FTIR spectroscopy characterization of poly (vinyl alcohol)hydrogel with different hydrolysis degree and chemically crosslinked with glutaraldehyde
Herman S.Mansur ⁎,Carolina M.Sadahira,Adriana N.Souza,Alexandra A.P.Mansur
Department of Metallurgical and Materials Engineering,Federal University of Minas Gerais,Rua Espírito Santo,35,30.160-030,Centro,
Belo Horizonte,MG,Brazil
Received 20October 2006;received in revised form 5July 2007;accepted 19October 2007
斯特林冲锋Available online 4December 2007
Abstract
In this work,poly (vinyl alcohol)(PV A)hydrogels with different degree of hydrolysis (DH)were prepared by chemical crosslinking with glutaraldehyde (GA).The nanostructure of the resulting hydrogels was investigated by Fourier Transform Infrared Spectroscopy (FTIR)and Synchrotron small-angle X-ray scattering characterization (SAXS).In vitr o tests were performed by swelling ratio assays in different p
H solutions.The infrared spectra of the crosslinked PV A showed absorption bands of the acetal bridges resulted from the reaction of the GA with the OH groups from PV A.Also the FTIR spectroscopy was used to determine the crystallinity of the PVA film based on the relative intensity of the vibration band at 1141cm −1.The results have showed an increase of hydrogel crystallinity with higher DH of PV A.SAXS patterns have clearly indicated important modifications on the PV A semicrystalline structure when it was crosslinked by GA.The swelling ratio was significantly reduced by chemically crosslinking the PV A network.PV A-derived hydrogel with chemically modified network was found to be pH-sensitive,indicating a high potential to be used in drug delivery polymer system.©2007Elsevier B.V .All rights reserved.
Keywords:FTIR spectroscopy;Hydrogel;Crosslinking;PV A;Hybrids
1.Introduction
Recently new developments in the medical field have been performed with the objective of evaluating the uses of hydrogels as a properly controlled system to deliver drugs [1–6].This trend is justified since there are similarities of the physical properties of hydrogels with the human tissues due to the great amount of water and low interfacial tension with water and/or biological fluids [7–9].
Among the systems studied the poly (vinyl alcohol)(PVA)hydrogel and its related products appeared as the ones most interesting for pharmaceutical applications,such as drug deli-very systems [10–14].Poly (vinyl alcohol)is a hydrophilic semicrystalline polymer produced by polymerization of vinyl acetate to poly (vinyl acetate)(PVAc),and subsequent hydro-
lysis of PV Ac to PV A.This reaction is incomplete resulting in polymer with different degree of hydrolysis [4].Com-mercial PVA is available in highly hydrolyzed grades (degree of hydrolysis above 98.5%)and partially hydrolyzed ones (degree of hydrolysis from 80.0to 98.5%)[15].The degree of hydrolysis or the content of acetate groups in PV A affects its chemical properties,solubility and crystallizability [15–16].
The polymer network structure can be tailored at a nanoscale order by physical and chemical crosslinking [17–20].Therefore a whole set of novel biomedical applications such as drug delivery,wound healing and tissue engineering scaffolds with nanostructure control are currently under investigation by several research groups.Stimuli-responsive hydrogels are one of the more promising types of polymeric materials.The water uptake of such hydrogels depends on the environmental con-ditions for instance pH,ionic strength,temperature,and elect-rical or magnetic field [21–25].
In the present work we have studied the use of partially hydrolyzed poly (vinyl alcohol)chemically crosslinked with
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Materials Science and Engineering C 28(2008)539–
548
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⁎Corresponding author.Tel.:+553132381843;fax:+553132381815.E-mail address:hmansur@demet.ufmg.br (H.S.Mansur).
0928-4931/$-see front matter ©2007Elsevier B.V .All rights reserved.doi:10.1016/j.msec.2007.10.088
glutaraldehyde for preparation of pH-sensitive hydrogel net-work for potential use in drug delivery systems.As far as we know,this is the first report of PVA-derived systems chemically crosslinked with bi-functional aldehyde to be investigated and characterized at nano-order level as pH-sensitive hydrogel.2.Experimental procedure
The detailed information regarding to all PV A used in this study with different degrees of hydrolysis and polymerization are showed in Table 1.All the data about DH and Mw (Molecular weight)were obtained from supplier technical data sheet (Celanese Chemicals-USA has kindly donated PV A samples).
