“…The RIS model conceptualizes improvements to sparse innovation systems (what is referred to below as 'densification') by focusing on linkage-building processes (Tödtling & Trippl, 2005), and we specifically highlight the property of cross-border RIS (Lundquist & Trippl, 2013;Trippl, 2010) as potentially sparse innovation systems as where the border continually undermines interaction between innovators in various ways (Perkmann, 2007). Borders may hinder knowledge flows, labour mobility and access to critical resources (Cerina, Chessa, Pammolli, & Riccaboni, 2014;Miörner & Trippl, 2016;Miörner, Zukauskaite, Trippl, & Moodysson 2017) by raising the opportunity costs of cross-border interaction, channelling knowledge resource-search processes to remain within national boundaries, and reducing complementarities (Leick, 2012;Lundquist & Trippl, 2013).…”