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DissolutionandDrugreleaseprofilesofphosphateglassesdopedwithhighvalencyoxides

E.El-Meliegy1*,M.Farag*andJ.Knowles***NationalResearchCentre,Dept.ofBiomaterials,El-TahrirStreet,Dokki,Cairo,Egypt.**BiomaterialsandTissueEngineering,UCLEastmanDentalInstitute,UniversityCollegeLondon

Abstract:

ThispaperinvestigatesphosphateglassesincorporatingVanadiumandMolybdenumoxides

for effective management of dissolution and drug release. These glass formulations are

foundtoreducetherateofdissolutionfromtheglasssurfaces.Thedrugfunctionalgroups

of Vancomycin molecules loaded by immersion showed stronger hydrogen bonding with

Vanadium doped glasses and consequently lower rate of drug release over two weeks

indicatingbettersurfaceattachmentwiththedrugmoleculesandslowdrugreleaseprofiles.

Thiscanbeexplainedbythestrongadherenceofdrugmoleculestoglasssurfacescompared

withthemolybdenumcontainingglasses(PM5andPM10).Thestrongattachmentrelatesto

hydrogenbondingbetweentheamino-functionalgroupsofVancomycinandthehydratedP-

O-Hgroupsintheglassnetwork.Inconclusion,therateofdissolutionofdopedglassesand

therateofdrugreleasecanbeadministeredtodeliverthedrugmoleculesoverweeks.

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1. Introduction

Becauseoftheincreaseinthenumberofaccidents,multipletraumavictims,andageingof

the population, the demand for bone reconstruction is constantly growing. Therefore,

research and development of new bone grafting materials became the main interest of

scientists.Calciumphosphateceramics, suchashydroxyapatite,havebeenwidelyusedas

bonegraftingmaterials,due to their similarity in chemical compositionwithhumanbone

body[1].But, too lowbioresorbability rateatnormalphysiologicalconditions [2]makesa

limitation to apply such materials successfully in some biomedical applications require a

highly biodegradable and bioresorbable materials. However, bioactive glasses, such as

phosphate-based glasses are considered desirable alternativematerials. Bioactive glasses

havetheabilitytobondwithtissue[3]),aswellas,theflexibilityofcontrollingdegradation

bychangingtheirchemicalcomposition.

Calciumphosphateglasseshavedemonstratedasuperiormaterialformedicalusesdueto

their sustained and controlled solubility[4], which make them potentially useful for

promoting the regeneration of soft and hard tissues. Additionally, their chemical

compositionisclosetothatoftheinorganicpartofbone,whichnominatedthemforuseas

alternativematerialsforsilicatebioglasses.Inaddition,phosphateglassesarebioresorbable

and biodegradablematerials because of their solubility in human body [5], which allows

themtobeusedasbiodegradablesuturethreadandasdrugdeliveryvehicles[6].

Recently, phosphate glasses have been used as suitable carriers for the delivery of

therapeutic ions, such as silver and copper [7]. Phosphate-based glasses have previously

been examined for tissue engineering applications including transitionmetal ions such as

Fe3+,Cu+andCu2+,Zn2+,andTi2+,whichhaveshowntoimprovecellattachment,activatethe

synthesis of enzymes involved in the first step of protein biosynthesis and exhibit

antibacterial properties [8]. Consequently, phosphate glasses are used as potential

substratesinbonetissueengineering[9].

However, vanadium andmolybdenum oxides are expected tomodify phosphate glasses’

network,andcontrolthedegradationrateoftheglasses.Fromanotherview,itisproposed

that their ions have a therapeutic action into the body. Vanadium compounds (such as

Polyoxovanadates)havedemonstratedapplicationsinmedicineandprovedefficienteffect

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againstleukemia,breastadenocarcinoma,testicular,renal,andgastrointestinalcancersand

hepatomas.[10].

