Enabling Selectively Tunable Mechanical Properties of Graphene Oxide/Silk Fibroin/Cellulose Nanocrystal Bionanofilms

Abstract

Enhancing and manipulating the mechanical properties of graphene oxide (GO)-based structures are challenging because the GO assembly is easily delaminated. We develop nacre-like bionanofilms whose in-plane mechanical properties can be manipulated through water vapor annealing without influencing their mechanical properties in the thickness direction. These bionanofilms are prepared from GO, silk fibroin (SF), and cellulose nanocrystals (CNCs) via a spin-assisted layer-by-layer assembly. The postannealing mechanical properties of the films are determined with atomic force microscopy (AFM) bending and nanoindentation, and it is confirmed that the mechanical properties of the bionanofilms are altered only in the in-plane direction. While AFM bending shows Young’s moduli of 26.9, 36.3, 24.3, and 41.4 GPa for 15, 15 annealed, 30, and 30 annealed GO/SF/CNC trilayers, nanoindentation shows reduced moduli of 19.5 ± 2.6 and 19.5 ± 2.5 GPa before and after annealing, respectively. The unaltered mechanical properties of the bionanofilms along the thickness direction after annealing can be attributed to the CNC frame in the SF matrix acting as a support against stress in the thickness direction, while annealing reorganizes the bionanofilm structure. The tunability of the bionanofilms’ mechanical properties in only one direction through structure manipulation can lead to various applications, such as e-skin, wearable sensors, and human–machine interaction devices.

Creep Behavior of Graphene Oxide, Silk Fibroin, and Cellulose Nanocrystal Bionanofilms

“…The thickness of the synthesized GO monolayer was 1–2 nm and the lateral size was on the order of micrometers. [ 29 ] GO was confirmed to be in the form of a 2D material. SF solution was obtained from Bombyx mori silkworm cocoons.…”

“…The diameter of the synthesized CNC was around 4–5 nm, and the length was around 135–140 nm. [ 29 ] The thickness of SF film was about 3.8 nm. [ 5 ]…”

“…The average thickness increment per bilayer of nanocomposite is about 3.6 nm. [ 29 ] The desired thickness of 180 nm was achieved with 50 bilayers.…”

“…The diameter of the synthesized CNC was around 4-5 nm, and the length was around 135-140 nm. [29] The thickness of SF film was about 3.8 nm. [5] SA-LbL method was used to fabricate GO-SF-CNC nanocomposites.…”

Enhanced formation of bioactive and strong silk–bioglass hybrid materials through organic–inorganic mutual molecular nucleation induction and templating

“…4 To enhance the mechanical strength of silk materials, different strategies have been used such as incorporation of particles or silk fibers as reinforcing materials, blending or crosslinking with other polymers such as chitosan, cellulose, polyacrylamide and sodium alginate. 5 Another approach that has been explored to enhance the mechanical properties of regenerated silk materials is reinforcing with inorganic materials. 6…”