## 1 Introduction
For example, the influence of temperature and humidity on the adsorbed water layer on micro scale monocrystalline silicon (Si) films has been investigated in air, using an Si-MEMS kHz-frequency resonator [12]. Water proof or water insensitive three-axis MEMS based accelerometers have been presented [13] for encouraging their operation in laboratory scale experiments. The theory of water electrolysis in a closed electrochemical cell has been described [14] to develop a new actuation principle for MEMS. A special apparatus has been employed to study the adhesive friction due to water in the nanometer range, where the water layer thickness greatly affects friction and adhesion [15]. Heat transfer characteristics of isolated bubble of water were investigated by local wall temperature measurement using a novel MEMS based sensor [16]. MEMS-OR-PAM (optical-resolution photoacoustic microscopy) has also been proved [17] to be a powerful tool for studying highly dynamic and time-sensitive biological phenomena. Although MEMS still have not developed their potential for surgery applications, there are many more examples of their use in biomedical instruments [18; 19; 20]. The mechanical characteristics of cells provide information on their functionality and their state of health, while their geometry can be linked to genetic alterations and apoptosis; the importance of these analyses could help in the collection of phenotypic information or for the diagnosis of pathological disorders [21]. For example, a study[22] was conducted about the viscoelasticity of L92 cells, to investigate their cellular structure, notoriously linked to important physiological functions. In addition, applications of microspectroscopic techniques [23] have been conducted to characterize the viscoelastic properties of living cells. The study of the mechanical properties of cells, also concerns the muscle cells: for example the mechanical response, in terms of strength and displacement, of some smooth muscle cells subjected to elongation has been studied [24] with the aim of better understanding the links between their functionalities and their structure. A study [25] on skeletal muscle cells described how the relationship between the stiffness and the force exerted by some actin filaments can indicate the physiological state of the actin cytoskeleton. Moreover, the mechanical properties of tissue-engineered vascular constructs have been studied by monitoring pressure and diameter variations of vascular constructs submitted to hydrostatic loading [26]. A silicon microgripper has also been proposed [27] to characterize the mechanical stiffness of biological tissues, with the wider prospective of developing a professional inspecting instrument for laboratory measurements or surgical operations. More recently, new emerging MEMS-Technology based instruments for biomedical and surgical applications have been developed. In fact, based on a new concept hinge [28; 29], a class of different microgrippers, equipped with rotary comb-drives, has been developed [30; 31; 32; 33], also in significant environments [34], and fabricated [35; 36]. Thanks to their size, these instruments are expected to be employed in surgery and diagnostics. This class of microsystem is the focus of the present investigation.