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sodium alginate nanofiber hydrogel
Materials Letters 126 (2014) 169–173
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Novel hydroxyapatite nanorods crystal growth in silk fibroin/sodium alginate nanofiber hydrogel Jinfa Ming n, Shiyu Bie, Zhijuan Jiang, Peng Wang, Baoqi Zuo National Engineering Laboratory for Modern Silk, College of Textile and Clothing Engineering, Soochow University, Suzhou 215123, China
art ic l e i nf o
a b s t r a c t
Article history: Received 14 December 2013 Accepted 5 April 2014 Available online 13 April 2014
Silk fibroin/sodium alginate (SF/SA) nanofiber hydrogels were used as organic template to control hydroxyapatite (HAp) crystal growth at room temperature. Scanning electron microscopy demonstrated rectangular column and size-controllable HAp nanorods formed, and the crystalline structure of nanorods crystals was confirmed by energy dispersive X-ray spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. Time-dependent experimental results also exhibited HAp nanorods with rectangular column growth in the mineralization process. SF/SA nanofiber hydrogels had an important impact on the morphology of crystals due to the strong electrostatic interaction between hybrid molecular and Ca2 þ ions. The regulating formation mechanism of HAp nanorods by SF/SA nanofiber hydrogels may extend the understanding of the potential for using biomimetic principles to synthesize bone-like composite materials. & 2014 Elsevier B.V. All rights reserved.
Keywords: Crystal growth Composite materials Hydrogel Hydroxyapatite
1. Introduction Hydroxyapatite (HAp), a class of calcium phosphate-based material, has been used for a variety of biomedical applications, including bone substitutes [1], matrices for drug release control [2], etc. Many chemical methods have emerged for the preparation of HAp with control over their size and morphology, such as coprecipitation [3], solid-state reactions [4], hydrothermal method [5,6], sol–gel synthesis [7,8] and reflux method [9]. These methods, however, mostly prepare irregular forms of powder [10]. Presently, organic templates are found to control the nucleation and growth of inorganic crystals with controllable morphology [11,12]. Moreover, in several works, the mineral growth environment occurred in gel state [13]. In our study, we used SF/SA nanofiber hydrogels to regulate and control HAp crystal growth. SF protein and SA polysaccharides can form a nanofiber hydrogel biopolymer system, which can better mimic the real mineralization system of bone more than a single protein system [14]. At the same time, in this nanofiber hydrogel system, SF and SA molecules can easily coordinate the divalent cations (i.e., Ca2 þ ) through the ionic interaction between the carboxylic acid groups located on the polymer molecular chain and the chelating cation [15]. These chelating ions provide the location site of crystal and facilitate the crystal growth in hydrogel microenvironment.
n
Corresponding author. Tel.: þ 86 512 67061157; fax: þ 86 512 67246786. E-mail address: [email protected] (J. Ming).
http://dx.doi.org/10.1016/j.matlet.2014.04.025 0167-577X/& 2014 Elsevier B.V. All rights reserved.
Here, we report novel SF/SA nanofiber hydrogels as organic template to synthesize rectangular column and size-controllable HAp nanorods at room temperature. The effect of time-dependent growth study on the morphology of HAp has been investigated.
