Bioactive poly(etheretherketone) composite containing calcium polyphosphate and multi-walled carbon nanotubes for bone repair: Mechanical property and in vitro biocompatibility

Abstract

Poly(etheretherketone) exhibits good biocompatibility, excellent mechanical properties, and bone-like stiffness. However, the natural bio-inertness of pure poly(etheretherketone) hinders its applications in biomedical field, especially when direct bone-implant osteo-integration is desired. For developing an alternative biomaterial for load-bearing orthopedic application, combination of bioactive fillers with poly(etheretherketone) matrix is a feasible approach. In this study, a bioactive multi-walled carbon nanotubes/calcium polyphosphate/poly(etheretherketone) composite was prepared through a compounding and injection-molding process for the first time. Bioactive calcium polyphosphate was added to polymer matrix to enhance the bioactivity of the composite, and incorporation of multi-walled carbon nanotubes to composite was aimed to improve both the mechanical property and biocompatibility. Furthermore, the microstructures, surface hydrophilicity, and mechanical property of multi-walled carbon nanotubes/calcium polyphosphate/poly(etheretherketone) composite, as well as the cellular responses of MC3T3-E1 osteoblast cells to this material were investigated. The mechanical testing revealed that mechanical performance of the resulting ternary composite was significantly enhanced by adding the multi-walled carbon nanotubes and the mechanical values obtained were close to or higher than those of human cortical bone. More importantly, cell culture tests showed that initial cell adhesion, cell viability, and osteogenic differentiation of MC3T3-E1 cells were significantly promoted on the multi-walled carbon nanotubes/calcium polyphosphate/poly(etheretherketone) composite. Accordingly, the multi-walled carbon nanotubes/calcium polyphosphate/poly(etheretherketone) composite may be used as a promising bone repair material in dental and orthopedic applications.

Keywords

Poly(etheretherketone)calcium polyphosphate multi-walled carbon nanotubes composite mechanical property cellular responses bone repair

Introduction

In the past few years, there has been a substantial increase in the number of accidents, which resulted in unavoidable bone or dental defects. Furthermore, with the aging population, the elderly people are more likely to suffer from bone fractures, imposing significant economic and social burden to our society every year.¹ At present, the most popular bone reconstruction materials are inert metal alloys. However, metallic implants such as stainless steel and chromium–cobalt alloys release cytotoxic metal ions in vivo after long time corrosion in human body fluids,^2–4 leading to some postoperative complications like allergy and inflammation.⁵ Moreover, metallic materials also showed a stress-shielding problem on account of the mismatch of elastic modulus between metal alloys and human cortical bones.⁶ Hence, considerable attention was directed toward the development of polymer composites for the fabrication of novel bone substitution materials.

Among polymers and their composites, poly(etheretherketone) (PEEK) is regarded as a prime candidate for replacing traditional surgical metal implants due to its good biocompatibility, excellent mechanical properties, and bone-like stiffness.^7,8 Nevertheless, PEEK is still a bioinert polymer because it has hydrophobic surface and unable to contribute to the formation of good bone–implant integration due to the lack of chemical bond between implants and human bone tissue.⁹ To settle this problem, various bioactive fillers such as hydroxyapatite (HA),^10–12 bioactive glass (BG),¹³ and β-tricalcium phosphate (β-TCP)¹⁴ have been incorporated into PEEK polymers through blending to obtain composites with enhanced bioactivity.

Calcium polyphosphate (CPP) is a natural polymer that exists in bone-forming cells as well as blood platelets.¹⁵ As another calcium phosphate-based bio-ceramic with similar chemical structure of HA, CPP has been designed as scaffolds for bone repair and regeneration because of its appropriate mechanical performance, excellent biocompatibility, and recognized osteo-conductivity.^16–19 CPP has an inductive effect on the growth of osteoblast cells because the energy produced by the breakage of P-O-P bonds between [PO₃] units can accelerate the breaking of high-energy anhydride linkages of the adenosine triphosphate.²⁰ Müller et al.²¹ have indicated that bioactivity of alkaline phosphatase expression of CPP was even prior to HA and β-TCP by investigating in vitro cellular responses of SaOS-2 cells. Qin et al.²² also reported that CPP possessed better cytocompatibility compared with HA for dental tissue engineering. However, up to now, although conventional HA/PEEK composites have been studied extensively and already used for spine fusion applications,^7,23 no investigation has been made on the preparation of CPP-based PEEK composite, not to speak of its bioactivity and biocompatibility.

