METHOD FOR PREPARING SILK FIBROIN FILM BY WET FILM COATING

Abstract

Provided is a method for preparing silk fibroin film by wet film coating, including: (1) scrape coating a regenerative silk fibroin wet films on selected substrates, drying, to obtain regenerated silk fibroin films after drying; (2) Putting the dried silk fibroin film in water, so that the silk fibroin film can be detached peeled from the substrate after subsequent drying; and (3) drying Exfoliate the further dried silk fibroin film and peeling from the substrate. It is the first time to realize the preparation of free-standing fibroin film by wet film coating. The silk fibroin film has properties of ultra-thin, flexible, transparent, permeable, excellent biocompatibility, etc., thus being suitable for applications in flexible electronics, such as epidermal electronics. In addition, the method is not only suitable for industrial batch production of the fibroin film, but also matched with the existing film processing technologies such as roll-to-roll and nano-imprint.

Claims

1. A method for preparing silk fibroin film by wet film coating comprising: (1) scrape coating a regenerativable silk fibroin wet film on a substrate, drying, to obtain a regenerativable silk fibroin film, wherein the thickness of the regenerativable silk fibroin wet film is in the range of 0.1 μm to 200 μm; (2) putting the regenerativable silk fibroin film in water for 0.1 min to 20 mins, so that the regenerativablesilk fibroin film can be peeled from the substrate after subsequent drying; and (3) drying the regenerativable silk fibroin film and peeling from the substrate.

2. The method according to claim 1, wherein, the regenerativable silk fibroin wet film comprises silk protein and formic acid.

3. The method according to claim 2, wherein, the regenerativable silk fibroin wet film further comprises inorganic salt.

4. The method according to claim 3, wherein, the inorganic salt is an inorganic salt of lithium or calcium.

5. The method according to claim 1, wherein, material of the substrate is PET or PI.

6. The method according to claim 2, wherein, material of the substrate is PET or PI.

7. The method according to claim 3, wherein, material of the substrate is PET or PI.

8. The method according to claim 4, wherein, material of the substrate is PET or PI.

9. The method according to claim 1, wherein, droplet contact angle of the substrate is less than 90°.

10. The method according to claim 2, wherein, droplet contact angle of the substrate is less than 90°.

11. The method according to claim 3, wherein, droplet contact angle of the substrate is less than 90°.

12. The method according to claim 4, wherein, droplet contact angle of the substrate is less than 90°.

13. The method according to claim 5, wherein, droplet contact angle of the substrate is less than 90°.

14. The method according to claim 6, wherein, droplet contact angle of the substrate is less

15. The method according to claim 7, wherein, droplet contact angle of the substrate is less than 90°.

16. The method according to claim 8, wherein, droplet contact angle of the substrate is less than 90°.

17. The method according to claim 1, wherein, in step (2), putting the regenerativable silk fibroin film in water is soaking or rinsing the regenerativable silk fibroin film with water.

18. The method according to claim 2, wherein, in step (2), putting the regenerativable silk fibroin film in water is soaking or rinsing the regenerativable silk fibroin film with water.

19. The method according to claim 3, wherein, in step (2), putting the regenerativable silk fibroin film in water is soaking or rinsing the regenerativable silk fibroin film with water.

20. The method according to claim 4, wherein, in step (2), putting the regenerativable silk fibroin film in water is soaking or rinsing the regenerativable silk fibroin film with water.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0026] FIG. 1 shows a digital photo of the ultra-thin and flexible silk fibroin film obtained in Example 1.

[0027] FIG. 2 shows an UV-vis diffuse reflectance spectrum of the ultra-thin and flexible silk fibroin film obtained in Example 1.

[0028] FIG. 3 shows a mechanical tensile curve of the ultra-thin and flexible silk fibroin film obtained in Example 2.

[0029] FIG. 4 shows a SEM image of the ultra-thin and flexible silk fibroin film obtained in Example 2.

[0030] FIG. 5 shows a thermogravimetric analysis spectrum of the ultra-thin and flexible silk fibroin film obtained in Example 3.

[0031] FIG. 6 shows a FT-IR spectrum of the ultra-thin and flexible silk fibroin film obtained in Example 3.

