a novel injectable, cohesive and toughened si-hpmc (silanized-hydroxypropyl methylcellulose)...

Acta Biomaterialia xxx (2014) xxx–xxx

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Acta Biomaterialia

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A novel injectable, cohesive and toughened Si-HPMC(silanized-hydroxypropyl methylcellulose) compositecalcium phosphate cement for bone substitution

http://dx.doi.org/10.1016/j.actbio.2014.03.0091742-7061/� 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Tel.: +33 2 40 68 31 97; fax: +33 2 40 68 31 99.E-mail address: [email protected] (F. Tancret).

Please cite this article in press as: Liu W et al. A novel injectable, cohesive and toughened Si-HPMC (silanized-hydroxypropyl methylcellulose) comcalcium phosphate cement for bone substitution. Acta Biomater (2014), http://dx.doi.org/10.1016/j.actbio.2014.03.009

Weizhen Liu a,b, Jingtao Zhang a,b, Gildas Rethore b,c, Khalid Khairoun b, Paul Pilet b,c, Franck Tancret a,⇑,Jean-Michel Bouler b, Pierre Weiss b,c

a Université de Nantes, Polytech Nantes, Institut des Matériaux Jean Rouxel, Rue Christian Pauc, BP 50609, 44306 Nantes Cedex 3, Franceb Université de Nantes, INSERM, UMR 791, LIOAD, Faculté de Chirurgie Dentaire, BP 84215, 44042 Nantes Cedex 1, Francec Centre Hospitalier Universitaire de Nantes, 1 place Alexis Ricordeau, 44093 Nantes Cedex 1, France

a r t i c l e i n f o

Article history:Received 18 November 2013Received in revised form 11 February 2014Accepted 11 March 2014Available online xxxx

Keywords:Bone regenerationCalcium phosphate cementsHydroxyapatiteHydrogelMechanical properties

a b s t r a c t

This study reports on the incorporation of the self-setting polysaccharide derivative hydrogel (silanized-hydroxypropyl methylcellulose, Si-HPMC) into the formulation of calcium phosphate cements (CPCs) todevelop a novel injectable material for bone substitution. The effects of Si-HPMC on the handling prop-erties (injectability, cohesion and setting time) and mechanical properties (Young’s modulus, fracturetoughness, flexural and compressive strength) of CPCs were systematically studied. It was found thatSi-HPMC could endow composite CPC pastes with an appealing rheological behavior at the early stageof setting, promoting its application in open bone cavities. Moreover, Si-HPMC gave the composite CPCgood injectability and cohesion, and reduced the setting time. Si-HPMC increased the porosity of CPCsafter hardening, especially the macroporosity as a result of entrapped air bubbles; however, it improved,rather than compromised, the mechanical properties of composite CPCs, which demonstrates a strongtoughening and strengthening effect. In view of the above, the Si-HPMC composite CPC may be particu-larly promising as bone substitute material for clinic application.

� 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

1. Introduction

The applications of calcium phosphate cements (CPCs) havebeen increasing in different fields, such as orthopedic surgery, den-tistry, maxillofacial surgery and reconstructive surgery [1–3], sincethey were first proposed by LeGeros et al. [4] and Brown and Chow[5] in the early 1980s. CPCs are commonly considered as good can-didates for bone substitution because of their good biocompatibil-ity, bioactivity and bone-replacement ability (osteoconductivity)[6,7]. These materials are obtained by mixing one or several reac-tive calcium phosphate powders with an aqueous solution to forma paste that hardens in vivo through a low-temperature settingreaction [8,9]. The products formed in this setting reaction havemany similarities with the mineral phase of the natural bone.

A major advantage of CPCs compared to traditional calciumphosphate bioceramics is that they are usually injectable and canself-set in vivo in the bone cavity without machining. This propertyis important in clinical applications that involve intricate bone

cavities or narrow defect sites, and favors the development of min-imally invasive surgical techniques [10,11]. As bone-fillingcements, CPCs have to be distinguished from the classic bone‘‘cement’’ commonly used to fix joint prosthesis, namely poly-methyl methacrylate, which is not degradable and often causesnecrosis of the surrounding tissue due to either the high curingtemperatures or the effects of leaching of methyl methacrylatemonomer [12,13].

Although CPCs appear highly promising for bone regenerationand have already been commercialized [14,15], it is generallyaccepted that there are still some crucial issues that need to beaddressed to satisfy clinical requirements and the needs of sur-geons [16,17]. Specifically, CPCs without any additives normallydemonstrate poor injectability due to liquid–solid phase separa-tion (so-called filter-pressing) [18,19]. Moreover, extraosseouscement leakage has been reported to be a major complication inboth acrylic and calcium phosphate cement applications relevantto vertebroplasty or kyphoplasty procedures [20]. In most cases,the purely inorganic CPC pastes tend to disintegrate upon earlycontact with blood or biological fluids due to their weak cohesion[21]. The release of calcium phosphate particles into the blood

posite

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2 W. Liu et al. / Acta Biomaterialia xxx (2014) xxx–xxx

stream might cause some risks, such as pulmonary embolism andcardiovascular deterioration, by stimulating blood coagulation[22]. Besides the poor handling properties, another challenge fac-ing CPCs is that their mechanical properties are much differentfrom those of the cortical or even the cancellous bone, not onlyin terms of strength, but especially in terms of toughness, ductilityand fatigue resistance [23], preventing them from being applied inload-bearing places. In addition, due to their high brittleness, anyoverload may cause cracking of the material and the release of deb-ris in the body.

Numerous studies have been dedicated to improving the afore-mentioned performances of CPCs for broader clinic applications.Previous studies have shown that CPC performances can be tai-lored by changing different factors, including cement composition,particle size, the liquid-to-powder (L/P) ratio [24–27] and prepara-tion processing (such as compaction) [28,29]. In addition, many or-ganic or inorganic additives [21,30], such as citric acid [31–33],chitosan [34,35], cellulose ethers [36,37], gelatin [38], collagen[39], sodium alginate [40], hyaluronic acid [41], polymer fibers[23,42–44] and their admixtures, have been added either in thepowder phase or in the liquid phase to improve the handling andmechanical properties of CPCs.

Among these approaches, incorporating polymers into the for-mulation of CPCs is attracting much attention because it has beenconsidered as a useful strategy to overcome the intrinsic limita-tions of inorganic CPCs [45]. The cellulose ethers, such as methyl-cellulose and hydroxypropyl methylcellulose, are particularlyinteresting as polymer candidates due to their good biocompatibil-ity and rheological properties [2,46]. Even small amounts (a fewweight per cent) of cellulose ethers can not only dramatically im-prove the injectability and cohesion of CPC pastes [2,45], but alsoincrease the fracture toughness of hardened CPC products[36,37]. However, cellulose ethers generally tend to delay the set-ting time of CPCs. A long setting time could cause problems, espe-cially in some traumatology cases, because of the inability of thecement to support stresses during this time period [26]. On theother hand, despite good cohesion, composite CPC pastes (espe-cially with high L/P ratios) generally tend to flow away (in otherwords, they cannot maintain their shape and/or position) fromthe place where they are implanted at the initial stage, which re-stricts their application to only closed bone defects (cavities).

