- Email: [email protected]
zein microcomposites using an epoxy-coated electrospraying head
Materials Letters 93 (2013) 125–128
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Smooth preparation of ibuprofen/zein microcomposites using an epoxy-coated electrospraying head Wenbing Li a,nn, Deng-Guang Yu b,n, Kun Chen a, Guanghua Wang a, Gareth R. Williams c a
College of Chemical Engineering and Technology, Wuhan University of Science and Technology, Wuhan 430081,China School of Materials Science & Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China c School of Human Sciences, Faculty of Life Sciences and Computing, London Metropolitan University, 166-220 Holloway Road, N7 8DB, London, UK b
a r t i c l e i n f o
abstract
Article history: Received 1 September 2012 Accepted 17 November 2012 Available online 23 November 2012
This study investigated the preparation of ibuprofen/zein microcomposites using a modified electrospraying process, in which the spraying head was coated with an epoxy resin to prevent clogging. Scanning electron microscopy images demonstrated that the microparticles from the modified process (1.78 70.31 mm) had more homogeneous structures with narrower size distributions than those (1.84 70.64 mm) from the traditional route. Differential scanning calorimetry analyses verified that the guest drug ibuprofen was converted into an amorphous state in all the zein-based composites. Compared with those from the traditional process, the microparticulate composites from the modified process provided better sustained drug release profiles, as indicated by in vitro dissolution tests. The novel preparation method reported here will facilitate the preparation of new functional materials using electrospraying. & 2012 Elsevier B.V. All rights reserved.
Keywords: Electrospraying Polymeric composites Epoxy-coated Powder technology Sustained release
1. Introduction
2. Experimental section
Electrohydrodynamic atomization (EHDA) is becoming increasingly popular for producing micro- and nano-particles, fibers and polymer films [1–8]. Although the implementation of EHDA is facile, clogging of the needle is commonly experienced, especially when a high-volatility solvent is used [9–13]. Zein is a mixture of proteins from corn gluten meal with a wide variety of applications. Recently, the electrospinning of zein into nanofibers for various applications, particularly in the biomedical field has been reported [9,10,14]. However, clogging is a serious problem. Kanjanapongkul et al. [9,10] reported that needle clogging occurs with a zein concentration as low as 10 wt% in ethanol/water solutions. They put forward a method to prevent clogging by introducing additional solvent to the spinneret nozzle. Later, Yu et al. developed a modified coaxial electrospinning process, where organic solvents or surfactant/salt solutions were exploited as sheath fluids to permit the smooth and continuous preparation of polymer nanofibers [11–13]. In this study, a modified electrospraying process, characterized by application of an epoxy resin (EP)-coated spraying head, was developed for the continuous preparation of zein-based microcomposites.
Materials: Zein was obtained from Aldrich (Milwaukee, WI, USA; purity of 98%). Ibuprofen was purchased from the Hubei Biocause Pharmaceutical Co., Ltd. (Hubei, China). Anhydrous ethanol was provided by the Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Epoxy (EP) resin and its hardener were purchased from the Jiaojiang Qinfen Chemical Factory (Taizhou, Zhejiang, China). Preparation: A co-dissolving solution, consisting of 12% zein and 2% ibuprofen (w/v) in 85% ethanol aqueous solution, was prepared for electrospraying. To coat the needle in EP resin, EP and the hardener were mixed and then the resultant mixture was rapidly applied around the needle tip, taking care not to obstruct the aperture. The applied voltage used for the experiments was 20 kV, supplied by a high-voltage generator (ZGF 60 kV/2 mA, Shanghai Sute Corporation, Shanghai, China). Microparticles were collected on aluminum foil at a distance of 15 cm. The microparticles from traditional and modified electrospraying were denoted as M1 and M2, and were produced via a stainless steel needle and an EP-coated needle, respectively. Characterization: The surface morphologies of the microparticles were assessed using a Quanta FEG450 field-emission scanning electron microscope (FESEM, FEI Corporation, Netherlands). Their average size was determined by measuring the diameters of over 100 particles in FESEM images using the Image J software (National Institutes of Health, MA, USA). Differential scanning
nn
Corresponding author. Corresponding author at: Wuhan University of Science and Technology, 947 Heping Road, Wuhan 430081, China. Tel./fax: þ 86 27 68862870. E-mail addresses: [email protected] (W. Li), [email protected] (D.-G. Yu). n
0167-577X/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2012.11.064
126
W. Li et al. / Materials Letters 93 (2013) 125–128
calorimetry (DSC) analysis were carried out using an MDSC 2910 differential scanning calorimeter (TA Instruments Co., DE, USA). In vitro dissolution tests were performed according to the Chinese Pharmacopoeia (2005 edition), a paddle method using an RCZ-8A dissolution apparatus (Tianjin University Radio Factory, Tianjin, China). All experiments were conducted at 37 1C with stirring at 50 rpm, using 0.2 g of microparticles in 800 mL physiological saline. At pre-determined time intervals, aliquots of 5 mL were withdrawn for sampling and replaced by an equal volume of physiological saline to maintain a constant volume. After filtration through a 0.22 mm membrane (Millipore, MA, USA) and appropriate dilution, the sample solutions were analyzed at 273 nm (lmax for ibuprofen) with a UV spectrophotometer (Unico Instrument Co., Ltd., Shanghai, China).