[0032] FIG. 7 shows a SEM image of the cross-section of the ultra-thin and flexible silk fibroin film obtained in Example 3.

[0033] FIG. 8 shows the FT-IR spectrum of the amide I band in Example 3.

DESCRIPTION OF EMBODIMENTS

[0034] The commercially available wet film coating devices (such as a scraper, four-side preparation device, wire rod, etc.) can be used to scrape and coat the regenerative silk fibroin wet film on a substrate. The preset scraping thickness ranges from 0.1 μm to 1000 μm. In addition, the present disclosure uses common regenerative silk fibroin solution, such as the mixture of silk fibroin, formic acid, and inorganic salts (such as an inorganic salt of lithium or calcium), and the mixture of silk fibroin and hexafluoro-isopropyl alcohol (HFIP), etc. These raw materials are easy-to-get and low-cost. The silk fibroin can be selected from mulberry silk fibroin, tussah silk fibroin, castor silk fibroin, Antheraea Yamamai silk fibroin, and so on. For peeling mechanically the regenerative silk fibroin film from the substrate after drying, the regenerative silk fibroin film is treated by being put in water, such as soaking or rinsing. The time in water can be adjusted depending on the hydrophilic properties of the substrate and thickness of the film. Generally, the more hydrophilic the substrate, the shorter the time putting in water required; and the thinner the film, the shorter the time putting in water required. The contact angle of the substrate used in the present disclosure is preferably less than 90°, so that the obtained silk fibroin film will has a better flatness.

[0035] Further descriptions with specific examples and figures are shown as below.

EXAMPLE 1

[0036] 0.5 wt % LiCl/formic acid solution was prepared, 0.4 g degummed silk fibers were dissolved in 7.8 mL of the above solution and ultrasonicated for 1 h. The solution was filtered by PTFE membrane with pore diameter of 0.45 μm to obtain the regenerative silk fibroin solution.

[0037] A clean PET substrate with a contact angle of 79.1° was used, and a film scraper with a scraper of 0.1 μm thickness was preset. A regenerative silk fibroin film was scrape-coated onto the substrate. The substrate coated with the wet film was placed on a hotplate at 60° C. for 5 min, immersed in water for 0.5 min, then dried at 60° C. on the hotplate. After dried, the regenerative silk fibroin film was peeled off mechanically from the substrate, obtaining a free-standing flexible silk fibroin film with about 0.05 μm thickness and having good flatness.

EXAMPLE 2

[0038] 8.7 wt % LiBr/formic acid solution was prepared, 2.5 g degummed silk fibers were dissolved in 5.7 mL of the above solution and ultrasonicated for 1 h. The solution was filtered by PTFE membrane with pore diameter of 0.45 μm to obtain the regenerative silk fibroin solution.

[0039] A clean PI substrate with a contact angle of 82° was used, and a four-side preparation device with 200 μm thickness was employed. A regenerative silk fibroin film was scrape-coated onto the substrate. The substrate coated with the wet film was placed on a hotplate at 60° C. for 10 min, immersed in water for 20 min, then dried at 60° C. on the hotplate. After dried, the regenerative silk fibroin film was peeled off mechanically from the substrate, obtaining a free-standing flexible silk fibroin film with about 25 μm thickness and having good flatness.

EXAMPLE 3

[0040] 4.8 wt % CaCl.sub.2/formic acid solution was prepared, 1.3 g degummed silk fibers were dissolved in 6.8 mL of the above solution and ultrasonicated for 1 h. The solution was filtered by PTFE membrane with pore diameter of 0.45 μm to obtain the regenerative silk fibroin solution.

[0041] A clean PET substrate with a contact angle of 85° was used, and a four-side preparation device with 100 μm thickness was employed. A regenerative silk fibroin film was scrape-coated onto the substrate. The substrate coated with the wet film was placed on a hotplate at 60° C. for 10 min, immersed in water for 5 min, then dried at 60° C. on the hotplate. After dried, the regenerative silk fibroin film was peeled off mechanically from the substrate, obtaining a free-standing flexible silk fibroin film with about 9 μm thickness and having good flatness.

EXAMPLE 4

[0042] 4.8 wt % CaCl.sub.2/formic acid solution was prepared, 1.3 g degummed silk fibers were dissolved in 6.8 mL of the above solution and ultrasonicated for 1 h. The solution was filtered by PTFE membrane with pore diameter of 0.45 μm to obtain the regenerative silk fibroin solution.

