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EVALUATION OF SWELLING AND MECHANICAL PROPERTIES OF NANOSTRUCTURED CHITOSAN/GOLD FILMS J.H. Rodriguez 1* , G. Ayala 1 , L.C.O Vercik 1 , A. Vercik 1 . 1 Basic Sciences Department ZAB/FZEA, University of São Paulo, Av. Duque de Caxias Norte 225, 13635-900 Pirassununga, SP, Brazil. *E-mail: [email protected] Mechanical properties of organic materials have attracted attention for optimizing engineered biocompatible and biodegradable materials, with promising potential applications in biomedicine and food engineering. Polymers obtained from natural sources have unique features such as high biodegradability, non-toxicity, and different mechanical properties, depending on the composition and structure. The properties of the polymer matrix can be improved by including various elements. For example, gold nanoparticles have already been used to improve electrical conductivity and as signal boosters in the development of biosensors [1,2], but they can also affect mechanical properties, limiting the lifetime of the devices. In recent years, the production of low-cost metal nanoparticles with biological resources have had a promising approach for use; the green synthesis is used for the production of gold nanoparticles, using nontoxic chemicals and renewable materials through environmentally friendly wastes [3]. This work aims to show first results of a study on the effects of the incorporation of AuNPs into chitosan films for use in biosensors. The presence of AuNPs modifies the type of interaction and intermolecular strength of a chitosan matrix having a direct correlation with the alteration of the physical and chemical properties of nanostructured films of chitosan. In this first study we showed that AuNPs affect the polymer viscosity whereas the Young’s modulus is not altered. [1] Yinyong Li, Xiaolei Guo, Pengfei Lin, Congcheng Fan, Yihu Song. Preparation and Functional properties of blend films of gliadins and chitosan. Carbohydrate Polymers. 81, 2010, 484-490 [2] Wei, D., & Quian, W., Facile synthesis of Ag and Au nanoparticles utilizing chitosan as a mediator agent. Colloids and surface B: Biointerfaces 62, 2008, 136- 142 [3] G.S. Ghodake, N.G. Deshpande, Y.P. Lee, E.S. Jin. Pear fruit extract-assisted room-temperature biosynthesis of gold nanoplates. Colloids and surfaces B: Biointerfaces 75, 2010, 584-589 Addition of AuNPs lead to appreciable morphological differences between chitosan (Fig. 2A) and chitosan/AuNPs films (Fig. 2B). Nanostructured films present a granular structure, which is not observed in chitosan films. These results are consistent with those reported by EDS, Figure 2C shows the absence of gold particles whereas Figure 2D shows the presence of AuNPs. On the other hand, the presence of nanoparticles in the polymer matrix directly affects the types of bonds present in chitosan allowing greater absorption of moisture, which is directly related to the concentration of AuNPs and the hydrogen potential present in the medium. In an acidic medium, the higher moisture absorption was observed for the matrix with a highest concentration of nanoparticles (13 mM) Fig . 3A, whereas in basic medium the matrix with a lower concentration of nanoparticles (8 mM) exhibited higher absorption of moisture (Fig 3B) . Figure 4A shows how the concentration AuNPs affect the mechanical properties of the film exhibiting an increase of Young’s modulus for films with AuNPs independently of the concentration (approximately the same value for the samples with varying AuNPs). Figure 4B shows the creep test results for the samples with AuNPs; in this case, the characteristic time depends on the AuNPs concentration. AuNPs 90 º C for 3h HAuCl 4 (8 mM & 13 mM) 4 mL Chitosan solution (6.92 mg/ml) 10 mL Chitosan solution (20 mg/ml) 13.5 mL AuNPs (8 mM & 13 mM) 13. mL Films drying 24h • SEM and EDS was used for analysis of surface morphology of the organic films containing the AuNP and to confirm the presence of elemental gold. • The swelling of the nanostructured matrix was performed with buffer solution at pH acid (5) and basic (9). The water absorption capacity (swelling) of the samples was calculated by weighing the samples at fixed times and passed over filter paper to remove excess surface water. Figure 1. Tensile and Creep test • The mechanical characterization of chitosan films was performed in a texturometer Stable Micro System (Figure 1). Tensile and Creep tests were carried out in samples of pure chitosan and chitosan with AuNPs. Figure 2. Morphological comparison via SEM of polymeric films without AuNPs (A) and with AuNPs (B). EDS of both type of samples are shown in (C) and (D). The characteristic peaks of Au are shown. A Ca peak in the pure chitosan sample is associated to residuals of the decarbonation process. Figure 3. Water uptake related weight gain with respect to time for chitosan with different concentrations of AuNPs in acidic pH (A) and basic pH (B) Figure 4. Effects of the AuNP on the mechanical properties: A) Stress-strain curve; B) Creep tests for films with AuNP (8mM and 13mM). The Young’s Modulus and characteristic times are shown in the figure. FAPESP, CAPES, IQ-Unesp (Araraquara) A B C D t (s) 736 501
