Graphene oxide reinforced poly(vinyl alcohol): nanocomposite scaffolds for tissue engineering applications

Abstract

In this study, graphene oxide (GO) is incorporated into poly(vinyl alcohol) (PVA) for the purpose of improving the mechanical properties. Nanocomposite scaffolds with an interconnected porous structure are fabricated by selective laser sintering (SLS). The results indicate that the highest improvements in the mechanical properties are obtained, that is, a 60%, 152% and 69% improvement of compressive strength, Young's modulus and tensile strength is achieved at the GO loading of 2.5 wt%, respectively. The reason can be attributed to the enhanced load transfer due to the homogeneous dispersion of GO sheets and the strong hydrogen bonding interactions between GO and the PVA matrix. The agglomerates and restacking of GO sheets occur on further increasing the GO loading, which leads to the decrease in the mechanical properties. In addition, osteoblast-like cells attach and grow well on the surface of scaffolds, and proliferate with increasing time of culture. The GO/PVA nanocomposite scaffolds are potential candidates for bone tissue engineering.

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1 Introduction

PVA, a water-soluble synthetic polymer, can be used as a scaffold material for good biodegradability and biocompatibility.^1–3 It provides excellent pH stability, flexibility and semi permeability, which are necessary for cell survival.^4,5 Recently, PVA has been used in a number of biomedical applications including bone substitute material, bone scaffold coatings, cartilage implants, etc.^6–11 However, PVA has a rather low mechanical strength since it is a ductile polymer.¹² One of the most effective methods for improving the mechanical properties of a polymer is to incorporate a reinforcement phase.^13–16

GO has very high mechanical properties (Young's modulus >0.5–1 TPa, tensile strength ∼130 GPa),^17,18 making it as the best candidates for reinforcement phase of polymer. It consists of a two-dimensional sheet of covalently bonded carbon atoms bearing various oxygen functional groups (such as hydroxyl, carboxyl and epoxy groups) on its surface.^19,20 Therefore, GO is hydrophilic and can be readily dispersed in water as individual sheets. Meanwhile, the oxygen functional groups can form strong hydrogen bonding interactions with polymer molecule chains that also contain a lot of surface hydrophilic groups (such as hydroxyl and carboxyl groups),^21–23 which can enhance the interfacial adhesion between them and eventually improve the mechanical properties.

Wang et al.²⁴ prepared GO-reinforced PVA composite films and found that a 212% improvement of tensile strength and a 34% increase in elongation at break are achieved by addition of 0.5 wt% of GO. Xu et al.²⁵ prepared a kind of PVA/GO composite film simply by vacuum filtration and found that the Young's modulus and tensile strength of the film containing 3 wt% GO increased by 70% and 128%, respectively. Wang et al.²⁶ fabricated GO/PVA composite nanofibers using electrospinning method and found that a loading of 0.02 wt% GO increased the tensile strength of the nanofibers 42 times. Furthermore, studies^27–29 have demonstrated that GO has excellent biocompatibility, enhanced cellular attachment and proliferation, and good apatite forming ability.

Herein, GO is introduced as a reinforcement phase to enhance the mechanical properties of PVA. The GO/PVA nanocomposite scaffolds are successfully fabricated via SLS technique, and the microstructure, mechanical properties and cytocompatibility are investigated. The phase composition and the interaction between GO and PVA matrix are investigated using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The microstructure is characterized by scanning electron microscope (SEM). The compressive and tensile properties are investigated by compression and tensile tests, respectively. Meanwhile, the cytocompatibility is confirmed by the growth of MG-63 cells on the scaffolds.