3. Results and discussion Traditional electrospraying was conducted using a standard 20 G metal needle (with an inner and outer diameter of 0.60 and 0.91 mm, respectively). This is made up of 06Cr19Ni10 (GB24511 in China) austenitic stainless steel, comprising steel, C ( r0.07%), Cr (17.00–19.00%), Ni (8.00–10.00%), Mn ( r2.00%), Si (r1.00%) and traces of S and P. A typical electrospraying process is shown in Fig. 1(a). As the polymer solution leaves the spinneret a Taylor cone can initially be seen to form, followed by a short straight jet, which subsequently breaks up into fine droplets resulting from the Coulomb explosion under the electrical field [8]. The process of clogging can be seen to develop from Fig. 1(a–c); this took a time period of only ca. 2 min, meaning that frequent manual removal of the gel-like substance collecting on the nozzle of the spraying head was needed for continuous electrospraying. The modified process was observed when an EP-coated 20 G metal needle was exploited as the spraying head was depicted in Fig. 1(d–f). No clogging was observed in this process, which ran smoothly and continuously with minimum user intervention. As a protein, zein can easily interact with heavy metal elements in the spraying head through electrostatic interactions and chelation [15]. In traditional electrospraying, the applied electrical force needs to be adequate not only to overcome the viscous drag force at the droplet-air interface but also to surpass the drag force from
the spraying head; this is crucial to prevent clogging. When the EPcoated spraying head was introduced, interactions between metal elements in the needle and the biopolymer in the solution were eliminated. This not only exploited the electrical forces more effectively during electrospraying, but also made it much more difficult for the gel to cling onto the spraying head and thus to clog and interrupt electrospraying. In the traditional electrospraying process, interactions between the spraying head and spinning solutions, as well as the formation of gel-like substances on the spinneret, made atomization inhomogeneous, as indicated by the white dots of different sizes in Fig. 1(a) and (b). In stark contrast, atomization is seen to be homogeneous when using the EP-coated spraying head, as illustrated in Fig. 1(e) and (f). Clogging is usually thought to occur as a result of the high viscosity of the polymer solution and the usage of high-volatility solvents [9–12]. The results reported herein suggest that the situation is more complex, and that interactions between the polymer solution and the spraying head also influence the occurrence of clogging. FESEM images of the microparticles produced from electrospraying are given in Fig. 2. As anticipated, the microparticles generated via the traditional process (M1; diameters 1.8470.64 mm, Fig. 2a and b) were less homogeneous than those prepared by modified electrospraying (M2; diameters 1.7870.31 mm, Fig. 2c and d). The latter had a narrower diameter distribution and fewer satellites visible on the surface of the microparticles. Clogging and interruption of spraying due to the formation of a gel-like substance on the spinneret in the traditional process led not only to decreased productivity, but also affected the microparticle quality in an adverse fashion. DSC tests were performed to determine the physical status of ibuprofen in the microcomposites (see Fig. 3a). The DSC curve of pure ibuprofen exhibited a single endothermic response corresponding to its melting point of 77.4 1C. Being an amorphous biopolymer, zein did not show any fusion peaks or phase transitions. The DSC thermograms of M1 and M2 did not show any characteristic peaks of ibuprofen, suggesting that ibuprofen was no longer present as a crystalline material and was converted into an amorphous state in the microcomposites. The rapid evaporation of solvent in electrospraying and the favorable second-order interactions which can arise between zein and IBU are both likely to have played roles in the formation of amorphous composites.