2. Materials and methods Bombyx mori silk was purchased from Zhejiang, China. Calcium chloride, diammonium hydrogen phosphate, ammonium hydroxide, and ethanol (Sinopharm Chemical Reagent Co. Ltd., Shanghai, China) were of analytical grade and used without further purification. All solutions were prepared with deionized water. SF solution was prepared following the procedure described previously [15]. Briefly, Bombyx mori silk fibers were degummed three times in 0.05 wt% Na2CO3 solution at 100 1C for 30 min, rinsed thoroughly and dried. The extracted SF was dissolved in a mixture of solvent composed of LiBr/ethanol/H2O (44/45/11, wt/ wt/wt) at 70 1C for 4 h, yielding a 10 g dL 1 solution. SF solution (2.0 wt%) was obtained after dialysis for 4 days and filtration. SA (2 g) was dissolved in deionized water to obtain a uniform 0.5 wt% SA solution at room temperature. Then, SF and SA aqueous solutions with 70/30 ratio were mixed by stirring, and the concentration of the mixture solution was controlled at 1.0 wt%. The mixed solution was stored overnight at 5 1C to avoid and premature precipitation of the protein, which occurred at room temperature. Finally, hydrogels were prepared by adding 1 mL blended solution in 24 well plates (Coring, USA). The solutions
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were allowed to gel in an incubator at 37 1C. In addition, SA hydrogels were gelled by adding 10 mM Ca2 þ solution. The morphology of all hydrogels was interconnected nanofiber networks (Fig. 1). Nanofiber hydrogels were used as templates to mineral HAp crystals. The mineralization process was as follows: first, hydrogels were treated in 75% (v/v) ethanol for 30 min to prepare the waterinsoluble hydrogels. The water-insoluble hydrogels were immersed directly in CaCl2 solution (2.22 g CaCl2 dissolved in 100 mL deionized water) for 1 h at room temperature. Then, the samples were immersed in (NH4)2HPO4 solution (1.578 g (NH4)2HPO4 dissolved in 100 mL deionized water). Ammonium hydroxide was added to adjust the pH to 8. After being reacted for 48 h at room temperature, the final samples were rinsed with distilled water and lyophilization for characterization. After mineralization, the samples were directly lyophilized. This lyophilization process does not change the existential state of HAp crystal in nanofiber hydrogels. At the same time, the lyophilized samples were fractured in liquid nitrogen for preparing SEM samples. The morphology of samples was observed by scanning electron microscopy (SEM, S4800, and Hitachi) with an energy dispersive X-ray spectroscopy (EDS) analyzer. The crystal structures of crystals were analyzed with an X-ray diffraction instrument (X Pert-Pro MPD, PANalytical, Netherlands) in a transmittance mode and FTIR on Nicolet5700 (Thermal Nicolet Company, USA) in an absorbance mode.
3. Results and discussion The morphology of HAp induced by different templates is shown in Fig. 2. As control sample, Fig. 2A–d showed the needle-shaped HAp crystals without organic templates at room temperature. For the XRD patterns, the sample displayed characteristic 2θ peaks appearing at 25.71, 31.81, 33.81, 39.81, 46.81, 49.51, and 53.21, corresponding to the diffraction planes (002),
(211), (202), (310), (222), (213), and (004) of the HAp crystallites (Fig. 2B–d), respectively, which was consistent with the crystalline nature of HAp in the literature [16]. For SF hydrogel template, flower-type HAp crystals were obtained and the shape of the individual crystal was more flakelike as opposed to the needle-like crystal (Fig. 2A–a). However, Fig. 2A–b showed HAp nanorods with typical width of 345.20 7 96.59 nm and lengths up to 5 μm, when SF/SA nanofiber hydrogels were added. In addition, Fig. 2A–c depicted the SEM image of spherical-like HAp crystals, which was controlled by SA hydrogel template. The crystalline structures of crystals prepared by different organic templates at mineralization 1 h were examined by XRD (Fig. 2B). The diffraction of all samples was seen at 2θ values (002), (211), (202), (310), (222), (213), and (004) (Fig. 2B), which was consistent with HAp sample preparing by solution-precipitation method without template (Fig. 2B–d). At the same time, these HAp crystals were further proved by EDS (Fig. 2C). Fig. 3 showed SEM images of HAp crystals prepared by SF/SA nanofiber hydrogel templates at different mineral times. From the SEM micrograph of Fig. 3a, it depicted the crystal sample was composed of many regular nanorods at mineralization 1 h at room temperature. The crystal structure of nanorods was HAp crystals, which was confirmed by XRD and FTIR (Fig. 4). The diffraction peaks such as (002), (211), (310), (222), (213), and (004) were seen in Fig. 4A–a. At the same time, peaks at 560–610 cm 1 and 1000–1100 cm 1 were attributed to phosphate groups in HAp (Fig. 4B–a). When the mineralization time increased 6 h, HAp nanorods with about 310.937 84.46 nm in width were grown (Fig. 3b). With the mineralization time increasing to 48 h, the elongated nanorods crystals were observed (Fig. 3c–e). The crystalline structure of HAp crystals was also examined using XRD and FTIR (Fig. 4). For the XRD patterns, the samples exhibited the diffraction planes (002), (211), (310), (222), (213), and (004) of HAp crystallites. Therefore, in the mineralization process, the morphology of HAp crystals was not influenced by mineralization times at room temperature.
