Abstract
Spray drying and electrospraying are well-established drying processes that already have proven their value in the pharmaceutical field. However, there is currently still a lack of knowledge on the fundamentals of the particle formation process, thereby hampering fast and cost-effective particle engineering. To get a better understanding of how functional particles are formed with respect to process and formulation parameters, it is indispensable to offer a comprehensive overview of critical aspects of the droplet drying and particle formation process. This review therefore closely relates single droplet drying to pharmaceutical applications. Although excellent reviews exist of the different aspects, there is, to the best of our knowledge, no single review that describes all steps that one should consider when trying to engineer a certain type of particle morphology. The findings presented in this article have strengthened the predictive value of single droplet drying for pharmaceutical drying applications like spray drying and electrospraying. Continuous follow-up of the particle formation process in single droplet drying experiments hence allows optimization of manufacturing processes and particle engineering approaches and acceleration of process development.
Highlights
The need for more sophisticated particles for pharmaceuticals, food products, ceramics, and catalysis has increased in recent years [1]
Wulsten et al applied scanning electron microscopy (SEM) to characterize the morphology of particles obtained after drying of itraconazole and poly(vinylpyrrolidone-co-vinyl acetate) (PVP-VA) 64/HPMC dissolved in ethanol and DCM mixtures [29]
In indus(1tr1i)al spray drying for example, such small particles are generated, indicating that the characteristic drying rate curve (CDRC) could result in where pv,s and pv,g are the vapor pressure at the fully wetted surface and in the bulk gas of the environment, respectively, and the constant β1 is the external mass transfer coefficient
Summary
The need for more sophisticated particles for pharmaceuticals, food products, ceramics, and catalysis has increased in recent years [1]. Solvent evaporation will take place at the droplet surface and, after drying is completed, the final particles can be collected [5] The difference between both techniques is that, in the case of spray drying, drying occurs at an increased temperature, while in the case of electrospraying the application of a high voltage leading to small droplets makes it possible to dry the droplets at room temperature. The diffusional motion of the solutes towards the center of the droplet becomes lower than the reduction rate of the droplet diameter due to the constant rate solvent loss At this point, crust formation will occur due to solute enrichment at the droplet surface, leading to decreased drying rate and introducing the second drying stage [1]. FFiigguurree22. .SScchheemmaattiicc iilllluussttrraattiioonn ooffssiinngglleeddrroopplleettddrryyininggmmeetthhooddss:: ((AA))GGllaassssfiflialammeenntt,,((BB))AAccoouussttiicc lleevvitiatatitoionnororlelveivtaittaiotinonbybayiraflirowfl,owwh, ewrehbeorethbaottrhanasdtruacnesrd(uocrearng(oe)raanngdea) raenfldecatorre(fyleeclltoowr )(yaerellonwee)daerde tnoeoebdteadin taocooubsttaicinwaacvoeuss(tgicreewna)v, (eCs)(Fgrreeee-nfa),ll (mCe)thForede,-wfahllerme eathmoodn,owdihspereersae dmroopnloedt igsepneerrsaetodrr(orpedle)t pgreondeurcaetos rth(reeddr)opprloedt u(mceosdtihfieeddrforopmletd(emSooduifziaedLifmroametdael.S[o1u])z.a Lima et al [1])
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