Aswellas,itwasprovedthatvanadiumhastheanti-diabeticpropertieswhichwasinitiated

in 1985 by John McNeill [11] and used as inhibitors to various phosphate-metabolizing

enzymes through binding to the proteinmatrix.On the other hand, peroxo-molybdenum

complexeshaveshownanantitumoreffect[12].However,despitetheproventherapeutic

valuesofvanadiumandmolybdenumcompoundsinbiomedicine,thereisnoclearevidence

aboutthesuitabilityofphosphateglassesasdrugdeliverycarriers.

Thus,theapplicationofphosphateglassesindrugdeliverysystemscouldbeveryuseful,but

their fast degradation behavior is hindering the application in this approach. Therefore,

numberofhighvalencyelementswassuggestedasdopantsintophosphateglassesinorder

tocontroltherateofdissolutionandinrole,improvethedegradationprofileofglassesfora

therapeutic action. Thephosphate glassesmodifiedwith theVanadiumandMolybdenum

willbeevaluatedforlocaldrugdeliverycarriers.Thisfactwouldbesuccessful,ifitcouldbe

possibletomodifythecontrolleddissolutionandpotentialbiodegradation.

Inthiswork,vanadiumandmolybdenumdopedphosphateglasseswillbepreparedinatrial

tocontrolthedegradationratesandionreleaseofphosphateglassesandinvestigatetheir

useasdrugdeliverycarriers.Vancomycinantibacterialdrugwasselectedasadrugmodelin

thisstudyduetoitsbroad-spectrumantibioticabilitytotreatseriousinfections,whichmay

be associated with application of bone-filling materials, orthopedic implants or bone

replacements.

2.Materialsandmethods

2.1.Glasspreparation

Thebasephosphateglasseswerepreparedbymelting. The chemical compositionsof the

studiedphosphateglassesinMol%areshowninTable1.Theglasscompositionsformulated

using NaH2PO4 99.0% Sigma, calcium carbonate (CaCO3) 99% Sigma aldrich, Phosphorus

pentoxide (P2O5) 99% Sigma Aldrich and Vanadium(V) oxide (V2O5) 99.6% Aldrich and

Molybdenum(IV) oxide (MoO2) 99% Aldrich. The precursors were weighed to satisfy the

proposed glass formulations and placed into a 200ml platinum crucible. Care was taken

whileweighing Phosphorus pentoxide in order to avoidmoisture content. The crucible is

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placedintoafurnaceattemperature750-1200oCfor1haccordingtothemeltingpointof

theglassbatches.

Themoltenglasseswere thenpoured intoapreheatedgraphitemolds inorder todesign

glassblocksbycasting.Theglassblockswereannealedattherightannealingtemperature

accordingtotheresultsofthermalanalysis,at350oC/1h,andthenallowedtocooltoroom

temperature, in order to remove the residual stresses in the glass. The glass rods were

obtainedandcutinto12mmdiameter,2mmthickdiscsusingadiamondsaw.

2.2.Characterizationofglasses

2.2.1.DTA

Glass powders were prepared grinding and screened to pass a 75µm sieve. The thermal

characterization was carried out using a Setaram differential thermal analyzer (Setaram,

France).Powderglasssampleswerescannedataheatingrateof10oC/minupto1000oCin

ordertodetermineglasstransition(Tg),crystallization(Tc),and(Tm)meltingtemperatures.

2.2.2.FourierTransformInfraredSpectroscopy

The infrared absorption spectra of the phosphate glass powders were analyzed at room

temperature in thewavenumber rangeof4000–400cm-1usingFourier transform infrared

(JASCOFT/IR-4600).The2mgsamplesweremixedwith200mgKBrinanagatemortarand

pressedintoapellet.Foreachsample,theFTIRspectrumwasnormalizedwithablankKBr

pellet.

