The effect of homogenization method on the

http://informahealthcare.com/mnc ISSN: 0265-2048 (print), 1464-5246 (electronic) J Microencapsul, 2013; 30(7): 692–700 ! 2013 Informa UK Ltd. DOI: 10.3109/02652048.2013.778906

ORIGINAL ARTICLE

The effect of homogenization method on the properties of carbamazepine microparticles prepared by spray congealing Rodrigo Molina Martins, Silvia Siqueira, Marcela Olaia Machado, and Luis Alexandre Pedro Freitas

Abstract

Keywords

The aim of this study was to investigate the influence of ultrasound and high-shear mixing on the properties of microparticles obtained by spray congealing. Dispersions containing 10% carbamazepine and 90% carrier GelucireÕ 50/13 (w/w) were prepared using magnetic stirring, high-shear mixing, or ultrasound. Each preparation was made using hot-melt mixing spray congealing to obtain the microparticles. All microparticles presented a spherical shape with high encapsulation efficiency (499%). High-shear mixing and ultrasound promoted a decrease in the size of microparticles (D90) to 62.8 4.1 mm and 64.9 3.3 mm, respectively, while magnetic stirring produced microparticles with a size of 84.1 1.4 mm. The use of ultrasound led to microparticles with increased moisture content as identified through sorption isotherm studies. In addition, rheograms showed distinct rheological behaviour among different dispersion preparations. Therefore, the technique used to prepare dispersions for spray congealing can affect specific characteristics of the microparticles and should be controlled during the preparation.

High-shear mixer, rheological behaviour, solid dispersion, ultrasound

Introduction Improving the dissolution properties of pharmaceuticals is extremely important, especially because the percentage of poor water-soluble drugs developed by the pharmaceutical industry has increased in recent years (Hu et al., 2004; Liu et al., 2010; Bohr et al., 2011). Drugs that are poorly soluble in water tend to be eliminated from the gastrointestinal tract before they have had the chance to fully dissolve and be absorbed into the circulatory system (Liversidge and Cundy, 1995). Therefore, one of the major challenges currently of the pharmaceutical industry is designing formulation strategies that improve the water solubility of these drugs (Vasconcelos et al., 2007). One of several approaches used to promote the enhancement of water solubility of these drugs is the preparation of solid dispersions (SDs). SD is defined as the dispersion of one or more active ingredients in solid inert carriers prepared by fusion, solvent, or solvent–fusion methods (Serajuddin, 1999; Al-Hamidi et al., 2010). Currently, SD preparation can be supported by spray drying (Araujo et al., 2010; Martins et al., 2012a, 2012c, 2013), supercritical fluids (Sethia and Squillante, 2004), and spray congealing (Emas and Nyqvist, 2000; Passerini et al., 2006; Mccarron et al., 2008; Martins et al., 2012b) to increase the stability of the ingredients, reduce the particle size and promote scale up (Vasconcelos et al., 2007). Spray congealing is gaining considerable attention among other methods for the preparation of microparticles of poorly

Address for correspondence: Luis Alexandre Pedro Freitas, Faculdade de Cieˆncias Farmaceûticas de Ribeiraõ Preto, Nucleo de Apoio a` Pesquisa em Produtos Naturais e Sinte´ticos, Universidade de Saõ Paulo, Avenida do Cafe´, s/n. 14040-903, Ribeiraõ Preto, SP, Brazil. Tel: +55 16 36024225. E-mail: [email protected]

History Received 23 July 2012 Revised 6 February 2013 Accepted 11 February 2013 Published online 27 March 2013

