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Research Article Calcium Alginate and Calcium Alginate-Chitosan Beads Containing Celecoxib Solubilized in a Self-Emulsifying Phase Lorena Segale, Lorella Giovannelli, Paolo Mannina, and Franco Pattarino Dipartimento di Scienze del Farmaco, Universit` a del Piemonte Orientale, Largo Donegani 2, 28100 Novara, Italy Correspondence should be addressed to Lorena Segale; [email protected] Received 4 December 2015; Revised 25 February 2016; Accepted 9 March 2016 Academic Editor: Vitor M. Correlo Copyright © 2016 Lorena Segale et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In this work alginate and alginate-chitosan beads containing celecoxib solubilized into a self-emulsifying phase were developed in order to obtain a drug delivery system for oral administration, able to delay the drug release in acidic environment and to promote it in the intestinal compartment. e rationale of this work was linked to the desire to improve celecoxib therapeutic effectiveness reducing its gastric adverse effects and to favor its use in the prophylaxis of colon cancer and as adjuvant in the therapy of familial polyposis. e systems were prepared by ionotropic gelation using needles with different diameters (400 and 600 m). Morphology, particle size, swelling behavior, and in vitro drug release performance of the beads in aqueous media with different pH were investigated. e experimental results demonstrated that the presence of chitosan in the formulation caused an increase of the mechanical resistance of the bead structure and, as a consequence, a limitation of the bead swelling ability and a decrease of the drug release rate at neutral pH. Alginate-chitosan beads could be a good tool to guarantee a celecoxib colon delivery. 1. Introduction Drug delivery systems containing biodegradable natural polymers are the object of more and more research studies considering the advantages that these materials can offer [1]. Among them, those containing alginate and chitosan have been widely exploited in pharmaceutical field [2–4]. Alginate is a water soluble natural biopolymer extracted from brown algae and composed of alternating blocks of 1-4 -L-guluronic and -D-mannuronic acid residues [5]. is polymer forms hydrogels in presence of divalent cations like Ca 2+ , Ba 2+ , Sr 2+ , and Zn 2+ [6, 7] and this characteristic allows preparing drug loaded beads [8]. e mechanism of this gelation process involves guluronic residues with the specific chelation of Ca 2+ forming the so-called “egg-boxstructure [9]. Many researchers focused their attention on the development of calcium alginate beads as controlled drug delivery systems for the oral administration of drug molecules and proteins [10–12]. Chitosan is a biocompatible, biodegradable, nontoxic, linear polysaccharide composed of D-glucosamine and N- acetyl-D-glucosamine units linked by -(1-4) glycosidic linkages [13]. Chitosan can be derived by partial deacetylation of chitin from crustacean shells and it is widely used for cell culture, drug delivery, and food additives [14–16]. Cross-linking of alginate and chitosan in a hydrogel is used to provide materials useful for medical and pharma- ceutical applications; the obtained systems are characterized by enhanced stability compared to those obtained with a single polymer [17, 18]. In controlled drug delivery alginate- chitosan polyelectrolyte complex has received much attention in recent years [12, 19–22]. e two polymers form the polyelectrolyte complex via the ionic interaction between the carboxyl residues of alginate and the amino residues of chitosan. e alginate-chitosan beads can be produced by different methods: the two-step procedure and the one-step procedure [23]. In the first one, calcium alginate gel beads are produced by dropping a solution of alginate into a gelling bath containing calcium ions. e resulting beads are then transferred into a chitosan solution to form the membrane on their surface. e one-step procedure requires that the droplets of alginate solution fall into an aqueous solution containing both the gelling agent for alginate (e.g., calcium ions) and chitosan [24]. e choice of the production method Hindawi Publishing Corporation Scientifica Volume 2016, Article ID 5062706, 8 pages http://dx.doi.org/10.1155/2016/5062706
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Page 1: Research Article Calcium Alginate and Calcium Alginate ...

