Yu, D.-N., et al.: Wetting and Supercontraction Properties of … THERMAL SCIENCE: Year 2019, Vol. 23, No. 4, pp. 2189-2193 2189

WETTING AND SUPERCONTRACTION PROPERTIES OF SPIDER-BASED NANOFIBERS

by

Dan-Ni YU, Dan TIAN, Chan-Juan ZHOU, and Ji-Huan HE

* National Engineering Laboratory for Modern Silk, College of Textile and Clothing Engineering,

Soochow University, Suzhou, China

Original scientific paper https://doi.org/10.2298/TSCI1904189Y

Spider dragline silk has the highest strength among all natural or artificial fibers. This paper is to take full advantage of this property to enhance polyvinyl alcohol nanofibers by adding spider powders in the spun solution by the electrospinning. The obtained spider-based nanofiber shows much higher toughness than its poly-vinyl alcohol partner. We also find that the spider-based nanofibers have su-percontraction and wetting properties similar to those in the spider silks. This paper sheds a new light on a new trend of nanobiomimetics. Key words: spider silk proteins, nanofiber, biomaterial, supercontraction

Introduction

Spider dragline silk has been fascinating human-being for thousands of years due to its excellent mechanical properties [1-12], and it is a source for biomaterials [13-16] for tissue engineering applications [17-19], and many methods have been proposed to produce artificial fibers mimicking the natural silks [20, 21]. The classical approach is to use spider silk pro-teins to fabricate nanofibers by the electrospinning, though some properties can be enhanced, but it is far behind the natural silks. In this paper, we suggest a novel way to fabricate nano-fibers using spider powders.

This approach is hinted by ancient Chinese medicine. According to Compendium of Materia Medica, a magnum opus of historic significance, written by China’s medicine king, Li Shizhen (July 3, 1518-1593), the spider powders, instead of spider silk proteins, have many medicinal functions [22], and spider-based nanofibers are extremely suitable for fabrication of wound-bandages. This paper focuses itself on the mechanical property of the spider-based nanofibers, other properties will be reported in a series of forthcoming papers.

Materials and methods

Spider powders. Spiders were caught in trees near the campus of Soochow Universi-ty, and were killed and ground into powers.

Morphology. The morphology of produced nanofibers was observed using SEM, (Hitachi S-4800, Japan).

* Corresponding author, e-mail: hejihuan@suda.edu.cn ––––––––––––––

Yu, D.-N., et al.: Wetting and Supercontraction Properties of … 2190 THERMAL SCIENCE: Year 2019, Vol. 23, No. 4, pp. 2189-2193

Supercontraction test. A 26.8 cm × 37.8 cm spider-based nanofiber membrane with weight of 0.0323 g was put above a hot water with a constant temperature of 80 °C for 40 minutes.

Wetting test. Contact angle was measured using optical contact angle meter system (DSA100, KRUSS, Germany).

Mechanical test. Material testing machine (INSTRON-3365, INSTRON, America), was used for measure stress-strain curves.

The PVA solution. 10 wt.% polyvinyl alcohol (PVA) solution was prepared using a binary solvent system with ethanol/water weight ratio of 1/9.

Spider-based solution. The spider powders were added to PVA solution to prepare for 0.1 wt.% and 0.5 wt.% spider-based solutions, respectively. The mixed solution was stirred for one hour using a heating magnetic stirrer (DF-101S, XINRUI, China) under the temperature of 80 °C, and then the solution was put on a magnetic stirrer (HJ-6A, GONGYI, China) to be stirred for one hour at the temperature of 24 °C until a transparent solution was obtained, which was further ultrasonically stirred in a ultrasonic cleaner (SL-5200DT, SHUNLIU, China) for 20 minutes under the temperature of 30 ℃.

Electrospinning process. The electrospinning was used in our experiment, the exper-imental set-up was same as that in [23]. Electrospinning was performed at voltage of 19 kV with electric current of 0.01 mA at the room temperature of 22.9±1 °C, humidity of 50±2%, the aluminum foil collector was placed 20 cm away from the needle.

