Colloquia

Samenvatting

Utilizing external magnetic fields generated from a rotating permanent magnet actuator for the swimming of microrobots such as an untethered magnetic robot (UMR) or a wireless clot retriever (WCR) is beneficial for wireless engagements with gelatin phantoms mimicking as blood clots in terms of their viscoelastic properties and internal microstructure. Moreover, the swimming of these microrobots enables to determine their velocities over a range of different actuation frequencies of the applied external magnetic field, thus giving more insight into their wireless locomotion and trajectory. Silicon oil is chosen as the medium in which the UMR and WCRs swim, due to its contribution of a low Reynolds number (Re ≪ 1), thus promoting the creep regime (laminar flow), which is a necessary factor for a stable and effective helical propulsion. One UMR and three WCRs were taken and were made to swim in two directions, forwards and backwards between a range of 1hz till 15 hz, where the step-out frequencies were observed for each. In the case of the UMR, the step-out was observed at 12 Hz and 8 Hz in the forward and backward motion respectively and for the WCRs, the step-out was observed for WCR 1 (short WCR) was 12 Hz and 14 Hz in the forward and backward directions respectively. WCR 2 and WCR (both long WCRs) have the same design and dimensions and their step-out was noticed at 9 Hz in the forward and backward directions.

Moreover, through the use of rheological tests like oscillation frequency and flow sweep, the characterization of the gelatin phantoms used to mimic blood clots was successfully carried out. Gelatin phantom of 2.5% wt/wt concentration was used to penetrate using the WCR and thus its mechanical properties were compared with blood clots to observehow the mechanical properties of one align with the other. four different blood clots were utilized for this comparison, namely the L-minus, L-plus, N-minus and N-plus. L depicts an 18% content of hematocrit and N depicts 30% hematocrit. Plus and minus indicate the presence and absence of fibrinogen respectively. The 2.5% concentration phantom showed its behaviour corresponding to the 30% hematocrit clot sample in the flow sweep test and a correspondence to the 18% hematocrit clot sample, suggesting that this phantom indeed aligns to blood clots with respect to its mechanical properties.