## 4. Degradable Sensor Materials
### Degradable Polymeric Materials  
The commonly used biodegradable polymer materials for implantable biodegradable electronic devices mainly include the following types: 1. Polymers and copolymers; 2. polysaccharide materials; 3. Biomass materials, organometallic materials, etc. * Polymers and copolymers:  
Polybactic acid and its derivatives: Polylactic acid and its derivatives can be synthesized from renewable resources such as corn starch or sucrose. They exhibit properties analogous to those of traditional plastics and find extensive applications in the field of medical health [148]. Nevertheless, they also possess certain limitations. For instance, polylactic acid demonstrates strong hydrophobicity, which leads to poor cell affinity, thereby impeding its interaction with cells and tissue compatibility [149]. Moreover, acidic by-products may be generated during the in vivo degradation process, causing the pH value at the implantation site to drop significantly, thus triggering an aseptic inflammatory response [150]. Polylactic acid (PLA): A linear polyester formed by the polycondensation or ring-opening polymerization of lactic acid monomers (C\({}_{3}\)H\({}_{6}\)O\({}_{3}\)). Its degradation product is lactic acid, which is harmless to the human body. It supports minimally invasive implantation and biodegradation. When PLA is combined with chitosan (CHIT), both the mechanical strength and biodegradability of the material are improved [151]. Poly (lactic-co-glycolic acid) (PLGA): It is a copolymer of polylactic acid and polyglycolic acid. It is suitable for orthopedic implants. By adjusting the ratio of the two, PLGA can have a controllable biodegradation rate [152]. Polycaprolactone (PCL): PCL is a semi-crystalline polymer. Due to the hydrophobicity of bulk PCL, its degradation rate is relatively slow, making it suitable for implantable devices that require long-term functionality. The degradation rate of PCL can be enhanced by preparing it into electro spun fibers [153]. * Polysaccharides:  
Polysaccharides represent the most abundant natural biopolymers. In recent years, they have drawn increasing attention as versatile substances applicable across diverse biomedical domains. They possess a broad spectrum of sources and relatively low costs [154]. As natural polymers, their structures bear resemblance to those of biological macromolecules such as the natural extracellular matrix, endowing them with certain potential in cell therapy [155]. Moreover, polysaccharides can serve as components of drug carriers and implantable scaffolds [156]. Nevertheless, precisely due to their natural origin, polysaccharides exhibit some limitations during certain usage scenarios that demand precise control. For instance, issues such as microbial contamination, a decline in viscosity during storage, and uncontrolled thickening and hydration rates may arise. These limitations are anticipated to be mitigated through modification [157; 158]. Such as cellulose [159], chitosan [160], alginate [161], etc., have good biocompatibility and biodegradability. Researchers have conducted thorough studies on their biodegradability in the human body. * Biomass Materials and Molecular Ferroelectric Materials: Natural fibers, including bamboo fiber, hemp fiber, and kenaf fiber, offer renewable and biodegradable alternatives to synthetic reinforcing materials in composite materials. These fibers possess excellent mechanical properties and can be integrated into polymer matrices to enhance strength, stiffness, and durability. By means of fiber pretreatment techniques and composite formulations, the compatibility and adhesion between natural fibers and polymer matrices can be optimized, thereby enabling the preparation of sustainable composite materials suitable for a wide range of applications [162]. Nevertheless, natural biomass materials also exhibit certain drawbacks. For instance, they often display uneven performance, relatively inferior mechanical strength, and vulnerability to bacterial infection.