“…Acto-myosin contractility has been shown indispensable for sprout initiation (Kniazeva & Putnam, 2009), branching and orientation of invading endothelial cells (Elliott et al, 2015), capillary-like tube formation (Mabeta & Pepper, 2009), and sprout maintenance (Kniazeva & Putnam, 2009). However, limited data is available on quantifying tractions exerted by endothelial sprouts (Du et al, 2016;Du, Herath, Wang, Asada, & Chen, 2018;Kniazeva et al, 2012;Vaeyens et al, 2020;Yoon et al, 2019) and discrepancies exist between studies about the impact of cellular tractions on invasiveness (Indra et al, 2011;Koch, Münster, Bonakdar, Butler, & Fabry, 2012;Kraning-Rush, Califano, & Reinhart-King, 2012;Munevar, Wang, & Dembo, 2001;Peschetola et al, 2013). While tip cell pulling on stalk cells, stalk cell pushing on tip cells, or both, have previously been postulated as mechanical forces that underlie sprout elongation (Betz et al, 2016;De Smet et al, 2009;Gerhardt, 2008;Geudens & Gerhardt, 2011;Santos-Oliveira et al, 2015;Sauteur et al, 2014;Schmidt et al, 2007;Travasso, 2011), collagen deformations indicative of tip cell pulling were recently reported (Vaeyens et al, 2020;Yoon et al, 2019).…”