Fig. 1. SEM images of nanofiber hydrogels and its FTIR results: (a) SF hydrogel, (b) SF/SA hydrogel, and (c) SA hydrogel.
J. Ming et al. / Materials Letters 126 (2014) 169–173
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Fig. 2. SEM images (A) and XRD data (B) of HAp crystals prepared by different hydrogel templates and its energy spectrum (C). The hydrogel templates were as follows: (a) SF hydrogel, (b) SF/SA hydrogel, (c) SA hydrogel, and (d) HAp crystals were prepared by the solution-precipitation method without template.
In this experiment, SF/SA nanofiber hydrogels were acted as organic template to regulate and control HAp crystals. When SF/SA nanofiber hydrogels were treated in CaCl2 solution, SF and SA molecules were all easily coordinated with Ca2 þ ions. In SF molecules, the –C-O- and –N-H- groups had been preferentially coordinated with Ca2 þ ions [17,18]. At the same time, SA molecules were easily contacted with solutions of divalent cations such as Ca2 þ ions, forming the so-called “egg-box” model [15]. This “egg-box” model was confirmed by Morris et al. [19]. According to double-layer theory, when PO34 ions were added, Ca2 þ ions on the SF and SA molecules get attached to the PO34 and OH- groups by electrostatic interaction as a driving force to further gather more Ca2 þ ions, until the concentration is favorable for heterogeneous nucleation of HAp [17]. The stereo-chemical geometry and the charge distribution in hydrogel complexes were supposed to endow SF and SA molecules with the capability to control the crystallization process [20]. With the continuous reaction, nanocrystals were grown and attached along these
organic chains to form nanorods. The coalescence of nanorods with the same direction finally formed the partially oriented bundles. In addition, in this mineralization process, HAp nucleation was also influenced by the space limitation of nanofiber hydrogels.
4. Conclusion SF/SA nanofiber hydrogels acted as organic template to control HAp crystals at room temperature. The obtained HAp crystals were nanorods with rectangular column morphology, whose crystalline structure was confirmed by EDS, XRD and FTIR. Time-dependent experiment showed the growth of elongated HAp nanorods crystals in mineralization process. Therefore, SF/SA nanofiber hydrogels may provide a feasible organic template for the fabrication of HAp crystals with controllable configuration.
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Fig. 3. SEM images of HAp crystals prepared by SF/SA nanofiber hydrogel templates at room temperature. The mineralization time was as follows: (a) 1 h, (b) 6 h, (c) 12 h, (d) 24 h, and (e) 48 h.
Fig. 4. XRD (A) and FTIR (B) of HAp crystals prepared by SF/SA hydrogel templates; the mineralization time was as follows: (a) 1 h, (b) 6 h, (c) 12 h, (d) 24 h, and (e) 48 h.
J. Ming et al. / Materials Letters 126 (2014) 169–173
Acknowledgment The work was supported by National Science Foundation of China (No. 81271723), and Doctoral Candidate Academic Award Project of Soochow University (No. 5832003611). References [1] Hing KA, Best SM, Tanner KE, Bonfield W, Revell PA. J Biomed Mater Res A 2004;68A:187–200. [2] Komlev VS, Barinov SM, Koplik EV. Biomaterials 2002;23:3449–54. [3] Ming JF, Zuo BQ. Mater Chem Phys 2012;137:421–7. [4] Pramanik S, Agarwal AK, Rai KN, Garg A. Ceram Int 2007;33:419–26. [5] Han JK, Song HY, Saito F, Lee BT. Mater Chem Phys 2006;99:235–9. [6] Suchanek WL, Byrappa K, Shuk P, Riman RE, Janas VF, TenHuisen KS. Biomaterials 2004;25:4647–57.
