oa The Use of CT and Rapid Prototyping to Produce an Exact Replica of the Normal Human Aortic Root for Tissue Engineering

Introduction: Tissue engineered heart valves offer a promising alternative for the replacement of diseased heart valves avoiding the limitations faced with currently available bioprosthetic and mechanical heart valves. The aim of the tissue engineering is producing living heart valves that can be used to replace those affected by congenital and acquired disease, especially in younger patients. The central challenge of any tissue engineering project is to replicate the three dimensional architecture, physical and cellular function of the tissue to be replaced. Aortic valve function critically depends on the geometry and interaction between its component parts. The three dimensional design contributes several important functions to the valves; these include optimal hemodynamic performance, smooth opening and closing characteristics, passive dynamism, influence in ventricular function and coronary flow. Current prosthetic stented valves have the disadvantage of presenting high transvalvular gradients, incomplete regression of left ventricular hypertrophy and the rigid stent produces a residual obstruction in transaortic flow and reduces effective orifice area. This leads to a negative effect on ventricular function after aortic valve replacement and long-term survival. Recent advances in computed tomography scan, image processing and rapid prototyping offer the unique opportunity to recreate the phenotypic geometric relationship of the aortic root. Therefore it offers the possibility to produce a tissue engineered stentless valve with better hemodynamic performance with improved left ventricular function. Methods: Computed tomography scans were obtained via a Siemens Definition Flash with a slice thickness of 0.6 mm and a slice increment of 0.3 mm. DICOM were imported into Mimics (Materialise, Leuven, Belgium) for three dimensional reconstructions of the blood volumes. The processed files were exported as STL files into 3-matic (Materialise, Leuven, Belgium) to create various images showing the cross sections and models of interest. These STL files were used as the basis for the molds with suitable modification for 3D printing and the spraying process. The molds were three dimensionally printed (Objet 260 Connex, Stratasys, US) in three longitudinal segments each including the sinus, the adjoining aortic wall and the cusp. These were used to produce a scaffold which has the same physiological shape as a normal aortic root. The stentless valve scaffold was fabricated by using a custom made jet spraying device (Design RT, UK) to form anisotropic nanofibrillar poly ϵ-Caprolactone scaffold. The custom made device was developed with a computer controlled spray head with x, y, z, and angular movement to follow any complex shape. Results: Computed tomography scanned images were processed to form various models for three dimensional printing. The printed models were adjusted to produce various sleeves and molds for jet spraying. The resulting three dimensional nanofibrillar scaffold was an exact replica of the aortic root as defined by the computed tomography scan images and is being developed as a stentless tissue engineered heart valve. Conclusion: It is concluded that the use of computed tomography scan based model of the normal aortic root can reproduce a 3D scaffold with the same geometry. This is an important step towards personalized tissue engineered heart valves. Further studies are required to characterise the functional implications of this method.