ARTICLE pubs.acs.org/IECR
Novel Interpenetrating Polymer Network Hydrogel Microspheres of Chitosan and Poly(acrylamide)-grafted-Guar Gum for Controlled Release of Ciprofloxacin Praveen B. Kajjari, Lata S. Manjeshwar,* and Tejraj M. Aminabhavi† Department of Chemistry, Karnatak University, Dharwad 580 003, India ABSTRACT: Acrylamide-grafted-guar gum (pAAm-g-GG) was prepared and blended with chitosan (CS) to form interpenetrating polymer network (IPN) hydrogel microspheres by the emulsion cross-linking method using glutaraldehyde (GA) as a cross-linker. The microspheres encapsulated up to 74% of ciprofloxacin (CFX), an antibiotic drug, having a plasma half-life of 4 h and the release of CFX was extended up to 12 h. Scanning electron microscopy (SEM) confirmed their spherical structure with smooth surfaces; Fourier transform infrared spectroscopy (FTIR) confirmed the grafting reaction as well as chemical stability of CFX in the blend IPN hydrogel microspheres. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) techniques confirmed the molecular level dispersion of CFX in the matrix. Swelling of microspheres performed in pH 7.4 buffer media was used to understand the drug release kinetics. In vitro release of CFX in pH 1.2 and 7.4 media showed a dependence on blend composition of the IPN, extent of cross-linking as well as initial drug loading. In vitro release data was analyzed using empirical equations, namely, KorsmeyerPeppas, to compute the diffusion exponent (n), whose value ranged between 0.19 and 0.33, indicating non-Fickian transport of CFX through the blend IPN hydrogel microspheres.
1. INTRODUCTION Naturally occurring biopolymers have been the most widely used controlled release (CR) devices for extending the plasma lifetime of the short-acting drugs.1,2 Such biopolymers, being the natural products of living organisms or plants, are relatively inexpensive and are capable of a multitude of chemical modifications.3,4 Because of their natural origin they are biodegradable, nontoxic, and biocompatible. Among such naturally available biopolymers, chitosan (CS), a cationic polysaccharide and a copolymer of β-(1,4) linked 2-acetamido-2-deoxy-D-glucopyranose and 2-amino-2-deoxy-D-glucopyronose, is obtained from the deacetylation of chitin that finds wide applications in biomedical areas.5,6 The cross-linked CS swells in aqueous media due to its cationic nature in response to changes in pH of the media. Therefore, CS has been widely used as a hydrogel polymer for the CR of proteins, DNA,7,8 vaccines, and genes.911 Guar gum (GG) is another popularly used water-soluble polysaccharide, extracted from the seeds of cyamopsis tetragonoloba that belongs to the luguminosoe family. GG is a galactomannan, consisting of a (14)-linked β-D-mannopyranose backbone, with a random branch unit of an α-D-galactose unit. GG has a high level of galactose substitution along the mannan backbone and on an average, for every 1.5 and 2-mannose residues, there is a galactose residue.12 However, its uncontrolled rate of hydration, decreased viscosity upon storage and microbial contamination limits its applications in the biomedical area. To improve its physicochemical properties, efforts have been made to develop the graft copolymer of GG with other polymers like acrylamide (AAm) for use in CR applications.4,13 Interpenetrating polymer network (IPN) microhydrogels are the preferred devices in the drug delivery area because of their ability to encapsulate a wide variety of drugs exhibiting CR characteristics.14,15 The blend IPN hydrogels have been widely r 2011 American Chemical Society