2.2.3.Invitrodegradationtest

Invitrodegradationtestwasperformedbydeterminingtheconcentrationsofionsreleased

fromtheglassesuponimmersionofbulkglassdiscs(13mmdiameterand2mmthick)intris-

HClbuffersolution.[13].Theconcentrationsofions(calcium,phosphorus,molybdenumand

vanadiumions)releasedintothesolutionandpHofincubatedsolutionsweremeasuredat

thepredeterminedtimes(1,3,7,18and28days).Ontheotherhand,theeffectofsolution

ontheglasssurfaceswasexaminedbySEM-EDX(ModelQuanta250FEG)afterimmersionin

SBF(simulatedbodyfluid)for1week.SBFwaspreparedaccordingtoKokubo2006[14].

2.2.4.Drugdeliveryexperiment

DrugLoading:

Theglasspowdersamples(200mg)wereloadedwithvancomycin-HClthroughimmersionin

10mldrug solution (5mg/ml) for 2daysunder static condition. Thedrug solutionswere

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collected, and the absorbance was measured by UV-visible spectroscopy at wavelength

282nm. The concentrations of non-adsorbed drug were determined by plotting the

absorbanceonthestandardcurve.

Drugrelease:

Fordrugreleaseevaluation,eachsamplewasimmersedin10mloftris-HClbuffersolution,

pH7.4,at37°Cupto30days.Ateachpredeterminedtime(1,3,6,12hours,1,3,7,14,21

and30days),2mlof immersedsolutionwascollectedandreplacedby2mlfreshtris-HCl

buffer solution. The collected solutionswere kept at –20oC up till themeasurement. The

concentrationsof releaseddrug in the collected solutionsweredeterminedbymeasuring

theabsorbanceusingUV-visiblespectrophotometeratwavelength282nm(UnicoUV2000,

n=3).Theconcentrationswerecalculatedbycomparisonwiththestandardcurve.

3. Resultsanddiscussion:

3.1. Thermalanalysis

The DTA patterns shown in Table 2 and Figure 1a displayed peak midpoint of the glass

transitiontemperature,thecrystallizationandmeltingtemperaturesofthedifferentglasses

under investigation.Theglasstransitiontemperatures (Tg),werefoundto increasebythe

increase in theMoO3 andV2O5 contents. The transition temperature (Tg) are 405oC, 407,

435,447,and477oCforP0,PM5,PM10,PV5andPV10,respectively.Theobviousincreaseof

the transition temperatures could be attributed to the higher ionic field strength (IFS) of

Mo6+ (2.15) and V5+ cations compared with that of Na+ (0.19) according to Dietzel [15].

Therefore,Mo6+andV5+bondsarestrongerthanNa+bonds.Thus,moreenergywouldbe

requiredtobreakthesebonds.

Moreover,allglasssamplesshowedtwocrystallizationpeaksandtwomeltingtemperatures

peaks indicating the possibility of evolving two crystalline phases on further higher

temperatureheattreatment.Thesecondexothermicpeaksofcrystallization(Tc2)ofglasses

containingMowerestrongerandsharper,butatlowertemperaturecomparedwiththose

obtainedbyV-containingglassesasshowninTable2.

Alternatively, both Tm1 and Tm2 melting temperatures of the vanadium containing group

werelowerthanthecorrespondingmeltingtemperaturesofmolybdenumcontaininggroup.

Where,Tm1temperatureswere734,766oCforPM5andPM10,and720,670oCforPV5and

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PV10, respectively,whileTm2temperatureswere799,824oC forPM5andPM10,and766,

796oCforPV5andPV10,respectively,asshowninFig.1andTable2.

3.2. FTIR

TheresultsofFTIRspectraofP0,PM5,PM10,PV5andPV10glassesinthefrequencyregion

between4000and400cm-1areshowninFigure2.Abroadbandislocatedaround3463cm-

1. Thisband couldbeattributed to symmetric stretchingofO–Hgroups inH2Omolecules

thatmightbeoriginatedfromoriginatedfromabsorbedwater.Thebandbecomessharper

andstrongerwithincreasingthecontentofMoO3orV2O5.Furthermore,thebandlocated

around1636cm-1 isassignedtobendingvibrationmodeofP-O-H.[16].Theresultsreflect

theincreaseincovalentcharacteroftheP–ObondswiththeincreaseoftheMoO3orV2O5

contentsandtheincreaseofO-Hbondlength[17].