water-soluble drugs, such as carbamazepine (Passerini et al., 2002), praziquantel (Passerini et al., 2006), indomethacin (Fini et al., 2008) and glimepiride (Ilic et al., 2009), because it is cost effective and requires no solvent thus being an environmentally friendly technique (Passerini et al., 2010). In addition, spray congealing produces solid dispersion microparticles with a spherical morphology and microspheres that have very narrow particle distributions (Cavallari et al., 2005; Fini et al., 2010). However, spray congealing has some limitations, such as the inability to produce microparticles from highly viscous dispersions (Albertini et al., 2008), hence the need to employ some formulation technologies such as ultrasound or high-shear mixer that decrease the viscosity of the shear thinning dispersions. Ultrasound and high-shear mixer devices are generally used for promoting a greater homogenization of formulations (Maa and Hsu, 1996; de Castro and Priego-Capote, 2007). In addition, both techniques have emerged as green technologies because they do not involve organic solvents, thus highlighting their role in environmental sustainability (Hou et al., 2003; Chemat et al., 2011). Recently, spray congealing technology, combined with an ultrasound atomizer, has been used to obtain microparticles of poorly water-soluble drugs (Cavallari et al., 2007). However, more studies are required to verify whether the use of these homogenization methods can promote changes in the physicochemical characteristics of microparticles produced by spray congealing. Therefore, the purpose of the present study has been to investigate the influence of ultrasound and high-shear mixer on the properties of microparticles obtained by spray congealing using carbamazepine (CBZ) as a poorly water-soluble model drug and a polyoxylglyceride (GelucireÕ 50/13) as a hydrophilic carrier. Three dispersions containing 10% CBZ and 90%

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Faculdade de Cieˆncias Farmaceûticas de Ribeiraõ Preto, Nucleo de Apoio a` Pesquisa em Produtos Naturais e Sinte´ticos, Universidade de Saõ Paulo, Ribeiraõ Preto, SP, Brazil

Effect of homogenization on carbamazepine microparticles

DOI: 10.3109/02652048.2013.778906


Õ

Gelucire 50/13 (w/w) were prepared. The dispersions differed only in the type of preparation employed: the first dispersion was prepared by magnetic stirring (SC), the second by high-shear mixing (SCHSM), and the third using ultrasound (SCUS). First, the rheological behaviour of these dispersions was observed to determine whether the incorporation of solid particulates altered the flow characteristics of these systems in a considerable manner. In turn, properties such as the apparent viscosity, dynamic viscosity and flow index may indirectly affect certain microparticle attributes such as particle size and dissolution rate (Moelants et al., in press). Second, each dispersion was microparticulated using a mini spray drier that had been modified to be used as a spray congealing system to produce microstructured solid dispersions. The characterization of microparticle properties was performed using traditional techniques such as scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRPD) and sorption isotherms. Third, particle size distribution and encapsulation efficiency were determined and were followed by in vitro dissolution measurements that compared the microparticles with the pure drug.

Material and methods Materials Carbamazepine was purchased from Cristalia Farmoquı´mica Ltda. (Saõ Paulo, Brazil). GelucireÕ 50/13 was supplied by Gatefosse´France (Saint-Priest, France). All other chemicals were of analytical grade. Dispersion preparation Three dispersions containing 10% CBZ and 90% GelucireÕ 50/13 (w/w) were prepared. In the first step, the carrier (GelucireÕ ) was melted at a temperature above its melting point (70 C), and then, CBZ was added and dispersed slowly with the aid of a glass rod. The preparation of the SC microparticle dispersion sample used a magnetic stirrer with heating (TE 0851, TecnalÕ , Piracicaba, Brazil) at 100 rpm. The SCHSM dispersion employed a high-shear mixer (Turratec TE-102, TecnalÕ , Piracicaba, Brazil) at 14 000 rpm. The last dispersion sample, SCUS, used an ultrasound homogenizer (DES500, Unique, Indaiatuba, Brazil) at 20 kHz. The temperature of the dispersion was monitored before and after the ultrasound process. All dispersions were homogenized for 5 min. The amount of dispersion used in each experiment was 100 g. In the second step, each dispersion was microparticulated by spray congealing.

