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Development of mucoadhesive sericin/alginate particles loaded with ibuprofen for sustained drug delivery Emanuelle D. Freitas a , Jacyara M.M. Vidart a , Edson A. Silva b , Meuris G.C. da Silva a , Melissa G.A. Vieira a,∗ a Department of Processes and Products Design, School of Chemical Engineering, University of Campinas–UNICAMP, Albert Einstein Avenue, 500, 13083-852, Campinas, SP, Brazil b School of Chemical Engineering, State University of West Paraná–UNIOESTE, Faculdade Street, 645, 85903-000, Toledo, PR, Brazil

a r t i c l e

i n f o

Article history: Received 16 October 2017 Received in revised form 1 December 2017 Accepted 13 December 2017 Available online xxx Keywords: Sericin Alginate Ibuprofen Sustained drug release

a b s t r a c t A sericin/alginate blend was successfully applied as a matrix for incorporation of ibuprofen. This provided a sustained release formulation, which could improve the therapeutic efficacy of ibuprofen and patient adherence to treatment. Sericin increased the proportion of drug incorporated into the particles (i.e., the drug incorporation efficiency), with incorporation rates between 73.01% ± 1.70% and 94.15% ± 4.21%. Alginate affected the drug release, and the particles with the maximum alginate mass fraction tested (2.8%) showed sustained release through a dissolution mechanism, reaching equilibrium after about 1400 min. Analysis of the incorporation efficiency and the drug release time showed the best results were for formulations with a high alginate content. Scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction analysis were used for particle characterization to study the incorporation of ibuprofen. The particle size range was 0.80 ± 0.13 to 1.08 ± 0.11 mm. The size distributions of sericin-containing particles showed a good fit with the Gaussian model. © 2018 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Introduction Among the different routes of administration for drug delivery, the most common is the oral route, which usually results in immediate release. This route has disadvantages, such as the requirement for frequent administration and the occurrence of adverse reactions, and development of alternative drug delivery systems is of interest (Ummadi, Shravani, Rao, Reddy, & Nayak, 2013). The use of existing molecules in modified delivery systems bypasses the expense and time taken for development of new drug molecules (Tiwari et al., 2012). Ibuprofen is a non-steroidal anti-inflammatory drug. It provides pain relief and suppresses inflammation through its analgesic, anti-inflammatory, and antipyretic properties. Ibuprofen has a short half-life (2 h) (Busson, 1986), requiring multiple administrations to maintain effective plasma concentrations. The necessity of repeated doses may reduce treatment compliance and thus clinical efficacy. Development of a modified drug release form for ibupro-

∗ Corresponding author. E-mail address: [email protected] (M.G.A. Vieira).

fen may improve its action in humans (Khalifa, El-Hussein, Morrah, Mostafa, & Hamoud, 2014). One possible pharmaceutical form for modified drug release is the multiparticulate system. In this type of system, multiple dosage forms contain a partial dosage of the drug, and together, all subunits provide the recommended total dose. Consequently, multiparticulates are less dependent on gastric emptying, better distributed in the gastrointestinal tract, and cause less local irritation compared with a conventional oral dose (Dey, Majumdar, & Rao, 2008). The small units may be composed of natural or synthetic polymeric microparticles. In this context, a blend of sericin and alginate has been investigated as a promising natural polymeric matrix system for pharmaceutical applications (da Silva, Vidart, da Silva, Gimenes, & Vieira, 2017). The two main proteins in silk are fibroin and, to a lesser extent, sericin. Sericin, a water-soluble globular protein, is known as silk glue and contains 18 amino acids. In the silk industry, fibroin is separated from sericin by a degumming process, and sericin is usually disposed of in wastewater as a by-product (Aramwit, Siritientong, & Srichana, 2012). However, this protein has important biological activities. It is biocompatible, biodegradable, and has good gelling, moisture retention capacity, and bioadhesion.

https://doi.org/10.1016/j.partic.2017.12.011 1674-2001/© 2018 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

