Engineering smooth muscle tissue with a predefined structure.

Nonwoven meshes of polyglycolic acid (PGA) fibers are attractive synthetic extracellular matrices (ECMs) for tissue engineering and have been used to engineer many types of tissues. However, these synthetic ECMs lack structural stability and often cannot maintain their original structure during tissue development. This makes it difficult to design an engineered tissue with a predefined configuration and dimensions. In this study, we investigated the ability of PGA fiber-based matrices bonded at their fiber crosspoints with a secondary polymer, poly-L-lactic acid (PLLA), to resist cellular contractile forces and maintain their predefined structure during the process of smooth muscle (SM) tissue development in vitro. Physically bonded PGA matrices exhibited a 10- to 35-fold increase in the compressive modulus over unbonded PGA matrices, depending on the mass of PLLA utilized to bond the PGA matrices. In addition, the bonded PGA matrices degraded much more slowly than the unbonded matrices. The PLLA bonding of PGA matrices had no effect on the ability of cells to adhere to the matrices. After 7 weeks in culture, the bonded matrices maintained 101 +/- 4% of their initial volume and an approximate original shape while the unbonded matrices contracted to 5 +/- 1% of their initial volume with an extreme change in their shape. At this time the bonded PGA matrices had a high cellularity, with smooth muscle cells (SMCs) and ECM proteins produced by these cells (e.g., elastin) filling the pores between PGA fibers. This study demonstrated that physically bonded PGA fiber-based matrices allow the maintenance of the configuration and dimensions of the original matrices and the development of a new tissue in a predefined three-dimensional structure. This approach may be useful for engineering a variety of tissues of various structures and shapes, and our study demonstrates the importance of matching both the initial mechanical properties and the degradation rate of a matrix to the specific tissue one is engineering.