Research ArticleCalcium Alginate and Calcium Alginate-Chitosan BeadsContaining Celecoxib Solubilized in a Self-Emulsifying Phase

Lorena Segale, Lorella Giovannelli, Paolo Mannina, and Franco Pattarino

Dipartimento di Scienze del Farmaco, Universita del Piemonte Orientale, Largo Donegani 2, 28100 Novara, Italy

Correspondence should be addressed to Lorena Segale; [email protected]

Received 4 December 2015; Revised 25 February 2016; Accepted 9 March 2016

Academic Editor: Vitor M. Correlo

Copyright © 2016 Lorena Segale et al. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

In this work alginate and alginate-chitosan beads containing celecoxib solubilized into a self-emulsifying phase were developedin order to obtain a drug delivery system for oral administration, able to delay the drug release in acidic environment and topromote it in the intestinal compartment. The rationale of this work was linked to the desire to improve celecoxib therapeuticeffectiveness reducing its gastric adverse effects and to favor its use in the prophylaxis of colon cancer and as adjuvant in the therapyof familial polyposis. The systems were prepared by ionotropic gelation using needles with different diameters (400 and 600 𝜇m).Morphology, particle size, swelling behavior, and in vitro drug release performance of the beads in aqueous media with differentpH were investigated. The experimental results demonstrated that the presence of chitosan in the formulation caused an increaseof the mechanical resistance of the bead structure and, as a consequence, a limitation of the bead swelling ability and a decrease ofthe drug release rate at neutral pH. Alginate-chitosan beads could be a good tool to guarantee a celecoxib colon delivery.

1. Introduction

Drug delivery systems containing biodegradable naturalpolymers are the object of more and more research studiesconsidering the advantages that these materials can offer [1].Among them, those containing alginate and chitosan havebeen widely exploited in pharmaceutical field [2–4].

Alginate is a water soluble natural biopolymer extractedfrom brown algae and composed of alternating blocks of1-4 𝛼-L-guluronic and 𝛽-D-mannuronic acid residues [5].This polymer forms hydrogels in presence of divalent cationslike Ca2+, Ba2+, Sr2+, and Zn2+ [6, 7] and this characteristicallows preparing drug loaded beads [8]. The mechanism ofthis gelation process involves guluronic residues with thespecific chelation of Ca2+ forming the so-called “egg-box”structure [9]. Many researchers focused their attention onthe development of calcium alginate beads as controlleddrug delivery systems for the oral administration of drugmolecules and proteins [10–12].

Chitosan is a biocompatible, biodegradable, nontoxic,linear polysaccharide composed of D-glucosamine and N-acetyl-D-glucosamine units linked by 𝛽-(1-4) glycosidic

linkages [13]. Chitosan can be derived by partial deacetylationof chitin from crustacean shells and it is widely used for cellculture, drug delivery, and food additives [14–16].

Cross-linking of alginate and chitosan in a hydrogel isused to provide materials useful for medical and pharma-ceutical applications; the obtained systems are characterizedby enhanced stability compared to those obtained with asingle polymer [17, 18]. In controlled drug delivery alginate-chitosan polyelectrolyte complex has receivedmuch attentionin recent years [12, 19–22]. The two polymers form thepolyelectrolyte complex via the ionic interaction betweenthe carboxyl residues of alginate and the amino residues ofchitosan. The alginate-chitosan beads can be produced bydifferent methods: the two-step procedure and the one-stepprocedure [23]. In the first one, calcium alginate gel beadsare produced by dropping a solution of alginate into a gellingbath containing calcium ions. The resulting beads are thentransferred into a chitosan solution to form the membraneon their surface. The one-step procedure requires that thedroplets of alginate solution fall into an aqueous solutioncontaining both the gelling agent for alginate (e.g., calciumions) and chitosan [24].The choice of the productionmethod

Hindawi Publishing CorporationScientificaVolume 2016, Article ID 5062706, 8 pageshttp://dx.doi.org/10.1155/2016/5062706

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Table 1: Composition of calcium alginate and calcium alginate-chitosan beads.