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Consequently, sericin is a promising material for pharmacological, cosmetic, and medical applications (Padamwar & Pawar, 2004). The chemical characteristics of sericin allow for blending with other polymers to produce an environmentally friendly biodegradable polymer (Zhang, 2002). Alginate has been evaluated for this purpose, especially in drug delivery, to obtain improved mechanical properties and drug release kinetics (Zhang, Liu, Huang, Wang, & Wang, 2015). Alginates are natural polysaccharides extracted from marine brown algae (Tønnesen & Karlsen, 2002). They are composed of mannuronic acid (M) and guluronic acid (G) blocks arranged in (M)n , (G)n , or (MG)n sequences (da Silva et al., 2017). This polymer has many applications, especially because of its gelling ability in the presence of divalent cations (Leong et al., 2016). In the pharmaceutical field, alginate application is limited by its low mechanical strength, fast drug release, and lack of bioadhesion (Zhang et al., 2015). A blend of alginate with other polymers, such as chitosan (Liu et al., 2016), has been proposed to improve alginate’s characteristics for pharmaceutical applications. In this work, ibuprofen was incorporated into a sericin and alginate blend to obtain a gastro-resistant particle and sustained drug release. To fulfil this purpose, different formulations were prepared with various sodium alginate contents. The influence of a chemical crosslinking agent (poly (ethylene glycol) diglycidyl ether, abbreviated PEGDGE and more simply called PEG throughout the following sections) in the blend was evaluated. This reagent has a terminal epoxy group (cyclic ether of three atoms) that is capable of chemically crosslinking with both sericin and alginate (Lee & Yuk, 2007; Motta, Barbato, Foss, Torricelli, & Migliaresi, 2011). It is also a known acceptable drug excipient (Zhang, Le, Wang, Zhao, & Chen, 2012). Although previous studies have investigated alginate beads loaded with ibuprofen (Khazaeli, Pardakhty, & Hassanzadeh, 2008; Nagpal et al., 2012) and other polymers blends such as poly(vinyl alcohol)/chitosan (Morgado, Miguel, Correia, & AguiarRicardo, 2017), an ibuprofen-loaded sericin and alginate blend has not yet been proposed. The incorporation efficiency and in vitro dissolution were evaluated to optimize the formulation. The particles produced were characterized by scanning electron microscopy (SEM) for the morphology, Fourier transform infrared spectroscopy (FTIR) for the functional groups, and optical microscopy (OM) for the mean diameter and size distribution. Materials and methods Materials A sericin solution was obtained from silkworm (Bombyx mori) cocoons, kindly provided by Bratac Silk Mills Company (Brazil). Solid commercial sodium alginate and PEG as a viscous liquid (average Mn = 526) were purchased from Sigma–Aldrich (USA). Ibuprofen powder was purchased from Purifarma (Brazil). The reagents used were of analytical grade. Calcium chloride was purchased from AnidrolTM (Brazil). Hydrochloric acid (37%), trisodium phosphate, monopotassium phosphate, and sodium hydroxide were purchased from Dinâmica (Brazil). Solutions were prepared using ultrapure water (Reverse Osmosis, Gehaka, Brazil).

Table 1 Labeling and contents of ibuprofen (Ibu) formulations. Formulation

Sericin (% w/v)

Alginate (% w/v)

Ibuprofen (% w/v)

PEG (% w/w)

Ibu 1 Ibu 2 Ibu 3 Ibu 4 Ibu 5

2.5 2.5 2.5 2.5 –

1.0 1.5 2.8 2.8 2.8

2.0 2.0 2.0 2.0 2.0

– – – 10.0 –

clave (AV-18, Phoenix, Brazil) with a cocoon to water ratio of 40 g of cocoons per 1 L of water. The mixture was kept at 120 ◦ C and 1 kgf/cm2 g (98066.5 Pag) for 40 min, and then filtered (80-g qualitative filter paper) to separate fibroin. The sericin solution was stored at room temperature (25 ◦ C) for about 12 h to stabilize the hydrogel, and protein granules appeared. Next, it was frozen for at least 24 h. After that, it was thawed at room temperature (25 ◦ C). This step was conducted to cryoconcentrate the sericin, as detailed by da Silva et al. (2014). The sericin solution was filtered (80-g qualitative filter paper), and high molecular weight sericin was obtained and heated in an autoclave for 10 min at 1 kgf/cm2 g to dissolve all protein granules. Next, the mass fraction of sericin in the solution was adjusted to 2.5% w/v by dilution with ultrapure water.