As recognized, multi-walled carbon nanotubes (MWCNTS) have been extensively used as ideal reinforcing fillers in many thermoset or thermoplastic polymers for improving the mechanical performance of composites.^24–27 Moreover, MWCNTS are generally non-toxic and exhibit a good biocompatibility as they can promote the adhesion and proliferation of osteoblasts on their surfaces.^28,29 Thus, MWCNTS can enhance the mechanical properties as well as biocompatibility of resulting composites.

Taken together, to combine the advantages of the various components, a novel MWCNTS/CPP/PEEK composite was fabricated by hybridizing bioactive CPP and MWCNTS into PEEK for the first time. The morphology, surface hydrophilicity, and mechanical properties of the resulting biocomposite were investigated. In addition, adhesion, proliferation, metabolic activity, and osteogenic differentiation of the newborn mouse pre-osteoblast cells (MC3T3-E1) on the ternary composites were also evaluated in vitro to examine the potential of this biomaterial for biomedical load-bearing applications.

Experiment

Materials

A commercially available PEEK powder (450P; Victrex plc, Lancashire, UK) was used as received (Figure 1(a)) and mean particle diameter of PEEK was 113 μm as shown in particle size distribution in Figure 2(a). The melting point and density of this medium-viscosity-grade PEEK polymer were measured to be 343°C and 1.3 kg/m³, respectively. MWCNTS aqueous dispersion was supplied by Chengdu Organic Chemicals Co., Ltd. (Chengdu, China). The outside diameter of the nanotubes is about 50 nm, length about 10–30 μm, and purity more than 95 wt% (see Figure 1(c)). Monocalcium phosphate (MCP) was purchased from Sigma-Aldrich Co., Ltd (St. Louis, USA). and other reagents (analytically pure) were obtained from Kelong Chemical Reagent Co., Ltd. (Chengdu, China). All the reagents were used as received without further purification.

Preparation and characterization of CPP particles

MCP was first added in corundum crucible (300 mL) and calcined at 500°C for 5 h. Then, the temperature was raised to 800°C and kept for next 20 h. Subsequently, the resulting powder was heated to 1200°C under atmospheric conditions, resulting in powder melting. Then, the melt was promptly quenched in distilled water. The amorphous frit was milled and screened to yield powder (Figure 1(b)). The average size of CPP powder was approximately 21 µm (see Figure 2(b)). Finally, resulting CPP powder was annealed at 600°C for 25 h to increase the crystallinity of inorganic polymer matrix and characterized by the X-ray diffraction measurement (XRD Space Universal; SEIFERT, Germany). The average chain length of CPP was detected by the analysis of liquid-state ³¹P nuclear magnetic resonance (³¹P-NMR) measurements.

Preparation of MWCNTS/CPP/PEEK composites

For each sample, quantitative amount of PEEK and CPP particles (20 wt%) were first dispersed independently in 200 mL of ethanol and then treated in an ultrasonic bath for 30 min. Then, the separate PEEK and CPP turbid solution were mixed under intensive magnetic stirring for 4 h. After that, MWCNTS aqueous dispersion was added dropwise into the mixed solution and the MWCNTS content was maintained at 2 wt%, 4 wt%, and 6 wt%. The aqueous mixture was under constant stirring and ultrasonic bath for another 2 h. Subsequently, the mixture was filtered through suction filtration and was dried in vacuo at 120°C for 24 h to make sure that all the solvent was completely removed. Finally, the mixture was further molded by an injection-molding machine (BOY-22A, Munich, Germany) to obtain various specimens. The main processing parameters were shown below: barrel temperature, 340°C–385°C; nozzle temperature, 395°C; injection pressure, 13–18 MPa. Mini dumb-bell–shaped specimens were used for tensile test. Rectangular specimens were molded for bending test and circular disks were mainly used for cell culture test. The specimens of pure PEEK and CPP/PEEK composites were also prepared in accordance with the same processing and used as control group. The chemical compositions of all samples are listed in Table 1.

Table 1.

Samples of PEEK, CPP/PEEK, and MWCNTS/CPP/PEEK composites.

Samples	MWCNTS (wt%)	CPP (wt%)
PEEK	0	0
20% CPP/PEEK	0	20
2% MWCNTS/20% CPP/PEEK	2	20
4% MWCNTS/20% CPP/PEEK	4	20
6% MWCNTS/20% CPP/PEEK	6	20

PEEK: poly(etheretherketone); MWCNTS: multi-walled carbon nanotubes; CPP: calcium polyphosphate.