Fig. 1. The electrospraying process: (a–c) the development of clogging in traditional electrospraying; (d–f) the implementation of modified electrospraying; the insets in (d) show a photo of the spraying head and the coating parameters.
W. Li et al. / Materials Letters 93 (2013) 125–128
127
Fig. 2. FESEM images of ibuprofen/zein microparticles and their size distributions: (a, b) M1 and (c, d) M2.
Fig. 3. (a) DSC traces of M1, M2, and the individual components, (b) drug release from the microparticles and (c) the hydrogen bonding interactions possible between ibuprofen and zein (n ¼6).
Both IBU and zein molecules can act as potential proton donors because they possess free hydroxyl or amino groups, and also can act as potential proton acceptors for hydrogen bonding since they possess carbonyl groups (Fig. 3c). To evaluate the functional performance of the microcomposites, in vitro dissolution tests were conducted and the drug release profiles are shown in Fig. 3(b). Compared with the M1 material from traditional electrospraying, M2 (from the modified process) provided better sustained drug release. M2 displayed a smaller burst release of 21.3% (cf. 27.7% for M1) after 1 h of release, and also a shorter ‘‘tailing-off’’ exhaustion time period [10]. The satellites on the surface of the M1 particles will exacerbate the initial burst release, while the presence of some large particles will prolong the exhaustion time since with the latter it will take a long
time for the drug to diffuse from inside of the particles to the dissolution medium. The much greater homogeneity of M2 ameliorates both these problems, yielding a more favorable release profile.
4. Conclusion This study successfully developed a modified electrospraying process, where an EP-coated spraying head was exploited for the preparation of ibuprofen/zein microcomposites. FESEM images demonstrated that the microparticles from the modified process had more homogeneous structures and a narrower size distribution than those from traditional electrospraying. DSC results indicated
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W. Li et al. / Materials Letters 93 (2013) 125–128
that ibuprofen was converted into an amorphous state in both microcomposites, probably as a result of hydrogen bonding between zein and ibuprofen. In vitro dissolution tests demonstrated that the micoparticles from the modified process provided better sustained drug release profiles, and hence this modification will be beneficial in the development of advanced pharmaceutical materials.
Acknowledgments This work was supported by the key project of Shanghai Municipal Education Commission (no.13ZZ113) and the Specialized Research Fund for the Doctoral Program of Higher Education of China (20114219110002). References [1] Luo CJ, Stoyanov SD, Stride E, Pelan E, Edirisinghe M. Chem Soc Rev 2012;41:4708–35. [2] Chakraborty S, Liao IC, Adler A, Leong KW. Adv Drug Delivery Rev 2009;61:1043–54.
[3] George MC, Braun PV. Angew Chem Int Ed 2009;48:8606–9. [4] Salata OV. Current Nanosci 2005;1:25–33. [5] Nangrejo M, Bernardo E, Colombo P, Farook U, Ahmad Z, Stride E, et al. Mater Lett 2009;63:4835. [6] Enayati M, Ahmad Z, Stride E, Edirisinghe M. J R Soc Interface 2010 667–75. [7] Yu DG, Williams GR, Yang JH, Wang X, Yang JM, Li XY. J Mater Chem 2011;21:15957–61. [8] Deniz AE, Vural HA, Ortac- B, Uyar T. Mater Lett 2011;65:2941–3. [9] Kanjanapongkul K, Wongsasulak S, Yoovidhya T. Chem Eng Sci 2011;65:5217–25. [10] Kanjanapongkul K, Wongsasulak S, Yoovidhya T. J Appl Polym Sci 2011;118:1821–9. [11] Yu DG, Yu JH, Chen L, Williams GR, Wang X. Carbohydr Polym 2012;90:1016–23. [12] Yu DG, Williams GR, Gao LD, Bligh SWA, Yang JH, Wang X. Colloids Surf A, Physicochem Eng Aspect 2012;396:161–8. [13] Yu DG, White K, Yang JH, Wang X, Qian W, Li Y. Mater Lett 2012 78–80. [14] Nie W, Yu DG, Branford-White C, Shen XX, Zhu LM. Mater Res Innovations 2012;16:14–8. [15] Blundell TL, Jenkins JA. Chem Soc Rev 1977;6:139–71.
