Designing of Biodegradable Interpenetrating Polymer Network of Poly ...

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International Journal of Pharmaceutical Sciences and Nanotechnology

Volume 1 • Issue 2 • July - September 2008 Paper Research

Designing of Biodegradable Interpenetrating Polymer Network of Poly(vinyl alcohol-co-acrylic acid)/sodium chloride hydrogel : An Approach to Drug Delivery Debajyoti Ray1*, Prafulla Kumar Sahoo2 and Guru Prasad Mohanta3 1

Department of Pharmaceutics, Sri Jayadev College of Pharmaceutical Sciences, Bhubaneswar, India, 752101. Polymer Research Unit, Department of Chemistry, Utkal University, Bhubaneswar, India, 751004. 3 Department of Pharmacy, Annamalai University, Annamalai nagar, Tamil Nadu, India, 608002. 2

ABSTRACT: Interpenetrating polymer network (IPN) hydrogel based on polyvinyl alcohol (PVA) networking with polyacrylic acid (PAA), generated insitu, were prepared by without any added crosslinker, using benzoyl peroxide an initiator and sodium chloride (NaCl) as additive. The response of the hydrogels with and without NaCl was observed by studying their swelling behavior, biodegradability and thermal stability. Scanning electron microscopic study revealed that the pores of the prepared IPN were mostly open in presence of NaCl, thus making the hydrogel macroporous. (PVA-co-PAA)/NaCl was found to be more biodegradable than without NaCl. The IPN hydrogel showed comparatively higher swelling at intestinal pH than that of gastric medium and presence of NaCl in the IPN increases the swelling properties in both media. Thermal stability of IPN was affected by copolymerization, due to increasing porosity of the IPN. The prepared nontoxic, hydrophilic IPN hydrogel system holds good for further drug delivery studies in connection to its superswelling and biodegradablity. KEY WORDS: IPN Hydrogel, swelling studies, biodegradability, SEM, Thermal studies.

Introduction of the polymer decreases and the hydrogel becomes rubbery. Interpenetrating polymer networks are defined as a mixture of two or more interwinding crosslinked polymers where one of the network polymers is crosslinked in the presence of the other, that could help improve the mechanical strength and resiliency of the polymer (Sperling, 1981). The water-uptake properties of the hydrogels are attributed to the ionization of functional groups, which depends upon the pH and ionic strength of the external medium where the hydrogel is placed, thus making the system pH-sensitive. Particularly, synthetic polymers like poly(methyl methacrylate) (Liu et. al., 2007), poly(acrylic acid) (Siemoneit et. al., 2006), poly(N,N-iso-propylacrylamide) (Sdelen et. al., 2004), and natural polysaccharide such as chitosan (Qu et. al.,2000) have been used as pH-sensitive drug delivery systems.

Over one third of marketed drugs world wide are chiral, Now-a-days hydrogels have become popular carriers for drug delivery applications due to their biocompatibility and resemblance to biological tissues (Hoffman, 2002; Peppas et. al., 2000; Lowman et. al., 2004; Peppas et. al., 2004; Ichikawa et. al., 2001; Torres-Lugo et. al., 2000. From a structural point of view, hydrogels are three-dimensional hydrophilic polymer networks that swell in water or biological fluid without dissolving due to chemical or physical crosslinks (Peppas et. al., 1993). Hydrogels can be used to target the release of a drug or protein to a specific area of body (Peppas et. al., 2000; Peppas et. al., 2004; Mohapatra et. al., in press; Peppas et. al., 2004; Soppimath et. al., 2002) simultaneously control the release kinetics due to their three-dimensional structure (Scott et. al., 1999; Brazel et. al., 1999; Lowman et. al., 1999). Hydrogel-based devices belong to the group of the swelling-controlled drug delivery systems (Colombo et. al., 200). When the polymer network comes in contact with aqueous solutions, the thermodynamic compatibility of the polymer chains and water causes the polymer to swell. As water penetrates inside the glassy network, the glass transition temperature

The present work focuses on the development of a new Interpenetrating polymer network [IPN] hydrogel from PVA, copolymerized with a hydrophilic monomer,AA and its homopolymer PAA that is formed in situ, in the presence of NaCl and in absence of an added crosslinker to highlight its swelling, biodegradability property. The capacity of the hydrogel to absorb large amount of water are the added advantages for drug delivery applications.

