Evaluation of a bio-based hydrophobic cellulose laurate film asbiomaterial—Study on biodegradation and cytocompatibility

Lucie Cr�epy,1,2,3 Francine Monchau,1,4 Feng Chai,1,5 Gw�ena€el Raoul,1,5,6 Philippe Hivart,1,4

Hartmut F. Hildebrand,1,5 Patrick Martin,1,2,3 Nicolas Joly1,2,3

1Univ Lille Nord de France, F-59000 Lille, France2CNRS, UMR 8181, Unit�e de Catalyse et de Chimie du Solide, UCCS, F-59650 Villeneuve d’Ascq, France3UArtois, IUT B�ethune, UCCS, F-62408 B�ethune, France4Universit�e d’Artois, Laboratoire de G�enie Civil et g�eo-Environnement (LGCgE EA 4515), Equipe Biomat�eriaux Artois, IUT/

GMP, BP 819, F-62408 B�ethune Cedex, France5Groupe de Recherche sur les Biomat�eriaux, INSERM U1008, Universit�e du Droit et de la Sant�e-Lille 2, Facult�e de M�edecine-

Pole Recherche, 1 Place de Verdun, 59045 LILLE cedex, France6Service de Chirurgie Maxillo-faciale, Hopital Roger Salengro, CHRU de Lille, F-59037 LILLE cedex, France

Received 29 June 2011; revised 21 October 2011; accepted 22 November 2011

Published online 10 February 2012 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/jbm.b.32665

Abstract: The study aims to validate an original bio-basedmate-

rial, obtained by grafting fatty chains, and more especially lauric

chains (C12) onto cellulose, for medical applications. The me-

chanical properties of the synthesized cellulose laurate (C12) are

close to those of petrochemical ones such as low density poly-

ethylene. This cellulose-based polymer is transparent, flexible,

and hydrophobic. To evaluate the stability of the cellulosic films

in biological fluids the samples are soaked in simulated body

fluid or blood plasma for a few hours to 6 months, and then sub-

mitted to mechanical and chemical analyses. The simultane-

ously performed cytocompatibility tests were the colony-

forming viability, the vitality and cell proliferation tests using

NIH 3T3 fibroblasts and MC 3T3 osteoblast-like cells. The results

show the stability, the biocompatibility, and the noncytotoxicity

of the synthesized cellulose laurate films. This biomaterial may

so be considered for surgical applications.VC 2012 Wiley Periodicals,

Inc. J BiomedMater Res Part B: Appl Biomater 100B: 1000–1008, 2012.

Key Words: cellulose laurate, bio-based film, cytotoxicity,

cytocompatibilty, degradation

How to cite this article: Cr�epy L, Monchau F, Chai F, Raoul G, Hivart P, Hildebrand HF, Martin P, Joly N. 2012. Evaluation of a bio-based hydrophobic cellulose laurate film as biomaterial—Study on biodegradation and cytocompatibility. J Biomed Mater ResPart B 2012:100B:1000–1008.

INTRODUCTION

Biomaterials are widely used in medical fields. Among all,polymers form a versatile class of biomaterials that havebeen extensively investigated for medical and related appli-cations. This can be attributed to the inherent flexibility insynthesizing or modifying polymers matching the physicaland mechanical properties of various tissues or organs ofthe body. Some natural polymers also often possess goodcytocompatibility, making them very useful for scaffold andconstructs in tissue engineering. Different polymer classes,namely biodegradable and bioadsorbable polymers, are cur-rently under testing for providing the optimal substrates forcell and tissue growth, such as the polydioxanone (PDS), thecopolymers of lactic acid (PLA) and glycolic acid for tissueengineering scaffold,1–4 polyanhydrides and polyamino acidsfor drug delivery system.5

Comparing with petrochemical polymers such as poly-ethylene, polypropylene, polyamide, polyethylene terephtha-late, polytetrafluoroethylene, polymethyl methacrylate, sili-

cone, and so on, bio-based polymers offer the advantage ofbeing similar to biological macromolecules, for which the bi-ological environment is prepared to recognize and deal withmetabolically. Owing to their similarity with the extracellu-lar matrix, natural polymers may also avoid the stimulationof chronic inflammation or immunological reactions and tox-icity, often detected with synthetic polymers.6,7 Anotheradvantage is that these ‘‘bio-based materials’’ are obtainedfrom renewable resources.

