Development of a self-powered microfluidic platform for lab-on-a-chip applications
With the constant world population growth and ageing, several medical conditions are becoming a burden both in terms of deaths and cost for the health care system. For this reason, research institutions and biopharma companies all over the world are developing new diagnostic tools which allow early detection of many medical conditions, from cancer to infectious diseases, and monitoring of chronical pathologies. In fact, a timely diagnose is key since it would allow to start the treatment before the disease reaches an irreversible stage. Similarly, for chronic diseases, a frequent monitoring of the disease progression is crucial in order to tailor the medical treatments patient-by-patient. Currently, most of the clinical analysis and medical check-ups are done in centralized settings, like hospitals, which ensure high throughput and automation. However, this approach requires highly trained operators and expensive bulky equipment. Moreover, it can take up to several days to obtain the analysis results which hampers early diagnosis and frequent monitoring. This is even more true in developing countries, where access to centralized laboratories is even more complicated and the infrastructures available are limited.
Point-of-care testing (POCT) aims to solve this problem by bringing the analysis closer to the patient and ensuring the results within a few minutes. In this way, the doctor or the patients itself can take prompt actions both in terms of diagnose and treatments. Recently, interest has grown for lab-on-a-chip (LOC) devices since they integrate several laboratory techniques (i.e. sample preparation, mixing, dilutions) in a tiny microfluidic chip. Thus, LOC devices are ideal candidates for POCT and in particular self-powered LOC which do not require any power-source or external equipment, are ideal both for developed and developing countries.
In this framework, the global aim of this PhD thesis was to provide an innovative self-powered LOC microfluidic platform for POCT. More specifically, this PhD is divided into three main sub-objectives: i) to study and further develop the SIMPLE technology, a hybrid LOC self-powered pulling platform, towards POCT applications, ii) to develop an innovative self-powered infusion pump (iSIMPLE) and iii) to combine the two concepts with an in-house developed microfluidic hydrophobic valving system enabling complex liquid manipulation.
In particular, in the first part of the thesis, the SIMPLE, a self-powered pulling pump which relies on the capillary action of a paper pump to pull liquids into a microfluidic channel network, was investigated. First, a biosensor for detection of creatinine (biomarker of chronic kidney disease) in blood plasma was developed. It integrates an enzymatic bioassay on a SIMPLE chip and by means of a colorimetric read-out mechanism, it was used to detect creatinine over the clinically relevant range using only 5 µL of plasma within 5 min. Tests were done in a single blind study. Second, a smart designing tool for SIMPLE-based chips was developed. An analytical model of the SIMPLE was first derived and validated. Then, the model was used as prediction tool providing precise chip design parameters to avoid the time-consuming trial-and-error approach needed to achieve a required flow rate for specific applications (i.e. different bioassay steps). Finally, sample preparation was integrated in a SIMPLE-based device as it is a crucial step for POCT. Since biological samples, like whole blood, need to be treated before the analysis, a blood-to-plasma separation unit was integrated on a SIMPLE-based chip. This approach exploited the pulling force of the SIMPLE and a filtration porous material to extract plasma into the microfluidic channel for further analysis. This system is fast, self-powered, robust and its separation efficiency rivals the one of standard analytical methods.
In the second part of this thesis, an innovative self-powered infusion pump (iSIMPLE) was developed and characterized. Contrary to SIMPLE, iSIMPLE can push liquids generating high pressure, properties difficult to achieve in self-powered microfluidic devices. These unique properties were exploited for drug delivery applications and ex vivo experiments demonstrated that iSIMPLE in combination with a small needle, can inject highly viscous liquids (i.e. vaccine, drugs) into a skin-mimicking matrix in a controlled and repeatable way.
Finally, in the last research part of this work, more complex liquid manipulation was achieved by developing a new hydrophobic valving concept and integrating it with SIMPLE and iSIMPLE. A versatile, robust and simple-to-fabricate super-hydrophobic valve was used to i) make iSIMPLE activation error-proof, ii) combine two SIMPLE to enable sample splitting into two different channels, necessary for performing POCT multiplexing analysis, and iii) combine SIMPLE and iSIMPLE to achieve an unprecedented liquid manipulation for a self-powered microfluidic platform, namely shuttling of liquid.
The work presented in this PhD thesis proved the potential of the SIMPLE/iSIMPLE technology for POCT. Nevertheless, as for every new technology, further research should be carried out to i) integrate new features on the SIMPLE/iSIMPLE technology (i.e. heating on-chip), ii) combine this concept with robust, sensitive and versatile detection techniques (i.e. fiber optic surface plasmon resonance, digital assay) and iii) validate its therapeutics potential with in vivo drug delivery experiments.