1 Introduction Ischemic wounds can be linked to many debilitating diseases such as myocardial infarction, diabetes mellitus and chronic limb ischemia. The damage can affect a variety of tissues including myocardium, nerve, skin and skeletal muscle. The ability to enhance tissue perfusion in an ischemic wound through re-vascularisation is still the main challenge despite the major advances in surgical techniques (Tenna et al., 2014). Therapeutic angiogenesis (Takeshita et al., 1994) is a promising strategy to treat ischemic wound diseases which can be enhanced by employing VEGF to promote neovascularisation (Yoon et al., 2004). This concept has attracted many researchers since the mid-90s and despite the promising findings from numerous in vitro and in vivo animal studies (Cartland et al., 2016; Takeshita et al., 1994; Yu et al., 2015); there are inconsistencies from clinical trials (Eppler et al., 2002; Henry et al., 2001; Kusumanto et al., 2006). This was attributed to the short half-life of VEGF and susceptibility to degradation when injected directly in its solution form (Eppler et al., 2002; Kleinheinz et al., 2010). Overcoming this limitation by increasing the VEGF dose can be toxic at high systemic levels (Karvinen et al., 2011; Tayalia and Mooney, 2009). Therefore, targeted VEGF delivery using controlled release formulations appears to be a better approach to promote neovascularisation at the target tissue. This type of localised delivery requires a careful understanding of the microenvironment required for physiologic angiogenesis, which is dependent on spatiotemporal presentation of the delivered VEGF (Blau and Banfi, 2001). Polymeric materials present a promising approach in controlling tissue VEGF presentation at the target tissue. They can provide physical protection of the payload until it is released. This also includes tailored release kinetics in term of timing in addition to achieving localised delivery with a minimally invasive injectable formulation (Silva and Mooney, 2007). Such polymeric formulations employ a lower VEGF dose for achieving a better outcome in term of Spatiotemporal release of VEGF from biodegradable polylactic-co-glycolic acid microspheres induces angiogenesis in chick chorionic allantoic membrane assay Omar Qutachi a, ⁎ omar.qutachi@dmu.ac.uk Anthony J. Bullock b Giulia Gigliobianco b Sheila MacNeil b a Leicester Institute for Pharmaceutical Innovation, Leicester School of Pharmacy, De Montfort University, Leicester, UK b Department of Materials Science and Engineering, Kroto Research Institute, North Campus, University of Sheffield, Broad Lane, Sheffield S3 7HQ, United Kingdom ⁎ Corresponding author at: School of Pharmacy, Faculty of Health and Life Sciences De Montfort University, Leicester LE1 9BH, United Kingdom. Abstract While vascular endothelial growth factor (VEGF) is an acknowledged potent pro-angiogenic agent there is a need to deliver it at an appropriate concentration for several days to achieve angiogenesis. The aim of this study was to produce microspheres of biodegradable polylactic-co-glycolic acid (PLGA) tailored to achieve sustained release of VEGF at an appropriate concentration over seven days, avoiding excessive unregulated release of VEGF that has been associated with the formation of leaky blood vessels. Several formulations were examined to produce microspheres loaded with both human serum albumin (HSA) and VEGF to achieve release of VEGF between 3 and 10 ng per ml for seven days to match the therapeutic window desired for angiogenesis. In vitro experiments showed an increase in endothelial cell proliferation in response to microspheres bearing VEGF. Similarly, when microspheres containing VEGF were added to the chorionic membrane of fertilised chicken eggs, there was an increase in the development of blood vessels over seven days in response, which was significant for microspheres bearing VEGF and HSA, but not VEGF alone. There was an increase in both blood vessel density and branching – both signs of proangiogenic activity. Further, there was clearly migration of cells to the VEGF loaded microspheres. In summary, we describe the development of an injectable delivery vehicle to achieve spatiotemporal release of physiologically relevant levels of VEGF for several days and demonstrate the angiogenic response to this. We propose that such a treatment vehicle would be suitable for the treatment of ischemic tissue or wounds. Keywords: Chorioallantoic membrane; Vascular endothelial growth factor; Angiogenesis; Polylactic-co-glycolic acid; Sustained release