Moreover, the band appeared near to 490 cm-1, is attributed toO-P-O bending vibration

mode [18]. The band near to 509 cm-1 was assigned to harmonic of the P=O bending

vibration [19]. The bands observed around 903cm-1 and 745 cm-1 are attributed to

asymmetric stretching and symmetric stretching modes of the bridging oxygen atoms

bonded to a phosphorus atom (P–O–P) in a Q2 phosphate tetrahedron [20]. Both bands

were shifted to higher frequencies with the content of the MoO3 or V2O5. The bands

allocated around970cm-1 and1093 cm-1were attributed to symmetric stretchingof non-

bridgingoxygen(NBOs)inQ0tetrahedra[21],andasymmetricstretchingvibrationofP-O-P

of the group (PO3-2) [22]. The band observed at 1122 cm-1 is assigned to the symmetric

stretching vibrations of PO3-2 groups [23]. Thebandnoted at 1161 cm-1 attributed to the

symmetricstretchingvibrationmodeofO-P-O[24].Thebandpresentednearto1244cm-1is

assignedtoP=OasymmetricstretchingvibrationofPO2[25],suchbandwasincreasedwith

increaseofMoandVcations.

From FTIR results it could be noted that, the intensities of different vibration bands of

phosphatestructures increasedby increase in thecontentofMoO3orV2O5.Suchoxides

increased the number of non-bridging oxygens (NBOs) in the phosphate network, but in

parallel, they acted as ionic cross-linker among NBOs, and thus, increase the ionic bond

strengthanddecreasetheP-Obonds.

3.3. Glasssolubility

3.3.1. Weightloss

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Theweight losspercentagevs. the time is represented inFigure3. It couldbeelucidated

that the solubilityof glassdecreasedwith theadditionofMoO3andV2O5.Moreover, the

solubilitiesofvanadium-containingglassesare lowercomparedwiththatofmolybdenum-

containingglasses.Theweight losspercentagesofthephosphateglasses(P0,PM5,PM10,

PV5 and PV10) are found 26.9%, 9.9%, 5.5%, 2.2% and 1.7%, respectively at the end of

incubationperiod(28days).Thefactthatagreewithconclusionpreviouslyreportedthatthe

additionoftransitionmetaloxidesreducesignificantlythedegradationofglass[26].

TheadditionofMoO3orV2O5oxidesincreasedthebondingstrengthofglassnetworkasa

resultoftheincreaseintheionicfieldstrengthcomparedwithNa2O.Inthecurrentworka

progressive increase in the concentrations of released Mo6+ and V5+ cations results in a

substantial increase in the ionic strength of the incubation medium. Therefore, the

incorporationofMoO3andV2O5inthephosphateglassesdecreasedthedissolutionratesof

asaresultofthespontaneousincreaseintheelectrostaticinteractionsinthehydratedlayer

[27].

3.3.2. pHmeasurements

The pH of incubatedmediumof the studied phosphate glasses as a function of time are

showninFigure4.ThepHvaluesdecreasedcontinuouslyinallcasestotheminimumvalues

after7daysofincubation.ThepHvalueswerefound5.79,6.09,6.03,6.10and6.49forP0,

PM5,PM10,PV5andPV10,respectively.Thereafter,forincubationtimemorethan1week,

pHvalueswerefoundcontinuously increasingtoreach7.00,7.40,7.41,8.06and8.53,for

P0, PM5, PM10, PV5 and PV10 glasses, respectively. The incubatedmedium of the base

glassshowedthelowestpHvaluesasaresultofgeneratingacidicspeciesbythedissolution

of phosphorus cations released from the breakage of P–O–P bonds associated with the

[PO4]units.

According to thepreviously stated theory of glass dissolution [28], thephosphate glasses

under investigationdissolve inaqueousmedium in twosteps; thehydration stepand the

breakagestep.Thehydrationstep,whereahydratedlayerisformedontheglasssurfaceas

aresultofNa+andH+exchange,asrepresentedinEquation(1).Thebreakagestep,where,

the continuous attack of water results in breaking up of P-O-P bonds and accordingly

breakingofglassnetworkandreleaseof[PO4]units,asrepresentedinEquation(2).

