State-of-the-art techniques for imaging the vascular microenvironment in craniofacial bone tissue engineering applications

Abstract

Vascularization is a crucial step during musculoskeletal tissue regeneration via bioengineered constructs or grafts. Functional vasculature provides oxygen and nutrients to the graft microenvironment, facilitates wound healing, enhances graft integration with host tissue, and ensures the long-term survival of regenerating tissue. Therefore, imaging de novo vascularization (i.e. angiogenesis), changes in microvascular morphology and the establishment and maintenance of perfusion within the graft site (i.e. vascular microenvironment or VME) can provide essential insights into engraftment, wound healing, as well as inform the design of tissue engineering (TE) constructs. In this review, we focus on state-of-the-art imaging approaches for monitoring the VME in craniofacial TE applications, as well as future advances in this field. We describe how cutting-edge in vivo and ex vivo imaging methods can yield invaluable information regarding VME parameters that can help characterize the effectiveness of different TE constructs, and iteratively inform their design for enhanced craniofacial bone regeneration. Finally, we explicate how the integration of novel TE constructs, preclinical model systems, imaging techniques and systems biology approaches could usher an era of "image-based tissue engineering".

MicroCT-based imaging of microvasculature within bone and peri-implant tissues

“…Angiogenesis is a physiological process essential for skeletal development and growth, for bone healing and regeneration; the established vascularization is crucial for successful bone formation and repair (Wernike et al, 2010, Roche et al, 2012, Carulli et al, 2013, Filipowska et al, 2017, Ren et al, 2022). Besides carrying nutrients and growth factors, the newly formed vessels are a delivery route of the stem cells and progenitors to the defect site (Kuttappan et al, 2018, Kurobane et al, 2019, Grosso et al, 2017).…”

“…There are many research areas which could benefit from an improved three-dimensional (3D) imaging of the vasculature within bone tissue: bone metastatic disease, bone biology, tissue engineering, implantology, reconstructive surgery and healing of both small and critical size bone defects with or without bone grafts. Most synthetic bone grafts fail to bridge critical sized defects due to their inability to promote vascularization (Lovett et al, 2009, Ren et al, 2022). Proper simultaneous non-destructive 3D imaging of the vasculature within bone tissue and of the bone tissue itself, especially in case of large bone grafts, has been a challenge for decades (Mercado-Pagan et al, 2015, Ren et al, 2022).…”

“…Most synthetic bone grafts fail to bridge critical sized defects due to their inability to promote vascularization (Lovett et al, 2009, Ren et al, 2022). Proper simultaneous non-destructive 3D imaging of the vasculature within bone tissue and of the bone tissue itself, especially in case of large bone grafts, has been a challenge for decades (Mercado-Pagan et al, 2015, Ren et al, 2022). The structural nature of skeletal tissue makes direct 3D imaging of its vasculature extremely difficult letting histology, a destructive and two-dimensional approach, remain a gold standard for years (Nunez et al, 2017).…”

“…Intravascular contrast-agent-enhanced microCT has the potential to overcome this obstacle. It has been applied and gained popularity as the method of choice for the evaluation of angiogenesis in bone tissue engineering and remodeling applications (Young et al, 2008, Roche et al, 2012, Ren et al, 2022). Barium sulfate and Microfil have been applied as the two most common contrast agents in studies about the vascularization of the bone tissue.…”

“…MicroCT is the only available approach to non-destructively investigate an intact bone-implant interface in 3D (Yi et al, 2019). Beyond the study of the anatomy and physiology of angiogenesis and vasculature of the bone organ, the contribution of the vascular component in the healing process around bone-borne implants is also considered an area of study meriting further experimentation (Ren et al, 2022, Al Subaie et al, 2015). To date, few studies have tried to visualize the vasculature surrounding implants using microCT imaging and, to the best of our knowledge, none have managed to resolve the micro-vascular component in a large animal model due to technical limitations of the perfused contrast agent and the applied microCT imaging technique.…”