Cyclic mechanical strain regulates the development of engineered smooth muscle tissue


We show that the appropriate combinations of mechanical stimuli and polymeric scaffolds can enhance the mechanical properties of engineered tissues. The mechanical properties of tissues engineered from cells and polymer scaffolds are significantly lower than the native tissues they replace. We hypothesized that application of mechanical stimuli to engineered tissues would alter their mechanical properties. Smooth muscle tissue was engineered on two different polymeric scaffolds and subjected to cyclic mechanical strain. Short-term application of strain increased proliferation of smooth muscle cells (SMCs) and expression of collagen and elastin, but only when SMCs were adherent to specific scaffolds. Long-term application of cyclic strain upregulated elastin and collagen gene expression and led to increased organization in tissues. This resulted in more than an order of magnitude increase in the mechanical properties of the tissues.

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Figure 1: (A and B) Proliferation (C) elastin production, and (D) collagen production of SMCs subjected to cyclic strain (hatched bar) or no strain (white bar) for four days in serum-free medium.
Figure 2: (A) Proliferation (B) elastin production, and (C) collagen production of SMCs on bonded PGA and collagen scaffolds subjected to cyclic strain (hatched bar) or no strain (white bar) for four days or two weeks in 10% (vol/vol) serum-containing medium.
Figure 3: (A) Western blot of adsorbed proteins stripped from serum-exposed PGA scaffolds (PGA) and type I collagen sponge (COLLAGEN) probed with an anti-vitronectin antibody (Vitronectin) and anti-fibronectin antibody (Fibronectin).
Figure 4: (A–C) Hematoxylin-eosin stained cross sections and (D) quantification of cell alignment (percentage of cells aligned parallel to direction of tissue section) in SM tissues engineered with type I collagen sponges and subjected to cyclic strain (A–B) or no strain (C) for 10 weeks in 10% (vol/vol) serum-containing medium.
Figure 5: Scanning electron micrographs of cells on surface of SM tissues engineered with type I collagen sponges and subjected to cyclic strain (A–B) or no strain (C) for 10 weeks (A and C) or 20 weeks (B) in 10% (vol/vol) serum-containing medium.
Figure 6: The Young's modulus (A) and ultimate strength (B) of engineered SM tissues subjected to mechanical stimulation (cyclic strain), no strain (control tissue), and the scaffolds alone (no cells) over time in culture.


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This work was supported by the National Science Foundation (BES-9501376) and a fellowship to J.N. from the Organogenesis Training Grant (NIH 5T32 HD07505-02). We are grateful to Elizabeth Smiley for her help with northern blot analysis.

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Correspondence to David J. Mooney.

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