2 Materials and methods

2.1 Materials

GO (purity >99%, single layer ratio >99%) is purchased from Nanjing Jcnano Technology Co., Ltd (Nanjing, China), with a diameter of 1–5 μm and a thickness of 0.8–1.2 nm. It is synthesized from graphite powders using a normal Hummers method. PVA powders (average molar weight MW = 89 000–98 000 g mol⁻¹, polymerization degree PD = 1700) are purchased from Nippon Synthetic Chemical Industry Co., Ltd (Tokyo, Japan), with 99% degree of hydrolysis and the particle size ranging from 20 to 200 μm. Human osteoblast-like MG-63 cell line is obtained form American Type Culture Collection (ATCC, Rockville, MD). Dulbecco's modified Eagle's medium (DMEM) and fetal bovine serum (FBS) are obtained from Life Technologies (Gibco®, Carlsbad, CA, USA). Phosphate buffer solution (PBS) is prepared from NaCl, KCl, Na₂HPO₄·2H₂O and KH₂PO₄, which are obtained from Sigma-Aldrich (Beijing, China). Other chemical reagents are analytical grade and use without further purification. All solutions are prepared using doubly distilled Millipore water and filtered by 0.45 μm membrane before use.

2.2 Preparation of GO/PVA composite powders

A preparation procedure for GO/PVA composite powders with GO loadings from 0 to 4.5 wt% is as follows: 2 g of PVA powders is weighted accurately using an electronic balance (Model FA1004, Changzhou Hengzheng Electronic Instrument Co., Ltd., China) with an accuracy of 0.1 mg. The powders are added to 30 mL of deionized water and the solutions are treated with an ultrasonic cleaning device (SK3300H, Shanghai Kudos Ultrasonic Instrument Co., Ltd., China) for 30 min at room temperature. Meanwhile, 2 mg of GO is added to 12 mL deionized water and ultrasonically dispersed for 60 min. A certain volume of the GO solutions are added into the flask after PVA is homogeneous dispersion in water, and then ultrasonically dispersed for 30 min. Finally, the homogeneous GO/PVA solutions are poured into a culture dish and evaporated slowly in air to form the GO/PVA composite powders which are then kept in an electrothermal blowing dry box (101-00S, Guangzhou Dayang Electronic Machinery Equipment Co., Ltd, China) at 50 °C until the weight reaches a constant value. A series of GO/PVA composite powders with various GO loadings (0, 0.5, 1.5, 2.5, 3.5 and 4.5 wt%) are produced.

2.3 Fabrication of nanocomposite scaffolds

The GO/PVA nanocomposite scaffolds are fabricated layer by layer using a home-made SLS system which mainly consist of a 100 W CO₂ laser (model Firestar® t-Series, Synrad Co., USA) with the wavelength 1064 nm. Manufacturing parameters for the scaffolds, namely laser power, scan speed, spot diameter, scan spacing and layer thickness, are set at 5 W, 400 mm min⁻¹, 1.6 mm, 2.7 mm and 0.1–0.2 mm, respectively. After the SLS process is completed, the scaffolds are allowed to cool inside the processing chamber for approximately 30 min and then removed from the powders bed. Unsintered powders surrounding the scaffold are brushed off and the scaffolds are cleaned by compressed air. The experimental specimens are divided into groups based on 0, 0.5, 1.5, 2.5, 3.5 and 4.5 wt% of GO loading and named as GO-0, GO-0.5, GO-1.5, GO-2.5, GO-3.5 and GO-4.5, respectively.

2.4 Characterizations

The morphologies of the raw PVA powders, the raw GO, the GO/PVA composite powders and the nanocomposite scaffolds are imaged using SEM (FEI Quanta-200, FEI Co., USA) at an accelerating voltage of 20 kV. All the specimens are placed onto carbon-coated copper substrates and sprayed with a thin layer of gold/palladium for 120 s using an auto fine coater (JFC-1600, JEOL, Ltd., Japan) before observation. The raw GO is observed using a field emission transmission electron microscope (TEM, JEM-2100F, JEOL Ltd., Japan) at 200 kV. The phase composition analysis is performed using XRD (D8-Advance, German Bruker Co., German) equipped with a Cu Kα radiation source (40 kV, 40 mA). The scaffolds are cut into thin pieces with thickness of about 1 mm and the surface of these specimens are scanned at the rate of 8° min⁻¹, a step size of 0.02° over the 2θ range of 10–50°. The functional groups of the specimens are investigated using FTIR (Nicolette TM 6700, Thermo Scientific Co., USA) by the KBr pellet method. The FTIR spectra are recorded in 400–4000 cm⁻¹ range with 2 cm⁻¹ resolution.

