*Review* **In Vivo Tracking of Tissue Engineered Constructs**

**Carmen J. Gil 1, Martin L. Tomov 1, Andrea S. Theus 1, Alexander Cetnar 1, Morteza Mahmoudi 2,3 and Vahid Serpooshan 1,4,5,\***


Received: 2 July 2019; Accepted: 13 July 2019; Published: 16 July 2019

**Abstract:** To date, the fields of biomaterials science and tissue engineering have shown grea<sup>t</sup> promise in creating bioartificial tissues and organs for use in a variety of regenerative medicine applications. With the emergence of new technologies such as additive biomanufacturing and 3D bioprinting, increasingly complex tissue constructs are being fabricated to fulfill the desired patient-specific requirements. Fundamental to the further advancement of this field is the design and development of imaging modalities that can enable visualization of the bioengineered constructs following implantation, at adequate spatial and temporal resolution and high penetration depths. These in vivo tracking techniques should introduce minimum toxicity, disruption, and destruction to treated tissues, while generating clinically relevant signal-to-noise ratios. This article reviews the imaging techniques that are currently being adopted in both research and clinical studies to track tissue engineering scaffolds in vivo, with special attention to 3D bioprinted tissue constructs.

**Keywords:** in vivo imaging; tissue engineering; 3D bioprinting; additive manufacturing; scaffold tracking; magnetic resonant imaging (MRI); computed tomography (CT); ultrasound; fluorescence spectroscopy; bioluminescence; optical coherence tomography; photoacoustic imaging; magnetic-particle imaging; multimodal imaging
