Design, Production and Characterization of Additive Manufactured Scaffolds for Bone Tissue Engineering (Ontwerp, productie en karakterisatie van laagsgewijs geproduceerde scaffolds voor botweefselengineering)
Design, Production and Characterization of Additive Manufactured Scaffolds for Bone Tissue Engineering
For the treatment of large or non-healing bone defects, no optimal solution exists to date. All currently available therapies have important drawbacks. To resolve this clinical problem, there is a strong tendency towards regeneration of the bone tissue in the defect. This new approach, called bone tissue engineering (BTE), combines the advantages of autografts and allografts by using cell-seeded porous structures (bone scaffolds), and eliminates problems such as donor site scarcity, immune rejection and pathogen transfer. Despite the tremendous increase of research in this field, no true clinical bone tissue engineering products are available yet. This gap between the amount of research and clinical products can be attributed to the lack of knowledge on bone scaffold key properties and their effect on biological outcome. To obtain this knowledge the production of bone scaffolds with high controllability and repeatability in terms of mechanical and morphological parameters is strongly demanded. Additive manufacturing (AM) techniques are capable of producing porous structures with a controlled architecture, owing to their layer-wise building and direct link with a computer aided design (CAD) model. This will allow the production of scaffolds with tailored structural properties which can be used to investigate their biological outcome. The general aim of this PhD study was to develop a robust production protocol consisting of a design step, AM technique and characterization methods to produce both biodegradable polycaprolactone (PCL) and bio-inert Ti6Al4V scaffolds with a highly controlled internal porous architecture. Furthermore, the research described in this dissertation aimed at answering following three questions: 1. Can we produce bone scaffolds with controlled mechanical and morphological properties?2. Can we use the controlled SLM process to evaluate morphological and mechanical influencing parameters of bone scaffolds?3. Can we alter the surface chemistry of Ti6Al4V and PCL bone scaffolds to improve their in-vitro cell performance? The research described in this dissertation resulted in two robust AM techniques, namely selective laser sintering (SLS) and selective laser melting (SLM), for the production of biodegradable PCL and Ti6Al4V bone scaffolds with controlled morphological and mechanical properties. By using the controlled Ti6Al4V scaffolds a first step was taken in evaluating the effect of key design parameters on the behavior of in-vitro osteogenic cell behavior. The results achieved in this dissertation directly lead to a novel hypothesis suggesting that a thoroughly defined gradient architecture produced with a robust AM technique might improve cell seeding and proliferation, which can be used in further research. Finally, as the surface chemistry cannot be altered during the AM production process, different surface post-treatment steps were used to successfully alter the surface chemistry of the as-produced PCL and Ti6Al4V scaffolds. In conclusion, this PhD study shows that the AM techniques SLS and SLM can be useful to produce highly porous bone scaffolds with repeatable and controllable morphological and mechanical properties. Subsequently, these controllable bone scaffolds can be used for post-treatment, in-vitro and in-vivo experiments.