**1. Introduction**

Over the past few years, there has been an increasing demand on the employment of flexible materials for various applications in biomedical field. This has led to the significant growth of the movable structure development [1,2]. The flexible material having good mechanical properties with high surface strength and high elasticity has enabled tremendous innovation in the development of microelectromechanical systems (MEMS) devices in which the electrical and mechanical property of the material are the most important characteristics of the technology [3]. One of the most interesting materials is polymer that currently can be found in various biomedical instrumentation due to its excellent mechanical properties, compactness, precise control and biocompatibility as well [4].

The flexibility characteristic of polymer is beneficial in obtaining large and controlled structure deformation of the movable parts. These movable parts include diaphragm (thin membrane), pillars, cantilevers or the combination of pillars and movable structures [5,6]. This class of functional material plays very important role in the development of MEMS electromagnetic (EM) actuators, for example the microfluidic delivery system found in drug delivery, bio-cell preparation system and lab on chip [7]. The system can also include micropumps, microvalve, micromixer, microgripper and micromanipulators [8–11].

Studies on electromagnetically driven MEMS actuators in the field of biomedical instrumentation are currently increasingly popular in which the improvements of the mechanical structures and the material properties of the movable part became the most interesting topics. The development studies were done in order to enable e fficient and precise structure movement for control, manipulation or analysis purpose of the biomedical samples [12,13]. These studies also have led to the invention of flexible structure possessing sensitive interaction with magnetic induction, to be the most important mechanism in electromagnetic actuation. The moving structures should be made of soft and elastic material, able to continuously vibrate and capable of reacting to mechanical pressure and magnetic field exposures [14].

Several reports have been recently published to introduce the interaction between magnetic flux generated from electromagnetic coil and rotating magne<sup>t</sup> field [15,16]. This interaction is the basic principal operation of the electromagnetic actuator that produces magnetic force to enable the movement of a movable structure. The basic electromagnetic actuator structure consists of a flexible movable membrane, electromagnetic coil, magnetic chamber or spacer and bulk permanent magnet. Initially, a thin membrane attached with permanent magne<sup>t</sup> has been the common structure used as the moving membrane of the MEMS electromagnetic actuator [17]. Unfortunately, the structure with attached bulk magne<sup>t</sup> su ffers from high volume and low reliability, especially when the membrane operates in long vibration mode [18]. Therefore, some innovations in the material structure have been developed in order to obtain a compact and reliable actuator.

The MEMS structures are usually made of glass, silicon, silicon nitride and metals [19,20]. Those materials are the common materials in MEMS technology due to the excellent mechanical properties and matured technology process [21]. However, silicon and glass are easy to break as they have low fracture strain which is about 0.1% [22–24]. Meanwhile, metals are very sensitive to chemical and environmental e ffect [25]. Some other disadvantages of those conventional MEMS materials, especially for the use as movable structure, are fragile and low flexibility. These drawbacks make them less favorable compared to polymers.

On the other hand, polymers in MEMS have been used since several years ago as a photosensitive material [26], sacrificial layer [27], passive structure for microchannel [28], microchamber and passive micromixer [29] and as the functional layer of micro-structured devices, such as actuators [30] and sensors [31,32]. Polymer has good mechanical properties with Young's modulus lower than silicon and metal, which makes it highly elastic and at the same time possesses high strength [33–38]. In conjunction with MEMS actuators, the mentioned mechanical properties are useful in obtaining large membrane deformation under external magnetic stimulus. Furthermore, the most important fact is that the polymeric structure of MEMS device can be fabricated in inexpensive way, cheaper than silicon-based micro-processing cost [39–41].

It was also reported that microstructures working under extreme vibration condition like actuators need enhancement in terms of material quality, design and technological concepts in order to increase the lifetime and effectiveness of the structures [38]. Therefore, some magnetic polymers become more preferable as the structures will have high elasticity, easy to fabricate and photo-patternable.

Some popular polymers have been identified and explored to become the flexible material for actuation purposes. The common actuator materials that have been reported in the literatures include PMMA, parylene, polyimide and PDMS elastomer. The properties of those materials are summarized in Table 1.


**Table 1.** Material properties of popular polymers used in microelectromechanical systems (MEMS).