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Accordingly, the incorporationofMoO3 andV2O5 oxides on the extent ofNa2O results in

reducing the rate of hydration and the rate of breakdown of the phosphate bonds.

Accordingly,therateofdissolutionisfoundtodecreaseandthevaluepHisshownincrease.

However,alinearincreaseofpHvaluesmightbeattributedtothereleaseofCa2+ionsinto

the solution and chelation with the released phosphate species. Furthermore, Na+ ions

releasedintothesolutionduetotheH+ion-exchangemighttakepartinanincreaseofpH.

Expectedly, theamountofphosphate species chelatingwith releasedMo6+andV5+ ions

waslarger,becauseoftheirhighvalencystates.

3.3.3. Ionsreleaseconcentrations

TheionicreleaseofCa2+,Pspecies,Mo6+andV5+areshowninFigures5-7.Thedissolution

curves of Ca2+, P ions (Figure 5-6) showed non-linear release. Accordingly, P0 glass

represented thehighest calcium ion release followedbyPM5 sample.While, it showeda

nearlysteadystatereleaseassociatedwithPM10andPV10glasses.Thus,theincorporation

ofMoandVoxidesintotheglassnetworksdecreasedthedegradationofglass,andhence,

decreased the leachingof ions fromglassnetwork.On theotherhand, forP0,PM10and

PV10, the maximum P- ion concentration recorded after 7 days, while, it was nearly

constant release for PM5 and PV5. However, these resultsmight be apparently different

frompHvaluesmentionedbecauseofthecomplexandrepeateddissolution-depositionof

phosphorusinthesolution.Asitwasexpected,theconcentrationsofreleasedions;Moand

V,increasedlinearlywiththeprogressoftime,Figure7.

Eq. (1)

Eq. (2)

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3.3.4. EffectofSBFonsurfacesofthestudiedphosphateglasses:

SEM micrographs coupled with EDX analysis of P0, PM5, PM10, PV5 and PV10 after

immersioninSBFfor1weekareshowninFigure8.Themicrographsrepresentedthatsome

spherical aggregates were detected on P0 glass surface, which it might be some kind of

precipitatedCa-phosphatespecies.While,thesurfaceofPM5glasswassmooth,lookedlike

adjacentairbubblesandtherewasnoconnectedlongitudinalgrooveslikethatobservedon

thesurfaceofPM10glass.Furthermore,therewerenohydroxylcarbonateapatitedetected

onthesurfacesofPM5andPM10glass.Incontrary,flower-shapedcrystalsarefoundonthe

surfaces of PV5 and PV10 glasses, such crystalsmore likely formed by the deposition of

released vanadium and phosphate ions. These results are confirmed by EDX elemental

analyses(wt%)ofglassessurfaces,asshowninTable3.

ThepercentagesofvanadiumelementonthesurfacesofPV5andPV10glassesweremuch

more than thecorrespondingpercentagesofmolybdenumelementdetectedonPM5and

PM10glassessurfaces.TheresultsofMoandVionsconcentrationsintheincubatingliquid

(as mentioned before) were opposite. This proved that surfaces of V-containing glasses

covered by crystal layermainly composed of vanadium, and the released vanadium ions

consumedtoformsuchcrystals.

3.4. Drugreleaseprofile

The in vitro Vancomycin release of the different phosphate glasses (P0, PM5, PM10, PV5

andPV10)overaperiodof14daysareshowninFigure9.Allglasseshavethesamedrug

releaseprofile,whereas,thereleasewasmainlydividedintotwostages.Thefirststageisa

burstreleaseoccurringduringthefirstdayofincubation,andthesecondstageisobserved

along the rest time of immersion showing a sustained drug release. The base phosphate

glass(P0)showedthehighestrateofreleasewhereasmorethan90%ofthedrugisreleased

attheendoftheincubationperiod.

