Design of a novel crosslinked HEC-PAA porous hydrogel composite for dissolution rate and solubility enhancement of efavirenz

G Model

IJP 14952 1–9 International Journal of Pharmaceutics xxx (2015) xxx–xxx

Contents lists available at ScienceDirect

International Journal of Pharmaceutics journal homepage: www.elsevier.com/locate/ijpharm

Design of a novel crosslinked HEC-PAA porous hydrogel composite for dissolution rate and solubility enhancement of efavirenz

1 2

3 Q1 4 5 6 7 8

M. Mabrouk a,b , D.R. Chejara a , J.A.S. Mulla a,c , R.V. Badhe a , Y.E. Choonara a , P. Kumar a , L.C. du Toit a , V. Pillay a, * a Wits Advanced Drug Delivery Platform Research Unit, Department of Pharmacy and Pharmacology, School of Therapeutic Sciences, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, 7 York Road, Parktown, 2193, South Africa b Biomaterials Department, National Research Centre, 33El Bohouth St.(former EL Tahrir St.), Dokki, Giza P.O. 12622, Egypt c Department of Pharmaceutics, M.M.U. College of Pharmacy, Rajiv Gandhi University of Health Sciences, Bangalore, Karnataka, India

A R T I C L E I N F O

A B S T R A C T

Article history: Received 6 March 2015 Received in revised form 27 May 2015 Accepted 31 May 2015 Available online xxx

The purpose of this research was to synthesize, characterize and evaluate a Crosslinked Hydrogel Composite (CHC) as a new carrier for improving the solubility of the anti-HIV drug, efavirenz. The CHC was prepared by physical blending of hydroxyethylcellulose (HEC) with poly(acrylic acid) (PAA) (1:1) in the presence of poly(vinyl alcohol) (PVA) (as a crosslinker) (1:5) under lyophilization. Efavirenz was loaded in situ into the CHC in varying proportions (200–600 mg). The CHC demonstrated impressive rheological properties (dynamic viscosity = 6053 mPa; 500 s
1) and tensile strength (2.5 mPa) compared with the native polymers (HEC and PAA). The physicochemical and thermal behavior also confirmed that the CHC was compatible with efavirenz. The incorporation of efavirenz in the CHC increased the surface area (4.4489–8.4948 m2/g) and pore volume (469.547–776.916 Å) of the hydrogel system which was confirmed by SEM imagery and BET surface area measurements. The solubility of efavirenz was significantly enhanced (150 times) in a sustained release manner over 24 h as affirmed by the in vitro drug release studies. The hydration medium provided by the CHC network played a pivotal role in improving the efavirenz solubility via increasing hydrogen bonding as proved by the zeta potential measurements (
18.0 to +0.10). The CHC may be a promising alternative as an oral formulation for the delivery of efavirenz with enhanced solubility. ã2015 Published by Elsevier B.V.

Q3 Keywords: Hydrogel composite Physical crosslinking Efavirenz Rheology Dissolution rate Oral solubility

9

1. Introduction

10

HIV/AIDS is the most deadly disease of our time. Globally an estimated 35.3 million people were living with HIV in 2012. There were 2.3 million new HIV infections globally in 2012, showing a 33% decline in the number of new infections from 3.4 million in 2001. At the same time the number of AIDS deaths is also declining with 1.6 million AIDS deaths in 2012, compared to 2.3 million in 2005 (United Nations AIDS Report, 2013). The continual administration of high and frequent doses of at least two or more antiretroviral (ARV) drugs improves the pharmacotherapy of patients (Andrews and Friedland, 2000). A limited number of ARVs have been approved by the US FDA for the treatment of AIDS especially for paediatric administration (Giaquinto et al., 2008). Among the ARVs, efavirenz is a widely prescribed HIV-1 specific drug which has very poor aqueous solubility (water solubility =

11 12 13 14 15 16 17 18 19 20 21 22 23

Q2

* Corresponding author. Tel.: +27 11 717 2274; fax: +27 11 642 4355/86 553 4733. E-mail address: [email protected] (V. Pillay).

4 mg/mL). This Non-Nucleoside Reverse Transcript Inhibitor (NNRTI) is utilized in the initial stages of pediatric HIV. However, due to its low bioavailability the drug is administrated in doses between 200 and 600 mg per day (Lindenberg et al., 2004; Wintergerst et al., 2008; Sosnik et al., 2009). The side-effects or potential discontinuation of the treatment course is achieved Q4 mainly by cumbersome therapeutic monitoring of efavirenz. During the last decade several researchers have reported on the enhancement of efavirenz solubility using various formulation strategies. For example, Kolhe et al. (2014) reported on the Q5 improvement of dissolution and bioavailability of efavirenz using a hydrophilic polymer, surfactant and plasticizer. Sunitha and coworkers (2014) explored the synthesis of self-emulsifying drug delivery systems for improving the oral solubility of efavirenz. Lariz et al. (2014) investigated the effect of solid dispersions of efavirenz in PVP-k30 and Deshmukh and Kulakrni (2012) developed a self-micro-emulsifying drug delivery system of efavirenz with improved dissolution rate for oral delivery. In addition, Chaitanya et al. (2014) demonstrated the individual and combined effects of b-cyclodextrin and Lutrol1 in enhancing the

http://dx.doi.org/10.1016/j.ijpharm.2015.05.082 0378-5173/ ã 2015 Published by Elsevier B.V.

