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Copyright copy 2010 American Scientific PublishersAll rights reservedPrinted in the United States of America

Journal ofNanoscience and Nanotechnology

Vol 10 7126ndash7129 2010

A Biocompatible Chitosan CompositeContaining Phosphotungstic Acid Modified

Single-Walled Carbon Nanotubes

Qichao Zhao1 Jing Yin2 Xunda Feng1 Zujin Shi3 Zigang Ge2lowast and Zhaoxia Jin1lowast1Department of Chemistry Renmin University of China 100872 Beijing Peoplersquos Republic of China

2Department of Biomedical Engineering College of Engineering Peking University 100871 Beijing Peoplersquos Republic of China3College of Chemistry and Molecular Engineering Peking University 100871 Beijing Peoplersquos Republic of China

Surface modification of carbon nanotubes is crucial for the dispersion and interfacial adhesion ofcarbon nanotubes in polymer composites Here we present a novel method to construct single-walled carbon nanotubechitosan composites using phosphotungstic acid as an anchor reagentto modify single-walled carbon nanotubes The most direct benefit from this method is that thismodification is mild but effective the induced defects on single-walled carbon nanotubes are neg-ligible based on Raman and transmission electron microscopy observations and homogeneousdispersion of single-walled carbon nanotubes in chitosan matrices and strong binding betweensingle-walled carbon nanotubes and chitosan are achieved Moreover according to the results oftetrazolium-based colorimetric assays in vitro we demonstrate that the produced phosphotungstic-acid-modified single-walled carbon nanotubechitosan composites have good biocompatibility Thusour study provides a feasible route to fabricate biocompatible composites containing single-walledcarbon nanotubes for potential application in bone tissue engineering

Keywords Single-Walled Carbon Nanotube Chitosan Phosphotungstic Acid CompositeBiocompatible

1 INTRODUCTION

The application of carbon nanotubes (CNTs) as biomed-ical materials and devices has been an active topicrecently1 Since carbon nanotubes are effectively reinforc-ing filler in polymer composite2 the natural3 or synthetic4

biodegradable polymers which lack the necessary mechan-ical strength for bone tissue engineering have been con-sidered to be reinforced by carbon nanotubes To ensurethe mechanical improvement in CNTchitosan compositeshomogeneous dispersion of CNTs in chitosan matrices andstrong binding between carbon nanotubes and chitosan5

are two crucial points The dispersion of CNTs in chitosancan be achieved by covalent or non-covalent modifica-tion of CNTs However numerous studies have indicatedthat severe chemical functionalization of single-walled car-bon nanotubes (SWCNTs) may produce many defects onthe surface of SWCNTs and thus destroy the intrinsicstructure of SWCNTs6 resulting a weakening mechanicalstrength of SWCNTs On the other hand a very recentstudy has reported that osteoblast (a bone-forming cell)

lowastAuthors to whom correspondence should be addressed

attachment and their overall growth is a function of carbongraphitization7 In this study we develop an alternativemethod to fabricate SWCNTchitosan composites usingphosphotungstic acid (PW12) as a special binder agent Itwas observed that PW12-modified SWCNT was homoge-neously dispersed in chitosan matrices and the interfacialadhesion between chitosan and SWCNT was significantlyimproved Furthermore the most important advantage ofthis method was that the intrinsic structure of SWCNTscould be preserved To determine the biocompatibility ofthe obtained PW12-SWCNTchitosan composites the cyto-toxicity of the composites was investigated in vitro byquantization of growth of L-929 cells with the compos-ites over 48 hours using 3-[45-dimethylthiazolyl-2]-25-diphenyl tetrazolium bromide (MTT) colorimetric assaysIt was found that these composites are biocompatible toL-929 cell

2 EXPERIMENTAL DETAILS

Phosphotungstic acid (H3PW12O40 middot xH2O) chitosan(reagent grade with a deacetylation degree above 90)acetic acid hydrochloric acid and H2O2 were obtained