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The apparent viscosity was determined at a shear rate of 21.6 s1. This shear rate value is equivalent to the shear at the tip of the atomizing nozzle during the spray congealing. The rheological behaviour of dispersions was determined in quadruplicate. Preparation of microparticles by spray congealing The microparticles were produced using a mini spray drier model LM MSD 0.5 (Labmaq do Brasil Ltd, Ribeiraõ Preto, Brazil) with a capacity of drying of up to 0.5 L h1. The cylindrical drying chamber is made of borosilicate glass and has a diameter of 13 cm with 51 cm in height. This apparatus was modified to be used as a spray congealing system and was operated in concurrent flow. A g HP chiller (Labmaq do Brasil Ltda, Ribeiraõ Preto, Brazil) was connected to the outlet of the air blower, and the air was chilled in the range 17 1 C. Atomization was carried out with a doublefluid pneumatic nozzle with a 1.2 mm orifice. This spray nozzle was jacketed in its whole extension, allowing the flow of heating fluid pumped from a thermostatic oil bath at 140 C. Each melted dispersion was fed using a peristaltic pump (Labmaq do Brasil Ltda, Ribeiraõ Preto, Brazil) that had been equipped with a custom-made heated head operating at a constant temperature of 80 C. The silicone tubing was heated by a flexible heating belt along the distance from the peristaltic pump to the spray nozzle. The microparticles produced were separated from the air by a glass cyclone and were collected in glass flasks. Figure 1 shows a schematic diagram of the spray congealing apparatus. After atomization, the microparticles were stored in a vacuum desiccator until further analysis. The following set of conditions was kept fixed for all experiments: a dispersion feed rate of 4.0 mL min1, a cooling air flow rate of 1.0 m3 min1, an atomization pressure of 7.0 bar and a spray nozzle air flow of 50.0 L min1 (Martins et al., 2012b). Determination of the encapsulation efficiency The encapsulation efficiency (EE) was determined by evaluating the amount of CBZ entrapped in the microparticles. Nine milligrams of each batch was dispersed in water (100 mL) and stirred for 24 h at 25 1 C. The solutions were filtered (0.22 mm), and their drug content was analysed with a UV/Vis spectrophotometer model 330W (Camspec, Co. Garforth, UK) at 288 nm. The EE was calculated as the ratio between the actual drug content and the theoretical amount of drug content in the microparticles (Gelfuso et al., 2011; Martins et al., 2012b) that was expressed as a percentage. Each sample was assayed in triplicate. Particle size analysis

Determination of the dispersions’ rheological behaviour

Rheological behaviour of dispersions was observed at 70 C using a cone and plate (controlled stress) rheometer R/S Plus (Brookfield Co., Middleborough, MA) and a CP-25 spindle. The shear rate varied from 10 to 1000 rpm (increasing shear) and from 1000 to 10 rpm (decreasing shear) for a total run time of 120 s. The Ostwald-de-Waele relationship was fitted to data from the rheograms obtained: ¼ k n

ð1Þ

where is the shear stress, g is the shear rate, k is the consistency index, and n is the flow index. When n ¼ 1, the flow is considered Newtonian; when n41, the flow is classified as shear thickening; and when n51, the flow is classified as shear thinning (Ratsimbazafy et al., 1999). The software, RHEOCALC version V 1.01 (Brookfield Co., Middleborough, MA) was used to calculate the flow index, thixotropy and apparent viscosity values.

The particle size distribution was determined by laser diffraction in a LSÔ 13 320 apparatus (Beckman Coulter, Miami, FL). The dispersion medium used was water. The values of D10, D50 and D90 were determined and were used to calculate the span ((D90 D10)/D50). Span represents a measurement of the width of the size distribution (Ilic et al., 2009), where D10, D50 and D90 are the diameter sizes, and the given percentage value is the percentage of particles smaller than that size. A high span value indicates a wide size distribution (Gavini et al., 2006). Each sample was analysed in triplicate. Differential scanning calorimetry DSC measurements were performed using a DSC-50 (Shimadzu Co., Kyoto, Japan) apparatus, and 5 mg of each sample was placed into aluminium pans under a nitrogen flow rate of 50 mL min1. These samples were then heated from 30 to 220 C at a scanning rate of 10 C min1.

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Figure 1. Schematic diagram of spray congealing apparatus showing heating of peristaltic pump head, pumping hose and jacketed spray nozzle. Cooled air and molten spray fed from top of the chamber.