Please cite this article in press as: Mabrouk, M., et al., Design of a novel crosslinked HEC-PAA porous hydrogel composite for dissolution rate and solubility enhancement of efavirenz. Int J Pharmaceut (2015), http://dx.doi.org/10.1016/j.ijpharm.2015.05.082

24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

G Model

IJP 14952 1–9 2 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87

M. Mabrouk et al. / International Journal of Pharmaceutics xxx (2015) xxx–xxx

solubility and dissolution rate of efavirenz while Bodakunta et al. (2013) reported used a liquid–solid compaction technique. The synergistic performance of blended polymeric micelles comprising linear and branched poly(ethylene oxide)-poly (propylene oxide) for more effective encapsulation of efavirenz was described by Diego et al. (2011). As demonstrated, numerous formulation strategies have been prototyped in an attempt to enhance the aqueous solubility of efavirenz. However, to the best of our knowledge, none to date have concluded on the use of an aqueous hydrogel-based system for this purpose. Although hydrogels have many remarkable advantages in pharmaceutical formulation science, a key outstanding characteristic of hydrogels in drug solubility enhancement is their high surface-area-to-volume ratio that allows for a rapid response and maximum interaction with the surrounding bio-environment. Hydrogels are three-dimensional hydrophilic polymer networks that exhibit volume or phase transition in response to external environmental changes, such as ionic strength, pH, temperature, electronic, pressure and magnetic fields. Hydrogels have attracted the attention of many scientists in the field of controlled drug release (Qiu and Park, 2001; Gupta et al., 2002). Recently, improving the properties of conventional hydrogels, especially the response rate has been explored through several techniques such as the formation of porous or superporous structures (Chen and Park, 2000; Gemeinhart et al., 2000; Cheng et al., 2003; Zhang et al., 2003a,b; Serrano et al., 2004; Tang et al., 2005), the addition of polymer particles within the gel network (Zhang et al., 2005) as well as cold treatment (Zhang and Zhuo, 1999) or freeze-drying of swollen hydrogels (Kato et al., 2003). The main objective in this work was to synthesize and characterization a new porous hydrogel composite prepared by physical crosslinking and lyophilization of hydroxyethylcellulose (HEC) and polyacrylic acid (PAA) in the presence of polyvinyl alcohol (PVA) as a Crosslinked Hydrogel Composite (CHC) for enhancement of the dissolution rate and solubility of efavirenz. The selection of the polymers was directed by their valuable properties in terms of gelation and foaming properties. PVA was used as a plasticizer and physical crosslinker due to its hydrogen bonding capability. Physicochemical, thermal behavior and rheological properties of the prepared CHC with reference to the native polymers was investigated using various characterization techniques to determine the final properties of the new CHC. Furthermore, determination of the drug dissolution rate was established at varying pH values simulating gastrointestinal tract conditions to

evaluate the effect of the prepared CHC on the oral dissolution rate and solubility of efavirenz.

88

2. Materials and methods

90

2.1. Materials

91

Polyacrylic acid (PAA) with an average Mw = 450,000 g/mol and 2-hydroxyethylcellulose(HEC) (Mw = 90,000 g/mol) were purchased from Sigma–Aldrich (St. Louise, MO, USA). Polyvinyl alcohol (PVA) (87–89% hydrolyzed) (average Mw = 13,000– 23,000 g/mol) was purchased from Sigma–Aldrich (St. Louise, MO, USA). Efavirenz (EFV) 99.0% (UV, IR and HPLC) was purchased from Xing Cheng Chemphar (China). The water used was Milli-Q water from a Millipore Water Purification System.

92

2.2. Synthesis of the physical crosslinked hydrogel composite (CHC)

100

A porous networked hydrogel was prepared by physical crosslinking and subsequent lyophilization. A physical blend of PAA (10% w/v) and HEC (10% w/v) solutions was prepared and incubated at 70  C for 2 h. Furthermore, 10 mL of PVA (10% w/v) solution was added to the HEC-PAA blend after cooling to room temperature (21  C) and agitated for 48 h. Efavirenz (EFV) was dispersed as a solid in the resulting homogenous blend solution and the drug:polymer ratios were set as follows in consideration of the EFV effective dosing range between 200 and 600 mg per day: (F1) (200 mg EFV:100 mg CHC), F2 (300 mg EFV:100 mg CHC) and F3 (600 mg EFV:100 mg CHC). The resultant drug-loaded polymer blend was then frozen for 24 h at
80  C and thereafter lyophilized (Virtis2KBTXL-75 Benchtop SLC Freeze Dryer, UK) for 24 h at
64  C. Identical formulations were prepared without EFV loading as control samples. All the lyophilized samples were kept under a desiccator until further characterization. The proposed mechanism of CHC formation is demonstrated in Fig. 1.

101

2.3. Characterization of the HEC-PAA crosslinked hydrogel composite

118

2.3.1. Rheological analysis of the CHC Dynamic rheological measurements were performed using a Haake Mars (II) Modular Advanced Rheometer System equipped with cone plate geometry (Rotor C35/1, D = mm, 1 Titan) at a gap of 0.050 mm. The CHC was homogenized before measuring the theological properties. Four types of experiments were performed:

119

Fig. 1. Proposed hydrogen bond interactions occurring within the polymeric network of the CHC.

Please cite this article in press as: Mabrouk, M., et al., Design of a novel crosslinked HEC-PAA porous hydrogel composite for dissolution rate and solubility enhancement of efavirenz. Int J Pharmaceut (2015), http://dx.doi.org/10.1016/j.ijpharm.2015.05.082

89

93 94 95 96 97 98 99

102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117

120 121 122 123 124

G Model

IJP 14952 1–9 M. Mabrouk et al. / International Journal of Pharmaceutics xxx (2015) xxx–xxx 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149