7126 J Nanosci Nanotechnol 2010 Vol 10 No 11 1533-48802010107126004 doi101166jnn20102834

Delivered by Ingenta toInstitute of Molecular and Cell Biology

IP 13713212369Mon 21 Nov 2011 065839

RESEARCH

ARTIC

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Zhao et al A Biocompatible Chitosan Composite Containing Phosphotungstic Acid Modified SWCNTs

from Sinopharm Chemical Reagent Co Ltd RawSWCNT materials were produced by arc-discharge methodand the purification process of SWCNT was reportedpreviously8 The PW12-modified SWCNT was obtainedfollowed the procedure reported by Fei et al9 ThePW12-SWCNTchitosan composite films were obtainedby mixing PW12-SWCNT suspension and chitosan solu-tion (1 wv in 01 M acetic acid) with different ratio(SWCNTs 02 wt 05 wt and 1 wt) and casting tothin films And a porous sponge (SWCNT 05 wt) wasproduced by freeze-drying method The PW12-modifiedSWCNTs and PW12-SWCNTchitosan composites werecharacterized by X-ray photoelectron spectroscopy (XPSPerkin-Elmer PHI-5300 ESCA) transmission electronmicroscopy (Hitachi 9000 HRTEM accelerating voltage100 kV) scanning electron microscopy (SEM JEOLJSM-7401F) and Raman spectroscopy (632 nm JobinYvon HR-800)Mouse fibroblasts (L-929 cells) were cultured in the

Dulbeccorsquos Modified Eagle Medium (DMEM) containing10 fetal bovine serum (FBS) 100 UmL penicillin and100 mgmL streptomycin All cells were cultured at 37Cin a humidified atmosphere of 5 CO2 The in vitro cyto-toxicity of PW12-SWCNTchitosan composites was evalu-ated by the MTT (3-[45-dimethylthiazolyl-2]-25-diphenyltetrazolium bromide) colorimetric assay method10 All datawere expressed as the average with standard error Statis-tic analyses of in vitro assessments were performed usingthe one-way ANOVA test and the Fisher LSD and tukeymethod as multiple comparison procedure with a p valueof 005

3 RESULTS AND DISCUSSION

Figure 1 is a typical TEM image of PW12-modifiedSWCNTs It is observed that the SWCNT was exfoliated

100 nm

Fig 1 The small bundles of SWCNTs dispersed in PW12 aqueoussolution

Fig 2 XPS curve of PW12 modified SWCNT magnified W(VI) andW(V) valance states and their atomic ratios The insert figure is the XPSsurvey of PW12 modified SWCNT

in small bundles of several to twenty nanometers that indi-cating a good dispersion in PW12 solution To thoroughlyunderstanding the interaction between carbon nanotubeand PW12 XPS and Raman spectroscopy was conductedto characterize the PW12-modified SWCNT The exis-tence of tungsten (W) in XPS survey confirmed theanchoring of PW12 on SWCNTs after the modification(Fig 2) The detailed analysis of W4f speaks revealedthat there were two different states of W4f W(VI) andW(V) which can be attributed to the charge transferfrom carbon surface to PW12 similar in PMo12 mod-ified carbon11 Raman spectroscopy presented not onlythe information about the structure change of SWCNTs

Fig 3 Raman spectra of original SWCNTs PW12-modified-SWCNTand PW12-SWCNTchitosan composites

J Nanosci Nanotechnol 10 7126ndash7129 2010 7127

Delivered by Ingenta toInstitute of Molecular and Cell Biology

IP 13713212369Mon 21 Nov 2011 065839

RESEARCH

ARTIC

LE

A Biocompatible Chitosan Composite Containing Phosphotungstic Acid Modified SWCNTs Zhao et al

