Characterization of 3D-Bioplotting of polycaprolactone-bioactive glass composite scaffolds for Tissue Engineering Applications

Abstract

Tissue engineering is an emerging field which combines engineering and life science in order to develop biological substitutes to regenerate, restore and repair defective tissues. One approach is the generation of three-dimensional matrices or scaffolds to create a temporary matrix with a similar host environment for cells to eventually proliferate to eventually form an organized tissue system. Additive Manufacturing (AM) processes provides a tool to manufacture these scaffolds in a patient-specific way. Scaffolds requirements are strict and are widely studies for a better performance. Extrusion based AM processes such as 3D-Bioplotting offers flexibility in terms of the input material as the scaffolds are constructed by an ink ejected with pneumatical pressure following an input STL file. This Thesis investigate the relation between the 3D-Bioplotting, fabrication parameters and scaffolds characterization in order to improve and understand the behavior of these geometries. First, the scaffold fabrication is detailed. Scaffolds of Bioglass and Polycaprolactone were printed in different geometries. Wells, cylinders and cubes with controlled pore size and porosity were used for the different experiments. A prior parameters screening and selection showed the best printing parameters for the different combination of materials. A preliminary study suggests the need for an external system in order to improve the quality of the samples. The lack of control over temperature of the 3D-Bioplotter was restore with the introduction of a new fan setup. Scaffolds fabrication was improved with a custom-made python script which analyze the captures 2 images of the bioplotter while printing to allow for small tune of the parameters while printing. The code allows to measure strut diameter and drastically improves the final scaffolds resolution. Furthermore, the code was use for scaffold characterization, providing a new tool to measure the inner structure. Samples had a homogeneous inner structure measure with the code and verify with a micro-CT. Porosity measurement was also check and a trend was found with the captured images. Mechanical characterization showed different results with the literature, were the addition of BG decrease the mechanical properties of the sample. Biological behavior showed a similar trend with positive results at first week but negative at the second one. Rheological characterization of the inks allows a better understanding of them and generate additional information for the printing process. A combination of formulas describes the shear at the tip of the bioplotter nozzle. The behavior of the material at these shears were analyzed reporting viscosity, storage, and loss modulus. Furthermore, this information also suggests the need of an additional cooling system in order to keep the shape of the printed struts, the fan set up. Additionally, the rheological characterization was annexed with the printing speed with a series of formulas, finding a relation between the viscosity and the needed printing speed of the machine. This relation was correlate with experimental data and a small deviation was found, allowing to effectively predict the feasibility of printing for new materials and reducing the set-up time and costs. The thesis gives a guide for scaffold fabrication and a new tool for inner characterization.