explored for the CR of antiasthamatic, anti-inflammatory, antibiotic, antihypertensive, and antituberculosis drugs.1618 However, the blend IPN of CS with grafted copolymers of GG and AAm has not been explored as a CR device. Earlier, we reported on pAAm-g-GG microgels prepared by an emulsion cross-linking method using GA as a cross-linker for the CR of verapamil hydrochloride (water-soluble drug) and nifedipine (water-insoluble drug) and studied their water uptake capacity.4 It was shown that the system is more hydrophilic and a water-soluble drug such as verapamil hydrochloride can be released within 2 h. Thus, plain pAAm-g-GG would not serve as a good CR system. On the other hand, plain CS is not hydrophilic enough to respond quickly to the release of a short-lived drug. Hence, the hydrophilicity of CS needs to be improved for a better CR. To address these drawbacks, we have undertaken to prepare the CR system based on the graft copolymer of GG and AAm blended with chitosan as this system was not studied before for the CR of CFX, which is the most prominent member of fluoroquinolone antibiotic drug, having a plasma half-life of 4 h. This wide-spectrum antibiotic is frequently used to treat and prevent the infections caused by bacteria such as enteric, respiratory, and urinary tract infections, gastrointestinal surgery, typhoid fever, gonorrhea, osteomyelitis, and septicemia. CFX acts by inhibiting bacterial enzymes, the DNA gyrase.19,20 In this study, formulations of CFX with the blend IPN of CS and pAAm-g-GG have been prepared and characterized to understand the drug-polymer interactions, particle morphology, and drug release characteristics in acidic as well as alkaline pH conditions to recommend the safe usage of CFX in oral applications. Received: June 16, 2011 Accepted: October 22, 2011 Revised: September 13, 2011 Published: October 23, 2011 13280
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2. EXPERIMENTAL SECTION 2.1. Materials. Ciprofloxacin was received as a gift sample from a local drug company. Chitosan of medium molecular weight (viscosity = 600 cP) and degree of deacetylation of 80% was purchased from Aldrich Chemical Co., (Milwaukee, WI); guar gum, acrylamide, reagent grade glutaraldehyde solution 25% (v/v), n-hexane, and light liquid paraffin oil were all purchased from S.D. Fine Chemicals, Mumbai, India. Span-80 was purchased from Loba Chemicals, Mumbai, India. All other chemicals were used without further purification. 2.2. Synthesis of Poly(acrylamide)-g-Guar Gum. The graft copolymer of GG and acrylamide was prepared by free radical polymerization as described before.4 Briefly, 2 g of GG was dispersed in 150 mL of deionized water, which was allowed to hydrate and then dissolved by stirring overnight in a 250 mL round-bottom flask. In another flask, 0.12 mol of acrylamide was dissolved in 20 mL of water, which was then added to the GG solution and stirred further for 1 h. To this solution, 30 mL of 0.005 mol ceric ammonium nitrate was added as an initiator to carry out the polymerization at 60 °C by continuously purging nitrogen gas for 6 h in a water bath under constant stirring. After complete polymerization, a sufficient amount of acetone was added to precipitate the graft copolymer and washed several times with methanol to remove the homopolymer. The polymer was dried under vacuum (60 mmHg) at 40 °C for overnight, and the mass of the copolymer was measured to calculate the percent grafting efficiency as % grafting efficiency ¼
mass of graft copolymer 100 mass of ðAAm þ GGÞ
ð1Þ
2.3. Preparation of Blend IPN Hydrogel Microspheres. Blend IPN hydrogel microspheres of chitosan and poly(acrylamide)-grafted-guar gum (pAAm-g-GG) were prepared by a water-in-oil (w/o) emulsion cross-linking method.1 Briefly, 20 mL of 2% (w/v) polymer solution was prepared by dissolving varying amounts of CS and pAAm-g-GG in 2% (v/v) acetic acid. The required amount of CFX (10, 20, or 30% w/w) was dissolved in polymer solution and stirred for 2 min, which was then added slowly to light liquid paraffin oil (100 g, w/w) containing 1% w/w Span-80 under constant stirring (600 rpm) using Eurostat high-speed stirrer (IKA Labortechnik, Staufen, Germany) for 10 min. To this w/o emulsion, the required amount of GA (2.5, 5, or 7.5 mL) was added slowly and stirred for another 2 h to obtain the hardened microspheres. A suction pump connected with Buckner funnel was used to filter the hardened microspheres through Whatmann filter paper #40 under normal tap suction pump. Surface-adhered oil was removed by washing with n-hexane, and the unreacted trace amount of GA was deactivated by adding 0.1 M glycine solution. The absence of GA was confirmed by the Brady test.21 The microspheres were airdried at 40 °C for 24 h and stored in a desiccator until further use. Formulation details are given in Table 1. The same procedure was used to prepare F3 formulation without CFX and hereafter is referred to as the placebo microsphere. 