EVALUATION OF SWELLING AND MECHANICAL PROPERTIES OF

NANOSTRUCTURED CHITOSAN/GOLD FILMS J.H. Rodriguez1*, G. Ayala1, L.C.O Vercik1, A. Vercik1.

1Basic Sciences Department ZAB/FZEA, University of São Paulo, Av.

Duque de Caxias Norte 225, 13635-900 Pirassununga, SP, Brazil.

*E-mail: jrodriguezll@usp.br

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 90ºC for 3h

HAuCl4 (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)

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