Among the various natural polymers, cellulose is themajor polymeric constituent of plant cell wall and the mostabundant naturally occurring polysaccharide, constituted ofglucose repeating units, connected by b-(1,4)-glucosidic link-ages. Cellulosic materials exhibit, poor degradation in vivo8

and do not need special treatment for eliminating the risk fac-tors (immune responses, viral risk) as chitin,9,10 their animal-derived counterpart. Cellulose and its derivatives are widelyused as tough versatile materials without modification (fiberfor paper and textiles), or after chemical modifications.11–13

Correspondence to: N. Joly; e-mail: nicolas.joly@univ-artois.fr

1000 VC 2012 WILEY PERIODICALS, INC.

Cellulose acetate is the most current cellulosic compound14

traditionally used for dialysis membranes. Moreover, manynew applications15 are being developed such as hemostaticsponges or bone cement for articular prostheses.

The originality of our work consists in the validation formedical applications of a fatty cellulosic lauric ester.16 It is anew application for such hydrophobic bio-based material.

In this study, preparation, characterization (via contactangle measurement, 1H NMR, and infrared spectroscopies),mechanical properties (via uniaxial tensile tests) and biode-gradation of cellulose laurate film in simulated body fluid(SBF) and blood plasma have been investigated. Further-more, the cellular responses of epithelial cells, osteoblasts,and fibroblasts to this cellulose laurate film are studied bycell viability, cell vitality, and cell proliferation tests in orderto determine the cytocompatibility of this material.

EXPERIMENTAL

Chemical procedure of material preparationThe bio-based cellulose esters (CEs) synthesis is performedby cellulose acylation with lauroyl fatty chains (C12). Exceptspecific mention, all reagents are stored at room temperatureand used without further purification. Briefly, CEs areobtained by grafting lauroyl chloride (LCl, 98%, Aldrich) ontomicrocrystalline cellulose (20 lm, Aldrich)16 in homogeneousmedia composed of anhydrous lithium chloride (LiCl, 99%,Acros) and N,N-dimethylacetamide (DMAc, 99%, Acros) of6.7% (w/v) LiCl/DMAc.17,18 The final concentration of the so-lution is 20 g of cellulose per liter of LiCl/DMAc system.

The dissolved cellulose (150 mL of stock solution, 3 g,18 mmol) and N,N-dimethyl-4-aminopyridine (99%, Acros:6.6 g, 162 mmol, 3 equiv. per anhydroglucose unit) arestirred at 80�C until complete solubilization. LCl (30.8 mL,126 mmol, 7 equiv. per anhydroglucose unit) are thenadded. The reaction media is heated at 80�C during 3 h.The product is precipitated by addition of methanol (�99%,Prolabo) and the solid is purified by a repeated solubiliza-tion/precipitation process using chloroform (�99%, Pro-labo) and methanol respectively, and finally air-dried atroom temperature.19 The final product (12 g) is obtained asa white powder with a weight increase of 300% from theinitial cellulose. CEs are then transformed into plastic filmby the casting method (10% w/v in chloroform).16

Chemical characterizationCE film is characterized by FT-IR spectroscopy using aBruker Vector 22 FT-IR apparatus equipped with a diamondreflection accessory. 1H NMR spectroscopy is performed indeuterated chloroform (CDCl3, Aldrich, stored at 4�C) usinga Bruker DRX-300 Spectrometer (operating at 300 MHz) todetermine the degree of substitution (DS) by an integrationmethod described elsewhere.20 The DS is defined as thenumber of fatty chains grafted per anhydroglucose unit(maximum value of 3).