2.4. Fourier Transform Infrared Spectral Measurements (FTIR). FTIR spectra were taken on Nicolet (Impact 410, Milwaukee, WI) spectrophotometer to confirm the grafting, cross-linking as well as to investigate the chemical stability of CFX in the microspheres. FTIR spectra of the plain GG, pAAmg-GG, placebo microspheres, CFX-loaded microspheres, and
Table 1. Formulation Details along with % Encapsulation Efficiency (% EE) and % Water Uptake formulation
CS
pAAm-g-GG
codes
(% w/w)
(% w/w)
CFX
GA EE water uptake
F0 F1
100 90
0 10
10 10
5 5
72 69
202 212
F2
90
10
20
5
67
218
F3
90
10
30
5
63
226
F4
80
20
10
5
65
219
F5
70
30
10
5
58
230
F6
90
10
10
2.5
64
235
F7
90
10
10
7.5
74
193
(% w/w) (mL) (%)
(% w/w)
plain CFX were all taken on the KBr grounded powder prepared as pellets by applying a pressure of 600 kg/cm2. Spectral scanning was done between the wavelengths of 4000 and 500 cm1. 2.5. Differential Scanning Calorimetry (DSC). DSC (Rheometric Scientific, Surrey, UK) was performed on plain GG, pAAm-g-GG, placebo microspheres, CFX-loaded microspheres, and pristine CFX. Samples were heated from 10° to 400 °C at the heating rate of 10 °C/min in an inert nitrogen atmosphere by maintaining a flow rate of 20 mL/min. 2.6. X-ray Diffraction (XRD). Crystallinity of CFX after encapsulation was evaluated by XRD recorded for placebo microspheres, CFX-loaded microspheres, and pristine CFX using the X-ray diffractometer (Bruker model D8 Advance, Germany). Scanning was done up to 2θ of 80°. 2.7. Scanning Electron Microscopy (SEM). SEM images were taken on CS and pAAm-g-GG blend IPN hydrogel microspheres prepared by cross-linking with 5 mL of GA and loaded with 10% (w/w) of CFX. Microspheres were sputtered to form a gold coating of 10 nm thickness to make them conducting and placed on a copper stub. Scanning was done using the JEOL model 6390 LA, Japan, instrument available at the Sophisticated Test and Instrumentation Center, Cochin University, Kochi, India. 2.8. Estimation of Drug Loading and Encapsulation Efficiency. CFX content was estimated in distilled water by grinding 10 mg of microspheres to get the powder using an agate mortar, extracting for 18 h at 25 °C in 50 mL of water and sonicating for 1 h. The solution was centrifuged to remove the polymeric debris and washed twice to completely extract the CFX. The clear supernatant liquid was analyzed by UV spectrophotometer (model Anthelic, Secomam, Ales, France) at the fixed λmax value of 277 nm, which is the characteristic value for CFX. The % CFX loading and % encapsulation efficiency (% EE) were calculated using the following equations: ! % CFX loading ¼
weight of CFX in microspheres weight of microspheres
% encapsulation efficiency ¼
100
ð2Þ
! theoretical CFX loading 100 CFX loading
ð3Þ 2.9. Swelling Studies. Equilibrium water uptake of the crosslinked microspheres loaded with CFX was determined by measuring the extent of swelling of the matrix in pH 7.4 buffer medium. To ensure complete equilibrium, samples were allowed 13281
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to swell up to 24 h at the physiological temperature of 37 °C. Excess surface-adhered liquid droplets were removed by blotting with soft tissue papers and the swollen microspheres were weighed accurately to (0.01 mg using an electronic microbalance (model AT20, Mettler, Greifensee, Switzerland). The hydrogel microspheres were dried in an oven at 40 °C for 5 h until no change was observed in the dry mass of the samples. The % equilibrium water uptake was then calculated as Ms Md 100 ð4Þ % equilibrium water uptake ¼ Md where Ms and Md are the masses of swollen and dried microspheres, respectively. 