after PW12 modification but also the charge transferbetween SWCNT and PW12 (Fig 3) It is clearly observedthat the radial breathing mode (RBM) of PW12-modifiedSWCNT has broader line width and relatively lower inten-sity than that of pure SWCNT due to the modificationand the RBM of the composite has a remarkable up-shift comparing to that of SWCNT and PW12-SWCNTthat can be attributed to the partial intercalation of chi-tosan molecules into the SWCNT12 Moreover the tangen-tial G-band modes of the PW12-modified SWCNT showsignificant decrease in Breit-Wigner-Fano (BWF) asym-metry indicating a chemical doping13 of SWCNTs afterPW12 modification But such a charge transfer betweenPW12 and SWCNT has not induced the destruction ofSWCNTs which was identified by the kept D band fea-tures of SWCNTs after PW12-modified The morphologyof PW12-SWCNTchitosan complex was observed by SEM(Fig 4) In a fracture surface it can be clearly foundthat chitosan are smoothly covered with SWCNTs So thePW12 anchoring on SWCNTs surface via chemisorptionhas effectively improved the dispersion of SWCNTs in chi-tosan and enhanced the binding in PW12-SWCNTchitosancomposites without inducing significant structure damni-fication of SWCNTsSince PW12 was used as an anchor agent to fabricate

the PW12-SWCNTchitosan composites it is important toassure that no cytotoxic materials were imparted in PW12-SWCNTchitosan composites The tetrazolium-based col-orimetric assay (MTT test) a commonly used method10

was carried out to quantitatively determine the biologi-cal response of cells to the PW12-SWCNTchitosan com-posites Figure 5 summarizes the MTT assay results offour PW12-SWCNTchitosan composites The percentagesof viable cells after the exposure to various compositeswere above 85 in most instances throughout 2 daysThe 15 difference compared with the blank sample wasattributed to the occupancy of partial space of the wellsby the tested samples The optical microscopy showedthat adherence and proliferation of L-929 cell with the

Fig 4 The SEM image of the fracture surface of PW12-SWCNTchitosan composite film

blank 02 05 1CNT sponge PC00

02

04

06

08

10

12

Per

cent

age

24 hr

48 hr

Fig 5 The MTT assay results of different PW12-SWCNTchitosancomposites compared to polystyrene disk (blank sample) Based on statis-tic analysis all PW12-SWCNTchitosan films showed no distinguisheddifference in MTT assays (24 hours and 48 hours)

PW12-SWCNTchitosan films are as well as they did onpolystyrene disks (Fig 6) indicating that the compositeswere non-cytotoxic to mouse fibroblast Therefore PW12-SWCNTchitosan composites are a promising candidatefor tissue engineering study A further study is on theway to investigate the cell attachment and development

(a)

(b)

100 microm

100 microm

Fig 6 The L-929 cells cultured 2 days with (a) blank (polystyreneplastic) disk and (b) PW12-SWCNTchitosan composite (1) film

7128 J Nanosci Nanotechnol 10 7126ndash7129 2010

Delivered by Ingenta toInstitute of Molecular and Cell Biology

IP 13713212369Mon 21 Nov 2011 065839

RESEARCH

ARTIC

LE

Zhao et al A Biocompatible Chitosan Composite Containing Phosphotungstic Acid Modified SWCNTs

behavior on the surfaces of PW12-SWCNTchitosancomposites

4 CONCLUSIONS

Homogeneous dispersion of SWCNTs in chitosan andenhanced interfacial adhesion with chitosan matri-ces was successfully developed using PW12 as ananchor agent Detailed XPS analysis demonstrated thata charge transfer occurred between PW12 and SWCNTresulting over 7 W(V) on SWCNT surfaces Ramanspectroscopy revealed that PW12 produced a chemical-like modification on SWCNT but it will not damnifythe intrinsic structure of SWCNTs The PW12-modifiedSWCNT with a negative surface charge can assemblewith positively charged chitosan by electrostatic inter-action inducing a strong interfacial interaction betweenSWCNT and chitosan matrices Biocompatibility of PW12-SWCNTchitosan composites was evaluated by MTT assaywith L-929 cell line as a model which demonstratedthat the obtained composites have favorable cytocompat-ibility for the potential use as scaffolds for bone tissueengineering

Acknowledgments The authors gratefully acknowl-edge the National Nature Science Foundation of China