Mechanical properties tests (compressive and tensile tests) are performed using a universal testing machine (WD-D1, Shanghai Zhuoji instruments Co. LTD, China) at room temperature. For the compressive tests, the scaffold specimens (L × W × H = 16 × 16 × 12 mm³) are placed between two circular platens. All the specimens are compressed at a crosshead speed of 0.5 mm min⁻¹. The compressive strength is calculated by the loading force divided by the cross-section area. The Young's modulus is defined by the slope in the initial linear section of the stress–strain curve. For the tensile tests, the size of the specimens is 16 × 5 × 5 mm³, and the loading rate is 0.5 mm min⁻¹ with a gauge length of 10 mm.

2.5 Cell culture

MG-63 cells are cultured in DMEM containing 10% FBS, 5% penicillin/streptomycin antibiotics at 37 °C in a humidified atmosphere of 5% CO₂ and the medium is changed every 2 days. When the cells reach confluence, they are removed from the culture dish using 0.25% trypsin ethylenediaminetetraacetic acid (EDTA), centrifuged, and resuspended in DMEM. The scaffolds specimens (16 × 16 × 12 mm³) are sterilized by immersing in 70% ethanol for 30 min, washed three times with sterile distilled water for 30 min, and exposed to ultraviolet (UV) light for 30 min on each side. Then, 2 × 10⁵ cells per mL of the cell suspension is pipetted onto the scaffolds. The cells are permitted to adhere to the scaffolds for 30 min, and then 700 μL of medium is added to each well of a 12-well plate. The seeded scaffolds are maintained at 37 °C in a humidified atmosphere of 5% CO₂ and 95% humidified air for 1 day, 3, 5 and 7 days, and the medium is changed every 2 days. At predetermined time points, the scaffold-cell constructs are removed and rinsed with PBS three times. Cells on scaffolds are fixed at room temperature with 2.5% glutaraldehyde solution for 24 h. The scaffolds are then dehydrated through a series of graded ethanol solutions for 10 min. Scaffolds are allowed to dry overnight, coated with gold/palladium, and viewed under SEM (Tescan, Mira 3 FEG-SEM, TESCAN Co., Czech) at an accelerating voltage of 5.0 kV.

2.6 Statistical analysis

All quantitative data are presented as means ± standard error and are derived from at least six independent specimens. Statistical analysis is performed using Origin 8.0 (OriginLab Co., USA). Statistical comparisons are carried out using IBM SPSS Statistics version 19 (IBM Co., USA). Data are taken to be significant when *P < 0.05 and very significant when **P < 0.01, respectively.

3 Results and discussion

Well dispersed GO/PVA composite powders are prepared by ultrasonic dispersion as described in the materials and methods section. The micrograph of the raw PVA powders is shown in Fig. 1(a). The PVA powders are irregular in shape and widely distribution in particle sizes (approximately 20–200 μm). The TEM image of the raw GO is shown in Fig. 1(b). The GO has a silk like appearance and the wrinkles are clearly observed. The wrinkles are very important for preventing aggregation of graphene caused by van der Waals forces during drying process.^30,31 The digital photos of GO/PVA suspension with different GO loading are shown in Fig. 1(c). The color of the suspension changes from brown-yellow to black as the GO loading increases. The GO sheets are homogeneous dispersion in the PVA solution and the suspensions are very stable after ultrasonic dispersion for 30 min, and there is no precipitate or color change after standing for two weeks. The micrographs of the GO-2.5 composite powders are shown in Fig. 1d and e. The GO sheets are well dispersed in the PVA powders and intimately anchored on the PVA surface. Previous studies have shown that the GO sheets have enhanced interfacial interaction with PVA matrices and may hold considerable potential as new carbon-based nanofiller.³²

Fig. 1 (a) SEM image of the raw PVA powders, (b) TEM image of the raw GO, (c) photographs of GO/PVA suspension with different GO loading after ultrasonic dispersion, (d and e) SEM images of the GO-2.5 composite powders.