2.10. In Vitro Drug Release. Drug release from the blend IPN hydrogel microspheres with different extent of cross-linking, blend composition, and % drug loading was investigated in HCl solution (pH = 1.2) initially for 2 h, and then in phosphate buffer of pH 7.4 until the completion of dissolution. These experiments were performed in triplicate in a dissolution tester (LabIndia, Mumbai, India) equipped with eight baskets at the stirring speed of 100 rpm. A weighed quantity (equivalent to 10 mg of CFX) of each CFX-loaded sample was placed in 500 mL dissolution medium at the physiological temperature of 37 °C. Then, a 5 mL sample aliquot was withdrawn at different time intervals, but 5 mL of fresh dissolution media was replenished back to maintain the constant volume, that is, sink conditions. The CFX concentration was determined spectrophotometrically at the fixed λmax value of 277 nm. In vitro release data were collected in triplicate for each sample, but the average values are considered in data analysis and graphical display. 2.11. Release Kinetics Analysis. To investigate the kinetics of CFX release from the microspheres, in vitro release data were fitted to the following empirical equations, namely, zero-order, first-order, and Higuchi, respectively, as follows: Q t ¼ Q 0 K0 t
ð5Þ
ln Qt ¼ ln Q0 K1 t
ð6Þ
Qt ¼ Kh t 1=2
ð7Þ
where Qt is the percentage of drug release at time t, Q0 is the initial amount of drug in the microspheres and K0, K1, and Kh are the respective rate constants. To confirm the release mechanism, in vitro release results have been fitted to KorsmeyerPeppas equation:22,23 Mt =Mα ¼ Kp t n
ð8Þ
Here, Mt/Mα is the fraction of drug released at time t, Kp is the rate constant, and n is the release exponent. The estimated n value is used to assess the release mechanism.
3. RESULTS AND DISCUSSION In this research, graft copolymer of GG with acrylamide was synthesized using ceric ammonium nitrate (CAN) as an initiator.4,13 The mechanism of formation of the copolymer is shown in Scheme 1. The grafting efficiency was found to be 82%. The blend IPN hydrogel microspheres were prepared from pAAm-g-GG with CS by cross-linking the matrices with GA as shown in Scheme 2. Repeated washings of the microspheres with glycine converted the amine group of glycine to imine bond with
Scheme 1. Scheme for the Synthesis of pAAm-g-GG
aldehydic group of unreacted GA, which was deactivated. The absence of unreacted GA was confirmed by Brady’s test21,24 that showed a negative test. Thus, formulations of this study have extremely low levels of GA, indicating their safe applications. 3.1. % Encapsulation Efficiency. The % EE varied from 58 to 74 (see Table 1), and was dependent on blend composition, extent of cross-linking and % CFX loading. With increasing amount of pAAm-g-GG in the matrix, a decrease in % EE was observed for F1, F4, and F5 formulations, due to the formation of a loose network and that drug particles may have leached out of the matrix. The extent of cross-linking of the matrix was varied by varying the amount of cross-linking agent under constant reaction time or varying the reaction time by keeping the amount of cross-linker constant in all the formulations. Interestingly, the extent of cross-linking showed a significant effect on % EE as can be observed for F5, F6, and F7 formulations, since at increased cross-linking a more rigid network structure is formed, thereby reducing the possibility of leaching of drug particles from the matrix, while preparing the microspheres, thus causing the retention of more of drug particles by the matrix. The % EE also depends on % CFX loading as seen with F1, F2, and F3 formulations for which a decrease in % EE is observed with an increase in % CFX loading, because at high CFX loading, more of the CFX particles are leached out of the matrix along with some water molecules also during the formulation step. 3.2. FTIR Analysis. FTIR (Figure 1) was employed to confirm the grafting reaction between GG and acrylamide in the presence of ceric ammonium nitrate. The FTIR spectrum of pAAm-g-GG shows a sharp peak at ∼1672 cm1 due to the stretching of the carbonyl group of the grafted poly(acrylamide) chain, while a new peak at 1459 cm1, corresponding to CN bending vibrations is seen that was not observed in the spectrum of GG. 13282
