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Materials Science and Engineering B 169 (2010) 134–137

Contents lists available at ScienceDirect

Materials Science and Engineering B

journa l homepage: www.e lsev ier .com/ locate /mseb

he mechanical study of acrylic bone cement reinforced with carbon nanotube

u-Hsun Nien ∗, Chiao-li Huangepartment of Chemical and Materials Engineering, National Yunlin University of Science and Technology, Douliou, Yunlin 64002, Taiwan

r t i c l e i n f o

rticle history:

a b s t r a c t

Bone cement is used as filler between prosthesis and bone for fixation and force distribution. The major

eceived 3 June 2009eceived in revised form 8 October 2009ccepted 12 October 2009

eywords:one cement

composition of bone cement is polymethylmethacrylate (PMMA). Some disadvantages of PMMA bonecement are found such as significant poor mechanical properties which may cause failure of the cement.In this paper, we exploited carbon nanotube to enhance the mechanical properties of bone cement. Themechanical properties of the bone cement were characterized using tensile and compressive analysis aswell as dynamic mechanical analysis (DMA). The result shows that carbon nanotube is able to enhancethe mechanical properties of the modified bone cement.

MMAarbon nanotube

. Introduction

Bone cement is used as a grouting agent between the pros-hesis and the bone as well as a method to anchor prosthesis inrthopedic implants such as total hip replacement. Basically, boneement consists of two portions: (1) powder portion includingre-polymerized methylmethacrylate (PMMA) and initiator (ben-oyl peroxide) and (2) liquid portion including methylmethacrylateMMA) monomer and promoter (N,N-dimethyl-p-toluidine). Whenwo portions are mixed, the initiation is activated by promotershat make the free radicals (initiators). The free radicals react with

onomers for polymerization [1]. Some disadvantages of PMMAone cement are found such as significant poor mechanical prop-rties which may cause failure of the cement. For instance, PMMAone cement is considerably weaker than bone [2] and the tensiletresses of PMMA bone cement are comparatively low [3]. Vallo etl. used cross-linked PMMA beads to prepare cements by replacing0% of the PMMA powder and showed an increase in the flexuraltrength value of 22.4%. The cross-linked beads resulted in moreffective reinforcing filler than plain PMMA beads [4]. Basgorenayt al. modified acrylic bone cement by addition of hydroxyapatitend ammonium nitrate. A linear relation was observed in compres-ion strength (from 98 to 111 MPa) and in tensile strength (from7 to 21 MPa) upon HA addition, and in the compression strengthfrom 103 to 85 MPa) and in the tensile strength (from 22 to 17 MPa)

ith NA addition [5]. Kwon et al. prepared bone cements incor-orated with montmorillonite (MMT) to improve their mechanicalroperties. The measured compressive strength of the bone cementith 1 wt % MMT was 113.6 ± 3.9 MPa, which is higher than that of

∗ Corresponding author. Tel.: +886 5 534 2601x4611; fax: +886 5 5312071.E-mail address: nienyh@yuntech.edu.tw (Y.-H. Nien).

921-5107/$ – see front matter © 2009 Elsevier B.V. All rights reserved.oi:10.1016/j.mseb.2009.10.017

© 2009 Elsevier B.V. All rights reserved.

the bone cement without MMT (110.1 ± 2.0 MPa). The measuredtensile strength of the control bone cement with 1 wt % MMT was27.2 ± 4.4 MPa, which is higher than that of the bone cement with-out MMT (22.3 ± 3.8 MPa) [6].

Carbon nanotube is known for a larger aspect ratio and highermodulus [7]. Kearns and Shambaugh found that the tensile strengthof polypropylene fibers reinforced with carbon nanotube couldincrease 40% [8]. There are several studies related to the preparationand characterization of carbon nanotube/poly(methyl methacry-late) composites. For example, Jin et al. studied multi-walled carbonnanotube/poly(methyl methacrylate) composites fabricated bymelting blending and found that the nanotube was well dis-persed in the polymer matrix and the storage modulus of thecomposites was significantly increased [9]. Stephan et al. pre-pared poly(methyl methacrylate)-singlewalled carbon nanotubecomposites by solution mixing [10]. Cooper et al. used a poly-mer extrusion technique to prepare carbon nanotube mixed ina poly(methyl methacrylate) matrix and found that the impactstrength was significantly improved by even small amounts ofsinglewall nanotube [11]. Jia et al. prepared poly(methyl methacry-late)/carbon nanotube composites by an in situ process. Theirstudies show that carbon nanotube could participate in the poly-merization of PMMA initiated by AIBN and form a strong combininginterface between the carbon nanotube and the PMMA matrix[12].

