Bioluminescent imaging: emerging technology for non-invasive imaging of bone tissue engineering.

Bone tissue engineering is a multidisciplinary research area in which new strategies are developed to treat patients with large bone defects as occurring during e.g. hip revisions, upon trauma or in spinal fusions. In vivo evaluation of bone formation in animal models is highly relevant for graft evaluation but is time-consuming, invasive and difficult to quantify. As a consequence, most in vivo studies ignore the dynamic nature of bone regeneration and the molecular processes underlying it. In vivo bioluminescent imaging (BLI) is a relatively young research field with great potential that may overcome these problems. BLI encompasses non-invasive imaging of luciferase gene activity using cooled charge coupled device cameras in luciferase transgenic animals or in grafted, luciferase transgenic cells. The imaging procedure is technically simple and quantifiable. Because luciferase expression can be put under the control of tissue-specific regulatory elements, BLI allows non-invasive imaging of processes highly relevant to bone tissue engineering like differentiation, apoptosis, vasculogenesis and inflammation. In this review, we describe the basic principle of BLI and discuss transgenic animals and constructs currently available for application in bone tissue engineering. Furthermore, we reflect on technical developments that will make BLI even more promising for future application in bone tissue engineering research.