(a) dynamic viscosities at different shear rates (b) frequency sweeps, (c) stress sweeps and (d) temperature ramp analysis of the CHC. Oscillatory stress sweeps were performed by applying an increasing shear stress logarithmically from 0.05 to 200 Pa at a fixed frequency of 1 Hz. A value of 1 Hz was selected due to the fact that frequency sweep experiments (in the case of individual polymers) the elastic modulus does not dominate the viscous modulus over the entire frequency range as they are in solution form (Fig. 2(b)). Furthermore, lower test frequencies are preferable for assessing behavior over prolonged scales, however the test duration is increased. In fact most oscillatory testing is carried out at frequencies in the range 0.01–10 Hz (Garai and Nandi, 2008a,b). Oscillatory frequency sweeps were performed between 50 and 0.10 rad s
1at a constant shear stress of 1 Pa. The temperature ramp experiment was performed in the temperature range of 20–70  C at a constant frequency of 1 Hz. Vegetable oil of low viscosity was used around the cone-plate geometry to minimize solvent evaporation at higher temperature. 2.3.2. Tensile strength analysis of the CHC The tensile strength of the CHC with and without PVA (physical crosslinker) was measured to evaluate the effect of PVA employing Textural Profile Analysis(TA.XTplus Texture Analyzer Stable Microsystems, Surrey, England). CHC films with and without PVA were prepared (30  10  1 mm) (L  W  T) and the tension speed was set at 0.5 mm/s with a starting tension force of 1 kg.

3

2.3.3. Physicochemical integrity characterization of the CHC Phase analysis and chemical bonds between the atoms before and after EFV-loading were analyzed employing XRD and FTIR, respectively. A Rigaku MiniFlex600 Benchtop X-ray Diffractometer (Rigaku Corporation, Tokyo, Japan) fitted with a 600W (40 Kv– 15 mA) X-ray generator, a counter monochromator to cut X-rays other than Cu Ka X-rays, and a high intensity D/tex Ultra high speed 1D detector was used for phase assessment of the CHC before and after EFV loading with reference to the native polymers, HEC, PAA and PVA. ATR-FTIR spectra were recorded for all samples to confirm the presence of physical crosslinking by characteristic functional group determination using a PerkinElmer Spectrum 2000 FTIR spectrometer, employing a single-reflection diamond MIRTGS detector (PerkinElmer Spectrum 100, Llantrisant, Wales, UK). All samples were analyzed by a universal ATR polarization accessory for the FTIR spectrum series at a resolution of 4 cm
1. Samples were placed on a diamond crystal running each sample 100 times in order to reduce the signal to noise ratio to a minimum of 10 in the range of 4000–600 cm
1 using a constant pressure of 120 psi.

150

2.3.4. Thermodynamic behavior of the CHC The thermal behavior of the CHC before and after EFV-loading was determined by differential scanning calorimeter (DSC; Mettler Toledo, DSC1, STARe System, Schwerzenback, Switzerland). Samples (10  1 mg) were placed into 40 mL aluminium pans and heated from 20 to 500  C with a heating rate of 10  C/min.

170

Fig. 2. Rheograms of the HEC-PAA hydrogel against the native polymers, (a) shear viscosities, (b) frequency sweep, (c) stress sweeps and (d) temperature ramp studies.

Please cite this article in press as: Mabrouk, M., et al., Design of a novel crosslinked HEC-PAA porous hydrogel composite for dissolution rate and solubility enhancement of efavirenz. Int J Pharmaceut (2015), http://dx.doi.org/10.1016/j.ijpharm.2015.05.082

151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169

171 172 173 174 175

G Model

IJP 14952 1–9 4 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224

M. Mabrouk et al. / International Journal of Pharmaceutics xxx (2015) xxx–xxx

2.3.5. Morphology and surface area characterization of the CHC The internal morphology and surface area of the CHC before and after EFV-loading was investigated using both scanning electron microscope (SEM) and BET surface area measurement. SEM analysis was undertaken using a PhenomTM SEM (FEI Company, OR). Samples were rendered electrically conductive before analysis through gold-sputter coating (SPI ModuleTM Sputter Coater, SPI Supplies, PA) and were attached to the SEM stub using adhesive carbon tape. The BET surface area measurements were computed utilizing a Porositometric Analyzer (Micromeritics ASAP 2020, Norcross, GA, USA). Briefly, 100 mg of the lyophilized CHC samples underwent 2 stages of analysis, first following a degassing stage and thereafter an absorption and desorption cumulative phase for accurate analysis of surface area. 2.3.6. In vitro drug release studies Drug release studies were performed using a USP 33 Apparatus II (Erweka DT 700 GmbH Germany) in which CHC formulations containing EFV (either 200, 300 or 600 mg) (n = 3) were placed within the dissolution vessel under a stainless steel ring-mesh assembly for preventing the paddle inflicting physical/mechanical damage to the samples and potentially altering the release profiles obtained due to unstable hydrodynamics (Pillay and Fassihi, 2000). Each vessel contained 900 mL simulated gastrointestinal fluid (SGIF) (ranging from pH 1.2, 4, 6.8 and 7.4 at 37  C). The rotating paddle method was set at a rotational speed of 50 rpm and the dissolution apparatus was calibrated for a 2 h run at pH 1.2 and pH 4, 4 h at pH 6.8 and 24 h at pH 7.4 with samples taken at 30 min intervals. Sampling involved the removal of 5 mL of dissolution media with subsequent replacement of fresh buffer in order to maintain sink conditions. Samples were then subject to UV spectroscopy analysis for EFV concentration analysis at 270 nm as reported previously (Anton et al., 2013). 2.3.7. Compressive strength analysis The effect of EFV on the compressive strength of the CHC was determined using a Texture Analyzer (TA.XTplus Texture Analyser Stable Microsystems, Surrey, England). Lyophilized cylindricallyshaped samples with dimensions of (10  10 mm) (L  D) were compressed according to the following conditions: pre-test speed of 0.5 mm/s, starting compression force of 1 kg, distance of 5 mm (50% of the sample length), test speed of 1 mm/s and an acquisition rate of 200 points/s. 2.3.8. Assessment of the mechanism of EFV solubility via zeta potential analysis In order to determine the mechanism of EFV solubility enhancement, the zeta potential of pure EFV and EFV-loaded CHC samples were measured using a Zeta Sizer NanoZS (Malvern Instruments, Worcestershire, UK). Samples (50 mg) were suspended in 10 mL of deionized water and filtered using a 0.22 mm filter before analysis.