X-ray powder diffraction Samples were analysed by the XRPD technique using a D5005 Bruker-Siemens diffractometer (Siemens AG Co., Munich, ˚ ). The scanning Germany) with CuKa radiation ( ¼ 1.5418 A angle ranged from 2 to 40 in 2 steps of 0.2 and a delay time of 2 s per step. The current and the voltage applied were 30 mA and 40 kV, respectively. Scanning electron microscopy The morphological characteristics of the microparticles were observed by SEM using a XL-30 FEG-SEM microscope (Phillips Co., Eindhoven, the Netherlands). The samples were coated with gold/palladium under argon atmosphere using a sputter coater Bal-Tec SCD 005 (Leica Microsystems Co., Wetzlar, Germany). Photomicrographs were then taken at an acceleration voltage of 25 kV.

for all microparticle samples. The isotherms were determined by the dynamic dew point isotherm (DDI) method in an AquaSorp Isotherm Generator (Decagon Device Inc., Pullman, WA) at a flow rate of 300 mL min1 within a range of aw between 0.20 and 0.85 at a temperature of 40 C. The samples used in each analysis weighed 500 mg. The data analysis was performed using SorpTracTM version 1.14 (Decagon Device Inc., Pullman, WA). The obtained sorption isotherms were mathematically analysed by Double Log Polynomial (DLP) models (Nurtama and Lin, 2010). This model can be expressed using the following equation: m¼b3 x3 þb2 x2 þb1 xþf

ð2Þ

where m is the moisture in g/100 solids or g/g solids, x ¼ ln(ln(aw)), f is a constant, and b1 – b3 are coefficients. Moisture content is reported percentage-wise as MC (%) ¼ m 100.

FT-IR spectroscopy FT-IR spectroscopy was used to investigate possible physicochemical interactions between the drug and carrier caused by the three mixing processes studied (Brittain et al., 1991). The samples used for spectral measurements were prepared according to the KBr technique. A Nicolet Prote´ge´ 450 FT-IR (Nicolet Inst. Inc, Madison, WI) spectrophotometer was operated within a scan range of 4000 to 500 cm1. Sorption isotherms The relationship between water activity (aw) and moisture content (MC) was determined using sorption isotherms measured

In vitro dissolution studies The dissolution rates of CBZ and microparticle samples were determined using the paddle method (apparatus 2, USP XXX) at a stirring rate of 75 rpm and at 37 1 C in a NE 330-8 dissolutor (Nova E´tica Ltd, Vargem Grande Paulista, SP, Brazil). The dissolution medium was deionized water (900 mL), and the samples were filled with 180 mg of microparticles corresponding to 18 mg of CBZ. Aliquots (2 mL) were withdrawn after 5, 10, 15, 30 and 60 min. Subsequently, they were filtered (0.22 mm), and their CBZ contents were determined by spectrophotometry at 288 nm. Each sample was assayed in sextuplicate.


DOI: 10.3109/02652048.2013.778906

SC

Gelucire 50/13 1500

1250 1000

shear stress (Pa)

shear stress (Pa)

Figure 2. Rheograms of GelucireÕ 50/13 and of dispersions prepared by magnetic stirrer (SC), high-shear mixer (SCHSM) or produced by ultrasound (SCUS), determined with R/S Plus Brookfield rheometer from 0 to 1000 s1. Run time 120 s.

750 500

1000

500

250 0 0

200

400

600

shear rate (s-1)

800

0 0

1000

200

400

800

1000

800

1000

SCUS

1500

1500

shear stress (Pa)

shear stress (Pa)

600

shear rate (s-1)

