oa Bio-inspired Anisotropic Nanofibrillar Matrices for Heart Valve Engineering

Our strategy for heart valve tissue engineering is the use of autologous cells to populate appropriate template matrices. In this context, an important goal is to devise a suitable biomimetic scaffold that supports proper cell growth and cell-matrix interactions by reproducing the specific anisotropic fibrillar structure of valves extracellular matrix (ECM). A novel type of highly porous anisotropic nanobrillar matrices was developed and evaluated with regards to structure, mechanical properties and ability to support human adipose derived stem cell (hADSC) colonization, growth and ECM production in vitro. Nanofibrillar structures were obtained by jet-spraying poly (ε-caprolactone) dissolved in chloroform on a variably rotating drum. Morphological evaluations of the structures were performed using scanning electron microscopy while porosity was calculated from polymer density, weight and volume. Elastic modulus of dry scaffolds (10x6x1 mm, n=5) was measured with a planar biaxial test bench with displacement rate of 0.05 mm/s. Human adipose derived stem cells (500,000) were top and rotary seeded on nanofibrillar discs (diameter 1 cm and thickness 0.8 mm) and cultured in 10 ml of complete medium under rotation (10 rpm) for 18 days. Histology (DAPI staining), DNA quantification and immunohistochemistry were used to characterize the resulting cellularized structures. The speed of drum rotation was adjusted up to 3000 rpm to produce highly aligned fibres (600 nm of average diameter) from the sprayed polymer. In conjunction with fibres anisotropy, the scaffolds Young's modulus was simultaneously increased (from 0.3 to 0.7 Mpa) and decreased (from 0.3 to 0.01 Mpa) longitudinally and orthogonally to fibre alignment, respectively. In addition, fibre alignment further increased scaffolds porosity from 97 % (isotropic) to 99%. Anisotropic matrices allowed a more extensive cellular invasion than isotropic scaffolds, possibly linked to their higher porosity and therefore open structure. hADSC proliferated significantly (up to 6-fold DNA increase), bridged the entire scaffolds thicknesses after 10 days and produced their own ECM as evidenced by collagen I production. This study highlights the potential of a newly developed highly porous anisotropic nanofibrillar matrices as substrate for tissue engineering, and in particular for heart valve engineering.