Mechanical performance tests of composites

The mechanical properties such as modulus and strength of composites were carried out using a universal testing machine (CMT4503, SANS, Shenzhen, China) at room temperature. The tensile testing was conducted in terms of the ASTMD638 procedures and the cross-head speed was 1 mm/min. The bending testing was measured using the ASTMD790-10 procedures. For each set of composite, five duplicate samples were tested. The average values and standard deviation were reported.

Morphological investigation

The morphologies and microstructure of fracture surfaces of the composites were examined by a field emission scanning electron microscopy (JSM-5900LV; JEOL, Tokyo, Japan). Before observation, to avoid charging effects, the surface of composites was coated with a thin gold plated layer.

Water contact angle

A goniometer (SL200L; KINO, Boston, MA, USA) was used to measure the water static contact angle at room temperature and atmospheric pressure. The drop volume of distilled water was 3 μL. Each PEEK, CPP/PEEK, and MWCNTS/CPP/PEEK composites specimen was measured five times in different locations to report an average value of water contact angle.

Cell culture

Mouse embryo osteoblastic MC3T3-E1 (ATCC, CRL-2593, BeNa Culture Collection, Beijing, China) cells were used to assess the cellular biocompatibility and the biological responses of PEEK, CPP/PEEK, and MWCNTS/CPP/PEEK composites. Prior to cell culture, all the injection-molded specimens were effectively sterilized by ethylene oxide. Then, the specimens were immersed in culture medium without fetal bovine serum for 1 day. After that, all the samples were placed in 96-well culture plates. The MC3T3-E1 osteoblasts were directly cultured on the surface of specimens in α-modified essential medium supplemented with 10 vol% fetal calf serum, 100 mg/L streptomycin, and 100 U/mL penicillin in a humidified incubator at 37°C with 5% carbon dioxide. The culture medium was replaced every day.

Cell adhesion analysis

Fluorescent staining and microscopy analysis were also used to investigate the cell adhesion and viability of osteoblasts on the PEEK and MWCNTS/CPP/PEEK composite surface. After cell incubation for 4 and 8 h, each sample was rinsed twice with phosphate-buffered saline (PBS) and fixed with 4% paraformaldehyde solution for 30 min. Then, living MC3T3-E1 osteoblast cells were stained using acridine orange-ethidium bromide (AO-EB; Sigma) (0.1 g/mL). Then, the cells continued being incubated with AO-EB for 30 min in the dark and subsequently observed by a fluorescence inversion microscope system (OLYMPUS BX60; Olympus, Tokyo, Japan) after being rinsed three times with PBS.

Cell proliferation and spreading

Cell proliferation and metabolic viability were estimated depending on 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. For all the samples, the cell density was 5 × 10⁴ cells/well. The samples were incubated under a humidified condition at 37°C containing 5% carbon dioxide. Then, at the determined time of 1, 4, and 7 days, MTT solution (5 mg/mL) was added to every well and the cells continued to be cultured for another 3.5 h at the same condition. After that, supernatant culture medium was aspirated and dimethyl sulfoxide (DMSO) was added in each well. Finally, the plates were swayed and the optical density (OD) was measured by a microplate reader (Multiskan FC; Thermo, Waltham Mass, USA).

Scanning electron microscopic assay for cell morphology

Following the incubation of 1, 4, and 7 days, each specimen was rinsed twice with PBS and the attached cells were fixed with 2.5% glutaraldehyde. After fixation, samples were dehydrated in a gradient series of ethanol aqueous solutions (30%, 50%, 70%, 80%, 90%, 95%, 100%, v/v). Then, the dehydrated cells were dried under vacuum and covered with gold prior to SEM observation.

Alkaline phosphatase activity assay

In the alkaline phosphatase (ALP) activity measurement, after being cultured on substrates for 7, 10, and 14 days, osteoblast cells on each sample surface were lysed by the lysis solution for 1 h. Then, cell lysates were centrifuged and the supernatant was aspirated to another 96-well plates. Afterward, the quantitative 4-nitrophenyl phosphate was added in each well. The 4-nitrophenyl phosphate was hydrolyzed to colored 4-nitrophenol by ALP. Finally, the ALP activity was measured using a multimode microplate reader (Multiskan FC; Thermo). The ALP activity was normalized to the total protein concentration using BCA protein assay kit (Sigma-Aldrich, USA).

