Advantages and challenges of the spray drying technology for the production of pure drug particles and drug loaded polymeric carriers

Developments of the spray-drying technology 4.1 Introduction of the Nano Spray Dryer B-90 4.2 Scale-up from Mini Spray Dryer B-290 to industrial scale 4.3 Production of nanocomposite

Alejandro Sosnik, Katia P Seremeta

PII: S0001-8686(15)00076-7

DOI: doi: 10.1016/j.cis.2015.05.003

Reference: CIS 1537

To appear in: Advances in Colloid and Interface Science

Please cite this article as: Sosnik Alejandro, Seremeta Katia P., Advantages and lenges of the spray-drying technology for the production of pure drug particles and

chal-drug-loaded polymeric carriers, Advances in Colloid and Interface Science (2015), doi:

10.1016/j.cis.2015.05.003

This is a PDF file of an unedited manuscript that has been accepted for publication.

As a service to our customers we are providing this early version of the manuscript The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Institute of Nanobiotechnology, National Science Research Council (CONICET),

Buenos Aires, Argentina 3

Department of Pharmaceutical Technology, Faculty of Pharmacy and Biochemistry,

University of Buenos Aires, Buenos Aires, Argentina

4

Department of Basic and Applied Sciences, Universidad Nacional del Chaco Austral,

Pcia Sáenz Peña, Chaco, Argentina

*Corresponding author

Prof Alejandro Sosnik, Ph.D

Laboratory of Pharmaceutical Nanomaterials Science, Department of Materials Science and Engineering, Technion-Israel Institute of Technology

Technion City, 3200003 Haifa, Israel

Email: alesosnik@gmail.com, sosnik@tx.technion.ac.il

of submicron particles with high yield, even for small sample amounts, have been introduced into the market This review describes the most outstanding advantages and challenges of the spray-drying method for the production of pure drug particles and drug-loaded polymeric particles and discusses the potential of this technique and the more advanced equipment to pave the way toward reproducible and scalable processes that are critical to the bench-to-bedside translation of innovative pharmaceutical products

Keywords: Spray-drying; pure drug particles; polymeric nanoparticles; polymeric

microparticles; nanocomposite microparticles; drug-encapsulation

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Content

1 The spray-drying technique

2 Main advantages of the spray-drying process

3 Main challenges of the spray-drying process

4 Developments of the spray-drying technology

4.1 Introduction of the Nano Spray Dryer B-90

4.2 Scale-up from Mini Spray Dryer B-290 to industrial scale

4.3 Production of nanocomposite microparticles

5 Spray-drying process applied to overcome biopharmaceutical disadvantages of drugs

5.1 Production of pure drug particles

5.2 Production of drug-loaded polymeric carriers

5.2.1 Prolonged and targeted drug delivery systems

5.2.2 Polymorphic changes of drugs after spray-drying process

5.2.3 Conservation of the activity of active agents after spray-drying process 5.2.4 Different routes of administration of drug-loaded polymeric carriers

6 Conclusions and perspectives towards translation into clinics

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1 THE SPRAY-DRYING TECHNIQUE

Spray-drying is a technique based on the transformation of a fluid into a dry powder by atomization in a hot drying gas stream that is generally air [1] The spray-drying process consists of four fundamental steps: (i) atomization of the liquid feed, (ii) drying of spray into drying gas, (iii) formation of dry particles and (iv) separation and collection of the dry

product from the drying gas [2-4] Figure 1 shows a scheme of the conventional

spray-drying process First, the fluid is fed into the spray-drying chamber by a peristaltic pump through an atomizer or nozzle that can be a rotary atomizer, a pressure nozzle or a two-fluid nozzle and the atomization occurs by centrifugal, pressure or kinetic energy, respectively [5] The small droplets generated (micrometer scale) are subjected to fast solvent evaporation [6,7] leading to the formation of dry particles that are separated from the drying gas by means of a cyclone or bag filter that deposes them in a glass collector

situated in the bottom of the device [8,9] Heng et al described in detail the major

phases involved in spray-drying process [10] In addition, a description of the emergence and evolution of this technology and the hardware used in the process is available in the literature [11] The fluid feeds in spray-drying can be solutions, suspensions, emulsions, slurries, pastes or melts [12-14] Solid products obtained after the process have the advantage of higher chemical and physical stability compared to liquid formulations In addition, they can be used as precursors for the production of other suitable dosage forms such as capsules or tablets [15-17]

The operation configurations in spray-drying can be open-loop or closed-loop The

former uses air as drying gas that is not re-circulated, while the latter an inert gas (e.g., nitrogen) that is re-cycled in the drying chamber throughout the entire process The

current flow (opposite direction) (Figure 2) In the first case, the final product is in

contact with the coolest air, hence is preferable for the drying of heat-sensitive materials [2] In the second case, the dry product is in contact with the hottest air and therefore it cannot be used with temperature-sensitive materials, but is desirable in terms of higher thermal efficiency In addition, there are intermediate configurations with mixed flow between co-current and counter-current [20-21]

The variables that affect the characteristics of the product and that can be tuned are (i)

process parameters, (ii) properties of the liquid feed and (iii) equipment design (Table 1)

[6, 9, 22-26] For example, high flow rate of the liquid feed, large nozzle diameter and high formulation concentration favor the formation of larger particles Conversely, low surface tension, high atomization pressure and small nozzle diameter render smaller particles Regarding the particles morphology, faster solvent evaporation rate (lower point boiling) usually leads to particles that are more porous due to shorter time for the droplets shrinkage [21,27-29] Finally, the air outlet temperature is dependent on other process variables [9,24] Nandiyanto and Okuyama reviewed in detail the particle design (i.e control of size and morphology) during the spray-drying process to suit specific applications [30]

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2 MAIN ADVANTAGES OF THE SPRAY-DRYING PROCESS

Spray-drying is a technique widely used in the pharmaceutical, chemical, materials, cosmetic and food industries [3, 31-32] The first patent concerning this technology was

in the early 1870s Thereafter, spray-drying underwent a constant development and

evolution [11] Patel et al recently reviewed the patents employing spray-drying in the

pharmaceutical, the food and the flavor industry [33] In general, this technique is very appealing both under laboratory and industrial setups because it is rapid, continuous, reproducible, single-step, and thus, scalable without major modifications [1,28,34] In this context, the final drying step required in other common techniques used to produce particles (e.g., emulsion/solvent evaporation) is not required in spray-drying [35-37] Moreover, a successful bench-to-bedside translation greatly depends on the fulfillment

of two conditions: scalability and cost-effectiveness Spray-drying complies with both [38,39] Moreover, when spray-drying is compared to other drying processes commonly used in industry such as freeze-drying, it is shorter and cheaper because it does not involve deep cooling, usually associated with great energy consumption [32,40-43] Therefore, some researchers have explored the use of spray-drying as an alternative method to freeze-drying [2,17,44-46]

