Nanomaterial-functionalized Silk And Its Applications

Silk from Bombyx mori cocoons is a natural fiber consisting of two main proteins: fibroin and sericin. Because of its luxury sheen and excellent skin affinity, silk has been regarded as "queen of textiles" and used in the textile industry for thousands of years. Although silk could provide a lot of unique properties, it possesses some drawbacks, such as photo-induced aging and yellowish, easy to wrinkle, and microorganism-caused degradation. In recent years tremendous efforts have been dedicated to the surface functionalization and modification of silk for antibacterial and anti-UV properties.As advances of nanotechnology, various nanomaterials have been immobilized on silk to render it unique functions. It is regarded as one of the best strategies for the fabrication of antibacterial or anti-UV silk. Two types of approaches have been developed to fabricate nanomaterial-functionalized silk. In the first approach silk surface is coated with pre-synthesized nanomaterials, in which at least two steps are needed:synthesis of nanomaterials and immobilization of them on silk surface. The other approach is applied to directly in situ grow nanomaterials on silk fibers without the pre-synthesis step. Nanomaterials are produced via the electrostatic adsorption or exchange of metal ions, followed by a reduction step. Modification of silk with nanosilver has already been reported, but the use of toxic reductants or expensive gamma-ray irradiation source for the reduction step greatly hinders the application of nanosilver-coated silk. Therefore, there is an urgent need to develop a facile and green approach for the production of nanosilver-coated silk, which may be extended to textile industry. Zinc oxide (ZnO) nanomaterials have also been used to functionalize silk for antibacterial and anti-UV applications. However, the growth of ZnO nanorods array on silk fibers has not been realized. Moreover, the use of ZnO nanorods array-functionalized silk for antibacterial, anti-UV and physiological sensing has not been investigated either.In this thesis a UV-assisted one-step synthesis of silver nanoparticles (Ag NPs) on silk was investigated firstly. Then, a layer-by-layer (LbL) self-assembled polymetric film-coated silk was employed to controllably grow Ag NPs for high loading density. The antibacterial activities of the modified silk have also been evaluated with both Gram-positive and Gram-negative microbes. To extend the applications of ZnO nanomaterials on silk modification, a low-temperature hydrothermal approach was explored to grow ZnO nanorods arrays on silk fibers for antimicrobial, UV-protection and physiological sensing. Detailed information of this project is as follows:1. UV-assisted in situ synthesis of Ag NPs on silk fibers for antibacterial applicationA UV-assisted in situ synthesis approach is developed to directly immobilize Ag NPs on the degummed silk. Results show that Ag NPs with excellent crystalline structures are efficiently attached on the silk surface in an irradiation time-dependent manner. The immobilization of Ag NPs could enhance the thermal degradation and tensile strength of silk in a certain range. The antibacterial activity is evaluated by the growth curve, zone of inhibition and dual staining assays, clearly demonstrating its bacterial growth inhibition ability and bactericidal effects to both Escherichia coli (E.coli) and Staphylococcus aureus (S.aureus).2. Controllable in situ synthesis of Ag NPs on polymeric film-modified silk for antibacterial applicationA poly(dimethyldiallylammonium chloride) (PDDA)/poly(acrylic acid) (PAA) multilayered film was assembled on silk fibers via a layer-by-layer self-assembly approach to provide more surface sites for silver ion binding. The UV-assisted synthesis was conducted to in situ grow Ag NPs on the polymeric film-coated silk. Uniform Ag NPs with the diameter of 10 nm are immobilized on the (PDDA/PAA)n coated silk. The amount of Ag NPs can be easily tailored by changing the bilayer number of the multilayered film. The excellent antimicrobial activity is demonstrated with the growth curve and zone of inhibition assays.3. Growth of highly oriented ZnO nanorod arrays on silk fibers for UV-protection and antibacterial applicationsA low-temperature hydrothermal deposition approach was developed to grow ZnO nanorod arrays on silk surface. The experimental conditions were optimized to in situ synthesize ZnO nanorod array. It is observed that the arrays with a high surface density, good orientation and hexagonal structures are successfully fabricated on the silk. The immobilization of the ZnO nanorod array enhances the thermal stability of the silk and also provides excellent antibacterial and UV-protective capability.4. A single silk fiber-based mechanical sensor for wearable physiologyTaking the advantages of the piezoelectric property of ZnO nanorod, we developed a mechanical sensing device with one single ZnO nanorod arrays-modified silk fiber. Since the sensor can convert mechanical energy to electrical signals, it is utilized to monitor the behaviors like finger knocking, pressing and bending. Its potentials for physiological measurements are also demonstrated by sensing the human body abdominal and heartbeat. Interestingly, it is found that the device can also be applied to differentiate pitches generated from a xylophone.In summary, a one-step UV-assisted in situ synthesis approach is developed to fabricate Ag NPs-coated silk fibers with good antibacterial activity. LbL self-assembled polymeric films are further coated on silk surface to controllably tailor the size and density of Ag NPs. In addition, silk fibers modified with highly oriented ZnO nanorod arrays are prepared using a low-temperature hydrothermal deposition approach for UV-protective and antibacterial applications. The ZnO nanorod arrays-functionalized silk fibers are also employed to fabricate a single-fiber based mechanical sensor, which could be utilized to monitor human physiological parameters. This project may not only provide new approach for silk surface modification of nanomaterials, but also extend the applications of silk in wearable electronics.