Physical characterizationUniaxial tensile tests are performed on the CE film in orderto determine its mechanical property. Five repeated tests

are performed on each film. Tensile drawing is conductedon a uniaxial tensile machine at room temperature, usingdumbbell-shaped specimens with L0 ¼ 24 mm, l0 ¼ 5 mmof gauge length and width, respectively. The tensile tests arecarried out at a constant crosshead speed of 1.44 mm/min,which corresponds to an initial strain rate of 3.5 � 10�2

s�1. The elastic modulus (E), the tensile strength (rR) andthe tensile strain (eR) are deduced from these tests.21

The hydrophobicity of the CE film is determined by thesessile-drop contact angle method with a contact-angle goni-ometer equipped with a special optical system and a camera(Apollo Instruments OCA 20). A drop (3 lL) of ultra-purewater (Sigma) is placed on the CE fixed film and the imageof drop is immediately sent via the camera to the computerfor analysis. Temperature and moisture are constant duringthe experiment (20�C and 68%, respectively). The measure-ments are repeated by deposing at least four drops on eachside of the film specimen, and final results are presented bythe mean of measured drops.

The surface modifications of cellulose films are charac-terized by scanning electron microscopy (SEM, Hitachi2460N, tungsten filament) equipped with an energy disper-sive X-ray (EDX) detector (Sigma Kevex). All samples arecoated with a mix of gold/palladium (Fisons InstrumentsPolaron).

In vitro degradation testsDestined for biomedical application, it is important to char-acterize the variations of those above mentioned propertiesof CE films in contact with the organism, in particular bio-degradation properties. To approach the in vivo conditions,the in vitro CE film degradation studies are conducted inSBF, as proposed by Kokubo and Takadama22 and bloodplasma, as proposed by Nieddu et al.23 for various timeperiods up to 6 months. The SBF is prepared by dissolvingreagent-grades: NaCl (Prolabo), NaHCO3 (Merck), KCl (Pro-labo), K2HPO4.3H2O (Merck), MgCl2.6H2O (Prolabo), andNa2SO4 (Prolabo) in bi-distilled water. The pH of the solu-tion is adjusted to 7.4 with tris-buffer and 1M HCl at 37�C.The blood plasma (blood transfusion center, CHRU, Lille) isobtained from whole blood by centrifugation and stored at�28�C in frozen aliquot ready for use.

Polymer discs (d ¼ 15 mm) are placed in tissue cultureplates with 1 mL of SBF in each well. Degradation is carriedout in an incubator at 37�C. Seven specimens are taken out,washed with bi-distilled water, and dried at 37�C.

Otherwise, for the degradation tests in blood plasma,dumbbell-shaped CE film specimens are one by one weighedas mass (W0) and then placed in sterilized bottles filledwith 20 mL of plasma. The degradation process is carriedout in an incubator under shaker set (InnovaV

R

40, NewBrunswick Scientific) at 100 rpm and 37�C for various timeperiods. Every week, the plasma solution is decanted offand replaced with 20-mL fresh plasma. At the end of eachtime point, the specimens are removed from plasma andrinsed in distilled water under agitation for six times (eachtime for 1 min), then dehydrated in air for 12 h, and finallyin oven at 37�C for 24 h to constant weight (Wt).

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Corresponding weight loss is calculated by (W0 � Wt)/W0.Specimens are then analyzed by 1H NMR analysis and me-chanical tests.

Evaluation of cytocompatibilityThe degradation due to UV rays is done during 15 and 45min per face to assess the nonphysico-chemical degradationof the cellulose laurate. For each biological evaluation, eachsample is irradiated with UV for 15 min on each face.