As previously mentioned, another remarkable advantage of spray-drying is the possibility to dry a broad spectrum of compounds including heat-sensitive substances without major detrimental effects [26,47] This owing to the atomization of the liquid into small droplets with high surface area-to-volume ratio that results in very fast solvent evaporation [7] For example, in a co-current flow setup, the product temperature is 10

to 20°C below the air outlet temperature [48,49] Moreover, although during the drying

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process, the droplets could be exposed to high temperature, this exposure time is extremely short (in the range of milliseconds or seconds) [18,35,50] Under these conditions, drug degradation is not anticipated [51] The spray-drying technique was conceived as a dehydration process used to prolong the lifespan of the product At the same time, it has increasingly attracted the interest of researchers to encapsulate drugs, extracts, aromatic oils, pigments, and flavors within different types of carriers such as polymeric nanoparticles (NPs) and microparticles (MPs) and nanocomposite MPs [42,43,52] In addition, spray-drying is a processing method with great inherent potential

to produce pure drug particles [39] Table 2 summarizes the main advantages of

spray-drying over conventional methods for the production of pure drug particles and polymeric carriers A remarkable advantage is that the powders obtained by spray-drying have better flow properties than the conventional formulations For example,

Anish et al obtained MPs of poly(D,L-lactide acid) (PLA) both by spray-drying and

double emulsion/solvent evaporation with angle of repose of 29.7º and 42.2º, respectively, indicating excellent flow property in the first case and poor in the second one [26] Finally, regarding the yield of the process, at industrial scale is generally close

to 100% [53]

3 MAIN CHALLENGES OF THE SPRAY-DRYING PROCESS

Regardless of the numerous advantages displayed by this technology, when traditional spray-dryers are used, the yield strongly depends on the work scale Thus, yields are high in larger scale setups because the fraction lost is an increasingly smaller component of the total production volume [37,54], while in laboratory scale they are still far from optimal, the yield being in the 20-70% range [5,12,14] Generally, low yield is

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due to the loss of product in the walls of the drying chamber, amounts being relatively constant In addition, fine particles (<2 µm) usually pass into the exhaust air due to ineffective separation capacity of cyclone [8,53,55] However, some separators (e.g.,

filter systems) are effective under industrial settings to increase the yield [8] Cevher et

al obtained spray-dried chitosan microspheres loaded with vancomycin hydrochloride

from a 1% v/v acetic acid solution containing different polymer:drug ratios (1:1, 2:1, 3:1 and 4:1, w/w) using a laboratory scale spray-dryer (Mini Spray Dryer B-191, Büchi) to be

implanted in proximal tibia of rats with methicillin-resistant Staphylococcus aureus

osteomyelitis [56] After spray-drying, the microspheres were collected and weighed to determine the production yield, values being relatively low (~47-50%) owing to the small batch size (200 mL of 0.5% w/v polymer solution) and the loss of some liquid droplets inside the wall of the drying chamber [56] The production of particles at the nanometer scale is limited not only by the low separation capacity of cyclone but also because insufficient forces of liquid atomization (pressure and centrifugal) to obtain large amount

of submicron particles [23,57] This phenomenon affects the size and size distribution that might be crucial in the development of certain drug delivery systems, especially envisioned for intravenous administration [58-60]

4 DEVELOPMENTS OF THE SPRAY-DRYING TECHNOLOGY

4.1 Introduction of the Nano Spray Dryer B-90

Aiming to overcome the main drawbacks of this technology and extend its application to the production of more complex particle configurations, Büchi (Labotechnik AG, Switzerland) introduced the Nano Spray Dryer B-90 which is the fourth and newest generation of laboratory scale spray-dryers developed by the company following the

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previous generations (Mini Spray Dryers B-190, B-191 and B-290) [10] This device is suitable for the production of fine particles (300 nm-5 µm) with satisfactory yield, even for small sample amounts (milligrams) [61,62] This feature is very relevant especially at the very early stages of product development and when expensive materials, such as monoclonal antibodies, are used [63] This spray-dryer contains a vibrating mesh spray with small orifices (4.0, 5.5 or 7.0 μm) that is driven by a piezoelectric actuator at a specific ultrasonic frequency (60 kHz) producing ultra-fine droplets that result in small

particles after drying with narrow and reproducible size distribution Lee et al obtained

spray-dried bovine serum albumin (BSA) NPs from aqueous solutions of BSA (1-2% w/v) and Tween® 80 surfactant (0.05% w/v) using Nano Spray Dryer B-90 with different

mesh spray size [5] Figure 3 shows the scanning electron microscopy (SEM) images of

the particles obtained with 4.0, 5.5 and 7.0 µm spray meshes orifices, corresponding to particles sizes of approximately 0.7, 1.2 and 2.6 µm, respectively [5] A similar tendency was observed by other authors where the average particle size and the size polydispersity became smaller with decreasing mesh aperture sizes [64] Moreover, this innovative device contains a high-efficiency electrostatic powder collector that allows high yields above 70% when process and formulation parameters undergo appropriate optimization In addition, it uses a laminar drying gas flow through the drying chamber resulting in mild, uniform and instant heating [4-5,14,23,61] On the other hand, it should

be noted that the diameter of the orifices of the vibrating mesh spray is smaller than the nozzles of conventional spray-dryers (500-700 μm), resulting in higher processing times and preventing the use of some highly viscous polymer solutions [57] In addition, sometimes products deposit as a heavy crust on the vibrating mesh of the device and

