biodegradable and elastomeric poly(glycerol sebacate) as a ...€¦ · biodegradable and...

Research ArticleBiodegradable and Elastomeric Poly(glycerol sebacate) asa Coating Material for Nitinol Bare Stent

Min Ji Kim1 Moon Young Hwang1 JiHeung Kim2 and Dong June Chung1

1 Department of Polymer Science and Engineering Sungkyunkwan University Suwon 440746 Republic of Korea2 School of Chemical Engineering Sungkyunkwan University Suwon 440746 Republic of Korea

Correspondence should be addressed to Dong June Chung djchungskkuedu

Received 10 January 2014 Revised 4 March 2014 Accepted 2 April 2014 Published 13 May 2014

Academic Editor Yoshihiro Ito

Copyright copy 2014 Min Ji Kim et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

We synthesized and evaluated biodegradable and elastomeric polyesters (poly(glycerol sebacate) (PGS)) using polycondensationbetween glycerol and sebacic acid to form a cross-linked network structurewithout using exogenous catalysts Synthesizedmaterialspossess good mechanical properties elasticity and surface erosion biodegradation behavior The tensile strength of the PGS wasas high as 028plusmn 0004MPa and Youngrsquos modulus was 0122plusmn 00003MPa Elongation was as high as 2378plusmn 064 and repeatedelongation behavior was also observed to at least three times the original length without ruptureThe water-in-air contact angles ofthe PGS surfaces were about 60∘ We also analyzed the properties of an electrospray coating of biodegradable PGS on a nitinol stentfor the purpose of enhancing long-term patency for the therapeutic treatment of varicose veins disease The surface morphologyand thickness of coating layer could be controlled by adjusting the electrospraying conditions and solution parameters

1 Introduction

Biodegradable elastomers are important materials for a widevariety of medical applications Elastomers have gainedpopularity because they can provide stability and structuralintegrity in mechanically dynamic environments withoutirritation to the host tissues [1 2] and they exhibitmechanicalproperties similar to those of soft tissues [3ndash5] For the specialscaffold requiring strong mechanical properties tough andbiodegradable elastomers (poly(120576-caprolactone) (PCL) [6 7]poly(glycerol sebacate) (PGS) [8] and their blended materi-als) were frequently adapted for in vivo tissue regenerationor substitution trials in many clinical fields [9ndash11] But theseattempts were mainly related to the improvement of tissueregeneration capability drug sustainability and cell adhesionproperties through electrospinning process [12ndash14]

Stent surgery is widely used for therapeutic treatment ofcoronary artery and varicose veins disease and several kindsof commercialized baremetal stents have beenused in clinicalsettings in spite of their risks including inflammation latethrombosis or restenosis and fracture formation in long-term duration

To reduce such complications we selected PGS asbiodegradable and elastic polymer for the enhancement ofmechanical strength and durability of bare nitinol stentwhich is used for the interventional treatment of superficialfemoral artery disease PGS (one of the excellent toughand biodegradable polymers) was obtained as low molecularweight (lt10000) prepolymer through polycondensation andoften blended with PCL for satisfying electrospray conditionbecause of its weak solution property (low viscosity in organicsolvent) After electrospray coating their own tough andelastic behaviors were exhibited through additional curingreaction

In this study we synthesized relatively high molecularweight (31000 in 119872

119908) PGS prepolymer and examined the

suitability for electrospray coating method (a useful tech-nique to obtain uniform coating layer on three-dimensionalstructures [15ndash20]) and we also confirmed the biodegradableand elastomeric properties after postcuring For the basicstudy of this purpose we measured the surface morphologyand thickness of the coated films to study the feasibility ofPGS as a novel coating material for nitinol bare stent By thismethod we expect that stent durability which is essential

Hindawi Publishing CorporationBioMed Research InternationalVolume 2014 Article ID 956952 7 pageshttpdxdoiorg1011552014956952

