particle size is increased. Thus, it is desirable that the encapsulated protein particle size be minimized to limit initial release. We have investigated the effect of formulation on spray freeze-dried bovine serum albumin (BSA) as a model protein. Atomization conditions were fixed such that in the absence of excipient, the particle size of the sonicated powder was submicron, and there was substantial protein degradation (loss of monomer). Addition of low concentrations of surfactants (up to the CMC) or mannitol (up to the point where it tended to crystallize upon dehydration) resulted in partial stabilization without impacting particle size. Trehalose was successful in stabilizing the protein; however, there was a marked increase in particle size at the highest levels tested. Ammonium sulfate provided partial stabilization, but also tended to form crystals and increase particle size. FTIR measurements showed a loss of native secondary structure upon spray freeze drying that was ameliorated by addition of trehalose. Other excipients did not prevent structural perturbations. In general, stabilization of spray freeze-dried BSA was related to lowering of the specific surface area in the powder. A balance must be achieved when spray freeze drying proteins intended for encapsulation in sustained-release systems.     

Optimization of a spray drying process to prepare dry powder microparticles containing plasmid nanocomplex

Successful gene delivery to the lung depends not only on precise and effective design of a nanosized nucleic acid delivery system but also on well engineered liquid or solid microparticles. In present work, we tried to statistically optimize spray dried formulations of low molecular weight chitosan-plasmid nanocomplexes via a D-optimal design with respect to five critical responses: yield of the process, microparticle sizes, nanocomplex sizes, DNA stability and relative transfection efficiency. Nonocomplex formulations prepared by different amounts of solid contents and leucine ratio, and spray dried immediately with varying inlet temperature, feed rate and spray air flow rate. Mean results fitted to 2FI models except for relative transfection efficiency, which fitted in a quadratic model. According to the fitted models, the most important pure factors influencing each response determined to be feed rate for yield and DNA stability, feed fluid concentration for microparticle size, inlet temperature for nanoparticle size and leucine concentration for relative transfection efficiency. However, two-factor interactions have more important roles in microparticle size, nanocomplex size and DNA stability. It was concluded that the optimized formulation could be obtained when all the independent variables were at their maximum tested values, except for feed fluid concentration, which should be in its middle point.     

Water-free microencapsulation of proteins within PLGA microparticles by spray drying using PEG-assisted protein solubilization technique in organic solvent

Poly(d,l-lactic-co-glycolic acid) (PLGA) microparticles encapsulating therapeutic proteins were prepared under a water-free formulation condition. Bovine serum albumin (BSA) and recombinant human growth hormone (rhGH) were homogeneously solubilized as nano-scale complexes in methylene chloride phase by using polyethylene glycol (PEG) as a complex-forming agent. The organic phase containing dissolved PLGA and PEG/protein complexes was directly spray dried to obtain PLGA microparticles encapsulating proteins. They exhibited sustained release profiles of BSA and rhGH up to 30 days with reduced initial bursts. The released protein molecules from the microparticles maintained structural integrity without aggregation, suggesting that the current single-step protein microencapsulation method without using water could be potentially applied for sustained delivery of a wide range of therapeutic protein drugs that are not soluble in organic solvents.     

Spray freeze drying for dry powder inhalation of nanoparticles

Formulating nanoparticles for delivery to the deep lung is complex and many techniques fail in terms of nanoparticle stability. Spray freeze drying (SFD) is suggested here for the production of inhalable nanocomposite microcarriers (NCM). Different nanostructures were prepared and characterized including polymeric and lipid nanoparticles. Nanoparticle suspensions were co-sprayed with a suitable cryoprotectant into a cooled, stainless steel spray tower, followed by freeze drying to form a dry powder while equivalent compositions were spray dried (SD) as controls. SFD-NCM possess larger specific surface areas (67–77 m²/g) and lower densities (0.02 g/cm³) than their corresponding SD-NCM. With the exception of NCM of lipid based nanocarriers, SFD produced NCM with a mass median aerodynamic diameter (MMAD) of 3.0 ± 0.5 μm and fine particle fraction (FPF ⩽ 5.2 μm) of 45 ± 1.6% with aerodynamic performances similar to SD-NCM. However, SFD was superior to SD in terms of maintaining the particle size of all the investigated polymeric and lipid nanocarriers following reconstitution (S_f/S_i ratio for SFD ≈ 1 versus >1.5 for SD). The SFD into cooled air proved to be an efficient technique to prepare NCM for pulmonary delivery while maintaining the stability of the nanoparticles.     

Thermoanalytical techniques for the investigation of the freeze drying process and freeze-dried products

A key challenge facing the pharmaceutical industry is the production of biotechnological drug products such as proteins in a stable form. Freeze-drying is preferred for manufacturing such products because of the low temperatures used. However, the protein may still degrade during the process necessitating the inclusion of a protectant. This review describes the range of thermal analysis techniques that have been used to investigate the properties of formulations to be freeze dried and the resultant products. This approach has allowed insight into the key parameters required for design of formulations and processes that will generate the best possible products.     

