Biomedical Engineering Reference
In-Depth Information
SHG images together with schematic illustrations of secondary structure features such as β-sheet con-
tent and alignment. Strong SHG signals were obtained for single silk fibers which exhibit a high degree
of β-sheet alignment, Figures 18.11a and 18.11b. When the material is rearranged into an aqueous film
or a gel, the β-sheet arrangement is randomized resulting in no SHG signal (data not shown). However,
after compression and stretching an aqueous film recaptures some β-sheet ordering, resulting in SHG
from the material (Figures 18.11c and 18.11d). For a silk fibroin scaffold, Figures 18.11e and 18.11f, par-
tial β-sheet alignment can be observed locally around pores, Figure 18.11f, and some SHG signal can be
detected at the pore edges, as shown in Figure 18.11e.
18.5 Skeletal Muscle tissue engineering
Loss of skeletal muscle function can be induced by a number of factors, for example, congenital defects,
tumor ablation, prolonged denervation, traumatic injury or myopathies. Tissue engineering does offer
methods for reconstruction of lost skeletal muscle function; however, a number of requirements for syn-
thetic muscle tissue must be fulfilled. A parallel arrangement of muscle fibers consisting of myosin/actin
filaments as well as acetylcholine receptors must be achieved. In addition, the tissue must be vascular-
ized in order to have efficient transport of oxygen, carbon dioxide, nutrients, and waste products. This is
particularly important since relatively large amounts of synthetic tissue may be required. Furthermore,
the tissue must be innervated, that is, the muscle fibers must be connected to motor neurons for control.
Skeletal muscle tissue harbors its own organ-specific mesenchymal stem cells, the so-called satellite
cells, and a number of cell-scaffold constructs using this type of cells have been investigated for syn-
thesis of muscle tissue (Koning et al. 2009, Liao and Zhou 2009). The SHG-active myosin filaments in
muscle fibers allow them to be visualized by means of SHG microscopy, as exemplified by the two SHG
images shown in Figure 18.12, measured on a mouse diaphragm. Thus, SHG microscopy provides an
excellent tool for characterization of skeletal muscle tissue (Nucciotti et al. 2010, Plotnikov et al. 2008,
2006), for example by measuring sarcomere lengths to gauge function, and generally a valuable instru-
ment for this branch of tissue engineering.
18.6 Summary
SHG microscopy has developed into a powerful imaging tool for use within tissue engineering. Although
restricted to certain molecular structures, of non-centrosymmetric arrangement, this includes the
important fibrillar structural protein collagen type I, the major component of native extracellular
FIgurE 18.12
SHG images measured on a mouse diaphragm showing the skeletal muscle tissue structure with
fibers (a) and myo-filaments (b).
