Bilişimsel büyüme modellemesi ve cerrahi arteriel rekonstruksiyon planlaması

Approximately 1 in 100 children are born with a clinically significant congenital heart defect. Surgical treatment of congenital heart disease (CHD) involves complex vascular reconstructions utilizing artificial and native surgical materials. The objective of this thesis is to establish a predictive computational model for the volumetric growth of arterial tissue following complex cardiovascular patch reconstructive surgeries for pediatric and newborn patients. For the first time in the literature, the growth mechanics and performance of the growing arterial tissue domain in contact with artificial cardiovascular patches is established in this thesis. In the first part, this thesis proposes a new in silico patient-specific pre-surgical planning framework for patch reconstruction and investigates its computational feasibility. The proposed protocol is applied to the patch repair of main pulmonary artery (MPA) stenosis in the Tetralogy of Fallot CHD template. Implantation of different unloaded patch shapes is simulated through a quasi-static finite-element vascular model with shell elements and the effects of stenosis grade, the three-dimensional shape of the surgical incision and material properties of the artificial patch are investigated. Stress-strain data obtained in-house, through the biaxial tensile tests to obtain the mechanical properties of common surgical patch materials, Dacron, Polytetrafluoroethylene (PTFE), human pericardium and porcine xenopericardium. Finite-element model is experimentally validated through the actual patch surgery reconstructions performed on the 3D printed anatomical stenosis replicas. According to our findings, the shorter incisions made at the throat result in relatively low local peak stress values compared to other patch design alternatives. Longer cut and double patch cases are the most effective in repairing the initial stenosis. The microstructure for mature vessels has been investigated in detail in literature while there is limited information about the embryonic stages, in spite of their importance in the prognosis of congenital heart defects. It is hypothesized that the embryonic vasculature represents a disorganized but dynamic soft tissue, which rapidly evolves towards a specialized multi-cellular vascular structure under mechanical loading. Hence in the second part of thesis, the microstructural evolution process of the embryonic pharyngeal aortic arch structure was simulated using an in ovo validated long-term growth and remodeling computational model, implemented as an in-house FEBio plugin. Optical coherence tomography-guided servo-null pressure measurements are assigned through the critical embryonic stages. The accumulation of key microstructural constituents was recorded through zoom confocal microscopy for all six embryonic arch arteries. The total amount and the radial variation slope of the Collagen along the arch wall thickness in different arches and for different embryonic times, with different dimension scales, were normalized and compared statistically. The arch growth model shows that the stress levels around the lumen boundary increases from 270 Pa (embryonic Stage 18) to a level higher than 600 Pa (embryonic Stage 24), depending on matrix content production rates, while the homeostatic strain level is kept constant. The statistical tests show that although the total Collagen level changes with embryonic time, it proves radial localization around lumen, in accordance with numerical model results. In third part, combining the methodology developed in the Part 1 and 2 of this thesis, an elastic-growing material model was developed in the open source FEBio software suite to first examine the surgical patch reconstruction process for an idealized MPA anatomy as a benchmark model and then for the patient-specific pulmonary arteries of a newborn. Following patch reconstruction, high levels of stress and strain are compensated by growth on the arterial tissue. As the growth progresses, the arterial tissue is predicted to stiffen to limit elastic deformations. We simulated this arterial growth up to the age of 18 years, when somatic growth plateaus. Our research findings show that the non-growing patch material remains in a low strain state throughout the simulation timeline, while experiencing high stress hot-spots. This new computational approach is effective for the pre-surgical planning of complex patch surgeries to quantify the unbalanced growth of native arteries and artificial non-growing materials to develop optimal patch biomechanics for improved postoperative outcomes.