SCHSM


695

1000

500

1250 1000 750 500 250

0

0

200

Results and discussion Rheological behaviour of dispersions Figure 2 presents the rheograms of GelucireÕ 50/13, SC, SCHSM and SCUS. The linearity test applied to the logarithmic form of the Ostwald-de-Waele relationship presented R2 coefficients of determination above 0.93 for all dispersions tested. In Figure 2, an increase of hysteresis in the dispersions containing CBZ can be observed. The flow indexes (Table 1) of all preparations were less than 1, indicating the shear thinning character of these dispersions. This behaviour was not observed with the GelucireÕ 50/13 (n ¼ 0.95 0.01) dispersion, which could be considered a Newtonian fluid because its flow index value is very close to 1. Interestingly, the dispersion produced by ultrasound (SCUS) had the highest flow index (n ¼ 0.84 0.01), while the SC (n ¼ 0.65 0.01) and SCHSM (n ¼ 0.63 0.00) indexes were lower and were similar to each other. The same occurred with the values of thixotropy, where SCUS (18 100 1100 Pa s) showed a lower value when compared to SC (46 270 2177 Pa s) and SCHSM (42 980 1961 Pa s), which showed similar values. A corresponding trend was also observed for the apparent viscosity values (Table 1). Thixotropy is a term to describe an isothermal phenomenon in which the apparent viscosity decreases with time during shearing, followed by a gradual recovery when the stress is removed (Lee et al., 2009). The thixotropic behaviour results from relatively weak attractive forces between the particles. They will cause the formation of flocs, which normally evolve into a space-filling particulate network. However, the interparticle bonds are weak enough to be broken by the mechanical stresses that occur during flow (Mewis and Wagner, 2009). In addition, the rheological properties of dispersions are influenced mainly by two parameters: the solids concentration and the size of the flocs present in the dispersion (Fischer et al., 2009). Only the floc sizes could account for differences in rheological behaviour in this study because the solids concentration present in the melt carrier was fixed at 10%. Ultrasound mechanical waves promote acoustic cavitation that leads to the disaggregation and size reduction of agglomerates, thus improving homogenization (Jambrak et al., 2008). Therefore, the use of ultrasound to prepare the SCUS most

400 600 800 shear rate (s-1)

1000

0 0

200

400

600

shear rate (s-1)

Table 1. Rheological parameters for lipidic carrier (GelucireÕ 50/13) and molten dispersions after magnetic stirring (SC), high-shear mixing (SCHSM) and ultrasound (SCUS) at 70 C.

Samples GelucireÕ 50/13 SCUS SCHSM SC

Correlation coefficient (r2)

Thixotropy (Pa/s)

1.38 0.07a 0.95 0.01d

0.98 0.01g

2607 312i

2.42 0.09b 0.84 0.01e 4.48 0.14c 0.65 0.00f 4.88 0.19c 0.63 0.01f

0.98 0.00g 0.93 0.00h 0.93 0.00h

18 100 1100j 42 980 1961k 46 270 2177k

Viscosity (Pa s)

Flow index

Student’s t-test shows significance (p50.05). Values represented by different letters were significantly different.

likely led to a better dispersion of CBZ aggregates in the carrier, which decreased the values of apparent viscosity and thixotropy. However, the results indicate that magnetic stirring and high-shear mixing was not able to decrease the size of the agglomerates in a similar level. In this case, only miscibility in the carrier contributed to the amount of reduction in the size of the carbamazepine particles or agglomerates. Microparticle size and morphology The particle size measurements of the microparticle dispersion samples presented in this study are given in Table 2. The microparticles containing only GelucireÕ 50/13 showed the values of D50, D90, and span lower than the other samples. This means that the presence of 10% CBZ in the SDs promoted an increase in microparticle sizes (Martins et al., 2012d). The data in Table 2 also show that microparticles have smaller sizes than raw CBZ (D10 ¼ 4.1, D50 ¼ 60.0, and D90 ¼ 261.7 mm), which can be explained by the CBZ/Gelucire 50/13 miscibility. During the hot melt mixture preparation, CBZ crystals partially solubilize in molten Gelucire 50/13, thus decreasing its size. However, microparticles produced by spray congealing assisted by highshear mixing, SCHSM, and ultrasound, SCUS, showed decreased values of D90 and span when compared to the microparticles produced by magnetic stirring, SC. However, particle size and span values of SCHSM and SCUS showed no significant difference.

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Figure 3. SEM micrographs of raw CBZ and microparticles, where (a) and (b) show Carbamazepine (CBZ) at 2000 and 4000, respectively, (c) shows GelucireÕ 50/13 (GEL) at 2000, (d) SC at 2000, (e) SCHSM at 2000 and (f) SCUS at 2500.