[7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20]
173
Liu DM, Troczynski T, Tseng WJ. Biomaterials 2001;22:1721–30. Kim S, Kumta PN. Mater Sci Eng B 2004;111:232–6. Yang S, Chen JD, Wang ZH, Zhang H, Zhang QQ. Mater Lett 2013;96:177–80. Wang YJ, Zhang SH, Wei K, Zhao NR, Chen JD, Wang XD. Mater Lett 2006;60:1484–7. Yao J, Tjandra W, Chen YZ, Tam KC, Ma J, Soh B. J Mater Chem 2003;13:3053–7. Kong XD, Cui FZ, Wang XM, Zhang M, Zhang W. J Cryst Growth 2004;270: 197–202. Ma YF, Feng QL, Bourrat X. Mater Sci Eng C 2013;33:2413–20. Palmer LC, Newcomb CJ, Kaltz SR, Spoerke ED, Stupp SI. Chem Rev 2008;108:4754–83. Ming JF, Zuo BQ. J Cryst Growth 2014;386:154–61. Ruksudjarit A, Pengpat K, Rujijanagul G, Tunkasiri T. Curr Appl Phys 2008;8: 270–2. Wang J, Yu F, Qu LJ, Meng XC, Wen G. Biomed Mater 2010;5:1–5. Rhee SH, Lee JD, Tanaka J. J Am Ceram Soc 2000;83:2890–2. Morris ER, Rees DA, Thom D. Carbohydr Res 1978;66:145–54. Teng SH, Shi JJ, Peng BX, Chen LJ. Compos Sci Technol 2006;66:1532–8.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Novel hydroxyapatite nanorods crystal growth in silk fibroin/sodium alginate nanofiber hydrogel Jinfa Ming n, Shiyu Bie, Zhijuan Jiang, Peng Wang, Baoqi Zuo National Engineering Laboratory for Modern Silk, College of Textile and Clothing Engineering, Soochow University, Suzhou 215123, China
art ic l e i nf o
a b s t r a c t
Article history: Received 14 December 2013 Accepted 5 April 2014 Available online 13 April 2014
Silk fibroin/sodium alginate (SF/SA) nanofiber hydrogels were used as organic template to control hydroxyapatite (HAp) crystal growth at room temperature. Scanning electron microscopy demonstrated rectangular column and size-controllable HAp nanorods formed, and the crystalline structure of nanorods crystals was confirmed by energy dispersive X-ray spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. Time-dependent experimental results also exhibited HAp nanorods with rectangular column growth in the mineralization process. SF/SA nanofiber hydrogels had an important impact on the morphology of crystals due to the strong electrostatic interaction between hybrid molecular and Ca2 þ ions. The regulating formation mechanism of HAp nanorods by SF/SA nanofiber hydrogels may extend the understanding of the potential for using biomimetic principles to synthesize bone-like composite materials. & 2014 Elsevier B.V. All rights reserved.
Keywords: Crystal growth Composite materials Hydrogel Hydroxyapatite
1. Introduction Hydroxyapatite (HAp), a class of calcium phosphate-based material, has been used for a variety of biomedical applications, including bone substitutes [1], matrices for drug release control [2], etc. Many chemical methods have emerged for the preparation of HAp with control over their size and morphology, such as coprecipitation [3], solid-state reactions [4], hydrothermal method [5,6], sol–gel synthesis [7,8] and reflux method [9]. These methods, however, mostly prepare irregular forms of powder [10]. Presently, organic templates are found to control the nucleation and growth of inorganic crystals with controllable morphology [11,12]. Moreover, in several works, the mineral growth environment occurred in gel state [13]. In our study, we used SF/SA nanofiber hydrogels to regulate and control HAp crystal growth. SF protein and SA polysaccharides can form a nanofiber hydrogel biopolymer system, which can better mimic the real mineralization system of bone more than a single protein system [14]. At the same time, in this nanofiber hydrogel system, SF and SA molecules can easily coordinate the divalent cations (i.e., Ca2 þ ) through the ionic interaction between the carboxylic acid groups located on the polymer molecular chain and the chelating cation [15]. These chelating ions provide the location site of crystal and facilitate the crystal growth in hydrogel microenvironment.
