Spider Silk for Lenses

An image of the spider used in the study and the dome lens generated on its dragline silk. (Source: C.-Y. Liu)

Spider silk is useful for a variety of biomedical appli­cations. It exhibits mechanical properties superior to synthetic fibers for tissue engi­neering, and it is not toxic or harmful to living cells. One unexpected appli­cation for spider silk is its use in the creation of biocompatible lenses for biological imaging appli­cations. A team of researchers from Tamkang University and National Yang-Ming University in Taiwan presents now the feasi­bility of creating lenses capita­lizing on the pro­perties of natural spider silk material.

A spider can spin several different types of silks, each with different properties and functions. To create the spokes of their web, spiders use a type of silk known as dragline silk. “Dragline silk is an interes­ting natural material because of its significant features, such as high elasticity, great toughness and large tensile strength,” said Cheng-Yang Liu, a professor at National Yang-Ming Uni­versity. Compared to its weight, the strength of dragline silk is greater than steel.

The scientists collected smooth, uniform dragline silk from Pholcus phalan­gioides spiders, commonly known as daddy longlegs, and dripped a resin onto the silk fiber. As the resin condensed on the fiber, the wetting properties of the silk naturally formed it into a dome shape, which they found could be used as an optical lens. The mechanical and optical pro­perties of the silk also make it ideal for supporting the lens.

When they shined a laser onto the lens, it generated a high-quality photonic nanojet – a type of beam that can provide large-area, super-reso­lution imaging for biomedical appli­cations. By tuning the length of time the silk spends under the resin drip, the size of t­he dome lens can be changed, allowing the photonic nanojets to be optimized for the desired type of imaging.

“The dome lens with flexible photonic nanojets is suitable for imaging the nano­scale objectives in different depths within bio­logical tissue,” Liu said. After addi­tional testing, the researchers hope this type of spider silk-based lens can be used to deliver light for bio­logical imaging and operation. (Source: AIP)

Reference: C. B. Lin et al.: Optimal photonic nanojet beam shaping by mesoscale dielectric dome lens, J. Appl. Phys. 127, 243110 (2020); DOI: 10.1063/5.0007611

Link: Dept. of Mechanical and Electro-Mechanical Engineering, Tamkang University, New Taipei City, Taiwan

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