Cell viability by colony-forming method. The cell viabilitytests can evaluate the relative plating efficiency (RPE) andsubsequently the 50% lethal concentration (LC50 or RPE50) by the colony-forming assay with the epithelial cell line(L132 cells, ATCC-CCL5).24,25 Following the Internationaland European Standards (ISO10993-5/EN30993-5), theL132 epithelial cell line is selected for its good reproducibil-ity and cloning efficiency of about 37%.26 It allows rankingthe cytotoxicity effect of any chemical substance by compar-ison of the LC50.27

The viability evaluation is realized by observing the cellresponse to the cellulose laurate powder, that is, the finalproduct obtained just before the casting process. The pow-der is sieved through a 100-lm sieve. Briefly, in MEM me-dium supplemented with 10% fetal calf serum (FCS, Gibco,Invitrogen), the L132 cells are continuously exposed togradually increasing concentrations (0, 25, 50, 100, 200,400 mg/L) of cellulose powder without renewal of thegrowth medium during the experiments. After a 9-day cul-ture period, the medium is removed and the colonies arestained with crystal violet (0.2%). The numbers of coloniesare then counted under a binocular microscope. At least sixrepeated experiments are performed in triplicates for eachconcentration group. Results are expressed as mean values6 SD with respect to the control (medium without cellulosepowder, 100%). Nickel powder is tested as positive control.

Cell vitality and proliferation tests with osteoblasts andfibroblasts. In vitro biological tests are performed followingthe ISO 10993-5/EN 30993-5 standards with the immortal-ized mouse embryonic fibroblast cell line, NIH3T3(ATCCV

R

CRL-1658) and the immortalized mouse calvariumosteoblast-like cell line, MC3T3-E1 (ATCCV

R

CRL-2593). TheNIH3T3 cells are cultured in Dulbecco’s Modified Eagle Me-dium (Gibco) supplemented with 10% of newborn calf se-rum (Gibco). MC3T3-E1 cells are cultured in alpha ModifiedEagle Medium (aMEM, Gibco) supplemented with 10% of

FCS (Gibco). Both medium are supplemented with 50 lg/mL gentamicin (Gibco) and 1 lg/mL amphotericin B(Gibco). Cells are incubated at 37�C and 5% CO2 atmos-phere and 100% relative humidity.

Cell vitality and proliferation tests are realized on thedisk samples (A15 mm) of CE films and performed in 24-well cell tissue culture polystyrene (TCPS) plates (Nunc).Before cell seeding, the disk samples are sterilized underUV light (15 min for each side). Our preliminary study ofthe influence of UV irradiation on the degradation of CEfilms showed that there is no detectable physico-chemicalsurface modification after 15- or 45-min irradiation perside.

Cell growth is investigated by counting the number ofcells after 3 and 6 days of culture without renewal of themedium. NIH3T3 or MC3T3-E1 cells (1 � 104) are seededin each well and the relative cell growth rate for each testgroup is expressed as a percentage of control, that is, cellsgrowing on TCPS. After 3- and 6-days of incubation, firstcell vitality is determined via the Alamar blue fluorescentmethod. The culture medium is removed and replaced by0.5 mL of culture medium diluted with nontoxic AlamarBlue dye (Interchim, Montluçon, France). After 3 h of incu-bation, two aliquots of 0.15 mL of each well are transferredinto 96-well plates (Nunc, Polylabo, Strasbourg, France) andthe fluorescent intensity is measured by a Twinkle LB970fluorometer (Berthold Technology, GmbH & Co. KG, Ger-many) at 590 nm. The cell vitality rate is expressed as apercentage of control cultures. Immediately after the vitalitytest, the cells are detached by a 0.05% trypsin-EDTA solu-tion and then counted by a cell counter (Z1, Coulter Elec-tronics, UK). The relative proliferation rates of test groupsare calculated as the ratio of the cell number on the testsamples to that on the TCPS control. The final results arerated as the mean of four separate triplicate assays. One-way ANOVA (SPSS 11.0 software) is applied to determinethe statistical significance of the differences observedbetween groups: p < 0.05 is considered as significant.

RESULTS

Physico-chemical characterizationCellulose laurate is obtained by grafting fatty chains directlyonto the polysaccharidic backbone via the acylation of cellu-lose with lauroyl chloride (C12; Scheme 1).