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not only reduce the yield but also might contaminate the fine particles collected due to the burst of the crust on the collector [61] Other limitation of the device is that the vibrating mesh causes mechanical shear of atomization and shear-sensitive substances

can be altered [65] Heng et al reviewed on the advances of Nano Spray Dryer B-90 for

the production of NPs suited for several drug delivery applications and presented a schematic diagram of this device and the functional principle of mesh vibration and the electrostatic particle collector [10] Several authors used this spray-dryer for the

production of NPs and MPs For example, Li et al evaluated its performance in the

production of polymeric particles using five representative wall materials (arabic gum, whey protein, polyvinyl alcohol or PVA, modified starch and maltodextrin) dissolved in ultrapure water (0.1, 1 and 10% w/w) [14] The micrographs of SEM showed homogeneous and spherical particles and the peak maxima of size distributions were

below 1 μm in all cases (Figure 4) The yield varied from 43.0% to 94.5%, according to

the type and concentration of the wall material [14] Furthermore, the authors showed the utility of this device for encapsulation of lipid nano-emulsions (<100 nm) obtained by

a low-energy method and mixed in a later stage with 1% w/w wall material aqueous solution (weight ratio of 1:4) The non-aggregated submicron solid particles obtained were re-dispersible in water without size increase Finally, they also obtained nano-crystals of both hydrophilic (sodium chloride, 0.1 and 1% w/w in water) and lipophilic (furosemide, 1.25% w/w in acetone) compounds by spray-drying, resulting in homogeneous powders with size peaks between 517 and 993 nm in the first case and 1.24 µm in the second case The yield values were between 69.3% and 85.4% [14]

Using the same equipment (with spray mesh diameter of 7.0 µm), Harsha et al obtained

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mucoadhesive carbopol 934P microspheres loaded with sitagliptin (a new anti-diabetic drug) from a solution of polymer and drug in water for sustained drug release after oral administration [66] The effect of three factors, namely carbopol concentration, inlet temperature and feed flow rate, on the yield were studied by means of a central composite design The former two factors had major, while the latter had minor effect on the yield; values under different settings ranged from 64% to 92% for a powder amount

of 500 mg This allowed the optimization of the conditions for the preparation of microspheres with high yield Drug-loaded microspheres presented free flowing with angle of repose of 24º and narrow size distribution in the 2-8 µm range [66] Even though, this new device has extended the possibilities of the spray-drying technique, there are still limitations to scale up the process to the pilot and the industrial scales

4.2 Scale-up from the Mini Spray Dryer B-290 to the industrial scale

Despite the remarkable advantages presented by the Nano Spray Dryer B-90 with respect to previous generations of laboratory scale spray-dryers, the Mini Spray Dryer B-

290 enables the more straightforward scale-up of the process initially to pilot and later

on to industrial production [67] However, to achieve this, equipment designed for larger

scale is required (see below) Table 3 summarizes the major differences between both

systems Zhu et al developed a formulation and production process at pilot scale to

stabilize a recombinant hemagglutinin (rHA) influenza antigen, HAC1, as a model vaccine candidate [54] First, eight HAC1 formulations containing different excipients were produced using the Mini Spray Dryer B-290 and powders were characterized by differential scanning calorimetry (DSC), X-ray powder diffraction (XRD) and SEM Then, the potency of the HAC1 antigen in all formulations was measured using a single radial

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immunodiffusion assay Immunogenicity studies were conducted in mice to evaluate the effect of the formulation components and the spray-drying process on the

immunogenicity of the HAC1 vaccine Based on the in vitro evaluation of the antigen

content (process loss and stability), the antigen structure, the powder properties and the

in vivo immunogenicity, one formulation (containing 7.5% trehalose, 2.5% hydrolyzed

gelatin and 360 μg/mL HAC1) was selected for pilot scale-up using conditions that were established in the laboratory scale spray-dryer Three batches of 50 g particles in the 0.5-30 μm size range (100-fold larger than the laboratory scale) were obtained in a pilot scale laboratory dryer BLD-1 (Bend Research, Inc., Bend, Oregon) with yields >90% Results of pilot scale formulation replicated the findings observed for the optimized formulation at the laboratory scale All three batches maintained stable physical properties and antigen content throughout the 6-month stability study at storage temperatures from -20ºC to 50 ºC Moreover, they induced an immune response that was equivalent to the bulk HAC1 vaccine control, suggesting that the pilot scale process did not alter the immunogenicity of the HAC1 antigen and that the production process is amenable to industrial scale production [54] Due to the challenging nature of the scale-

up process, two important spray-dryer producers (Büchi Labortechnik AG and GEA Niro A/S in small and large scale, respectively) reported on a practical procedure to scale up

a spray-drying process from Mini Spray Dryer B-290 to Niro MOBILE MINORTM (pilot plant spray-dryer) with two-fluid nozzle [68] The critical process conditions were maintained constant during the scale-up, while those with the least impact were adjusted In this way, they produced a powder with similar residual moisture content (~0.05 kg water/kg powder) and similar particle size (~20 µm), but at a higher production

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rate (feed flow rate of 1.41 kg/h instead of 0.60 kg/h) [68] Laboratory scale is appropriate for use in preclinical stages of drug development These results place the Mini Spray Dryer B-290 as a reliable laboratory scale model to optimize the process parameters towards the larger production scale required in the clinical stage [69]

4.3 Production of nanocomposite microparticles

One strategy to minimize the loss of fine particles during the separation and collection step in traditional spray-dryers is to produce MPs composed of self-assembled NPs with

or without carrier materials (nanocomposite MPs) where the size growth increases the collection extent Furthermore, these MPs are more physically stable than the NPs because the smaller size of the NPs could lead to strong inter-particle interactions and

subsequent aggregation [60, 70-73] Oliveira et al observed these interactions between

NPs obtained from aqueous solutions of different polymers (arabic gum, cashew nut gum, sodium alginate, sodium carboxymethyl cellulose and Eudragit® RS100) and a model drug (vitamin B12) by means of the Nano Spray Dryer B-90 [57] NPs were subjected to agglomeration during the drying process resulting in micrometer particles when determined by a laser diffraction technique However, when they were analyzed

by SEM, individual NPs clustered together were observed, which explained the greater size determined by laser diffraction [57] To prevent irreversible aggregation phenomena

of the NPs after spray-drying, “spacer” excipients such as sucrose, trehalose, and leucine can be used [74] In addition, in some cases, the small size and the insufficient inertia of the NPs limit their administration For example, NPs with a small aerodynamic

diameter (d ae) between 100 nm and 1 µm cannot be used for inhalation because the small size precludes their retention in the airways and favor their elimination by

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exhalation [63,75] Therefore, NPs could be replaced by nanocomposite MPs with a

more suitable d ae in the 1-5 µm range that undergo deposition in the lung [73,76,77]