2 BioMed Research International

factor for the therapeutic treatment of varicose veins diseasewill enhance

2 Experimental

21 Materials and Synthesis of PGS [2 8] The PGS poly-mer was synthesized by polycondensation of 01mol eachof glycerol (glycerin 990 Samchun Pure Chemical CoSeoul Korea) and sebacic acid (Tokyo Chem Indus CoTokyo Japan) Both reagents were mixed together in athree-necked flask at 130∘C under an argon environment for3 h and the pressure of reaction flask was reduced from1 Torr to 40mTorr After pressure reduction the reaction wascontinued for 45 h at 120∘C under a reduced atmosphereThen partly cross-linked PGS prepolymerwas obtained (yieldfor viscous liquid phase polymer above 80) Supplementalcross-linking (postcuring) reaction of PGS prepolymer wasdone in vacuum oven at 100∘C for additional 48 hours

22 Polymer Characterization The resulting material aftersupplemental cross-linking was soaked in 100 ethanolfor 24 h and was subsequently soaked in PBS for 24 h toremove unreacted reagents prior to instrumental analysis andmechanical testing

Polymer synthesis was confirmed by GPC 1H-NMR andFT-IRmeasurements GPC (gel permeation chromatographyWaters 515 Styragel column Milford MA USA) was usedto measure the time-dependent molecular weight changes ofPGS prepolymer A PGS solution (1 wt) was prepared inchloroform (as the mobile phase of GPC) for the measure-ments The elution rate of the mobile phase was adjusted to1mLmin and a styrene standard was used for molecularweight calibration 1H-NMR (nuclear magnetic resonanceVarian Unity Inova 500MHz Germany) spectra for PGSprepolymer were obtained using CDCl

3as a solvent The

chemical composition was determined by calculating thesignal integrals of ndashCOCH

2CH2CH2ndash at 12 15 and 22 ppm

for sebacic acid and ndashCH2CHndash at 37 42 and 52 ppm

for glycerol Also each functional group of the synthesizedpolymers was examined by FT-IR (Bruker IFS-66S FT-IRBruker Optics Germany)

Tensile tests after postcuring were conducted on 22 times6 times 15mm (according to ASTM standard D412-a) polymerstrips cut from polymer sheets on a UTM LR30K Plus (LyordInstrument Ltd West Success UK) equipped with a 250Nload cell

The strain rate was 50mmmin and all samples wereelongated to failure Values were converted to stress-strainand Youngrsquos modulus was calculated from the initial slopeusing 4ndash6 samples The cross-linking density (119899) was calcu-lated according to the theory of rubber elasticity using thefollowing equation [2 21]

119899 =1198640

3119877119879

=120588

(119872119908)119888

(1)

where 119899 represents the number of active network chainsegments per unit volume (molm3) (119872

119908)119888

represents themolecular weight between cross-links (gmol) 119864

0represents

Youngrsquos modulus (Pa)119877 is the universal gas constant119879 is theabsolute temperature (K) and 120588 is the measured elastomerdensity (gcm)

Swelling by hydration of postcured PGS was conductedby the immersion of cross-linked PGS samples in PBS (phos-phate buffered solution) deionized water and ethanol Theswelling ratio was calculated using the following equation

Swelling ratio () =119882119904minus119882119900

119882119900

times 100 (2)

where 119882119904represents the weight of swollen PGS and 119882

119900

represents the weight of dried PGSTo calculate the surface energy of the polymers we

measured the contact angles in deionized water dode-cane 1122-tetrabromoethane and glycerin using a contactangle meter (GBX DIGIDROP Scientific InstrumentationRomans France) at room temperature The surface energywas calculated by the following

120574119904= 120574119886

119904

+ 120574119887

119904

+ 120574119888

119904

120574 (1 + cos 120579) = 2radic120574119886119904

sdot 120574119886

119871

+ 2radic120574119887

119904

sdot 120574119887

119871

+ 2radic120574119888

119904

sdot 120574119888

119871

(3)

where 120574119886119904

120574119887119904

120574119888119904

were collected from a previous report [22]