XRD is performed to characterize the quality of GO sheets dispersion in the PVA matrix. The patterns of the raw PVA powders, GO powders and GO-2.5 composite powders are shown in Fig. 2(a). Diffraction peaks of raw PVA powders are found at 19.50° (main), as well as 11.24°, 22.90° and 44.30° (minor).³³ The diffraction peak of GO is found at about 10.80°, which is consistent with those reported in the literature.^34,35 However, after GO is dispersed into the PVA matrix, the GO-2.5 composite powders only show the PVA diffraction peak, and the characteristic peak of GO disappears. It may be due to the relatively low content of GO in the PVA matrix.³⁶ The XRD patterns of the nanocomposite scaffolds with different CO loading are shown in Fig. 2(b). The diffraction peaks of GO-0 are same as the raw PVA powders. There are also no GO characteristic diffraction peaks in the patterns of the GO-0.5, GO-1.5 and GO-2.5. However, the diffraction peaks of GO at 10.80° appear for GO-3.5 and GO-4.5. It means that GO sheets are not individually dispersed in PVA matrix but rather in the form of few-layer GO.

Fig. 2 (a) XRD patterns of the raw PVA powders, GO powders and GO-2.5 composite powders, (b) XRD patterns of the nanocomposite scaffolds with different CO loading.

FTIR spectroscopy is a fast and sensitive method for detecting various chemical bonds in materials. The functional groups of the raw PVA powders, GO powders and GO-2.5 composite powders are shown in Fig. 3(a). In the spectrum of PVA, the bands at 3447, 2933 and 1660 cm⁻¹ are attributed to the O–H stretching vibration, C–H asymmetric stretching vibration and C=O stretching vibration in PVA.^37–39 The characteristics bands at 3417, 1715, 1618, 1400 and 1100 cm⁻¹ are assigned to the O–H stretching vibration, C=O stretching vibration of the carboxylic group, C=C stretching mode of the sp² network, O–H deformations of the C–OH groups and C–O stretching vibration, respectively.^40–42 There is no obvious change in the spectrum of the GO-2.5 composite powders as compare with raw PVA powders. The spectra of the nanocomposite scaffolds with different GO loading are shown in Fig. 3(b). Compared with GO-0 and GO-0.5, the O–H stretching peak shifts to a higher wavenumber (3471 cm⁻¹) and the C=O stretching peak (1660 cm⁻¹) is enhanced in the GO-1.5, GO-2.5, GO-3.5 and GO-4.5, which indicates that the presence of hydrogen bonding interactions between the hydroxyl groups on the PVA molecular chains and the oxygen-containing functional groups of GO.⁴³ Previous studies have shown that the oxygen-containing functional groups of GO can generate strong hydrogen bonding with the PVA matrix.^44,45

Fig. 3 (a) FTIR pattern of the raw PVA powders, GO powders and GO-2.5 composite powders, (b) FTIR pattern of the nanocomposite scaffolds with different CO loading.

