## 4. Degradable Sensor Materials  
Implant materials, which are required to remain within the human body for an extended period, must exhibit biocompatibility with the recipient's body. In accordance with the international standard ISO 10993 [118], medical devices implanted in the human body are obligated to undergo biological evaluation. The objective of this evaluation is to ensure that the implanted device will not inflict harm on the human body. This comprehensive evaluation encompasses the assessment of the physical and chemical properties of the product materials. More specifically, it involves evaluating the compatibility of the mechanical parameters of the implant material with the surrounding human tissues and determining whether its chemical composition will trigger harmful reactions, such as tissue inflammation. Additionally, toxicological evaluation is an integral part of this process, aiming to investigate whether the material and its degradation products are toxic or carcinogenic. Moreover, the degradation characteristics of the implant material are of utmost importance. Under the environmental conditions of the implantation site, including specific temperature, pressure, and chemical composition, it is essential to examine whether the degradation rate of the implanted device aligns with the design requirements. The criteria for implantable materials expounded in this article are grounded in the standards promulgated by the International Organization for Standardization, rather than the mandatory standards of any specific country or region. These criteria function as an auxiliary instrument to assist researchers in material selection. The ISO 10993 standard defines an implantable medical device as one that is anticipated to be completely introduced into the human body or replace the epithelial or ocular surface via clinical intervention and is expected to remain in position following implantation. Materials implanted in the human body must undergo a variety of tests stipulated by ISO 10993. The objective is to safeguard humans from potential biological hazards associated with the utilization of medical devices. The test items typically encompassed in this standard include vitro cytotoxicity tests, skin irritation tests, sensitization tests, and so on. Cytotoxicity: Cytotoxicity experiments employing cell culture techniques can be utilized to ascertain cell death, cell growth inhibition, colony formation, and other cellular responses induced by medical devices, materials, and their extracts. Sensitization test: The sensitization experiment serves to assess the potential contact sensitization reactions of medical devices, materials, and their extracts. This experiment is indispensable as even minute amounts of potential leachable substances can trigger sensitization, thereby leading to allergic reactions. Skin Irritation (Including Intradermal Reaction): The irritation assay serves to quantify the potential irritating impacts of medical devices, materials, and their extracts at relevant sites. The intradermal reaction assay is employed to assess the local tissue response to the extracts of medical devices. Additionally, the intradermal reaction can be applied to medical devices that are not amenable to skin or mucosal irritation testing (such as the implantable medical devices addressed in this article). Blood Compatibility: The blood compatibility assay is designed to evaluate the effects of medical devices or materials in contact with blood on blood or its components. Acute/Chronic Toxicity: In cases where there is a potential for the absorption of toxic leachable substances and degradation products, the acute toxicity experiment serves as a valuable tool to assess the potential hazards associated with an animal model's exposure to medical devices, materials, and their extracts either once or multiple times within a 24 h period. This experimental approach provides insights into the immediate effects of such exposures.