Micro-electromechanical system (MEMS) gas sensors represent a system that is capable of detecting the existence and concentration of gasses in the atmosphere. These sensors have become incredibly popular and have been widely used in a variety of fields, including the biomedical field. Over the years, several gas sensors have been developed to detect and analyze a wide range of gases. As sensor applications are expected to be further extended in the near future, it is, therefore, essential to review crucial types of gas sensors, their features, challenges, and a range of important applications. This paper presents a comprehensive review of the state-of-the-art gas sensors, which have been developed for gas sensing applications using MEMS technology. The working principle, the structure, the sensitive material and the important characteristics of each of these sensors are discussed. The focus of this review is on applications surrounding the use of electrochemical, optical and acoustic gas sensors for biomedical applications.

Micro-electromechanical-system (MEMS) based actuators, which transduce certain domains of energy into mechanical movements in the microscopic scale, are increasingly contributing to the areas of biomedical engineering and healthcare applications. They are enabling new functionalities in biomedical devices through their unique miniaturized features. An effective selection of a particular actuator, among a wide range of actuator types available in the MEMS field, needs to be made through the assessment of many factors involved in both the actuator itself and the target application. This paper presents an overview of the state-of-the-art MEMS actuators that have been developed for biomedical applications. The actuation methods, working principle, and imperative features of these actuators are discussed along with their specific applications. An emphasis of this review is placed on temperature-responsive, electromagnetic, piezoelectric, and fluid-driven actuators towards various application areas including lab-on-a-chip, drug delivery systems, cardiac devices and surgical tools. It also highlights the key issues of MEMS actuators in light of biomedical applications.