(Grant 50503025) and Renmin University of China forfinancial support

References and Notes

1 L P Zanello B Zhao H Hu and R C Haddon Nano Lett 6 562(2006)

2 P M Ajayan and J M Tour Nature 447 1066 (2007)3 S F Wang L Shen W D Zhang and Y J Tong Biomacro-

molecules 6 3067 (2005)4 S Bhattacharyya S Guillott H Dabboue J F Tranchant and J P

Salvetat Biomacromolecules 9 505 (2008)5 G M Spinks S R Shin G G Wallace P G Whitten S I Kim

and S J Kim Sensor Actuat B-Chem 115 678 (2006)6 A Garg and S B Sinnott Chem Phys Lett 295 273 (1998)7 J S Czarnecki K Lafdi and P A Tsonis Tissue Eng 14 255

(2008)8 H J Li L Feng L H Guan Z J Shi and Z N Gu Solid State

Commun 132 219 (2004)9 B Fei H F Lu Z G Hu and J H Xin Nanotechnology 17 1589

(2006)10 ISO-10993-5 Biological evaluation of medical devicesndashPart 5 Tests

for cytotoxicity ANSIAAMI Arlington VA (1999)11 P Garrigue M H Delville C Labrugere E Cloutet P J Kulesza

J P Morand and A Kuhn Chem Mater 16 2984 (2004)12 K J Gilmore S E Moulton and G G Wallace Carbon 45 402

(2007)13 Z Yu and L Burs J Phys Chem B 105 1123 (2001)

Received 4 September 2009 Accepted 30 October 2009

J Nanosci Nanotechnol 10 7126ndash7129 2010 7129

Delivered by Ingenta toInstitute of Molecular and Cell Biology

IP 13713212369Mon 21 Nov 2011 065839

RESEARCH

ARTIC

LE

Zhao et al A Biocompatible Chitosan Composite Containing Phosphotungstic Acid Modified SWCNTs

from Sinopharm Chemical Reagent Co Ltd RawSWCNT materials were produced by arc-discharge methodand the purification process of SWCNT was reportedpreviously8 The PW12-modified SWCNT was obtainedfollowed the procedure reported by Fei et al9 ThePW12-SWCNTchitosan composite films were obtainedby mixing PW12-SWCNT suspension and chitosan solu-tion (1 wv in 01 M acetic acid) with different ratio(SWCNTs 02 wt 05 wt and 1 wt) and casting tothin films And a porous sponge (SWCNT 05 wt) wasproduced by freeze-drying method The PW12-modifiedSWCNTs and PW12-SWCNTchitosan composites werecharacterized by X-ray photoelectron spectroscopy (XPSPerkin-Elmer PHI-5300 ESCA) transmission electronmicroscopy (Hitachi 9000 HRTEM accelerating voltage100 kV) scanning electron microscopy (SEM JEOLJSM-7401F) and Raman spectroscopy (632 nm JobinYvon HR-800)Mouse fibroblasts (L-929 cells) were cultured in the

Dulbeccorsquos Modified Eagle Medium (DMEM) containing10 fetal bovine serum (FBS) 100 UmL penicillin and100 mgmL streptomycin All cells were cultured at 37Cin a humidified atmosphere of 5 CO2 The in vitro cyto-toxicity of PW12-SWCNTchitosan composites was evalu-ated by the MTT (3-[45-dimethylthiazolyl-2]-25-diphenyltetrazolium bromide) colorimetric assay method10 All datawere expressed as the average with standard error Statis-tic analyses of in vitro assessments were performed usingthe one-way ANOVA test and the Fisher LSD and tukeymethod as multiple comparison procedure with a p valueof 005

3 RESULTS AND DISCUSSION

Figure 1 is a typical TEM image of PW12-modifiedSWCNTs It is observed that the SWCNT was exfoliated