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Smooth preparation of ibuprofen/zein microcomposites using an epoxy-coated electrospraying head Wenbing Li a,nn, Deng-Guang Yu b,n, Kun Chen a, Guanghua Wang a, Gareth R. Williams c a
College of Chemical Engineering and Technology, Wuhan University of Science and Technology, Wuhan 430081,China School of Materials Science & Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China c School of Human Sciences, Faculty of Life Sciences and Computing, London Metropolitan University, 166-220 Holloway Road, N7 8DB, London, UK b
a r t i c l e i n f o
abstract
Article history: Received 1 September 2012 Accepted 17 November 2012 Available online 23 November 2012
This study investigated the preparation of ibuprofen/zein microcomposites using a modified electrospraying process, in which the spraying head was coated with an epoxy resin to prevent clogging. Scanning electron microscopy images demonstrated that the microparticles from the modified process (1.78 70.31 mm) had more homogeneous structures with narrower size distributions than those (1.84 70.64 mm) from the traditional route. Differential scanning calorimetry analyses verified that the guest drug ibuprofen was converted into an amorphous state in all the zein-based composites. Compared with those from the traditional process, the microparticulate composites from the modified process provided better sustained drug release profiles, as indicated by in vitro dissolution tests. The novel preparation method reported here will facilitate the preparation of new functional materials using electrospraying. & 2012 Elsevier B.V. All rights reserved.
Keywords: Electrospraying Polymeric composites Epoxy-coated Powder technology Sustained release
1. Introduction
2. Experimental section
Electrohydrodynamic atomization (EHDA) is becoming increasingly popular for producing micro- and nano-particles, fibers and polymer films [1–8]. Although the implementation of EHDA is facile, clogging of the needle is commonly experienced, especially when a high-volatility solvent is used [9–13]. Zein is a mixture of proteins from corn gluten meal with a wide variety of applications. Recently, the electrospinning of zein into nanofibers for various applications, particularly in the biomedical field has been reported [9,10,14]. However, clogging is a serious problem. Kanjanapongkul et al. [9,10] reported that needle clogging occurs with a zein concentration as low as 10 wt% in ethanol/water solutions. They put forward a method to prevent clogging by introducing additional solvent to the spinneret nozzle. Later, Yu et al. developed a modified coaxial electrospinning process, where organic solvents or surfactant/salt solutions were exploited as sheath fluids to permit the smooth and continuous preparation of polymer nanofibers [11–13]. In this study, a modified electrospraying process, characterized by application of an epoxy resin (EP)-coated spraying head, was developed for the continuous preparation of zein-based microcomposites.
Materials: Zein was obtained from Aldrich (Milwaukee, WI, USA; purity of 98%). Ibuprofen was purchased from the Hubei Biocause Pharmaceutical Co., Ltd. (Hubei, China). Anhydrous ethanol was provided by the Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Epoxy (EP) resin and its hardener were purchased from the Jiaojiang Qinfen Chemical Factory (Taizhou, Zhejiang, China). Preparation: A co-dissolving solution, consisting of 12% zein and 2% ibuprofen (w/v) in 85% ethanol aqueous solution, was prepared for electrospraying. To coat the needle in EP resin, EP and the hardener were mixed and then the resultant mixture was rapidly applied around the needle tip, taking care not to obstruct the aperture. The applied voltage used for the experiments was 20 kV, supplied by a high-voltage generator (ZGF 60 kV/2 mA, Shanghai Sute Corporation, Shanghai, China). Microparticles were collected on aluminum foil at a distance of 15 cm. The microparticles from traditional and modified electrospraying were denoted as M1 and M2, and were produced via a stainless steel needle and an EP-coated needle, respectively. Characterization: The surface morphologies of the microparticles were assessed using a Quanta FEG450 field-emission scanning electron microscope (FESEM, FEI Corporation, Netherlands). Their average size was determined by measuring the diameters of over 100 particles in FESEM images using the Image J software (National Institutes of Health, MA, USA). Differential scanning
nn
Corresponding author. Corresponding author at: Wuhan University of Science and Technology, 947 Heping Road, Wuhan 430081, China. Tel./fax: þ 86 27 68862870. E-mail addresses: [email protected] (W. Li), [email protected] (D.-G. Yu). n
0167-577X/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2012.11.064
126
W. Li et al. / Materials Letters 93 (2013) 125–128
calorimetry (DSC) analysis were carried out using an MDSC 2910 differential scanning calorimeter (TA Instruments Co., DE, USA). In vitro dissolution tests were performed according to the Chinese Pharmacopoeia (2005 edition), a paddle method using an RCZ-8A dissolution apparatus (Tianjin University Radio Factory, Tianjin, China). All experiments were conducted at 37 1C with stirring at 50 rpm, using 0.2 g of microparticles in 800 mL physiological saline. At pre-determined time intervals, aliquots of 5 mL were withdrawn for sampling and replaced by an equal volume of physiological saline to maintain a constant volume. After filtration through a 0.22 mm membrane (Millipore, MA, USA) and appropriate dilution, the sample solutions were analyzed at 273 nm (lmax for ibuprofen) with a UV spectrophotometer (Unico Instrument Co., Ltd., Shanghai, China).
