Ajou News

NEW Prof. Kim Sung-hwan engineers a silk protein for artificial tissues

  • 2020-11-02
  • 63

Using an engineered silk protein, a team of researchers led by Prof. Kim Sung-hwan (Departments of Physics and Energy Systems Research) has succeeded in developing artificial tissues capable of generating energy. The invention is expected to accelerate the development of next-generation healthcare devices that can be incorporated into existing human tissues.

Prof. Kim’s human-friendly artificial skin, made of an engineered silk protein and capable of harvesting electric energy from human motions, was published in the August 23 online issue of Nano Energy, a renowned international publication, and entitled, “Self-powered artificial skin made of engineered silk protein hydrogel.”

There is a fast-growing body of research worldwide on materials for next-generation electronic healthcare devices for human-machine interfacing. Such devices are to detect and analyze vital signs automatically, and developing them requires electronic materials that can provide as much flexibility and elasticity as actual human skin. Countless researchers have thus dedicated themselves to developing materials and devices that combine flexible substrates with electrodes and electronics to read and analyze various vital signs from the human body. These materials are today known as electronic skin.

It is crucial for electronic skin devices to run on their own, without relying on outside power sources. One way to achieve this is to develop a piezoelectric energy-harvesting mechanism capable of transforming differences in pressure resulting from the wearer’s motions into electric energy. Existing piezoelectric materials are mostly inorganic oxides whose crystalline structures are capable of high levels of piezoelectricity. The majority of these materials, however, are neither skin-friendly nor flexible enough to serve as a second skin for humans. Materials with sufficient flexibility, on the other hand, lack the needed piezoelectric capability. When pressure hits and deforms the existing molecular structure of a given substance, electric charges arise in parts of that substance, which can be harvested to generate energy. The greater the quantity of charges generated due to structural deformation, the more piezoelectric the substance is. Therefore, flexible materials, by definition, fare worse than hard ones in piezoelectric energy generation.

Prof. Kim’s team sought to resolve this problem with proteins—particularly silk proteins available from natural sources—as they are a core component of the skin. Silkworm-derived proteins are a skin-friendly and high-molecular biomaterial with superior physical and chemical properties. 

In an effort to transform the silk protein at the molecular level, the team applied glycerol and created a transparent and flexible hydrogel film. The resulting product is similar to human skin, taking the research community a step closer to finding an ideal artificial electronic counterpart.

Prof. Kim’s team, moreover, combined the transparent silk protein with a zinc oxide (ZnO) nanorod to maximize the material’s piezoelectric performance. This ensures that a wearable device made with the new material would stay comfortably on the wearer’s skin and reliably harvest electric energy from the wearer’s motions, including touches and flexing of the joints. The team indeed demonstrated that its piezoelectric material can harvest sufficient amounts of energy from normal human motions to charge and operate small electronic devices, such as light-emitting diodes (LEDs) and blood oximeters. Accordingly, the team’s invention can be applied to a variety of sensors, including those for electronics and human motion detectors.

Prof. Kim explained: “Although there has been significant progress in research on harvesting energy from the human body, the problems related to human-machine interfacing has comparatively been neglected. My team and I have found a clue in proteins, which compose the natural skin, to develop interfaces capable of bridging the material difference between the human body and electronic devices.”

He added: “Our project is significant in that our invention can help increase the application of biomaterials to a variety of electronic devices. We hope to see our product applied to a wide range of healthcare products and soft robotics in the future.”

[Description] A conceptual diagram of Prof. Kim’s self-powered artificial skin. It can be attached to human skin to capture and harvest energy from the wearer’s motions. The amount of energy so harvested is enough to operate small devices.