* Corresponding author: Debajyoti Ray Ph: +91 674 2463615; Fax: +91 674 2463370 e-mail: [email protected]

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Debajyoti Ray et al. : Designing of Biodegradable Interpenetrating Polymer Network of…

CH CH2

CH2

C=O

CH OH(Na)

OH CH2

Poly vinyl alcohol(PVA)

CH2 = CH

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(Na)OH

C

CH2

O C

O

CH2

CH2

O

C

CH

CH

C

OH(Na)

COOH (PVA-co-PAA) / NaCl

Acrylic acid(AA)

Scheme. 1 Formation of (PVA-co-PAA)/NaCl IPN.

Materials and Methods PVA with an average molecular weight of 65,000-86,000 and NaCl were purchased from CHD India Ltd., Acrylic acid (AA) and benzoyl peroxide (BPO) were purchased from E.Merck, India. All other chemicals were of reagent grade and used without further purification.

Preparation of Interpenetrating polymer network (IPN) The polymerization was carried out in a specially designed jacketed reaction vessel having an inlet and an outlet port. The inlet port was connected with the nitrogen line. PVA and AA solutions in deionized water were charged into the reaction vessel at 50:50 (wt.%) ratio. The solution was stirred at 400-500rpm for 15 min. Then the initiator, BPO [2.5%(w/v)], and Nacl [1.0-5.0%(w/v)] were added in a proper variation of concentrations without cross-linking agent and the temperature was maintained at 800C with stirring. After 3 hrs of reaction, a gel was formed, washed with distilled water, and then dried in a vacuum oven at 600C to get a constant weight of the hydrogel (PVA-coPAA)/NaCl. A similar procedure was adopted to prepare PVA-co-PAA hydrogel without adding NaCl.

Fourier Transformed Spectrophotometry

Infrared

(FTIR)

FT-IR studies of PVA, PAA and (PVA-co-PAA)/NaCl were carried out at room temperature by FT-IR Spectrophotometer( FT-IR , Paragon-500) using KBr pellet .All the spectra were recorded in the range of 400-4000 cm -1.The results are shown in Fig-1.

samples were heated in air to a temperature of 5000C at the rate of 100C/min starting from room temperature i.e 28±20C. The results are shown in Fig-2.

Biodegradation by cultured quantitative estimation of CO2

media

and

A cultured medium was prepared by taking agar nutrient broth. The nutrient broth so prepared was sterilized maintaining at a pressure of 15 lb/in2 at 1210C for 20 minute. Then to 10 ml of sterilized broth 0.1 g each of the samples i.e. (PVA-co-PAA)/NaCl and (PVA-co-PAA) were taken in test tubes under aseptic conditions. To the medium, bacteria i.e., E .coli was inoculated. The extent of biodegradation through E .coli was studied by weight loss basis and the amount of CO2 evolved (Saikos et. al.,1996) during the incubation periods of 8, 15, 21 and 28 days.

Quantitative estimation of free CO2 The cultured sample ('X' ml) and blank solution were titrated against Na2CO3 (N/50) ('Y’ml) using phenolphthalein indicator until the pink color persists for at least 30sec. The amount of CO2 released was determined using the following calculation. = N1V1 (CO2) = N1 x X = Strength = Free CO2 = Free C O2 =

N 2V 2 (Na2CO3) (1 /50) x Y (Yx22)/ (5OxX) [(Y x 22 x 1000) / (50 x X)] mg/l [(440 x Y)/ X] ppm.

Scanning Electron Microscopy (SEM) Thermogravimetric Analysis (TGA) Thermogravimetry is the study of the relationship between samples mass and its temperature to examin the thermal stability of samples. TGA of the samples were carried out using a Shimadzu DTG-50 Thermal Analyzer. The

To study the surface morphology and biodegradation of the prepared hydrogels, the SEM of (PVA-co-PAA)/NaCl before and after biodegradation were recorded by Scanning electron microscope– JEOL JSM-5000, Japan at 15 kV. The results are shown in Fig-5(a) and 5(b).

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Degradation condition

Study

in

simulated

intestinal

The degradation of (PVA-co-PAA)/NaCl IPN was studied on weight loss basis. They were conditioned to minimum weight at 37±1 0C in an oven containing desiccant prior to being immersed into 100 ml of a simulated fed intestinal fluid (0.05M Potassium dihydrogen orthophosphate, 0.015M Sodium hydroxide and 10 g/lt. Pancreatin, pH adjusted to 6.8 by Sodium hydroxide). The specimens were removed at regular intervals of 4 hours, being taken out of the solution, blotted on filter paper to remove surface solution and dried in an oven at 50 0C to constant weight in order to determine eventual weight loss, taking an average of two readings. The results are shown in Fig-6.