23 In Vitro Degradation The degradation test was con-ducted using an enzyme solution (porcine liver esterase 40unitsmL in PBS) an NaOH solution (01mM) and PBS (pH70) Disk-type postcured PGS specimens (10mm in diameter2mm in thickness) were degraded under in vitro conditionsfor predetermined time intervals Degradation profiles weremeasured by incubating PGS in three kinds of solutions(20mL) at 37∘C with shaking After the predetermined incu-bation time the samples were removed washed in deionizedwater dried at 90∘C for seven days andweighed to determinethe weight loss The degradation ratio was calculated bycomparing the initial weight (119882

0) with the weight measured

at a given time point (119882119905)

24 Electrospray Coating of PGS on Nitinol Stents Nitinolstents (10 times 75mm diameter times length) were kindly providedfrom SampG Bio Co (Sungnam Korea) and used as specimensin the PGS prepolymer coating experiments They werecleaned before use in a waterethanol (1 1 in volume ratio)solution using an ultrasonic cleaner The experimental setupand processing conditions for the electrospray coating areshown in Figure 1 An acetone and ethanol mixture (3 7 involume ratio) was used as a solvent for the PGS prepolymer(119872119908= 31000 gmol) solution The electrospray coating pro-

cess was done using eSpray electrospraying system (NanoNCSeoul Korea) equipped with 20mL syringe fitted with aneedle (32 gauge ID 01mm and OD 023mm)on KDS

BioMed Research International 3

Solution in

Nozzle

Aerosol spray

SubstratePolymer

High-voltage supply

Substrate nitinol (shape memory alloy) stent

∙ Distance 5ndash15 cm∙ Voltage 169 kV

∙ Solvent ethanol acetone∙ Concentration 1wtndash10wt∙ Nozzle 32G

∙ 1 day on vacuum∙ 80

∘C

∙ Rate 06 mLh∙ Volume 05ndash3mL

⟨Electrospray coating condition⟩

⟨After cross-linking process⟩

syringe pump

Figure 1 Schematic diagram of the electrospray coating process

Glycerol

Sebacic acid

Polyester containing hydroxyl group

Condensation polymerization

OH

OH

OH

OO

OH

O

CR

O

C RO O

O

CR

O

C

OH

OH

HO

HO

HOHO

HOHO HO

HO

minusH2O

+n

Figure 2 Polycondensation of glycerol and sebacic acid yielding the PGS polymer

100 syringe pump (KD Science HollistonMA USA) Nitinolstent was rotating on the collector side connected with elec-trode during electrospray coating process After electrospraycoating for the supplemental cross-linking of coatedPGS thecoated stentswere placed in a vacuumoven at 100∘C for 48 hrsadditionally

The morphologies of the coated surfaces were char-acterized by scanning electron microscopy (SEM S-2400Hitachi Tokyo Japan) The polymer-coated surfaces weresputter-coated with Au-Pd using a sputtering system beforeSEM observation To evaluate the thickness of the coatedpolymer films on the stent strut the morphology of thecross-sectionally cut surface in a liquid nitrogen environmentwas investigated with SEM

3 Results and Discussion

31 Polymer Characterization The PGS polymer was pre-pared by polycondensation of glycerol and sebacic acid(Figure 2) after 48 hours of reaction time The resulting

polymer had a small number of cross-linking points andhydroxyl groups directly attached to the backbone as wereseen by spectroscopic analysis After 48 hours of reactiontime the obtained partly cross-linked PGS prepolymer hada weight-average molecular weight (119872

119908) of 31000 and a

number average molecular weight (119872119899) of 2300 (as deter-

mined by GPC) with polydispersity index (PDI) of 130 Themolar composition of the PGSprepolymerwas approximately1 1 glycerolsebacic acid as confirmed by 1H NMR analysis(proton peaks of ndashCOCH

2CH2CH2ndash shown at 12 15 and

22 ppm and proton peaks of ndashCH2CH shown at 31 42

and 52 ppm data not shown) In addition we observedFT-IR peaks at 1800ndash1600 cmminus1 (C=O) 3500ndash3200 cmminus1 (ndashOH) and 1375 cmminus1 (ndashCH) (data not shown) which confirmsthe existence of ester groups formed through polyconden-sation