100 nm

Fig 1 The small bundles of SWCNTs dispersed in PW12 aqueoussolution

Fig 2 XPS curve of PW12 modified SWCNT magnified W(VI) andW(V) valance states and their atomic ratios The insert figure is the XPSsurvey of PW12 modified SWCNT

in small bundles of several to twenty nanometers that indi-cating a good dispersion in PW12 solution To thoroughlyunderstanding the interaction between carbon nanotubeand PW12 XPS and Raman spectroscopy was conductedto characterize the PW12-modified SWCNT The exis-tence of tungsten (W) in XPS survey confirmed theanchoring of PW12 on SWCNTs after the modification(Fig 2) The detailed analysis of W4f speaks revealedthat there were two different states of W4f W(VI) andW(V) which can be attributed to the charge transferfrom carbon surface to PW12 similar in PMo12 mod-ified carbon11 Raman spectroscopy presented not onlythe information about the structure change of SWCNTs

Fig 3 Raman spectra of original SWCNTs PW12-modified-SWCNTand PW12-SWCNTchitosan composites

J Nanosci Nanotechnol 10 7126ndash7129 2010 7127

Delivered by Ingenta toInstitute of Molecular and Cell Biology

IP 13713212369Mon 21 Nov 2011 065839

RESEARCH

ARTIC

LE

A Biocompatible Chitosan Composite Containing Phosphotungstic Acid Modified SWCNTs Zhao et al

after PW12 modification but also the charge transferbetween SWCNT and PW12 (Fig 3) It is clearly observedthat the radial breathing mode (RBM) of PW12-modifiedSWCNT has broader line width and relatively lower inten-sity than that of pure SWCNT due to the modificationand the RBM of the composite has a remarkable up-shift comparing to that of SWCNT and PW12-SWCNTthat can be attributed to the partial intercalation of chi-tosan molecules into the SWCNT12 Moreover the tangen-tial G-band modes of the PW12-modified SWCNT showsignificant decrease in Breit-Wigner-Fano (BWF) asym-metry indicating a chemical doping13 of SWCNTs afterPW12 modification But such a charge transfer betweenPW12 and SWCNT has not induced the destruction ofSWCNTs which was identified by the kept D band fea-tures of SWCNTs after PW12-modified The morphologyof PW12-SWCNTchitosan complex was observed by SEM(Fig 4) In a fracture surface it can be clearly foundthat chitosan are smoothly covered with SWCNTs So thePW12 anchoring on SWCNTs surface via chemisorptionhas effectively improved the dispersion of SWCNTs in chi-tosan and enhanced the binding in PW12-SWCNTchitosancomposites without inducing significant structure damni-fication of SWCNTsSince PW12 was used as an anchor agent to fabricate

the PW12-SWCNTchitosan composites it is important toassure that no cytotoxic materials were imparted in PW12-SWCNTchitosan composites The tetrazolium-based col-orimetric assay (MTT test) a commonly used method10

was carried out to quantitatively determine the biologi-cal response of cells to the PW12-SWCNTchitosan com-posites Figure 5 summarizes the MTT assay results offour PW12-SWCNTchitosan composites The percentagesof viable cells after the exposure to various compositeswere above 85 in most instances throughout 2 daysThe 15 difference compared with the blank sample wasattributed to the occupancy of partial space of the wellsby the tested samples The optical microscopy showedthat adherence and proliferation of L-929 cell with the

Fig 4 The SEM image of the fracture surface of PW12-SWCNTchitosan composite film

blank 02 05 1CNT sponge PC00

02

04

06

08

10

12

Per

cent

age

24 hr

48 hr

Fig 5 The MTT assay results of different PW12-SWCNTchitosancomposites compared to polystyrene disk (blank sample) Based on statis-tic analysis all PW12-SWCNTchitosan films showed no distinguisheddifference in MTT assays (24 hours and 48 hours)

PW12-SWCNTchitosan films are as well as they did onpolystyrene disks (Fig 6) indicating that the compositeswere non-cytotoxic to mouse fibroblast Therefore PW12-SWCNTchitosan composites are a promising candidatefor tissue engineering study A further study is on theway to investigate the cell attachment and development

(a)

(b)

100 microm

100 microm

Fig 6 The L-929 cells cultured 2 days with (a) blank (polystyreneplastic) disk and (b) PW12-SWCNTchitosan composite (1) film

