## 2 Experimental Characterization of MEMS-Technology Based Instruments in Operational Environments  
In spite of MEMS' great potential for biomedical applications, only a few studies [37] focus on their characterization in an operational environment.  
In fact, SEM observation is often a necessity to characterize MEMS, but this means it could be detrimental for the assessment of tests under real operational conditions, basically because tests are performed in vacuum conditions.  
Considering the extensively spread biomedical applications, it is also worth mentioning the Optical Coherence Tomography (OCT), which is an optical imaging technique used primarily to investigate the internal microstructure of biological tissues, in ophthalmology and in dentistry [38]. The main advantage of OCT compared to other traditional systems is that this method offers the possibility of a non-invasive in vivo visualization of the tissue with high-resolution three-dimensional images [39]. Despite the axial resolution of some OCT systems (such as Ultrahigh-resolution OCT) [40] that can reach a few micrometers [41], the lateral resolution is affected by the diffraction limits due to the spot size in the focal plane of the probe beam. In fact, the lateral resolution often presents values between 10 and 20 \(\upmu\)m [42; 43]. Indeed, the above mentioned values of lateral resolution, together with higher costs, make OCTs less attractive than the light microscopy for the characterization of microgrippers in operational conditions.  
Considering the above mentioned characteristics for SEM and OCT, traditional light microscopy is quite competitive since it allows test stands to be less expensive in a widespread range of test conditions.  
In this investigation a performance characterization of some comb-driven microgrippers in operative condition has been carried out.  
The characterization of MEMS-Technology based microgrippers has been recently approached by using a profilometer [44], while the present work will show that a more simple commercial light microscope is still capable to satisfy the same activity with no detriment of measurement significance. Since optical microscopy is widely used in laboratories, it is believed that this paper might have some impact on the future characterizations of microsystems in air, wet or liquid environments. The importance of micromanipulation of mobile micro-particle suspended in liquid well has been recently underlined and a visual-servo automatic micromanipulating system has been presented [45].  
Since the intrinsic resolution of optical microscopy is generally rather worse than SEM or profilometer imaging, its real aptitude and efficacy in examining micro-objects remains something that must be validated. Therefore, the present paper will endorse microscopy observation to characterize a microsystem in environmental conditions, by comparing the results obtained by means of both optical microscope and profilometer image analysis techniques. This is justified since the optical devices are the most suitable for carrying out measurements on microsystems without contact and in operative conditions.  
In this work, the above mentioned characterization involved the measurements of the angular displacements of a rotary comb-drive embedded into an independently developed microgripper, when a voltage is applied to the device. This is obtained by an in-house Image Analysis Software (IAS) implemented by the authors. The analysis of the measurement results has been achieved by means of uncertainty models for the evaluation of the corresponding error sources. For this purpose, the two image acquisition systems and the corresponding measurement chains will be described, together with the analysis of the relative sources of uncertainty. Finally, the measurements carried out with the Optical Profilometer System (OPS) and Light Trinocular Microscope (LTM) systems will be analyzed to check whether the two groups of results could be considered comparable and consistent within the interval of experimental uncertainties.