Tissue Engineering

Non-Destructive Evaluation and Imaging A significant amount of the data collected by cell biologists and tissue engineers relies on invasive imaging techniques to visualize dynamic structural and functional properties of engineered tissues. Optical coherence tomography allows these structural and functional properties to be imaged nondestructively and noninvasively, in real time and in three dimensions. With OCT, one can image the developmental process of engineered tissues from changes in tissue microarchitecture, to cell–matrix adhesions. These findings demonstrate the potential for optical coherence tomography in applications in cell and tissue biology, tissue engineering, and drug discovery.

Elastography Among the many parameters used to characterize engineered tissues, the biomechanical elastic properties have become important, particularly to map the stiffness or softness in an anatomically meaningful presentation and provide more useful clinical information. Using a technique called Optical Coherence Elastography (OCE), it is possible to measure the biomechanical properties of tissue when applying externally uniform compressive forces or cyclical forces.

OCE of engineered tissues. (a–d) Structural OCT images on days 0, 3, 7, and 10, respectively, of the boundary between the cell-seeded region (left) and the cell-free region (right). (e–h) Displacement maps on days 0, 3, 7, and 10, respectively, color-coded using the scale in s. (i–l) Strain maps on days 0, 3, 7, and 10, respectively, using the color scale in t. (m–p) Corresponding histology from the cell-seeded tissue regions. (q) Histological image of cells after 10 days of incubation without embedded microspheres. (r) Histological image of a cell-free scaffold and microspheres. Scale bar, 300 µm in a–l; 20 µm in m–r.   Ko HJ, Tan W, Stack R, Boppart SA. Optical coherence elastography of engineered and developing tissue. Tissue Engineering, 12:63-73, 2006. PDF   Phase-resolved OCE map of human breast tissue elasticity. a, B-mode OCT image of breast tissue. The left side of this image represents the adipose tissue while the right side of the image represents the tumor tissue. b, Histology image corresponding to a. c, Map of elasticity by sinusoidally-driven phase-resolved OCE. d, Error map of elasticity by sinusoidally-driven phase-resolved OCE. Unit for color bar is kPa.   Liang X, Oldenburg AL, Crecea V, Chaney EJ, Boppart SA. Optical micro-scale mapping of dynamic biomechanical tissue properties. Optics Express, 16:11052-11065, 2008. PDF

Developmental Biology OCT provides a method of imaging specimens in developmental biology. It can provide information similar to that gathered through histology studies, but the in vivo imaging capabilities of OCT allow for imaging over extended periods of time without complications. Furthermore, functional and three-dimensional imaging can be obtained with high-speed systems. Three-dimensional image set of a Xenopus laevis(African frog) tadpole. Top-OCT image of a beating chicken embryo heart. Bottom-M-mode image of a beating chick embryo heart. The M-mode scan takes repeated axial scans without moving the incident beam, so it can easily detect movement. Sagittal OCT images of the E10.5 mouse embryo. (a) and (c) Computational sections along sagittal planes extracted from the 3-D OCT dataset. (b) and (d) Corresponding H and E-stained histological sections. (e) through (h) Zoomed OCT images of the embryonic heart, showing details of internal structures at varying cross sectional planes. (i) 3-D volume rendering of the OCT dataset. (j) Digital photograph of the E10.5 mouse embryo that was imaged with OCT. The entire set of 256 2-D sagittal OCT images can be viewed in Movie l. Abbreviations: ba, branchail arch; hp, hepatic primordia; fv, fuorth ventricle; sv, subcardinal vein; vch, ventricular chamber; cav, cushion tissue lining the atrio-ventricular canal; ach, atrial chamber; bc, bulbus cordis; and uc, umbilical cord. Scale bars=200 µm (a) through (d) and (i); 100 µm (e) through (h): and 1mm (j). OCT of the embryonic mouse heart (E14.5 and E17.5). (a) and (c) OCT images. (b) and (d) corresponding H and E-stained histology, and (e) 3-D OCT volume rendering of the E14.5 murine heart. (f) and (h) OCT images, (g) and (i) corresponding histology, and (j) 3-D OCT volume rendering of the E17.5 murine heart. Abbreviations: ach, atrial chamber; vch, ventricular chamber; otv, outflow tract of ventricle; ao, aorta; and pt, pulmonary trunk. Scale bar=200µm

Neural Imaging It has been previously shown that optical scattering increases in electrically stimulated axons, and this activity can be detected with OCT. To capture the effects of electrical stimulation on optical properties of neural tissue, nerve fibers from the abdominal ganglion of Aplysia californica were imaged before, during and after electrical excitation. Images taken during stimulation showed reversible local increases in scattering compared to images taken before stimulation.

Current research efforts are investigating the varying optical signals from single neurons using our high-resolution integrated microscope that combines optical coherence microscopy (OCM) with multi-photon microscopy (MPM). Correlations are being established between optical scattering and birefringence changes, single-unit electrical activity, and responses from fluorescent voltage-sensitive dyes.

Microfluidics Improved microfluidic devices are possible with the aid of advanced visualization techniques such as OCT, Doppler OCT, and Multiphoton Microscopy (MPM). These modalities can image microstructure and function within complex three-dimensional microfluidic mixers. Microfluidic devices are good analogs to microcapillary networks.