Such partly cross-linked PGS prepolymer (viscous liquidphase) can be solved in polar organic solvent owing to theremained ndashOH groups in PGS and applied for stent coatingmaterial But fully cross-linked PGS polymer after postcuring


0 50 100 150 200 250000

005

010

015

020

025

030

035

040

Tens

ile st

ress

(MPa

)

Elongation ()

Figure 3 Stress-strain curves of PGS after postcuring for additional48 h at 100∘C

could not dissolve in any kinds of organic solvent and showselastic behaviors

32 Mechanical Tests and Swelling Ratio Tensile test resultsof thin strips of fully cross-linked PGS through supplementalcross-linking process revealed a stress-strain curve charac-teristic originating from elastomeric and tough materials(Figure 3) Permanent deformation was not observed duringthe tensile tests Youngrsquos modulus and elongation at break ofthe PGS were 0122 plusmn 00003MPa and 2378 plusmn 064 (those ofPCL were 225 plusmn 11MPa and 93 plusmn 9 in membrane type [23])In another report Youngrsquos modulus of PGSPCL blendedmembrane is also increased according to the increase of PCLratio in composite [11] These data meant that PGS showedmore elastic behavior than that of PCL and the PGS couldbe elongated repeatedly to several times its original lengthwithout rupture The ultimate tensile strength is greater than03MPa The value of Youngrsquos modulus of PGS is locatedbetween that of ligaments (inKPa range) and tendons (inGParange) and the strain to failure of PGS is similar to that ofarteries and veins (over 260 elongation)

Also the cross-linking density (119899) and relative molec-ular mass between cross-links ((119872

119908)119888

) were calculatedusing the density and Youngrsquos modulus of the samples aspreviously described (see (1)) The cross-linking density was164molm3 and the relative molecular mass between cross-links was about 58000 gmol

The degree of swelling of the elastomeric networks inethanol was about 85 (Figure 4) However the degree ofswelling of PGS in deionized water and PBS was about 5Therefore the synthesized polymer should not excessivelyswell in in vivo conditions

33 Contact Angle Measurements Interfacial characteristicsof coating polymers are significantly important for filmscoating printing and adhesives Water-in-air contact angleof coated PGS surface is about 60∘ (that of PCL is 120∘ [9])and such hydrophilicity of PGS is related to the remainedndashOH groups after postcuring as shown in Figure 2 This

EtOH PBS0

20

40

60

80

100

H2O

Swel

ling

degr

ee (

)

Figure 4 The solvent-dependent swelling behaviors of PGS

0 2 4 6 8 1050

60

70

80

90

100

Enzyme NaOH PBS

Time (days)

Rem

aini

ng m

ass (

)

Figure 5 Degradation studies of PGS in solvents (998771 PBSe 01mMNaOH ◼ enzyme solution) at 37∘C

is greatly related to the formation of H bonding betweenPGS and metal and also affected the adhesion property ofPGS on metal stent In addition we calculated the surfaceenergy using (3) of the three-component system for thesurface tension method with dodecane (a nonpolar solvent)1122-tetrabromoethane (a polar solvent) and glycerin (ahydrogen-bonding solvent) The surface energy of the PGSpolymer was 6313 dynecm This value is relatively highcompared to those of polytetrafluoroethylene (191 dynecm)and polyethylene (331 dynecm)

34 In Vitro Degradation Studies We examined the degra-dation characteristics of PGS under in vitro conditions(Figure 5) Agitation for nine days in NaOH solution at 37∘Ccaused the polymer to degrade by 30 as measured bychange of a dry sample In enzyme degradation the PGS


(a)

(b)

Figure 6 Surface morphology observation of PGS-coated stent by SEM (a) an uncoated nitinol stent and (b) a PGS-coated stent under theelectrospinning conditions of 10 wt PGS solution in acetone and ethanol mixture (3 7 in volume ratio) at 06mLh flow rate

polymer was degraded by 25 over nine days in esterasesolutions while it degraded by 10 in PBS solutions