225

3. Results and discussion

226

3.1. Reaction mechanism of the HEC-PAA crosslinked hydrogel composite

227 228 229 230 231 232 233 234 235

The physical crosslinking of HEC with PAA occurs by lyophilization of the blend in the presence of PVA. This mechanism depends on an increase of hydrogen bonding through PVA doping. In the present work Milli-Q water was used as the reaction medium. Under neutral conditions, HEC is able to react with the hydroxyl groups in both PAA and PVA. According to this assessment a proposed scheme of hydrogen bond interaction in the polymeric network of the newly formed HEC-PAA CHC is presented in Fig. 2.

3.2. Assessment of the rheological properties of the CHC

236

The shear viscosities of the CHC, HEC and PAA at 10% (w/v) are shown in Fig. 2. The dynamic viscosity (h) decreased with increasing shear rate (g ), indicating shear thinning behavior of all samples. This study revealed that the shear viscosity of the CHC was higher than the native polymers (i.e., PAA and HEC) even at the same concentration (Fig. 2(a)). Moreover, the CHC was found to have a gradual decrement in the viscosity with increasing shear rate to achieve an equilibrium viscosity while in the case of native PAA and HEC equilibrium was achieved rapidly. In the frequency sweep experiment, the CHC displayed an elastic modulus (G0 ) dominating the viscous modulus (G00 ) with varying frequencies throughout the experiment. However, they converged at the lower frequencies (Fig. 2(b)). In the case of native PAA and HEC, the elastic modulus did not dominate the viscous modulus over the native frequency range as these already existed in solution form. This confirmed the presence of strong crosslinks within the newly formed CHC network. The elastic modulus of the CHC was found to be frequency independent and significantly higher than the viscous modulus (G00 ) of the hydrogel system owing to its gel nature (Garai and Nandi, 2008a,b). Furthermore, the stiffness of the CHC was measured using an oscillatory stress sweep measurement technique (Fig. 2(c)). From this experiment it was deduced that the CHC was much mechanically stiffer since results displayed higher G0 values which was greater than the yield point (higher shear stress) compared with the native polymers (HEC and PAA). These rheological results were correlated with the tensile strength measurements. In the temperature ramp study the CHC did not reveal any crossover region between G0 and G00 . In addition, G0 remained higher than G00 over the native temperature range (20– 70  C) while the native polymers (HEC and PAA) showed a definite crossover region. This indicated the absence of the gel melting temperature for the CHC (Fig. 2(d)).

237

3.3. Tensile strength analysis

269

The tensile testing indicated both the strength and elasticity of the prepared CHC films as demonstrated in Fig. 3. It has been reported that a film suitable for biomedical application should be robust but also possess some degree of flexibility (Oyen, 2014). Results showed that the CHC film had a high tensile strength reflected by the Young’s modulus that was obtained for the CHC (0.58 MPa). This was followed by the CHC film without PVA (0.18 MPa). The difference in tensile strength between the CHC and the PVA-free CHC was not significant. However, the elongation at

270

Fig. 3. Tensile strength of the CHC with and without PVA (N = 3 SD  0.2).

Please cite this article in press as: Mabrouk, M., et al., Design of a novel crosslinked HEC-PAA porous hydrogel composite for dissolution rate and solubility enhancement of efavirenz. Int J Pharmaceut (2015), http://dx.doi.org/10.1016/j.ijpharm.2015.05.082

238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268

271 272 273 274 275 276 277 278

G Model

IJP 14952 1–9 M. Mabrouk et al. / International Journal of Pharmaceutics xxx (2015) xxx–xxx

5

Fig. 4. XRD spectra of (a) before EFV-loading and (b) after EFV-loading. 279

287

break point was improved considerably for the CHC compared to the PVA-free sample. During elongation, the movement and alignment of PVA within the polymeric network created voids for the rearrangement of molecular chains within the CHC acting as a plasticizer. Thus, the CHC exhibited a comparatively higher elongation at break point and higher tensile strength than without PVA. These results are consistent with the data discussed under the rheological analysis and confirm the physical crosslinking of HEC with PAA in the presence of PVA.

288

3.4. Evaluation of the physicochemical properties of the CHC

280 281 282 283 284 285 286

289 290 291 292 293 294 295 296 297 298 299 300 301 302 303

The CHC maintained its physical stability due to the presence of reversible physical junction domains associated with hydrogen bonding, hydrophobic interactions, chain entanglements, crystallinity, and/or ionic complications (Sophie et al., 2005). In order to identify the changes in crystallinity XRD analysis was performed on all samples. However, XRD results alone were not sufficient to prove the physical crosslinking process between the two polymers and therefore FTIR was also used as a further confirmatory approach. XRD patterns of PVA, HEC, PAA and the CHC are presented in Fig. 4(a). The amorphous structure of PVA and HEC was clearly noted, while PAA had a semi-crystalline structure. Therefore, the CHC displayed both amorphous and crystalline nature due to the physical combination between the native polymers (HEC and PAA) suggesting that physical crosslinking has no effect on the resultant phase. When EFV was entrapped within

the CHC matrix as shown in (Fig. 4(b)), the sharp crystalline peaks of the EFV increased the crystallinity of the surrounding polymer system due to its relatively high concentration. The increasing peak sharpness indicated EFV was successfully entrapped within the CHC matrix and formed a new solid phase of CHC–EFV with high crystallinity. The EFV-loaded samples showed diffraction patterns similar to that of pure EFV, indicating that the crystallinity of the drug was not affected by the in situ drug loading process. The CHC prepared by lyophilization may have a significant impact for biomedical applications, especially as a polysaccharidebased hydrogel due to the well-documented biocompatibility, low or non-toxicity and degradability under physiological conditions either enzymatically or chemically (Lozinsky, 2002; Vlierberghe et al., 2011). FTIR spectra are shown in Fig. 5(a and b). Clearly, it was observed that HEC (a polysaccharide) showed a broad band at 3440 cm
1 due to O

