Instant Adhesion of Amyloid-like Nanofilms with Wet Surfaces

Abstract

The adhesion and modification of wet surfaces by an interfacial adlayer remain a key challenge in chemistry and materials science. Herein, we report a transparent and biocompatible amyloid-like nanofilm that breaks through the hydration layer of a wet surface and achieves strong adhesion with a hydrogel/tissue surface within 2 s. This process is facilitated by fast amyloid-like protein aggregation at the air/water interface and the resultant exposure of hydrophobic groups. The resultant protein nanofilm adhered to a hydrogel surface presents an adhesion strength that is 20 times higher than the maximum friction force between the upper eyelid and eyeball. In addition, the nanofilm exhibits controllable tunability to encapsulate and release functional molecules without significant activity loss. As a result, therapeutic contact lenses (CLs) could be fabricated by adhering the functionalized nanofilm (carrying drug) on the CL surface. These therapeutic CLs display excellent therapeutic efficacy, showing an increase in cyclosporin A (CsA) bioavailability of at least 82% when compared to the commercial pharmacologic treatment for dry eye syndrome. Thus, this work underlines the finding that the bioinspired amyloid-like aggregation of proteins at interfaces drives instant adhesion onto a wet surface, enabling the active loading and controllable release of functional building blocks.

Figure 1

Macroscopic PTHLF nanofilm floating at the air/water interface and its formation mechanism. (A) Schematic illustration of the PTHLF film formed at the air/water interface and ambient temperature by mixing HLF and TCEP in water. (B) AFM image of the film. (C) Photograph of a film floating on Milli-Q water. (D) Optical transparency of the film coated on quartz glass. The inset image shows the corresponding photograph.

Figure 2

Adhesion mechanism between the PTHLF nanofilm and hydrogel. (A) Schematic showing the interaction between the PTHLF nanofilm and hydrogel. Representative snapshots of PTHLF (at air/water interface) adhesion on the PHEMA hydrogel at (B) 0 ns, (C) 0.02 ns, and (D) 80 ns. (E) Number of hydrophobic and hydrophilic residues in contact with the PHEMA hydrogel as a function of time. (F) Number of residues in contact with the PHEMA hydrogel at 0.02 ns (20 ps). (G) Maximum energy of different residues interacting with the PHEMA hydrogel at 80 ns. (H) Energy distribution of the PTHLF residues interacting with the PHEMA hydrogel.

Figure 3

Various PTHLF film-modified hydrogels and the peeling strength between the film and hydrogels. (A) Schematic illustration of the process of the PTHLF film modifying the hydrogel surface. (B) Photograph of the dyed PTHLF film-coated agarose hydrogel after immersion in Milli-Q water. (C) Pictures of the water droplets on bare agarose hydrogel and the PTHLF film-coated agarose hydrogel. (D) Water contact angles on the different PTHLF film-coated hydrogels. (E) LSCM image of the agarose hydrogel modified with the PTHLF film dyed by ThT. (F) Water contact angle on the PTHLF film-coated agarose hydrogel treated with organic solvents, extreme pH conditions, and ultrasonication. (G) Scheme of the peeling strength measurement process. (H) Peeling strength versus time after adhering the PTHLF film on the agarose hydrogel. (I) Peeling strength between the different hydrogels and PTHLF film. Values represent the mean and standard deviation (n = 3–5). The typical conditions of PTHLF film formation were 7 mg/mL HLF, 50 mM TCEP at pH 6.98, and incubation for 2 h.

Figure 4

Encapsulation and release of CsA and HA in the PTHLF film. (A) Schematic cartoon showing the release process of functional molecules from the functionalized CL with the PTHLF nanofilm coated. (B) Schematic illustration showing the one-pot encapsulation of CsA and HA in the nanofilm prepared by simply mixing HLF (7 mg/mL in Milli-Q water), TCEP (50 mM in Milli-Q water), CsA (7.5 mg/mL in aqueous ethanol), and a solution of HA and incubating for 12 h at room temperature. (C) Evaluation of the nonspecific adsorption of proteins on the bare and PTHLF-coated CL surfaces (tested by a bicinchoninic acid (BCA) assay). (D) LSCM image of the PTHLF film encapsulating CsA-FITC. (E) Experimental loading density and loading ratio of CsA in the PTHLF film at different feeding doses of CsA. (F) Optical transparency of the functionalized PTHLF film coated on quartz glass. (Inset: a photograph of the functionalized CL). (G) Release curve of the encapsulated CsA from the functionalized film.

Figure 5

In vivo biocompatibility evaluation of the functionalized CL in the eyes of normal SD rats. Representative slit lamp field images (A) and corresponding anterior segment clinical scores (C) of SD rats at 0, 1, 3, 5, and 7 days after various treatments with pristine CL (0 μg) and drug-loaded functionalized CL at different CsA loading doses (25, 34, and 49 μg). Representative images of corneal fluorescein staining (B) and clinical scores (D) at 0, 1, 3, 5, and 7 days after various treatments. (E) Representative immunohistochemical analysis images of corneas at 7 days after various treatments. (F) Representative post-treatment TUNEL staining images of corneas at 7 days after various treatments. Statistical significance: p < 0.01 (*), p < 0.001 (**), p < 0.0005 (***), p < 0.0001 (****).

Figure 6

In vivo evaluation of the DES SD rats model after different intervention treatments. Representative slit lamp field images (A) and corresponding anterior segment clinical scores (C) of SD rats at 0, 1, 3, 5, and 7 days after various treatments with the untreated control, PTHLF/HA film-coated CL, functionalized nanofilm (21 μg)-coated CL, and Restasis. Representative post-treatment images of corneal fluorescein staining (B) and clinical scores (D) at 0, 1, 3, 5, and 7 days after various treatments. (E) STT (Schirmer tear test) scores of SD rats at 0, 1, 3, 5, and 7 days after various treatments. (F) TBUT of normal SD rats, DES SD rats at 0 days, DES SD rats without treatments after 7 days, and DES SD rats with various treatments after 7 days. (G) Representative immunohistochemical analysis images of the cornea and conjunctiva at 7 days after various treatments. The scale bar is 150 μm. (H) Representative images of the TUNEL staining of corneas at 7 days with various treatments. The scale bar is 150 μm. Expression of IL-1β (I) and IL-6 (J) mRNA in the corneas of SD rats at 7 days with various treatments. Statistical significance: p < 0.01 (*), p < 0.001 (**), p < 0.0005 (***), p < 0.0001 (****).