Induction of directional sprouting angiogenesis by matrix gradients.

The fate of any tissue engineering implant relies upon an adequate oxygen and nutrients supply throughout the cellular construct and, hence, by the ability of the scaffold to induce and guide vascular ingrowth. However, implant vascularization is usually an uncontrolled process that takes several weeks. In this work, we assessed the feasibility of controlling vascular sprout rate and direction within three-dimensional collagen-hyaluronic acid semi-interpenetrated networks by modulating the spatial distribution of the matricellular cues. Results indicated that increasing amount of hyaluronic acid (HA) within the matrix led to a progressive inhibition of sprouting. In HA-rich matrices, the sprout number and the propagation rate showed a 2.7- and 4-fold reduction, respectively, compared to collagen matrices. Furthermore, by creating HA gradients within the collagen network, we were able to direct and enhance the sprouting rate. This study provides an experimental platform for controlling vascularization of engineered tissues.