H stretching vibrations. The O

H bending was also seen at 1355 cm
1. Aliphatic C

H stretching and bending vibrations are indicated by bands at 2929 and 1429 cm
1. Bands at 1020 and 1050 cm
1 represent the C

O

C stretching vibrations, while a band at 1145 cm
1 was attributed to C

O stretching vibrations as previously reported (AL-Kahtania and Sherigara, 2014). The FTIR spectrum of PAA showed a strong band at 1720 cm
1 corresponding to the vibration stretching of carboxylic acid groups C¼O and O

H stretching at 3065 cm
1. PAA possessed the characteristic asymmetrical COO

band at 1410 cm
1 and
1 symmetrical COO

band at 1472 cm (Yu-Li et al., 2014). The FTIR spectrum of PVA proved the presence of an “OH” group peak of

Fig. 5. FTIR spectra of (a) before EFV-loading and (b)after EFV-loading.

Please cite this article in press as: Mabrouk, M., et al., Design of a novel crosslinked HEC-PAA porous hydrogel composite for dissolution rate and solubility enhancement of efavirenz. Int J Pharmaceut (2015), http://dx.doi.org/10.1016/j.ijpharm.2015.05.082

304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330

G Model

IJP 14952 1–9 6

M. Mabrouk et al. / International Journal of Pharmaceutics xxx (2015) xxx–xxx

Fig. 6. DSC profiles of (a) before EFV-loading and (b) after EFV-loading.

360

alcohol at 3470 cm
1, which was assigned to a stretching vibration of the OH group. In addition, acidic groups were present based on the band at 1730 cm
1 corresponding to C¼O stretching (Mabrouk et al., 2013). Moreover, it was expected that the FTIR spectrum of the CHC obtained by physical crosslinking would reveal all characteristic bands of the native polymers. However, the diminished O-H bending band at 1355 cm
1 can be attributed to hydrogen bonding. The EFV spectrum showed the presence of the following characteristic bands: 3314 cm
1 (NH stretch vibration), 2249 cm
1 (CRC stretching vibration), 1742 cm
1 (C¼O stretching vibration), 1601 cm
1 and 1494 cm
1 (C¼C of benzene ring stretching vibration), 1240 cm
1 (CN stretch) and1165 cm
1 (CO stretching vibration). In the region of lower frequency bands at 1073 cm
1 and 1037 cm
1 were assigned to CH deformation vibrations on the plane and at 976 cm
1 and 926 cm
1 on the CH out of plane deformation. Finally, a CF stretching vibration was observed at a frequency of 689 cm
1 and 652 cm
1 as documented in other investigations (Bodakunta et al., 2013; Lariza et al., 2014). A few hydrogel bands are diminished in the FTIR spectra of EFVloaded CHC due to the high intensity bands of EFV. Moreover, any hydrogen bonding that occured between the hydrogel and EFV were not considered detrimental to the chemical integrity of the system. The FTIR spectrum of the EFV-loaded CHC was generally similar in terms of overlapping bands of EFV and the drug-free CHC except for the band at 2750 cm
1 that was diminished due to overlap with the high intensive bands of EFV specifically in the region of 2700–2800 cm
1. This indicated that the chemical integrity between the hydrogel components and the drug EFV was maintained.

361

3.5. Assessment of the thermodynamic properties of the CHC

362

The thermal behavior of the HEC-PAA hydrogel blend doped with PVA was investigated by DSC to estimate how the thermal transitions of the prepared blend were affected by the addition of PVA to form the CHC and compared with the native polymers.DSC profiles are shown in Fig. 6(a). An endothermic peak was observed at approximately 100  C for all samples due to the minute quantity of moisture present in the samples. The DSC profiles of the HECPAA hydrogel blend were similar but with remarkable changes observed at the exothermic peak at about 181  C due to the doping

331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359

363 364 365 366 367 368 369 370

of PVA. The increase in the melting endotherm of the HEC-PAA hydrogel blend doped with PVA (425  C) compared with both pure HEC (380  C) and PAA (330  C) suggested an elevation of crystallinity. The improved thermal behavior of the CHC may be attributed to the increased interaction between modular groups of HEC and PAA with PVA which hindered the free rotation of the polymeric chains in the hydrogel composite. This in turn facilitated the formation of the CHC (Nigrawal et al., 2012). The thermal behavior of EFV may be identified by an endothermic peak corresponding to the temperature range between 136.86 and 141.75  C, characteristic of the melting process of its crystalline structure as shown in Fig. 6(b) (Lariza et al., 2014). It was also observed that EFV was present in a crystalline form as confirmed by XRD. This infers that there was a relative decrease in crystallinity of the EFV-loaded hydrogel compared to pure EFV that has led to the enhancement of the dissolution rate and solubility of EFV. This result was also supported by truncated broadening of the hydrogel Tg peak from 188–280  C to 185–300  C.

371

3.6. Assessment of morphology and surface structure of the CHC

389

The microstructural properties such as porosity, pore size and surface area of the CHC directly affected the dissolution rate, solubility and EFV release profile (Huixia et al., 2012). SEM images and the surface area of CHC samples have been analyzed as shown in Fig. 7(a and b) and Table 1 in order to determine the effect of EFV on the CHC and the hydrogel effect on the EFV microstructure. Cross-sectional SEM images of the CHC in Fig. 7(a) showed a highly interconnected porous CHC gel with irregular porous structures. Likewise the EFV-loaded CHC exhibited a highly interconnected porous composite gel but in an ordered pattern surface area and pore width, diameter and volume that was higher than the drugfree CHC. This was confirmed by BET surface area measurements shown in Fig. 7(c and d). The surface of the EFV-loaded CHC was characterized by EFV crystal deposition that was present in the form of small needle-shaped structures without affecting the morphological appearance as shown in Fig. 7(b–d). The porous medium of the CHC facilitated and enhanced the dissolution rate and solubility of EFV as demonstrated in the in vitro release study.

