- Email: [email protected]
ovalbumin biocomposite scaffolds
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Effect of modified cellulose nanocrystals on microstructural and mechanical properties of polyvinyl alcohol/ovalbumin biocomposite scaffolds Anuj Kumar a, Yuvraj Singh Negi a,n, Veena Choudhary b, Nishi Kant Bhardwaj c a
Department of Polymer and Process Engineering, Indian Institute of Technology Roorkee, India Centre for Polymer Science and Engineering, Indian Institute of Technology Delhi, India c Avantha Centre for Industrial Research and Development (ACIRD), Yamuna Nagar, Haryana, India b
art ic l e i nf o
a b s t r a c t
Article history: Received 25 October 2013 Accepted 3 May 2014
In order to improve the functional compatibility and mechanical performance of biocomposite scaffolds, two different biocomposite scaffolds based on ovalbumin (OVA)/polyvinyl alcohol (PVA) reinforced with unmodified and aminated cellulose nanocrystals (CNCs) cross-linked with glutaraldehyde (GA) were fabricated by a freeze drying process. It was observed that the microstructure and mechanical properties of the biocomposite scaffolds were not affected to a great extent by the presence of aminated CNCs. At a compressive strain of 70%, the compressive strengths of PVA/OVA (porosity: 85%) (a), PVA–CNCs/OVA (porosity: 87.4%) (b), and PVA–CNCs–NH2/OVA (porosity: 87.7%) (c) were 0.08 MPa, 0.21 MPa and 0.26 MPa, respectively. & 2014 Published by Elsevier B.V.
Keywords: Ovalbumin Cellulose nanocrystals Biomaterials Microstructure Freeze drying Compressive strength
1. Introduction For the development of porous polymeric scaffolds, many biomaterials have extensively been studied but ovalbumin (OVA) has not been studied well for reconstruction of organs. Recently, OVA based biocomposite has attracted considerable attention as a substitute for bone tissue engineering [1,2]. The OVA (a glycoprotein found in chicken egg whites) comprises 386 amino acids with 10% of the amino acid sequence conserved when compared with human serum albumin and comprises mainly α-helix and β-sheet structures [3,4]. It can be used to produce biocompatible scaffolds that support in osteoblast adhesion and mineralization into 3D porous structures [5]. Recent studies revealed the application of OVA with hydroxyapatite (HA) [2,6] for bone tissue engineering applications. Also, the properties of OVA based scaffolds [1] and the effect of cellulose nanocrystals (CNCs) on OVA based porous scaffolds [7] were studied for improving mechanical properties to prevent immediate failure upon implantation. Hence, the fabrication of OVA based scaffolds is attempted to improve their properties through the freeze drying method. Among different fabrication techniques used, freeze drying has been a promising technique to fabricate porous structures with controlled porosity such as scaffolds [8,9]. n
Corresponding author. Tel.: þ 91 132 2714303. E-mail address: [email protected] (Y.S. Negi).
CNCs have remarkable properties (unique strength, low density, biocompatibility, biodegradability and surface properties) which make them ideal reinforcing agents in polymer matrices [10] and mainly serve to increase the mechanical performance of the scaffold. PVA as a biomaterial is used in different biomedical applications [11,12]. In this work, we proposed to fabricate PVA/OVA/(CNCs or CNCs–NH2) biocomposite scaffolds using the freeze drying method to study the functional compatibility of the cellulose nanocrystals (CNCs or CNC–NH2) and OVA–NH2 PVA was used as a binder into composite solution of OVA and CNCs because it renders the segregation of CNCs in OVA solution and gives nearly homogenous and stable solution. The effect of CNCs and aminated CNCs (creating amino (–NH2) groups on nanocrystals like OVA) on morphological, structural and mechanical properties was investigated in PVA/OVA based biocomposite scaffolds. This study provides the primary insight if modification of CNCs is necessary or not to fabricate the biocomposite scaffolds which may promisingly be used in bone tissue engineering.
2. Experimental Materials: Egg albumin (flakes) and PVA (PVA: 85–89% degree of hydrolysis) were supplied by HiMedia Laboratories Pvt. Ltd. and Fisher Scientific, respectively.
http://dx.doi.org/10.1016/j.matlet.2014.05.038 0167-577X/& 2014 Published by Elsevier B.V.