Statistical analysis

The numerical data in experiment was expressed as the average value ± standard deviation. Statistical analysis was determined according to Student’s t test analysis, and a statistical difference was defined as statistically significant only if p < 0.05.

Results and discussion

Characterization of CPP powder

Figure 3(a) shows the XRD pattern of the prepared CPP particles. From the pattern, it was found that XRD peaks of CPP were in agreement with the characteristic diffraction peaks of XRD profile of β-CPP (JCPDS #77-1953), especially three high characteristic peaks.³⁰ The results of this analysis suggested the desired crystalline phase of β-CPP for the resulting CPP powder.

Figure 3(b) shows the liquid-state ³¹P-NMR spectra of CPP powder. Q⁰ corresponded to orthophosphate groups having no bridging oxygen, whereas Q¹ described an end phosphate group with only one oxygen bridging to a neighboring tetrahedral, and Q² described an internal phosphate with two oxygen bridging to two neighboring tetrahedral, which was indicative of a long-chain polyphosphate structure in CPP.³¹ Comparative average polymerization degree was calculated by integrating standardized delimited areas under the respective peaks for the ortho groups (Q⁰), end groups (Q¹), and internal groups (Q²)

P D = \frac{Q^{0} + Q^{1} + Q^{2}}{Q^{0} + \frac{1}{2} Q^{1}}

(1)

As shown in Figure 3(b), there was no chemical displacement of Q⁰, indicating a complete reaction of MCP. The polymerization degree of CPP calculated through equation (1) was approximately 40. The value was close to the chain length of natural medium-chain CPP from human platelets,¹⁵ ensuring the biocompatibility of the synthetic CPP we used.

Morphology of MWCNTS/CPP/PEEK composites

Figure 4 shows the typical SEM images of MWCNTS/CPP/PEEK composite. A brittle fracture surface was observed and some particles with high electron density (white dots) were uniformly distributed in the PEEK matrix, showing the homogeneity was maintained after injection molding (Figure 4(a)). Morphologies and chemical compositions of the white dots were characterized by SEM and energy dispersive spectroscopy (EDS), respectively, as shown in Figure 4(b) and (c). It was seen that C and O elements could be detected in addition to Ca and P elements, indicating that the white dots were dispersive CPP particles (see Figure 4(c)). Besides, closer examination revealed that the main fracture mechanism was adhesive failure, as seen from the particulate debonding (red circles in Figure 4(b)), suggesting the presence of weak interaction at the CPP-PEEK interface. MWCNTS (4 wt%) showed a homogeneous dispersion in PEEK composite and no obvious ring holes were found around the MWCNTS due to a good interfacial adhesion between MWCNTS and PEEK matrix phases (Figure 4(d)). However, when the MWCNTS content reached 6 wt%, some large clusters and aggregates were observed (Figure 4(e)), which might induce defects in reinforcement phase.

Mechanical properties of MWCNTS/CPP/PEEK composites

Mechanical properties of PEEK, CPP/PEEK, and MWCNTS/CPP/PEEK samples are summarized in Table 2. The CPP fillers enhanced the tensile modulus of PEEK. For example, at 20 wt% CPP content, the tensile modulus of binary composites increased from 3.87 to 6.25 GPa, almost increasing 61.4%. It is worth mentioning that the addition of MWCNTS also enhanced the tensile modulus of CPP/PEEK composites. The addition of 6 wt% MWCNTS to PEEK matrix increased tensile modulus of composite to 7.56 GPa. This improvement resulted from the inherent nature of MWCNTS, of which the elastic modulus was 0.9 TPa and far exceeded that of CPP and PEEK matrix.³²

Table 2.

Mechanical properties of PEEK and its composites.

Samples	Tensile strength (MPa)	Bending strength (MPa)	Tensile modulus (GPa)
PEEK^a	91 ± 1.4	140 ± 3.8	3.87 ± 0.21
20% CPP/PEEK	67 ± 3.6	107 ± 5.2	6.25 ± 0.38
2% MWCNTS/20% CPP/PEEK^a	74 ± 2.9	123 ± 2.7	6.72 ± 0.19
4% MWCNTS/20% CPP/PEEK^a	88 ± 3.0	142 ± 2.6	7.12 ± 0.16
6% MWCNTS/20% CPP/PEEK^a	79 ± 5.8	127 ± 3.5	7.56 ± 0.20
Human cortical bone³³	50–150	100–170	7–30

PEEK: poly(etheretherketone); MWCNTS: multi-walled carbon nanotubes; CPP: calcium polyphosphate.