7128 J Nanosci Nanotechnol 10 7126ndash7129 2010

Delivered by Ingenta toInstitute of Molecular and Cell Biology

IP 13713212369Mon 21 Nov 2011 065839

RESEARCH

ARTIC

LE

Zhao et al A Biocompatible Chitosan Composite Containing Phosphotungstic Acid Modified SWCNTs

behavior on the surfaces of PW12-SWCNTchitosancomposites

4 CONCLUSIONS

Homogeneous dispersion of SWCNTs in chitosan andenhanced interfacial adhesion with chitosan matri-ces was successfully developed using PW12 as ananchor agent Detailed XPS analysis demonstrated thata charge transfer occurred between PW12 and SWCNTresulting over 7 W(V) on SWCNT surfaces Ramanspectroscopy revealed that PW12 produced a chemical-like modification on SWCNT but it will not damnifythe intrinsic structure of SWCNTs The PW12-modifiedSWCNT with a negative surface charge can assemblewith positively charged chitosan by electrostatic inter-action inducing a strong interfacial interaction betweenSWCNT and chitosan matrices Biocompatibility of PW12-SWCNTchitosan composites was evaluated by MTT assaywith L-929 cell line as a model which demonstratedthat the obtained composites have favorable cytocompat-ibility for the potential use as scaffolds for bone tissueengineering

Acknowledgments The authors gratefully acknowl-edge the National Nature Science Foundation of China

(Grant 50503025) and Renmin University of China forfinancial support

References and Notes

1 L P Zanello B Zhao H Hu and R C Haddon Nano Lett 6 562(2006)

2 P M Ajayan and J M Tour Nature 447 1066 (2007)3 S F Wang L Shen W D Zhang and Y J Tong Biomacro-

molecules 6 3067 (2005)4 S Bhattacharyya S Guillott H Dabboue J F Tranchant and J P

Salvetat Biomacromolecules 9 505 (2008)5 G M Spinks S R Shin G G Wallace P G Whitten S I Kim

and S J Kim Sensor Actuat B-Chem 115 678 (2006)6 A Garg and S B Sinnott Chem Phys Lett 295 273 (1998)7 J S Czarnecki K Lafdi and P A Tsonis Tissue Eng 14 255

(2008)8 H J Li L Feng L H Guan Z J Shi and Z N Gu Solid State

Commun 132 219 (2004)9 B Fei H F Lu Z G Hu and J H Xin Nanotechnology 17 1589

(2006)10 ISO-10993-5 Biological evaluation of medical devicesndashPart 5 Tests

for cytotoxicity ANSIAAMI Arlington VA (1999)11 P Garrigue M H Delville C Labrugere E Cloutet P J Kulesza

J P Morand and A Kuhn Chem Mater 16 2984 (2004)12 K J Gilmore S E Moulton and G G Wallace Carbon 45 402

(2007)13 Z Yu and L Burs J Phys Chem B 105 1123 (2001)

Received 4 September 2009 Accepted 30 October 2009

J Nanosci Nanotechnol 10 7126ndash7129 2010 7129

Delivered by Ingenta toInstitute of Molecular and Cell Biology

IP 13713212369Mon 21 Nov 2011 065839

RESEARCH

ARTIC

LE

A Biocompatible Chitosan Composite Containing Phosphotungstic Acid Modified SWCNTs Zhao et al

after PW12 modification but also the charge transferbetween SWCNT and PW12 (Fig 3) It is clearly observedthat the radial breathing mode (RBM) of PW12-modifiedSWCNT has broader line width and relatively lower inten-sity than that of pure SWCNT due to the modificationand the RBM of the composite has a remarkable up-shift comparing to that of SWCNT and PW12-SWCNTthat can be attributed to the partial intercalation of chi-tosan molecules into the SWCNT12 Moreover the tangen-tial G-band modes of the PW12-modified SWCNT showsignificant decrease in Breit-Wigner-Fano (BWF) asym-metry indicating a chemical doping13 of SWCNTs afterPW12 modification But such a charge transfer betweenPW12 and SWCNT has not induced the destruction ofSWCNTs which was identified by the kept D band fea-tures of SWCNTs after PW12-modified The morphologyof PW12-SWCNTchitosan complex was observed by SEM(Fig 4) In a fracture surface it can be clearly foundthat chitosan are smoothly covered with SWCNTs So thePW12 anchoring on SWCNTs surface via chemisorptionhas effectively improved the dispersion of SWCNTs in chi-tosan and enhanced the binding in PW12-SWCNTchitosancomposites without inducing significant structure damni-fication of SWCNTsSince PW12 was used as an anchor agent to fabricate

