The effect of radiation on the thermal properties of ...

The effect of radiation on the thermal properties of chitosan/mimosa tenuiflora and chitosan/mimosa tenuiflora/multiwalled carbon nanotubes (MWCNT) composites for bone tissue engineering S. A. Martel-Estrada, E. Santos-Rodríguez, I. Olivas-Armendáriz, E. Cruz-Zaragoza, and C. A. Martínez-Pérez Citation: AIP Conference Proceedings 1607, 55 (2014); doi: 10.1063/1.4890703 View online: http://dx.doi.org/10.1063/1.4890703 View Table of Contents: http://scitation.aip.org/content/aip/proceeding/aipcp/1607?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Thermal expansion of multiwall carbon nanotube reinforced nanocrystalline silver matrix composite AIP Conf. Proc. 1591, 374 (2014); 10.1063/1.4872607 Effects of high energy electrons on the properties of polyethylene / multiwalled carbon nanotubes composites: Comparison of as-grown and oxygen-functionalised MWCNT AIP Conf. Proc. 1593, 290 (2014); 10.1063/1.4873784 Thermal stability and electrical conductivity of multiwalled carbon nanotube (MWCNT)/polymethyl methacrylite (PMMA) nanocomposite prepared via the coagulation method AIP Conf. Proc. 1455, 212 (2012); 10.1063/1.4732494 Mechanical properties of multi-walled carbon nanotube (MWCNT)/polymethyl methacrylite (PMMA) nanocomposite prepared via the coagulation method AIP Conf. Proc. 1455, 208 (2012); 10.1063/1.4732493 Thermal properties of heat storage composites containing multiwalled carbon nanotubes J. Appl. Phys. 104, 113537 (2008); 10.1063/1.3041495

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 189.172.240.99 On: Sat, 19 Jul 2014 15:35:36

The effect of radiation on the thermal properties of chitosan/mimosa tenuiflora and chitosan/mimosa tenuiflora/multiwalled carbon nanotubes (MWCNT) composites for bone tissue engineering S.A. Martel-Estrada1, E. Santos-Rodríguez2, I. Olivas-Armendáriz3, E. CruzZaragoza4, C.A. Martínez-Pérez3 1

2

Instituto de Arquitectura, Diseño y Arte, Universidad Autónoma de Cd. Juárez, Av. Del Charro 450 Norte. Col. Universidad, C.P: 32310, Cd. Juárez, Chihuahua, México.

ICTP Meso-American Centre for Theoretical Physics (ICTP-MCTP) Universidad Autónoma de Chiapas. Ciudad Universitaria, Carretera Zapata Km. 4, Real del Bosque (Terán), 29040, Tuxtla Gutiérrez, Chiapas.

3

Instituto de Ingeniería y Tecnología, Universidad Autónoma de Cd. Juárez, Av. Del Charro 450 Norte, Col. Universidad, C.P. 32310, Cd. Juárez, Chihuahua, México 4

Instituto de Ciencias Nucleares. Universidad Nacional Autónoma de México. Circuito Exterior s/n, Ciudad Universitaria. Delg. Coyoacán. C.P. 04510, México DF.

Abstract. The purpose of this study is to examine the effect of gamma radiation and UV radiation on the microstructure, chemical structure and thermal stability of Chitosan/Mimosa Tenuiflora and Chitosan/Mimosa Tenuiflora/MWCNT composites scaffolds produced by thermally induced phase separation. The composites were irradiated and observed to undergo radiation-induced degradation through chain scission. Morphology, thermal properties and effects on chemical and semi-crystalline structures were obtained by scanning electronic microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), FT-IR analysis and X-ray Diffraction. A relationship between radiation type and the thermal stability of the composites, were also established. This relationship allows a more accurate and precise control of the life span of Chitosan/Mimosa Tenuiflora and Chitosan/Mimosa Tenuiflora/MWCNT composites through the use of radiation in materials for use in tissue engineering. Keywords: Chitosan, MWCNT, Mimosa Tenuiflora, Radiation. PACS: 78, 81, 82, 87

INTRODUCTION Tissue engineering approaches includes the development of porous scaffolds that could induce the formation of bone from the surrounding tissue 1. These scaffolds are fabricated from polymeric composites that mimic the structure and function of the natural extracellular matrix (ECM) 2. Response of the organism to the implanted scaffold depends on numerous factors. One of the most important is sterility. Different procedures can be used for the sterilization of polymers such as sterilization by ethylene oxide gas, low temperature plasma, injection molding process, Radiation Physics AIP Conf. Proc. 1607, 55-64 (2014); doi: 10.1063/1.4890703 © 2014 AIP Publishing LLC 978-0-7354-1243-9/$30.00

