Incremental Stretch Increases Strength and Toughness while Growing Engineered Trileaflet Heart Valves

Tissue engineered heart valves (TEHVs) represent a promising method for fulfilling the needs of young, growing individuals with an insufficient valve function. Many current approaches that use natural biomaterials rely on either very long culture times or a secondary polymer network to create viable mechanical properties. While these materials can create correct sizes or mechanical properties, issues such as dilation of grafts still occur when strengthening does not correlate with a stretch in size. Utilizing an adaptable, mechanical anchorage-based culture system, we inquired how fibrin with encapsulated stem cells could be stimulated to both grow and strengthen under an incrementally increasing stretch (iStretch). We modified our culture system to assess how the timing and magnitude of stretch affect both linear and planar tissues, additionally creating leaflet-shaped tissues. In this study, we show that iStretch stimulates cell alignment and increases tissue modulus, failure stress, and toughness while achieving a 100% increase in tissue length. The timing of iStretch increments also drives cell differentiation, with almost doubling of a remodeling mesenchymal phenotype achieved with early increments. Planar leaflet tissues stretched to 50% greater diameter over 14 days increased in cell density and vimentin expression. When placed in a pulse duplicator system, engineered trileaflet valves opened completely to a maximal effective orifice area and coapted with systolic ventricular pressures up to 80 mmHg. These results demonstrate the potential of iStretch for generating both rapid growth and the strengthening of engineered tissues.