Enhancing Vascularization through the Controlled Release of Platelet- Derived Growth Factor-BB

Using delivery systems to control the in vivo release of growth factors (GFs) for tissue engineering applications is extremely desirable as the clinical use of GFs is limited by their fast in vivo turnover. Hence, the development of effective platforms that are able to finely control the release of GFs in vivo remains a challenge. Herein, we investigated the ability of multiscale microspheres, composed by a nanostructured silicon multistage vector (MSV) core and a poly(dl-lactide-co-glycolide) acid (PLGA) forming outer shell (PLGA-MSV), to release functional platelet-derived growth factor-BB (PDGF-BB) to induce in vivo localized neovascularization. The in vitro release of PDGF-BB was assessed by enzyme-linked immunosorbent assay (ELISA) over 2 weeks and showed a sustained, zero-order release kinetics. The ability to promote in vivo localized neovascularization was investigated in a subcutaneous injection model in BALB/c mice and followed by intravital microscopy up to 2 weeks. Fully functional newly formed vessels were found within the area where PLGA-MSVs were localized and covered 3.0 ± 0.9 and 19 ± 5.1% at 7 and 14 days, respectively, showing a 6-fold increase in 1 week. The distribution of CD31+ and α-SMA+ cells was detected by immunofluorescence on harvested tissues. CD31 was significantly more expressed (4-fold increase) compared to the untreated control. Finally, the level of up-regulation of angiogenesis-associated genes (Vegfa, Vwf, and Col3a1) was assessed by q-PCR, resulting in a significantly higher expression where PLGA-MSVs were localized (Vegfa: 2.32 ± 0.50 at 7 days and 4.37 ± 0.75 at 14 days; Vwf: 4.13 ± 0.82 and 7.74 ± 0.91; Col3a1: 5.43 ± 0.37 and 6.66 ± 0.89). Altogether, our data supported the conclusion that the localized delivery of PDGF-BB from PLGA-MSVs induced the localized de novo formation of fully functional vessels in vivo. With this study, we demonstrated that PLGA-MSV holds promise for accomplishing the controlled localized in vivo release of GFs for the design of innovative tissue engineering strategies.