Table 2. Efficiency of Carbamazepine (CBZ) encapsulation and particle size distribution parameters for lipidic carrier (GelucireÕ 50/13), raw CBZ and spray congealed solid dispersions prepared by magnetic stirring (SC), high-shear mixing (SCHSM) and ultrasound (SCUS). Samples

EE (%)

GEL SC SCHSM SCUS CBZ

– 99.33 0.8 100.2 0.6 100.0 0.5 –

D10 (mm) D50 (mm) 6.7 0.8 8.4 0.3 7.5 0.3 7.9 0.6 4.1

D90 (mm)

16.6 0.9 35.8 3.0 24.9 0.3 84.1 1.4 23.2 0.7 62.8 4.1 22.9 3.3 64.9 3.3 60.0 261.7

Span 1.75 0.10 3.04 0.05 2.39 0.25 2.50 0.24 4.3

As shown above, the dispersions produced by ultrasound promoted modifications in rheological properties of the dispersion causing a decrease in particle size. Notably, the drug content was the same in all three dispersions. Therefore, the decrease in the values of D90 and span of SCUS when compared to SC could be assigned to using ultrasound. Figure 3 shows photomicrographs comparing microparticles obtained by spray congealing to those of pure drug, i.e. sample CBZ. The microparticles in samples SC, SCHSM and SCUS were spherical in shape with drug crystals on the surface of the particles (Figure 3d–f). The CBZ presented well-defined prismatic crystals characteristic of b-form (Sethia and Squillante, 2004) and heterogeneous particle size shown in Figure 3(a and b). However, the shape of the crystals on the surfaces of SC, SCHSM and SCUS appear to be mostly needle-like. Figure 3(c) shows microparticles containing only carrier, sample GEL. Similarly, GEL microparticles had a spherical shape but with a smoother surface than SC, SCHSM and SCUS. In general, the spray

congealing processes used in this study did not seem to cause changes in the shape of the microparticles, corroborating results from other studies that also obtained spherically shaped microparticles by spray congealing (Passerini et al., 2002, 2006; Albertini et al., 2008). Encapsulation efficiency The EE of CBZ is shown in Table 2. The EE values ranged from 99.33 to 100.2% and were calculated based on the drug content in the microparticles, which was quantified by spectrophotometry. The results show a high EE of 100%. The EE values in this study are similar to the EE of 98% (Passerini et al., 2002) obtained using 10% of drug in carrier by spray congealing. However, the EE values for samples SC, SCHSM and SCUS showed no significant difference when compared to each other. This behaviour shows that the use of high-shear mixing and ultrasound did not promote changes in the content of CBZ in the microparticles. Physicochemical characterization of microparticles To study the solid state of the drug and to check whether the use of high-shear mixing or ultrasound promoted changes or chemical interactions, DSC, XRPD and FT-IR analyses were conducted. Firstly, DSC analysis showed that endothermic peaks of CBZ in microparticles disappeared (Figure 4), whereas CBZ showed two characteristic endothermic peaks at 163 and 192 C, which are concerned with the melting of forms. The absence of CBZ melting peaks is likely due to the low concentration of the drug in the SC, SCHSM, and SCUS samples. Furthermore, the heating


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Figure 4. DSC traces of carbamazepine (CBZ), GelucireÕ 50/13 (GEL), spray congealing with magnetic stirring (SC), spray congealing assisted by high-shear mixer (SCHSM) and spray congealing assisted by ultrasound (SCUS) at a scanning rate of 10 C min1 under nitrogen flux of 50 mL min1.