Ibuprofen incorporation in the alginate/sericin blend and preparation of particles The sericin solution 2.5% w/v was heated in autoclave at 70 ◦ C for 10 min to dissolve protein granules and stirred on an UltraturraxTM (T18, IKA, USA) at temperature up to 55 ◦ C. Sodium alginate was then added, and the mixture was stirred at 4000 rpm. After homogenization, ibuprofen was added and dispersed with stirring at 8000 rpm. The formulations prepared were labeled as Ibu 1–Ibu 5 (Table 1). For the Ibu 4 formulation, PEG was added to crosslink sericin and alginate, and to evaluate its influence on drug particles. The preparation of particles followed an ionotropic gelation method adapted from Khandai et al. (2010). This is a simple, rapid, and inexpensive process that is widely used (Agüero, Zaldivar-Silva, ˜ & Dias, 2017). The solution containing sericin/alginate and Pena, ibuprofen was dropped into a calcium solution (CaCl2 , 3% w/v), which is an ionic crosslinking agent of alginate, under continuously magnetic stirring. The particles produced were stirred in jar test (JT203, Milan, Brazil) at 100 rpm for 30 min for complete crosslinking, washed with deionized water, and dried at room temperature.

Ibuprofen incorporation efficiency To determine the incorporation efficiency, 0.1 g of dried particles was added to 500 mL of phosphate buffer (pH 6.8) and kept overnight. Three dispersions were prepared for each formulation. The dispersion was sonicated (1510RMTH, Branson, USA) for 15 min and filtered through a 0.45-␮m filter. The ibuprofen content of the filtrate was determined spectrophotometrically (UVmini1240, Shimadzu, Japan) at 222 nm. The incorporation efficiency was determined using Eq. (1). Experimental drug content . Theoretical drug content

Sericin extraction

Incorporation efficiency =

We used the method presented by da Silva, da Silva, Vieira, Gimenes, and da Silva (2016) to obtain sericin. Initially, silkworm cocoons were cleaned and cut into 1-cm2 pieces. These pieces were washed with tap water, rinsed with ultrapure water, and then dried in an oven at 45 ◦ C. The sericin extraction was performed in an auto-

The theoretical drug content was calculated based on the fraction of the drug initially added to the particle, the mass of dried particles (0.1 g), and the volume of phosphate buffer solution (500 mL) used in the evaluation of the incorporation efficiency.

(1)

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In vitro drug release study The blend employed in the present study is similar to that evaluated by Vidart, da Silva, Rosa, Vieira, and da Silva (2018) for the incorporation of diclofenac sodium. They showed the particles were gastro-resistant, and drug release in an acidic medium was close to 2%. This characteristic was attributed to the presence of alginate, which was also confirmed by Arica et al. (2005), who verified the gastro-protective characteristics of ibuprofen-loaded alginate beads. The in vitro release profile of ibuprofen was obtained according to the ibuprofen sustained release monograph specified in U.S. Pharmacopeia XXIX (USP, 2006) using a USP dissolution apparatus 1 (UDT-814-6, Logan, USA). Drug particles equivalent to 200 mg of ibuprofen were placed in a basket at 50 rpm, and the medium (phosphate buffer, pH 7.2) was maintained at 37.0 ± 0.5 ◦ C. At predetermined intervals, 5-mL aliquots were withdrawn and 5 mL of fresh medium was added. The drug concentration in each aliquot was determined spectrophotometrically. Kinetic modeling of drug release To evaluate the drug release kinetics and mechanisms, several mathematical models were fitted to the in vitro drug release experimental data as detailed below (Costa & Lobo, 2001; Dash, Murthy, Nath, & Chowdhury, 2010). Zero order model This model is usually applied to describe dosage forms that do not disaggregate, and that release the drug slowly. It is represented by Eq. (2), in which Q is the drug release at time t and k0 is the zero order release constant expressed in units of concentration/time. Q = k0 t

(2)

First order model This model describes drug release from conventional formulations, where the drug release decays exponentially over time. This model is represented by Eq. (3), in which Q0 is the initial amount of drug released, Q is the drug released at time t, and k1 is the first order release constant expressed in reciprocal time. In Q = In Q0 − k1 t.