Volume 1 • Issue 2 • July - September 2008

of a crosslinked IPN polymer. Addition of NaCl to the hydrogel increases the swelling and water absorption. Probably it is due to less crosslinking in presence of NaCl.

Fourier Transformed Spectrophotometry

Infrared

(FTIR)

Comparative FTIR spectra of PVA, PAA, and (PVA-coPAA)/NaCl are shown in Fig-1. The characterstics peak of PVA is located at 3340 cm-1 for hydroxyl group and others are due to C-H stretching vibration. In PAA, peak at 1715 cm-1 is due to –COOH acid group. In (PVA-co-PAA)/NaCl hydrogel, in addition to the –COOH group peak at 1715 cm-1, another peak at 1780 cm-1 appeared for ester group indicating reaction between the –OH group of PVA with the –COOH group of PAA resulting in network formation.

Swelling behavior study The pH-dependent equilibrium swelling of the IPN hydrogel with and without NaCl were studied both in the simulated gastric and intestinal pH conditions using 0.1 N HCl and phosphate buffer (0.1M, pH 7.4), respectively. IPN hydrogel were allowed to swell completely for about 24 hours to attain equilibrium at 37 0C. Adhered liquid droplets on the surface of the particles were removed by blotting with tissue papers and the swollen hydrogel were weighed and dried in an oven at 60 0C for 5 hours until there was no change in the dry mass of the samples. From the equilibrium mass%, M1 of the sample, water uptake, S was calculated by measuring the dry mass, M0 using the equation: %S = [(M1 – Mo) / Mo) X 100

Results and Discussion AA was graft copolymerized and crosslinked with PVA in absence and in presence of additive, NaCl, to form IPN hydrogels of PVA-co-PAA, and (PVA-co-PAA)/NaCl .The reaction mechanism of IPN formation between PVA and AA is proposed to occur in two ways: at first the AA is grafted onto the PVA backbone by radical copolymerization. Secondly, the reaction between some of the hydroxyl groups of PVA and some of the carboxylic groups of PAA formed by homopolymerization of AA occurs to form an ester linkage resulting in the formation

Fig. 1 FTIR spectra of (a) PVA, (b) PAA, (c) (PVAco-PAA)/NaCl IPN.

Thermogravimetric Analysis (TGA) The comparative thermal behavior of PVA, PAA, and (PVA-co-PAA)/NaCl are shown in Fig-2. From the curves, the temperature of decomposition were found to be 2300C for PVA, 1700C for PAA and 1900C for (PVA-coPAA)/NaCl. The results indicate a decrease in thermal behavior by copolymerization and crosslinking. This might be due to the increasing porosity of the hydrogel network.


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Fig. 2 TGA thermograms of (a) PVA, (b) PAA, (c) (PVA-co-PAA)/NaCl IPN.

Fig. 3 Biodegradation of PVA-co-PAA and (PVA-co-PAA)/NaCl by E.coli measured by weight loss, BPO[2.5%(w/v)], NaCl [1.0 % (w/v)]

Biodegradation study Biodegradation study through E.coli was studied for PVAco-PAA, and (PVA-co-PAA)/NaCl hydrogels. At first, the degradation was calculated from the percentage of weight loss after different periods of incubation, that is 8,15,21,28 days. From the Fig-3, it is clearly visible that (PVA-coPAA)/NaCl is more degradable than PVA-co-PAA as it

absorbs more water in its network and rapidly enhancing the biodegradation. Again from the Fig-4 it is confirmed that, (PVA-coPAA)/NaCl shows the higher rate of biodegradation in comparison to PVA-co-PAA, measured by the amount of CO2 evolved from the cultured medium at different periods of incubation, that is 8,15,21,28 days.

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Fig. 4 Biodegradation of PVA-co-PAA and (PVA-co-PAA)/NaCl by E.coli measured by evolved CO2, BPO [2.5%(w/v)], NaCl [1.0 % (w/v)].

