Nanofiber based scaffold fabrication, characterization and optimization for tissue engineering aortic heart valve

Abstract

The four valves in a mammalian heart provide a unidirectional, unobstructed blood flow pathway as a result of synchronic movement of valves’ leaflets during cardiac cycle. When one of the valves malfunctions, the medical choice is to replace the original valve with an artificial one. However, the inability to grow or to remodel an artificial valve leads to the innovation of tissue engineering heart valve (TEHV). The previously tissue engineered heart valve tends to be rigid, have low degradation rate and adverse structure which leads to TEHV failure. This study presents the design and fabrication of an aortic heart valve (AOHV) based on tissue engineering (TE) principle via electrospinning method. In TE, a three-dimensional (3D) scaffold with proper design, structure, and mechanical properties that resembles the original tissue is required as an initial template for tissue regeneration. For this purpose, materials’ ratio tuning and process optimization as well as the 3D scaffold design were considered. Initially, five different ratios of poly-L-lactic acid (PLLA)/thermoplastic polyurethane (TPU) blends containing 1% (w/v) maghemite (?-Fe2O3) nanoparticles were electrospun and characterized in terms of morphology, degradation rate, biological compatibility and mechanical properties. The existence of three components in the mats was confirmed by Fourier transform infrared and energy-dispersive X-ray spectroscopy. Scanning electron microscopy images illustrated well fabricated nanofibers with smaller diameter distribution for PLLA. The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay using human skin fibroblast cell indicates desired proliferation on the samples. Blood biocompatibility results in terms of clotting time, fibrin formation, and hemolysis were almost in the normal range. Samples’ degradation rate was investigated over 24 weeks where the PLLA shows 47.15% loss in mass versus 6.7% loss for TPU. High tensile strength and an extremely low elongation-at-break were determined from the stress-strain curve for PLLA, while TPU exhibits high elasticity. Overall, 50:50% of (1% ?-Fe2O3) loaded PLLA/TPU mats are the most appropriate. Next, a two-level Taguchi (L8) experimental design followed by the response surface methodology (RSM) were used to optimize the fabrication process where the elastic modulus is the response while the factors investigated were A-flow rate (2-3 ml/h), B-voltage (20-30 kV), Cmaghemite% (1-3% w/v), D-solution concentration (10-15 wt.%) and E-collector rotating speed (1000-2000 rpm). From the signal-to-noise ratio values, the influences of the factors were ranked as: D>B>C>E>A. The empirical quadratic model obtained consists of the voltage-B and second order effect of flow rate-(A)2, voltage-(B)2, maghemite %-(C)2 and concentration-(D)2. The optimum elastic modulus of the scaffold was found to be 35.24±0.64 MPa. Finally, an AOHV template was designed and installed as the electrospinning collector to fabricate the 3D scaffold based on the optimum ratio and settings. Later, the human aortic smooth muscles cell migration and proliferation, as well as the elastic modulus loss percent of the optimum 3D scaffold after cell seeding were checked during 34 days of incubation. Overall, the structural, biological and mechanical specifications of the fabricated TEHV have successfully proved that it can be a potential alternative in AOHV replacement surgery.