390

Please cite this article in press as: Mabrouk, M., et al., Design of a novel crosslinked HEC-PAA porous hydrogel composite for dissolution rate and solubility enhancement of efavirenz. Int J Pharmaceut (2015), http://dx.doi.org/10.1016/j.ijpharm.2015.05.082

372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388

391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407

G Model

IJP 14952 1–9 M. Mabrouk et al. / International Journal of Pharmaceutics xxx (2015) xxx–xxx

7

Fig. 7. SEM images of (a) CHC before EFV-loading, (b) pure EFV and (c, d) the EFV-loaded CHC. 408 409 410 411 412 413 414 415 416 417 418 419

3.7. In vitro drug release study The aim was to enhance the dissolution rate and solubility of EFV for maximizing the quantity of drug released in the gastrointestinal tract (GIT). The cumulative drug release (%CDR) profiles of EFV-loaded CHC formulations are shown in Fig. 8. All formulations had shown negligible release (up to 1.5%) in the first hour at pH values of 1.2 and 4.0 owing to the fact that the CHC exhibited swelling and degradation resistance at acidic pH. EFV was gradually released from the CHC in a sustained manner (up to 90% which is approximately 150 times more of the native EFV solubility value) in the remaining (22 h) at pH 6.8 and 7.4, with no significant burst release observed in each case. This may be

explained due to that, with prolonged time, small parts of the CHC became unstable and gradually swelled and eroded, while the remaining regions were stable enough during the EFV release process enabling gradual swelling and erosion combined with sustained EFV release. The absence of a burst release was due to pH

Table 1 BET Surface area and porosity measurements of the hydrogel before and after efavirenz loading. Sample

BET surface area (m2/g)

Average pore diameter (4V/A) (Å)

Pore volume (Å)

Hydrogel/Efavirenz 600 (F3) Hydrogel/Efavirenz 300 (F2) Hydrogel/Efavirenz 200 (F1) Hydrogel (control)

8.4948

70.29

776.92

6.1432

60.38

676.50

5.5231

52.64

533.35

4.4489

40.36

469.55

Fig. 8. Cumulative EFV release in gastrointestinal simulated pH buffers of Formulation 1 (200 mg EFV:100 mg CHC), Formulation 2 (300 mg EFV:100 mg CHC) and Formulation 3 (600 mg EFV:100 mg CHC) against pure EFV (N = 3 SD  0.5).

Please cite this article in press as: Mabrouk, M., et al., Design of a novel crosslinked HEC-PAA porous hydrogel composite for dissolution rate and solubility enhancement of efavirenz. Int J Pharmaceut (2015), http://dx.doi.org/10.1016/j.ijpharm.2015.05.082

420 421 422 423 424

G Model

IJP 14952 1–9 8

M. Mabrouk et al. / International Journal of Pharmaceutics xxx (2015) xxx–xxx

strength between 1 and 18 MPa from 10 to 60% strain. For samples loaded with EFV the mechanical properties were remarkably decreased compared with the native CHC. It is noted that with increasing the concentration of loaded EFV the mechanical properties decreased. These results are consistent with the results of porosity and surface area which indicated that porosity and surface area increased as the EFV concentration increased leading to a decrement of the mechanical properties. However, higher porosity and surface area are also substantially recommended for solubility enhancement (Yuvaraja and Khanam, 2014).

Fig. 9. Bar graph showing the compressive strength of the CHC with and without EFV (N = 3 SD  0.2). 425

435

sensitivity of the hydrogel thus making it more resistant to acidic pH. This was confirmed by the in vitro EFV release behavior (Fig. 8). These results revealed the advantages of using the CHC as a new drug carrier. The CHC formulation increased the %CDR due to its impressive microstructure as illustrated by the morphology and surface area achieved. The solubility enhancement correlated to the change in crystallinity that was confirmed by the DSC analysis. It is worth noting that CHC influenced the EFV dissolution rate which in turn affected the solubility equilibrium value. The CHC exhibited relatively high EFV-loading efficiency and adjustable drug release properties suitable for controlled drug delivery.

436

3.8. Assessment of the compressive strength of the CHC matrix

426 427 428 429 430 431 432 433 434

437 438 439 440 441 442 443

The compressive strength of all formulations with reference to the native hydrogel is presented in Fig. 9.The native hydrogel had superior compressive strength (up to 6.5 MPa) due to the presence of PVA as affirmed previously by the tensile strength measurements. This result is consistent with the results of Stammen et al. (2001) who indicated that the physically crosslinked PVA hydrogel prepared by lyophilization exhibited an increase in compressive

Q6 444 445 446 447 448 449 450 451 452 453

3.9. Zeta potential analysis

454

The zeta potential is a function of particle surface charge. Therefore it is related to the electrostatic repulsion between particles. The zeta potential has been proven to be extremely relevant to assessing drug solubility enhancement (Sunitha et al., 2014). In order to predict the mechanism of enhancing the dissolution rate and solubility of native EFV and the EFV-loaded CHC, samples were dispersed in deionized water, and the zeta potential measurements were determined in Fig. 10. The zeta potential measurements were specifically conducted in deionized water to avoid the influence of pH transitions. DLS results shows the zeta potential values obtained for the two samples native EFV and the EFV-loaded CHC. Clearly, it was noted that native EFV had a negative zeta potential, while the EFV-loaded CHC had both negative and positive zeta potential values owing to presence of the hydrogel. Results suggested that the CHC masked the positive charges for EFV through increased hydrogen bonding leading to the improvement of drug solubility. A decrease in crystallinity coupled with a change in zeta potential is important factors that played a role in increasing the EFV solubility.