Please cite this article as: Kumar A, et al. Effect of modified cellulose nanocrystals on microstructural and mechanical properties of polyvinyl alcohol/ovalbumin biocomposite scaffolds. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.05.038i
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A. Kumar et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
Preparation of porous biocomposite scaffolds: An aqueous suspension of CNCs was prepared from chemically purified cellulose as previously reported [13]. The surface of the CNCs was chemically modified as described elsewhere [14]. The final concentration
of the CNCs and CNCs–NH2 suspension was made to 1 wt%. OVA solution (5 wt%) was prepared as described elsewhere [1]. 10 g of PVA was prepared in distilled water at 65–75 1C for 3 h. The final solution was prepared in two successive steps: (1) aqueous
Fig. 1. FE-SEM micrographs of (a) neat PVA scaffold and (b) PVA/OVA biocomposite scaffold.
Fig. 2. FE-SEM micrographs of (a,b) OVA, (c,d) PVA–CNCs/OVA, and (e,f) PVA–CNCs–NH2/OVA biocomposite scaffolds.
Please cite this article as: Kumar A, et al. Effect of modified cellulose nanocrystals on microstructural and mechanical properties of polyvinyl alcohol/ovalbumin biocomposite scaffolds. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.05.038i
A. Kumar et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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suspensions of CNCs and aminated CNCs were mixed with the PVA solution in (50/50) wt% ratio at room temperature and then heated at 65–75 1C for 2 h with constant stirring for homogenous solution; the final pH of PVA/CNCs and PVA/CNCs–NH2 solutions was about 7.0, (2) the prepared solutions were mixed with an OVA solution with 1 ml glutaraldehyde (GA) as a cross-linker with constant and slow stirring at room temperature for the overnight. Then the obtained solutions were poured into cylindrical molds and kept in a deep freezer at 40 1C for 12 h and freeze dried at 40 1C for 2 days. Characterization: The scaffolds were characterized by a Field emission scanning electron microscope (FE-SEM-FEI Quanta 200F), Fourier transform infrared spectrophotometer (FTIR-Thermo Nicolet, USA), X-ray diffraction diffractometer (XRD-Bruker AXS D8 Advance), SEM image analysis (ImageJ Software), and the porosity was calculated by liquid displacement method using ethanol which is not a solvent for the scaffolds [15]. The compressive strength of scaffolds was measured at a crosshead speed of 2 mm min 1 at 25 1C using Universal Testing Machine (UTM, Instron 3365) with 5 kN load cell.
3. Results and discussion Morphology: FE-SEM images show the morphology and microstructure of neat PVA scaffold (a) and PVA/OVA biocomposite scaffold (b) as shown in Fig. 1 and OVA (Fig. 2(a and b) as pore channels having a smooth surface), PVA–CNCs/OVA (Fig. 2(c and d)) and PVA–CNCs–NH2/OVA (Fig. 2(e and f)) biocomposite scaffolds which exhibit highly interconnected porous structures having open pore channels with different lamellae walls where pores are either interconnected or separated via walls.
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Structural analysis: The IR spectra of the OVA, PVA, CNCs, CNCs– NH2, PVA–CNCs/OVA and PVA–CNCs–NH2/OVA are shown in Fig. 3(a and b). The characteristic peaks of OVA appear at 3292–3299 cm 1 (N–H stretching), 3072 cm 1 (O–H stretching), 2956 cm 1 (C–H stretching), 1652–1650 cm 1 (amide-I, CQO stretching), 1550– 1539 cm 1 (amid-II, C–N stretching and N–H bending), 1448– 1457 cm 1 (C–H stretching), 1395 cm 1 (C–H bending), 1314 cm 1 (COO ), 1240–1238 cm 1 (amide-III, C–N stretching and N–H bending), 1162 cm 1 and 1071 cm 1 (C–O–H bending) [6,2,16] but freeze dried OVA shows main characteristic peaks at 3303, 1651, 1544, 1460, 1397, 1240 cm 1 respectively. Here, freeze drying induces the structural changes mainly in the amide-I, II, or III region (an increase in βsheet content) [17,18]. The CNCs show characteristic peaks similar to cellulose at 3436 cm 1 (O–H stretching), 1636 cm 1 (deformation of –OH groups), 1500–1200 cm 1 (deformation of primary and secondary –OH groups), 1150 cm 1 (C–O–C asymmetric bridge stretching) and 1062 cm 1 (C–O symmetric stretching), and 897 cm 1 (β-Glucosidic linkages) and 