The efficiency of the synthesis and the chemical struc-ture of the product are confirmed by FT-IR and 1H NMR

SCHEME 1. Acylation of cellulose with lauroyl chloride.

1002 CREPY ET AL. BIO-BASED HYDROPHOBIC CELLULOSE LAURATE FILM

analyses respectively, which well correspond to above theo-retical schema of the final product.

FT-IR: 3400 cm�1 (OAH stretching); 2800–2900 cm�1

(CAH antisymmetric and symmetric stretching); 1740 cm�1

(OAC[dbons]O stretching); 720 cm�1 (A(CH2)4A rocking).1H NMR: d (ppm, 300 MHz, in CDCl3 using TMS as inter-

nal standard) 0.89 (3H, t, ACH3); 1.26 (14H, m, A(CH2)7A);1.60 (2H, m, ACH2ACAC¼¼O); 2.34 (2H, m, ACH2AC¼¼O);3.00–5.00 (7H, m, Hsugar).

This bio-based product is then casted into plastic filmwithout any additives. Both FT-IR and 1H NMR analyses con-firm the absence of residual chloroform and DMAc from thematerial preparation process in the final product. Moreover,1H NMR analyses [Figure 1(a)] are used as a quantitativemethod to determine the DS,20 which is defined as the num-ber of fatty chains grafted per glucose unit. The resultsshow that the final CE film has a DS value of 2.9 6 0.1, cor-responding to a highly substituted polymer (DSmax ¼ 3).

Chemical stability and evolution of mechanical andphysical characteristics in SBFBefore studying the influence of the SBF on the celluloselaurate properties, we first control the stability of this bio-

based material at the sterilization step with UV irradiations.1H NMR spectrum [Figure 1(b)] of a sample presents no DSvariation or chemical modifications compared with the ref-erence. Thus, this analysis confirms the stability of celluloselaurate at this sterilization step.

The chemical stability of a material to a soaking in abody fluid after sterilization is a crucial property for itsmedical applications. To determine this ability, celluloselaurate samples are immersed in SBF for different periodswithout agitation.28 The chemical integrity (evolution of DSvalues) of cellulose-based plastic is analyzed by 1H NMRin order to evaluate the influence of the contact with aphysiologic fluid on the cellulose laurate chemicalstructure.29,30

1H NMR spectra [Figure 1(c)] of cellulose laurate showthat the contact with SBF up to 6 months has no influenceon the chemical structure of the cellulose laurate. Celluloselaurate material has a good chemical stability and is notdamaged by immersion in SBF. These results are confirmedby the DS values, which present no significant evolution (DS¼ 2.8 6 0.1).

Furthermore, uniaxial tensile tests and contact anglemeasurements are performed onto soaked cellulose lauratefilms to determine the influence of immersion in SBF up to6 months on their mechanical characteristics: elastic modu-lus (E), tensile strength (rR) and tensile strain level (eR),and also on their hydrophobicity (film/water contact anglevalues; ywater).

FIGURE 1. 1H NMR spectra of cellulose laurate (a) reference (without

any treatment), (b) UV irradiations (45 min per side), (c) soaked in

SBF at 37�C for 6 months.

TABLE I. Evolution of Weight Loss, Mechanical Properties,

and Surface Contact Angle of Cellulose Laurate After

Soaking in SBF at 37�C

Sample Ea (MPa) rRb (MPa) eR

c (%) ywaterd (�)

Reference 132 6 3 11.4 6 0.4 75 6 5 95 6 2SBF 1 month 130 6 3 10.9 6 0.4 80 6 5 73 6 2SBF 3 months 135 6 3 10.7 6 0.4 70 6 5 72 6 2SBF 6 months 133 6 3 11 6 0.4 75 6 5 49 6 2

a Elastic modulus.b Tensile stress.c Tensile strain level.d Water/plastic contact angle.

