Projection Stereolithographic Fabrication of BMP-2 Gene-activated Matrix for Bone Tissue Engineering

Currently, sustained in vivo delivery of active bone morphogenetic protein-2 (BMP-2) protein to responsive target cells, such as bone marrow-derived mesenchymal stem cells (BMSCs), remains challenging. Ex vivo gene transfer method, while efficient, requires additional operation for cell culture and therefore, is not compatible with point-of-care treatment. In this study, two lentiviral gene constructs - (1) Lv-BMP/GFP, containing human BMP-2 and green fluorescent protein (GFP) gene (BMP group); or (2) Lv-GFP, containing GFP gene (GFP group) - were incorporated with human BMSCs into a solution of photocrosslinkable gelatin, which was then subjected to visible light-based projection stereolithographic printing to form a scaffold with desired architectures. Upon in vitro culture, compared to the GFP group, cells from BMP group showed >1,000-fold higher BMP-2 release, and the majority of them stained intensely for alkaline phosphatase activity. Real-time RT-PCR also showed dramatically increased expression of osteogenesis marker genes only in the BMP group. 3.5 months post-implantation into SCID mice, the micro-computed tomography imaging showed detectable mineralized areas only in the BMP group, which was restricted within the scaffolds. Alizarin red staining and immunohistochemistry of GFP and osteocalcin further indicated that the grafted hBMSCs, not host cells, contributed primarily to the newly formed bone.