As research into the pathologies of COVID-19 advanced, we soon understood that microthrombi or microclots in the lungs of COVID-19 patients was a hallmark sign of the disease. In a recent article "SARS-CoV-2 spike protein S1 induces fibrin(ogen) resistant to fibrinolysis: Implications for microclot formation in COVID-19" from Lize M. Grobbelaar et al. ; researchers used Cellix's standardised Vena8 Fluoro+ biochips and microfluidic syringe pumps to model microclot formation where samples included platelet poor plasma (PPP) from COVID-19 patients and PPP from healthy patients with spike protein subunit 1 (S1) added. Spike protein is a membrane glycoprotein found on the Coronavirus. This S1 subunit of the spike protein is responsible for receptor binding, . Further paper publications have shown that the spike protein can be shed by the virus and it has been found in various organs, even crossing the blood-brain barrier, .
Researchers set out to investigate if the spike protein interfered with blood flow, comparing naïve healthy PPP samples, with and without added spike protein, to PPP samples from COVID-19 positive patients (before treatment). Let's take a closer look at the researchers' experimental set-up, how they modelled microclot formation and what they learned in the process:
Standard Experimental set-up
Using Cellix's VenaFlux platform which includes a microfluidic syringe pump (e.g. Mirus Evo syringe pump) and Vena8 Fluoro+ biochips:
Microchannel of the Vena8 Fluoro+ biochip was flushed with distilled water at 1mL/min for 1 minute.
Microchannels were coated with thrombin: thrombin was pumped through the microchannel at 50μL/min for 90 seconds; then left to stand for 5 minutes.
The sample (control, control with spike protein or COVID-19) was pumped at a flow rate or 10μL/min for 5 minutes while a video recorded the microclot formations.
After the flow was stopped, a set of images was taken. The sample was left for another 5 minutes to enable observation of any further changes and another set of images was taken.
Results & Discussion
Figure 7 from the article by Grobbelaar et al. ; shows the microclots formed within the thrombin-coated microchannel of the Vena8 Fluoro+ biochip.
A) Healthy PPP clot with a small clot formation (arrow), with B) no clot formed in the healthy PPP sample;
C and D) examples of clots from COVID-19 PPP samples and
E and F) healthy PPP clot with spike protein added.
As illustrated in Figure 7 from this article, there was little or no clot formation in healthy PPP samples. The microclot observed in A) was positioned at the walls of the microchannel - this is more consistent with regular healthy blood flow where unactivated (bi-convex