FIGURE 2. SEM of cellulose laurate plastic film (a) reference, (b) soaked in SBF at 37�C for 2 days, (c) soaked in SBF at 37�C for 6 days.

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The results presented in Table I show no significantinfluence on the mechanical properties. The elastic modulusis about 133 MPa, the tensile strength reaches 11 MPa, andthe tensile strain level is 75%.

Contact angle variations are conversely observed aftersoaking in SBF. The cellulose-based film is initially hydro-phobic since ywater > 90� .31 After soaking for 1 month inSBF at 37�C, the contact angle significantly decreases at 73� ,then stabilizes until 3 months, and finally decreases at 49�

after 6 months (Table I). Thus, this cellulose-based materialbecomes more hydrophilic after 1-month immersion in SBF.

To understand this phenomenon, SEM analyses are per-formed on the film surface. A superficial layer of aggregatesappears after 2-day immersion in SBF and partially coversthe cellulose laurate film surface after a 6-day immersion(Figure 2).

Spot analysis further shows the presence of phospho-rous, calcium, and detectable traces of magnesium in the ag-gregate (Figure 3). The presence of these hydrophilic saltaggregated on the plastic surface may explain the changesin surface hydrophobicity of cellulose laurate samplesbefore and after immersion in SBF.

Degradation in blood plasmaChemical and mechanical properties of cellulose laurate arealso studied after different periods of immersion in blood

plasma. Samples are soaked in this fluid up to 3 months,and each sample has been characterized.

Same results than after an immersion in SBF areobserved, that is, no significant influence on the chemicaland mechanical properties (Table II). The elastic modulus isabout 133 MPa, the tensile strength reaches 11 MPa, andthe tensile strain level is about 80%. Only the contact angleof this bio-based film lightly decreases until 89� after soak-ing for 3 months in blood plasma. This value lays at thelimit of the hydrophobic threshold.

Biological evaluationThe cell viability tests on L132 cells confirm the excellentcytocompatibility of cellulose laurate. Until 400 lg/mL, thesurvival rate is 86% (Figure 4) with respect to TCPS con-trols. The nickel, used as a positive control for its cytotoxiceffects, has a relative survival rate of 15% for the 100 lg/mL concentration.32

To assess the cell response to this new material, cell cul-tures are conducted with mouse fibroblasts cell line (NIH-3T3) and osteoblastes cell line (MC3T3-E1). Both cell typesare inoculated directly on the cellulose-based material, for 3and 6 days. The vitality of the fibroblasts and osteoblasts oncellulose laurate is characterized through the Alamar Bluetest.33 Cell vitality of fibroblasts is about 55% (normalizedby TCPS) and 70% at 6 days [Figure 5(a)]. Same evolutionis observed for osteoblasts, whose cell vitality of which

FIGURE 3. EDX analyses of cellulose laurate plastic film (a) reference, (b) soaked in SBF at 37�C for 2 days, (c) soaked in SBF at 37�C for 6 days.

[Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

TABLE II. Evolution of DS, Weight Loss, Mechanical Properties, and Surface Contact Angle of Cellulose Laurate After Soaking

in Blood Plasma at 37�C

Sample DSa Weight Loss (%) Eb (MPa) rRc (MPa) eR

d (%) ywatere (�)

Reference 2.6 6 0.1 0.12 132 6 3 11.4 6 0.4 75 6 5 95 6 2Blood plasma 1 month 2.7 6 0.1 0.03 130 6 4 11.2 6 0.5 84 6 12 88 6 4Blood plasma 3 months 2.7 6 0.1 0.19 136 6 5 11.1 6 0.3 80 6 5 89 6 3

a Degree of substitution.b Elastic modulus.c Tensile stress.d Tensile strain level.e Water/plastic contact angle.

1004 CREPY ET AL. BIO-BASED HYDROPHOBIC CELLULOSE LAURATE FILM

increases from 66 to 83%, at 3 and 6 days, respectively[Figure 5(b)].