Alternatively, the incorporation of the high valence oxides affected obviously the rate of

drug release. Thephosphate glasses dopedwithMoandVoxides showed lower rates of

drug release.The releasepercentagesofdrugmoleculesof theglasseswere foundabout

25%,25%,45%,55%and70%inPV5,PV10,PM5,PM10andP0respectively,inthefirstday

of incubation. The release percentages of PM5, PM10, PV5 and PV10 were found about

72.5%,86.8%,54.5%and44.8%,respectively,attheendofincubationtime.Interestingly,

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Vanadiumcontainingglasses(PV5andPV10)demonstratedlowerrateofdrugrelease.This

meansthatthedrugisstronglyadheredtotheirsurfacescomparedwiththeMo-containing

glasses (PM5 and PM10). The results might be explained by the concept of hydrogen

bonding between the hydroxyl and amino-functional groups in the Vancomycin and the

hydratedP-O-Hgroupsinthephosphateglassnetwork[29].

A representation for the way of attachment of vancomycinmolecules to the surfaces of

molybdenumandvanadiumdopedphosphateglassesareshowninFigure10.Thediagram

isbasedon thehydrogenbondingofdrugmolecules to theglass surfaces.The ionic field

strengthofvanadiumisstrongerthanthatofmolybdenum,thus,alargerdipoleeffectand

thereforealargereffectivenegativechargeontheoxygenforhydrogenbonding.Whenthe

V-Obondbecameincontactwiththedrug,itformedstrongerhydrogenbondingbetween

the oxygen and the drug functional groups. Vanadium doped glasses displayed better

surfaceattachmentwiththedrugmoleculesshowingasustaineddrugreleaseprofileover

thetwoweeksfollowingthefirstdayofincubation.

To determine the in vitro releasemechanism of Vancomycin drug from different glasses,

different dissolution data were fitted to two known release models; Higuchi[30] and

Korsmeyer-Peppas[31].Thekineticequations,andtheregressioncoefficient,R2,wereused

asanindicationofdatafitting.Thedifferentkineticequationsare;

Higuchi model [30] which is useful for studying the release of water soluble and poorly

solubledrugsfromvarietyofmatrices,includingsolidsandsemisolidsisbeingrepresented

byequation(1):

Qt=KHt1/2(1)

Korsmeyer-Peppasmodel[31]isbeingrepresentedbyequation(2):

Qt/Q0=KKtn(2)

Tofindoutthemechanismofdrugrelease,first60%drugreleasedatawerefittedinsuch

model.WhereQtistheamountofdrugreleasedintimet,Q0istheinitialamountofdrugin

the sample, KH and KK are Higuchi and Korsmeyer-Peppas constants, and n is kinetic

exponent. In order to determine which model is suitable for drug release kinetics, the

regressioncoefficients,R2,werecalculatedby regressionanalysis.Peppas [32]used thisn

value in order to characterize the drug release mechanism. The values of n and their

corresponding releasemechanism are represented in Table 4. For the case of cylindrical

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tablets,0.45=ncorresponds toaFickiandiffusionmechanism,0.45<n<0.89attributed to

non-Fickiantransport,n=0.89toCaseII(relaxational)transport,andn>0.89tosupercase

II transport. The kinetic exponent, n, can be determined by plotting of log cumulative

percentagedrugreleaseversuslogtime.

The regression coefficient, R2, and release rate (KH) calculated from Higuchi model, and

Regressioncoefficient,R2,andkineticexponent,n, calculated fromKorsmeyer-Peppasare

shown inFigure9andTable5. Itwasnoted fromR2 comparison that the invitro release

profilesofVancomycinfromallglasssamplescouldbebestexpressedbyKorsmeyer-Peppas

(R2>0.9),andthenvaluesofthismodelforPM5,PM10,PV5andPV10sampleswerelower

than0.45.ThedrugreleasemechanismforallglassformulationsfollowedFickiandiffusion

(i.e.controlledrelease).Ontheotherhand,thevaluesofn>0.45forP0glassindicatingthat

the dissolution of the base glass follows non-Fickian diffusion. Accordingly, two

simultaneous processes happened; drug diffusion and glass erosion. Alternatively, the

release profiles of PV5 and PV10 samples could be expressed by Higuchi model, which

indicated that diffusion was the predominant mechanism of drug release from such

samples. Interestingly, it could be tailored the release mechanism by changing the glass

composition.