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Scheme 2. Scheme Representing the Blend IPN Structure Formation
The NH stretching vibrations appearing as a shoulder peak at 3236 cm1 of the graft copolymer further supports the grafting reaction.4,13 For CFX, the peak at 1707 cm1 is due to the carboxylic acid CdO stretching vibration, whereas the one at 1623 cm1 corresponds to the keto carbonyl moiety. The band at 1270 cm1 is attributed to the coupled carboxylic acid CO stretching and OH deformation. The peaks at 3380 and 3530 cm1 are due to the OH stretching vibrations of the carboxylic acid group and NH group of secondary amine, respectively. A sharp peak at 1458 cm1 is due to the CN stretching.19,20 Compared to the spectrum of CS, two sharp bands at 1695 and 1529 cm1 are observed for plain CS
microspheres cross-linked with GA. Thus, the observed frequency at 1695 cm1 corresponds to the stretching of the imine bond (CdN) formed between the amine group of CS and aldehydic group of GA. Monteiro and Airoldi23 suggested a different mode of crosslinking, wherein cross-linking is formed with not only one GA molecule, but also due to the polymerization of GA, consequently forming a higher cross-linked chain. In this process, the ethylenic bond (CdC) is formed, whose stretching is observed at 1529 cm1, confirming the cross-linking reaction between CS and GA.25 However, these bands are not prominent in case of placebo microspheres due to the overlapping of the bands of pAAm-g-GG. Also, GA interacts with the adjacent OH groups 13283
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Figure 1. FTIR spectra of CS, CS-GA, GG, pAAm-g-GG, placebo microspheres, CFX-loaded microspheres (F3), and pristine CFX.
of pAAm-g-GG to form an ether linkage as depicted in Scheme 2, which is confirmed by a peak at 1248 cm1 for the placebo microspheres.4 However, a peak observed at 3402 cm1 corresponds to NH and OH stretching vibrations of pAAm-g-GG as well as that of CS. For the blend IPN hydrogel microspheres, some additional bands are observed, which are due to the CFX, and these are not prominent, as these must have merged with the bands of the host polymer matrix. 3.3. DSC Analysis. Differential scanning calorimetry was used to confirm the grafting reaction as well as to check the crystallinity of CFX in the polymer matrix. Figure 2 displays the DSC thermograms of (A) GG, (B) pAAm-g-GG, (C) placebo microspheres, (D) CFX-loaded microspheres, and (E) pristine CFX drug. For GG, two endothermic transitions, one at 73 °C and another at 297 °C, are observed, whereas pAAm-g-GG exhibits three endothermic transitions at 72°, 247°, and 294 °C. A new endothermic transition at 247 °C for graft copolymer is due to
the enhanced interaction between the carbonyl group of the graft copolymer and the hydroxyl group of GG, which confirmed the grafting reaction. In the case of placebo microspheres, peaks at 77°, 265°, and 320 °C are due to the endothermic transition of CS and pAAm-gGG in blend IPN hydrogel microspheres. For CFX, two endothermic transitions are observed, one at 152 °C due to the loss of water of crystallization and another at 328 °C due to the melting of CFX.19,20 In the case of CFX-loaded microspheres, the peaks at 79°, 268°, and 320 °C correspond to endothermic transitions with no peak corresponding to CFX, confirming the amorphous dispersion of CFX in the blend IPN hydrogel microspheres. 3.4. X-RD Analysis. X-ray diffractograms of (A) placebo microspheres, (B) CFX-loaded microspheres, and (C) pristine CFX are displayed in Figure 3. The CFX shows characteristic peaks between 2θ of 8° and 26° due to its crystalline nature, but these peaks have disappeared in CFX-loaded microspheres, since 13284
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Figure 4. SEM photographs of drug-loaded microspheres.
