High-resolution imaging techniques in tissue engineering

S. Wang, I.V. Larina

Baylor College of Medicine, Houston, TX, United States

I ntroduction

The rapid development of the tissue engineering field is producing attractive techniques to replace and regenerate damaged or lost tissues for restoration of proper tissue functions. In order to evaluate tissue engineering techniques, visualization and monitoring of cellular behavior, extracellular matrix composition, and scaffold structure and biocompatibility are essential. Traditionally, histology and scanning electron microscopy are the gold standards for high-resolution imaging and characterization in tissue engineering. However, the invasive nature of these two approaches requires destruction of the sample, which consequentially prevents live analysis and functional assessment as well as three-dimensional (3-D) quantifications. The application of live, 3-D, and nondestructive imaging techniques in tissue engineering is growing rapidly due to the increased capability to achieve a better understanding of the critical biological processes during the formation and growth of tissues and organs. Such ability plays a critical role in developing new and powerful biomaterials as well as advancing tissue engineering techniques to improve human health.

A number of noninvasive live imaging techniques have been utilized in tissue engineering (Nam et al., 2015; Vielreicher et al., 2013; Appel et al., 2013), including X-ray computed tomography (Izadifar et al., 2014), magnetic resonance imaging (Xu et al., 2008), nuclear imaging (positron emission tomography and single photon emission computed tomography) (Ventura et al., 2014), ultrasonic imaging (Kreitz et al., 2011), optical imaging (Smith et al., 2010), and photoacoustic imaging (Cai et al., 2013b). These techniques have been widely used for the characterization of biomaterials, visualization of important structures, and monitoring of major processes in tissue engineering, as reviewed by several studies (Nam et al., 2015; Vielreicher et al., 2013; Appel et al., 2013). Fig. 8.1 summarizes the spatial imaging scales (resolution and field of view) of these techniques. It can be seen that due to employing a short wavelength of radiation, optical imaging and photoacoustic imaging are able to provide micro and submicroscale spatial resolution, capable of resolving cellular and microstructural information in tissue engineering. This high-resolution information can provide great insights into the developmental processes of functional tissue constructs such as cell viability and growth, extracellular matrix orientation, and scaffold degradation.

In this chapter, we review high-resolution imaging techniques in tissue engineering, focusing on the optical and photoacoustic imaging techniques that have

Monitoring and Evaluation of Biomaterials and their Performance in vivo. http://dx.doi.org/10.1016/B978-0-08-100603-0.00008-0

Copyright © 2017 Elsevier Ltd. All rights reserved.

Spatial imaging scales of commonly used imaging techniques in tissue engineering

Figure 8.1 Spatial imaging scales of commonly used imaging techniques in tissue engineering. Each imaging technique is assigned a space with respect to the spatial resolution and the field of view. CT, computed tomography; MRI, magnetic resonance imaging.

micron level and submicron level spatial resolving capability. Specifically, we include phase contrast microscopy (PCM), confocal microscopy (CM), multiphoton microscopy (MPM), optical coherence tomography (OCT), photoacoustic microscopy (PAM), Raman spectroscopy (RS), and multimodality imaging based on these techniques. For each technique, we first describe its basic principle, with emphasis on the spatial imaging scales and contrast mechanisms, and then review in detail the specific imaging approaches and applications of each technique in tissue engineering. Lastly, we discuss emerging high-resolution techniques that have an attractive potential in the tissue engineering field. Throughout the review, we will emphasize the applications in three aspects: (1) morphological imaging with structural visualization and dynamic monitoring, (2) functional imaging with biomechanical characterization and perfusion analysis, and (3) molecular imaging with subcellular component identification and molecule distribution. We aim for this review to provide useful references for the researchers working in the tissue engineering field.

 
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