35 Electrospray Coating on a Nitinol Stent The surfacemorphologies of bare and coated stents were observed usingSEM (Figure 6) Compared to bare stents coated stentshad smoother surfaces Also we observed the concentrationeffects of the coating materials on the resulting surfacemorphologies and thickness

From the microscopic images of cross-sectional area ofstent strut as shown in Figure 7 PGS polymer was wellcoated over the whole area of strut through electrospraymethod in spite of concentration difference of PGS solutionsWhen a 1mL of PGS concentration (1 wt) was sprayedthe surface was rough and the thickness of the polymercoating was about 14 120583m However the coated stent withsame volume of a PGS concentration (10wt) showed asmooth surface and a thickness of about 60 120583m likely causedby solvent evaporation during the electrospray coating Inhigh concentration polymer solutions the solvent evaporatesmuch less than in low concentration solutions leaving thickand smooth surfaces In addition the coating thickness canbe adjusted simply using the law of conservation of mass

This shows that the polymeric droplets were continuouslydeposited on the polymer film during the electrosprayingThus the surface morphologies and thickness can be con-trolled by changing the concentration and amount of polymersolution

4 Conclusion

In this study we synthesized biocompatible and elastomericbiomaterials (PGS poly (glycerol sebacate)) through con-densation polymerization These polymers exhibit tunablemechanical properties and considerable flexibility We alsostudied the degradation characteristics of the PGS poly-mers For application to biomedical implants we exam-ined an electrospray coating of PGS on metal stents Byexamining the solution parameters we confirmed that thesurface morphology of the coated film is related to thePGS solution concentration and the thickness of the filmis linearly proportional to the volume and concentrationIt is expected that drug-eluting stents coated with a drugand PGS polymers can be applied practically in clinicalapplications


N

(a)

N

(b)

Figure 7 Cross-sectional SEM images of PGS coated on stent struts with volume differences 1mL of 1 wt PGS solution (a) and 10wt PGSsolution (b) in acetone and ethanol mixture (3 7 in volume ratio)

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work was supported by a grant from the FundamentalRampD Program for Core Technology of Materials funded bytheMinistry of Knowledge and Economy (Grant NoM2009-10-0013) and also supported by the Fundamental TechnologyRampD Program for Society of the National Research Founda-tion (NRF) funded by the Ministry of Science ICT amp FuturePlanning (Grant No 2013M3C8A3075845)

References

[1] R Langer and J P Vacanti ldquoTissue engineeringrdquo Science vol260 no 5110 pp 920ndash926 1993

[2] Y Wang G A Ameer B J Sheppard and R Langer ldquoA toughbiodegradable elastomerrdquo Nature Biotechnology vol 20 no 6pp 602ndash606 2002

[3] A P Pego A A Poot DW Grijpma and J Feijen ldquoBiodegrad-able elastomeric scaffolds for soft tissue engineeringrdquo Journal ofControlled Release vol 87 no 1ndash3 pp 69ndash79 2013

[4] J Yang A R Webb and G A Ameer ldquoNovel citric acid-basedbiodegradable elastomers for tissue engineeringrdquo AdvancedMaterials vol 16 no 6 pp 511ndash516 2004

[5] F Gu H M Younes A O S El-Kadi R J Neufeld andB G Amsden ldquoSustained interferon-120574 delivery from a pho-tocrosslinked biodegradable elastomerrdquo Journal of ControlledRelease vol 102 no 3 pp 607ndash617 2005

[6] S M Mantila Roosa J M Kemppainen E N Moffitt P HKrebsbach and S J Hollister ldquoThe pore size of polycaprolac-tone scaffolds has limited influence on bone regeneration in anin vivo modelrdquo Journal of Biomedical Materials Research A vol92 no 1 pp 359ndash368 2010

[7] K-J Wu C-S Wu and J-S Chang ldquoBiodegradability andmechanical properties of polycaprolactone composites encap-sulating phosphate-solubilizing bacterium Bacillus sp PG01rdquoProcess Biochemistry vol 42 no 4 pp 669ndash675 2007