Results and discussion

Hydrophobicity and morphology analysis

Spider webs are of hydrophobicity [24], while the PVA nanofibers are of hy-drophilcity, the contact angle is 35.5°, see fig. 1. We want to check if the additive of spi-der powders can change hydrophilcity of PVA nanofibers to hydrophobicity of spider-based PVA nanofibers as that for the spider-web.

The SEM illustration of nanofibers was given in figs. 1-3. It is obvious that the average diameters of the nanofibers increase with the spider powders from 225 nm for the 10 wt.% PVA solution to 414 nm for the PVA solution with 0.5 wt.% spider powders. While the contact angles increase from 35.5o to 76.6o, revealing that the hydrophobicity increases by spider powders, this property is reflected by the hydrophobicity of spider web.

Figure 1. The SEM illustrations for 10 wt.% PVA solution, the average diameter is about 225 nm, and the contact angle is 35.5°

Yu, D.-N., et al.: Wetting and Supercontraction Properties of … THERMAL SCIENCE: Year 2019, Vol. 23, No. 4, pp. 2189-2193 2191

Figure 2. The SEM illustration for PVA solution with 0.1 wt.% spider powders, the average diameter is about 351 nm, and the contact angle is 53.3°

Figure 3. The SEM illustration for PVA solution with 0.5 wt.% spider powders, the average diameter is about 414 nm, and the contact angle is 76.6°

Supercontraction analysis

Supercontraction is common phenomenon for spider dragline silk [25-27], an un-restrained silk can shrink up to 50% of its original length, and a constrained fiber can gen-erate substantial forces during supercontraction. Figure 4 shows the supercontraction property of unrestrained PVA nanofiber membrane with 0.5 wt.% spider powders. Table 1 shows the effect of spider powders on shrinking, weight gain and contact angle of nano-fiber membrane.

Figure 4. Supercontraction of spider-based PVA nanofiber membrane; (a) the original nanofiber membrane with 0.5 wt.% spider powders, (b) shrunk membrane, (c) the reverse side of the shrunk membrane

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Table 1. Effect of spider powders on shrinking, weight gain and contact angle of nanofiber membrane

Length shrinking rate [%]

Width shrinking rate [%]

Weight gain [%]

Contact angle [°]

Without spider powders 15.71 17.99 7.07 35.5±2.06

With 0.1 wt.% spider powders 15.05 16.97 7.50 53.3±3.07

With 0.5 wt.% spider powders 12.96 14.18 8.98 76.6±1.02

Mechanical analysis

The spider dragline silk is famous for its strongest mechanical property among all natu-ral and artificial fibers. The stress of the PVA membrane reaches its maximum, e. g., 5.77 MPa, when the strain is 78.0%. The addi-tion of spider powders can greatly improve maximal stress from 6.37 MPa for 0.1 wt.% spider powders to 13.31 MPa for 0.5 wt.% spi-der powders; while the strain decrease from 45.7% to 40.5%, see fig 5.

Conclusions

Artificial fibers mimicking spider fibers seem to have seized remarkable attention, this

paper gives a new step to produce spider-based nanofibers with some amazing behaviours similar to those of the spider silks. Especially the mechanical strength can be greatly increased by adding spider powders, this can be explained using the geometrical potential theory [28, 29]. The water contracting ability of the obtained spider-based nanofiber can be used as a moisture sensor. The method described in this paper can be extended to fabrication of silk-worm-based or other animal filaments-nanofibers having some special functions.

Acknowledgments

The work is supported by Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), National Natural Science Foundation of China under grant No. 11372205.

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Paper submitted: April 13, 2018 © 2019 Society of Thermal Engineers of Serbia. Paper revised: November 25, 2018 Published by the Vinča Institute of Nuclear Sciences, Belgrade, Serbia. Paper accepted: November 27, 2018 This is an open access article distributed under the CC BY-NC-ND 4.0 terms and conditions.