Q = Q0 ⎣1 − e



−(t−T ) a

⎤ b

⎦.

(4)

Higuchi model This model considers drug release as a diffusion process based on Fick’s law. Drug diffusion through the matrix is the rate limiting step. This model is represented by Eq. (5), in which Q is the drug release at time t and kH is the Higuchi dissolution constant (Higuchi, 1961, 1963). Q = kH t 1/2 .

Analysis

Equipment

Parameters

Optical microscopy

Model DC4-456H, National Stereo Microscope, Brazil Model LEO 440i, LEO Electron Microscopy, UK Model Nicolet 6700, Thermo Scientific, USA

500 particles diameters were measured –

Scanning electron microscopy Fourier transformed infrared spectroscopy

Sample analyzed as KBr pastille form in the range 4000–400 cm−1

Korsmeyer–Peppas model This model is a semi-empirical model that analyzes Fickian and non-Fickian release of drugs from swelling and non-swelling polymeric systems. Eq. (6) describes this model, in which Q/Q∞ is the drug fraction released at time t, kKP is the kinetic constant, and n is the diffusion exponent related to the drug release mechanisms. The values of n can be interpreted as follows: n = 0.45 or 0.43, for Fickian diffusion; 0.45 < n < 0.89 or 0.43 < n < 0.85, for non-Fickian release (anomalous); n = 0.89 or 0.85, for Case-II transport (drug diffusion through gel swelling/relaxation); and n > 0.89 or n > 0.85, for Super Case-II transport, and all for cylindrical or spherical shape, respectively (Ritger & Peppas, 1987). Q = kKP t n . Q∞

(6)

Hopfenberg model This is a general mathematical equation developed to describe drug release from surface-eroding devices with a variety of geometries. The erosion of the matrix is the rate-limiting step. Eq. (7) describes this model, in which Q is the drug release at time t, Q∞ is the total amount released, k is the erosion rate constant, C0 is initial drug concentration in the matrix, a0 is the initial radius for a sphere or cylinder, and n is equal to 2 for a cylinder and 3 for a sphere (Hopfenberg, 1976).



Q kt =1− 1− Q∞ C0 a0

n .

(7)

Characterization of the sericin/alginate particles loaded with ibuprofen

(3)

Weibull model This is an empirical equation, successfully applied to almost all kinds of dissolution curves. Although it is not appropriate to characterize release kinetics, it can describe the dissolution curve in terms of its parameters. Eq. (4) represents this model, in which Q is the drug release at time t, Q0 is the initial amount of drug released, T is the lag time, a is a scale parameter defining the process time scale, and b is the shape parameter and characterizes the dissolution curve as exponential (b = 1), S-shaped (b > 1), or parabolic (b < 1).

⎡

3

(5)

Drug particles were characterized to evaluate ibuprofen incorporation. All of the characterization techniques are described in Table 2. Micrographs at 1000× of formulations Ibu 1–Ibu 5 were obtained for cross-sections of the particles to observe their insides. The particles were cut manually using a scalpel. Results and discussion Ibuprofen incorporation efficiency The ibuprofen incorporation efficiency in the sericin and alginate blend (Ibu 1, Ibu 2, and Ibu 3) ranged from 73.01% ± 1.70% to 94.15% ± 4.21% (Fig. 1). The Ibu 5 particles, which did not contain sericin, had the lowest incorporation efficiency (57.85% ± 1.74%). This is evidence that sericin is important in improving ibuprofen incorporation. The structural characteristics of sericin, which is composed of 18 amino acids with strong polar side groups (i.e., hydroxyl and carboxyl) (Zhang, 2002), could contribute to this. Strong crosslinking of sericin and alginate occurred during particle production, and this could prevent drug loss. The Ibu 5 particles contained only alginate, which could have allowed for loss of more drug crystals. Nagpal et al. (2012) evaluated the incorporation of ibuprofen in a matrix of alginate and magnesium stearate, and the incorporation efficiency obtained with a similar amount of algi-

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4 Table 3 Dissolution model parameters for formulations Ibu 1–Ibu 5. Model