670 cm 1 (C–OH out-of-plane bending). In case of aminated CNCs (CNCs–NH2), intensity of bands between 1500 and 1200 cm 1 decreased due to –OH group substitution of carbon 6 and other significant changes with N–H band (1640–1500 cm 1) and with the shift of the bands 898, 670, and 613 cm 1 observed in CNCs to 899, 672, and 614 cm 1 (C–OH stretching and bending) for aminated CNCs (as shown in Fig. 3a) [11,19,20,21]. The characteristic peaks of PVA (PVA-85–89) [11,12] can be associated with other constituents in PVA–CNCs/OVA and PVA–CNCs–NH2/OVA biocomposite scaffolds. The structural changes due to GA cross linking (presence of Schiff base) in biocomposite scaffolds can be analyzed in amide-I region (1600–1700 cm 1) [1] and the presence of duplet at (2860– 2880 cm 1 and 2750–2730 cm 1) [22,23]. XRD spectrum (Fig. 3c) exhibits characteristic peaks of CNCs at around 2θ¼ 16.51, 22.51, and 33.41 representing typical structure of
Fig. 3. (a) FT-IR spectra of CNCs and CNCs–NH2, (b) FT-IR spectra of OVA, PVA, CNCs, CNCs–NH2, PVA–CNCs/OVA, and PVA–CNCs–NH2/OVA, (c) XRD patterns of OVA, PVACNCs/OVA, and PVA-CNCs-NH2/OVA biocomposite scaffolds.
Please cite this article as: Kumar A, et al. Effect of modified cellulose nanocrystals on microstructural and mechanical properties of polyvinyl alcohol/ovalbumin biocomposite scaffolds. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.05.038i
A. Kumar et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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scaffolds. At the compressive strain of 70%, the compressive strengths of PVA/OVA (a), PVA–CNCs/OVA (b), and PVA–CNCs–NH2/OVA (c) were 0.08 MPa, 0.21 MPa, and 0.26 MPa, respectively. Regardless of the type of CNCs, biocomposite scaffolds showed nearly similar structural, microstructural, and mechanical properties.
Acknowledgments One of the authors Mr. Anuj Kumar acknowledge the financial support from the Ministry of Human Resource Development (MHRD), New Delhi and Indian Institute of Technology Roorkee (IIT Roorkee), India, for providing other infrastructures required for Q3 PhD research work. Fig. 4. Compressive stress–strain curves of (a) PVA/OVA, PVA–CNCs/OVA (b), and (c) PVA–CNCs–NH2/OVA biocomposite scaffolds.
cellulose-I [12,13,24,25] and PVA showed three main characteristic peaks at 19.41 (strong), 22.51 (medium), and 40.31 (weak) [26]. Both PVA–CNCs/OVA and PVA–CNCs–NH2/OVA biocomposite scaffolds show similar diffractograms. Here, the presence of OVA has induced the characteristic peaks of OVA [2,4] showing highly amorphous character. The degrees of crystallinity of PVA–CNCs/ OVA and PVA–CNCs–NH2/OVA scaffolds calculated according to amorphous subtraction method [27] were 25.5%, and 28.09%, respectively. Mechanical properties: The compressive property (stiffness) of the scaffold influences the features of cells and tissues [28]. OVA scaffold has a very brittle nature with low mechanical performance but OVA based scaffolds containing CNCs (both unmodified and modified) showed higher mechanical properties (flexibility and strength) as compared to neat OVA and PVA/OVA based scaffolds. The compressive stress–strain curves for PVA/OVA, PVA–CNCs/OVA, and PVA–CNCs–NH2/OVA biocomposite scaffolds are shown in Fig. 4. The compressive stress–strain curves show a typical soft-tissues behavior exhibiting three regions as a linear elastic region (I) due to the bending of pore edges, a stress plateau (II) due to progressive collapsing of pore walls by plastic yielding, brittle crushing, and densification (III) due to collapsing of pores followed by loading of the edges and faces of pore walls against one another [29]. At compressive strain of 70%, the compressive strengths of PVA/OVA (porosity: 85%, pore channel size: 4240 μm long axis and 434 μm short axis) (a), PVA–CNCs/ OVA (porosity: 87.4%, pore channel size: 4 170 μm long axis and 415 μm short axis) (b) and PVA/CNCs–NH2/OVA (porosity: 87.7%, pore channel size: 4200 μm long axis and 415 μm short axis) (c) were 0.08 MPa, 0.21 MPa and 0.26 MPa, respectively. The incorporation of CNCs increased the mechanical performance of the PVA/CNCs/OVA biocomposite scaffolds. However, PVA/CNCs/ OVA and PVA/CNCs–NH2/OVA biocomposite scaffolds showed a nearly similar mechanical behavior.