process that occurs in DSC analysis causes subsequent melting of carrier and drug dissolution in the melted carrier (Damian et al., 2000; Passerini et al., 2002). DSC curves of the three samples (SC, SCHSM, and SCUS) are similar, showing only one endothermic peak at the melting temperature of the carrier, which is 45 C. Moreover, the enthalpy values (DH) of the SC (141.4 J g1), SCHSM, (135.7 J g1) and SCUS (130.3 J g1) samples are lower than that of pure carrier GEL sample (146.2 J g1). The DH values obtained from DSC of microparticle samples containing CBZ showed that the use of high-shear mixing or ultrasound promoted a decrease in DH, which could be related to a possible decrease in crystallinity of CBZ and GEL. Figure 5(a–e) shows the FT-IR spectra of samples SC, SCHSM, SCUS, CBZ, and GEL. The FT-IR spectra of CBZ correspond with that previously reported for b-form (Rustichelli et al., 2000). Characteristic bands of CBZ are found at 3465 cm1 for the –NH valence vibration, at 1677 cm1 for the –CO–R vibration, at 1605–1595 cm1 for the ranges of –C¼C– and –C¼O vibration and for the –NH deformation (Grzesiak et al., 2003; Sethia and Squillante, 2004; Martins et al., 2012a), at 1610, 1488 and 763 cm1 due to the presence of an aromatic ring. GEL presents a large band between 3650 cm1 and 3100 cm1 due to the stretching of free OH groups, an intense peak at 1739 cm1 belonging to the C¼O group, one at 1468 cm1 for the C–H deformation of alkyl group, one at 1114 cm1 due to the –C–O stretching, and a double at 964 cm1, which is characteristic of the polyethylene glycol groups (Passerini et al., 2002; Potluri et al., 2011). The spectra of the SC, SCHSM and SCUS samples show no new bands, which are similar to the spectrum of the GEL. In addition, it was not possible to identify differences among the spectra of these samples. Figure 6 shows the XRPD of CBZ and microparticle dispersion of the GEL, SC, SCHSM, and SCUS samples. The CBZ is in crystalline form with intense diffraction peaks at 13.1 , 15.4 , 16 , 25 , 27.5 , and 32.1 of 2 corresponding to b-form (Otsuka et al., 2000). The diffractogram of GEL shows peaks that are typical of triglycerides observed at 19.1 and 23.2 of 2 called ‘‘short spacing’’ (Cavallari et al., 2005). The XRPD of the SC, SCHSM and SCUS samples shows two new peaks at 5.0 and 8.9 of 2 corresponding to polymorphic a-form. Notably, polymorphic modifications occurred due to the high temperatures used to prepare these formulations (Rustichelli et al., 2000; Martins et al., 2012b). Therefore, the use of high-shear mixing or

Figure 5. FT-IR spectra of SC (a), SCHSM (b), SCUS (c), CBZ (d) and GEL (e) with scan range from 4000 to 500 cm1.

Figure 6. XRPD of carbamazepine (CBZ), GelucireÕ 50/13 (GEL), spray congealing with magnetic stirring (SC), spray congealing assisted by high-shear mixer (SCHSM) and spray congealing assisted by ultrasound (SCUS). Scanning angle from 2 to 40 in 2Q steps and delay time of 2 s per step.

ultrasound to prepare the dispersions, when compared to the dispersion prepared by magnetic stirring, did not promote changes in the solid-state or promote chemical interactions between the functional groups of the microparticles constituents. Sorption isotherms Figure 7 shows the adsorption and desorption isotherms of microparticles in samples SC, SCHSM, and SCUS at 40 C.

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Figure 7. Sorption and desorption isotherms of microparticles SC, SCUS and SCHSM at 40 C, using dynamic dew point method (DDI) with at air flow rate of 300 mL min1 and aw range from 0.20 to 0.84.

SC 12

DESORPTION

MC (%)

9 6 3 0

ADSORPTION

0.1 0.3 0.5 0.7 0.9

aw


SCHSM

12

12

9

9

MC (%)

MC (%)