n
Corresponding author. Tel.: þ 86 512 67061157; fax: þ 86 512 67246786. E-mail address: [email protected] (J. Ming).
http://dx.doi.org/10.1016/j.matlet.2014.04.025 0167-577X/& 2014 Elsevier B.V. All rights reserved.
Here, we report novel SF/SA nanofiber hydrogels as organic template to synthesize rectangular column and size-controllable HAp nanorods at room temperature. The effect of time-dependent growth study on the morphology of HAp has been investigated.
2. Materials and methods Bombyx mori silk was purchased from Zhejiang, China. Calcium chloride, diammonium hydrogen phosphate, ammonium hydroxide, and ethanol (Sinopharm Chemical Reagent Co. Ltd., Shanghai, China) were of analytical grade and used without further purification. All solutions were prepared with deionized water. SF solution was prepared following the procedure described previously [15]. Briefly, Bombyx mori silk fibers were degummed three times in 0.05 wt% Na2CO3 solution at 100 1C for 30 min, rinsed thoroughly and dried. The extracted SF was dissolved in a mixture of solvent composed of LiBr/ethanol/H2O (44/45/11, wt/ wt/wt) at 70 1C for 4 h, yielding a 10 g dL 1 solution. SF solution (2.0 wt%) was obtained after dialysis for 4 days and filtration. SA (2 g) was dissolved in deionized water to obtain a uniform 0.5 wt% SA solution at room temperature. Then, SF and SA aqueous solutions with 70/30 ratio were mixed by stirring, and the concentration of the mixture solution was controlled at 1.0 wt%. The mixed solution was stored overnight at 5 1C to avoid and premature precipitation of the protein, which occurred at room temperature. Finally, hydrogels were prepared by adding 1 mL blended solution in 24 well plates (Coring, USA). The solutions
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were allowed to gel in an incubator at 37 1C. In addition, SA hydrogels were gelled by adding 10 mM Ca2 þ solution. The morphology of all hydrogels was interconnected nanofiber networks (Fig. 1). Nanofiber hydrogels were used as templates to mineral HAp crystals. The mineralization process was as follows: first, hydrogels were treated in 75% (v/v) ethanol for 30 min to prepare the waterinsoluble hydrogels. The water-insoluble hydrogels were immersed directly in CaCl2 solution (2.22 g CaCl2 dissolved in 100 mL deionized water) for 1 h at room temperature. Then, the samples were immersed in (NH4)2HPO4 solution (1.578 g (NH4)2HPO4 dissolved in 100 mL deionized water). Ammonium hydroxide was added to adjust the pH to 8. After being reacted for 48 h at room temperature, the final samples were rinsed with distilled water and lyophilization for characterization. After mineralization, the samples were directly lyophilized. This lyophilization process does not change the existential state of HAp crystal in nanofiber hydrogels. At the same time, the lyophilized samples were fractured in liquid nitrogen for preparing SEM samples. The morphology of samples was observed by scanning electron microscopy (SEM, S4800, and Hitachi) with an energy dispersive X-ray spectroscopy (EDS) analyzer. The crystal structures of crystals were analyzed with an X-ray diffraction instrument (X Pert-Pro MPD, PANalytical, Netherlands) in a transmittance mode and FTIR on Nicolet5700 (Thermal Nicolet Company, USA) in an absorbance mode.