Parameter

Formulation Ibu 1

Ibu 2

Ibu 3

Ibu 4

Ibu 5

Zero order

k0 2 Radj AIC

0.921 0.912 49.99

0.675 0.806 67.57

0.076 0.796 84.60

0.070 0.806 93.80

0.062 0.961 69.48

First order

k1 2 Radj AIC

0.015 0.739 55.25

0.014 0.827 69.62

0.002 0.907 72.29

0.002 0.894 82.39

0.001 0.907 77.47

Weibull

a (×103 ) b Td 2 Radj AIC

1.273 1.788 54.53 0.997 23.13

1.247 1.739 60.28 0.999 10.47

0.1409 0.768 627.9 0.912 70.18

0.1480 0.775 631.6 0.949 81.18

4.296 1.225 924.3 0.925 77.01

Higuchi

kH 2 Radj AIC

7.444 0.415 62.33

7.072 0.580 69.62

2.410 0.952 61.91

2.380 0.951 69.99

2.028 0.818 83.47

Korsmeyer–Peppas

kKP n 2 Radj AIC

1.412 1.380 0.903 50.68

2.313 1.419 0.831 64.36

1.946 0.505 0.953 63.19

2.009 0.457 0.950 71.57

0.225 0.671 0.976 63.30

Hopfenberg; n = 2

k 2 Radj AIC

0.006 0.899 48.59

0.006 0.939 53.43

0.0006 0.882 76.58

0.0005 0.879 85.80

0.0004 0.954 70.12

Hopfenberg; n = 3

k 2 Radj AIC

0.005 0.853 51.20

0.004 0.912 56.15

0.0004 0.894 74.75

0.0004 0.888 84.18

0.0003 0.941 72.58

The numbers that appear in bold and italic are for the model with the best fit for each formulation.

polar side groups and improves the physical and mechanical properties of a blend (Lee & Yuk, 2007). These improvements aid drug incorporation. In vitro drug release study Drug release from particles Ibu 1 and Ibu 2 reached equilibrium after 120 min, whereas that from Ibu 3, Ibu 4, and Ibu 5 took about 1400 min to reach equilibrium (Fig. 2). Greater amounts of alginate slowed down the drug release, leading to sustained drug delivery. This outcome is related to the high degree of cross-linking provided by a large amount of alginate. Hence, particle swelling in the presence of solvent was reduced, and drug release was delayed (Wang, Zhang, Hu, Yang, & Du, 2007). No significant difference was observed in dissolution profile when PEG was added (formulation Ibu 4). Kinetic modeling of drug release Fig. 1. Ibuprofen incorporation efficiency for the formulations (Ibu 1–5) detailed in Table 1.

nate to that used in the present research was close to 40%. Arica et al. (2005) also evaluated alginate beads loaded with ibuprofen, and achieved incorporation efficiencies between 6.5% ± 1.5% and 14.8% ± 2.1%. In comparison with these other blends, the sericin and alginate blend used in the present study gave better incorporation efficiencies. A comparison between Ibu 1, Ibu 2, and Ibu 3 showed that the particles with the highest alginate content (Ibu 3) had the lowest incorporation efficiency. Thus, alginate seems to control the drug incorporation, following the same explanation of Ibu 5. Formulation Ibu 4 contained PEG, whereas Ibu 3 did not. This reagent improved the incorporation efficiency through similar behavior to sericin and alginate binding. PEG is a crosslinking agent that promotes covalent chemical cross-linking between polypeptide chains through

The kinetic models presented in Section “Kinetic modeling of drug release” were applied to the experimental data. Table 3 presents the parameters obtained for each model, the adjusted 2 ), and the Akaike information cricoefficient of determination (Radj terion (AIC), which was used to choose the best model for the experimental data. Although the coefficient of determination (R2 ) is commonly used to compare different models, it tends to increase on the addition of more parameters. Consequently, when models 2 is more with different numbers of parameters are compared, Radj appropriate (Kalam et al., 2007). AIC gives the best fit based on maximum likelihood. The model with the smallest AIC value among a set of models is the one that gives the best fit (Costa & Lobo, 2001). Different models were better fit to the experimental data, depending on the formulation (Table 3). Ibu 1 and Ibu 2, which had short equilibrium time (100 min), were better fit by the Weibull model. This is a general empirical equation that is unable to charac-