In order to evaluate the dispersion state of the GO sheets in the PVA matrix, the surface morphologies of the GO-0, GO-0.5, GO-2.5 and GO-4.5 are observed using SEM, as shown in Fig. 4. PVA powders are melted and connected together while micropores are obtained after SLS process (Fig. 4a and b). The additions of GO sheets in the PVA matrix can change the surface morphologies (Fig. 4c and e). Few GO sheets is embedded in the PVA matrix and randomly distributed in the GO-0.5 (Fig. 4c), which may due to the low concentration of GO sheets in the PVA matrix. The GO sheets are more obviously and homogeneously distributed throughout the GO-0.5 (Fig. 4d). The homogeneous dispersion of GO sheets in the PVA matrix is beneficial to the significant improvement of mechanical properties.^46,47 In contrast, the GO sheets are severely agglomerated in the matrix (Fig. 4e and f) due to the higher concentration which makes GO to form irreversible agglomerates or even restack due to van der Waals force.⁴⁸ The agglomeration of GO sheets will reduce the specific surface area and cause sliding between the layers of the GO sheets, which result in a deterioration of the mechanical properties.⁴⁹ These results are in agreement with the results of previous studies that low concentrations of carbon-based nanofiller can uniformly dispersed in the polymer matrix, while carbon-based nanofiller are easily aggregation at higher concentrations.^50,51

Fig. 4 Surface morphologies of the scaffolds with different GO loading (a and b) 0 wt%, (c) 0.5 wt%, (d) 2.5 wt% and (e and f) 4.5 wt%.

The compressive and tensile mechanical behaviors of the nanocomposite scaffolds are important since scaffolds mostly undergo compressive or tensile stress when use as the bone substitutes. The typical compressive stress–strain curves for GO-0, GO-0.5, GO-1.5, GO-2.5, GO-3.5 and GO-4.5 are shown in Fig. 5(a). It is obvious that the addition of GO into the polymer matrix has a dramatic influence on the compressive properties of scaffolds. We can summarize this data by focusing on the compressive strength and Young's modulus as shown in Fig. 5(b). The compressive strength and Young's modulus are increased by 60% from 149.87 to 240.49 kPa and by 152% from 0.98 to 2.47 MPa as the GO loading is increased from 0 to 2.5 wt%, and then decreased to 199.32 kPa and 2.13 MPa as the loading is further increased to 4.5 wt%, respectively. The compressive strength and Young's modulus of GO-0.5, GO-1.5, GO-2.5, GO-3.5 and GO-4.5 are significant differences from those of (p < 0.05 or p < 0.01). The compressive strength of trabecular bone and cortical bone range from 0.1 to 16 MPa and from 130 to 180 MPa, respectively.^52,53 The compressive strength of the GO reinforced PVA scaffolds is falling in the range of trabecular bone but is much lower than that of cortical bone.

Fig. 5 Compressive properties of GO-0, GO-0.5, GO-1.5, GO-2.5, GO-3.5 and GO-4.5: (a) stress–strain curves, (b) compressive strength and Young's modulus. *P < 0.05 and **P < 0.01 (compared with GO-0), n = 6.

The tensile strength and elongation at break of the GO-0, GO-0.5, GO-1.5, GO-2.5, GO-3.5 and GO-4.5 are shown in Fig. 6(a). Like the compressive strength and Young's modulus, the tensile strength and elongation at break increase as the GO loading is increased up to 2.5 wt% and then decrease with further GO addition. The maximum tensile strength and elongation at break are 929.54 kPa and 164.6%, respectively. The tensile strength and elongation at break of GO-0.5, GO-1.5, GO-2.5, GO-3.5 and GO-4.5 are markedly higher than those of GO-0 (p < 0.05 or p < 0.01). The tensile fracture surface of GO-2.5 and GO-4.5 are shown in Fig. 6b and c, respectively. Layered structure with uniformly dispersed GO in the PVA matrix can be clearly seen (Fig. 6b). Such a layered structure indicates that GO is coated with the PVA matrix and the presence of strong hydrogen bonding interactions between GO and PVA. Such hydrogen bonding is important because it is required to transfer load more efficiently. The layered structure becomes more obviously as increase of GO loading in PVA matrix (Fig. 6c). The GO in the PVA matrix are crumpled and wrinkled, and restacked with each other.

