Imaging cardiac extracellular matrices: a blueprint for regeneration

Abstract

Once damaged, cardiac tissue does not readily repair and is therefore a primary target of regenerative therapies. One regenerative approach is the development of scaffolds that functionally mimic the cardiac extracellular matrix (ECM) to deliver stem cells or cardiac precursor populations to the heart. Technological advances in micro/nanotechnology, stem cell biology, biomaterials and tissue decellularization have propelled this promising approach forward. Surprisingly, technological advances in optical imaging methods have not been fully utilized in the field of cardiac regeneration. Here, we describe and provide examples to demonstrate how advanced imaging techniques could revolutionize how ECM-mimicking cardiac tissues are informed and evaluated.

Figure 1

Multimodality and high-resolution imaging techniques. (a) Second harmonic generation (SHG) image of collagen and (b) two-photon fluorescence image of elastin in an atherosclerotic artery. (c) Merged image of (a) collagen (green) and (b) elastin (red). Reproduced, with permission, from [27]. (d) The region of interest is highlighted by the circles and a cross in the inset marks a centroid position. (e) Fiducials selected for correlation with yellow circles and numbers. (f) Same fiducials as in (e) present from a tomogram of the cells of interest. (g) Slice of high magnification tomogram. The cross marks the centroid coordinates of the fluorescent patch transformed into tomogram coordinates. The inner circle corresponds to a probability radius of 50% (33 nm), outer circle to 80% (89 nm). Reproduced, with permission, from [45]. Imaging a sheep aorta region by (h) an atomic force microscopy (AFM) optical system and (i) fluorescence microscopy (FM). The location of the AFM tip is indicated by a dotted line. The start (S) and end (E) points of a series of 5 μm AFM scans are indicated by arrows. In (j) and (k), collagen fibrils (CF) are evident from amplitude scans collected. Reproduced, with permission, from [47]. (l) Cryo-scanning electron microscopy (cryo-SEM) of bone marrow-derived human mesenchymal stem cells (hMSCs) in 3D poly(ethylene glycol)-diacrylate hydrogel/collagen type I composite (unpublished work). (m) Note connections established by cells and ECM in a 3D environment. (n) Laser-scanning optical-resolution photoacoustic microscopy of vasculature within a Swiss Webster mouse ear, two pairs of parallel veins (1) and arteries (2). Reproduced, with permission, from [69].