[0043] A clean PET substrate with a contact angle of 90.4° was used, and a four-side preparation device with 100 μm thickness was employed. A regenerative silk fibroin film was scrape-coated onto the substrate. The substrate coated with the wet film was placed on a hotplate at 60° C. for 10 min, immersed in water for 5 min, then dried at 60° C. on the hotplate. After dried, the regenerative silk fibroin film was peeled off mechanically from the substrate, obtaining a free-standing flexible silk fibroin film with about 13 μm thickness and having good flatness.

EXAMPLE 5

[0044] 4.8 wt % CaCl.sub.2/formic acid solution was prepared, 1.3 g degummed silk fibers were dissolved in 6.8 mL of the above solution and ultrasonicated for 1 h. The solution was filtered by PTFE membrane with pore diameter of 0.45 μm to obtain the regenerative silk fibroin solution.

[0045] A clean PET substrate with a contact angle of 79.1° was used, and a film scraper with a scraper of 0.02 μm thickness was preset. A regenerative silk fibroin film was scrape-coated onto the substrate. The substrate coated with the wet film was placed on a hotplate at 60° C. for 5 min, immersed in water for 0.1 min, then dried at 60° C. on the hotplate. After dried, the regenerative silk fibroin film was peeled off mechanically from the substrate, obtaining a free-standing flexible silk fibroin film with about 0.01 μm thickness and having good flatness

[0046] FIG. 1 shows the digital photo of the silk fibroin film prepared in Example 1. Where, FIG. 1a shows the photo shot as placing the signing pen on the back of the film, and FIG. 1b shows the photo of the film pinched by fingers. It can be seen from FIGS. 1a and 1b, the silk fibroin film obtained exhibits excellent flexibility, transparency, and flatness.

[0047] FIG. 2 shows the UV-vis diffuse reflectance spectrum of the silk fibroin film obtained in Example 1, including the results of transmittance (FIG. 2a) and haze (FIG. 2b). It can be seen from FIG. 2, the silk fibroin film obtained exhibits >90% transparency in the visible band, and <2% optical haze by haze test.

[0048] FIG. 3 shows the mechanical tensile curve of the silk fibroin film obtained in Example 2. It can be seen from FIG. 3, the silk fibroin film exhibits >30 MPa tensile strength, up to 2.4% elongation at break, and Young's modulus is calculated for 15.8 MPa. Thus the tensile strength and the Young's modulus are obviously more than the silk fibroin gel film rich in water molecules.

[0049] FIG. 4 shows the SEM image of the silk fibroin film surface obtained in Example 2. Where, FIG. 4a is a higher magnification scanning electron microscope image, and FIG. 4b is a lower magnification scanning electron microscope image. It can be seen from FIG. 4, the silk fibroin film surface has a smooth surface and low roughness. The surface crystalline particles fluctuation is in nanometer level. There is no fibrous structure that can be observed on the surface.

[0050] FIG. 5 shows the thermogravimetric curve of the silk fibroin film obtained in Example 3. It can be seen from FIG. 5, the initial decomposition temperature of the silk fibroin film is 255° C., indicating that the film has good thermal processing performance compared with conventional plastic films. For example, metal electrodes can be evaporated on its surface.

[0051] FIG. 6 shows the FT-IR spectrum of the silk fibroin film obtained in Example 3. It can be seen from FIG. 6, the silk fibroin film exhibits absorption peaks centered at 1512 cm.sup.−1 and 1626 cm.sup.−1, respectively, indicating that the film contains stable silk II structures (β-sheet structure).

[0052] FIG. 7 shows the SEM image of the cross-section of the silk fibroin film obtained in Example 3. The sample is prepared by resin embedding and thinning. It can be seen from FIG. 7, the thickness of the silk fibroin film is about 9 μm. There is no fibrous structure in the cross-section.

[0053] FIG. 8 is the FT-IR spectrum of the amide I band of the silk fibroin film obtained in Example 3. It can be seen from FIG. 8, the direct water treatment of the film results in a high content of β-sheets, which is helpful to form a flexible film with stable mechanical properties.