Fig. 6 (a) Tensile strength (solid line, left axis) and elongation at break (dotted line, right axis) of GO-0, GO-0.5, GO-1.5, GO-2.5, GO-3.5 and GO-4.5, (b and c) the tensile fracture surface of (b) GO-2.5 and (c) GO-4.5. *P < 0.05 and **P < 0.01 (compared with GO-0), n = 6.

The mechanical properties increase as the GO loading is increased up to 2.5 wt%. It is believed that the homogeneous dispersion of GO sheets in the PVA matrix and the strong hydrogen bonding interactions between them are the main reason for the mechanical properties enhancements. The mechanical properties decrease with further increasing GO loading above 2.5 wt%. The reason is that GO sheets tend to form irreversible agglomerates or restacking due to the van der Waals force. A scheme of the GO sheets dispersion in the PVA matrix with various GO loadings is shown in Fig. 7. The GO sheets are individually dispersed in the PVA matrix when the GO loading is 0.5 wt% (Fig. 7c), which leads to a significant improvement in the mechanical properties. The edges of the GO sheets just join together side by side when the GO loading is 2.5 wt% (Fig. 7d), which is the ideal condition to enhance the mechanical behaviors with the greatest efficiency. The GO sheets are stacking together by layers when the GO loading is 4.5 wt% (Fig. 7e), which will weaken the efficiency of the mechanical properties improvement.

Fig. 7 Schematic representation of the PVA chains (a), the GO sheets (b), and the GO sheets dispersion in the PVA matrix with various GO loadings (c) 0.5 wt%, (d) 2.5 wt% and (e) 4.5 wt%.

As the GO-2.5 possess the optimal mechanical properties, we fabricate the GO/PVA nanocomposite scaffold with 2.5 wt% GO loading via SLS, as shown in Fig. 8. The scaffold has a stable three-dimensional structure with well-defined geometry (Fig. 8a and b). The size of the porous scaffold is approximately 20 × 20 × 12 mm³. The scaffold has an open, uniform and interconnected porous structure with a pore size of about 800 μm. The porous scaffold is composed of struts, and the wideness of the struts is around 1.9 mm (Fig. 8c). There are also pores less than 150 μm in size distributed on the surface of the strut (Fig. 8d). These pores are irregular in shape and randomly distributed throughout the surface. Previous studies showed that the pore size of 800 μm allows bone tissue ingrowth and eventually vascularisation,⁵⁴ while the pore sizes less than 150 μm are needed for capillary ingrowth, nutrient transport and metabolite removal of the cells growth on the scaffold.^55,56

Fig. 8 (a and b) Photographs of the GO/PVA nanocomposite scaffold with 2.5 wt% GO loading fabricated via SLS, (c) the struts of the scaffold, (d) the pores of the strut.

The interaction between human osteoblast-like cells and the GO/PVA nanocomposite scaffolds is one of the major factors, which determines the cytocompatibility of scaffolds. The morphologies of the MG-63 cells cultured on the surface of GO-2.5 and GO-0 scaffolds are shown in Fig. 9. The cells attach well and spread out on the scaffold surface, which indicates that the scaffold has no cytotoxic effect to the MG-63 cells. After 1 day of culture, cells are well spread and have many extend cytoplasmic processes (Fig. 9a). Cells proliferate on the surface and within the pores of scaffolds. Neighbor cells connect with each other through cytoplasmic extensions and pseudopodi (Fig. 9b and c). After 7 days of culture, the cells anchor tightly on the surface and almost complete cover the entire surface (Fig. 9d). Cells cultured on the GO-0 scaffolds have a less well-spread morphology compared to the cells grown on the GO-2.5 scaffolds (Fig. 9e and f). Cells cultured on the GO-2.5 scaffolds demonstrates a higher occurrence of the protrusive subcellular features such as filopodia indicating that the cells preferred the surface of GO/PVA composite scaffolds over that of pure PVA scaffold. Moreover, the cells covers almost the whole surface of GO-2.5 scaffolds while only about 30% of GO-0 scaffolds.