SCUS

6 3 0

6 3

0.1 0.3 0.5 0.7 0.9

0

0.1 0.3 0.5 0.7 0.9

aw

Sorption isotherms give the relation between the water activity, aw, which is directly related to the MC and the relative humidity (RH), in that RH ¼ aw 100. This relationship depends on the interaction between water and other ingredients (Martins et al., 2012a). Products that present low water activity with aw50.60 are often referred to as dry, those with aw in the range of 0.60–0.90 are considered intermediate moisture products, and those having aw higher than 0.90 are considered high-moisture products (USPXXX, 2007). All sorption isotherms may be classified as type III isotherms, which correspond to nearly non-hygroscopic or less hydrophilic material (Brunauer et al., 1940; Martins et al., 2012a). Table 3 shows the values for bi coefficients, standard errors (SE), and coefficients of determination R2 obtained upon fitting the experimental data from the SC, SCHSM and SCUS samples to the microparticle DLP model in Equation (2) (Nurtama and Lin, 2010). The values of the predicted MCs of microparticles are shown in Table 4. For aw values smaller than 0.6, the MC values are similar for all microparticle dispersion samples. It is extremely important that a product presents an MC below 5% to avoid microbial growth (Teixeira et al., 2011). However, for aw above 0.85, the SCUS shows MC values (13.58% and 12.42%) higher than the SCHSM (10.18% and 10.80%) and SC samples (10.52% and 11.14%) during adsorption and desorption, respectively. The use of ultrasound may promote a decrease in the crystallinity of CBZ and GEL, leading to an increase in moisture content in the SCUS under these conditions. This result corroborates the observations from thermal analysis, in which the SCUS sample showed decreased enthalpy values. Dissolution studies of microparticles Figure 8 displays the in vitro release profile of CBZ and the microparticle dispersion samples SC, SHSM, and SCUS. CBZ releases only up to 45% in 60 min. However, the dissolution profiles of SCUS, SHSM, and SC show amounts of CBZ released at 60 min of 98.9 4.18%, 97.0 2.48%, and 101.7 3.9%, respectively. Microparticles in the SCUS, SCHSM and SC samples showed greater drug release than pure CBZ. It is known from the Noyes– Whitney equation that a reduction in the drug particle size increases its dissolution rate (Horter and Dressman, 2001; Bohr

aw

Table 3. Coefficients, standard errors (SE) and coefficient of correlation (R2) of the double log polynomial (DLP) model adjusted to sorption isotherms of spray congealed solid dispersions prepared by magnetic stirring (SC), high-shear mixing (SCHSM) and ultrasound (SCUS). Adsorption

Desorption 2

Coefficients

SE

R2

0.999

b0: b1: b2: b3:

1.7923 2.5991 2.3799 0.0405

0.23

0.996

0.16

0.996

b0: b1: b2: b3:

1.9612 2.2104 0.9696 0.2715

0.12

0.998

0.19

0.995

b0: b1: b2: b3:

2.173 2.1224 1.8129 0.1445

0.14

0.998

Samples

Coefficients

SE

R

SCUS

b0: b1: b2: b3:

1.4735 3.1569 0.0499 1.0906

0.11

SCHSM

b0: b1: b2: b3:

1.5092 2.8878 0.3602 0.7708

SC

b0: b1: b2: b3:

1.6303 3.0853 0.5345 0.8414

et al., 2011). However, there were no significant differences among the release profiles of the microparticle samples prepared by spray congealing (p ¼ 0.05 using Student’s t-test). Thus, the use of ultrasound or high-shear mixing does not influence the dissolution rate of microparticles produced by spray congealing.

Conclusion The use of high-shear mixing and ultrasound to prepare microparticle dispersions neither promote polymorphic changes or chemical interactions, nor did it change their dissolution profile. However, ultrasound did influence the particle size, which was due to changes in the rheological properties of the dispersions. Additionally, ultrasound promoted a possible decrease in the crystalline state, as shown in studies using DSC and sorption isotherms. Therefore, the preparation technique of dispersions for spray congealing can affect specific characteristics of the microparticles obtained and should be controlled during the production process.


DOI: 10.3109/02652048.2013.778906

699

Table 4. Predicted moisture contents (MCs) (%) for spray congealed solid dispersions prepared by magnetic stirring (SC), high-shear mixing (SCHSM) and ultrasound (SCUS) using the double log polynomial (DLP) model at different water activities (aw). SCUS aw


0.30 0.60 0.80 0.85

SCHSM

SC

Adsorption

Desorption

Adsorption

Desorption

Adsorption

Desorption

0.88 3.90 9.78 13.58

1.39 4.62 9.39 12.42

0.96 3.52 7.63 10.18

1.59 3.96 8.37 10.80

1.04 3.72 7.59 10.52

1.85 4.37 8.95 11.14

Figure 8. In vitro dissolution profile of raw CBZ and microparticles (SC, SCHSM and SCUS). Apparatus 2 USP XXX, 75 rpm at 37 1 C and dissolution media deionized water. The results represent the mean SD of experiments performed in sextuplicate.

Declaration of interest The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.Financial supports from Fundaçaõ de Amparo a` Pesquisa do Estado de Saõ Paulo (FAPESP – 08/02848-9 and 08/07115-0) and CNPq (PQ-2) are gratefully acknowledged.

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