Abstract: Reconstruction of large bone defects remains a challenge in the orthopaedic clinic. Genetic modification of biomaterial scaffold provides the opportunity to control the cellular microenvironment by inducing expression of tissue inductive factors to promote angiogenesis and osteogenesis. Angiogenesis in tissue-engineering scaffolds is essential for supplying oxygen and nutrients to the cells, removing waste products, and ultimately functionalizing implanted scaffolds. However, it was difficult to visualize and measure angiogenesis in three-dimensional (3D) scaffolds or new bone in bone tissue engineering in vivo and non-invasively. Photoacoustic microscopy (PAM) is a novel imaging modality that can acquire volumetric data in a non-invasive manner. In this study, we fabricated lentivirus-mediated genetic modification of 3D-PLGA/nHAp scaffold (PH), which can deliver recombinant lentivirus carrying cytokine gene-pdgfb (LV-pdgfb). In vitro, the modified scaffolds (PHp) continuously released bioactive LV-pdgfb particles for up to 5 days, and expressed PDGF-BB and significantly promoted migration of bone marrow-derived MSCs (BMSCs). In vivo, we detected that there were significant increasing of expressing of pdgfb and angiogenesis related genes. In this preliminary study, by using acoustic-resolution PAM (AR-PAM) and optical-resolution PAM (OR-PAM), we have investigated the blood vessels pattern in mouse calvaria in vivo. We have confirmed that PAM is a useful tool in evaluating neovasculature in bone tissue. In the future, we will quantify the neovasculature in 3D-scaffold which assisted bone regeneration by PAM scanning, and correlate the neovasculature with new bone regeneration in a murine calvarial critical bone defect model in the future work.

Keywords: critical bone defects, 3D scaffold,genetically modified neovascularization,photo acoustic imaging, bone regeneration.