The purpose of this study is to enhance the mechanical proper-ties of bone cement with carbon nanotube. In this study, the varioussystems of bone cement reinforced with carbon nanotube were

fabricated. The mechanical properties of bone cement were charac-terized using tensile as well as compressive analysis and dynamicmechanical analysis (DMA). The results show that introduction ofcarbon nanotube is able to enhance the mechanical properties ofbone cement.

Y.-H. Nien, C.-l. Huang / Materials Science and Engineering B 169 (2010) 134–137 135

Table 1The composition of PMMA/CNT composites manufactured by in situ process.

MMA (g) CNT (g) BPO (g) Note

100 0.1 2 (100/0.1)100 0.2 2 (100/0.2)

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Table 3The tensile and compressive strength of the bone cements tested in this study.

Tensile strength(MPa)

SD Compressivestrength (MPa)

SD

System 1 40.49 1.79 105.33 21.92System 2 48.03 1.55 130 4.16System 3 48.36 1 130.16 3.83System 4 48.01 3.09 127.25 2.44

(23%) than that of MMT modified bone cement (2.7% increasingin compressive strength). Fig. 1 shows the stress–strain curves of

100 0.27 2 (100/0.27)100 0.43 2 (100/0.43)100 0.59 2 (100/0.59)100 0.75 2 (100/0.75)

. Materials and methods

.1. Preparation of PMMA/carbon nanotube powder

Multi-wall carbon nanotube (CNT) (40–60 nm in diameter,.5–40 mm in length) was purchased from Desunnano Co., Ltd. andsed as received without further treatment in this study. MMAonomer was supplied from Kanto Chemical Co., Inc. The compo-

ition of PMMA/CNT composites manufactured by in situ processs listed in Table 1. Benzoyl peroxide (BPO) was used as initiator.he procedure for fabrication of PMMA/carbon nanotube compos-tes was first dissolution of BPO in MMA monomer by stirring atoom temperature. After well mixture of BPO and MMA monomer,arbon nanotube was added into the mixture followed by sonica-ion and polymerized at 50 ◦C. When the mixture became viscous,t was poured into mold for further reaction by the process of bak-ng as following steps: (1) 60 ◦C for 2 h, (2) 80 ◦C for 2 h, and (3)00 ◦C for 3 h. PMMA/CNT powder was prepared from PMMA/CNTomposites ground by grinder.

.2. Preparation of bone cement reinforced with carbon nanotube

The commercial cement, OSTEOBOND, was used as well in thistudy. The OSTEOBOND was purchased from Zimmer (Warsaw, IN,SA). Several systems of bone cement reinforced with carbon nan-tube were prepared. The composition of liquid portion of the boneement was the same in each system. The compositions of the boneement in each system are shown in Table 2. The specimens of boneement were prepared by mixing at the ratio of 1/2 at the liquidortion to the powder portion and left to solidify in a designedhape.

.3. Analysis

The tensile and compressive strength of bone cement was char-

cterized using INSTRON 5582. The specimens for tensile analysisre referred to the work of Harper and Bonfield [13]. The specimensave the dimensions: 75 mm in length, 5 mm in width, approxi-ately 3.5 mm in thickness, with a gauge length of 25 mm. The

rosshead speed employed was 5 mm/min. The compressive anal-

able 2he composition of the bone cement in each system.

Powder portion (g) Commercial liquidportion (ml)

Commercialpowder

PMMA/CNT powder(pmma/cnt)a

System 1 20 0 10System 2 17 3 (100/0.1) 10System 3 17 3 (100/0.2) 10System 4 17 3 (100/0.27) 10System 5 17 3 (100/0.43) 10System 6 17 3 (100/0.59) 10System 7 17 3 (100/0.75) 10

a (pmma/cnt) indicates the ratio of PMMA/CNT by weight in pre-polymeric com-osites.

System 5 45.55 1.65 130.02 7.41System 6 45.86 4.23 129.06 3.37System 7 46.58 4.65 127.83 3.54

ysis of bone cement corresponded to ASTM F451. The crossheadspeed was 25 mm/min. The diameter and length of the specimenswere 6.0 mm and 12.5 mm, respectively.

The dynamic mechanical properties of bone cements were mea-sured using dynamic mechanical analysis (DMA 2980, TA Instru-ments), with the clamp of single cantilever. The dimensions of therectangular specimens for DMA were 35 mm × 11 mm × 2.7 mm.The measuring temperatures ranged from 25 to 150 ◦C at 3 ◦C/min,and the frequencies swept at 1 Hz, 3 Hz, 5 Hz, and 10 Hz. The glasstransition temperature of a sample was labeled using the tan ı peak,which occurs at the highest temperature.

