20708
A New Composite Approach to Engineering Functional Smooth Muscle Tissue and its
Application to Engineered Vascular Grafts
Michael Brown
Mentor: Andrew Putnam
Smooth muscle cells (SMCs) adopt a proliferative (synthetic) phenotype in tissue culture as opposed
to their normal differentiated (contractile) phenotype adopted in their native environment. To
engineer tissues that mimic native smooth muscle tissue in which SMCs express genes characteristic
of the contractile phenotype, it is imperative to provide both chemical and mechanical
morphogenetic inputs in the context of a realistic three-dimensional environment. In this study, we
proposed that a collagen sponge injected with a cell suspension mixed with a collagen gel solution
would provide a microenvironment that permits the expression of smooth muscle differentation
markers such as alpha-actin. Adopting a published approach, we sutured the collagenous sponge
around an impermeable mandrel to create a tubular matrix and injected a collagen gel precursor
solution containing human aortic SMCs. Upon gel formation, SMCs were entrapped within a
composite collagenous environment consisting of both an intimate microscale network (the gel) and
a larger macroscale scaffold (the sponge). After five weeks of in vitro culture, total cell numbers and
smooth muscle alpha-actin expression were analyzed. Although numerous cells remained viable
inside the construct, the actual amount was less than we injected into the matrix. Smooth muscle
alpha-actin was expressed in the tissue constructs, but only in very small amounts. Given that the
diffusion of oxygen and nutrients was likely unable to penetrate the composite matrix to support cell
viability throughout the entire 3-D space, future work will focus on generating a bioreactor system
capable of providing active (i.e., convective) transport of nutrients and oxygen.