References [1] Farrar G, Barone J, Morgan A. J Tissue Eng 2010:1–6. [2] Khasuwan P, Kuanchertchoo N, Wetprasit N, Supaphol P. Mater Sci Eng C 2012;32:758–62. [3] Hu HY, Du HN. J Protein Chem 2000;19:177–83. [4] Pal P, Mahato M, Kamilya T, Tah B, Sarkar E, Talapatra GB. J Phys Chem B 2011;115:4259–65. [5] Nair LS, Laurencin CT. Prog Polym Sci 2007;32:762–98. [6] Zhao H, He W, Wang Y, Zhang X, Li Z, Yan S, et al. Mater Lett 2008;62:3603–5. [7] Glaesemann BP.[M.Sc. thesis]. Blacksburg, Virginia : Virginia Polytechnic Institute and State University; 2011. [8] Barr SA, Luijten E. Acta Mater 2010;58:709–15. [9] Deville S, Saiz E, Tomsia AP. Biomaterials 2006;27:5480–9. [10] Wang H, Roman M. Biomacromolecules 2011;12:1585–93. [11] Sun P, Chen J, Liu ZW, Liu ZT. J Macromol Sci Part A: Pure Appl Chem 2009;46:533–40. [12] Kumar A, Negi YS, Bhardwaj NK, Choudhary V. Carbohydr Polym 2012;88:1364–72. [13] Kumar A, Negi YS, Choudhary, Bhardwaj NK. J Mater Phys Chem 2014;2:1–8. [14] Dong S, Roman MJ. Am Chem Soc 2007;129:13810–1. [15] Nie L, Chen D, Suo J, Zou P, Feng S, Yang Q, et al. Colloid Surf B 2012;100:169–76. [16] Xu C, He D, Zeng L, Luo S. Colloid Surf B 2009;73:360–4. [17] Dong A, Prestrelski SJ, Allison SD, Carpenter JF. J Pharm Sci 1995;84:415–23. [18] Griebenow K, Klibanov AM. Proc Natl Acad Sci USA 1995;92:10969–76. [19] Filho EC, de Melo JCP, Airoldi C. Carbohydr Res 2006;341:2842–50. [20] Schwanninger M, Rodrigues JC, Pereira H, Hinterstoisser B. Vib Spectrosc 2004;36:23–40. [21] Linder AP, Bergman R, Bodin A, Gatenholm P. Langmuir 2003;19:5072–7. [22] Mansur HS, Costa HS. Chem Eng J 2008;137:72–83. [23] Mansur HS, Sadahira CM, Souza AN, Mansur AAP. Mater Sci Eng, C 2008;28:539–48. [24] Chen WS, Yu HP, Liu YX, Chen P, Zhang MX, Hai YF. Carbohydr Polym 2011;83:1804–11. [25] Teixeira EM, Bondancia TJ, Teodoro KBR, Correa AC, Marconcini JM, Mattoso LHC. Ind Crops Prod 2011;33:63–6. [26] Costa-Junior ES, Barbosa-Stancioli EF, Mansur AAP, Vasconcelos WL, Mansur HS. Carbohydr Polym 2009;76:472–81. [27] Park S, Baker JO, Himmel ME, Parilla PA, Johnson DK. Biotechnol Biofuel 2010;3:1–10. [28] Discher DE, Janmey P, Wang YL. Science 2005;310:1139–43. [29] Gibson LJ. J Biomech 2005;38:377–99.