the PW12-SWCNTchitosan composites it is important toassure that no cytotoxic materials were imparted in PW12-SWCNTchitosan composites The tetrazolium-based col-orimetric assay (MTT test) a commonly used method10

was carried out to quantitatively determine the biologi-cal response of cells to the PW12-SWCNTchitosan com-posites Figure 5 summarizes the MTT assay results offour PW12-SWCNTchitosan composites The percentagesof viable cells after the exposure to various compositeswere above 85 in most instances throughout 2 daysThe 15 difference compared with the blank sample wasattributed to the occupancy of partial space of the wellsby the tested samples The optical microscopy showedthat adherence and proliferation of L-929 cell with the

Fig 4 The SEM image of the fracture surface of PW12-SWCNTchitosan composite film

blank 02 05 1CNT sponge PC00

02

04

06

08

10

12

Per

cent

age

24 hr

48 hr

Fig 5 The MTT assay results of different PW12-SWCNTchitosancomposites compared to polystyrene disk (blank sample) Based on statis-tic analysis all PW12-SWCNTchitosan films showed no distinguisheddifference in MTT assays (24 hours and 48 hours)

PW12-SWCNTchitosan films are as well as they did onpolystyrene disks (Fig 6) indicating that the compositeswere non-cytotoxic to mouse fibroblast Therefore PW12-SWCNTchitosan composites are a promising candidatefor tissue engineering study A further study is on theway to investigate the cell attachment and development

(a)

(b)

100 microm

100 microm

Fig 6 The L-929 cells cultured 2 days with (a) blank (polystyreneplastic) disk and (b) PW12-SWCNTchitosan composite (1) film

7128 J Nanosci Nanotechnol 10 7126ndash7129 2010

Delivered by Ingenta toInstitute of Molecular and Cell Biology

IP 13713212369Mon 21 Nov 2011 065839

RESEARCH

ARTIC

LE

Zhao et al A Biocompatible Chitosan Composite Containing Phosphotungstic Acid Modified SWCNTs

behavior on the surfaces of PW12-SWCNTchitosancomposites

4 CONCLUSIONS

Homogeneous dispersion of SWCNTs in chitosan andenhanced interfacial adhesion with chitosan matri-ces was successfully developed using PW12 as ananchor agent Detailed XPS analysis demonstrated thata charge transfer occurred between PW12 and SWCNTresulting over 7 W(V) on SWCNT surfaces Ramanspectroscopy revealed that PW12 produced a chemical-like modification on SWCNT but it will not damnifythe intrinsic structure of SWCNTs The PW12-modifiedSWCNT with a negative surface charge can assemblewith positively charged chitosan by electrostatic inter-action inducing a strong interfacial interaction betweenSWCNT and chitosan matrices Biocompatibility of PW12-SWCNTchitosan composites was evaluated by MTT assaywith L-929 cell line as a model which demonstratedthat the obtained composites have favorable cytocompat-ibility for the potential use as scaffolds for bone tissueengineering

Acknowledgments The authors gratefully acknowl-edge the National Nature Science Foundation of China

(Grant 50503025) and Renmin University of China forfinancial support

References and Notes

1 L P Zanello B Zhao H Hu and R C Haddon Nano Lett 6 562(2006)

2 P M Ajayan and J M Tour Nature 447 1066 (2007)3 S F Wang L Shen W D Zhang and Y J Tong Biomacro-

molecules 6 3067 (2005)4 S Bhattacharyya S Guillott H Dabboue J F Tranchant and J P