Figure 2. DSC thermogram of (A) GG, (B) pAAm-g-GG, (C) placebo microspheres, (D) CFX-loaded microspheres, and (E) pristine CFX.
Figure 3. XRD patterns of (A) placebo microspheres, (B) CFX-loaded microspheres, and (C) pristine CFX.
only the peak observed in the placebo is observed. The X-RD peak depends on the crystal size, but for all the CFX-loaded formulations, characteristic peaks of CFX have overlapped with those of the polymer. Thus, CFX-loaded formulations exhibit an amorphous nature, making it difficult to measure at the detection limit of the crystal size, confirming that CFX is dispersed at a
molecular level in the polymer matrix, as no crystals were found in the CFX-loaded formulations. 3.5. Scanning Electron Microscopy. Typical SEM images (Figure 4) taken for CFX-loaded microspheres at 100 and 250 magnifications confirm the spherical nature of the microspheres with smooth surfaces. However, few depressions observed on the surface of microspheres are due to the contraction of the more hydrophilic part of the IPN as a result of the loss of water during the drying process. The average particle size of the microspheres appears to be around 100 μm, or even less in some cases. In the SEM taken at 250 magnification, there is an indication of three different particle sizes, which are representatives of their class. The average of these particle sizes was estimated to be around 100 μm. 3.6. Swelling Studies. The % equilibrium water uptake data of the cross-linked microspheres (Table 1) indicate that as the amount of GA in the matrices increased from 2.5 to 7.5 mL (i.e., formulations F6, F1, and F7), equilibrium water uptake decreased from 236 to 193%, possibly due to the formation of a rigid network structure at higher cross-link density. Thus, crosslinking has an effect on equilibrium water uptake as well as on the in vitro release profiles. Formulations prepared with a higher amount of pAAm-g-GG exhibit higher % equilibrium swelling than those containing a smaller amount of pAAm-g-GG (formulations F1, F4, and F5) due to increased hydrophilic nature of pAAm-g-GG in the blend IPN hydrogel microspheres, giving higher water uptake values. As the % CFX-loading increased from 10 to 30% (F1, F2, and F3), the equilibrium water uptake also increased from 212 to 226%. This variation in water uptake is because of the dissolution of CFX along with the matrix swelling. When the CFX-loaded microspheres were in contact with the water medium, due to the matrix swelling, the water-soluble CFX might also have diffused out of the matrix and the voids created 13285
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Table 2. In Vitro Release Analysis from Various Kinetics Equations zero-order
first-order
r
r
Higuchi
KorsmeyerPeppas
formulation codes
Figure 5. (A) Extent of cross-linking on in vitro release profiles for formulations F6 (2.5 mL), F1 (5 mL), and F7 (7.5 mL). (B) Effect of pAAm-g-GG content on in vitro release profiles of F1 (10% w/w), F4 (20% w/w), and F5 (30% w/w) formulations. (C) Effect of % drug loading on in vitro release profiles of F1 (10% w/w), F2 (20% w/w), and F3 (30% w/w) formulations.