455

4. Conclusions

474

In recent years, many formulation strategies have been used to improve the aqueous solubility of EFV. However, the use of hydrogels has been somewhat limited. This work stressed the potential of using a novel CHC for modulating the dissolution rate and solubility of EFV for oral administration. The porous HEC-PAA hydrogel composite was prepared by physical crosslinking and

475

Fig. 10. Zeta potential measurements of pure EFV and EFV-loaded CHC.

Please cite this article in press as: Mabrouk, M., et al., Design of a novel crosslinked HEC-PAA porous hydrogel composite for dissolution rate and solubility enhancement of efavirenz. Int J Pharmaceut (2015), http://dx.doi.org/10.1016/j.ijpharm.2015.05.082

456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473

476 477 478 479 480

G Model

IJP 14952 1–9 M. Mabrouk et al. / International Journal of Pharmaceutics xxx (2015) xxx–xxx 481

490

lyophilization. A high concentration of up to 600 mg of EFV may be incorporated without altering its active form. This was confirmed by XRD and FTIR studies. The porosity and the surface area of the formulation increased with the increase of EFV concentration leading to an improvement in dissolution rate and oral solubility. Incorporating EFV within the CHC facilitated an increase in its drug release rate in vitro. The CHC exhibited relatively high drug loading and adjustable drug release properties. This allows implementation of the CHC in the evolution of oral drug delivery for poorly soluble drugs using a hydrogel-based system.

491

Conflict of interest

482 483 484 485 486 487 488 489

492

The authors confirm that there are no conflicts of interest.

493

Acknowledgements

494 Q7 495

This work was funded by the National Research Foundation (NRF) of South Africa.

496

References

497 498 499 500 501 502 503 504 505 506 507 Q8 508 509 510 511 512 513 514 515 Q9 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537

AL-Kahtania, A.A., Sherigara, B.S., 2014. Controlled release of diclofenac sodium through acrylamide grafted hydroxyethyl cellulose and sodium alginate. Carbohydr. Polym. 104, 151–157. Andrews, L., Friedland, G., 2000. Progress in the HIV therapeutics and the challenges of adherence to antiretroviral therapy. Infect. Dis. Clin. North Am. 14, 1–26. Anton, S., Maruthi, G., Velmurugan, A., et al., 2013. Development of analytical method for efavirenz by UV spectrophotometry using sodium hydroxide as solvent. Der Chem. Sin. 4 (3), 144–149. Bodakunta, S., Srujan, K.M., Subrahmanyam, K.V., et al., 2013. Enhancement of solubility of efavirenz by liqusolid compact technique. IJIPSR 1 (3), 347–359. Diego, C.A., Graciela, F., Emilio, R.C., et al., 2011. Synergistic encapsulation of the anti-hiv agent efavirenz within mixed poloxamine/poloxamer polymeric micelles. Nanomed.: Nanotechnol. Biol. Med. 7, 624–637. Chaitanya, V., Narahari, N.P., Kumar, S., et al., 2014. Enhancement of solubility dissolution rate and formulation development of efavirenz tablets employing b-CD ant lutrol: a factorial study. J. Glob. Trends Pharm. Sci. 5, 1356–1360. Chen, J., Park, K., 2000. Synthesis and characterization of superporous hydrogel composites. J. Control. Release 65 (1–2), 73–82. Cheng, S.X., Zhang, J.T., Zhuo, R.X., 2003. J. Biomed. Mater. Res. Part A 67, 96. Deshmukh, A., Kulakrni, S.H., 2012. Novel self micro-emulsifying drug delivery systems (smedds) of efavirenz. J. Chem. Pharm. Res. 4 (8), 3914–3919. Garai, A., Nandi, A.K., 2008a. Rheology of ()-camphor-10-sulfonic acid doped polyaniline-m-cresol conducting gel nanocomposites. J. Polym. Sci. Part B: Polym. Phys. 46 (1), 28–40. Garai, A., Nandi, A.K., 2008b. Rheology of polyaniline-dinonyl naphthalene disulfonic acid (DNNDSA) montmorillonite clay nanocomposites in the sol state: shear thinning versus pseudo-solid behavior. J. Nano Sci. Nanotechnol. 8 (4), 1842–1851. Gemeinhart, R.A., Chen, J., Park, H., et al., 2000. pH-sensitivity of fast responsive superporous hydrogels. J. Biomater. Sci. Polym. Ed. 11 (12), 1371–1380. Giaquinto, C., Morelli, E., Fregonese, F., et al., 2008. Current and future antiretroviral treatment options in pediatric HIV infection. Clin. Drug Invest. 28, 375–397. Gupta, P., Vermani, K., Garg, S., 2002. Hydrogels: from controlled release to pHresponsive drug delivery. Drug Discov. Today 10 (7), 569–579. Huixia, Y., Wenbo, W., Junping, Z., et al., 2012. Preparation characterization, and drug-release behaviors of a pH-sensitive composite hydrogel bead based on guar gum, attapulgite, and sodium alginate. Int. J. Polym. Mater. Polym. Biomater. 62, 369–376. Kato, N., Sakai, Y., Shibata, S., 2003. Wide-range control of deswelling time for thermosensitive poly (N-isopropyl acrylamide) gel treated by freeze-drying. Macromolecules 36 (4), 961–963.