One aim of this study, therefore, is to develop novel injectablecomposite CPCs which not only have a general improvement inboth injectability and cohesion but can also avoid prolonged set-ting time and can overcome the tendency of flowing away fromthe implant site, as found in many polymer composite CPCs. To thisend, a self-crosslinkable polysaccharide derivative, namely silan-ized hydroxypropyl methylcellulose (Si-HPMC), which is a cellu-lose-based hydrogel that has already been proposed forbiomedical applications [47,48], appears to be an attractive candi-date. The rationales of using Si-HPMC are as follows: first, Si-HPMChydrogel has been shown to be biocompatible and to be a potentialscaffold for three-dimensional culture and differentiation of osteo-blastic [49] and chondrocytic [50] cells in tissue engineering;moreover, due to its particular rheological properties and self-crosslinking, Si-HPMC has been mixed with biphasic calcium phos-phate ceramic particles to prepare injectable bone substitutes[51,52], effectively suppressing the long-term flow of the latter. Itis therefore expected that the addition of Si-HPMC into CPC mayalso restrain its flow from implant sites.

Strength, especially compressive strength, has been widelytested in studies of CPCs as a criterion (often the only criterion)evaluating their mechanical performance. However, this notion ap-pears to be inadequate in many cases. On the one hand, since com-plex three-dimensional loads are often applied at the site ofimplant, other mechanical properties (e.g. bending (tensile)

Please cite this article in press as: Liu W et al. A novel injectable, cohesive andcalcium phosphate cement for bone substitution. Acta Biomater (2014), http:/

strength and shear strength, as well as the corresponding elasticmodulus) also need to be taken into account. On the other hand,and more importantly, strength is not an intrinsic property, but de-pends both on the size of defects (e.g. pores) and on fracture tough-ness, which is a real limitation for CPCs. In fact, it is poor fracturetoughness, describing the resistance of a material to crack propaga-tion, and high brittleness which prevent CPCs from being used inload-bearing places. Unfortunately, however, unlike the abundantstudies on strength, fracture toughness is sparsely reported inthe literature [53]. Therefore, the other aim of the study is to sys-tematically investigate, after hardening, the mechanical propertiesof Si-HPMC composite CPCs, including compressive strength, flex-ural strength, Young’s modulus and fracture toughness, and to tryto relate these properties to microstructural features (such asporosity, pore size, crystal size and morphology), which are theintrinsic factors determining the mechanical performance of mate-rials but are often ignored.

In view of all the above-mentioned aims, in the present work Si-HPMC is incorporated into a-tricalcium phosphate (TCP)-basedapatitic CPCs, and the effects of Si-HPMC on the handling proper-ties (e.g. injectability, cohesion and setting time) and mechanicalproperties (e.g. Young’s modulus, fracture toughness, flexuralstrength and compressive strength) of the composite CPCs are sys-temically investigated.

2. Materials and methods

2.1. Fabrication of the solid phase of CPCs

All of the reagents used in this study were of analytical grade andwere used without any further purification. The a-TCP powder wassynthesized by heating a mixture of dicalcium phosphate anhydrous(CaHPO4; Alfa Aesar, Germany) and calcium carbonate (CaCO3;VWR, BDH, Prolabo) with a molar ratio 2:1 at 1360 �C for 15 h andsubsequently quenching it to room temperature. The phase purityof the synthesized a-TCP powder was checked by using X-ray dif-fraction (XRD, X’pert pro, PANalytical, Netherlands) and no otherphase was found. To prepare the solid phase of CPCs, 2 wt.% of pre-cipitated calcium-deficient hydroxyapatite (CDHA; Ca/P ratio: 1.6;BET specific surface area: 125 m2 g�1; average crystal size:23.1 nm [54]) was added to the a-TCP powder as a seed for subse-quent crystallization of apatite and the powder mixture was milledin a Mortar Grinder (Retsch RM100, Germany) for 1 h to get a finepowder. The mean particle size of the fine powder mixture was6 lm, as determined by laser diffraction granulometry (BeckmanCoulter LS230, USA) after dispersion in ethanol in an ultrasonic bath.

2.2. Preparation of the liquid phases of CPCs

The liquid phases of Si-HPMC composite CPCs were prepared bymixing Si-HPMC solutions and NaH2PO4 solution. Si-HPMC pow-der, the synthetic procedure of which was detailed by Bourgeset al. [55], was dissolved in NaOH solution to prepare Si-HPMCsolutions of different concentrations (2, 3 and 4% w/v, 1% w/v= 10 g l�1), using a method described by Fatimi et al. [56]. The finalpH value of the Si-HPMC solutions was around 12.8.

Si-HPMC solutions are stable in strong basic media (pH > 12.1).When the pH decreases, the gelation of Si-HPMC takes place, andthe Si-HPMC solution transforms into a hydrogel with a three-dimensional network of Si-HPMC chains [56–58]. The gelationprinciple of the Si-HPMC is illustrated in Fig. 1. In this study, a30 wt.% NaH2PO4 solution was mixed with Si-HPMC solutions ina syringe for 20 s to initiate the gelation of the latter, formingthe liquid phases of CPCs, with the final pH ranging from 7 to 8.During the above mixing process, Si-HPMC starts to gel, and the

toughened Si-HPMC (silanized-hydroxypropyl methylcellulose) composite/dx.doi.org/10.1016/j.actbio.2014.03.009


Fig. 1. Behaviors of silane groups of Si-HPMC [56]: (1) dissolution in basic solutionwith silanolate function formation, (2) transformation of silanolate into silanol bydecreasing the pH and (3) silanol condensation with formation of three-dimen-sional network of Si-HPMC chain.

W. Liu et al. / Acta Biomaterialia xxx (2014) xxx–xxx 3

point in time immediately after the above mixing for 20 s is de-fined as 0 min of the gelation time. The gel point of Si-HPMChydrogel in this formulation is about 30 min at 23 �C, determinedby a rheological method in oscillatory shear with a rotational rhe-ometer (RheoStress 300, Germany).

In order to compare the difference between HPMC and Si-HPMCcomposite CPCs, a 3% w/v HPMC (Methocel� E4M) solution with2.5 wt.% Na2HPO4 was used as the liquid phase for the HPMC com-posite CPC. The preparation of HPMC solution was described in aprevious study [37]. In addition, a 2.5 wt.% Na2HPO4 solution wasused as the liquid phase of the control cement which is purely inor-ganic CPC.

2.3. Preparation of Si-HPMC composite CPCs

The Si-HPMC composite CPCs were prepared at different L/P ra-tios and by using Si-HPMC solutions of different concentrations, asshown in Table 1. The pastes of Si-HPMC composite CPCs were pre-pared by manually mixing the above-prepared solid phase and li-quid phase in a mortar for around 1.5 min. The freshly preparedpaste was then used for the assessment of several handling prop-erties, as detailed in the following sections. In addition, cuboidspecimens (36 � 8 � 8 mm3) were prepared by pressing the pastesinto Teflon molds using a spatula. The molds containing the pasteswere immersed in a saline solution (0.9 wt.% NaCl) of 80 ml andincubated in a homothermal oven at 37 �C for 1 day. The specimenswere then removed from the mold and reincubated under thesame conditions for 4 days. After hardening, the surfaces of bulkspecimens were polished using a polishing machine with SiC pa-pers (grade P4000) to obtain flat and parallel faces.

Table 1Experimental series of Si-HPMC composite CPCs.a

2% 3% 4%

0.40 1.10 1.47

0.45 1.24 1.65

0.60 1.10 2.20

0.80 2.93

1.00 1.83 3.67

Si-HPMCMassfraction

L/Pb(%)

a The numbers in the first row represent the concentration of Si-HPMC in thepolymer solution. The numbers in the other rows represent the corresponding massfraction of Si-HPMC in the final cement without taking water into account.

b Liquid volume = volume of NaH2PO4 solution + volume of Si-HPMC solution.