55 to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: This article is copyrighted as indicated in the article. Reuse of AIP content is subject 189.172.240.99 On: Sat, 19 Jul 2014 15:35:36

steam, UV radiation, etc. On the other hand, sterilization by high energy radiation are usually used for polymers3. In the case of biomaterials with porous structure, the sterilization is crucial and its efficiency needs to be confirmed. Nevertheless, the effects of radiation on the polymer must be evaluated before the use of this procedure, because the use of radiation can cause changes in the mechanical properties, degradation behavior, morphology and structure of the material 3,4. Chitosan is a biopolymer composed of glucosamine and N-acetyl glucosamine residues with a β-1 , 4-linkage. Chitosan is biodegradable, bio-functional, biocompatible, and has antimicrobial properties. It is a natural polysaccharide that is soluble in aqueous acidic media and shows good biocompatibility and degradability 5. Chitosan has two main reactive groups that can be modified by grafting: the C-2 free amino groups and the hydroxyl groups in the C-3 and C-6 acetylated or deacetylated units3. For polymerization uses, the advantages of gamma radiation for Chitosan is that it does not require additional chemical initiators or toxic agents to promote polymerization. For instance, it was used 0.1-5 kGy of γ radiation for the chitosan polymerization during the film preparation6. On the other hand, Mimosa Tenuiflora (Willd.) Poiret is a plant with high content in tannins, alkaloids, triperpenoid glycosides, steroidal saponins, N-N-dimethytryptamine and serotonin, that has been evaluated as a bioactive material for tissue engineering 7 . Multiwalled Carbon Nanotubes are used to enhance the useful properties of a polymeric matrix material. Incorporate multiwalled carbon nanotubes into polymer matrices yields materials whose properties can be engineered for applications in tissue engineering 8. Also, MWCNTs have been considered one of the most effective nanofillers to improves the radiation resistance of polymers due to its good capability of free radical scavenging 9. In this work, the preparation of chitosan/mimosa tenuiflora/multiwalled carbon nanotubes by thermal induced phase separation is described. Although the effects of radiation on chitosan has been evaluated previously 10,11, to the best of our knowledge, the effects of radiation on the thermal properties in this kind of composite has not been reported. Therefore, in this work, the effects of UV and gamma radiation on morphology, crystallinity and thermal properties of this composite are described. EXPERIMENTAL PROCEDURE Materials and preparation of composites Chitosan was purchased from Sigma-Aldrich (United States). The molecular weight reported by the fabricant is 310,000-375000 Da (75-85 % deacetylated). Also, the apparent viscosity of the chitosan was obtained using a Brookfield viscometer according with the ASTM D2196-05 “Standard test methods for rheological properties of non-newtonian materials by rotational Brookfield viscometer at 25o C (1685cPs, 10 rpm; 1505 cPs, 20 rpm; 1388 cPs, 30 rpm; 1273 cPs, 50 rpm) . The bark of M. Tenuiflora was obtained directly in the region of Jiquipilas, Chiapas. Glacial acetic acid (Mallinckrodt, United States) was used as a solvent. Chitosan/M. Tenuiflora/Multiwalled carbon nanotubes(MWCNT) was prepared using the thermally induced phase separation technique. The MWCNT were fabricated and purified in our laboratory by spray pyrolysis method according with a previous published work 12. Powder


of Bark of M. Tenuiflora was obtained using a coffee grinder without any preparation. Then, Chitosan and M. Tenuiflora were mixed together at 80/20 ratio in 1% (%v/v) aqueous acetic acid solution. The solution was stirred for 1 h followed by 5 minutes of sonification in order to eliminate the gas from the gelatinous mixture. The composite was frozen at -20oC for 4 h and then the solvent was extracted by a freeze drying system Labconco Free Zone 2.5 for 2 days. In order to prepare the composite with MWCNT, the CNT were dispersed by sonification for 5 min at a room temperature, before add Chitosan and Mimosa Tenuiflora to the acetic acid solution. Finally, composites were treated using two sources of energy. Composites were irradiated by 60Co J-rays at a dose of 3 kGy (dose rate of 3.52 kGy/h) and for UV light radiation using a 254 nm lamp in Labconco ™ Purifier™ Class I and HEPAFiltered Safety Enclosures for 4 hours. The chemical characterization of the composites was developed in a FTIR-ATR spectrometer Nicolet 6700. All spectra were recorded using 100 scans and 16 cm−1 resolution. The X-ray diffraction patterns of the samples were analyzed between 2θ = 5 ◦ and 2θ = 80◦ with a step size of 2θ = 0.02◦ in an X-ray diffraction instrument in continuous mode (PANanalytical X’Pert PRO), using a Cu target. The morphology characterization was made in a Field Emission Scanning Electron Microscope JEOL JSM-7000F. Thermogravimetric analysis (TGA) and Differential Scanning Calorimetric (DSC) of composites was carried on SDT Q600 from TA Instruments (United States). The dry samples were heated from 30oC to 750◦C at 10◦C/min under nitrogen atmosphere with a flow rate of 80 mL/min. The first derivative of the mass-change with respect to time (DTG) was calculated and plotted as a function of the temperature. RESULTS AND DISCUSSION The behavior of the samples under irradiation can be explained as follows (Fig. 1). The J ray acted on the composite chain directly, breaking the 1,4 glycosidic bonds of chitosan after scission, and forming carbonyl groups and carboxyl groups11. According with the thermal results, in general the composite decompose before melting. The values of the temperature of maximum decomposition rate and the percentage of final decomposition of the composites are summarized in Table 1. The composite was thermally decomposed in the region of 239 ◦ C and 391 ◦ C as shown in Fig. 2a and 2b. This thermal decomposition could be attributed to a complex process including the dehydration of the saccharide rings of chitosan and mimosa tenuiflora and followed decomposition of chitosan backbone2,13. In general, as the percentage of MWCNTs increases, the thermal stability of the composites increases as well. The range of decomposition temperatures are not similar in the composites treated with UV and gamma radiation, but are similar among the composites treated previously with the same kind of radiation. It is important to note that 80/20/5 % treated with gamma radiation increases the initial and final temperatures of decomposition to 255 o C and 398o C. Also, the thermal stability of the composites was related with the content of MWCNT on the sample. It could be considered that the incorporation of MWCNT produced an increase in the


