for their high sensitivity, easy signal collection, fast response, and simplicity of design, which are favored in diverse fields. [2,5] Consequently, the requirements for strain and pressure sensing materials are also highly proliferating. [6] Hydrogels, a class of 3D networks formed by the cross-linking of hydrophilic polymer chains within an aqueous microenvironment, which not only exhibits high flexibility, excellent stretchability, deformation restorability, and self-healing ability, but also possesses good biocompatibility, biodegradability as well as non-toxicity, making them a promising material for flexible actuators, soft electronics, wearable sensors, and implantable medical devices. [7,8] Polyvinyl alcohol (PVA), as the largest water-soluble polymer in the world, has been widely used in the fabrication of physically crosslinked hydrogels through freezing-thawing process. [9,10] Due to their merits of safety, high flexibility, transparency, and mild and scalable preparation, PVA hydrogels are ideal candidates utilized for portable wearable sensor compared to other materials. [11] Cai and co-workers reported an extremely stretchable piezoresistive strain sensor based on various self-healing PVA hydrogels such as carbon nanotubes (CNTs), graphene, and silver nanowire/PVA hydrogels, which could effectively monitor multifarious human motion when used as wearable sensor. [12] Hu et al. successfully prepared a composite conductive hydrogel combining PVA, polyaniline and glycerin, which demonstrated high sensitivity of 2.14, fast response time (230 ms), and long cyclic stability as wearable sensors. [13] Building multiple network structure is a desirable method to strengthen mechanical performance by exerting synergistic effect. [11,14] Sodium alginate (SA) is a common natural polysaccharide with extraordinary biocompatibility and biodegradability, which is extensively used in food, pharmaceutical preparations, and wastewater treatment. [15] SA is capable of reacting with multi-valent metal ions to form hydrogels via crosslinking reaction. [7] However, the weak strength and instability are the main disadvantages of SA hydrogels, greatly limiting its application in various strength-demanding fields. [10,16] Accordingly, the blending of PVA and SA is properly adopted to form double physical crosslinking composite hydrogels, which can effectively improve the strength and stability of individual hydrogels. [17] As verified in several literatures, Zhang and co-workers synthesized one interpenetrating network hydrogel based on Flexible and wearable sensors are fast establishing their status as go-to devices for human motion detection. A bacterial cellulose-reinforced hydrogel is fabricated through a facile and scalable freezing-thawing process with Ca 2+ crosslinking for strain and pressure sensing. Polyvinyl alcohol/sodium alginate/bacterial cellulose/modified carbon nanotube and carbon black hydrogels assembled as piezoresistive strain sensors and capacitive pressure sensors exhibit an excellent synchronicity betw...