Formulation Sodium alginate (% w/w) Self-emulsifying phase (% w/w) Gelling bath Needle diameter (𝜇m)

Cal 600 1.5Celecoxib 27.4

CaCl2100mM 600Labrasol 68.5

TPGS 4.1

Cal 400 1.5Celecoxib 27.4

CaCl2100mM 400Labrasol 68.5

TPGS 4.1

CAlCh 600 1.5Celecoxib 27.4

CaCl2100mM + 0.2% chitosan 600Labrasol 68.5

TPGS 4.1

CAlCh 400 1.5Celecoxib 27.4

CaCl2100mM + 0.2% chitosan 400Labrasol 68.5

TPGS 4.1

is responsible for the properties of the beads because ofthe amount of bound chitosan in the resulting product. Atthe same time, the characteristics of the beads are affectedby the molecular weight of the selected polymers and/orby the percentages of the various residues in the polymericmolecules [25, 26].

Celecoxib, a fluorinated benzenesulfonamide derivative,is a nonsteroidal anti-inflammatory drug (NSAID) with ahighly selective cyclooxygenase-2 (COX-2) inhibitory action.It possesses anti-inflammatory, analgesic, and antipyreticactivities due to the inhibition of prostaglandin synthesiscatalyzed by COX-2. Recently, this drug was frequentlyinvestigated for its anticancer activity using in vitro andin vivo models [27–30]. Preclinical studies on celecoxibreported prominent anticancer activity against head and necksquamous cell carcinoma, colon cancer, breast cancer, andlung cancer [27, 28].

In this work alginate and alginate-chitosan beads con-taining celecoxib solubilized into a self-emulsifying phasewere developed in order to obtain a drug delivery system fororal administration, able to delay the drug release in acidicenvironment and to promote it in the intestinal compart-ment. The rationale of this work was linked to the desireto improve celecoxib therapeutic effectiveness reducing itsgastric adverse effects and to favor its use in the prophylaxisof colon cancer and as adjuvant in the therapy of familialpolyposis [31–33]. The aim of the current study was theevaluation and the comparison of the properties of celecoxibloaded calcium alginate and calcium alginate-chitosan beads.Morphology, particle size, swelling behavior, and in vitro drugrelease performance of beads in aqueousmedia with differentpH were investigated.

2. Materials and Methods

2.1. Materials. Celecoxib was obtained from Chemos GmbH(Regenstauf, Germany). Anhydrous calcium chloride andsodium alginate (molecular weight 120000–190000 g/mol;1.56 mannuronic-guluronic residues ratio) were purchasedfrom Sigma Aldrich (Milan, Italy), while low molecular

weight chitosan was from Fluka (Milan, Italy). Labrasol(caprylocaproyl macrogol-8 glycerides) was a gift of Gatte-fosse (Milan, Italy); TPGS (D-𝛼-tocopheryl polyethylengly-col 1000 succinate) was kindly donated by Isochem (Gen-nevillers, France). All other chemicals were of analyticalgrade.

2.2. Preparation of Calcium Alginate Beads. Calcium alginatebeads were prepared by gelation method using calciumions as cross-linking agent. In detail, a 1.5% (w/w) sodiumalginate aqueous solution was mixed with a drug loaded self-emulsifying phase in 4 : 1 ratio and added drop by drop toa 100mMCaCl

2solution [34]. The self-emulsifying phase

was prepared mixing weighed amounts of Labrasol andTPGS at 50∘C and dissolving celecoxib in the excipientsolution. The emulsion (sodium alginate solution and self-emulsifying phase) was manually extruded in the hardeningbath through needles with 400 or 600𝜇m inner diameter,under constant gentle stirring, at room temperature. After15 minutes, the beads were collected, washed with deionisedwater to eliminate the excess of calcium ions and then dried at40∘C overnight. The composition of prepared formulations,coded CAl 600 and CAl 400, was listed in Table 1.

2.3. Preparation of Calcium Alginate-Chitosan Beads. Cal-cium alginate-chitosan beads (identified as CAlCh 600 andCAlCh 400) were prepared according to the one stepmethod.The procedure was identical to that adopted in the case ofalginate beads with the exception that the hardening bathwas a 0.2% (w/w) chitosan solution in diluted acetic acid(1%) containing CaCl

2at a concentration of 100mM. The

composition of the chitosan formulations was reported inTable 1.