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Fig. 2. Ibuprofen dissolution profiles for the formulations (Ibu 1–5) in simulated enteric media (pH 6.8).

terize dissolution kinetic properties. The value of parameter b (>1) indicated a complex release mechanism with an S-shaped curve for Ibu 1 and Ibu 2. In case of Ibu 3 and Ibu 4, (b < 1), the dissolution curve was characterized as parabolic. In addition, from the a and b parameters, we estimated Td , the time to release 63.2% of drug (a = (Td )b ) (Patel et al., 2008). For both Ibu 1 and Ibu 2, a low Td was required to dissolve 63.2% of drug. Higher Td values for other formulations indicated they had slower release.

For Ibu 3 and Ibu 4, the best fit was obtained with the Higuchi model, which is a theoretical model that provides information about drug release kinetics. In this case, drug release is described as a diffusion process based on Fick’s law (Costa & Lobo, 2001). Thus, prolonged release was achieved by drug diffusion through the polymeric matrix. The Korsmeyer–Peppas model, which is a simple semi-empirical model, was also a good fit. This model is usually applied when the release mechanism is not well known. From its

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Fig. 3. Micrographs obtained by scanning electron microscopy of the pure drug (Ibu = ibuprofen), sericin/alginate particles (SerAlg), and sericin/alginate particles loaded with ibuprofen (Ibu 1–Ibu 5) at magnifications of (a) 150× and (b) 1000×.

parameter n, it is possible to analyze this mechanism for cylindrical and spherical shapes: 0.45 < n < 0.89 and 0.43 < n < 0.85 indicated an anomalous release (Fickian diffusion associated with Case II transport). This confirmed the diffusion shown by the Higuchi model (Chime, Onunkwo, & Oniyshi, 2013). Case II transport involves dissolution of the polymer and chain disaggregation (Ford et al., 1991). Similar observations were made by Guerra-Ponce et al. (2016), who evaluated the in vitro dissolution of sustained release matrix tablets containing ibuprofen. They found that carbopol loaded with ibuprofen gave extended drug release over 18 h and concluded that Case II transport was important for ibuprofen release. Formulation Ibu 5, composed of alginate and ibuprofen, had a better fit with the Korsmeyer–Peppas model, as in the previous discussion, and the zero order model. The latter describes systems where a drug’s release does not depend on its concentration, and matrix erosion controls release rather than diffusion (Chime et al., 2013; Ford et al., 1991).

Characterization of sericin/alginate particles loaded with ibuprofen Morphological analysis Micrographs at 150× and 1000× magnification were obtained for the sericin/alginate particles loaded with ibuprofen, the pure drug, and sericin/alginate particles with no drug incorporated (Fig. 3).

Table 4 Mean particle diameters and the adjusted coefficients of determination when fitting the measured size distribution with normal distribution for samples of formulations Ibu 1–Ibu 5. Formulation

Mean diameter (mm)

Ibu 1 Ibu 2 Ibu 3 Ibu 4 Ibu 5

1.08 ± 0.11 1.05 ± 0.10 0.96 ± 0.07 0.98 ± 0.09 0.80 ± 0.13

2 Radj

0.986 0.987 0.998 0.990 0.527

Optical micrographs showed the particles containing ibuprofen were spherical. However, the particles of Ibu 1 and Ibu 5 were elongated compared with the other particles. The surfaces of the particles containing ibuprofen were rougher than the particles containing only sericin/alginate, which could be caused by the ibuprofen trapped within the polymer matrix. The increased surface roughness could delay drug release by making it difficult for water to penetrate into the particles, which is required for particle swelling and disintegration. Particles size distribution The particles sizes were analyzed by OM and the mean diameter and size distribution were obtained by measuring the diameters of 2 for normal (Gaussian) 500 particles. The mean diameter and the Radj distribution fitting are shown in Table 4 and the size distributions are shown in Fig. 4.

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Fig. 4. Particle size distributions obtained for samples of formulations Ibu 1–Ibu 5.