The results show lower cell vitality on our bio-basedmaterial than on the TCPS control. As the vitality rate, thatis, the cell function, increases from the third and the sixthday of culture we observe a retarded cell growth, but not acytotoxic effect.

The simultaneous proliferation of fibroblasts and osteo-blasts is evaluated through counting the number of cells af-ter culture. It shows that the proliferation rates are similarfor both the third and the sixth day, as illustrated in Figure6. Proliferation rates evolve from 47 to 51% for fibroblasts,and from 64 to 59% for osteoblasts. This observation isconcomitant to the retarded evolution of cell vitality.

The proliferation of fibroblasts on the cellulose lauratereveals a retarded cell growth. The hydrophobic characterof the initial cellulose laurate could influence the fibroblastsresponse in retarding their proliferation, but does not altertheir physiological function.

DISCUSSION

Among the few biomaterials issued from plants, PLA andcellulose acetate are the most commonly used bio-basedmaterials in medical fields. Derived from the most abundantbio-based polymer on Earth, cellulose triacetates (80–100%of substitution) have a biocompatibility close to the bestsynthetic membranes34,35 and its mechanical properties arecompatible to hard and soft tissues.36,37 However, celluloseacetates generally require plasticizers to improve their me-chanical properties.14 Our interest of studying on celluloselaurate is based on the general properties of cellulose andthe particularity of laurate cellulose and lauric acid. Its slowdegradability can be modulated by modifying the length ofchain and the degree of crystallinity.13,38 Cellulosic esters(CEs) with a longer substituent (laurate in our case) exhib-ited plasticized polymer behaviors without any additiveunlike other bio-based polymers.39,40 Toward the goal of theapplication as scaffold material, it is flexible to be furtherfunctionalized for better integration into surrounding livingtissue.41

The design and synthesis of this cellulose laurate is orig-inal in the class of cellulose biomaterials. Fatty acid (C12)has been chosen for the reason it is one of the most abun-dant triglyceride constituents in vegetal oils. Moreover, theselauric chains are also known to have good antibacterialproperties.42

The present study is related to the synthesis of this bio-material and to the determination of its properties from atriple point of view: chemical, physical/mechanical, and bio-logical. The results have well proved that laurate cellulosecan be converted into films via casting method without add-ing plasticizers or other additives. Chemical analyses haveconfirmed the efficiency of the reaction and the absence inthe final product of residual traces of chloroform and DMAcfrom the synthesis process.

As a biodegradable and bioresorbable polymer widelyused in medical applications, PLA is often considered as anobject of comparison. Its major disadvantage consists in thefact that a tissue inflammatory reaction appears a few time

FIGURE 4. Survival curve of L132 in contact with cellulose laurate

and nickel powder established by colony-forming method (n ¼ 4).

[Color figure can be viewed in the online issue, which is available at

wileyonlinelibrary.com.]

FIGURE 5. Vitality of NIH3T3 fibroblasts (a) and MC3T3-E1 osteoblasts (b) for 3 and 6 days (blue and pink color, respectively) on cellulose lau-

rate samples with respect to ThermanoxVR

and TCPS controls (100%; n ¼ 2). [Color figure can be viewed in the online issue, which is available at

wileyonlinelibrary.com.]

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after its implantation2–4 with the release of lactic acid, andsubsequently an acidification of the surrounding tissue dur-ing its degradation.43 As shown by our study, the chemicalstructure of cellulose laurate is rather stable and resist toUV irradiation up to at least 45 min and to biological fluidssuch as SBF or blood plasma up to at least 3 months. More-over, the degradation product of cellulose laurate could onlybe the free fatty acid, which is known to be nontoxic andprotecting endothelial cell lysosomes from labilizing.44

On a physical and mechanical property point of view,some important parameters of PLA (L-PLA, crystalline form,and D,L-PLA, amorphous form) and cellulose triacetatebased on studies reported in the literature and those of cel-lulose laurate from our study are listed in Table III.