2.4. Assessment of handling properties

The behavior of the freshly prepared CPC pastes was observedwhen the specimens were removed from the mold immediatelyafter preparation. The injectability of the CPC pastes was testedusing a 5 ml syringe fitted with an orifice of 1.2 mm inner diame-ter, as described in a previous study [37]. The CPC paste was pre-pared and immediately packed into the syringe. After that, thesyringe plunger was manually shifted to eliminate the trappedair between the orifice and the gasket of the plunger. Four minutesafter the initial mixing of the CPC powder and liquid, the CPC pastewas extruded from the syringe by a multifunction testing machine(TAHD plus, Stable Micro Systems, UK) at a speed of 15 mm min�1

until a maximum force of 200 N was reached. The force duringextrusion was recorded, and the mass of the paste extruded fromthe syringe was weighed and divided by the original mass of thepaste inside the syringe to calculate the percentage of extrudedmass. The tests were performed at 25 �C with �50% relativehumidity, as measured by a hygrothermograph. Each measure-ment was carried out in triplicate. To assess the cohesion, the new-ly prepared CPC paste was packed into a syringe and thenimmediately injected into a saline solution at 37 �C, with thebehavior of the cement being observed during hardening.

The setting times of the CPCs were tested with Gillmore needlesconsisting of a light needle (113.4 g in weight and 2.12 mm indiameter) and a heavy needle (453.6 g in weight and 1.06 mm indiameter) (H-3150, Humboldt Mfg. Co., USA) according to theASTM C266 standard. The newly prepared CPC paste was packedinto a stainless-steel mold and flatted with a spatula. The initialsetting time and the final setting time were determined, respec-tively, as the time when the light and heavy needle could not markthe surface of CPC paste with a complete circular impression forthe first time. The measurement of the setting times was con-ducted with 100% relative humidity at 37 �C. Each test was per-formed in triplicate.

2.5. Measurement of mechanical properties and porosity

The mechanical properties of CPC specimens were tested inwet conditions, i.e. immediately after taking the specimens outof the hardening solution. A standard three-point bending testwith a span of 32 mm was used to load the CPC specimens andto measure their Young’s modulus and flexural strength at acrosshead speed of 0.1 mm min�1 on a computer-controlled uni-versal testing machine (MTS, USA). Specimen deflection was mea-sured using a linear variable differential transformer, with aprecision of <1 lm. As for fracture toughness, it was tested onchevron-notched CPC specimens (36 � 8 � 8 mm3) following aprocedure described by Dlouhy et al. [59], using the same bend-ing setup as for the Young’s modulus and flexural strength. Thepreparation process of the chevron notches in CPC specimenswas detailed in a previous study [37]. Subsequently, the halvesproduced from the measurement of fracture toughness were cutto a size of approximately 16 � 8 � 8 mm3, and half of them wereused to measure the compressive strength at a loading speed of0.5 mm min�1 on the same machine. A single sheet of thin card-board was inserted between the loading plates and the specimensto compensate for any surface irregularities of specimens in con-tact with the loading plates and to ensure a uniform loaddistribution.

The remaining halves from the fracture toughness testing weredried in a homothermal oven at 37 �C for several days until therewas no more weight loss and then used to determine the porosity,P, through gravimetry, using the following equation:

P ¼ ðqCDHA � qÞ=qCDHA ð1Þ




where qCDHA is the density of fully dense CDHA and q is the appar-ent density of CPC specimens determined by dividing their weightby their volume. An Accupyc II 1340 density analyzer was used tomeasure the qCDHA of control and Si-HPMC composite CPC speci-mens. The average qCDHAs of the control CPCs and Si-HPMC compos-ite CPCs were 2.79 and 2.74 g cm�3, respectively, and these valueswere used to determine the porosity of the control and compositeCPC specimens. Six specimens were measured for each porosity set.

2.6. Phase and microstructure characterization

After measurement of their compressive strength, the CPC spec-imens were crushed into powder and their compositions wereexamined by using Cu Ka radiation (40 kV, 40 mA) in a continuousscanning mode. The diffraction angle 2h varied from 10� to 80� at astep size of 0.0167�, with a collection time of 20 s per step. Theinfrared absorption spectra of the CPC specimens were character-ized by Fourier transform infrared spectroscopy (FTIR; Magna-IR550, Nicolet Co., USA) in the range of 4000–400 cm�1. Finally, thefracture surfaces of CPC specimens were observed using a scanningelectron microscope (SEM; Merlin, Carl Zeiss, Germany) equippedwith an energy-dispersive X-ray (EDX) microanalyzer.

2.7. Statistical analysis

All data were presented as mean values ± standard deviation(SD). One-way analysis of variance was performed to determineany significant effects of the variables. Tukey’s multiple compari-son procedures were used to group and rank the measured values,and Dunn’s multiple comparison tests were used on data with non-normal distribution or unequal variance. A probability value (p) of<0.05 was considered as statistically significant.

3. Results

3.1. Handling properties

Fig. 2 shows the behavior of the freshly prepared CPC pasteswith or without polymer, when the specimens were removed fromthe mold immediately after preparation. The control CPC paste(without polymer) cannot maintain its cuboid shape and spreadsover a large area on the glass plate due to a low viscosity(Fig. 2A). Similarly, the HPMC composite CPC paste cannot keepits cuboid shape either, though it appears to have a higher viscosity(Fig. 2B). In contrast, the Si-HPMC composite CPC paste can pre-serve its cuboid shape very well, without severe damage

Fig. 2. Rheological behavior of the freshly prepared CPCs specimens: (A) controlcement; (B) HPMC composite cement; and Si-HPMC composite cement (C) afterremoval from the mold, (D) under bending, (E) after bending and (F) aftercompressing and stretching. L/P = 1.0 ml g�1 and the concentration of HPMC (E4M)or Si-HPMC in the liquid phase is 3%. The illustrations in (A–C) and (D–F) wereperformed around 6 and 8 min, respectively, after the initial mixing of the CPCpowder and liquid.


(Fig. 2C). Moreover, the Si-HPMC composite CPC paste exhibits aspecial behavior at the early stage of setting: it can undergo ex-treme bending without breaking (Fig. 2D) and can largely maintainthe bent shape after unloading (Fig. 2E). Similarly, it can keep itscompressed or stretched shape to a great extent when the corre-sponding stresses have been removed (Fig. 2F). It is worth notingthat the extreme bending in Fig. 2D was produced mainly for illus-trative purposes; it may not be expected to occur in a realapplication.

The injectability of the Si-HPMC composite CPCs at different L/Pratios and with various gelling times of Si-HPMC was determinedfrom the mass percentage of extruded paste (Supplementary data,Table S1). Except the composite CPC with an L/P ratio of 0.4, all thecomposite CPCs prepared at higher L/P ratios were extruded com-pletely. The extrusion curves recorded during injection (Fig. 3A)further illustrate the extrusion process. The overshoot at the begin-ning of the curve is caused by the yield stress, which is the criticalforce that must be applied to make the paste start to flow. The sub-sequent plateau is related to the load needed to maintain the pasteflow. Both the yield stress and the extrusion force (in plateau stage)increase with either a decrease in L/P ratio or an increase in gellingtime of Si-HPMC. At the end of the extrusion, the force increasessteeply until reaching the maximal extrusion force (�200 N),which is caused by the mechanical contact between the syringeplunger and the syringe’s bottom when all the paste has beenextruded.