The particles containing ibuprofen had a size range from 0.80 ± 0.13 to 1.08 ± 0.11 mm. Considering the error value of each measurement, we assumed that all formulations had similar diameters. However, the average particle size decreased on addition of more alginate, as observed for formulations Ibu 1, Ibu 2, and Ibu 3. The particle with no sericin was the smallest (Table 4). The alginate probably reduced the particle size by the high degree of crosslinking, which would increase aggregation of the molecules. Among the particles, those with the lowest mean diameters had the lowest incorporation efficiencies and showed better sustained release behavior, which is evidence that this parameter affects both incorporation and dissolution. Arica et al. (2005) produced alginate beads loaded with ibuprofen and obtained particles with a size range of 1.15 ± 0.4 to 3.15 ± 0.6 mm. For encapsulation of the beads in gelatinous pharmaceutical capsules, the smaller

particles sizes obtained in the present work may be more advantageous. 2 (Table 4). Except for Gaussian fitting was used to obtain the Radj formulation Ibu 5, which contained no sericin, all of the formula2 values. These tions followed a normal distribution with high Radj results indicate that the presence of sericin improves the normal distribution of the particle sizes. The best fitting was obtained for 2 = 0.998). Ibu 3 (Radj Functional groups FTIR spectra were obtained for the pure drug (Ibu), a sericin/alginate blend (SerAlg), and all ibuprofen formulations (Fig. 5). Characteristic bands were observed for sericin and alginate. Bands at 1510 and 1580 cm−1 were attributed to C C and C O stretching of carboxyl groups, respectively. The band at 1530 cm−1

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fitting. An analysis of all the results showed that a low amount of alginate led to greater incorporation efficiencies. However, these particles did not achieve sustained release. Thus, even though particles containing more alginate (Ibu 3 and Ibu 4) had lower incorporation efficiencies than those with less alginate, they were the best particles when considering both incorporation efficiency (for multi-particulate systems) and sustained drug release. Acknowledgments The authors thank CNPq (Proc. 470615/2013-3 and 300986/2013-0) and FAPESP (Proc. 2015/13505-9 and 2016/050071) for financial support and BRATAC Company for providing the silkworm cocoons. References

Fig. 5. FTIR spectra obtained for formulations Ibu 1–Ibu 5, the pure drug (Ibu = ibuprofen), and a sericin/alginate blend (SerAlg).

was attributed to the N–H group, and the band at 1200–1000 cm−1 was assigned to characteristic saccharide absorptions of polysaccharides (Srisuwan & Baimark, 2013; Vidart et al., 2018). The spectra of formulations Ibu 1–Ibu 5 and the pure drug were similar, confirming the drug was incorporated in the particles. Some characteristic ibuprofen bands were observed in the spectra of formulations Ibu 1–Ibu 5. The bands at 1721 cm−1 and at 1231 cm−1 were assigned to C O stretching and C O stretching, respectively. The band at 779 cm−1 was assigned to CH2 vibrations. These peaks are known as the fingerprint of ibuprofen. Other characteristic peaks were observed at 1507 and 746 cm−1 for C C stretching vibrations, at 936 cm−1 for CH3 rocking, and at 1462 cm−1 for CH3 asymmetric deformation (Ramukutty & Ramachandran, 2012). The similarity between the spectra shown in Fig. 5 was evidence that ibuprofen did not react with the sericin/alginate blend. Therefore, ibuprofen will be stable in the prepared formulations. Conclusions A sericin/alginate blend was successfully applied to ibuprofen incorporation through an ionic gelation technique, and this provided sustained drug release. The incorporation efficiency was improved by addition of sericin, as well as PEG, with an incorporation efficiency range of 73.01% ± 1.70% to 94.15% ± 4.21%. The release time was affected by the amount of alginate added. Formulations containing large amounts of alginate had sustained release, with equilibrium achieved after 1400 min. According to mathematical modeling, this sustained release was mainly achieved by drug diffusion through the matrix. Characterization by SEM and FTIR showed ibuprofen incorporation. OM showed that the particle size range was 0.80 ± 0.13 to 1.08 ± 0.11 mm. Furthermore, the addition of sericin improved the particle size distribution Gaussian

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Please cite this article in press as: Freitas, E. D., et al. Development of mucoadhesive sericin/alginate particles loaded with ibuprofen for sustained drug delivery. Particuology (2018), https://doi.org/10.1016/j.partic.2017.12.011