Evaluación computacional en andamios por prototipado rápido para la ingeniería de tejidos

Abstract

In tissue engineering, the ultimate goal of the development of degradable porous scaffolds integrated with cells is the regeneration of new living tissue to repair biological defects. Scaffolds have certain requirements depending on the application, since they have to provide cells physiological conditions for specific tissue regeneration. In vitro analysis of scaffolds efficiency for tissue engineering is normally very expensive and it is generally difficult to control the processes that occur within the scaffolds. In this thesis numerical simulation were used in order to understand the influence of the morphology of scaffolds and culture conditions on different cellular processes, simulating in vitro experiments. Due to the need to optimize some of those cellular processes such as, cell seeding and cell culture different methodologies and scaffolds pores design were proposed to control the cellular responses.Physic-chemical culture conditions can be reproduced using bioreactor systems since testing these factors using the dynamic environment of bioreactors has been proved to be more efficient that testing the same factors experimentally under static conditions. Also testes done under static conditions uses small scaffolds but some tissue defects happen in a larger scale. Thus, in this thesis a method to analyze a perfusion bioreactor at a larger scale is proposed. The goal is to apply the results from an experimental level to a clinical application, where a larger graft is necessary. This methodology can be used to create an articular cartilage capable to fully cover the knee (diameter = 50 mm). One method that ensures the implementation of the macroscopic properties (permeability) of the biomaterial was developed. Using fluid dynamics simulations, the bioreactor design to provide better distribution of cells in the scaffold (seeded) and the right amount of stimulus (culture) was determined. Briefly, simulation predictions for the articular cartilage formation showed that cartilage growth is more uniform for a more homogeneous fluid-flow distribution.Different pores morphologies from rapid-prototyping fabrication were numerically evaluated. Two scaffold designs were proposed, one with gyroid morphology and the other with hexagonal prism shape. For both designs porosities of 55% and 70% were tested. In addition, different mechanical stimuli were computed to study the effect on cell adhesion. Mechanical stimuli are known to determine cell differentiation through a mechano-regulation theory. According to this theory, optimization of external conditions for cell differentiation were discussed comparing the effect of fluid-flow and axial compression. Fluid-flow was demonstrated to be more effective for cell differentiation on scaffolds that axial compression. The gyroid architectures lead to a better accessibility of the fluid into the scaffold, which can be related with higher efficiency during cell seeding.Based on the fact that the gyroid structure leads to a most effective distribution of the fluid, a system to control cell seeding was developed. The parameters of the system were: 1) the prediction of mechanical stimuli (numerically), 2) the distribution of gyroid pore (fabrication) and 3) the experimental verification. The scaffolds were reconstructed based on micro CT images. Two type of scaffold were studied; one with isotropic pore size distribution (412 ± 13 µm) and another with a gradual variation of pore size (250-500 µm). The results showed that on the isotropic scaffolds, the stimuli calculated were more uniform (15s-1 y 24 s-1)and varied gradually (12s-1 -38 s-1) in the second type of scaffold. The distribution of the seeded cells also follows the pattern of distribution of stimuli and pores.Finally, a new methodology to evaluate cell seeding under perfusion conditions was proposed. The entire process for cell seeding was simulated using a Lagrangian multiphase model.