Melt‐Compounded Keratin‐TPU Self‐Assembled Composite Film as Bioinspired e‐Skin

Abstract

stimuli from the external environment. [1,2] Because of the promise in advanced humanoid robotics, biomedical prostheses, surgical electronic gloves, etc., [3][4][5][6][7][8][9][10][11] immense interests are being motivated for mimicking the human skin by developing stable, flexible, and biocompatible artificial skin of human skin like rheology, tribology, and tactile sensing capability. However, the tactile sensing artificial skin is precisely known as electronic-skin (e-skin). [6,7] Although silicone rubber is being used to develop artificial skins or e-skins for different applications, [3][4][5][6][7] because of its elastic property, durability, shapeability, nontoxicity, and skin like refractive index, [12] it is cost-intensive and non-biodegradable. [13] Due to hydrophobic nature of silicone rubber, limitations also exist in simulating the tribomechanical performance of human skin properly over the full range of conditions. [14] Solution-based processing technique can be considered as another disadvantage of silicone rubber.Different biopolymers viz., cytoskeletal keratinocytes, tissues, cells, collagens are being potentially employed for developing bio-inspired artificial skins and organs. [8][9][10][11] Apart from the biocompatibility and biodegradability, these biopolymers provide skin like keratin-elastin composition, [8][9][10][11] a similar trend of viscoelastic properties, [15][16][17] and skin like porous morphology. [1] Isolation of the biopolymers, and/or its modifications are required for fabrication of artificial skin. The methods are mainly solution based, tedious and time-consuming.Tactile sensing capability is one of the major concerns of artificial skin (alias e-skin). In this recent years, different kinds of sensors based on different working principles, such as triboelectric nanogenerators (TENGs) are being fabricated using various flexible polymers, which not only perform as effective tactile sensors but also harvest abundant mechanical energy being wasted during our daily life movement, simply by contact electrification and electrostatic induction method. [4][5][6][18][19][20] Most of the TENGs have relatively complex structures consisting of pair of triboelectric surfaces with adequate patterning and texturing, and two induction electrodes, which require tricky operation mode and large working space. It is noteworthy to mention that human skin shows positive triboelectric property, whereas maximum polymers used in TENG fabrication are negative triboelectric material. [5,21] Inspired by the keratin-elastin composition of human skin, here an artificial skin (alias electronic (e)-skin) is developed through solvent-free extrusion based melt mixing of thermoplastic polyurethane (TPU) with the biowaste human hair keratin. Self-assembled composite film of TPU and keratin (i.e., PUK) shows leg skin equivalent coefficient of friction value of 0.26 ± 0.05, cheek skin equivalent average surface roughness (Ra) of 0.047 ± 0.07 µm, cytoskeletal keratin intermediate filament network like rheological be...

Eggshell membrane reinforced polypropylene biocomposite and its tactile assessment

“…The ESM was resourced from WES through the physical separation and pulverization methods, which may result the ESM into its denatured form. [34,51] During melt-mixing, the denatured ESM interacted with the PP matrix through nonpolar-nonpolar interaction and occupied within the interstitial spaces of PP. Consequently, the composite was enhanced with polar functionalities with increasing the ESM content.…”

“…Herein, it is important to mention that the materials exhibiting better touch-feeling sensation for example, leather, fur, silk, feather, PA, and so on are found to be located as tribopositive material in the triboelectric series. [51][52][53][54] Considering this apparent relation between the tactile property and triboelectricity, herein, we have approached the triboelectric investigation to realize the touch-feeling property of the composites (containing ESM of 5 μm), as described below.…”

“…According to the triboelectric series, the PP is a tribonegative material, whereas the ESM having the similar functionalities like keratin, human hair, leather, fur, silk, feather, and so on is considered as a tribopositive material. [51] It is assumed here that with increasing the tribopositive ESM content, the tribopositive character of the ESM/PP biocomposite is increased. In general, the triboelectricity is generated during the contact of materials of opposite triboelectric polarity.…”

“…[51][52][53][54][55][56] During contact the tribopositive material (mainly having electron donating groups) donates the electron whereas tribonegative material (mainly having electron withdrawing groups) attracts the electron. [51][52][53][54][55][56] Consequently, there will be a polarization and flow of electron resulting in electrical output response. In this investigation, we have chosen the tribonegative polytetrafluoroethylene (PTFE) and the tribopositive PA6 as friction surfaces to realize the increase of tribopositive character of the composite with increasing the ESM content.…”

“…[1,49] Considering the lowering of friction coefficient is associated with improving the pleasantness, [50] reduction of in-plane COF with increasing the ESM, although preliminary supported the improvement of touch-feeling property of the composite, the overall results were found to be unclear towards assessing the touch-feeling sensation. In this context, as it has been found that the materials being used for different commodity products exhibiting better touch-feeling performance are usually tribopositive materials, for example, leather, feather, fur, silk, PA, and so on, and ESM also being a tribopositive material, [51][52][53][54] herein it can be prejudiced that the incorporation of tribopositive ESM within the tribonegative PP matrix may enhance the tribopositive character of the ESM/PP composite and resulting in its improved pleasantness (or, touch-feeling property). In addition to the COF measurement, herein, we have approached the triboelectric investigation to be a plausible alternative to realize the touch-feeling sensation of the composites.…”