Hadinoto et al obtained large hollow carrier particles without carrier materials from

suspensions of biocompatible acrylic polymer NPs loaded with a model drug (salbutamol sulfate or aspirin) initially obtained by a nanoprecipitation technique [71] The large hollow aggregates particles, whose shells were composed of primary NPs, exhibited a

large geometric diameter (d g ~ 10-15 µm) but with a small d ae (1≤ d ae ≤3 µm) highly suitable for dry powder inhaler (DPI) applications with ability to disassociate into primary NPs once they are exposed to alveolar lung region SEM images of the large hollow

nanoparticulate aggregates are presented in Figure 5A (aspirin-loaded particles) and Figure 5B (salbutamol sulfate-loaded particles) and it is noteworthy that some very fine

particles (d g ≤3 µm) also were observed In addition, Figure 5C,D showed the

nanoparticulate aggregates that compose the surface of the large hollow particles [71]

On other hand, water-soluble carbohydrate excipients such as lactose, sucrose, trehalose or mannitol increase the size of the drug carrier to the micrometer scale and maximize lung deposition and retention [75,78,79] These excipients are widely used due to their non-toxicity and biodegradability after pulmonary administration [70,80] In addition, the United States Food and Drug Administration (US-FDA) has approved them

as pharmaceuticals [50] In these cases, excipient MPs act as inert carriers of NPs enabling their fast release due to the high aqueous solubility of microcarriers [81] Therefore, a requisite of these systems is that the MPs re-disperse or disassociate completely into primary NPs when they are exposed to the physiological medium because the NPs have the ability to delay or avoid unwanted mucociliary clearance [48,

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79,80] Figure 6 schematizes the decomposition of nanocomposite MPs into NPs after

pulmonary administration [72] Ungaro et al developed tobramycin-loaded lactide-co-glycolide acid) (PLGA) NPs embedded in an inert microcarrier of lactose

poly(D,L-referred to as nano-embedded MPs (NEM) for pulmonary prolonged delivery system [75] Tobramycin-loaded PLGA NPs were prepared by a modified emulsion/solvent diffusion technique in the presence of helper polymers such as PVA and alginate to optimize size, surface properties, drug loading and release up to one month These

drug-loaded NPs (250-300 nm) displayed good in vitro antimicrobial activity against P aeruginosa planktonic cells Then NPs were dispersed in a lactose aqueous solution

and this dispersion was diluted with ethanol (ethanol/water ratio 1:1) for obtaining NEMs Dispersions were processed in a Mini Spray Dryer B-190 equipped with a high-performance cyclone and the produced NEMs displayed very good flow properties with about 100% of the capsule content being emitted during aerosolization and very low

mass median aerodynamic diameter (MMAD) of approximately 3.4 µm In vivo

biodistribution studies showed that PVA-modified alginate/PLGA NPs reached the deep

lung after intra-tracheal administration in rats (Figure 7) [75] Following this same

concept, other authors developed nanocomposite MPs for suitable pulmonary administration [48,70,72,78,80,82] However, the performance of DPIs highly depends

on formulation and device design and usually DPIs producing d ae of 3-6 µm deposit about 40-70% of the dose in the mouth-throat region due to inertial impaction, whereas particles in the size range 400-900 nm achieve near zero deposition in this region [83] Therefore, an excipient enhanced growth (EEG) strategy that delivers an inhaled submicron particle formulation to minimize depositional losses in mouth and throat was

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proposed The particles combined drug and hygroscopic excipients that after inhalation absorb humidity of the lungs, increasing the particles size (2-4 µm) and weight and

ensuring lung deposition [83] Thus, Son et al developed a submicrometer powder

formulation suitable for EEG application from a convenient DPI platform using albuterol sulfate, mannitol, L-leucine, and poloxamer 188 as model drug, hygroscopic excipient, dispersibility enhancer and surfactant, respectively [83] The combination particles were obtained from a water:ethanol (80:20% v/v) solution containing 0.5% solids using the

Nano Spray Dryer B-90 Figure 8 shows a SEM image of an optimized formulation with

d ae of 2.3 µm that exhibited excellent aerosolization properties using a conventional DPI (Aerolizer®), with only 4.1% of mouth-throat deposition using a realistic model In addition, emitted doses were greater than 80% of the capsule content [83]

5 SPRAY-DRYING PROCESS APPLIED TO OVERCOME BIOPHARMACEUTICAL DISADVANTAGES OF DRUGS

5.1 Production of pure drug particles

Micro and nanotechnology strategies represent very effective means to overcome biopharmaceutical drawbacks and sustain, control and target the release of drugs For example, drugs with poor aqueous solubility often exhibit limited oral absorption and erratic bioavailability because the dissolution rate is the limiting factor for the absorption Thus, the slow dissolution rate is compensated by the administration of higher doses [84-87] A strategy to overcome this drawback is the production of NPs and MPs of pure drug that provide a larger surface area-to-volume ratio and hence a faster drug dissolution rate than the raw material [88] The effect of the size on the dissolution rate

is expressed by the Noyes-Whitney equation [89,90]

This equation indicates a directly proportional relation between the dissolution rate and the specific surface area of the solid [88] Thus, increased drug dissolution rate allows a faster absorption rate and thus, it is usually associated with enhanced bioavailability [89] Spray-drying is a potential technology to produce pure drug particles with their associated benefits [14,64,91,92]

5.2 Production of drug-loaded polymeric carriers

Many drugs undergo degradation in the physiological environment, this phenomenon leading to a decrease of the bioavailability [86] Therefore, the incorporation of the drug into particles could protect the cargo against harsh conditions such as chemical and

enzymatic degradation [28,93] For example, Seremeta et al encapsulated the anti-HIV

didanosine within poly(epsilon-caprolactone) (PCL) MPs both by suspension and simple emulsion followed for spray-drying to avoid its fast gastric degradation that leads to low oral bioavailability (20-40%) [51] The device used in this study was a Mini Spray Dryer B-191 Drug-loaded MPs were spherical with average diameter between 36 and 118 μm

(Figure 9) and yield between 37.7% and 64.9% Oral administration of the optimized

formulation to rats resulted in a statistically significant 2.5-fold increase of the drug

bioavailability with respect to a didanosine aqueous solution (Figure 9C) [51]

Spray-drying enables the encapsulation of active agents of diverse physicochemical properties

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within different polymer matrices (synthetic, semi-synthetic or natural origin) under very

mild and non-detrimental conditions and with high encapsulation efficiency (%EE) and loading capacity (%LC) [16,94] An additional advantage is that this technology is less

dependent on the solubility of the drug and the polymer than other methods [37] (Table 2) The particles can be obtained directly by spray-drying of solutions or suspensions

containing the compounds to dry or by atomizing particles pre-formed by emulsification, de-solvation or solvent displacement method The particles obtained in both cases present different features Usually when the particles are produced by a previous method and this technology is used to remove the solvent where the particles were suspended, the size of the particles remains practically unchanged after re-dispersion in

aqueous media [95,96] Beck-Broichsitter et al obtained two formulation types loaded

with sildenafil (as model drug) for pulmonary administration using Nano Spray Dryer