3. Results and discussion Traditional electrospraying was conducted using a standard 20 G metal needle (with an inner and outer diameter of 0.60 and 0.91 mm, respectively). This is made up of 06Cr19Ni10 (GB24511 in China) austenitic stainless steel, comprising steel, C ( r0.07%), Cr (17.00–19.00%), Ni (8.00–10.00%), Mn ( r2.00%), Si (r1.00%) and traces of S and P. A typical electrospraying process is shown in Fig. 1(a). As the polymer solution leaves the spinneret a Taylor cone can initially be seen to form, followed by a short straight jet, which subsequently breaks up into fine droplets resulting from the Coulomb explosion under the electrical field [8]. The process of clogging can be seen to develop from Fig. 1(a–c); this took a time period of only ca. 2 min, meaning that frequent manual removal of the gel-like substance collecting on the nozzle of the spraying head was needed for continuous electrospraying. The modified process was observed when an EP-coated 20 G metal needle was exploited as the spraying head was depicted in Fig. 1(d–f). No clogging was observed in this process, which ran smoothly and continuously with minimum user intervention. As a protein, zein can easily interact with heavy metal elements in the spraying head through electrostatic interactions and chelation [15]. In traditional electrospraying, the applied electrical force needs to be adequate not only to overcome the viscous drag force at the droplet-air interface but also to surpass the drag force from
the spraying head; this is crucial to prevent clogging. When the EPcoated spraying head was introduced, interactions between metal elements in the needle and the biopolymer in the solution were eliminated. This not only exploited the electrical forces more effectively during electrospraying, but also made it much more difficult for the gel to cling onto the spraying head and thus to clog and interrupt electrospraying. In the traditional electrospraying process, interactions between the spraying head and spinning solutions, as well as the formation of gel-like substances on the spinneret, made atomization inhomogeneous, as indicated by the white dots of different sizes in Fig. 1(a) and (b). In stark contrast, atomization is seen to be homogeneous when using the EP-coated spraying head, as illustrated in Fig. 1(e) and (f). Clogging is usually thought to occur as a result of the high viscosity of the polymer solution and the usage of high-volatility solvents [9–12]. The results reported herein suggest that the situation is more complex, and that interactions between the polymer solution and the spraying head also influence the occurrence of clogging. FESEM images of the microparticles produced from electrospraying are given in Fig. 2. As anticipated, the microparticles generated via the traditional process (M1; diameters 1.8470.64 mm, Fig. 2a and b) were less homogeneous than those prepared by modified electrospraying (M2; diameters 1.7870.31 mm, Fig. 2c and d). The latter had a narrower diameter distribution and fewer satellites visible on the surface of the microparticles. Clogging and interruption of spraying due to the formation of a gel-like substance on the spinneret in the traditional process led not only to decreased productivity, but also affected the microparticle quality in an adverse fashion. DSC tests were performed to determine the physical status of ibuprofen in the microcomposites (see Fig. 3a). The DSC curve of pure ibuprofen exhibited a single endothermic response corresponding to its melting point of 77.4 1C. Being an amorphous biopolymer, zein did not show any fusion peaks or phase transitions. The DSC thermograms of M1 and M2 did not show any characteristic peaks of ibuprofen, suggesting that ibuprofen was no longer present as a crystalline material and was converted into an amorphous state in the microcomposites. The rapid evaporation of solvent in electrospraying and the favorable second-order interactions which can arise between zein and IBU are both likely to have played roles in the formation of amorphous composites.