The Scheme 1shows the expected chemical crosslinking reaction between the PV A chains and GA catalyzed by hydro-chloric acid [4].
2.1.Preparation of PVA and PVA/GA films
PV A hydrogels were prepared by fully dissolving 5.0g and 10g of polymer powder without further purification in 100mL of Milli-Q water,under magnetic stirring,at temperature of 60°C ±2°C.PV A 5%and 10%(wt.%)solution was let to cool down to room temperature and the pH was corrected to 2.00±0.05with 1.0M HCl (P.A.Synth,Brazil).
PV A/GA hydrogels were prepared by mixing 20.0mL of PV A 5%and 10%(wt.%)aqueous solution with 1.0mL,2.0mL, 3.0mL and 5.0mL of GA (Sigma,USA,25%aqueous).Then,PV A/GA solution was poured onto plastic plates and allowed to dry and solidify for 72h at room temperature producing optically transparent films.In order to have statistical analysis,all experiments were conducted with at least triplicates of samples (n =3),where the values were averaged and standard deviation (SD)was used as
Table 1
Properties of PV A used in this work (Supplier Celanese Chemicals,USA)Trade name
Molecular weight —Mw (g/mol)
Degree of hydrolysis (%)Hydroxyl groups (%)[OH]Sample
identification Sample crosslinking identification
Celvol 60313,000–23,00078–8280±2PV A –80–13Celvol 20531,000–50,00087–8988±1PV A –88–31Celvol 10731,000–50,00098–98.898.4±0.4PV A –98–31Celvol 52385,000–12,400087–8988±1PV A –88–85PV A/GA/88/85/Celvol 42585,000–124,00095.5–96.596±0.5PV A –96–85PV A/GA/96/85/Celvol 32585,000–124,00098–98.898.4±0.4PV A –98–85PV A/GA/98/85/
Celvol 540146,000–186,00087–8988±1PV A –88–146Celvol 350
146,000–186,000
98–98.8
98.4±0.4
PV A –98–
146
Scheme 1.Chemical Reaction of PV A polymer with glutaraldehyde catalyzed by acid.
540H.S.Mansur et al./Materials Science and Engineering C 28(2008)539–548
error on graph plots.Although,in all swelling assays 5samples of each group (n =5)were used aiming to produce more representative and reliable results,due to the intrinsic variation expect for the immersion method.
2.2.Fourier Transform Infrared Spectroscopy characterization Fourier Transform Infrared Spectroscopy (FTIR)was used to characterize the presence of specific chemical groups in the materials.PV A films and PV A-derived hydrogels crosslinked with GA (PV A/GA)were obtained as 1–2mm thick films and analyzed by FTIR using Transmittance Mode.FTIR spectra were obtained in the range of wavenumber from 4000to 650cm −1during 64scans,with 2cm −1resolution (Paragon 1000,Perkin-Elmer,USA).The FTIR spectra were normalized and major vibration bands were associated with chemical groups.
2.3.In vitro analysis by swelling assays
Pure PV A and PV A chemically crosslinked samples were accurately weighted and placed in a 150ml measuring cylinder.The measuring cylinder was placed in a shaker (Innova TM 4330Refrigerated Incubator Shaker,New Brunswick Scientif-ic)thermostatically maintained at 37°C.A fixed volume (50ml)of phosphate-buffer solution at three different pH (pH 3,6and 9)was poured into t
he cylinder.The samples were removed at 30,60,90and 120min,blotted with soft paper to remove surface water and weighted.The degree of swelling,D s ,was calculated as indicated in Eq.(1):D s ¼
W m ÀD m
D m
Â100k ð1Þ
where D m is the weight of dry film,and W m is the weight of swollen film.
Table 2
Vibration modes and band frequencies in PV A and PV A crosslinked with glutaraldehyde Identification Chemical group Wavenumber (cm −1)References 1
PV A O –H from the intermolecular and intramolecular hydrogen bonds ν3550–3200[21–24]
PV A+GA
教学
论坛O –H from the intermolecular and intramolecular hydrogen bonds ν3550–3200
2PV A
C –H from alkyl groups ν2840–3000
PV A+GA C –H from aldehyde Two peaks in ν2830–26953PV A
C _O ν1750–1735PV A+GA C _O
ν1750–17354PV A C –O (crystallinity)ν1141
[7]
5PV A
葬月C –O –C ν1150–1085[21–24]PV A+GA C –O –C ν1150–10856
PV A
CH 2
δ1461–1417
[21–
24]
温州号导弹护卫舰Fig.1.Typical FTIR spectra from PV A (PV A-88-85).