thermal stability of the composite due to the high thermal stability of the MWCNTs themselves and that the radiation process promotes the interaction between MWCNTs and the free radicals produced by the irradiation14.

FIGURE 1. Molecular fragmentation of the chitosan, as the main component in the composite, due to radiation.

TABLE 1. Region and percentage of decomposition weight of the composites Composites Main Region Of Percentage Of Tmax(oC) o Decomposition ( C) Decomposition (Ch/Mim/MWCNT) Weight (%) 100/0/0 80/20/0 80/20/2% 80/20/5% 80/20/0J 80/20/2% J 80/20/5% J 80/20/0 UV 80/20/2% UV 80/20/5% UV

232-326 239-391 241-381 246-392 238-375 231-356 255-398 219-361 253-391 226-391

80-55 69.26 94.79 77.88 90.95 94.79 84.45 97.71 69.53 72.60

271.35 281.01 283.90 287.13 284.84 281.78 289.43 282.37 295.84 294.42

Maximum Degradation Rate (%/min) 2.771 5.845 4.976 5.627 5.988 4.957 6.879 6.272 10.860 8.299

Onset Degradation Temperature (oC) 327.18 335.01 304.97 315.41 315.14 305.49 313.59 315.37 317.65 319.76

There are two stages of degradation in the TGA curve of all samples. The initial weight loss of the composites (100–150 ◦ C) is due to evaporation of the absorbed moisture. This loss depends on the initial moisture content of the composites. The hydrophilic nature of chitosan is important to determine the thermal behavior of the composites. The second stage, is the severe weight loss that is called main region of decomposition in Table 1. It is due to the decomposition of the major components of the composites, mainly the thermal destruction of the pyranose ring and the rupture of the b-glycosidic-linkages between the glycosamine and Nacetylglucoamine moieties 15,16. So, the thermal decomposition of the composite starts with the breaking of the bond C-O-C and the formation of acetamide C2H5NO17. In order to examine the plots, the weight loss percentage of all samples was differentiated and the derived data are depicted in Table 1. The T max corresponds to the temperature at the maximum degradation rate. As it is showed on Figure 3a and 3b, all composites exhibit a single peak of fast thermal


degradation. According with Martel-Estrada (2010), an improved thermal stability would be achieved for the component with the lower T max if the measured T max shifts to the higher Tmax of another component due to the chemical interactions between the substances. The onset temperatures improve with UV treatment on the composites. On the other hand, the DTG profiles (Figure 3a and 3b) show that the composites have only single peak for all composites, indicating that the chemical interaction between the substances resulted in a relatively homogenous composition of the composites. Finally, Figure 4a and Figure 4b, show the DSC graphs of the composites, in which it is possible to identify that the heat flow behavior related to temperature in the samples is similar. So, Table 2 includes the glass transition temperatures of the composites. These temperatures were affected by the radiation treatment slightly for about 2o C. TABLE 2. Glass transition temperatures of the composites Composite Tg (oC) (Ch/Mim/MWCNT) 80/20/0 274.97 80/20/2% 287.80 80/20/5% 281.39 275.89 80/20/0 J 289.63 80/20/2% J 283.22 80/20/5% J 80/20/0 UV 286.42 80/20/2% UV 285.47 80/20/5% UV 285.06

FIGURE 2. TGA of composites before and after gamma radiation treatment and b) TGA of composites before and after UV radiation treatment.

In Figure 5 the morphology of the composites 80/20 Ch/Mim and 80/20/5 % Ch/Mim/MWCNT before and after radiation treatment is shown. The composites show a porous structure with an average pore size of 211.61 ± 14.65 μm. A higher magnification the images show that inside the big porous of the composites exist a highly interconnected porous structure (