4. Conclusion The biocomposite scaffolds were fabricated to investigate the effect of modified CNCs on microstructural and mechanical properties of PVA–CNCs/OVA and PVA–CNCs–NH2/OVA biocomposite
Please cite this article as: Kumar A, et al. Effect of modified cellulose nanocrystals on microstructural and mechanical properties of polyvinyl alcohol/ovalbumin biocomposite scaffolds. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.05.038i
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Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Effect of modified cellulose nanocrystals on microstructural and mechanical properties of polyvinyl alcohol/ovalbumin biocomposite scaffolds Anuj Kumar a, Yuvraj Singh Negi a,n, Veena Choudhary b, Nishi Kant Bhardwaj c a
Department of Polymer and Process Engineering, Indian Institute of Technology Roorkee, India Centre for Polymer Science and Engineering, Indian Institute of Technology Delhi, India c Avantha Centre for Industrial Research and Development (ACIRD), Yamuna Nagar, Haryana, India b
art ic l e i nf o
a b s t r a c t
Article history: Received 25 October 2013 Accepted 3 May 2014
In order to improve the functional compatibility and mechanical performance of biocomposite scaffolds, two different biocomposite scaffolds based on ovalbumin (OVA)/polyvinyl alcohol (PVA) reinforced with unmodified and aminated cellulose nanocrystals (CNCs) cross-linked with glutaraldehyde (GA) were fabricated by a freeze drying process. It was observed that the microstructure and mechanical properties of the biocomposite scaffolds were not affected to a great extent by the presence of aminated CNCs. At a compressive strain of 70%, the compressive strengths of PVA/OVA (porosity: 85%) (a), PVA–CNCs/OVA (porosity: 87.4%) (b), and PVA–CNCs–NH2/OVA (porosity: 87.7%) (c) were 0.08 MPa, 0.21 MPa and 0.26 MPa, respectively. & 2014 Published by Elsevier B.V.
Keywords: Ovalbumin Cellulose nanocrystals Biomaterials Microstructure Freeze drying Compressive strength
1. Introduction For the development of porous polymeric scaffolds, many biomaterials have extensively been studied but ovalbumin (OVA) has not been studied well for reconstruction of organs. Recently, OVA based biocomposite has attracted considerable attention as a substitute for bone tissue engineering [1,2]. The OVA (a glycoprotein found in chicken egg whites) comprises 386 amino acids with 10% of the amino acid sequence conserved when compared with human serum albumin and comprises mainly α-helix and β-sheet structures [3,4]. It can be used to produce biocompatible scaffolds that support in osteoblast adhesion and mineralization into 3D porous structures [5]. Recent studies revealed the application of OVA with hydroxyapatite (HA) [2,6] for bone tissue engineering applications. Also, the properties of OVA based scaffolds [1] and the effect of cellulose nanocrystals (CNCs) on OVA based porous scaffolds [7] were studied for improving mechanical properties to prevent immediate failure upon implantation. Hence, the fabrication of OVA based scaffolds is attempted to improve their properties through the freeze drying method. Among different fabrication techniques used, freeze drying has been a promising technique to fabricate porous structures with controlled porosity such as scaffolds [8,9]. n
Corresponding author. Tel.: þ 91 132 2714303. E-mail address: [email protected] (Y.S. Negi).
CNCs have remarkable properties (unique strength, low density, biocompatibility, biodegradability and surface properties) which make them ideal reinforcing agents in polymer matrices [10] and mainly serve to increase the mechanical performance of the scaffold. PVA as a biomaterial is used in different biomedical applications [11,12]. In this work, we proposed to fabricate PVA/OVA/(CNCs or CNCs–NH2) biocomposite scaffolds using the freeze drying method to study the functional compatibility of the cellulose nanocrystals (CNCs or CNC–NH2) and OVA–NH2 PVA was used as a binder into composite solution of OVA and CNCs because it renders the segregation of CNCs in OVA solution and gives nearly homogenous and stable solution. The effect of CNCs and aminated CNCs (creating amino (–NH2) groups on nanocrystals like OVA) on morphological, structural and mechanical properties was investigated in PVA/OVA based biocomposite scaffolds. This study provides the primary insight if modification of CNCs is necessary or not to fabricate the biocomposite scaffolds which may promisingly be used in bone tissue engineering.
2. Experimental Materials: Egg albumin (flakes) and PVA (PVA: 85–89% degree of hydrolysis) were supplied by HiMedia Laboratories Pvt. Ltd. and Fisher Scientific, respectively.
http://dx.doi.org/10.1016/j.matlet.2014.05.038 0167-577X/& 2014 Published by Elsevier B.V.
