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Page 8 of 16 Fan et al. Soft Sci 2024;4:11 https://dx.doi.org/10.20517/ss.2023.47

fiber surface provides natural advantages for frictional power generation. Moreover, Zhang et al.
constructed rough MXene films on leather fiber surfaces to improve the performance of frictional power
generation. The output voltage of the leather-based triboelectric nanogenerator (TENG) was stable under
cyclic impact for 4,000 s, which showed excellent durability. Furthermore, the array sensor was fabricated to
achieve the motion control of a mechanical hand, which demonstrated the potential in human-computer
[21]
interaction applications .
With the development of intelligent leather composites, conductive leather is widely used in various
[30]
industries . By utilizing the sensing capabilities of conductive leather, “dead skin” is “revitalized”,
providing a new electronic device design strategy for intelligent sensing, display, and interaction devices .
[42]
In the dyeing and finishing process of leather making, personalized design is carried out on leather
[62]
composites to obtain multi-stimuli responsive chromic devices . Zou et al. applied an electroluminescent
layer on the surface of the conductive leather composite and successfully illuminated them by designing
complex patterns such as flowers and words, demonstrating the excellent visual display ability of electronic
devices . Furthermore, the brightness of leather-based electronic devices could be varied with the amount
[42]
of pressure applied, which further controlled the light intensity of the device through pressure and provided
real-time visual feedback [Figure 3B]. This design strategy is simple and efficient; thus, it is expected to be
intensively applied to develop artificial intelligence and interactive electronic devices.

Electromagnetic interference shielding
With the popularization of electronic devices, concerns about electromagnetic radiation pollution and
electromagnetic shielding have become important . Generally, the main ways to shield electromagnetic
[31]
[63]
waves include reflection, absorption, and multiple reflections . It is beneficial for enhancing the
electromagnetic shielding effect by designing the structure and conductivity of the material. Leather has the
natural dielectric property, which enables dipoles to relax, resulting in dielectric loss to electromagnetic
[43]
wave energy under the action of electromagnetic waves . Secondly, after functionalization by various
conductive materials, the 3D collagen fiber network of the leather will induce electromagnetic waves to
undergo multiple reflections in the conductive network, resulting in Ohmic loss to consume
electromagnetic wave energy. For example, Bai et al. used polypyrrole (PPy), superconductive carbon black
(SCB), 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane (PFDTES), and PDMS to nano-engineer the design of
[64]
leather . The resulting PPy/SCB@PP-CFs with high conductivity (6.5 S/m) show significant
electromagnetic shielding ability [Figure 4A]. It also indicates that the thickness of leather composites is
positively correlated with electromagnetic shielding performance. As the thickness increases, the time for
multiple reflections of electromagnetic waves on leather increases; then, more electromagnetic wave energy
is consumed. At the same time, leather, as a promising natural material, has excellent X-ray protection
capabilities due to its multilayer woven structure that complements other functional materials [65-67] .

Flame retardant
Leather is inherently flammable since it is composed of a large number of collagen fibers and contains
[68]
elements such as carbon, nitrogen, hydrogen, and oxygen , which limits its applications. Therefore, it is
very important to develop leather composites with flame-retardant properties . Recently, many intelligent
[69]
fire-safe fabrics have been developed by modifying the surface of textiles with flame retardants [70-72] . The
preparation of leather requires tanning and fat-liquoring, which greatly facilitates the addition of flame
retardants and can be directly introduced into the leather-making process . Wang et al. in situ grew silica
[73]
particles on the 3D framework of leather and sprayed silica particles on the surface to obtain a thermal
insulation layer . The leather composite did not ignite after direct contact with the flame, demonstrating
[37]
its excellent flame retardancy [Figure 4B]. Lyu et al. added montmorillonite and layered double hydroxide
to leather during the fat-liquoring process to form a synergistic flame retardant system that enhances the