Division of Biomedical Engineering

Supervisors:
Dr. Thierry Baasch* and Prof. Thomas Laurell

*mail: Thierry.Baasch@bme.lth.se

The aim of the project is to mount and test microfabricated silicon glass chip for acoustic trapping like the acoustic trapping performed by seed particles in glass capillaries [1]. Acoustically enabled seed particle trapping has been used in capillaries to trap exosomes and bacteria. One major drawback of the current technology is its limitation to using capillaries as main vibrating bodies. Here we suggest a novel silicon chip design that creates the same acoustic field as the one that is used in trapping capillaries. If successful, the silicon chip design will have several advantages over glass capillaries. 1. The shape of the pressure field will be independent of the shape of the applied piezo-electric transducer. 2. Large freedom in designing the geometric of the trapping region, to make it large or smaller on demand and with respect to the application. 3. It could be possible to completely get rid of the seed particles as the seed structure can in a silicon chip be easily added into the trapping region during the micro fabrication. This would allow seed particle trapping without such a high sensitivity to frequency and without fear of losing the seed particle cluster etc. As shown by Fornell et al. [2] the trapping potential is crucial for the functionality of the application. In glass capillaries a potential well is formed, and the seed particles are trapped at the maxima of the mean squared velocity <vv>. The acoustic forces act along the gradient of this potential and are thus highly dependent its shape. Our silicon chip design is validated by numerical simulations, shown in fig. 1. The chamber design will lead to a potential well as in glass capillaries. The next step is to test the microfabricated devices in the laboratory and evaluate their performance in acoustic trapping of seed particles and extracellular vesicle extraction. The goal of the underlying Master’s Thesis project is to design and fabricate a holder to mount the chips in a microscope setup. Then the chips (shown in fig. 2) will be connected to microfluidic syringe pumps and their performance for trapping of seed particles will be assessed. Finally, the trapping, extraction and enrichment of nano-particles and/or vesicles will be validated.

[1] Hammarström, Björn, Thomas Laurell, and Johan Nilsson. "Seed particle-enabled acoustic trapping of bacteria and nanoparticles in continuous flow systems." Lab on a Chip 12.21 (2012): 4296-4304.
[2] Fornell, A., Baasch, T., Johannesson, C., Nilsson, J., & Tenje, M. (2021). Binary acoustic trapping in a glass capillary. Journal of Physics D: Applied Physics, 54(35), 355401.

Figure 1 a) Silicon trapping chip and b) trapping capillary. A piezoelectric transducer excites a local resonance that is used for the trapping of seed particles and by that the extraction and enrichment of extracellular vesicles. Red and blue indicate high and low acoustic trapping potential <vv>. The polystyrene seed particles will be trapped and held back against an external flow in the (local) maxima of the trapping potential. The special design of the trapping chamber in the silicon chip will support an acoustic field like the one in the trapping glass capillaries.

Figure 2. The chips are ready to be mounted and tested in our microfluidics labs!