A microfluidic device for rapid screening of plastic-consuming extremophiles

Plastic is everywhere around us. Due to its properties, such as low cost, versatility, durability and high strength-to weight ratio, it has become one of the most used material in the world; but these properties also make it very difficult to degrade in the environment e and recycle. In 2019, Europe plastic production almost reached 58 million tonnes, and 370 million globally. One of the most used type of plastic is polyethylene terephthalate (PET), a crude-oil derived synthetic polymer, used for containers, films, and fibers, in addition to bottles. Today, only 14% of plastic packaging is collected for recycling, and is mostly recycled into lower value products that cannot be further recycled. The plastic that doesn't get recycled is discarded in landfill or lost in the environment, where it not only bring damage to the animals that get entangled with fishing lines and plastic bag, but it also deteriorates and breaks into small pieces finally resulting in the formation of microplastics that can enter the animal and human food chain, which has been linked to various adverse health effects, including immune disorders and congenital disabilities, as well as cancer. Plastic microbeads derive also from commercial use like with cosmetic, toothpaste, or laundry.Several methods are used to recover PET, including physical, chemical and biological. Physical recycling is the easiest and less expensive strategy, and it uses processes such as cutting, heating, extrusion and so on, but it deteriorates the product's properties at each cycle. Chemical recycling does not bring great degradation or waste but it pollutes the environment and requires high quantities of energy. Biorecycling is emerging as a potential degradation mechanism due to its affordability and eco-friendly nature. At the moment, only a few bacterial enzymes has been found to be involved in the degradation of PET, and none of it do it efficiently. The aim of this thesis was, therefore, to develop a novel optically accessible droplet-based microfluidic device produced for the culture of extremophiles bacteria and tested for PET degradation. The first step was to perform a bioinformatic analysis to select a specific bacterial strain that is able to express an enzyme that could potentially degrade PET. Then, we proceeded with the design and fabrication of a microfluidic device that provide a useful platform to produce water-in-oil droplets, in which PET microplastics will be encapsulated together with the selected PET-degrading bacteria. After successful encapsulation, online monitoring test has been used into droplet-based microfluidic device in comparison with the classical methods of culture on agar plates. Lastly, some future perspective of the droplet-based microfluidic application has been proposed to optimize long term analyses.