颈椎活血胶囊喷雾干燥的工艺研究

目的选择颈椎活血胶囊喷雾干燥的最佳条件.方法应用正交试验法,以每小时药粉产量为考察指标,同时兼顾粉中有效成分,对影响颈椎活血胶囊喷雾干燥过程的因素进行考察.结果正交试验法设计的3个因素中,浸膏的相对密度影响最显著,进塔风压的影响较显著.结论最佳工艺条件为:进塔风温120℃,进塔风压-1 350 Pa,浸膏相对密度为1.15;采用喷雾干燥工艺生产出的颈椎活血胶囊有效成分中阿魏酸含量明显高于湿法制粒生产出的颈椎活血胶囊.     

New spray congealing atomizer for the microencapsulation of highly concentrated solid and liquid substances

A new pneumatic atomizer for spray congealing, called wide pneumatic nozzle (WPN), was developed. To evaluate its performance, microparticles containing highly concentrated either solid drug (Propafenone hydrochloride, PRF) or liquid nutraceutical (Vitamin E, VE) have been prepared and characterized. The results showed that the spray congealing nozzle enabled the production of spherical and not aggregated microparticles with high yields (95% w/w) and relatively narrow size distributions; moreover, increasing the viscosity of the suspension from 50 to 500 mPa s, the particle size increased. The loading of the drug was high for microspheres (50% for PRF and 30% for VE) and the encapsulation efficiency was good for all formulations. The drug release was easily modified according to the nature of the used excipients, as both lipophilic (carnauba wax, cetearyl and stearyl alcohols) and hydrophilic (PEG 4000) carriers were employed. Moreover the results evidenced that it was possible to encapsulate actives (VE) that are in a liquid form and to enhance their availability. In conclusion the developed spray congealing nozzle was able to nebulize very viscous systems that are usually not processed by conventional apparatus and to produce microspheres with high and uniform drug content.     

Correlation of laboratory and production freeze drying cycles

The purpose of this study was to develop the correlation of cycle parameters between a laboratory and a production freeze-dryer. With the established correlation, key cycle parameters obtained using a laboratory dryer may be converted to those for a production dryer with minimal experimental efforts. In order to develop the correlation, it was important to consider the contributions from the following freeze-drying components: (1) the dryer, (2) the vial, and (3) the formulation. The critical parameters for the dryer are the shelf heat transfer coefficient and shelf surface radiation emissivity. The critical parameters for the vial are the vial bottom heat transfer coefficients (the contact parameter Kcs and separation distance lv), and vial top heat transfer coefficient. The critical parameter of the formulation is the dry layer mass transfer coefficient. The above heat and mass transfer coefficients were determined by freeze-drying experiments in conjunction with mathematical modeling. With the obtained heat and mass transfer coefficients, the maximum product temperature, Tbmax, during primary drying was simulated using a primary drying subroutine as a function of the shelf temperature and chamber pressure. The required shelf temperature and chamber pressure, in order to perform a successful cycle run without product collapse, were then simulated based on the resulting values of Tbmax. The established correlation approach was demonstrated by the primary drying of the model formulation 5% mannitol solution. The cycle runs were performed using a LyoStar dryer as the laboratory dryer and a BOC Edwards dryer as the production dryer. The determined normalized dried layer mass transfer resistance for 5% mannitol is expressed as RpN=0.7313+17.19l, where l is the receding dry layer thickness. After demonstrating the correlation approach using the model formulation 5% mannitol, a practical comparison study was performed for the actual product, the lactate dehydrogenase (LDH) formulation. The determined normalized dried layer mass transfer resistance for the LDH formulation is expressed as RpN=4.344+10.85l. The operational templates Tbmax and primary drying time were also generated by simulation. The cycle run for the LDH formulation using the Edwards production dryer verified that the cycle developed in a laboratory freeze-dryer was transferable at the production scale.     

Gliadin matrices for microencapsulation processes by simple coacervation method

The aim of this study was to use a vegetal protein (gliadin) as a wall-forming component to produce microcapsules. The microencapsulation technique employed was the simple coacervation method and the encapsulated product was a non-food oil, hexadecane. Hexadecane was emulsified by a gliadin solution and the coacervation phenomena induced by adding a salt-solution in the continuous phase of the emulsion containing gliadin. The study of the coacervation conditions has shown that the richer in protein the continuous phase, the smaller the quantity of salt required. The main problem of the microencapsulation process by salting-out was to control the capsule size and the agglomeration of the capsules. This study succeeded in preventing the agglomeration phenomenon by adjusting the kinetics of the salt addition. When the feed rate of salt solution was very slow, this aggregation was considerably decreased. The suitable quantity of cross-linker (glutaraldehyde) to harden the microcapsules was determined by an electrophoresis method. The effect of different process parameters (gliadin concentration, quantity and addition kinetics of the coacervation agent, cross-linker concentration) was studied with regard to the final microcapsule characteristics (shape, size, composition, and mechanical resistance evaluated by a centrifugation test).