Please cite this article as: Kumar A, et al. Effect of modified cellulose nanocrystals on microstructural and mechanical properties of polyvinyl alcohol/ovalbumin biocomposite scaffolds. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.05.038i
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A. Kumar et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
Preparation of porous biocomposite scaffolds: An aqueous suspension of CNCs was prepared from chemically purified cellulose as previously reported [13]. The surface of the CNCs was chemically modified as described elsewhere [14]. The final concentration
of the CNCs and CNCs–NH2 suspension was made to 1 wt%. OVA solution (5 wt%) was prepared as described elsewhere [1]. 10 g of PVA was prepared in distilled water at 65–75 1C for 3 h. The final solution was prepared in two successive steps: (1) aqueous
Fig. 1. FE-SEM micrographs of (a) neat PVA scaffold and (b) PVA/OVA biocomposite scaffold.
Fig. 2. FE-SEM micrographs of (a,b) OVA, (c,d) PVA–CNCs/OVA, and (e,f) PVA–CNCs–NH2/OVA biocomposite scaffolds.
Please cite this article as: Kumar A, et al. Effect of modified cellulose nanocrystals on microstructural and mechanical properties of polyvinyl alcohol/ovalbumin biocomposite scaffolds. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.05.038i
A. Kumar et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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suspensions of CNCs and aminated CNCs were mixed with the PVA solution in (50/50) wt% ratio at room temperature and then heated at 65–75 1C for 2 h with constant stirring for homogenous solution; the final pH of PVA/CNCs and PVA/CNCs–NH2 solutions was about 7.0, (2) the prepared solutions were mixed with an OVA solution with 1 ml glutaraldehyde (GA) as a cross-linker with constant and slow stirring at room temperature for the overnight. Then the obtained solutions were poured into cylindrical molds and kept in a deep freezer at 40 1C for 12 h and freeze dried at 40 1C for 2 days. Characterization: The scaffolds were characterized by a Field emission scanning electron microscope (FE-SEM-FEI Quanta 200F), Fourier transform infrared spectrophotometer (FTIR-Thermo Nicolet, USA), X-ray diffraction diffractometer (XRD-Bruker AXS D8 Advance), SEM image analysis (ImageJ Software), and the porosity was calculated by liquid displacement method using ethanol which is not a solvent for the scaffolds [15]. The compressive strength of scaffolds was measured at a crosshead speed of 2 mm min 1 at 25 1C using Universal Testing Machine (UTM, Instron 3365) with 5 kN load cell.
3. Results and discussion Morphology: FE-SEM images show the morphology and microstructure of neat PVA scaffold (a) and PVA/OVA biocomposite scaffold (b) as shown in Fig. 1 and OVA (Fig. 2(a and b) as pore channels having a smooth surface), PVA–CNCs/OVA (Fig. 2(c and d)) and PVA–CNCs–NH2/OVA (Fig. 2(e and f)) biocomposite scaffolds which exhibit highly interconnected porous structures having open pore channels with different lamellae walls where pores are either interconnected or separated via walls.
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Structural analysis: The IR spectra of the OVA, PVA, CNCs, CNCs– NH2, PVA–CNCs/OVA and PVA–CNCs–NH2/OVA are shown in Fig. 3(a and b). The characteristic peaks of OVA appear at 3292–3299 cm 1 (N–H stretching), 3072 cm 1 (O–H stretching), 2956 cm 1 (C–H stretching), 1652–1650 cm 1 (amide-I, CQO stretching), 1550– 1539 cm 1 (amid-II, C–N stretching and N–H bending), 1448– 1457 cm 1 (C–H stretching), 1395 cm 1 (C–H bending), 1314 cm 1 (COO ), 1240–1238 cm 1 (amide-III, C–N stretching and N–H bending), 1162 cm 1 and 1071 cm 1 (C–O–H bending) [6,2,16] but freeze dried OVA shows main characteristic peaks at 3303, 1651, 1544, 1460, 1397, 1240 cm 1 respectively. Here, freeze drying induces the structural changes mainly in the amide-I, II, or III region (an increase in βsheet content) [17,18]. The CNCs show characteristic peaks similar to cellulose at 3436 cm 1 (O–H stretching), 1636 cm 1 (deformation of –OH groups), 1500–1200 cm 1 (deformation of primary and secondary –OH groups), 1150 cm 1 (C–O–C asymmetric bridge stretching) and 1062 cm 1 (C–O symmetric stretching), and 897 cm 1 (β-Glucosidic linkages) and 