3. Results and discussion The morphology of HAp induced by different templates is shown in Fig. 2. As control sample, Fig. 2A–d showed the needle-shaped HAp crystals without organic templates at room temperature. For the XRD patterns, the sample displayed characteristic 2θ peaks appearing at 25.71, 31.81, 33.81, 39.81, 46.81, 49.51, and 53.21, corresponding to the diffraction planes (002),
(211), (202), (310), (222), (213), and (004) of the HAp crystallites (Fig. 2B–d), respectively, which was consistent with the crystalline nature of HAp in the literature [16]. For SF hydrogel template, flower-type HAp crystals were obtained and the shape of the individual crystal was more flakelike as opposed to the needle-like crystal (Fig. 2A–a). However, Fig. 2A–b showed HAp nanorods with typical width of 345.20 7 96.59 nm and lengths up to 5 μm, when SF/SA nanofiber hydrogels were added. In addition, Fig. 2A–c depicted the SEM image of spherical-like HAp crystals, which was controlled by SA hydrogel template. The crystalline structures of crystals prepared by different organic templates at mineralization 1 h were examined by XRD (Fig. 2B). The diffraction of all samples was seen at 2θ values (002), (211), (202), (310), (222), (213), and (004) (Fig. 2B), which was consistent with HAp sample preparing by solution-precipitation method without template (Fig. 2B–d). At the same time, these HAp crystals were further proved by EDS (Fig. 2C). Fig. 3 showed SEM images of HAp crystals prepared by SF/SA nanofiber hydrogel templates at different mineral times. From the SEM micrograph of Fig. 3a, it depicted the crystal sample was composed of many regular nanorods at mineralization 1 h at room temperature. The crystal structure of nanorods was HAp crystals, which was confirmed by XRD and FTIR (Fig. 4). The diffraction peaks such as (002), (211), (310), (222), (213), and (004) were seen in Fig. 4A–a. At the same time, peaks at 560–610 cm 1 and 1000–1100 cm 1 were attributed to phosphate groups in HAp (Fig. 4B–a). When the mineralization time increased 6 h, HAp nanorods with about 310.937 84.46 nm in width were grown (Fig. 3b). With the mineralization time increasing to 48 h, the elongated nanorods crystals were observed (Fig. 3c–e). The crystalline structure of HAp crystals was also examined using XRD and FTIR (Fig. 4). For the XRD patterns, the samples exhibited the diffraction planes (002), (211), (310), (222), (213), and (004) of HAp crystallites. Therefore, in the mineralization process, the morphology of HAp crystals was not influenced by mineralization times at room temperature.
Fig. 1. SEM images of nanofiber hydrogels and its FTIR results: (a) SF hydrogel, (b) SF/SA hydrogel, and (c) SA hydrogel.
J. Ming et al. / Materials Letters 126 (2014) 169–173
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Fig. 2. SEM images (A) and XRD data (B) of HAp crystals prepared by different hydrogel templates and its energy spectrum (C). The hydrogel templates were as follows: (a) SF hydrogel, (b) SF/SA hydrogel, (c) SA hydrogel, and (d) HAp crystals were prepared by the solution-precipitation method without template.
In this experiment, SF/SA nanofiber hydrogels were acted as organic template to regulate and control HAp crystals. When SF/SA nanofiber hydrogels were treated in CaCl2 solution, SF and SA molecules were all easily coordinated with Ca2 þ ions. In SF molecules, the –C-O- and –N-H- groups had been preferentially coordinated with Ca2 þ ions [17,18]. At the same time, SA molecules were easily contacted with solutions of divalent cations such as Ca2 þ ions, forming the so-called “egg-box” model [15]. This “egg-box” model was confirmed by Morris et al. [19]. According to double-layer theory, when PO34 ions were added, Ca2 þ ions on the SF and SA molecules get attached to the PO34 and OH- groups by electrostatic interaction as a driving force to further gather more Ca2 þ ions, until the concentration is favorable for heterogeneous nucleation of HAp [17]. The stereo-chemical geometry and the charge distribution in hydrogel complexes were supposed to endow SF and SA molecules with the capability to control the crystallization process [20]. With the continuous reaction, nanocrystals were grown and attached along these
organic chains to form nanorods. The coalescence of nanorods with the same direction finally formed the partially oriented bundles. In addition, in this mineralization process, HAp nucleation was also influenced by the space limitation of nanofiber hydrogels.
