## 1 Introduction  
Soft strain sensors capable of withstanding large strains are found as important elements in various applications, such as wearable devices for monitoring human activity [1], and soft robotics for detecting deformation states [2]. With the developments in materials and fabrication technologies, different measurement mechanisms such as capacitance [3, 4], resistivity [5], piezoelectricity [6], and inductance [7] have been successfully applied to develop soft strain sensors. Especially, soft resistive strain sensors based on the strain-resistance response have attracted extensive interest due to their advantages in easy fabrication, low power consumption, and simple readout circuit [8]. Generally, a soft resistive sensor is a two-part composite, i.e., a conductive film as the sensing part and an elastic substrate as the supporting part. After adhering the two parts together, they share the same deformation pattern. Therefore, the stretch of the substrate changes the conductive paths in the conductive film, leading to the resistance variation. Apparently, the materials utilized in the two parts have great impacts on the performances of the soft strain sensors. To date, the preferential conductive materials for fabricating the conductive films are nanomaterials due to superior electrical, mechanical, and thermal properties. As a typical nanomaterial, the applications of graphene and its derivatives, including graphene oxide (GO) and reduced graphene oxide (rGO), in soft strain sensors, have been deeply discussed in the literature [9; 10; 11]. As the unique hexagonal lattice formed by its internal carbon atoms, graphene shows excellent optical, thermal, mechanical, and electrical properties [12]. For example, the resistivity of graphene is only about 10-8 \(\Omega\)/m, which is much lower than that of pure copper (0.017 \(\Omega\)/m) [13]. Additionally, the cross-sectional thermal conductivity of bulk GO is 100 times lower than that of graphite [14]. At present, the preparation methods of graphene mainly include mechanical exfoliation, graphite oxide reduction, chemical vapor deposition, and silicon carbide epitaxial growth [15]. Among them, the graphite oxide reduction method is not only low in cost, but also can realize the mass-production of graphene. With the development of the fabrication technology, graphene-based materials have experienced in-depth developments in many advanced fields. For example, in the light modulation field, graphene-based metasurfaces--due to the high absorption rate of electromagnetic waves of many different frequencies--have attracted wide interest [16; 17; 18]. In the field of flexible electronic devices, the graphene-based touch screens and electronic papers have excellent bending capability and stretchability [19]. Although graphene has many outstanding merits, such as cost-effectiveness, biocompatibility, and surface area (ultrahigh), its fragility restricts the stretch of a planar graphene film in a narrow range. In order to overcome this restriction, the textured graphene films with different microstructures/patterns (e.g., buckling pattern [20], kirigami-structured pattern [21], porous network structure [22]) have been proposed. For a strain sensor, it was found that the textured graphene films not only broaden its measurement range, but also improve its linearity, and even add new functionalities such as the detection of organic gas [23]. About the materials of the elastic substrates, elastomers with high stretchability and good elasticity such as polydimethylsiloxane (PDMS), Ecoflex, and thermoplastic elastomers (TPEs) are commonly adopted. The influence of the elastic substrate on the strain sensor was reviewed in [8]. Recently, fabric-based strain sensors using fabrics as the elastic substrates have also received widespread attention, which show advantages in diverse structures and strong adhesion of conductive nanomaterials over the elastomer-based strain sensors [24].