To assess the cohesion, the CPC pastes, with or without Si-HPMC, were injected into a saline solution immediately after prep-aration (<3 min), as shown in Fig. 3B and C. The control CPC pastesdisintegrated completely and the particles were deposited onto thebottom of the flat beaker (Fig. 3B), whatever the L/P ratio was (from0.4 to 1.0). In contrast, even with an L/P ratio of 1.0, the Si-HPMCcomposite CPC paste still maintained its injected noodle-like shapeuntil hardening up to 5 days later, and no disintegration was ob-served (Fig. 3C), indicating outstanding cohesion.

Fig. 4A shows the initial and final setting times of CPC pasteswith and without Si-HPMC (4%) at different L/P ratios. It appearsthat Si-HPMC did not change the initial setting time of the CPC

Fig. 3. (A) Extrusion force curves of Si-HPMC composite CPC pastes at different L/Pratios (L/P = 0.4, 0.6, 0.8 and 1.0 ml g�1) and with different gelling times of Si-HPMC(0 and 30 min) before mixing the solid and liquid phases of CPC. The concentrationof Si-HPMC in liquid solution is 4%; (B) control CPC pastes and (C) Si-HPMC (3%)composite CPC pastes injected into a saline solution immediately after preparation(within 3 min), L/P = 1.0 ml g�1. The total volume of the paste is around 2.7 ml.



Fig. 4. (A) Initial and final setting times of control cements and Si-HPMC (4%) composite cements with different L/P ratios. The final setting time of the control cement with anL/P ratio of 0.8 is much longer than 60 min, hence it is not shown in the figure. Each value is the mean of three measurements ± SD. The values indicated with dissimilar lettersare significantly different from each other (p < 0.05). For example, ‘‘a’’ is not significantly different from ‘‘ab’’ (p > 0.1); however, ‘‘a’’ is significantly different from ‘‘bc’’ and‘‘cd’’ (p < 0.05). (B) XRD patterns of control cement and Si-HPMC (4%) composite cement with L/P = 1.0 ml g�1. The gray pattern refers to control cement and the black patternrefers to Si-HPMC composite cement.


with an L/P ratio up to 0.6, but significantly reduced it for an L/Pratio of 0.8. The phenomenon of shortening setting times becomesmuch more obvious with regard to final setting times with increas-ing L/P ratios.

After hardening for 5 days, the final phases of control cementand Si-HPMC composite cement were examined by XRD (Fig. 4B).Similar to control cements, most of the a-TCP in the Si-HPMC com-posite CPCs transformed into CDHA. However, despite the fastersetting in the early stage, the final formation degree of CDHA inthe Si-HPMC composite cement seems to be slightly retarded, asindicated by the lower intensity of the peaks of CDHA and higherintensity of the peaks of a-TCP.

3.2. Porosity and mechanical properties

The total porosities of the control cements and Si-HPMC com-posite cements were measured and are plotted as a function ofthe L/P ratio (Fig. 5). As expected, the porosities of both control ce-ments and composite cements increase with increasing L/P ratio.Moreover, the porosity of the composite cements is higher thanthat of the control cements with the same L/P ratios, but the

Fig. 5. Porosity of control cement and Si-HPMC (4%) composite cement vs. L/P ratio.Each value is the mean of six measurements ± SD. The values indicated withdissimilar letters are significantly different from each other (p < 0.05).


difference between the two porosities tends to decrease globallywith increasing L/P ratio.

To examine the influences of Si-HPMC on the mechanical prop-erties of CPCs, Young’s modulus, fracture toughness, flexuralstrength and compressive strength of the Si-HPMC composite ce-ments were investigated (Table 2). From the viewpoint of materialscience, these mechanical properties should be determined by themicrostructure of cements, in which pores are one of the mostimportant factors. For this reason, and in order to better under-stand the effect of Si-HPMC on mechanical performance, all theabove mechanical properties of control cements and Si-HPMCcomposite CPCs are plotted on Fig. 6 as a function of total porosity(for simplicity, only the data of control cements and composite ce-ments with Si-HPMC of 4% are shown). Two trends can be ob-served. First, all the mechanical properties studied decrease withincreasing porosity, with regard to both control cements andSi-HPMC composite cements. This trend is consistent with otherstudies on CPC, and is due to the effect of porosity [53]. Secondly,compared to control cements, all the mechanical properties of thecorresponding Si-HPMC composite cements with the same L/Pratios increase or remain constant with increasing porosity (exceptfor the strengths of the Si-HPMC composite cements at low L/Pratios of 0.4 and 0.45). The curves, obtained by using a mathemat-ical model (power law), are fittings of mechanical properties ofcontrol cements. The above-mentioned points will be explainedin the discussion section.

The stress–displacement curves recorded during compressiontests of control cement and Si-HPMC composite cement are plottedin Fig. 7. An increase in the stress followed by a sharp drop was ob-served for the control cement, which corresponded to a typicalbrittle fracture. In contrast, a less linear increase in the stress fol-lowed by a progressive decrease was observed for the Si-HPMCcomposite cement with the same L/P ratio, indicating a less brittlefailure, corresponding to a progressive microcracking/macrocrack-ing of the material.

3.3. Microstructure

Fig. 8 shows the SEM images of fracture surfaces of control ce-ments and Si-HPMC composite cements with different L/P ratios.At low magnification (�50�), no large pores can be observed inthe control cement with an L/P ratio of 0.4 (Fig. 8A). In contrast,once Si-HPMC was added, many pores of tens or hundreds ofmicrometers can be easily found (Fig. 8B). When the L/P ratio



Table 2Mechanical properties: Young’s modulus (E), fracture toughness (KIC), compressive strength (rc), flexural strength (rf) and average porosity of the control CPCs and Si-HPMCcomposite CPCs at different L/P ratios.

L/P PAve. (%) E (GPa) KIC (MPa m1/2) rc (MPa) rf (MPa)

Control 0.40 45.27 7.51 ± 1.23 0.261 ± 0.012 41.70 ± 5.50 13.48 ± 1.060.45 48.14 0.217 ± 0.011 33.20 ± 4.000.60 56.27 2.57 ± 0.69 0.164 ± 0.020 12.10 ± 2.30 4.99 ± 1.300.80 64.71 1.22 ± 0.27 0.064 ± 0.002 4.74 ± 0.54 2.03 ± 0.321.00 69.40 0.39 ± 0.21 0.044 ± 0.005 2.48 ± 0.24 0.99 ± 0.20

Si-HPMC 2% 0.60 57.42 0.197 ± 0.008 14.15 ± 1.591.00 70.44 0.087 ± 0.008 2.72 ± 0.57

Si-HPMC 3% 0.40 48.67 0.284 ± 0.020 27.78 ± 2.630.45 50.88 0.253 ± 0.010 23.61 ± 1.82

Si-HPMC 4% 0.40 50.02 7.61 ± 0.57 0.320 ± 0.018 22.91 ± 1.53 8.44 ± 0.950.45 52.03 0.262 ± 0.012 18.96 ± 2.220.60 58.53 4.63 ± 0.56 0.240 ± 0.015 13.90 ± 1.06 5.81 ± 0.230.80 65.65 2.03 ± 0.21 0.167 ± 0.012 7.23 ± 0.77 3.89 ± 0.311.00 70.87 0.98 ± 0.19 0.123 ± 0.018 3.35 ± 0.32 2.17 ± 0.25

Each value is the mean of six measurements ± SD.