One of mechanical drawbacks of PLA, so as cellulose tri-acetate, is reported as its mechanical stiffness, particularlyin cartilage tissue engineering.45,46

Regarding to this, average elastic modulus value of cellu-lose laurate (133 MPa) is obviously lower than those of PLAand cellulose triacetate (1200–3000 and 2300 MPa, respec-tively). It confirms the effect of the grafted fatty chains,leading to a final product with more ductility but withoutadding any plasticizer. The low average elastic modulusvalue of cellulose laurate is thus an advantage to give betterelastic properties in application. Similar effect of fatty chainswas also found in tensile strain level (eR, about 75%), which

is much higher than that of PLA (2–6%). Cellulose lauratepossesses a tensile strength value (11 MPa) approaching tothat of cellulose acetate (about 10 MPa), while much lowerthan that of PLA (28–50 MPa).

The scar tissue adhesion after surgery occasionallycauses serious complications. Material surface hydrophilic-ity/hydrophobicity is an important concern for the forma-tion of scar adhesion. Unlike PLA (ywater ¼ 80�) and cellu-lose triacetate (ywater ¼ 60�), the strongly hydrophobiccharacter of the cellulose laurate (ywater ¼ 95�) can inducea strong decrease in adhesion by slowing down the adhe-sion and consequently proliferation rate of fibroblasts. Suchrelation between material surface hydrophobicity and celladhesion has been well documented by many studies26 andalso proved by our results from cell proliferation and vital-ity tests, which do not indicate a cytotoxic effect since thecell viability assays show an excellent cytocompatibility,even for very high concentrations of cellulose laurate. Theretarded, but then increasing cell growth and in particularcell vitality thus is due to the chemical characteristics.

Unlike PLA, cellulose laurate shows a chemical stabilityand the absence of resorption at least during the first 3months. It must be noticed that the cellulose laurate hydro-phobicity decrease shown by the decrease of contact anglevalue ywater from 90� to 72� (Table I) is due to the depositof phosphorous and calcium salts issued from the SBF (Fig-ure 3). It is not due to any material changes, and it onlyoccurs if the cell colonization step of the surface is per-formed after the soaking in SBF, enabling these salts to de-posit onto the not yet covered surface.

CONCLUSIONS

We have shown in this preliminary work a good perform-ance of the tested polymeric cellulose laurate film: MC3T3-E1 osteoblast-like cells and fibroblasts adhere and—although with a retarded effect—proliferate with increasingcell vitality/function.

We are aware of the limits of this original biopolymer topredict the behavior of the material in a target tissue, but

FIGURE 6. Proliferation of NIH3T3 fibroblasts (a) and MC3T3-E1 osteoblasts (b) for 3 and 6 days (blue and pink color, respectively) on cellulose

laurate samples with respect to ThermanoxVR and TCPS controls (100%; n ¼ 2). [Color figure can be viewed in the online issue, which is available

at wileyonlinelibrary.com.]

TABLE III. Comparison of the Mechanical Properties and

Surface Hydrophobicity Between the Cellulose Laurate and

Other Bio-Based Biomedical Polymers

Sample Ea (MPa)rR

b

(MPa)eR

c

(%)ywater

d

(�)

PLA[2,24] 1200–3000 28–50 2–6 80Cellulose triacetate[21,24] 2300 10 20–78 60Cellulose laurate 133 11 75 95

a Elastic modulus.b Tensile stress.c Tensile strain level.d Water/plastic contact angle.

1006 CREPY ET AL. BIO-BASED HYDROPHOBIC CELLULOSE LAURATE FILM

the choice of osteoblast-like cells and fibroblasts makes thetest system suitable to give insights into the effect of thefilm at the implant site. We recently got the allowance fromthe ministry to perform in vivo animal experiments.

ACKNOWLEDGMENTS

The authors thank Antonio Da Costa (UCCS Artois, Lens) forSEM and EDX analysis and Annie Lefebvre for her technical as-sistance in cytocompatibility tests.

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