B-90 [23] In first the case, submicron-to-micron particles (567-1129 nm) were produced by spray-drying of organic solutions of drug and PLGA In the second case, composite MPs (2.8-4.4 µm) were obtained from aqueous suspension of drug-loaded PLGA NPs produced by emulsion/solvent evaporation followed by spray-drying The surface of

submicron particles was smooth (Figure 10A) while the surface of composite MPs was decorated by single NPs (Figure 10B) and thus exhibited a larger specific surface area

Upon contact with aqueous media, the composite MPs underwent disintegration into individual NPs with only a negligible increase in mean particle size Aerodynamic parameters after aerosolization of both particle types were appropriate for deposition in deep lungs (≤ 4 µm) The in vitro release assays showed that composite MPs released the drug within 90 min, while the drug release from submicron particles was

or the glass transition temperature of others such as PLGA (Tg = 40-60ºC) or PLA (Tg < 60ºC) [28,35,98] In addition, organic solvent combinations can be used to adjust the solubility of the polymer and the drug and the boiling point that results in particles with the desired properties In the latter case, the advantage of water is associated with the non-toxicity and the reduction of the risk of explosion [1,114] Furthermore, mixtures of water and suitable water-miscible organic solvents such as ethanol could reduce the final boiling point of the solvent system and enable the spray-drying at lower temperature [74,80,83]

5.2.1 Prolonged and targeted drug delivery systems Noteworthy that the use of suitable

polymers could also modulate the release of the encapsulated drug, prolonging the particles/mucosa interaction and increasing the amount of drug that is absorbed [116] This would also ensure constant plasma drug concentrations for more prolonged time

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[49,117-120] For example, Gavini et al obtained spray-dried chitosan hydrochloride or

glutamate MPs for nasal administration of carbamazepine that due to its poor water solubility has slow and irregular gastrointestinal absorption [121] Firstly, a solution of drug in acetone and an aqueous solution of chitosan salt were homogenized and then

fed at a Mini Spray Dryer B-191 The volume surface diameter (d vs) of MPs was

approximately 2 µm with narrow size distribution and high %EE (89-95%) The loading

of carbamazepine into MPs led to an improvement of the in vitro dissolution/release rate

in phosphate buffer (pH 7.0) with respect to pure drug (powder raw), mainly due to

mucoadhesiveness In vivo tests in sheep showed that the nasal administration of

carbamazepine-loaded chitosan glutamate MPs remarkably increased the plasma concentration-time curve (AUC) by 5.6-fold compared to the pure drug powder

area-under-(Figure 11) In addition, the time to reach the maximum plasma concentration (tmax) at

10 min after administration of the MPs indicated very rapid drug absorption from the

nose (Figure 11) [121]

The particles also could target drugs to specific sites, contributing to decrease the effective dose, the administration frequency and/or the drug systemic toxicity and thus,

improve patient compliance [36,47,122,123] For example, Crcarevska et al designed a

targeted oral delivery system of Eudragit® S100-coated chitosan-Ca-alginate MPs loaded with budesonide against inflammatory bowel diseases in the colonic region using spray-drying process [124] Both alginate and chitosan exhibit mucoadhesive properties involving interactions with the intestinal mucus layer In addition, enteric coating of MPs with acid-resistant Eudragit® S100 avoided the nonspecific and premature adherence to other parts of gastrointestinal tract such as stomach (pH 2.0) and allowed colon-specific

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delivery (pH 7.4) of budesonide over a more prolonged period of time This system accelerated the healing in a rat model of induced colitis compared to uncoated MPs and drug suspension [124]

5.2.2 Polymorphic changes of drugs after spray-drying process Spray-drying can induce

polymorphic changes or amorphization of the encapsulated drug and enhance its

solubility and dissolution rate [85,114,125] For example, Tran et al developed solid

dispersion NPs to enhance the physicochemical properties and bioavailability of raloxifene (poorly water-soluble) using spray-drying [114] The formulation was prepared dissolving PVP K30 and Tween® 20 in water and dispersing raloxifene The resulting dispersion was fed to a Mini Spray Dryer B-190 and particles had a mean size of approximately 180 nm DSC and XRD assays showed that raloxifene changed from a

crystalline to an amorphous state after spray-drying (Figure 12) This change and size

reduction led to a significant increase in aqueous solubility and dissolution rate of drug Furthermore, oral administration at rats of the formulation showed higher maximum plasma concentration (Cmax, 3.3-fold) and AUC0-∞ (2.3-fold) than the pure drug powder

[114] Oh et al produced NPs loaded with flurbiprofen (poorly water-soluble) by

solidifying a nanoemulsion using sucrose as carrier via spray-drying [126] After reconstitution, NPs (300 nm) improved the dissolution rate by a factor of about 70,000 compared to flurbiprofen powder due to transformation of the drug from a crystalline to

an amorphous form and the reduction of the size to the nanoscale When these NPs were orally administered to rats, the AUC of the drug was about 9-fold higher than the one of the commercial product [126] The change from a crystalline to an amorphous form also stresses the potential of spray-drying to produce pure drug NPs [39]

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5.2.3 Conservation of the activity of active agents after spray-drying process The

conservation of the activity of active agents encapsulated after spray-drying process is important, especially in the case of sensitive substances such as proteins and genes Several studies showed that encapsulated products retained their activity after the

spray-drying process [17,37,82,98] For example, Jensen et al encapsulated siRNA

within of NPs of PLGA into nanocomposite MPs by double emulsion/solvent evaporation and spray-drying intended for inhalation and confirmed that the integrity and biological activity of siRNA were preserved after process [82] The siRNA extracted from the nanocomposite MPs appeared intact and of the same size as before spray-drying

process when evaluated by gel electrophoresis (Figure 13) In addition, there was no

significant difference between the activity of the siRNA extracted from nanocomposite MPs and the positive control siRNA determined in cell transfection assays [82]