Fig. 9 SEM images of the MG-63 cells attach and spread on the surfaces of GO-2.5 scaffolds (a–d) and GO-0 scaffolds (e and f) after (a) 1 day, (b and e) 3 days, (c) 5 days and (d and f) 7 days of incubation.

The relatively better cytocompatibility of GO-2.5 scaffolds compared to GO-0 scaffolds suggests that the addition of GO to PVA facilitates cell growth and promotes cell proliferation. Studies^57,58 showed that PVA and graphene both have good cytocompatibility, which can potentially be used for bone tissue engineering applications. Recently the researchers have demonstrated that GO have positive effects on grown, proliferation and differentiation of cells.⁵⁹ Liu et al.⁶⁰ found that GO can promote the attachment and proliferation of human cells because of the existence of the hydrophilic groups. Pandele et al.⁴¹ have prepared chitosan-polyvinyl alcohol/graphene oxide (CS-PVA/GO) nanocomposites and reported that the nanocomposites with higher content of GO led to a significant increase of the cell proliferation rate. Hence, it can be concluded that GO can be used as an ideal reinforcement phase to polymer for bone tissue engineering application.

Since PVA is a biodegradable polymer matrix, it may release GO nanosheets into bone and/or the bloodstream over an extended period after implant. Hence, interaction of GO nanosheets with bone and/or blood are also very important. A recent study showed that the toxicity of GO nanoplatelets was observed to be dose-dependent in human mesenchymal stem cells, displaying a significant cytotoxic effect only at high concentration of 100 μg mL⁻¹.⁶¹ In our manuscript, the concentration of GO nanosheets is about 20 μg mL⁻¹ after implantation in the human body. Another study on the effect of GO on Gram-negative E. coli revealed that GO has a useful bactericidal effect on E. coli because it caused bacterial membrane damage.⁶² Sasidharan et al.⁶³ studied the hemocompatibility of nano GO and concluded that the nano GO shows excellent compatibility with red blood cells, platelets, plasma coagulation pathways, an insignificant hemolytic effect (up to 75 μg mL⁻¹) and insignificant levels of coagulation. Hence, it can be concluded that GO in low concentration has been proven to be noncytotoxic for bone tissue engineering application.

4 Conclusions

The GO/PVA nanocomposite scaffolds with interconnected porous structure are fabricated using GO as a mechanical reinforcement phase via SLS. The GO sheets are homogeneous dispersion in the PVA matrix and the oxygen-containing functional groups of GO generate strong hydrogen bonding with PVA at 0–2.5 wt% loading of GO. A 60% increase in compressive strength, a 152% increase in Young's modulus and a 69% improvement of tensile strength are achieved by the addition of 2.5 wt% GO, indicating the efficient load transfer between GO and PVA matrix. However, the GO sheets agglomerate and restack with each other with further increasing GO loading (>2.5 wt%). And the efficiency of the mechanical improvement is weakened. Human osteoblast-like MG-63 cells growth and proliferation during cell culture studies demonstrate the good cytocompatibility of the scaffolds. Such GO/PVA nanocomposite scaffolds demonstrate a promising application in bone tissue engineering.

Acknowledgements

This work was supported by the following funds: (1) The Natural Science Foundation of China (51222506, 81372366, 81472058); (2) Overseas, Hong Kong & Macao Scholars Collaborated Researching Fund of National Natural Science Foundation of China (81428018); (3) Hunan Provincial Natural Science Foundation of China (14JJ1006); (4) Project supported by the Fok Ying-Tong Education Foundation, China (131050); (5) Shenzhen Strategic Emerging Industrial Development Funds (JCYJ20130401160614372); (6) The Open-End Fund for the Valuable and Precision Instruments of Central South University; (7) The faculty research grant of Central South University (2013JSJJ011, 2013JSJJ046); (8) State Key Laboratory of New Ceramic and Fine Processing Tsinghua University (KF201413); (9) The Fundamental Research Funds for the Central Universities of Central South University.

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