Conclusion:

Thedissolutionanddrugreleaseprofilesofphosphateglassesincorporatingvanadiumand

Molybdenumoxideswereinvestigated.Therateofglassdissolutionisfoundtobereduced

throughtheslowleachingofionsfromtheglasssurfaceswiththepresenceofhighvalance

oxides.

Vanadiumdoped glasses (PV5 and PV10) demonstrated lower rate of drug release in the

period following the first day of drug release indicating a slow drug release profiles

comparedwiththemolybdenumcontainingglasses(PM5andPM10).

The slow drug release rate relates to the hydrogen bonding between the hydroxyl and

amino-functional groups in theVancomycin andhydratedP-O-H groups in thephosphate

glassnetwork.

Inconclusion,therateofdissolutionofdopedglassesandtherateofdrugreleasecanbe

administeredtodeliverthedrugmoleculesoverseveralweeks.

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15

200 400 600 800 1000

799734

762734

502P0

407526

405

HeatF

low (µ

V)

Temperature (oC)

515

824

PM5

435

580

720

766

570PM10

630

781

538

796670

PV5

PV10 477

447

611

575

678

Figure1.DTApatternsofthedifferentphosphateglasses

16

Figure2.FT-IRspectraofthedifferentphosphateglasses

5 10 15 20 25 300

5

10

15

20

25

30

35

Wei

ght l

oss

(%)

Time (day)

P0 PM5 PM10 PV5 PV10

Figure3.weightloss%ofP0,PM5,PM10,PV5andPV10glasssamplesasafunctionoftime.

17

0 5 10 15 20 25 305.0

5.5

6.0

6.5

7.0

7.5

8.0

8.5pH

Time (day)

P0 PM5 PM10 PV5 PV10

Figure4.pHofP0,PM5,PM10,PV5andPV10glasssamplesasafunctionoftime.

5 10 15 20 25 300.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Ca io

n con

c. (m

mol/l)

Time (day)

P0 PM5 PM10 PV5 PV10

Figure5.ReleaseofCalciumcationsfromthephosphateglasses(P0,PM5,PM10,PV5and

PV10)asafunctionoftime

18

0 5 10 15 20 25 300.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

P io

n co

nc. (

mm

ol/l)

Time (day)

P0 PM5 PM10 PV5 PV10

Figure6.Releaseofphosphorouscationsfromthephosphateglasses(P0,PM5,PM10,PV5

andPV10)asafunctionoftime

0 5 10 15 20 25 300.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

Mo

& V

ions

con

c. (m

mol

/l)

Time (day)

PM5 PM10 PV5 PV10

19

Figure7.Releaseofmolybdenumandvanadiumcationsfromthephosphateglasses(P0,PM5,PM10,PV5andPV10)asafunctionoftime

20

Figure8.SEMphotographsandEDXanalysisofthedifferentphosphateglassesafter

immersioninSBFfor7days

0 50 100 150 200 250 300 3500

10

20

30

40

50

60

70

80

90

100

Cum

ulat

ive

rele

ased

dru

g %

Time (hours)

Po PM5 PM10 PV5 PV10

21

Figure9.Vancomycindrugreleaseprofilesofthedifferentphosphateglasses(P0,PM5,

PM10,PV5andPV10)usingtris-buffer(pH7.4)asincubatingmedium,andHiguchiand

Korsmeyer-Peppasmodelsfitting.

Figure10.aschematicdiagramofVancomycinmoleculesbondedwithMo-andV-containingphosphateglassessurfacesbyhydrogenbonding