Filtration & fluid control


Blood, sweat and tears F


iltration technologies have come a long way. Classically, they have been used mostly for sterilisation where micro-organisms are separated from the rest of the medium, leaving a sterile solution behind. They feature in other industrial processes too, from water desalination to bioprocessing. Increasingly, though, the medical device industry is applying filtration at smaller scales for advanced monitoring and diagnostic applications.


At its most basic level, filtration involves separating solid particles from a liquid or gas, via some kind of physical barrier or membrane. Smaller particles, like water molecules, can pass through the pores in this barrier, whereas larger particles like microbes cannot.


This simple principle, which every secondary school pupil could describe, becomes ‘microfiltration’ when the particles are very small


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(around 0.1–10μm), and ‘ultrafiltration’ when the separated species are much smaller still, typically in the 0.001–0.1μm range. Here, we are getting into the realm of microfluidics – the science of manipulating fluids on microscopic scales. “A microfluidic system works by precisely controlling and manipulating small fluid volumes,” explains Dr Taleieh Rajabi, a professor in the field of microfluidics and applied physics at RheinMain University of Applied Sciences, and head of precision microfluidics at a contract research organisation (CRO). “This enables continuous monitoring of health parameters; electrochemical sensors for real-time analysis of biofluids; and data transmission to smartphones or cloud platforms for further analysis and monitoring.”


Microfluidic platforms, often referred to as a ‘lab on a chip’, contain intricate networks of channels, chambers and control mechanisms. A fluid sample


www.medicaldevice-developments.com


Filtration is evolving beyond classical sterilisation and physical barrier function to support a range of emerging applications on microscopic scales. Abi Millar discusses how it is being used in liquid biopsy and in continuous-sampling wearable devices with Professor Taleieh Rajabi of RheinMain University of Applied Sciences.


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