Fig. 6. Mechanical properties: (A) Young’s modulus, (B) flexural strength, (C) fracture toughness and (D) compressive strength of control cements and Si-HPMC compositecements as a function of porosity. Each value is the mean of six measurements ± SD. The values indicated with dissimilar letters are significantly different from each other(p < 0.05). The red curves are fittings of the mechanical properties of the control cements using a power law, and they are fitted to assist the comparison of mechanicalproperties between composite cements and control cements with the same porosity.


increases to 1.0, no large pores can be seen in the control cementeither (Fig. 8C). For the Si-HPMC composite cement with an L/P ra-tio of 1.0, many pores larger than 100 lm can be found (Fig. 8D).

The microstructure of the control and Si-HPMC composite ce-ments with different L/P ratios is further revealed at a higher mag-nification (Fig. 9). As shown in the control cement with an L/P ratioof 0.4 (Fig. 9A), needle-like and plate-like apatite crystals can be


observed entangling each other. Also, a similar microstructurecan be found in the Si-HPMC composite cement with the sameL/P ratio (Fig. 9B). With the L/P ratio increasing to 1.0, the micro-structure of the control cement changes significantly, formingsphere-like apatite clusters consisting of numerous small and shortneedle-like crystals (Fig. 9C). In addition, these apatite clusters areheterogeneously distributed in the cement matrix, with large voids



Fig. 7. Stress vs. crosshead displacement curves of the control cement and Si-HPMCcomposite cement (L/P = 1.0).


between them (Fig. 9C and Supplementary data, Fig. S1). In con-trast, the microstructure of the Si-HPMC composite CPC remainssimilar when the L/P ratio increases from 0.4 to 1.0 (Fig. 9B and D).

Furthermore, some glue-like polymers, which seem to bederived from shrunken Si-HPMC hydrogel after drying, can beobserved on the fracture surface of Si-HPMC composite cement,sticking to neighboring apatite crystals, as indicated by the arrowin Fig. 10. Evidence of the existence of Si-HPMC in the compositecements was furthermore demonstrated by EDX and FTIR (Supple-mentary data, Figs. S2 and S3).

4. Discussion

This study aims, by incorporating the self-setting polysaccha-ride derivative hydrogel (Si-HPMC) into the formulation of CPCs,to improve both the handling and mechanical properties of the lat-ter. One of the most important features of Si-HPMC is its gellingreaction triggered by the decreased pH, generating a hydrogel witha three-dimensional network of Si-HPMC chains [55–57]. Whenadded into the formulation of CPC and starting to gel, Si-HPMC

Fig. 8. SEM images of the fracture surface of control CPC specimens, (A) L/P = 0.4 and (magnification of 50�.


would remarkably increase the viscosity of the CPC paste andendow it an appealing rheological behavior at the early stage ofsetting (Fig. 2). It can be bent, stretched and compressed easily,and can then largely maintain its shape when the stress isremoved, which suggests that the Si-HPMC composite CPC pastecan be arbitrarily deformed to adapt to complex or irregularshapes. Furthermore, and importantly, even at a high L/P ratioand when removed from the mold immediately after preparation,the Si-HPMC composite CPC can maintain its shape instead ofspreading away, thus showing its potential to not flow away froman implant site. This property gives the Si-HPMC compositecement an advantage in clinic applications, especially in the caseof open bone defects, from where a lot of CPC pastes tend to flowout, and where granular and bulk calcium phosphate ceramicsare therefore still commonly used. In addition, Baroud et al. [60]have demonstrated that using a high-viscosity cement can effec-tively prevent extraosseous cement leakage, which often occursduring vertebroplasty procedures, and can significantly enhancethe uniformity of cement infiltration into the trabecular boneskeleton. Based on its appealing rheological performance shown pre-viously, one may expect that the extraosseous cement leakage wouldprobably also be prevented by using a Si-HPMC composite cement.

The high viscosity is also thought to be responsible for the goodinjectability and cohesion of polysaccharide composite CPC pastes,as reported in previous studies [18,36,37,40]. Bohner et al. [61]proposed that the rheological properties (viscosity, injectabilityand cohesion) of CPC pastes are very important for their clinicapplication, and the use of hydrogels as mixing liquids of CPCs toincrease viscosity seems to be one of the best strategies for a gen-eral improvement in the rheological properties of CPC pastes. Thesame strategy has been used in this study to realize good injecta-bility and cohesion in CPC paste (Fig. 3). With regard to injectabil-ity, the extrusion curves recorded during injection (Fig. 3A) areuseful tools to explain the extrusion process. The extrusion forcesof Si-HPMC composite CPC pastes are generally constant in theirplateau stages, indicating that the pastes remain homogeneousand that no filter-pressing occurs during the extrusion. Theincreasing yield stress and extrusion force with decreasing L/P ra-tio are mainly attributed to greater friction between the grains at alower L/P ratio. When the L/P ratio decreases to 0.4, the Si-HPMCcomposite CPC paste was hardly extruded. This is probably because

C) L/P = 1.0, and Si-HPMC (4%) composite CPCs, (B) L/P = 0.4 and (D) L/P = 1.0, at a



Fig. 9. SEM images of the fracture surface of control CPC specimens, (A) L/P = 0.4 and (C) L/P = 1.0, and Si-HPMC composite CPCs, (B) L/P = 0.4 and (D) L/P = 1.0, at amagnification of 10,000�.

Fig. 10. SEM image showing polymer (indicated by the arrow) in the Si-HPMCcomposite cement (L/P = 0.6). The magnification of the SEM image is 20,000�.


the yield stress required to initiate the paste flow is very high,exceeding the maximum force that the machine can apply(�200 N). For the cement paste prepared using Si-HPMC with alonger gelling time (e.g. 30 min), the higher yield stress and extru-sion force are mainly due to the extra force needed to break the al-ready formed hydrogel network. Besides, under the same L/P ratio(from 0.6 to 1.0), the control CPC pastes can also be extruded com-pletely (Supplementary data, Table S1), though their poor cohesion(Fig. 3B) would limit their application.

Unlike many polymeric additives delaying setting of CPC[37,45], Si-HPMC reduces the setting time (Fig. 4A), and the mech-anism for this may mainly be attributed to its gelation effect. Infact, like HPMC, Si-HPMC molecules would adsorb to the surfaceof a-TCP particles and hence would be expected to delay the set-ting. However, Si-HPMC crosslinks to form a hydrogel with athree-dimensional network. Thus, it is very likely that the gelationeffect of Si-HPMC counteracts the influence of the delay of cementsetting caused by polymer adsorbing, and finally produces a stron-ger resistance which is related to an apparent faster setting. Thedecreased setting time endows the Si-HPMC composite CPC withadvantages especially in emergency cases or in open bone cavities,where a fast setting is much desired. With time, Si-HPMC further


crosslinks to form a complete hydrogel network which interfereswith the dissolution of Ca2+ and PO4

3� into water, therefore affect-ing the final formation degree of CDHA (Fig. 4B). However, a morecomprehensive kinetic study on the phase and microstructure evo-lution would be desirable.