by the drug particles are now occupied by the water molecules. Hence, more the amount of drug loading more will be the space available for water to occupy. 3.7. In Vitro Release Study. In vitro release of CFX from the matrices was investigated in gastric acidic (pH = 1.2) and intestinal (pH = 7.4) alkaline conditions. The dependence of in vitro release kinetics on the extent of cross-linking, blend composition and amount of CFX loading was evaluated both in pH 1.2 and 7.4 media at 37 °C. Results of % cumulative release versus time for CFX-loaded microspheres in the case of F1, F6, and F7 formulations are shown in Figure 5A, wherein the effect of cross-linking on in vitro release profiles was investigated. Microspheres cross-linked with 2.5 mL of GA (F6) showed higher release than those cross-linked with 5 mL of GA (F1). This could be the result of drug diffusion from the microspheres that depends on the mesh size of the polymeric network, which generally decreases at increased cross-linking. Similar release profiles are observed for F1 and F7 formulations, wherein the release of CFX is much slower, that is, only 60% of CFX was released at the 12 h.
K0
K1
r
Kh
r
Kp
n
F0
0.859 0.353 0.808 0.066 0.969 1.545 0.986
0.521
0.28
F1
0.891 0.354 0.814 0.635 0.968 1.553 0.989
0.549
0.26
F2
0.857 0.305 0.783 0.046 0.941 1.346 0.971
0.619
0.19
F3
0.796 0.325 0.712 0.044 0.889 1.448 0.927
0.633
0.19
F4
0.873 0.355 0.794 0.059 0.953 1.559 0.980
0.542
0.25
F5
0.859 0.350 0.786 0.053 0.950 1.551 0.983
0.599
0.23
F6
0.835 0.397 0.759 0.062 0.939 1.773 0.977
0.546
0.26
F7
0.905 0.350 0.795 0.081 0.974 1.528 0.982
0.444
0.33
The effect of pAAm-g-GG composition on in vitro release profiles presented in Figure 5B for F0, F1, F4, and F5 formulations confirm that % cumulative release is higher for F4 (20% w/w of pAAm-g-GG) than F1, which contains only 10% w/w of pAAm-g-GG. At higher composition of pAAm-g-GG in the matrix, swelling increased due to the higher hydrophilic nature of pAAm-g-GG in the blend IPN hydrogel microspheres, leading to higher release of CFX. Also, F5 showed higher % cumulative release of CFX than F4. As per in vitro release profiles of formulations F1, F2, and F3 displayed in Figure 5C, we find that F3 exhibits higher release than F1, whereas F2 exhibits an intermediate release pattern, indicating the dependence of drug release on the amount of CFX in the matrix. For instance, the release is slower for formulations containing a lower amount of CFX and vice versa. This is because, in the case of microspheres with higher drug loading, more CFX particles have the chance to be at surface of the microspheres compared to those microspheres with low drug loading. Thus, more of CFX particles are exposed to the dissolution media from higher drug-loaded formulations than those containing lower loading of CFX. 3.8. Analysis of Release Data. To understand the mechanism of drug release, in vitro release data have been analyzed using the kinetics equations that are empirical in nature.26,27 Correlation coefficients, r, as well as rate constants for each equation are given in Table 2. High value of correlation coefficient was observed in the case of the Higuchi equation compared to zero-order and first-order equations, suggesting that drug release is proportional to the square root of time. This indicates that the drug release from pAAm-g-GG and CS blend hydrogel matrix is a diffusion-controlled process. Release data have been fitted to the KorsmeyerPeppas kinetic equation,22,23 and the estimated n values that describe the drug release mechanism range from 0.19 to 0.33, indicating the non-Fickian nature of diffusion.
4. CONCLUSIONS Novel blend IPN hydrogel microspheres have been prepared using CS and pAAm-g-GG by the emulsion cross-linking method in the presence of GA as a cross-linker. The matrix extended the release of CFX from its original 4 h (plasma lifetime) to nearly 12 h, with no overshoot effect. The grafting reaction between AAm and GG was confirmed by FTIR and DSC. Encapsulation efficiency up to 74% was achieved and FTIR confirmed the IPN structure as well as chemical stability of CFX in the microspheres. DSC and XRD confirmed the molecular level dispersion of CFX in the blend IPN hydrogel microspheres. SEM confirmed 13286
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Industrial & Engineering Chemistry Research the spherical nature and smooth surfaces of the microspheres along with some depressions and the average diameter of the microspheres was around 100 μm or less. Swelling kinetics was dependent on the extent of cross-linking as well as the composition of pAAm-g-GG in the blend IPN hydrogel microspheres. The n values that ranged from 0.19 to 0.33 showed a dependence on the extent of cross-linking; these values suggest the in vitro release kinetics following a non-Fickian diffusion mechanism.
