Fabrication and integration of smart materials for flow control in microfluidic paper-based analytical devices

Resumen

Paper microfluidics represents a novel platform technology for fluid handling and fluid analysis for a variety of applications, featuring low cost, easy fabrication and operation and equipment independence. It is an expanding research area, since it is able to overtake some limitations that conventional microfluidics are straggling with since the beginning. Paper microfluidics is delivering microfluidic devices, which are interesting for the society, being an inherently cheap and simple technology, which could be implemented by the industry. In this thesis, the fabrication of the µPADs by two methods: double side ink stamping and wax printing were carried out where both fabrication methods have different advantages and drawbacks. For instance, ink stamping provides an easy and highly economic fabrication method for resource limited settings while wax printing is very functional method in a laboratory environment being considered as a cheap alternative when mass fabrication capabilities are introduced. The results of these investigations were presented in Chapter 3. The lack of effective handling and control of fluids on paper is the main reason for the low transition of µPADs from the laboratory to consumers’ hands. Therefore, this thesis has also investigated innovative solutions using smart functional materials based on ionic liquids (ionogels and poly ionic liquids) as alternatives to control fluid flow in µPADs. Firstly, a new concept for fluid flow manipulation in µPADs was investigated and presented in Chapter 4, by introducing two different ionogel materials as passive pumps. It was demonstrated that ionogels highly affected the fluid flow by delaying the flow from the inlet. They revealed two distinctive liquid flow profiles due to their different physical and chemical properties and thus water holding capacities. Then the ionogel materials were implemented as negative passive pumps at the outlet of the µPADs. The ionogel was able to continuously drive fluids through the µPAD and so, to control the flow direction and flow volume that reach the outlet. The results of these experiments are presented in Chapter 5. Finally a cholinium-based biocompatible crosslinked poly ionic liquid hydrogel was integrated in a µPAD as negative passive pump. This material has a very high wicking capacity and thus an excellent control on directing the fluid flow on the paper device. As exposed in Chapter 6, to the best of our knowledge, these hydrogel pumps have the highest capacity demonstrated in a µPAD up to now. To summarise, in this thesis, as presented in Chapter 7, the effect of temperature in the fabrication of µPADs by the wax printing method was deeply investigated for the first time, opening new avenues of controlling microfluidic dimensions in paper devices. Besides, a new fabrication method, “double side ink stamping” was developed for the easy fabrication of µPADs on site. Finally, the manipulation and delay of fluid flows as well as the control of the direction of the flow in µPADs was investigated in detail, by introducing simple, cheap, lightweight ionogels and poly ionic liquid hydrogel materials as passive pumps. Easy fabrication and integration of these polymer gels was achieved, eliminating the need of integration of external mechanical, relatively expensive, technologies, which are usually needed for the control of liquids in µPADs.