One of the most important microstructural features of CPCs isthat they are intrinsically microporous. Most of the microporesare left by the remaining aqueous solution after the cementitiousreaction, which includes the dissolution of initial inorganic com-pounds and the concomitant precipitation of apatite [62]. Theincreasing porosity in both control and composite cements withincreasing L/P ratio (Fig. 5) is mainly attributed to the higher pro-portion of liquid in the constant volume of the mold. In addition,similar to the HPMC composite cements [37], the higher porosityof Si-HPMC composite cements than that of the corresponding con-trol cements is a result of the pores left by air bubbles entrappedduring the mixing of the viscous composite cement paste (Fig. 8Band D). These entrapped air bubbles can then be regarded as mac-ropores in the final cements. However, although containing manymore macropores, the Si-HPMC composite cement with a high L/P ratio (e.g. 1.0) has just a slightly higher total porosity than thecontrol cement with the same L/P ratio (Fig. 5); this is due to a den-ser matrix (Fig. 9C and D and Supplementary data, Fig. S1).

In general, the mechanical properties of CPCs decrease withincreasing porosity [53]. However, in this study, even though theSi-HPMC composite CPC has a higher porosity than the controlCPC with the same L/P ratio (Fig. 5), its mechanical properties re-main constant or even increase with increasing porosity (Fig. 6),indicating that Si-HPMC has a reinforcing effect on CPC. In orderto prove this assumption, the mechanical properties of Si-HPMCcomposite cements should be compared with those of control ce-ments with the same porosities. However, it is practically impossi-ble to prepare control cements with exactly the same porosities asthose of composite cements. Thus, the curves of a mathematicalmodel (power law) used in our previous studies [37,63] were usedto fit the mechanical properties of the control cements to assist thecomparison (Fig. 6). Good fittings were obtained, indicating thevalidity of the application of the power law in CPCs. It is worth not-ing that the modeling of the mechanical properties of CPCs was notthe main purpose of present study, though it is a useful tool to helpto analyze and explain the results. Furthermore, the relative




increase in the mechanical properties of Si-HPMC composite ce-ments compared to ‘‘virtual’’ control cements with the same poros-ities (calculated using the fitted power laws) is plotted as afunction of the L/P ratio (Fig. 11).

As can be seen in Fig. 6A and C, both the Young’s modulus andthe fracture toughness of Si-HPMC composite CPCs are apparentlyhigher than those of control CPCs with the same porosities, show-ing that Si-HPMC does have a significant improvement on the twoproperties of CPC. Moreover, this improvement becomes moreobvious in composite cements with high L/P ratios (Fig. 11A andC). The enhancement of fracture toughness has also been observedin HPMC composite CPCs, and the toughening effect has beenattributed to a synergetic effect of homogenization of cementmicrostructure and crack bridging by polymer ligaments [37]. Be-cause of the similarity between HPMC and Si-HPMC, it can be ex-pected that similar toughening mechanisms may also operate inthe Si-HPMC composite cements.

Indeed, as revealed in Fig. 9C and D, the incorporation ofSi-HPMC can help to form a more homogeneous cement matrix,which may contribute to the improved fracture toughness. Themore homogenous matrix may also be responsible for the higherYoung’s modulus of Si-HPMC composite cements compared to con-trol cements (Fig. 7A and Fig. 11A). Except for the optimized micro-structure with improved homogeneity, the glue-like polymers,being the crosslinked Si-HPMC hydrogel with the three-dimen-sional network and sticking to neighboring apatite crystals(Fig. 10), can also contribute to increasing the toughness. In fact,

Fig. 11. The relative increase in (A) Young’s modulus, (B) flexural strength, (C) fractureratio, compared to virtual control cements with identical porosities.


the hydrogel can be regarded as a continuous network within aporous and continuous inorganic matrix. When the load increases,fracture initiates between the stiff and brittle inorganic crystals,but the soft hydrogel is able to deform; it stretches between thefaces of the forming crack and creates links between them, sup-porting a part of the total force. This bridging of the crack by poly-mer ligaments increases the measured fracture toughness.

Regarding flexural and compressive strengths, at low L/P ratios(e.g. 0.4, 0.45), the two strengths of Si-HPMC composite CPCs aregenerally lower than those of control CPCs with the same porosi-ties. In contrast, when L/P ratio increases from 0.6 to 1.0, bothstrengths of composite CPCs are higher than those of control CPCshaving identical porosities, suggesting that Si-HPMC does have astrengthening effect on CPCs (Fig. 6B and D). In addition, thisstrengthening effect tends to be more remarkable in compositeCPCs with higher L/P ratios (Fig. 11B and D).

The strength of a CPC is not an intrinsic property, but dependson the fracture toughness and on the size of the largest flaw inthe material. As for the composite CPCs with L/P ratios of 0.4and/or 0.45, the increase in toughness should contribute toincreasing the flexural and compressive strengths, but the large de-fects caused by concomitantly entrained air bubbles (Fig. 8B andD), which act as large critical flaws, seem to counteract this benefit.This is especially the case for low L/P ratios, where the increase intoughness is small (Fig. 11C), resulting in reduced strengths. More-over, it is worth mentioning that the relative increase in flexuraland compressive strengths (Fig. 11B and D) is calculated with

toughness and (D) compressive strength of composite cements as a function of L/P




respect to the microporous control cements, where few macrop-ores can be found (Fig. 8A and C). This character is much differentfrom the Si-HPMC composite cement, which contains numerousmacropores (Fig. 8B and D), indicating that the relative increasein both strengths of composite cements is likely underestimated.However, despite this, there is still a very obvious trend that Si-HPMC has a strong strengthening effect on CPC, especially for thecements with high L/P ratios (from 0.6 to 1.0).

The curve of the less-brittle failure of Si-HPMC composite ce-ment (Fig. 7) also demonstrates the positive effect of Si-HPMC onthe fracture behavior of CPC. This is due to the already mentionedrole of the deformable hydrogel, which is able to continue with-standing stresses even when the brittle inorganic matrix is broken.This toughening of the material through crack bridging bystretched polymer ligaments enables the material to deform beforecatastrophic failure, i.e. it endows a certain tolerance to damage.Similar fracture characteristics are also observed in fiber-contain-ing CPCs [64]. However, compared to these fiber-containing ce-ments, Si-HPMC composite CPCs are easier to process regardinginjectability, cohesion and polymer distribution, and therefore ap-pear to be an attractive alternative.

5. Conclusion

A self-setting polysaccharide derivative, Si-HPMC, was incorpo-rated into the formulation of CPC to prepare novel injectable CPCswith comprehensively improved performances. The addition of Si-HPMC significantly increases the viscosity of CPCs pastes, endow-ing them with good injectability and outstanding cohesion. Owingto the gelation of Si-HPMC forming a three-dimensional network,the Si-HPMC composite cement pastes have a faster setting time,and show at the early stage of setting an appealing rheologicalbehavior which prevents them from flowing out from an openbone cavity. After hardening, Si-HPMC demonstrates a significanttoughening effect on CPC, and this effect becomes more obviouswith increasing mass fraction of Si-HPMC, as well as with increas-ing L/P ratio. Moreover, although strengths are often compromisedat lower L/P ratios (0.4, 0.45) by entrained air bubbles, which act ascritical defects, Si-HPMC also shows a strengthening effect on CPCdue to increasing fracture toughness, and the effect is moreremarkable with increasing L/P ratio. In summary, compared tothe purely inorganic CPCs reported in this study and in a recent re-view [53], Si-HPMC composite CPCs show not only excellent han-dling properties but also comparable/improved mechanicalproperties, being less brittle and having a certain tolerance to dam-age. Moreover, compared to composite CPCs reinforced by fibers[53,63], Si-HPMC composite CPCs are more injectable and cohesive.They thus appear to be an attractive candidate for bone substitu-tion, especially in the case of open bone cavities.