670 cm 1 (C–OH out-of-plane bending). In case of aminated CNCs (CNCs–NH2), intensity of bands between 1500 and 1200 cm 1 decreased due to –OH group substitution of carbon 6 and other significant changes with N–H band (1640–1500 cm 1) and with the shift of the bands 898, 670, and 613 cm 1 observed in CNCs to 899, 672, and 614 cm 1 (C–OH stretching and bending) for aminated CNCs (as shown in Fig. 3a) [11,19,20,21]. The characteristic peaks of PVA (PVA-85–89) [11,12] can be associated with other constituents in PVA–CNCs/OVA and PVA–CNCs–NH2/OVA biocomposite scaffolds. The structural changes due to GA cross linking (presence of Schiff base) in biocomposite scaffolds can be analyzed in amide-I region (1600–1700 cm 1) [1] and the presence of duplet at (2860– 2880 cm 1 and 2750–2730 cm 1) [22,23]. XRD spectrum (Fig. 3c) exhibits characteristic peaks of CNCs at around 2θ¼ 16.51, 22.51, and 33.41 representing typical structure of
Fig. 3. (a) FT-IR spectra of CNCs and CNCs–NH2, (b) FT-IR spectra of OVA, PVA, CNCs, CNCs–NH2, PVA–CNCs/OVA, and PVA–CNCs–NH2/OVA, (c) XRD patterns of OVA, PVACNCs/OVA, and PVA-CNCs-NH2/OVA biocomposite scaffolds.
Please cite this article as: Kumar A, et al. Effect of modified cellulose nanocrystals on microstructural and mechanical properties of polyvinyl alcohol/ovalbumin biocomposite scaffolds. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.05.038i
A. Kumar et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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scaffolds. At the compressive strain of 70%, the compressive strengths of PVA/OVA (a), PVA–CNCs/OVA (b), and PVA–CNCs–NH2/OVA (c) were 0.08 MPa, 0.21 MPa, and 0.26 MPa, respectively. Regardless of the type of CNCs, biocomposite scaffolds showed nearly similar structural, microstructural, and mechanical properties.
Acknowledgments One of the authors Mr. Anuj Kumar acknowledge the financial support from the Ministry of Human Resource Development (MHRD), New Delhi and Indian Institute of Technology Roorkee (IIT Roorkee), India, for providing other infrastructures required for Q3 PhD research work. Fig. 4. Compressive stress–strain curves of (a) PVA/OVA, PVA–CNCs/OVA (b), and (c) PVA–CNCs–NH2/OVA biocomposite scaffolds.
cellulose-I [12,13,24,25] and PVA showed three main characteristic peaks at 19.41 (strong), 22.51 (medium), and 40.31 (weak) [26]. Both PVA–CNCs/OVA and PVA–CNCs–NH2/OVA biocomposite scaffolds show similar diffractograms. Here, the presence of OVA has induced the characteristic peaks of OVA [2,4] showing highly amorphous character. The degrees of crystallinity of PVA–CNCs/ OVA and PVA–CNCs–NH2/OVA scaffolds calculated according to amorphous subtraction method [27] were 25.5%, and 28.09%, respectively. Mechanical properties: The compressive property (stiffness) of the scaffold influences the features of cells and tissues [28]. OVA scaffold has a very brittle nature with low mechanical performance but OVA based scaffolds containing CNCs (both unmodified and modified) showed higher mechanical properties (flexibility and strength) as compared to neat OVA and PVA/OVA based scaffolds. The compressive stress–strain curves for PVA/OVA, PVA–CNCs/OVA, and PVA–CNCs–NH2/OVA biocomposite scaffolds are shown in Fig. 4. The compressive stress–strain curves show a typical soft-tissues behavior exhibiting three regions as a linear elastic region (I) due to the bending of pore edges, a stress plateau (II) due to progressive collapsing of pore walls by plastic yielding, brittle crushing, and densification (III) due to collapsing of pores followed by loading of the edges and faces of pore walls against one another [29]. At compressive strain of 70%, the compressive strengths of PVA/OVA (porosity: 85%, pore channel size: 4240 μm long axis and 434 μm short axis) (a), PVA–CNCs/ OVA (porosity: 87.4%, pore channel size: 4 170 μm long axis and 415 μm short axis) (b) and PVA/CNCs–NH2/OVA (porosity: 87.7%, pore channel size: 4200 μm long axis and 415 μm short axis) (c) were 0.08 MPa, 0.21 MPa and 0.26 MPa, respectively. The incorporation of CNCs increased the mechanical performance of the PVA/CNCs/OVA biocomposite scaffolds. However, PVA/CNCs/ OVA and PVA/CNCs–NH2/OVA biocomposite scaffolds showed a nearly similar mechanical behavior.