Fig. 5 Degradation studies of (PVA-co-PAA)/NaCl hydrogel IPN in physiological isotonic media, BPO [2.5%(w/v)] NaCl [1.0%(w/v)].

Degradation condition

study

in

simulated

intestinal

The degradation studies of the prepared hydrogel IPN were studied ion the basis of %Wt loss in simulated fed intestinal fluid at regular intervals. From the degradation study of (PVA-co-PAA)/NaCl IPN (Fig-5), it was found that as the immersion time increases, the weight loss also increases to become stabilized after about 20hours and extend up to 24hours.

Scanning electron microscopy (SEM) SEM photographs of (PVA-co-PAA)/NaCl IPN before and after bio-degradation are shown in Fig-6(a) and 6(b) respectively. The surface morphology of IPN clearly showed formation of interpenetrating network before biodegradation in Fig-6(a). The pores were mostly interconnected with large amount of NaCl that made the IPN macroporous.


Fig. 6(a) Scanning electron microscopy of (PVA-coPAA)/NaCl before biodegradation, BPO [2.5%(w/v)], NaCl [1.0%(w/v)].

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Fig. 6(b) Scanning electron microscopy of (PVA-coPAA)/NaCl after biodegradation, BPO [2.5%(w/v)], NaCl [1.0%(w/v)].

Fig. 7 pH dependent swelling properties of (PVA-co-PAA) and (PVA-co-PAA)/NaCl hydrogel at room temperature, BPO [2.5%(w/v)], NaCl[1.0%(w/v)].

Swelling Studies pH dependent equilibrium swelling experiments performed in gastric and intestinal pH conditions for the prepared IPN with and without NaCl are presented in Fig-7. From the figure it is clear that presence of NaCl in the IPN increases the swelling properties in both gastric and intestinal pH conditions. The effect of swelling ratio with different percentage of NaCl (1 to 5 wt.%) are studied in Fig-8. It was found that the swelling ratio increased and

attained maximum at 1% wt. NaCl and then decreased, thereby decreasing the hydrophilicity of the hydrogel. The prepared IPN hydrogel showed comparatively higher swelling at pH 7.4 medium. The difference may be due topresence of NaCl and the –COOH groups of PAA which are responsible for increased hydrophilic nature of the matrix. Thus the hydrogel became macroporous as evident from SEM studies about the open nature of pores before biodegradation.

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Fig. 8 Effect of [NaCl] on swelling ratio of (PVA-co-PAA)/NaCl at room temperature for 2 hours, BPO[2.5%(w/v)].

Conclusion

References

The significant result of the present work is the development of a novel mechanistic path of preparing a new IPN macroporous hydrogel in a nonconventional; way, in the absence of any added crosslinker. Swelling and biodegradation studies were investigated for PVA-co-PAA and (PVA-co-PAA)/NaCl IPN hydrogels prepared by emulsion copolymerization method using benzoyl peroxide as initiator and NaCl as additive. The biodegradation study by E.Coli showed that (PVA-co-PAA)/NaCl was more degradable than that without NaCl. From the pH dependent swelling studies, IPN hydrogel showed comparatively higher swelling at intestinal pH environment than that of gastric medium and presence of NaCl in the IPN increases the swelling properties in both media. The swelling ratio of the (PVA-co-PAA)/NaCl IPN were found to be maximum at 1%w/v NaCl concentration. The IPN hydrogel showed moderate thermal stability and the surface morphology by SEM revealed that the pores were mostly open in presence of NaCl, thus making the IPN macroporous. Keeping in view the different properties, it could be concluded that, in future studies the prepared IPN hydrogel can be used as drug delivery devices specially to intestine, with improving drug loading capacity as well as controlling the drug release behavior.

Brazel CS, Peppas NA. Mechanisms of solute and drug transport in relaxing, swellable, hydrophilic glassy polymers. Polymer 40: 3383-3398(1999).

Acknowledgement

Liu Y, Liu WO, Chen WX, Sun L, Zhang GB. Investigation of swelling and controlled-release behaviors of hydrophobically modified poly (methacrylic acid) hydrogels. Polymer 48: 2665-2671(2007).

Authors acknowledge Mr. Pradeep Kumar Rana, Utkal University for his support throughout the study.