5.2.4 Different routes of administration of drug-loaded polymeric carriers Finally, the

particles loaded with drugs obtained by spray-drying could be administered by different routes such as oral [127-132], pulmonary [12,23,82,133,134), ophthalmic [93,111,135], parenteral [22,38,136], nasal [60,120,121,137], and vaginal [138], stressing its great versatility For example, Başaran et al obtained NPs of chitosan of different molecular

weights (low, medium and high) loaded with cyclosporine A (10 and 25% of the polymer) for ocular administration For this, an ethanol solution of cyclosporine A was added to an acidic chitosan solution and the final solution was spray-dried via Mini Spray Dryer B-

190 to obtain the NPs [111] These had spherical shape and size between 317 and 681

nm with positive zeta potential ranging between +22 and +35 mV The NPs of chitosan

of medium molecular weight showed higher %EE of cyclosporine A and more uniform

another work, Bhowmik et al developed a melanoma cancer vaccine based in MPs of

albumin, ethylcellulose, HPMC acetate succinate and antigen (obtained from Cloudman S-91 melanoma cancer cells) [38] The MPs were obtained from aqueous solutions of polymers and antigen using the Mini Spray Dryer B-191 They presented spherical surface and mean particle size between 0.625 and 1.4 µm Antigen-loaded MPs were administered in suspension with citrate buffer and polyethylene glycol via transdermal route in mice during 8-week Subsequently, mice were challenged with live S-91 tumor cells to evaluate the efficacy of the vaccination The transdermal vaccinated mice showed no measurable tumor growth 35 days after tumor injection, while the non-vaccinated control group of animals developed a palpable tumor after approximately 11

days [38] Zhang et al developed a spray-dried mucoadhesive and pH-sensitive

microspheres formulation based on a poly(methacrylate) salt intended for vaginal delivery of a model HIV microbicide (tenofovir) to prevent HIV transmission [138] To prepare tenofovir-loaded microspheres, different amounts of Eudragit® S-100 and drug were added in deionized water with an appropriate amount of sodium hydroxide to achieve complete salification The solution was then spray-dried using a Mini Spray Dryer B-290 The formulation and process parameters were screened and optimized using a fractional factorial design The optimal microspheres formulation had spherical

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shape with average size of 4.73 µm (Figure 14), yield of 68.9%, %EE of 88.7%, %LC of

2% w/w and Carr’s index of 28.3 These microspheres released over 90% of its payload within 60 min in the presence of simulated human semen (pH 7.6) Conversely, only 20% of the drug was released under the acidic pH conditions of the normal vagina due

to the low solubility of the polymer Microspheres were cytotoxic and immunogenic to vaginal/endocervical epithelial cell lines, and non-toxic to normal

non-vaginal flora In vitro tests showed that their mucoadhesion was 2-fold higher than that

of a hydroxyethylcellulose gel formulation [138]

6 CONCLUSIONS AND PERSPECTIVES TOWARDS TRANSLATION INTO CLINICS

Spray-drying is widely used due to it is a rapid, continuous, reproducible, cost-effective, easily scalable and one-step process This technology is not only used for dehydration and conservation of products but also for encapsulation of substances within different carriers such as polymeric particles The particle sizes obtained are at submicron-to-micron scale and could be administered by different routes The fast drying process avoids significant degradation of the encapsulated drugs and allows the preservation of their activity after the process Although this technology has been used for many years,

it is still undergoing evolution In this context, the introduction of new equipment that enables the production of finer particles with narrower size distributions and that prevents high product loss on the walls of drying chamber has been fundamental to envision the scale-up of production process developed in the laboratory to pilot and industrial scales However, the available equipment does not allow scale-up to large scale as a conventional spray-dryers do In the same context, the investigation of new materials that can be processed by spray-drying is another relevant pillar to consolidate

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this technology and diversify its application in pharmaceutical product development and eventually reach the market

ACKNOWLEDGEMENTS KPS thanks a Ph.D scholarship of CONICET (Argentina)

AS thanks the European Union's - Seventh Framework Programme under grant agreement #612675-MC-NANOTAR

co-poly(D,L-[4] Schafroth N, Arpagaus C, Jadhav UY, Makne S, Douroumis D Nano and microparticle engineering of water insoluble drugs using a novel spray-drying process

Colloids Surf B Biointerfaces 2012;90:8-15 doi:10.1016/j.colsurfb.2011.09.038

[5] Lee SH, Heng D, Ng WK, Chan HK, Tan RB Nano spray drying: a novel method for

preparing protein nanoparticles for protein therapy Int J Pharm 2011;403:192-200

doi:10.1016/j.ijpharm.2010.10.012

[6] Elversson J, Millqvist-Fureby A, Alderborn G, Elofsson U Droplet and particle size relationship and shell thickness of inhalable lactose particles during spray drying J Pharm Sci 2003;92:900-10 doi:10.1002/jps.10352

[7] Fatnassi M, Tourné-Péteilh C, Peralta P, Cacciaguerra T, Dieudonné P, Devoisselle

JM, et al Encapsulation of complementary model drugs in spray-dried nanostructured materials J Sol-Gel Sci Technol 2013;68:307-16 doi:10.1007/s10971-013-3170-y

ACCEPTED MANUSCRIPT

27

[8] Ståhl K, Claesson M, Lilliehorn P, Lindén H, Bäckström K The effect of process variables on the degradation and physical properties of spray dried insulin intended for

inhalation Int J Pharm 2002;233:227-37 doi:10.1016/S0378-5173(01)00945-0

[9] Schoubben A, Blasi P, Giovagnoli S, Rossi C, Ricci M Development of a scalable procedure for fine calcium alginate particle preparation Chem Eng J 2010;160:363-9 doi:10.1016/j.cej.2010.02.062

[10] Heng D, Lee SH, Ng WK, Tan RB The nano spray dryer B-90 Expert Opin Drug Deliv 2011;8:965-72 doi:10.1517/17425247.2011.588206

[11] Cal K, Sollohub K Spray drying technique I: Hardware and process parameters J Pharm Sci 2010;99:575-86 doi:10.1002/jps.21886

[12] Rabbani NR, Seville PC The influence of formulation components on the aerosolisation properties of spray-dried powders J Control Release 2005;110:130-40 doi:10.1016/j.jconrel.2005.09.004

[13] Gómez-Gaete C, Fattal E, Silva L, Besnard M, Tsapis N Dexamethasone acetate encapsulation into Trojan particles J Control Release 2008;128:41-9 doi:10.1016/j.jconrel.2008.02.008

[14] Li X, Anton N, Arpagaus C, Belleteix F, Vandamme TF Nanoparticles by spray drying using innovative new technology: the Büchi nano spray dryer B-90 J Control Release 2010;147:304-10 doi:10.1016/j.jconrel.2010.07.113