2.4. Morphological and Particle Size Analysis. The morphol-ogy of the wet and dried beads and the particle size of thedried beads were analysed using a Motic SMZ168 stereomi-croscope and an image analysis software (Motic Image Plus2.0). For each formulation, the particle size was calculated asthe average value of the size of 20 dried particles.

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2.5. Drug Content. Sixmilligrams of drug loaded dried beadswas solubilized in phosphate buffer solution (100mL) atpH 6.8 added of 0.75% (w/v) sodium laurylsulphate at 70∘Cunder stirring for two hours. After cooling, the obtainedsolutions were filtrated and analysed spectrophotometricallyat 255 nm; the results are the average of at least threedeterminations.

2.6. Swelling Study. Swelling studies were carried out at 37∘Con dried beads put into three aqueous media characterizedby different pH: hydrochloric acid at pH 1.0 and phosphatebuffer at pH 6.8 and pH 7.4.

Accurately weighed amounts of calcium alginate andcalcium alginate-chitosan dried beads were put in glass vialscontaining 5mL of each fluid. After fixed time intervals (5,15, 30, 60, and 120 minutes), the samples were recovered,gently wiped with paper, and weighed again. The dynamicweight change of the beads with respect to time, definedas swelling degree (Sw), was calculated according to thefollowing equation:

Sw% =𝑊𝑡−𝑊0

𝑊0

× 100, (1)

where𝑊𝑡is the weight of the beads in the swollen state at time

𝑡 and𝑊0is the initial weight of the dried beads [35].

2.7. Celecoxib Release Study. The in vitro release studies wereperformed in hydrochloric acid at pH 1.0 and in phosphatebuffer at pH 6.8 and at pH 7.4 added of 0.75% sodiumlaurylsulphate to guarantee the maintenance of the sinkconditions.The studies were carried out by placing accuratelyweighed amounts of each formulation, equivalent to 8mgof celecoxib, in 500mL of the selected fluid at 37∘C undera rotation rate of 100 rpm (apparatus 2, paddle). Filteredsamples were withdrawn at specific time intervals withoutreplacement and analysed for celecoxib content using anUV spectrophotometer at 255 nm when the fluid was HCland phosphate buffer at pH 6.8 or at 256 nm in the case ofphosphate buffer at pH 7.4. Each experiment was done intriplicate.

The drug release performances of calcium alginate andcalcium alginate-chitosan beads were compared using thedissolution parameters t10%, t50%, and t90% which indicatethe time points at which 10%, 50%, and 90% of the drugwere released [36] and the f2 similarity parameter [37]. Forcurves to be considered similar f2 values should be close to100, and f2 values greater than 50 (50–100) ensure samenessor equivalence of the two curves.

2.8. Statistical Analysis. The results were statistically analysedto test significant differences by Student’s t-test, at 95%confidence interval; 𝑝 values less than 0.05 were consideredstatistically significant.

3. Results and Discussion

Alginate and alginate-chitosan beads were obtained byionotropic gelationmethod dropping an emulsion, composed

of alginate aqueous solution and the drug loading self-emulsifying phase, through 23G (600𝜇m) or 27G (400 𝜇m)needles, in a calcium chloride or in a calcium chloride-chitosan gelling bath. The excipients selected for the self-emulsifying phase were Labrasol, a liquid component withself-emulsifying and solubility enhancer properties, andD-𝛼-tocopheryl polyethylenglycol 1000 succinate as coemulsifyingand absorption enhancer agent (Table 1). The composition ofthe self-emulsifying phase was the same used in a previouswork [34].

Stereomicroscopic images of wet and dry alginate andalginate-chitosan beads are reported in Figures 1 and 2.Immediately after the preparation CAl 600 beads (Fig-ure 1(a)) show regular shape and homogeneous dimensions;they are white and opaque with a smooth, glossy, andhomogeneous surface.