[8] Y Wang Y M Kim and R Langer ldquoIn vivo degradationcharacteristics of poly(glycerol sebacate)rdquo Journal of BiomedicalMaterials Research A vol 66 no 1 pp 192ndash197 2003

[9] S Salehi M Fathi S H Javanmard et al ldquoGeneration ofPGSPCL blend nanofiberous scaffolds mimicking corneal


stroma structurerdquo Macromolecular Materials Engineering vol299 no 4 pp 455ndash469 2014

[10] S Sant C M Hwang S-H Lee and A Khademhos-seini ldquoHybrid PGS-PCL microfibrous scaffolds with improvedmechanical and biological propertiesrdquo Journal of Tissue Engi-neering and Regenerative Medicine vol 5 no 4 pp 283ndash2912011

[11] N Masoumi B L Larson N Annabi et al ldquoElectrospunPGSPCL microfibers align human valvular intestinal cellsand provide tunable scaffold anisotropyrdquo Advanced HealthcareMaterials 2014

[12] C G Park M H Kim M Park et al ldquoPolymeric nanofibercoated esophageal stent for sustained delivery of an anticancerdrugrdquo Macromolecular Research vol 19 no 11 pp 1210ndash12162011

[13] J Choi S B Cho B S Lee Y K Joung K Park and D GHan ldquoImprovement of interfacial adhesion of biodegradablepolymers coated on metal surface by nanocouplingrdquo Langmuirvol 27 no 23 pp 14232ndash14239 2011

[14] E Lih Q V Bash B J Park Y K Joung and D G HanldquoSurface modification of stainless steel by introduction of vari-ous hydroxyl groups for biodegradable PCL polymer coatingrdquoBiomaterials Research vol 17 no 4 pp 176ndash180 2013

[15] S B Cho C H Park K Park D J Chung and D K HanldquoBiodegradable PLGA polymer coating on biomedical metalimplants using electrosprayingrdquo Polymer vol 33 no 6 pp 620ndash624 2009

[16] S G Kumbar S Bhattacharyya S Sethuraman and C T Lau-rencin ldquoA preliminary report on a novel electrospray techniquefor nanoparticle based biomedical implants coating precisionelectrosprayingrdquo Journal of Biomedical Materials Research Bvol 81 no 1 pp 91ndash103 2007

[17] DH Kim Y I Jeong CWChung et al ldquoPreclinical evaluationof sorafenib-eluting stent for surppression of human cholangio-carcinoma cellsrdquo International Journal of Nanomedicine vol 8pp 1697ndash1711 2013

[18] H Xu J Su J Sun and T Ren ldquoPreparation and characteri-zation of new nano-composite scaffolds loaded with vascularstentsrdquo International Journal of Molecular Sciences vol 13 no 3pp 3366ndash3381 2012

[19] C Hu S Liu B Li H Yang C Fan and W Cui ldquoMicro-nanometer rough structure of a superhydrophobic biodegrad-able coating by electrospraying for initial anti-bioadhesionrdquoAdvanced Healthicare Materials vol 2 no 10 pp 1314ndash13212014

[20] R Bakhshi M J Edirisinghe A Darbyshire Z Ahmad andA M Seifalian ldquoElectrohydrodynamic jetting behaviour ofpolyhedral oligomeric silsesquioxane nanocompositerdquo Journalof Biomaterials Applications vol 23 no 4 pp 293ndash309 2009

[21] L H Sperling Introduction to Physical Polymer Science JohnWiley amp Sons New York NY USA 1992

[22] D I Ryu J H Kim and Y S Shin The Interfacial ScienceChonnam National University Press Kwangju Korea 1998