The surface of the gold-coated test specimens was observedusing Scanning Electron Microscope (SEM) (JEOL, JSM-6700F) at anaccelerating voltage of 10 kV.

3. Results and discussion

Table 3 shows the tensile and compressive strength of the bonecements tested in this study. System 1 is a commercial productwhich has tensile strength and compressive strength of 40.49 and105.33 MPa, respectively. Harper and Bonfield report that the ten-sile strength of Osteobond bone cement is 38.2 ± 2.65 MPa [13].Compressive strength of bone cement usually varies from 44 to103 MPa [2]. Systems 2–7 are the bone cements containing carbonnanotube. Both tensile and compressive strength of System 2 areabout 18% and 23%, respectively higher than that of System 1. Itindicates that the introduction of PMMA/CNT pre-polymeric com-posites is able to enhance mechanical properties of bone cement.Compared with Kwon’s study of MMT modified bone cementshowed in introduction section, the compressive strength of car-bon nanotube modified bone cement exhibited significant increase

Systems 1 and 2 tested in tensile strength. It indicates that thetoughness of System 2 is better than that of System 1. Therefore,

Fig. 1. The stress–strain curves of Systems 1 (a) and 2 (b) tested in tensile strength.

136 Y.-H. Nien, C.-l. Huang / Materials Science and Engineering B 169 (2010) 134–137

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Fig. 4. The glass transition temperatures of the bone cements measured using DMAat the frequencies of 1 Hz, 3 Hz, 5 Hz, and 10 Hz.

ig. 2. The storage moduli of the bone cement systems as a function of temperaturet the frequency of 3 Hz (a: System 1, h: System 2, i: System 3, j: System 4, k: System, l: System 6, m: System 7).

NT modified bone cement should be able to block crack propaga-ion.

Fig. 2 illustrates the storage moduli of the bone cement systemss a function of temperature at the frequency of 3 Hz. A storageodulus in DMA can be seen as the stiffness of material. At low

emperatures, the storage moduli of the all samples do not showignificant difference. Since only strength of the powder portionf bone cement was increased, the liquid portion of bone cementas remained the same as commercial product. However, when

he temperature increases to more than 100 ◦C, System 1 exhibitsigher storage modulus than the others. Fig. 3 is the tan ı values ofhe cement systems as a function of temperature at the frequencyf 3 Hz. The glass transition temperature of a sample was labeledsing the tan ı peak. Fig. 4 is the glass transition temperatures ofhe bone cements measured using DMA at the frequencies of 1 Hz,Hz, 5 Hz, and 10 Hz. System 1 (commercial product) has the high-st Tg among the bone cement. The lower Tg of the modified boneement may be due to carbon nanotube acted as plasticizer. The

ynamic mechanical properties of viscoelastic materials, such asolymeric composites, are time dependent. When sweep frequency

ncreases, the glass transition temperatures of the bone cementsxhibit higher. Fig. 5 is the storage moduli of the bone cements

ig. 3. The tan ı values of the cement systems as a function of temperature at therequency of 3 Hz (a: System 1, h: System 2, i: System 3, j: System 4, k: System 5, l:ystem 6, m: System 7).

Fig. 5. The storage moduli of the bone cements measured using DMA at the fre-quencies of 1 Hz, 3 Hz, 5 Hz, and 10 Hz.

measured using DMA at the frequencies of 1 Hz, 3 Hz, 5 Hz, and10 Hz. The storage modulus of bone cement also increases, whensweep frequency increases. Fig. 6 is the surface of the CNT mod-

ified bone cement observed using SEM. It is obvious that carbonnanotube existed in bone cement. Usui et al. uses CNTs to promotebone regeneration [14]. Therefore, it is expected for CNT modifiedbone cement in promoting bone regeneration.

Fig. 6. The surface of the CNT modified bone cement observed using SEM.

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Y.-H. Nien, C.-l. Huang / Materials Scie

. Conclusions

In this paper, we have prepared a new type of bone cementeinforced with carbon nanotube. In order to achieve better dis-ersion of carbon nanotube in bone cement, we first fabricatedMMA/CNT composites and then ground them as powder formo be introduced into bone cement. This kind of modified boneement exhibits excellent material properties such as tensile andompressive strength. The results show potential usage in clinicalpplications.

cknowledgement

The authors would like to thank National Science Council,aiwan for financial support under grant contract NSC 97-2221--224-068-.

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