Colombo P, Santi P, Bettini R, Brazel CS, Peppas NA. Drug release from swelling-controlled systems. In: Wise DL, Brannon-Peppas L, Klibanov AM, Langer RS, Mikos AG, Peppas NA, Trantolo DJ, Wnek GR, Yaszemski MJ (eds.) Handbook of pharmaceutical controlled release technology, Dekker, New York, 2000, pp. 183-209. Hoffman AS. Hydrogels for biomedical applications. Adv. Drug. Deliv. Rev. 43: 3-12 (2002). Ichikawa H and Peppas NA. Synthesis and characterization of pH responsive nanosized hydrogels of poly(methacrylic acid-gethylene glycol) for oral peptide delivery. In: Barratt G, Ducheˆ ne D, Fattal F, Legendre JY (eds.) New trends in polymers for oral and parenteral administration: from design to receptors, Editions de Sante´, Paris, 2001, pp. 261-264. Lowman AM, Dziubla TD, Bures P, Peppas NA. Structural and dynamic response of neutral and intelligent networks in biomedical environments. In: Peppas NA, Sefton MV (eds.) Molecular and cellular foundations of biomaterials, Academic Press, New York, 2004, pp. 75-130. Lowman AM, Peppas NA. Solute transport analysis in pHresponsive, complexing hydrogels of poly (methacrylic acid-g-ethylene glycol). J. Biomater. Sci Polym. Ed. 10: 999-1009 (1999).

Debajyoti Ray et al. : Designing of Biodegradable Interpenetrating Polymer Network of… Mohapatra R, Ray D, Swain AK, Sahoo PK. Release study of Alfuzosin Hydrochloride loaded to novel hydrogel P(HEMAco-AA). J. Appl. Polym.Sci. “in press”. Peppas NA, Huang Y, Torres-Lugo M, Ward JH, Zhang J. Physicochemical foundations and structural design of hydrogels in medicine and biology. Ann. Rev. Biomed. Eng. 2: 9-29(2000). Peppas NA, Wood KM, Blanchette JO. Hydrogels for oral delivery of therapeutic proteins. Expert. Opin. Biol. Ther. 4: 881-887(2004). Peppas NA, Khare AR. Preparation, structure and diffusional behavior of hydrogels in controlled release. Adv. Drug. Deliv. Rev. 11: 1-35(1993). Peppas NA, Bures P, Leobandung W, Ichikawa H. Hydrogels in pharmaceutical formulations. Eur. J. Pharm. Biopharm. 50: 27-46(2000). Peppas NA. Devices based on intelligent biopolymers for oral protein delivery. Int. J. Pharm. 277: 11-17(2004). Peppas NA. Molecular design and cellular response of novel intelligent mucoadhesive carriers for oral delivery of proteins. In: Saltzman WM, Chilkoti A, Luo D, Uhrich K (eds.) Biomaterials for drug delivery: architecture and application of biomaterials and biomolecular materials. MRS Proceedings, Pittsburgh, PA, 2004, pp. 381-392. Qu X, Wirsen A, Albertsson AC. Novel pH-sensitive chitosanhydrogels: swelling behavior and states of water. Polymer 41: 4589- 4598 (2000).

151

Soppimath KS, Aminabhavi TM, Dave AM, Kumbar SG, Rudzinski WE. Stimulus-responsive “smart” hydrogels as novel drug delivery systems. Drug. Dev. Ind. Pharm. 28: 957-974(2002). Scott RA, Peppas NA. Highly crosslinked PEG-containing copolymers for sustained solute delivery. Biomaterials 20: 1371-1380(1999). Sperling LH. Interpenetrating polymeric networks and related materials, Plenum press, New York, 1981. Siemoneit U, Schmitt C, Lorenzo AC, Luzardo A, Espinar FO, Concheiro A, M endez BJ. Acrylic/cyclodextrin hydrogels with enhanced drug loading and sustained release capability.Int.J.Pharm. 312: 66-74 (2006). Sdelen BT, Apohan NK, Güven O, Baysal BM. Preparation of poly (N-isopropylacrylamide/itaconic acid) copolymeric hydrogels and their drug release behavior. Int.J.Pharm. 278: 343-351 (2004) Saikos G, Bokias G. Inter polymer complexes of Poly (acrylamide) and Poly (N-isopropylacrylamide) with Poly (acrylic acid): a comparative study. Polym. Int. 41: 345 (1996). Torres-Lugo M, Peppas NA. Preparation and characterizationof P(MAA-g-EG) nanospheres for protein delivery applications. J. Nanopart. Res .4: 73-81(2000).