[23] L P K Ang Y C Zi R W Beuerman S H Teoh X Zhuand D T H Tan ldquoThe development of a serum-free derivedbioengineered conjunctival epithelial equivalent using an ultra-thin poly(120576-caprolactone) membrane substraterdquo InvestigativeOphthalmology and Visual Science vol 47 no 1 pp 105ndash1122006


factor for the therapeutic treatment of varicose veins diseasewill enhance

2 Experimental

21 Materials and Synthesis of PGS [2 8] The PGS poly-mer was synthesized by polycondensation of 01mol eachof glycerol (glycerin 990 Samchun Pure Chemical CoSeoul Korea) and sebacic acid (Tokyo Chem Indus CoTokyo Japan) Both reagents were mixed together in athree-necked flask at 130∘C under an argon environment for3 h and the pressure of reaction flask was reduced from1 Torr to 40mTorr After pressure reduction the reaction wascontinued for 45 h at 120∘C under a reduced atmosphereThen partly cross-linked PGS prepolymerwas obtained (yieldfor viscous liquid phase polymer above 80) Supplementalcross-linking (postcuring) reaction of PGS prepolymer wasdone in vacuum oven at 100∘C for additional 48 hours

22 Polymer Characterization The resulting material aftersupplemental cross-linking was soaked in 100 ethanolfor 24 h and was subsequently soaked in PBS for 24 h toremove unreacted reagents prior to instrumental analysis andmechanical testing

Polymer synthesis was confirmed by GPC 1H-NMR andFT-IRmeasurements GPC (gel permeation chromatographyWaters 515 Styragel column Milford MA USA) was usedto measure the time-dependent molecular weight changes ofPGS prepolymer A PGS solution (1 wt) was prepared inchloroform (as the mobile phase of GPC) for the measure-ments The elution rate of the mobile phase was adjusted to1mLmin and a styrene standard was used for molecularweight calibration 1H-NMR (nuclear magnetic resonanceVarian Unity Inova 500MHz Germany) spectra for PGSprepolymer were obtained using CDCl

3as a solvent The

chemical composition was determined by calculating thesignal integrals of ndashCOCH

2CH2CH2ndash at 12 15 and 22 ppm

for sebacic acid and ndashCH2CHndash at 37 42 and 52 ppm

for glycerol Also each functional group of the synthesizedpolymers was examined by FT-IR (Bruker IFS-66S FT-IRBruker Optics Germany)

Tensile tests after postcuring were conducted on 22 times6 times 15mm (according to ASTM standard D412-a) polymerstrips cut from polymer sheets on a UTM LR30K Plus (LyordInstrument Ltd West Success UK) equipped with a 250Nload cell

The strain rate was 50mmmin and all samples wereelongated to failure Values were converted to stress-strainand Youngrsquos modulus was calculated from the initial slopeusing 4ndash6 samples The cross-linking density (119899) was calcu-lated according to the theory of rubber elasticity using thefollowing equation [2 21]

119899 =1198640

3119877119879

=120588

(119872119908)119888

(1)

where 119899 represents the number of active network chainsegments per unit volume (molm3) (119872

119908)119888

represents themolecular weight between cross-links (gmol) 119864

0represents

Youngrsquos modulus (Pa)119877 is the universal gas constant119879 is theabsolute temperature (K) and 120588 is the measured elastomerdensity (gcm)

Swelling by hydration of postcured PGS was conductedby the immersion of cross-linked PGS samples in PBS (phos-phate buffered solution) deionized water and ethanol Theswelling ratio was calculated using the following equation

Swelling ratio () =119882119904minus119882119900

119882119900

times 100 (2)

where 119882119904represents the weight of swollen PGS and 119882

119900

represents the weight of dried PGSTo calculate the surface energy of the polymers we

measured the contact angles in deionized water dode-cane 1122-tetrabromoethane and glycerin using a contactangle meter (GBX DIGIDROP Scientific InstrumentationRomans France) at room temperature The surface energywas calculated by the following

120574119904= 120574119886

119904

+ 120574119887

119904

+ 120574119888

119904

120574 (1 + cos 120579) = 2radic120574119886119904

sdot 120574119886

119871

+ 2radic120574119887

119904

sdot 120574119887

119871

+ 2radic120574119888

119904

sdot 120574119888

119871

(3)

where 120574119886119904

120574119887119904

120574119888119904

were collected from a previous report [22]

