Are microfluidics-based blood viscometers ready for point-of-care applications? A review

In recent years, the engineering of blood viscometers for the diagnosis, prognosis, and prevention of cardiovascular and other diseases has been the subject of significant research interest. Conventional blood viscometers such as rotational viscometers and capillary viscometers typically rely on mechanical techniques in quantifying whole-blood viscosity, a process in which resistance to blood flow is measured in response to an applied force. The direct applicability of conventional viscometers as point-of-care diagnostic and clinical tools is subject to several limitations mainly related to their macro-structural features that augment the sampling size and reduce portability. The development of new fabrication technologies to scale down experimental processes has opened up the reality of miniaturizing existing concepts of blood viscometers into microchips, and paves the road for future development of blood viscometers. These micro-blood viscometers are advantageous because they use very small sample volumes for quick, routine clinical purposes. The easy fabrication of microsystems and large-scale production not only result in a lower cost, but also render these devices portable and disposable, both of which are highly desirable for clinical applications. The underlying challenges of these devices are associated with red blood cell clogging, measurement stability, reliability, and reproducibility. The present review discusses the state-of-the-art and emerging trends in the field of microfluidics to provide elegant solutions for quantifying blood viscosity with vastly improved efficacy and with the potential for use at the patient's bedside.