X‐ray phase contrast imaging of calcified tissue and biomaterial structure in bioreactor engineered tissues

Abstract

Tissues engineered in bioreactor systems have been used clinically to replace damaged tissues and organs. In addition, these systems are under continued development for many tissue engineering applications. The ability to quantitatively assess material structure and tissue formation is critical for evaluating bioreactor efficacy and for preimplantation assessment of tissue quality. Techniques that allow for the nondestructive and longitudinal monitoring of large engineered tissues within the bioreactor systems will be essential for the translation of these strategies to viable clinical therapies. X-ray Phase Contrast (XPC) imaging techniques have shown tremendous promise for a number of biomedical applications owing to their ability to provide image contrast based on multiple X-ray properties, including absorption, refraction, and scatter. In this research, mesenchymal stem cell-seeded alginate hydrogels were prepared and cultured under osteogenic conditions in a perfusion bioreactor. The constructs were imaged at various time points using XPC microcomputed tomography (µCT). Imaging was performed with systems using both synchrotron- and tube-based X-ray sources. XPC µCT allowed for simultaneous three-dimensional (3D) quantification of hydrogel size and mineralization, as well as spatial information on hydrogel structure and mineralization. Samples were processed for histological evaluation and XPC showed similar features to histology and quantitative analysis consistent with the histomorphometry. These results provide evidence of the significant potential of techniques based on XPC for noninvasive 3D imaging engineered tissues grown in bioreactors.

X-ray Phase Contrast Allows Three Dimensional, Quantitative Imaging of Hydrogel Implants

“…Our findings, combined with studies showing in vitro imaging of hydrogel samples 2 and full live mice 7 with an in-lab XPC system indicate the significant potential for imaging of hydrogels in animals with micro-focus X-ray tube. Depending on the implementation of the in-lab XPC system, the polychromatic nature of the micro-focus X-ray tube can be overcome.…”

“…However, imaging techniques based on X-ray phase contrast (XPC) have shown promise for imaging biomaterials and soft tissues with excellent depth penetration and high spatial resolution 2, 9, 10, 22, 49 . Contrast in XPC imaging results from X-ray absorption, refraction and ultra small angle scatter (USAXS), allowing materials and tissues with low X-ray absorption properties to be visualized and discriminated without the need for exogenous contrast agents.…”

Imaging of Hydrogel Microsphere Structure and Foreign Body Response Based on Endogenous X-Ray Phase Contrast

“…XPC imaging is a developing category of X-ray techniques that have shown significant potential for imaging biomaterial and soft tissue structures that are difficult to observe with other imaging modalities. Specifically, these techniques have been successful in observing hydrogels in tissue 30,31,35 and low-density scaffolds in water 46 and soft tissue. 33,34 The techniques enable highresolution, large volume imaging of these materials, without the need for exogenous contrast agents.…”

“…The ideal imaging technique would not require exogenous contrast and be nondestructive. X-ray phasecontrast (XPC) imaging is a class of X-ray-based techniques that enable imaging of biomaterial and soft tissue structures, [30][31][32][33][34][35] which are difficult to observe using other imaging modalities. These techniques enable high-resolution and large volume imaging of these samples in the absence of exogenous contrast agents.…”

Three‐dimensional imaging technologies: a priority for the advancement of tissue engineering and a challenge for the imaging community

“…X‐ray imaging provides detailed 3D information on tissue structure, but has limited potential on soft tissue samples. X‐ray techniques based on phase‐contrast (XPC) are very promising to overcome this limitation in TE because of their excellent spatial resolution and high tissue penetration depth both on calcified tissues by conventional X‐ray techniques, and also on soft tissues and biomaterials, and, noteworthy, without the need of exogenous contrast agents .…”