The drying process does not change the shape of beadsbut leads to the reduction of their dimensions and modifiesthe characteristics of their surface, which is irregular andwrinkled (Figure 1(b)). The loss of water induces a decreaseof the distance between the polymeric chains and a variationof the structure of the beads, which is not compact andcontinuous but composed of small micronuclei adheringto each other. The fully swollen CAlCh 600 particles areslightly yellow and quite regular in shape and show a smoothsurface (Figure 1(c)). In this case, the drying process affectsthe spherical shape of the beads (Figure 1(d)); they becomeellipsoidal; their dimension decreases and their surface is veryrough.Moreover, after drying a partial surface agglomerationof the beads is observed: it is attributable to the adhesive prop-erties of chitosan [38]. In the case of beads prepared usinga 400 𝜇m needle (Figures 2(a)–2(c)), the images recordedimmediately after the preparation give evidence that for boththe formulations (with or without chitosan) particles are nothomogeneous in diameters even if they are regular in shape.CAl 400 and CAlCh 400 dry beads (Figure 2(b)) have asurface characterized by asperity and concavity; moreover, inthe case of alginate-chitosan formulation the particle shapeis completely irregular and the presence of solid bridges ofchitosan is well evident which bind the beads impeding theirseparation.

Average size of celecoxib loaded beads is between 715and 896 𝜇m (Table 2). The diameter of the beads wassignificantly affected by the diameter of the needle usedduring preparation (𝑝 < 0.05). The addition of chitosan toalginate beads changes significantly their dimensions onlywhen the 400𝜇m needle was used (𝑝 < 0.05). Moreover, asindicated by the high values of the standard deviation, usingthe 400 𝜇m needle the final product is a family of particlesinhomogeneous in dimensions.

All the formulations contain high amount of drug(Table 2) homogeneously distributed in the excipient matrixand the differences among their drug content were notsignificant except for CAlCh 400 slightly lower than theothers (𝑝 < 0.001). The percentage of celecoxib in the beadsexceeds the theoretical value and this is due to the loss ofLabrasol during the curing time [34], justifiable consideringthe high affinity between this excipient and water whichdrives it out of the beads into the gelling bath.

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CAl 600

(a)

CAlCh 600

(b)

(c) (d)

Figure 1: Stereomicroscopic images of wet (a-b) (2xmagnification) and dry (c-d) (3xmagnification) beads obtained using a needle of 600 𝜇min diameter.

CAl 400

(a)

CAlCh 400

(b)

(c) (d)

Figure 2: Stereomicroscopic images of wet (a-b) (2xmagnification) and dry (c-d) (3xmagnification) beads obtained using a needle of 400 𝜇mdiameter.

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Table 2: Average diameter and celecoxib content of the dry beads.

Diameter (𝜇m) Drug content (%)CAl 600 896 ± 64.24 42.10 ± 1.30CAl 400 715 ± 80.96 43.63 ± 0.77CAlCh 600 881 ± 66.87 40.94 ± 1.37CAlCh 400 795 ± 103.70 39.78 ± 0.66

0

50

100

150

200

250

300

350

5 15 30 60 120

Swel

ling

(%)

Time (min)

CAl 600 CAl 400CAlCh 600 CAlCh 400

Figure 3: Swelling degree in hydrochloric acid at pH 1.0.

A peculiar property of alginate or alginate-chitosanmicroparticulate systems in the dry form is their ability,after contact with an aqueous fluid, to rehydrate, take up thefluid, and undergo a swelling process, mainly associated withthe hydration of the hydrophilic groups of polymers. Whenthe fluid is water, it penetrates into the particles filling thepores among the polymeric chains and causing an impor-tant swelling of the system, without erosion/disintegration.Selecting fluids with different pH, the swelling behavior ofthe beads could change. For this reason, the swelling abilityof calcium alginate and of calcium alginate-chitosan beadshas been evaluated in HCl at pH 1.0 and in phosphate buffersolutions at pH 6.8 and 7.4 (Figures 3–5).