4. Conclusion SF/SA nanofiber hydrogels acted as organic template to control HAp crystals at room temperature. The obtained HAp crystals were nanorods with rectangular column morphology, whose crystalline structure was confirmed by EDS, XRD and FTIR. Time-dependent experiment showed the growth of elongated HAp nanorods crystals in mineralization process. Therefore, SF/SA nanofiber hydrogels may provide a feasible organic template for the fabrication of HAp crystals with controllable configuration.
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J. Ming et al. / Materials Letters 126 (2014) 169–173
Fig. 3. SEM images of HAp crystals prepared by SF/SA nanofiber hydrogel templates at room temperature. The mineralization time was as follows: (a) 1 h, (b) 6 h, (c) 12 h, (d) 24 h, and (e) 48 h.
Fig. 4. XRD (A) and FTIR (B) of HAp crystals prepared by SF/SA hydrogel templates; the mineralization time was as follows: (a) 1 h, (b) 6 h, (c) 12 h, (d) 24 h, and (e) 48 h.
J. Ming et al. / Materials Letters 126 (2014) 169–173
Acknowledgment The work was supported by National Science Foundation of China (No. 81271723), and Doctoral Candidate Academic Award Project of Soochow University (No. 5832003611). References [1] Hing KA, Best SM, Tanner KE, Bonfield W, Revell PA. J Biomed Mater Res A 2004;68A:187–200. [2] Komlev VS, Barinov SM, Koplik EV. Biomaterials 2002;23:3449–54. [3] Ming JF, Zuo BQ. Mater Chem Phys 2012;137:421–7. [4] Pramanik S, Agarwal AK, Rai KN, Garg A. Ceram Int 2007;33:419–26. [5] Han JK, Song HY, Saito F, Lee BT. Mater Chem Phys 2006;99:235–9. [6] Suchanek WL, Byrappa K, Shuk P, Riman RE, Janas VF, TenHuisen KS. Biomaterials 2004;25:4647–57.
[7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20]
173
Liu DM, Troczynski T, Tseng WJ. Biomaterials 2001;22:1721–30. Kim S, Kumta PN. Mater Sci Eng B 2004;111:232–6. Yang S, Chen JD, Wang ZH, Zhang H, Zhang QQ. Mater Lett 2013;96:177–80. Wang YJ, Zhang SH, Wei K, Zhao NR, Chen JD, Wang XD. Mater Lett 2006;60:1484–7. Yao J, Tjandra W, Chen YZ, Tam KC, Ma J, Soh B. J Mater Chem 2003;13:3053–7. Kong XD, Cui FZ, Wang XM, Zhang M, Zhang W. J Cryst Growth 2004;270: 197–202. Ma YF, Feng QL, Bourrat X. Mater Sci Eng C 2013;33:2413–20. Palmer LC, Newcomb CJ, Kaltz SR, Spoerke ED, Stupp SI. Chem Rev 2008;108:4754–83. Ming JF, Zuo BQ. J Cryst Growth 2014;386:154–61. Ruksudjarit A, Pengpat K, Rujijanagul G, Tunkasiri T. Curr Appl Phys 2008;8: 270–2. Wang J, Yu F, Qu LJ, Meng XC, Wen G. Biomed Mater 2010;5:1–5. Rhee SH, Lee JD, Tanaka J. J Am Ceram Soc 2000;83:2890–2. Morris ER, Rees DA, Thom D. Carbohydr Res 1978;66:145–54. Teng SH, Shi JJ, Peng BX, Chen LJ. Compos Sci Technol 2006;66:1532–8.