[15] Berggren J, Frenning G, Alderborn G Compression behaviour and tablet-forming ability of spray-dried amorphous composite particles Eur J Pharm Sci 2004;22:191-

200 doi:10.1016/j.ejps.2004.03.008

ACCEPTED MANUSCRIPT

28

[16] Mu L, Teo MM, Ning HZ, Tan CS, Feng SS Novel powder formulations for controlled delivery of poorly soluble anticancer drug: application and investigation of TPGS and PEG in spray-dried particulate system J Control Release 2005;103:565-

75 doi:10.1016/j.jconrel.2004.12.023

[17] Takashima Y, Saito R, Nakajima A, Oda M, Kimura A, Kanazawa T, et al drying preparation of microparticles containing cationic PLGA nanospheres as gene carriers for avoiding aggregation of nanospheres Int J Pharm 2007;343:262-69 doi:10.1016/j.ijpharm.2007.05.042

Spray-[18] Cheow WS, Li S, Hadinoto K Spray drying formulation of hollow spherical aggregates of silica nanoparticles by experimental design Chem Eng Res Des 2010;88:673-85 doi:10.1016/j.cherd.2009.11.012

[19] Ní Ógáin O, Tajber L, Corrigan OI, Healy AM Spray drying from organic solvents to prepare nanoporous/nanoparticulate microparticles of protein: excipient composites designed for oral inhalation J Pharm Pharmacol 2012;64:1275-90 doi:10.1111/j.2042-7158.2012.01488.x

[20] Mujumdar AS (Editor) Handbook of Industrial Drying, Third Edition, 2006 US: Taylor & Francis Group (CRC Press)

[21] Raffin RP, Jornada DS, Ré MI, Pohlmann AR, Guterres SS Sodium loaded enteric microparticles prepared by spray drying: effect of the scale of production and process validation Int J Pharm 2006;324:10-8 doi:10.1016/j.ijpharm.2006.06.045 [22] Khan W, Kumar N Drug targeting to macrophages using paromomycin-loaded

pantoprazole-albumin microspheres for treatment of visceral leishmaniasis: an in vitro evaluation J

Drug Target 2011;19:239-50 doi:10.3109/1061186X.2010.492524

ACCEPTED MANUSCRIPT

29

[23] Beck-Broichsitter M, Schweiger C, Schmehl T, Gessler T, Seeger W, Kissel T Characterization of novel spray-dried polymeric particles for controlled pulmonary drug delivery J Control Release 2012;158:329-35 doi:10.1016/j.jconrel.2011.10.030

[24] Park CW, Li X, Vogt FG, Hayes D Jr, Zwischenberger JB, Park ES, et al Advanced spray-dried design, physicochemical characterization, and aerosol dispersion performance of vancomycin and clarithromycin multifunctional controlled release particles for targeted respiratory delivery as dry powder inhalation aerosols Int J

Pharm 2013;455:374-92 doi:10.1016/j.ijpharm.2013.06.047

[25] Sander C, Madsen KD, Hyrup B, Nielsen HM, Rantanen J, Jacobsen J Characterization of spray dried bioadhesive metformin microparticles for oromucosal administration Eur J Pharm Biopharm 2013;85:682-8 doi:10.1016/j.ejpb.2013.05.017 [26] Anish C, Upadhyay AK, Sehgal D, Panda AK Influences of process and formulation parameters on powder flow properties and immunogenicity of spray dried polymer particles entrapping recombinant pneumococcal surface protein A Int J Pharm 2014;466:198-210 doi:10.1016/j.ijpharm.2014.03.025

[27] Littringer EM, Zellnitz S, Hammernik K, Adamer V, Friedl H, Urbanetz NA Spray drying of aqueous salbutamol sulfate solutions using the nano spray dryer B-90—The impact of process parameters on particle size Dry Technol 2013;31:1346-53 doi:10.1080/07373937.2013.793701

[28] Wan F, Bohr A, Maltesen MJ, Bjerregaard S, Foged C, Rantanen J, et al Critical solvent properties affecting the particle formation process and characteristics of celecoxib-loaded PLGA microparticles via spray-drying Pharm Res 2013;30:1065-76 doi:10.1007/s11095-012-0943-x

ACCEPTED MANUSCRIPT

30

[29] Ngan LT, Wang SL, Hiep DM, Luong PM, Vui NT, Dinh TM, et al Preparation of chitosan nanoparticles by spray drying, and their antibacterial activity Res Chem Intermed 2014;40:2165-75 doi:10.1007/s11164-014-1594-9

[30] Nandiyanto AB, Okuyama K Progress in developing spray-drying methods for the production of controlled morphology particles: From the nanometer to submicrometer size ranges Adv Powder Technol 2011;22:1-19 doi:10.1016/j.apt.2010.09.011

[31] Sen D, Khan A, Bahadur J, Mazumder S, Sapra BK Use of small-angle neutron scattering to investigate modifications of internal structure in self-assembled grains of nanoparticles synthesized by spray drying J Colloid Interface Sci 2010;347:25-30 doi:10.1016/j.jcis.2010.03.033

[32] Gong P, Zhang L, Han X, Shigwedha N, Song W, Yi H, et al Injury mechanisms of lactic acid bacteria starter cultures during spray drying: a review Dry Technol 2014;32:793-800 doi:10.1080/07373937.2013.860458

[33] Patel BB, Patel JK, Chakraborty S Review of patents and application of spray drying in pharmaceutical, food and flavor industry Recent Pat Drug Deliv Formul 2014;8:63-78 doi:10.2174/1872211308666140211122012

[34] Krishnaiah D, Sarbatly R, Nithyanandam R Microencapsulation of Morinda citrifolia

doi:10.1016/j.cherd.2011.09.003

[35] Baras B, Benoit MA, Gillard J Parameters influencing the antigen release from spray-dried poly(DL-lactide) microparticles Int J Pharm 2000;200:133-45 doi:10.1016/S0378-5173(00)00363-X

ACCEPTED MANUSCRIPT

31

[36] A G, Ren L, Zhou Z, Lu D, Wang S Design and evaluation of biodegradable enteric microcapsules of amifostine for oral delivery Int J Pharm 2013;453:441-7 doi:10.1016/j.ijpharm.2013.06.019

[37] Bowey K, Swift BE, Flynn LE, Neufeld RJ Characterization of biologically active

insulin-loaded alginate microparticles prepared by spray drying Drug Dev Ind Pharm