23 In Vitro Degradation The degradation test was con-ducted using an enzyme solution (porcine liver esterase 40unitsmL in PBS) an NaOH solution (01mM) and PBS (pH70) Disk-type postcured PGS specimens (10mm in diameter2mm in thickness) were degraded under in vitro conditionsfor predetermined time intervals Degradation profiles weremeasured by incubating PGS in three kinds of solutions(20mL) at 37∘C with shaking After the predetermined incu-bation time the samples were removed washed in deionizedwater dried at 90∘C for seven days andweighed to determinethe weight loss The degradation ratio was calculated bycomparing the initial weight (119882

0) with the weight measured

at a given time point (119882119905)

24 Electrospray Coating of PGS on Nitinol Stents Nitinolstents (10 times 75mm diameter times length) were kindly providedfrom SampG Bio Co (Sungnam Korea) and used as specimensin the PGS prepolymer coating experiments They werecleaned before use in a waterethanol (1 1 in volume ratio)solution using an ultrasonic cleaner The experimental setupand processing conditions for the electrospray coating areshown in Figure 1 An acetone and ethanol mixture (3 7 involume ratio) was used as a solvent for the PGS prepolymer(119872119908= 31000 gmol) solution The electrospray coating pro-

cess was done using eSpray electrospraying system (NanoNCSeoul Korea) equipped with 20mL syringe fitted with aneedle (32 gauge ID 01mm and OD 023mm)on KDS


Solution in

Nozzle

Aerosol spray

SubstratePolymer

High-voltage supply





∘C




syringe pump


Glycerol

Sebacic acid



OH

OH

OH

OO

OH

O

CR

O

C RO O

O

CR

O

C

OH

OH

HO

HO

HOHO

HOHO HO

HO

minusH2O

+n







119908) of 31000 and a








0 50 100 150 200 250000

005

010

015

020

025

030

035

040

Tens

ile st

ress

(MPa

)

Elongation ()





119908)119888




EtOH PBS0

20

40

60

80

100

H2O

Swel

ling

degr

ee (

)


0 2 4 6 8 1050

60

70

80

90

100

Enzyme NaOH PBS

Time (days)

Rem

aini

ng m

ass (

)





(a)

(b)






4 Conclusion



N

(a)

N

(b)




Acknowledgments


References



























Solution in

Nozzle

Aerosol spray

SubstratePolymer

High-voltage supply





∘C




syringe pump


Glycerol

Sebacic acid



OH

OH

OH

OO

OH

O

CR

O

C RO O

O

CR

O

C

OH

OH

HO

HO

HOHO

HOHO HO

HO

minusH2O

+n







119908) of 31000 and a








0 50 100 150 200 250000

005

010

015

020

025

030

035

040

Tens

ile st

ress

(MPa

)

Elongation ()





119908)119888




EtOH PBS0

20

40

60

80

100

H2O

Swel

ling

degr

ee (

)


0 2 4 6 8 1050

60

70

80

90

100

Enzyme NaOH PBS

Time (days)

Rem

aini

ng m

ass (

)





(a)

(b)






4 Conclusion



N

(a)

N

(b)




Acknowledgments


References



























0 50 100 150 200 250000

005

010

015

020

025

030

035

040

Tens

ile st

ress

(MPa

)

Elongation ()





119908)119888




EtOH PBS0

20

40

60

80

100

H2O

Swel

ling

degr

ee (

)


0 2 4 6 8 1050

60

70

80

90

100

Enzyme NaOH PBS

Time (days)

Rem

aini

ng m

ass (

)





(a)

(b)






4 Conclusion



N

(a)

N

(b)




Acknowledgments


References



























(a)

(b)






4 Conclusion



N

(a)

N

(b)




Acknowledgments


References



























N

(a)

N

(b)




Acknowledgments


References


























biodegradable and elastomeric poly(glycerol sebacate) as a ...€¦ · biodegradable and...

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