Fig. 1. The electrospraying process: (a–c) the development of clogging in traditional electrospraying; (d–f) the implementation of modified electrospraying; the insets in (d) show a photo of the spraying head and the coating parameters.
W. Li et al. / Materials Letters 93 (2013) 125–128
127
Fig. 2. FESEM images of ibuprofen/zein microparticles and their size distributions: (a, b) M1 and (c, d) M2.
Fig. 3. (a) DSC traces of M1, M2, and the individual components, (b) drug release from the microparticles and (c) the hydrogen bonding interactions possible between ibuprofen and zein (n ¼6).
Both IBU and zein molecules can act as potential proton donors because they possess free hydroxyl or amino groups, and also can act as potential proton acceptors for hydrogen bonding since they possess carbonyl groups (Fig. 3c). To evaluate the functional performance of the microcomposites, in vitro dissolution tests were conducted and the drug release profiles are shown in Fig. 3(b). Compared with the M1 material from traditional electrospraying, M2 (from the modified process) provided better sustained drug release. M2 displayed a smaller burst release of 21.3% (cf. 27.7% for M1) after 1 h of release, and also a shorter ‘‘tailing-off’’ exhaustion time period [10]. The satellites on the surface of the M1 particles will exacerbate the initial burst release, while the presence of some large particles will prolong the exhaustion time since with the latter it will take a long
time for the drug to diffuse from inside of the particles to the dissolution medium. The much greater homogeneity of M2 ameliorates both these problems, yielding a more favorable release profile.
4. Conclusion This study successfully developed a modified electrospraying process, where an EP-coated spraying head was exploited for the preparation of ibuprofen/zein microcomposites. FESEM images demonstrated that the microparticles from the modified process had more homogeneous structures and a narrower size distribution than those from traditional electrospraying. DSC results indicated
128
W. Li et al. / Materials Letters 93 (2013) 125–128
that ibuprofen was converted into an amorphous state in both microcomposites, probably as a result of hydrogen bonding between zein and ibuprofen. In vitro dissolution tests demonstrated that the micoparticles from the modified process provided better sustained drug release profiles, and hence this modification will be beneficial in the development of advanced pharmaceutical materials.
Acknowledgments This work was supported by the key project of Shanghai Municipal Education Commission (no.13ZZ113) and the Specialized Research Fund for the Doctoral Program of Higher Education of China (20114219110002). References [1] Luo CJ, Stoyanov SD, Stride E, Pelan E, Edirisinghe M. Chem Soc Rev 2012;41:4708–35. [2] Chakraborty S, Liao IC, Adler A, Leong KW. Adv Drug Delivery Rev 2009;61:1043–54.
[3] George MC, Braun PV. Angew Chem Int Ed 2009;48:8606–9. [4] Salata OV. Current Nanosci 2005;1:25–33. [5] Nangrejo M, Bernardo E, Colombo P, Farook U, Ahmad Z, Stride E, et al. Mater Lett 2009;63:4835. [6] Enayati M, Ahmad Z, Stride E, Edirisinghe M. J R Soc Interface 2010 667–75. [7] Yu DG, Williams GR, Yang JH, Wang X, Yang JM, Li XY. J Mater Chem 2011;21:15957–61. [8] Deniz AE, Vural HA, Ortac- B, Uyar T. Mater Lett 2011;65:2941–3. [9] Kanjanapongkul K, Wongsasulak S, Yoovidhya T. Chem Eng Sci 2011;65:5217–25. [10] Kanjanapongkul K, Wongsasulak S, Yoovidhya T. J Appl Polym Sci 2011;118:1821–9. [11] Yu DG, Yu JH, Chen L, Williams GR, Wang X. Carbohydr Polym 2012;90:1016–23. [12] Yu DG, Williams GR, Gao LD, Bligh SWA, Yang JH, Wang X. Colloids Surf A, Physicochem Eng Aspect 2012;396:161–8. [13] Yu DG, White K, Yang JH, Wang X, Qian W, Li Y. Mater Lett 2012 78–80. [14] Nie W, Yu DG, Branford-White C, Shen XX, Zhu LM. Mater Res Innovations 2012;16:14–8. [15] Blundell TL, Jenkins JA. Chem Soc Rev 1977;6:139–71.