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Since their early stages of development, micro-electro-mechanical systems (MEMS) have shown potential for breakthroughs in the fabrication of medical tools. The miniaturization of various devices using MEMS technology has enabled minimally invasive treatments and in situ measurements. In this paper, we introduce two advancements in MEMS applications in the medical field: (1) microneedle devices for brain activity evaluation, a transdermal drug delivery system, and biological fluid sampling; and (2) miniaturized MEMS sensors for monitoring the conditions inside blood vessels and respiratory organs. In addition, we provide a summary of MEMS sensors used in developing new drugs, detecting vital signs, and other applications.

Cross-sectional imaging of isolated rat lungs was demonstrated by ultrahigh-resolution optical coherence tomography using supercontinua at 800, 1060, and 1300 nm wavelengths. The detailed structure of the trachea, including cartilage, mucosa, and annular ligaments, were observed clearly. In the imaging of visceral pleura and alveoli, when phosphate-buffered saline was instilled into the lung, the penetration depth of imaging was improved, and clear images of the fine structure of the lung, including alveoli, were observed owing to the index-matching effect. The wavelength dependence of the light source was discussed for the observation of fine structure and imaging contrast.