’ AUTHOR INFORMATION Corresponding Author
*Tel.: +91 836 2215286. Fax: +91 836 2771275. E-mail:
[email protected]. Notes †
CSIR Emeritus Scientist, SET’s College of Pharmacy, Dharwad 580 002, India.
’ ACKNOWLEDGMENT P.B. Kajjari and L. S. Manjeshwar thank the University Grants Commission (UGC), New Delhi, India (KU/SHA/UGC/ RFSMS/2009-10) for a fellowship to P.B. Kajjari. T. M. Aminabhavi thanks the CSIR [21(0760)/09/EMR-II], New Delhi, for the award of a Emeritus Scientist. ’ REFERENCES (1) Rokhade, A. P.; Shelke, N. B.; Patil, S. A.; Aminabhavi, T. M. Novel interpenetrating polymer network microspheres of chitosan and methylcellulose for controlled release of theophylline. Carbohydr. Polym. 2007, 69, 678–687. (2) Saravanan, M.; Panduranga Rao, K. Pectingelatin and alginategelatin complex coacervation for controlled drug delivery: Influence of anionic polysaccharides and drugs being encapsulated on physicochemical properties of microcapsules. Carbohydr. Polym. 2010, 80, 808–816. (3) Malafaya, P. B.; Gabriela, A. Naturalorigin polymers as carriers and scaffolds for biomolecules and cell delivery in tissue engineering applications. Adv. Drug Delivery Rev. 2007, 59, 207–233. (4) Soppimath, K. S.; Aminabhavi, T. M. Water transport and drug release study from Cross-linked polyacrylamide grafted guar gum hydrogel microspheres for the controlled release applications. Eur. J. Pharm. Biopharm. 2002, 53, 87–98. (5) Rokhade, A. P.; Patil, S. A.; Aminabhavi, T. M. Synthesis and characterization of semi-interpenetrating polymer network microspheres of acrylamide grafted dextran and chitosan for controlled release of acyclovir. Carbohydr. Polym. 2007, 67, 605–613. (6) Agnihotri, S. A.; Nadagouda, M. N.; Aminabhavi, T. M. Recent advances on chitosan based micro- and nanoparticles in drug delivery. J. Controlled Release 2004, 100, 5–28. (7) Mao, S.; Sun, W.; Kissel, T. Chitosan-based formulations for delivery of DNA and siRNA. Adv. Drug Delivery Rev. 2010, 62, 12–27. (8) Chen, S. C.; Wu, Y. C.; Mi, F. L.; Lin, Y. H.; Yu, L. C.; Sung, H. W. A novel pH-sensitive hydrogel composed of N,O-carboxymethyl chitosan and alginate cross-linked by genipin for protein drug delivery. J. Controlled Release. 2004, 96, 285–300. (9) Tang, Y.; Du, Y.; Li, Y.; Wang, X.; Hu, X. A thermosensitive chitosan/poly(vinyl alcohol) hydrogel containing hydroxyapatite for protein delivery Issue. J. Biomed. Mater. Res. 2009, 91A, 953–963. (10) Koping-Hoggard, M.; Tubulekas, I.; Guan, H.; Edwards, K.; Nilsson, M.; Varum, K. M.; Artursson, P. Chitosan as a nonviral gene delivery system. Structureproperty relationships and characteristics compared with polyethylenimine in vitro and after lung administration in vivo. Gene Ther. 2001, 8, 1108–21.
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