Salvetat Biomacromolecules 9 505 (2008)5 G M Spinks S R Shin G G Wallace P G Whitten S I Kim

and S J Kim Sensor Actuat B-Chem 115 678 (2006)6 A Garg and S B Sinnott Chem Phys Lett 295 273 (1998)7 J S Czarnecki K Lafdi and P A Tsonis Tissue Eng 14 255

(2008)8 H J Li L Feng L H Guan Z J Shi and Z N Gu Solid State

Commun 132 219 (2004)9 B Fei H F Lu Z G Hu and J H Xin Nanotechnology 17 1589

(2006)10 ISO-10993-5 Biological evaluation of medical devicesndashPart 5 Tests

for cytotoxicity ANSIAAMI Arlington VA (1999)11 P Garrigue M H Delville C Labrugere E Cloutet P J Kulesza

J P Morand and A Kuhn Chem Mater 16 2984 (2004)12 K J Gilmore S E Moulton and G G Wallace Carbon 45 402

(2007)13 Z Yu and L Burs J Phys Chem B 105 1123 (2001)

Received 4 September 2009 Accepted 30 October 2009

J Nanosci Nanotechnol 10 7126ndash7129 2010 7129

Delivered by Ingenta toInstitute of Molecular and Cell Biology

IP 13713212369Mon 21 Nov 2011 065839

RESEARCH

ARTIC

LE

Zhao et al A Biocompatible Chitosan Composite Containing Phosphotungstic Acid Modified SWCNTs

behavior on the surfaces of PW12-SWCNTchitosancomposites

4 CONCLUSIONS

Homogeneous dispersion of SWCNTs in chitosan andenhanced interfacial adhesion with chitosan matri-ces was successfully developed using PW12 as ananchor agent Detailed XPS analysis demonstrated thata charge transfer occurred between PW12 and SWCNTresulting over 7 W(V) on SWCNT surfaces Ramanspectroscopy revealed that PW12 produced a chemical-like modification on SWCNT but it will not damnifythe intrinsic structure of SWCNTs The PW12-modifiedSWCNT with a negative surface charge can assemblewith positively charged chitosan by electrostatic inter-action inducing a strong interfacial interaction betweenSWCNT and chitosan matrices Biocompatibility of PW12-SWCNTchitosan composites was evaluated by MTT assaywith L-929 cell line as a model which demonstratedthat the obtained composites have favorable cytocompat-ibility for the potential use as scaffolds for bone tissueengineering

Acknowledgments The authors gratefully acknowl-edge the National Nature Science Foundation of China

(Grant 50503025) and Renmin University of China forfinancial support

References and Notes

1 L P Zanello B Zhao H Hu and R C Haddon Nano Lett 6 562(2006)

2 P M Ajayan and J M Tour Nature 447 1066 (2007)3 S F Wang L Shen W D Zhang and Y J Tong Biomacro-

molecules 6 3067 (2005)4 S Bhattacharyya S Guillott H Dabboue J F Tranchant and J P

Salvetat Biomacromolecules 9 505 (2008)5 G M Spinks S R Shin G G Wallace P G Whitten S I Kim

and S J Kim Sensor Actuat B-Chem 115 678 (2006)6 A Garg and S B Sinnott Chem Phys Lett 295 273 (1998)7 J S Czarnecki K Lafdi and P A Tsonis Tissue Eng 14 255

(2008)8 H J Li L Feng L H Guan Z J Shi and Z N Gu Solid State

Commun 132 219 (2004)9 B Fei H F Lu Z G Hu and J H Xin Nanotechnology 17 1589

(2006)10 ISO-10993-5 Biological evaluation of medical devicesndashPart 5 Tests

for cytotoxicity ANSIAAMI Arlington VA (1999)11 P Garrigue M H Delville C Labrugere E Cloutet P J Kulesza

J P Morand and A Kuhn Chem Mater 16 2984 (2004)12 K J Gilmore S E Moulton and G G Wallace Carbon 45 402

(2007)13 Z Yu and L Burs J Phys Chem B 105 1123 (2001)

Received 4 September 2009 Accepted 30 October 2009

J Nanosci Nanotechnol 10 7126ndash7129 2010 7129