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条例H.S.Mansur et al./Materials Science and Engineering C 28(2008)539–548
2.4.Synchrotron small-angle X-ray scattering characterization (SAXS)
The SAXS spectra of PV A films were performed using the SAS beam line of the National Synchrotron Light Laboratory (LNLS,Campinas,Brazil).This beam line is equipped with an asymmetrically cut and bent silicon (111)monochromator (λ=1.608Å),which yields a horizontally focused X-ray beam.A set of slits defines the beam vertically.A position
sensitive X-ray detector (PSD)and a multichannel analyzer were used to determine the SAXS intensity,I (q ),as function of the modulus of the scattering vector q Eq.(2),being θhalf the scattering angle.q ¼4p k
4sen h ðÞ:
ð2Þ
Each SAXS pattern corresponds to a data collection time of 900s.From the experimental scattering i
ntensity produced by all the studied samples the parasitic scattering intensity produced by the collimating slits was subtracted.All SAXS patterns were corrected for the non-constant sensitivity of the PSD,for the time varying intensity of the direct synchrotron beam and for differences in sample thickness.Because of the mentioned normalization proce-dure,the SAXS intensity was determined for all samples in the same arbitrary units so that they can be directly compared.
3.Results and discussions
3.1.Characterization by FTIR spectroscopy
Table 2shows the most characteristic bands of PV A and their respective assignment.Fig.1shows the FTIR spectra of PV A (PV A –88–85).All major peaks related to hydroxyl and acetate groups were observed.The large bands observed between 3550and 3200cm −1are linked to the stretching O –H from the intermolecular and intramolecular hydrogen bonds (region (I)in Figs.3–5).The vibrational band observed between 2840and 3000cm −1refers to the stretching C –H from alkyl groups (region (II)in Figs.3–5)and the peaks between 1750–1735cm −1(region (III)in Figs.3–5)
are
Fig.2.Schematic vibration modes and band frequencies from PV A and PV A/GA:(a)PV A-98-85,(b)PV
A/GA/98/85.
Fig.3.FTIR spectra from PV A with different degree of hydrolysis (a)PV A-88-85,(b)PV A-96-85,(c)PV A-98-85.
542H.S.Mansur et al./Materials Science and Engineering C 28(2008)539–548
due to the stretching C _O and C –O from acetate group remaining from PV A [21–24].
Fig.2shows the FTIR spectra to PV A samples (PVA –88–85,PVA –96–85,PVA –98–85).The intensity of the 1750–1735cm −1is weak for PV As with high DH,indicating that only few acetate groups are present in the polymer chain and very strong for PV As with low DH.
The FTIR spectra of PV A (PVA –88–85,PV A –96–85,PV A –98–85)and PV A crosslinked with GA (PVA/GA/88/85,PV A/GA/96/85,PV A/GA/98/85)are presented in Figs.3–5.The reaction of the PV A with the GA results in a considerable reduction of the intensity of the O –H peaks (region (I)in Figs.3–5)from the hydrogel,indicating a possible formation of acetal bridges.According to the spectra obtained it is suggested that an excess of GA may be present is,even after the rinsing with water,since it was evidenced char-acteristic aldehyde bands.For instance,FTIR spectra of PV A/GA s
amples (region (II)in Figs.3–5)reveal two important bands at ν=2850and 2750cm −1of C –H stretching related to aldehydes,a duplet absorption with peaks attributed to the alkyl chain [30].Also,strong band from carbonyl group was verified (C _O at ν=1720–1740cm −1).These bands are overlapping and broadening PV A bands in these regions.In addition to that,by crosslinking PV A with GA,the O –H stretching vibration peak (ν=3330–3350cm −1)was relatively decreased when compared to pure PV A.Another
hypothesis
Fig.4.Schematic vibration modes and band frequencies from PV A and PV A/GA:(a)PV A-88-85,(b)PV
A/GA/88/85.
Fig.5.Schematic vibration modes and band frequencies from PV A and PV A/GA:(a)PV A-96-85,(b)PV A/GA/96/85.
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