Significant differences compared with the other four groups (p < 0.05).

Since CPP is a bio-ceramic material essentially, it exhibits mechanical weakness and high brittleness. Thus, both tensile and bending strength of CPP/PEEK composites dropped to 67 and 107 MPa, respectively. The tensile and bending strength of composite increased to 74 and 123 MPa after 2 wt% MWCNTS was incorporated into composite. Because of the good interfacial adhesion between MWCNTS and PEEK matrix as well as the uniform dispersion of nanotubes throughout the composites, MWCNTS can penetrate into and entangle with the polymer matrix (see Figure 4(d)), thus resulting in evident reinforcing results aforementioned. The optimal content of MWCNTS was proved to be 4 wt%, and in this proportion, corresponding tensile and bending strengths of CPP/PEEK composites were improved to 88 and 142 MPa. However, when the MWCNTS content increased to the 6 wt%, the mechanical strengths began to decrease and were even close to those 2 wt% MWCNTS-reinforced composite. This may be owing to the agglomeration of nanotubes in composite (see Figure 4(e)), which deteriorates rather than enhances the mechanical properties of the composites. As a general rule, inorganic bio-ceramics fillers can improve the modulus of composite at the expense of strength.³⁴ Based on the result of mechanical testing, appropriate amount of MWCNTS was confirmed to be able to compensate for the dramatical mechanical loss caused by the addition of fragile CPP.

As is well known, sufficient mechanical support is one of the crucial premises for successful application as bone substitution materials. The tensile strength of human cortical bone ranged from 50 to 150 MPa and tensile modulus ranged from 7 to 30 GPa, respectively. In this study, for the 4 wt% MWCNTS/20 wt% CPP/PEEK ternary composite, both the tensile and bending strengths exceeded the average values of human cortical bone, indicating its potential as a biomaterial for load-bearing implants.

Hydrophilic properties of composites

The wetting analysis of samples is shown in Figure 5 and the data results are summarized in Table 3. The contact angle of PEEK surface is 82.1° and decreased markedly to 65.7° after incorporation of CPP, suggesting that CPP/PEEK composites surface was more hydrophilic than pure PEEK. This is due to the hydrophilic surface of ceramic CPP in nature. Besides, adding MWCNTS further reduced contact angle of composites. When 6% MWCNTS was incorporated in CPP/PEEK composites, the contact angle further dropped to 60.8°. Similar tendency was also reported in other MWCNTS-reinforced PEEK composites.³⁵ Previous studies have confirmed that hydrophilic surfaces are more favorable for osteoblasts’ attachment and proliferation relative to hydrophobic surfaces.^36,37 In this regard, MWCNTS/CPP/PEEK composite provided a favorable surface for cell growth.

Table 3.

Water contact angles on PEEK, CPP/PEEK, and MWCNTS/CPP/PEEK composites.

Samples	Water contact angle (°)
PEEK^a	82.1 ± 0.5
20% CPP/PEEK^a	65.7 ± 0.3
2% MWCNTS/20% CPP/PEEK^a	64.1 ± 0.5
4% MWCNTS/20% CPP/PEEK^a	61.7 ± 0.4
6% MWCNTS/20% CPP/PEEK	60.8 ± 0.3

PEEK: poly(etheretherketone); MWCNTS: multi-walled carbon nanotubes; CPP: calcium polyphosphate.

Significant differences compared with the other four groups (p < 0.05).

Cell proliferation and metabolic viability

As is known to us, initial cell adhesion is important and responsible for the following cellular functions and eventual tissue integration.^38,39 After cell attachment, a series of processes including cell proliferation and differentiation continue to occur.^40,41 The qualitative analysis of AO-EB staining was examined to evaluate the cellular adherence of osteoblast cells on the surface of pure PEEK, CPP/PEEK, and MWCNTS/CPP/PEEK composites. As shown in Figure 6, after cell culture for 4 and 8 h, more osteoblast cells grew on the CPP/PEEK and MWCNTS/CPP/PEEK composites than on pure PEEK, suggesting that both binary and ternary composites appeared to be favorable for the cell adhesion and proliferation of MC3T3-E1 osteoblasts in the early stage. The morphologies and amount of cells on CPP/PEEK and MWCNTS/CPP/PEEK groups were not significantly different, which revealed that MWCNTS did not reduce cellular activity.

