This review collates around 100 papers that developed micro-electro-mechanical system (MEMS) capacitive microphones. As far as we know, this is the first comprehensive archive from academia on this versatile device from 1989 to 2019. These works are tabulated in term of intended application, fabrication method, material, dimension, and performances. This is followed by discussions on diaphragm, backplate and chamber, and performance parameters. This review is beneficial for those who are interested with the evolutions of this acoustic sensor.

In this study, we present a comprehensive review of polymer-based microelectromechanical systems (MEMS) electromagnetic (EM) actuators and their implementation in the biomedical engineering field. The purpose of this review is to provide a comprehensive summary on the latest development of electromagnetically driven microactuators for biomedical application that is focused on the movable structure development made of polymers. The discussion does not only focus on the polymeric material part itself, but also covers the basic mechanism of the mechanical actuation, the state of the art of the membrane development and its application. In this review, a clear description about the scheme used to drive the micro-actuators, the concept of mechanical deformation of the movable magnetic membrane and its interaction with actuator system are described in detail. Some comparisons are made to scrutinize the advantages and disadvantages of electromagnetic MEMS actuator performance. The previous studies and explanations on the technology used to fabricate the polymer-based membrane component of the electromagnetically driven microactuators system are presented. The study on the materials and the synthesis method implemented during the fabrication process for the development of the actuators are also briefly described in this review. Furthermore, potential applications of polymer-based MEMS EM actuators in the biomedical field are also described. It is concluded that much progress has been made in the material development of the actuator. The technology trend has moved from the use of bulk magnetic material to using magnetic polymer composites. The future benefits of these compact flexible material employments will offer a wide range of potential implementation of polymer composites in wearable and portable biomedical device applications.

A valveless electromagnetic (EM) micropump with a matrix-patterned magnetic polymer composite actuator membrane structure was successfully designed and fabricated. The composite membrane structure is made of polydemethylsiloxane (PDMS) that is mixed with magnetic particles and patterned in matrix blocks. The matrix magnetic composite membrane was fabricated using a soft lithography process and expected to have a compact structure having sufficient magnetic force for membrane deformation and maintained membrane flexibility. The magnetic membrane was integrated with the microfluidic system and functionally tested. The experimental results show that a magnetic composite actuator membrane containing of 6% NdFeB is capable of producing a maximum membrane deflection up to 12.87 µm. The functionality test of the EM actuator for fluid pumping resulted in an extremely low sample injection flow rate of approximately 6.523 nL/min. It was also concluded that there is a correlation between the matrix structure of the actuator membrane and the fluid pumping flow rate. The injection flow rate of the EM micropump can be controlled by adjusting the input power supplied to the EM coil, and this is believed to improve the injection accuracy of the drug dosage and have potential in improving the proficiency of the existing drug delivery system.

Nephrogenic diabetes insipidus (NDI), which can be congenital or acquired, results from the failure of the kidney to respond to the anti-diuretic hormone (ADH). This will lead to excessive water loss from the body in the form of urine. The kidney, therefore, has a crucial role in maintaining water balance and it is vital to restore this function in an artificial kidney. Herein, an ultrasensitive and highly selective aptameric graphene-based field-effect transistor (GFET) sensor for ADH detection was developed by directly immobilizing ADH-specific aptamer on a surface-modified suspended graphene channel. This direct immobilization of aptamer on the graphene surface is an attempt to mimic the functionality of collecting tube $V_2$ receptors in the ADH biosensor. This aptamer was then used as a probe to capture ADH peptide at the sensing area which leads to changes in the concentration of charge carriers in the graphene channel. The biosensor shows a significant increment in the relative change of current ratio from 5.76 to 22.60 with the increase of ADH concentration ranging from 10 ag/mL to 1 pg/mL. The ADH biosensor thus exhibits a sensitivity of 50.00 µA· ${\left(\mathrm{g}/\mathrm{mL}\right)}^{-1}$ with a limit of detection as low as 3.55 ag/mL. In specificity analysis, the ADH biosensor demonstrated a higher current value which is 338.64 µA for ADH-spiked in phosphate-buffered saline (PBS) and 557.89 µA for ADH-spiked in human serum in comparison with other biomolecules tested. This experimental evidence shows that the ADH biosensor is ultrasensitive and highly selective towards ADH in PBS buffer and ADH-spiked in human serum.

The motion of bioparticles in a microfluidic environment can be actively controlled using several tuneable mechanisms, including hydrodynamic, electrophoresis, dielectrophoresis, magnetophoresis, acoustophoresis, thermophoresis and optical forces.

Discussing the topic of the capability of dielectrophoresis (DEP) devices in terms of the selective detection and rapid manipulation of particles based on the DEP force (F_DEP) via contactless methods is challenging in medical research, drug discovery and delivery. Nonetheless, the process of the selective detection and rapid manipulation of particles via contactless DEP based on dielectric particles and the surrounding medium can reduce the effects of major issues, including physical contact with the particles and medium contamination to overcome operational difficulties. In this review, DEP microelectromechanical system (MEMS) microelectrodes with a tapered profile for the selective detection and rapid manipulation of particles were studied and compared with those of conventional designs with a straight-cut profile. The main objective of this manuscript is to review the versatile mechanism of tapered DEP MEMS microelectrodes for the purpose of selective detection and rapid manipulation. Thus, this review provides a versatile filtration mechanism with the potential for a glomerular-based membrane in an artificial kidneys’ development solution for implementing engineered particles and cells by lateral attraction as well as vertical repulsion in the development of lab-on-a-chip applications. For tapered DEP MEMS microelectrodes, the scope of this study methodology involved the characterisation of DEP, modelling of the polarisation factor and the dynamic dielectric changes between the particles and medium. Comprehensive discussions are presented on the capability of tapered DEP microelectrodes to drive the selected particles and the simulation, fabrication and testing of the tapered profile. This study revealed an outstanding performance with the capability of producing two regions of high electric field intensity at the bottom and top edges of the side wall of tapered microelectrodes. Observations on particle separation mainly by the lateral attraction force of particles with positive DEP on the y-axis and vertical repulsion force of particles with negative DEP on the z-axis proved an efficient and uniform F_DEP produced by tapered electrodes. In conclusion, this study confirmed the reliability and efficiency of the tapered DEP microelectrodes in the process of selective detection and rapid manipulation at a higher efficiency rate than straight-cut microelectrodes, which is significant in DEP technology applications.