In acidic environment (Figure 3), there are no differencesin the swelling ability of the four formulations; at this pH, themaximum swelling degree is not over 60%. The alginate andalginate-chitosan beads absorb part of the fluid; their weightinitially increases and then remains constant. At this pH, forthe alginate systems (CAl 600 and CAl 400), the carboxylategroups of the polymer localized on the surface of particles areprotonated and a layer of alginic acid forms. The insolubilityof alginic acid in this fluid and the formation of hydrogenbonds, responsible for an increase of the structure stability,impede the penetration of additional fluid into the deeperlayers of particles, limiting their swelling. The same swellingbehavior is observed for CAlCh 600 and CAlCh 400 systems.Even if, in acidic environment, chitosan is highly solubleand charged for the conversion of its amine units into NH3+

0

50

100

150

200

250

300

350

5 15 30 60 120

Swel

ling

(%)

Time (min)

CAl 600 CAl 400CAlCh 600 CAlCh 400

Figure 4: Swelling degree in phosphate buffer at pH 6.8.

0

50

100

150

200

250

300

350

5 15 30 60 120

Swel

ling

(%)

Time (min)

CAl 600 CAl 400CAlCh 600 CAlCh 400

Figure 5: Swelling degree in phosphate buffer at pH 7.4.

soluble form, the interaction of amino groups and protonatedcarboxylic groups is not strong enough to promote swelling.Thus, the limited total swelling behavior is dominated bycalcium alginate structure.

Figures 4 and 5 show that the formulations exhibithigh swelling ability at pH 6.8 and pH 7.4. For CAl 600formulation, the weight of particles grows rapidly, reaches apeak after 30 minutes, and then decreases abruptly becauseof the erosion/disintegration of the system. This behaviorcan be due to ion exchange reaction between Na+ (presentin the phosphate buffer) and Ca2+ linked to carboxylicgroups of alginate. Monovalent ions replace bivalent onescausing the breakup of the “egg-box” structure and theincrease of the distance between the polymeric chains andfavoring the fluid absorption and the swelling of the systems.

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0

20

40

60

80

100

0 15 30 45 60 75 90 105 120

CEL

rele

ased

(%)

Time (min)

CAl 600CAl 400

CAlCh 600CAlCh 400

Figure 6: Celecoxib release profiles in hydrochloric acid at pH 1.0.

0

20

40

60

80

100

0 60 120 180 240 300 360 420 480

CEL

rele

ased

(%)

Time (min)

CAl 600CAl 400

CAlCh 600CAlCh 400

Figure 7: Celecoxib release profiles in phosphate buffer at pH 6.8.

This process goes on until the osmotic pressure into thebeads balances the strength of the cross-linking bonds andphysical entanglements, which preserve the structure of thebeads. Thus, particles start to disintegrate and their weightdiminishes.

The results obtained from the swelling study evidencethat CAlCh 600 and CAlCh 400 beads are characterized by amore resistant structure compared to CAl 600 and CAl 400,probably attributable to the interactions between alginate andchitosan chains. The maximum swelling degree of chitosanbeads is lower than that of the alginate; alginate-chitosansystems are able to reach a swelling equilibrium in about 30minutes and to maintain their weight at a constant level untilthe end of the test. Probably the interactions between the twopolymers are responsible for the formation of particles witha considerable mechanical resistance, which limits the fluiduptake and the structure disintegration. Finally, comparing

0

20

40

60

80

100

0 60 120 180 240 300 360 420 480

CEL

rele

ased

(%)

Time (min)

CAl 600CAl 400

CAlCh 600CAlCh 400

Figure 8: Celecoxib release profiles in phosphate buffer at pH 7.4.

the swelling behavior of CAl 400 versus CAl 600 and CAlCh400 versus CAlCh 600 beads (same composition, differentdiameter of the needle used in the preparation process), it ispossible to note that in phosphate buffers CAl 400 andCAlCh400 reached a swelling maximum peak higher than that ofCAl 600 and CAlCh 600, respectively.

