Engineered Muscle Actuators: Cells and Tissues - Biomimetics: Biologically Inspired Technologies - page 255

Figure 9.1 (See color insert following page 302) (A) Self-organized skeletal muscle construct after 3 months
in culture, length ~12 mm. (B) Rat cardiac myocyte þ fibroblast monolayer in the process of delaminating and
self-organizing into a functional cardiac muscle construct, 340 h in culture. (C) Self-organized cardiac muscle
construct, attached to laminin-coated suture anchors, 380 h in culture. (D) Electrically elicited force trace from the
cardiac muscle construct shown in C, stimulation pulses shown below, contractile force trace shown above (raw
data, unfiltered).

stand-alone hybrid tissue actuators, or to engineer cardiac tissue for surgical transplantation in
cardiac reconstructive surgery.

Tendon (Ligament) tissue will self-organize in culture under the appropriate conditions. The fibro-
blasts within the tissue produce a prodigious amount of ECM material, with collagen fibers that are
oriented along lines of tensile stress, particularly at locations within the tissue where mechanical
interfaces are present (such as suture anchor materials, metal posts, etc.). Self-organization is driven
by loss of substrate adhesion and the generation of internal tensile stress by the action of the
fibroblasts on the order of 0 to 6 Pa, which can be experimentally controlled by external factors
such as the presence of ascorbic acid, serum concentration in the cell culture medium, pH, etc.

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Muscle Chimeras: One additional interesting technical possibility is the in vitro fusion of myogenic
precursor cells from different tissue sources to form chimeric self-organized engineered muscles.
Preliminary experiments demonstrate that skeletal muscle satellite cells from differing species will
fuse to form multinucleated myotubes with desirable contractile function. In addition, isolated
cardiac myocytes will fuse into preexisting myotubes in culture, to produce a skeletal-cardiac muscle
hybrid. Such chimeric muscle tissues are not known to exist in nature, but our preliminary data
indicate that they are both stable and functional in culture. The contractile function of such chimeric
cells and tissues could potentially be engineered to produce tissue-based actuators with combinations
of desired characteristics that would be advantageous for use in hybrid bioactuator applications.

9.8 ACELLULARIZED-RECELLULARIZED ECM ENGINEERED MUSCLES

The native ECM of muscle tissue occupies approximately less than 5% of the tissue volume, yet it
contains information about the complex architecture of muscle and the corresponding soft tissue