2013;39:457-65 doi:10.3109/03639045.2012.662985

[38] Bhowmik T, D’Souza B, Shashidharamurthy R, Oettinger C, Selvaraj P, D’Souza

MJ A novel microparticulate vaccine for melanoma cancer using transdermal delivery J Microencapsul 2011;28:294-300 doi:10.3109/02652048.2011.559287

[39] Tshweu L, Katata L, Kalombo L, Chiappetta DA, Höcht C, Sosnik A, et al Enhanced oral bioavailability of the antiretroviral efavirenz encapsulated in poly(epsilon-caprolactone) nanoparticles by a spray-drying method Nanomedicine (Lond.) 2014;9:1821-33 doi:10.2217/nnm.13.167

[40] Maury M, Murphy K, Kumar S, Mauerer A, Lee G Spray-drying of proteins: effects

of sorbitol and trehalose on aggregation and FT-IR amide I spectrum of an

doi:10.1016/j.ejpb.2004.07.010

[41] Tewa-Tagne P, Briançon S, Fessi H Spray-dried microparticles containing polymeric nanocapsules: formulation aspects, liquid phase interactions and particles

characteristics Int J Pharm 2006;325:63-74 doi:10.1016/j.ijpharm.2006.06.025

[42] Gharsallaoui A, Roudaut G, Chambin O, Voilley A, Saurel R Applications of

spray-drying in microencapsulation of food ingredients: an overview Food Res Int

2007;40:1107-21 doi:10.1016/j.foodres.2007.07.004

ACCEPTED MANUSCRIPT

32

[43] Mahdavi SA, Jafari SM, Ghorbani M, Assadpoor E Spray-drying

microencapsulation of anthocyanins by natural biopolymers: a review Dry Technol

2014;32:509-18 doi:10.1080/07373937.2013.839562

[44] Lane ME, Brennan FS, Corrigan OI Comparison of post-emulsification freeze drying or spray drying processes for the microencapsulation of plasmid DNA J Pharm Pharmacol 2005;57:831-8 doi:10.1211/0022357056406

[45] Rampino A, Borgogna M, Blasi P, Bellich B, Cesàro A Chitosan nanoparticles: preparation, size evolution and stability Int J Pharm 2013;455:219-28

doi:10.1016/j.ijpharm.2013.07.034

[46] Tshweu L, Katata L, Kalombo L, Swai H Nanoencapsulation of water-soluble drug, lamivudine, using a double emulsion spray-drying technique for improving HIV

treatment J Nanopart Res 2013;15:2040 doi:10.1007/s11051-013-2040-4

[47] Tobar-Grande B, Godoy R, Bustos P, von Plessing C, Fattal E, Tsapis N, et al Development of biodegradable methylprednisolone microparticles for treatment of articular pathology using a spray-drying technique Int J Nanomedicine 2013;8:2065-

76 doi:10.2147/IJN.S39327

[48] Lebhardt T, Roesler S, Uusitalo HP, Kissel T Surfactant-free redispersible

nanoparticles in fast-dissolving composite microcarriers for dry-powder inhalation Eur

J Pharm Biopharm 2011;78:90-6 doi:10.1016/j.ejpb.2010.12.002

[49] Kolakovic R, Laaksonen T, Peltonen L, Laukkanen A, Hirvonen J Spray-dried nanofibrillar cellulose microparticles for sustained drug release Int J Pharm 2012;430:47-55 doi:10.1016/j.ijpharm.2012.03.031

ACCEPTED MANUSCRIPT

33

[50] Sham JO, Zhang Y, Finlay WH, Roa WH, Löbenberg R Formulation and characterization of spray-dried powders containing nanoparticles for aerosol delivery to the lung Int J Pharm 2004;269:457-67 doi:10.1016/j.ijpharm.2003.09.041

[51] Seremeta KP, Reyes Tur MI, Martínez Pérez S, Höcht C, Taira C, López Hernández

OD, et al Spray-dried didanosine-loaded polymeric particles for enhanced oral

doi:10.1016/j.colsurfb.2014.09.055

[52] Tewa-Tagne P, Briançon S, Fessi H Preparation of redispersible dry nanocapsules

by means of spray-drying: development and characterisation Eur J Pharm Sci

2007;30:124-35 doi:10.1016/j.ejps.2006.10.006

[53] Bittner B, Morlock M, Koll H, Winter G, Kissel T Recombinant human erythropoietin (rhEPO) loaded poly(lactide-co-glycolide) microspheres: influence of the encapsulation technique and polymer purity on microsphere characteristics Eur J Pharm Biopharm 1998;45:295-305 doi:10.1016/S0939-6411(98)00012-5

[54] Zhu C, Shoji Y, McCray S, Burke M, Hartman CE, Chichester JA, et al Stabilization

of HAC1 influenza vaccine by spray drying: formulation development and process

scale-up Pharm Res 2014;31:3006-18 doi:10.1007/s11095-014-1394-3

[55] Maury M, Murphy K, Kumar S, Shi L, Lee G Effects of process variables on the powder yield of spray-dried trehalose on a laboratory spray-dryer Eur J Pharm Biopharm 2005;59:565-73 doi:10.1016/j.ejpb.2004.10.002

[56] Cevher E, Orhan Z, Mülazimoğlu L, Sensoy D, Alper M, Yildiz A, et al Characterization of biodegradable chitosan microspheres containing vancomycin and treatment of experimental osteomyelitis caused by methicillin-resistant Staphylococcus

ACCEPTED MANUSCRIPT

34

doi:10.1016/j.ijpharm.2006.03.014

[57] Oliveira AM, Guimarães KL, Cerize NN, Tunussi AS, Poço JG Nano spray drying

as an innovative technology for encapsulating hydrophilic active pharmaceutical ingredients (API) J Nanomed Nanotechnol 2013;4:6 doi:10.4172/2157-7439.1000186 [58] Andrade F, Rafael D, Videira M, Ferreira D, Sosnik A, Sarmento B Nanotechnology and pulmonary delivery to overcome resistance in infectious diseases Adv Drug Deliv

[61] Schmid K, Arpagaus C, Friess W Evaluation of the Nano Spray Dryer B-90 for

doi:10.3109/10837450.2010.485320

[62] Lee SH, Teo J, Heng D, Ng WK, Chan HK, Tan RB Synergistic combination dry

powders for inhaled antimicrobial therapy: formulation, characterization and in vitro evaluation Eur J Pharm Biopharm 2013;83:275-84 doi:10.1016/j.ejpb.2012.09.002