9

538 Kolhe, S., Chaudhari, P.D., Dhananjay, M., 2014. Dissolution and bioavailability 539 enhancement of efavirenz by hot melt extrusion technique. IOSR J. Pharm. 4, 47– 540 53. 541 Lariza, D.S.A., Mônica, F.R.S., Camila, T.A., et al., 2014. Solid dispersion of efavirenz in 542 PVP K-30 by conventional solvent and kneading methods. Carbohydr. Polym. 543 104, 166–174. 544 Lindenberg, M., Kopp, S., Dressman, J.B., 2004. Classification of orally administered 545 drugs on the World Health Organization model list of essential medicines 546 according to the biopharmaceutics classification system. Eur. J. Pharm. 547 Biopharm. 58, 265–278. 548 Lozinsky, V.I., 2002. Cryogels on the basis of natural and synthetic polymers: 549 preparation, properties and application. Russ. Chem. Rev. 71, 489–511. 550 Mabrouk, M., Mostafa, A.A., Oudadesse, H., et al., 2013. Fabrication characterization 551 and drug release of ciprofloxacin loaded porous polyvinyl alcohol/bioactive 552 glass scaffold for controlled drug delivery. Bioceram. Dev. Appl. S1:009. doi: 553 http://dx.doi.org/10.4172/2090-5025.S1-009. 554 Nigrawal, A., Chandra, P.S., Chand, N., 2012. Mechanical and thermal properties of 555 nano-cellulose obtained from sisal fiber reinforced polyvinyl alcohol (PVA) bio556 composites. J. Sci. Res. Rev. 1 (3), 40–50. 557 Oyen, M.L., 2014. Mechanical characterization of hydrogel materials. Int. Mater. Rev. 558 59, 44–59. 559 Pillay, V., Fassihi, R., 2000. A novel approach for constant rate delivery of highly 560 soluble bioactives from a simple monolithic system. J. Control. Release 67, 67– 561 78. 562 Qiu, Y., Park, K., 2001. Environment-sensitive hydrogels for drug delivery. Adv. Drug 563 Deliv. Rev. 53 (3), 321–339. 564 Serrano, A.A., Campillo, F.A.J., Go’mez, R.J.L., et al., 2004. Porous poly(2-hydroxyethyl 565 acrylate) hydrogels prepared by radical polymerisation with methanol as 566 diluent. Polymer 45 (26), 8949–8955. 567 Sophie, R., Mies, J., Stefaan, C., 2005. Self-gelling hydrogels based on oppositely 568 charged dextran microspheres. Biomaterials 26, 2129–2235. 569 Sosnik, A., Chiappetta, D.A., Carcaboso, A., 2009. Drug delivery systems in HIV 570 pharmacotherapy: what has been done and the challenges standing ahead. J. 571 Control. Release 138, 2–15. 572 Stammen, J.A., Williams, S., Ku, D.N., et al., 2001. Mechanical properties of a novel 573 PVA hydrogel in shear and unconfined compression. Biomaterials 22, 799–806. 574 Sunitha, R.M., Srikanthand, R.N., Mallikarjun, R.S., 2014. Solubility enhancement of 575 poorly water soluble drug efavirenz by solid self emulsifying drug delivery 576 systems. Int. J. Pharm. Res. Rev. 3 (4), 20–28. 577 Tang, C., Yin, C., Pei, Y.Y., et al., 2005. New superporous hydrogels composites based 578 on aqueous Carbopol1 solution (SPHCcs): synthesis, characterization and in 579 vitro bioadhesive force studies. Eur. Polym. J. 41 (3), 557–562. 580 United Nations AIDS report on the global Aids epidemic, 2013. http://www.unaids. 581 org/en/media/unaids/contentassets/documents/epidemiology/2013/gr2013/ 582 UNAIDS_Global_Report_2013_en.pdf (accessed October 2014). 583 Vlierberghe, V.S., Dubruel, P., Schacht, E., 2011. Biopolymer-based hydrogels as 584 scaffolds for tissue engineering applications: a review. Biomacromolecules 12, 585 1387–1408. 586 Wintergerst, U., Hoffmann, F., Jansson, A., et al., 2008. Antiviral efficacy, tolerability Q10 587 and pharmacokinetics of efavirenz in an unselected cohort of HIV-infected 588 children. J. Antimicrob. Chemother. 61, 1336–1339. 589 Yu-Li, L., Yijun, L., Hong-Ru, L., 2014. Evaluation of epirubicin in thermogelling and 590 bioadhesive liquid and solid suppository formulations for rectal administration. 591 Int. J. Mol. Sci. 15 (1), 342–360. 592 Yuvaraja, K., Khanam, J., 2014. Enhancement of carvedilol solubility by solid 593 dispersion technique using cyclodextrins, water soluble polymers and hydroxyl 594 acid. J. Pharm. Biomed. Anal. 96, 10–20. 595 Zhang, X.Z., Zhuo, R.X., 1999. A novel method to prepare a fast responsive, 596 thermosensitive poly (n-isopropyl acrylamide) hydrogel. Macromol. Rapid 597 Commun. 20 (4), 229–231. 598 Zhang, J.T., Cheng, S.X., Zhuo, R.X., 2003a. Preparation of macroporouspoly (N599 isopropyl acrylamide) hydrogel with improved temperature sensitivity. J. 600 Polym. Sci. Part A: Polym. Chem. 41 (15), 2390–2392. 601 Zhang, J.T., Cheng, S.X., Huang, S.W., et al., 2003b. Temperature sensitive poly(N602 isopropyl acrylamide) hydrogels with macroporous structure and fast response 603 rate. Macromol. Rapid Commun. 24 (7), 447–451. 604 Zhang, J.T., Huang, S.W., Xue, Y.N., et al., 2005. Poly(nisopropyl acrylamide) 605 nanoparticle-incorporated pnipaam hydrogels with fast shrinking kinetics 606 macromol. Rapid Commun. 26 (16), 1346–1350.

Please cite this article in press as: Mabrouk, M., et al., Design of a novel crosslinked HEC-PAA porous hydrogel composite for dissolution rate and solubility enhancement of efavirenz. Int J Pharmaceut (2015), http://dx.doi.org/10.1016/j.ijpharm.2015.05.082