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Overall, this review aims at presenting a helpful guidance to the engineering and design of optical microsystems for optogenetic applications.

This paper presents a new type of dry electrodes for acquisition of biopotentials and stimulation. These dry electrodes are composed by 16 microtip structures (by forming an array of 4 × 4 microtips), which were fabricated through bulk micromachining of a 1 0 0 -type silicon substrate in a potassium hydroxide (KOH) solution. The fabrication process was trimmed in a way that each microtip presents solid angles of 54.7 • , a width in the range 150-200 m, a height of 100-200 m, and an inter-microtip spacing of 2 mm. The electrodes have a thin layer (obtained by reactive DC-sputtering) of iridium oxide (IrO) to improve the contact with the skin. These dry electrodes penetrate the outer skin layer (i.e. stratum corneum that is 10 m thick) to allow a direct contact with the electrolyte fluids of the inner skin layers. The new electrode avoid the use of conductive gels and reduce the skin preparation time in EEG experiments, which may take about 45 min for a set of 32 standard silver/silver chloride (Ag/AgCl) electrodes. The electrode-electrolyte impedance spectrometry (IS) of the IrO thin-films was performed in a saline solution, 0.9% concentration by weight, to mimic the electrode-tissue interface. The IS measured results for the IrO coatings were comparable to the results observed for the standard Ag/AgCl electrodes. The new dry microtips array constitutes an inexpensive, low resistance and mechanically robust alternative electrode for non-invasive biopotential recording/stimulation with fast application on skin.

This paper presents a sensing electronic-free wearable solution for monitoring the body kinematics. The measuring of the knee movements, flexion and extension, with the corresponding joint acting as the rotation axis is shown as working principle. The proposed sensing system is based on a single optical Fiber-Bragg Grating (FBG) with a resonance wavelength of 1547.76 nm. The optical fiber with the FBG is placed inside a new polymeric foil composed by three flexible layers which facilitates its placement in the anatomic parts under investigation while maintaining full sensing capabilities. The way the device is placed in the specific body part to be measured enables the clear detection of the movements in respect to the joint. The proposed solution was tested using a prototype that was built to evaluate the device under different condition tests and also to assess the system's consistency. The designed and fabricated system demonstrates clear advantages in medical fields like physical therapy applications as optical fiber is not affected by electromagnetic interference nor does the system needs complex and expensive electronic systems and mechanical parts. Another advantage is the possibility to measure, record and evaluate specific mechanical parameters of the limbs' motion. Patients with bone, muscular and joint related health conditions, as well as athletes, are within the most important end-user applications.

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