References [1] Farrar G, Barone J, Morgan A. J Tissue Eng 2010:1–6. [2] Khasuwan P, Kuanchertchoo N, Wetprasit N, Supaphol P. Mater Sci Eng C 2012;32:758–62. [3] Hu HY, Du HN. J Protein Chem 2000;19:177–83. [4] Pal P, Mahato M, Kamilya T, Tah B, Sarkar E, Talapatra GB. J Phys Chem B 2011;115:4259–65. [5] Nair LS, Laurencin CT. Prog Polym Sci 2007;32:762–98. [6] Zhao H, He W, Wang Y, Zhang X, Li Z, Yan S, et al. Mater Lett 2008;62:3603–5. [7] Glaesemann BP.[M.Sc. thesis]. Blacksburg, Virginia : Virginia Polytechnic Institute and State University; 2011. [8] Barr SA, Luijten E. Acta Mater 2010;58:709–15. [9] Deville S, Saiz E, Tomsia AP. Biomaterials 2006;27:5480–9. [10] Wang H, Roman M. Biomacromolecules 2011;12:1585–93. [11] Sun P, Chen J, Liu ZW, Liu ZT. J Macromol Sci Part A: Pure Appl Chem 2009;46:533–40. [12] Kumar A, Negi YS, Bhardwaj NK, Choudhary V. Carbohydr Polym 2012;88:1364–72. [13] Kumar A, Negi YS, Choudhary, Bhardwaj NK. J Mater Phys Chem 2014;2:1–8. [14] Dong S, Roman MJ. Am Chem Soc 2007;129:13810–1. [15] Nie L, Chen D, Suo J, Zou P, Feng S, Yang Q, et al. Colloid Surf B 2012;100:169–76. [16] Xu C, He D, Zeng L, Luo S. Colloid Surf B 2009;73:360–4. [17] Dong A, Prestrelski SJ, Allison SD, Carpenter JF. J Pharm Sci 1995;84:415–23. [18] Griebenow K, Klibanov AM. Proc Natl Acad Sci USA 1995;92:10969–76. [19] Filho EC, de Melo JCP, Airoldi C. Carbohydr Res 2006;341:2842–50. [20] Schwanninger M, Rodrigues JC, Pereira H, Hinterstoisser B. Vib Spectrosc 2004;36:23–40. [21] Linder AP, Bergman R, Bodin A, Gatenholm P. Langmuir 2003;19:5072–7. [22] Mansur HS, Costa HS. Chem Eng J 2008;137:72–83. [23] Mansur HS, Sadahira CM, Souza AN, Mansur AAP. Mater Sci Eng, C 2008;28:539–48. [24] Chen WS, Yu HP, Liu YX, Chen P, Zhang MX, Hai YF. Carbohydr Polym 2011;83:1804–11. [25] Teixeira EM, Bondancia TJ, Teodoro KBR, Correa AC, Marconcini JM, Mattoso LHC. Ind Crops Prod 2011;33:63–6. [26] Costa-Junior ES, Barbosa-Stancioli EF, Mansur AAP, Vasconcelos WL, Mansur HS. Carbohydr Polym 2009;76:472–81. [27] Park S, Baker JO, Himmel ME, Parilla PA, Johnson DK. Biotechnol Biofuel 2010;3:1–10. [28] Discher DE, Janmey P, Wang YL. Science 2005;310:1139–43. [29] Gibson LJ. J Biomech 2005;38:377–99.
4. Conclusion The biocomposite scaffolds were fabricated to investigate the effect of modified CNCs on microstructural and mechanical properties of PVA–CNCs/OVA and PVA–CNCs–NH2/OVA biocomposite
Please cite this article as: Kumar A, et al. Effect of modified cellulose nanocrystals on microstructural and mechanical properties of polyvinyl alcohol/ovalbumin biocomposite scaffolds. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.05.038i