Performance of a flexible bioreactor for tendon tissue engineering

Tendon tears caused by age, trauma or sports-related injuries are an increasing problem. Rotator cuff injuries in particular often have a poor outcome due to the state of the tear and surgeries leading to re-rupturing of the repaired tendon. Tissue ngineering strategies aim to support the native tendon in its ability to self-repair through the application of cells and biomaterials. In recent years the importance of mechanical stimulation to tissue engineering constructs came into focus. In order to apply physiologically relevant stresses, new bioreactors capable of multiaxial stimulation need to be developed. One such bioreactor is presented in this work. The bioreactor consists of a filamentous electrospun scaffold, strongly resembling the native tendon structure. A flexible gas-permeable membrane encloses the system and maintains sterility. The aim of this thesis was to characterize the performance of this flexible bioreactor for tendon tissue engineering. The main objectives were to identify a seeding technique that would lead to an even cell distribution throughout the scaffold. Next a computational model was built and applied to investigate nutrient and metabolite distribution throughout the bioreactor, their influence on cell growth, and to gain insight in how different flow rates impact the system. The model was validated through a set of experiments. Lastly, factors that can improve cell retention on the scaffold needed to be identified. We identified that following seeding, the capillary effect was a greater determiner of cell distribution than seeding technique. The computational model was able to give us 3D spatial insight into the system that was otherwise not available. Furthermore it assessed the importance of the membrane being permeable to gasses, and it could assure us that stopping the media flow was not going to affect cell growth over a period of 20 hours. Through the validation experiment, superior outcomes were identified from higher flow rates, but shortcomings of the model were also highlighted. The sensors optimized for this set of experiments gave robust measurements with satisfying robustness which will be used in future work. Lastly, we could not identify the main reason for a lack of cell attachment to the scaffolds. Future work will include further investigations into the mechanisms behind poor cell retention on our scaffolds, and will see the expansion of the bioreactor as a mechanical stimulation platform.