Fig. 1. The timeline of the development of silk-based advanced materials for soft electronics: Bioresorbable electronics^[3] (2009); ultraconformal bioelectronics^[21](2010); flexible OTFTs^[22] (2011); transient electronics^[22](2012); conformal wireless biosensors^[22](2012); flexible solar cells^[31] (2014); bio-triboelectric generator^[31] (2015); bio-memristor^[33] (2015); carbonized silk fabric (CSF) wearable strain sensors^[34] (2016); silk-derived carbon based E-skins^[35] (2017); on-skin stretchable electrodes^[36] (2018); biodegradable and stretchable protein-based sensor^[37] (2019); all-textile electronic skin^[38] (2019); electronic skin for human thermoregulation^[39] (2020).

Fig. 2. Schema of the hierarchical network structures of SF fibers and none-fiber silk materials^[46]. Lv1: the amino acid sequence; Lv2: α-helix & β-sheet; Lv3: β-crystallites; Lv4: crystal network; Lv5: nanofibrils network.

Fig. 3. Mesoscopic functionalization of silk-based materials: (a) The chemical bonding between SF and GO^[47]; (b) the revisable structure changes of β-sheets and random coils under high thermal treatment^[17]; (c) a silk-based memristor^[33]; (d) silk nanofiber membrane for bio-triboelectric generator^[32]; (e) schematic of β-sheet-derived carbon basic structural units^[64].

Fig. 4. Design of silk-based strain sensor: (a) A graphite/silk flexible strain sensor with sheath-core structure^[34]; (b) a wearable strain sensor based on carbonized silk fabric^[65]; (c) an RSF-based hydrogel for monitoring human movement^[67]; (d) an RSF-based single electrode TENG and strain sensor integrated platform^[68].

Fig. 5. Design of silk-based pressure sensor: (a) An RSF-based biocompatible and degradable pressure sensor^[37]; (b) a silk fiber wrapped fibrous pressure sensors^[69]; (c) an wireless pressure sensor based on silk fabric^[38].

Fig. 6. Design of RSF-based electrophysiological sensors: (a) An RSF plasticized electrode for EMG monitoring^[36]; (b) a Ca²⁺ modified RSF adhesive^[72]; (c) a wearable Ag NW/RSF electrode for ECG monitoring^[73].

Fig. 7. Design of silk-based temperature and humidity sensor: (a) A silk-derived wearable temperature and pressure sensor^[74]; (b) a silk-based electronic fabric for temperature and pressure sensing^[69]; (c) a self-healable multifunctional electronic tattoos based on RSF^[75]; (d) an RSF-based heat-resistant electronic skin for thermoregulation^[39].

Table 1. Summary of properties and functions of silk-based wearable sensors.