Blood sampling using microneedles as a minimally invasive platform for biomedical diagnostics

Blood is the most important body fluid in humans, transporting nutrients into the tissues and organs while removing metabolic wastes from cells. Regular blood tests can reveal many physiological and biochemical indexes that are critical for diagnosis of various diseases and evaluation of therapeutic efficacy. However, the traditional hypodermal blood sampling method contradicts patient compliance due to the induced pain, bleeding and the requirement of skilled professionals. For point-of-care diagnosis, blood extraction systems are desired to be easy, safe and fast for collecting essential tiny volumes of sample. Microneedles have attracted considerable attention as a novel transdermal blood extraction tool with superior advantages, including painless experience, low cost and high safety. Moreover, various sensors and actuators can be integrated into the microneedle platform for continuously monitoring bio-analytes after extracting and guiding the blood sample into the analytical unit. In this review, we highlight the characteristics of skin structures and the existing blood sampling techniques in clinics and in nature, focusing on several critical aspects of microneedle platforms for transdermal blood extraction and analysis, including materials composition, actuator fabrication, sensing methods and the future prospects toward clinical translation.