The drug release profiles obtained from the differentformulations at pH of 1.0, 6.8, and 7.4 are shown in Figures6–8. The in vitro celecoxib release is affected by the pH ofthe selected fluid: the percentage of drug released in acidicmedium in two hours is quite low and varies between 12.70%and 24.53% (Figure 6). The delay of celecoxib release can beascribed to the reduced swelling ability of the systems in thisfluid; neither the composition of the beads nor their diameteraffects the drug release performance (f2 parameter valuesalways over 50). At pH 1.0, the release process is governedonly by the diffusion of the drug. This result allows satisfyingthe first object of this research work that is to minimize drugdelivery in acidic environment to promote and favor thisprocess at intestinal level.

In phosphate buffer at pH 6.8, the formulations arecharacterized by a drug release behavior affected by theircomposition and not significantly by their dimensions (Fig-ure 7). In this fluid, the systems initially swell and thenerode/disintegrate and, consequently, the drug release pro-cess is driven at first by diffusion and then by the polymericrelaxation. Alginate beads (CAl 600 and CAl 400) are ableto complete the celecoxib release in about eight hours; onthe contrary no more than 75% of the drug loaded inalginate-chitosan beads passes in solution after the same time.The comparison of the results from alginate and alginate-chitosan microparticle formulations reveals that the profilesare not similar having f2 values lower than 50. A possibleexplanation for such a behavior is the electrostatic interactionbetween carboxyl groups of the alginate and the amino groupof chitosan that improves the mechanical resistance of thepolymeric network reducing its swelling and erosion at pH6.8.

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Table 3: Time (min) necessary to release 10, 50, and 90% of theloaded drug.

CAl 600 CAl 400 CAlCh 600 CAlCh 400HCl

𝑡10% 24 12 31 85𝑡50% — — — —𝑡90% — — — —

pH 6.8𝑡10% 16 19 10 30𝑡50% 130 110 261 310𝑡90% 290 220 >8 h >8 h

pH 7.4𝑡10% 16 25 28 35𝑡50% 229 187 423 >8 h𝑡90% >8 h 444 >8 h >8 h

Surprisingly, the celecoxib release rate slows downmainlyfor CAlCh 400 formulation even if this formulation ischaracterized by the lowest particle size. Probably the smalldiameter and the high surface area of these particles lead tothe formation of a thicker chitosan layer around the beads,which opposes a great resistance to the fluid uptake and, as aconsequence, to the drug release.

Also at pH 7.4 the differences in the drug release per-formances can be attributed to the formulation compositionrather than to the particle dimensions (Figure 8). All theformulations showed an almost constant drug release rate.There are no differences between CAl 600 and CAl 400 andbetween CAlCh 600 and CAlCh 400 release curves; whenchitosan is in the beads, the drug release rate decreases.

The same conclusions are shown by the analysis of theresults of the drug release through the dissolution parameters(t10%, t50%, and t90%) (Table 3). The differences in therelease behavior of the beads are detected also through thedissolution parameters t10%, t50%, and t90% and are wellevident for the time necessary to release 50 and 90% ofthe loaded drug. In phosphate buffer solutions, alginate-chitosan beads require longer times to deliver 50 and 90% ofcelecoxib compared to alginate beads. Probably the presenceof the alginate-chitosan complex provokes a growth of thestructural wrinkles, irregularity and complexity of the beadstructure, which make the drug liberation difficult.

4. Conclusions

The investigated celecoxib loaded alginate and alginate-chitosan beads minimize the drug release in acidic environ-ment favoring this process at intestinal pH (6.8 and 7.4).The experimental results demonstrate that the presence ofchitosan in the formulation is responsible for an increase ofthe resistance of the bead structure and, as a consequence, fora limitation of the bead swelling ability and for a decrease ofthe drug release rate at neutral pH. Alginate-chitosan beadscould be a valuable vehicle of celecoxib for dosage formsuseful as adjuvant therapy in patients with familial polyposisand precancerous disease of colon.

Competing Interests

The authors declare that they have no competing interests.

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