The cell proliferation and morphologies of MC3T3-E1 osteoblast cells seeded on the material surface were observed through SEM imaging (Figure 7). After being incubated for 1 day, cells anchored tightly on the surfaces of CPP/PEEK and MWCNTS/CPP/PEEK composites through a small number of pseudopodia, whereas osteoblasts on the pure PEEK surface displayed an elongated and fusiform morphology with fewer pseudopodia. After cultivation for 4 days, osteoblasts grew and exhibited a more stretched cellular morphology on composites than those on pure PEEK. After being cultured for 7 days, osteoblast cells on MWCNTS/CPP/PEEK composites attached more firmly on material with larger coverage region than those on pure PEEK and CPP/PEEK surface. However, it is noted that the SEM figures are qualitative observations only. In order to understand the cytocompatibility of composites more deeply, the quantitative analysis will give a more accurate result.

Figure 8 demonstrates the cell metabolic activity of MC3T3-E1 osteoblast cells on PEEK, CPP/PEEK, and MWCNTS/CPP/PEEK composites surface using an MTT assay, and PEEK was regarded as the control group. The CPP/PEEK and MWCNTS/CPP/PEEK composite groups all showed higher OD values at every test point compared to the pure PEEK control, suggesting that addition of CPP promoted the proliferation of MC3T3-E1 cells. More importantly, it is worth noting that that after incorporation of MWCNTS into CPP/PEEK, the cell metabolic viability of MC3T3-E1 cells further increased, revealing that MWCNTS facilitated the proliferation of MC3T3-E1 cells.

In vitro osteo-differentiation evaluation

After attachment and proliferation, the osteogenic differentiation of osteoblast cells has a great influence on the bone formation at the interface between bone tissues and implants.⁴² As a marker for the early differentiation of osteoblasts, ALP regulates the inorganic phosphate metabolism by hydrolyzing phosphate esters and functions as a plasma membrane transporter for inorganic phosphates.⁴³ Therefore, ALP is one of the major osteogenic hallmarks and the ALP will increase during the osteo-differentiation of osteoblast cells. Figure 9 shows the ALP activity of MC3T3-E1 osteoblast cells seeded on PEEK, CPP/PEEK, and MWCNTS/CPP/PEEK composites. The quantitative analysis revealed that, for both binary and ternary composites, the expression level of ALP was significantly higher than that on pure PEEK after being cultured for 10 and 14 days. Several literature have demonstrated that CPP can activate osteoclasts and act as an inducer of ALP, having a positive influence on cell metabolism and triggering an upregulation of the ALP.^21,44 The MWCNTS have been reported by many research teams to possess bone induction potential.⁴⁵ It is interesting to note that the ALP activity of cells on MWCNTS/CPP/PEEK composites can further enhanced when compared to CPP/PEEK composite, indicating that an enhancement of the osteogenic differentiation. In a previous study, CNTS coating on the collagen sponge was found to promote the cell adhesion of MC3T3-E1 cells.⁴⁶ Furthermore, MWCNTS and carbon fiber have also been reported to improve osteoblastic proliferation and differentiation by promoting protein–material interactions.⁴⁷ The experimental results we got also ascertained the feasibility of introducing MWCNTS to PEEK for improving biocompatibility.

Conclusion

Biocompatible MWCNTS/CPP/PEEK composite was successfully fabricated through a compounding and injection-molding process for the first time. By combining the advantages of CPP and MWCNTS, this ternary composite exhibited appropriate mechanical property and good biocompatibility. The mechanical performance of the resultant composites was close to or higher than those of cortical bone. Furthermore, cellular experiment confirmed that the cell adhesion, proliferation, and differentiation of MC3T3-E1 osteoblast cells were promoted in vitro on the MWCNTS/CPP/PEEK composites. Moreover, the MTT and ALP results demonstrated that MWCNTS could further promote the cell vitality and osteogenic differentiation of osteoblast cells.

Thus, this MWCNTS/CPP/PEEK ternary composite with excellent mechanical property and improved bioactivity reveals the potential as a bone repair material for use in bone tissue engineering.

Footnotes

Acknowledgements

C.X. conceived and designed the experiments and performed the analysis with constructive discussions. J.C. performed the experiments. Y.L. and L.Z. analyzed the data. H.C. contributed reagents/materials/analysis tools.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article:This research was supported by the Science and Technology supporting program of Sichuan province, China (no. 2014SZ0128) and the Science and Technology project of Jiangsu province, China (no. BE201661).

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