Application of nanogenerators in oral and respiratory systems: a review

In recent years, with the advancement of precision medicine, oral health monitoring has become an important component in assessing human physiological indicators. However, due to the unique characteristics of the oral environment, such as high humidity, confined space, and complex conditions, traditional sensors often face challenges, including poor biocompatibility, frequent battery replacement, and size limitations. Moreover, high energy consumption in intraoral monitoring sensors leads to substantial maintenance costs for long-term wear. Therefore, the development of sensing systems with excellent biocompatibility, miniaturization, and self-powering capability has become a core requirement in long-term monitoring of the oral cavity and teeth. Compared with conventional sensors reliant on external power supplies, nanogenerators (NGs) based on triboelectric, piezoelectric, and pyroelectric effects can harvest oral biomechanical or environmental energy for continuous operation, thereby exhibiting immense potential and clinical value for frontier applications, such as critical care vital sign monitoring, exhaled gas analysis, and long-term stable monitoring of human organs. Despite the rapid development of NGs in oral and respiratory applications, there is still a distinct lack of a systematic review that bridges tailored material choices and structural designs with the specific and harsh clinical demands of the oral-respiratory environment. This review summarizes the functional implementation and self-powered sensor applications of NGs in areas such as respiratory monitoring, gas sensing, medical diagnostics, and electronic skin. Based on a summary of these categorized applications, the review concludes with a discussion of the application prospects and current challenges of NGs in the oral field.