As a prospective study, since the viscous Si-HPMC solution,when mixed with solid phase of CPC, is very apt to entrap air bub-bles, which act as macropores after hardening of CPC, it would bedesirable to fabricate macroporous Si-HPMC composite CPCs withcontrollable macroporosity by voluntarily entrapping numerousair bubbles into the CPC during preparation. Finally, studies explor-ing both in vitro and in vivo biological responses appear necessarybefore designing a clinical study that would demonstrate the po-tential efficacy of this promising Si-HPMC composite CPC.

Acknowledgements

Financial support for this study was provided by the regionalprogram BIOREGOS II (Pays de la Loire, France). J.Z. would like tothank the China Scholarship Council for funding. Excellenttechnical assistance from Fanch Guillou and Yann Borjon-Piron isgreatly acknowledged.


Appendix A. Figures with essential colour discrimination

Certain figures in this article, particularly Figs. 3–7 and 10, aredifficult to interpret in black and white. The full colour imagescan be found in the on-line version, at http://dx.doi.org/10.1016/j.actbio.2014.03.009.

Appendix B. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.actbio.2014.03.009.

References

[1] Chow LC. Calcium phosphate cements: chemistry, properties, and applications.Mater Res Soc Symp Proc 2000;599:27–37.

[2] Bohner M. Physical and chemical aspects of calcium phosphates used in spinalsurgery. Eur Spine J 2001;10:S114–21.

[3] Lewis G. Injectable bone cements for use in vertebroplasty and kyphoplasty:state-of-the-art review. J Biomed Mater Res B Appl Biomater 2006;76B:456–68.

[4] LeGeros RZ, Chohayeb A, Shulman A. Apatitic calcium phosphates: possibledental restorative materials. J Dent Res 1982;61:343.

[5] Brown WE, Chow LC. A new calcium phosphate setting cement. J Dent Res1983;62:672–9.

[6] Ginebra MP, Espanol M, Montufar EB, Perez RA, Mestres G. New processingapproaches in calcium phosphate cements and their applications inregenerative medicine. Acta Biomater 2010;6:2863–73.

[7] Ambard AJ, Mueninghoff L. Calcium phosphate cement: review of mechanicaland biological properties. J Prosthodont 2006;15:321–8.

[8] Ginebra MP, Fernandez E, DeMaeyer E, Verbeeck R, Boltong MG, Ginebra J, et al.Setting reaction and hardening of an apatitic calcium phosphate cement. J DentRes 1997;76:905–12.

[9] Bohner M. Reactivity of calcium phosphate cements. J Mater Chem2007;17:3980–6.

[10] Comuzzi L, Ooms E, Jansen JA. Injectable calcium phosphate cement as a fillerfor bone defects around oral implants: an experimental study in goats. ClinOral Implants Res 2002;13:304–11.

[11] Tamimi F, Torres J, Lopez-Cabarcos E, Bassett DC, Habibovic P, Luceron E, et al.Minimally invasive maxillofacial vertical bone augmentation using brushitebased cements. Biomaterials 2009;30:208–16.

[12] Bai B, Jazrawi LM, Kummer FJ, Spivak JM. The use of an injectable,biodegradable calcium phosphate bone substitute for the prophylacticaugmentation of osteoporotic vertebrae and the management of vertebralcompression fractures. Spine 1999;24:1521–6.

[13] Turner TM, Urban RM, Singh K, Hall DJ, Renner SM, Lim T, et al. Vertebroplastycomparing injectable calcium phosphate cement compared withpolymethylmethacrylate in a unique canine vertebral body large defectmodel. Spine J 2008;8:482–7.

[14] Van der Stok J, Van Lieshout EM, El-Massoudi Y, Van Kralingen GH, Patka P.Bone substitutes in the Netherlands – a systematic literature review. ActaBiomater 2011;7:739–50.

[15] Bajammal SS, Zlowodzki M, Lelwica A, Tornetta P, Einhorn TA, Buckley R, et al.The use of calcium phosphate bone cement in fracture treatment. A meta-analysis of randomized trials. J Bone Joint Surg Am 2008;90A:1186–96.

[16] Bohner M, Gbureck U, Barralet JE. Technological issues for the development ofmore efficient calcium phosphate bone cements: a critical assessment.Biomaterials 2005;26:6423–9.

[17] Bohner M. Design of ceramic-based cements and putties for bone graftsubstitution. Eur Cell Mater 2010;20:1–12.

[18] Bohner M, Baroud G. Injectability of calcium phosphate pastes. Biomaterials2005;26:1553–63.

[19] Habib M, Baroud G, Gitzhofer F, Bohner M. Mechanisms underlying the limitedinjectability of hydraulic calcium phosphate paste. Acta Biomater2008;4:1465–71.

[20] Schmidt R, Cakir B, Mattes T, Wegener M, Puhl W, Richter M. Cement leakageduring vertebroplasty: an underestimated problem? Eur Spine J 2005;14:466–73.

[21] Khairoun I, Driessens F, Boltong MG, Planell JA, Wenz R. Addition of cohesionpromoters to calcium phosphate cements. Biomaterials 1999;20:393–8.

[22] Krebs J, Aebli N, Goss BG, Sugiyama S, Bardyn T, Boecken I, et al. Cardiovascularchanges after pulmonary embolism from injecting calcium phosphate cement.J Biomed Mater Res B Appl Biomater 2007;82B:526–32.

[23] Canal C, Ginebra MP. Fibre-reinforced calcium phosphate cements: a review. JMech Behav Biomed Mater 2011;4:1658–71.

[24] Khairoun I, Boltong MG, Driessens F, Planell JA. Some factors controlling theinjectability of calcium phosphate bone cements. J Mater Sci Mater Med1998;9:425–8.

[25] Ginebra MP, Driessens F, Planell JA. Effect of the particle size on the micro andnanostructural features of a calcium phosphate cement: a kinetic analysis.Biomaterials 2004;25:3453–62.






http://refhub.elsevier.com/S1742-7061(14)00120-2/h0005




































































[26] Burguera EF, Xu H, Sun LM. Injectable calcium phosphate cement: effects ofpowder-to-liquid ratio and needle size. J Biomed Mater Res B Appl Biomater2008;84B:493–502.

[27] O’Hara RM, Dunne NJ, Orr JF, Buchanan FJ, Wilcox RK, Barton DC. Optimisationof the mechanical and handling properties of an injectable calcium phosphatecement. J Mater Sci Mater Med 2010;21:2299–305.

[28] Chow LC, Hirayama S, Takagi S, Parry E. Diametral tensile strength andcompressive strength of a calcium phosphate cement: effect of appliedpressure. J Biomed Mater Res 2000;53:511–7.

[29] Barralet JE, Gaunt T, Wright AJ, Gibson IR, Knowles JC. Effect of porosityreduction by compaction on compressive strength and microstructure ofcalcium phosphate cement. J Biomed Mater Res 2002;63:1–9.

[30] Bohner M, Merkle HP, Landuyt PV, Trophardy G, Lemaitre J. Effect of severaladditives and their admixtures on the physico-chemical properties of acalcium phosphate cement. J Mater Sci Mater Med 2000;11:111–6.

[31] Sarda S, Fernandez E, Nilsson M, Balcells M, Planell JA. Kinetic study of citricacid influence on calcium phosphate bone cements as water-reducing agent. JBiomed Mater Res 2002;61:653–9.

[32] Barralet JE, Hofmann M, Grover LM, Gbureck U. High-strength apatitic cementby modification with alpha-hydroxy acid salts. Adv Mater 2003;15:2091–4.

[33] Gbureck U, Barralet JE, Spatz K, Grover LM, Thull R. Ionic modification ofcalcium phosphate cement viscosity. Part I. Hypodermic injection and strengthimprovement of apatite cement. Biomaterials 2004;25:2187–95.

[34] Xu HHK, Simon Jr CG. Fast setting calcium phosphate-chitosan scaffold:mechanical properties and biocompatibility. Biomaterials 2005;26:1337–48.

[35] Takagi S, Chow LC, Hirayama S, Eichmiller FC. Properties of elastomericcalcium phosphate cement–chitosan composites. Dent Mater 2003;19:797–804.

[36] Cherng A, Takagi S, Chow LC. Effects of hydroxypropyl methylcellulose andother gelling agents on the handling properties of calcium phosphate cement. JBiomed Mater Res 1997;35:273–7.

[37] Liu WZ, Zhang JT, Weiss P, Tancret F, Bouler JM. The influence of differentcellulose ethers on both the handling and mechanical properties of calciumphosphate cements for bone substitution. Acta Biomater 2013;9:5740–50.

[38] Bigi A, Bracci B, Panzavolta S. Effect of added gelatin on the properties ofcalcium phosphate cement. Biomaterials 2004;25:2893–9.

[39] Tamimi F, Kumarasami B, Doillon C, Gbureck U, Nihouannen DL, Cabarcos EL,et al. Brushite–collagen composites for bone regeneration. Acta Biomater2008;4:1315–21.

[40] Ishikawa K, Miyamoto Y, Kon M, Nagayama M, Asaoka K. Non-decay type fast-setting calcium phosphate cement: composite with sodium alginate.Biomaterials 1995;16:527–32.

[41] Alkhraisat MH, Rueda C, Marino FT, Torres J, Jerez LB, Gbureck U, et al. Theeffect of hyaluronic acid on brushite cement cohesion. Acta Biomater2009;5:3150–6.

[42] Xu H, Quinn JB. Calcium phosphate cement containing resorbable fibers forshort-term reinforcement and macroporosity. Biomaterials 2002;23:193–202.

[43] Gorst N, Perrie Y, Gbureck U, Hutton AL, Hofmann MP, Grover LM, et al. Effectsof fibre reinforcement on the mechanical properties of brushite cement. ActaBiomater 2006;2:95–102.

[44] Zuo Y, Yang F, Wolke J, Li YB, Jansen JA. Incorporation of biodegradableelectrospun fibers into calcium phosphate cement for bone regeneration. ActaBiomater 2010;6:1238–47.

[45] Perez RA, Kim H, Ginebra M. Polymeric additives to enhance the functionalproperties of calcium phosphate cements. J Tissue Eng 2012;3(1). http://dx.doi.org/10.1177/2041731412439555.

[46] Andrianjatovo H, Lemaıtre J. Effects of polysaccharides on the cementproperties in the monocalcium phosphate/b-tricalcium phosphate system.Innov Tech Biol Med 1995;16:140–7.


[47] Vinatier C, Magne D, Moreau A, Gauthier O, Malard O, Vignes-Colombeix C,et al. Engineering cartilage with human nasal chondrocytes and a silanizedhydroxypropyl methylcellulose hydrogel. J Biomed Mater Res A2007;80:66–74.

[48] Laib S, Fellah BH, Fatimi A, Quillard S, Vinatier C, Gauthier O, et al. The in vivodegradation of a ruthenium labelled polysaccharide-based hydrogel for bonetissue engineering. Biomaterials 2009;30:1568–77.

[49] Trojani C, Weiss P, Michiels JF, Vinatier C, Guicheux J, Daculsi G, et al. Three-dimensional culture and differentiation of human osteogenic cells in aninjectable hydroxypropylmethylcellulose hydrogel. Biomaterials2005;26:5509–17.

[50] Vinatier C, Magne D, Weiss P, Trojani C, Rochet N, Carle GF, et al. A silanizedhydroxypropyl methylcellulose hydrogel for the three-dimensional culture ofchondrocytes. Biomaterials 2005;26:6643–51.

[51] Fellah BH, Weiss P, Gauthier O, Rouillon T, Pilet P, Daculsi G, et al. Bone repairusing a new injectable self-crosslinkable bone substitute. J Orthop Res2006;24:628–35.

[52] Trojani C, Boukhechba F, Scimeca JC, Vandenbos F, Michiels JF, Daculsi G, et al.Ectopic bone formation using an injectable biphasic calcium phosphate/Si-HPMC hydrogel composite loaded with undifferentiated bone marrow stromalcells. Biomaterials 2006;27:3256–64.

[53] Zhang JT, Liu WZ, Schnitzler V, Tancret F, Bouler JM. Calcium phosphatecements (CPCs) for bone substitution: chemistry, handling and mechanicalproperties. Acta Biomater 2014;10:1035–49.

[54] Obadia L, Rouillon T, Bujoli B, Daculsi G, Bouler JM. Calcium-deficient apatitesynthesized by ammonia hydrolysis of dicalcium phosphate dihydrate:influence of temperature, time, and pressure. J Biomed Mater Res B ApplBiomater 2007;80:32–42.

[55] Bourges X, Weiss P, Daculsi G, Legeay G. Synthesis and general properties ofsilated-hydroxypropyl methylcellulose in prospect of biomedical use. AdvColloid Interface Sci 2002;99:215–28.

[56] Fatimi A, Tassin JF, Quillard S, Axelos M, Weiss P. The rheological properties ofsilated hydroxypropylmethyl cellulose tissue engineering matrices.Biomaterials 2008;29:533–43.

[57] Fatimi A, Tassin JF, Turczyn R, Axelos M, Weiss P. Gelation studies of acellulose-based biohydrogel: the influence of pH, temperature andsterilization. Acta Biomater 2009;5:3423–32.

[58] Fatimi A, Axelos M, Tassin JF, Weiss P. Rheological characterization of self-hardening hydrogel for tissue engineering applications: gel pointdetermination and viscoelastic properties. Macromol Symp 2008;266:12–6.

[59] Dlouhy I, Holzmann M, Man J, Valka L. The use of chevron-notched specimensfor fracture-toughness determination of bearing steels. Kovove Mater1994;32:3–13.

[60] Baroud G, Crookshank M, Bohner M. High-viscosity cement significantlyenhances uniformity of cement filling in vertebroplasty: an experimentalmodel and study on cement leakage. Spine 2006;31:2562–8.

[61] Bohner M, Baroud G, Gasser B. Snapshot: critical aspects in the use ofinjectable calcium phosphates in spinal surgery. Biomaterials2010;31:4609–11.

[62] Espanol M, Perez RA, Montufar EB, Marichal C, Sacco A, Ginebra MP. Intrinsicporosity of calcium phosphate cements and its significance for drug deliveryand tissue engineering applications. Acta Biomater 2009;5:2752–62.

[63] Zhang JT, Tancret F, Bouler JM. Fabrication and mechanical properties ofcalcium phosphate cements (CPCs) for bone substitution. Mater Sci Eng CMater Biol Appl 2011;31:740–7.

[64] O’Hara RM, Orr JF, Buchanan FJ, Wilcox RK, Barton DC, Dunne NJ. Developmentof a bovine collagen–apatitic calcium phosphate cement for potential fracturetreatment through vertebroplasty. Acta Biomater 2012;8:4043–52.























































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a novel injectable, cohesive and toughened si-hpmc (silanized-hydroxypropyl methylcellulose)...

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