Systems for the automated 3D assembly of micro-tissue and bio-printing of tissue engineered constructs
Thesis DisciplineMechanical Engineering
Degree GrantorUniversity of Canterbury
Degree NameMaster of Engineering
Tissue engineering is a field devoted to the design and creation of replacement tissues with the ultimate goal of one day providing replacement organs. Traditional strategies to accomplish this through the bulk seeding of cells onto a single monolithic porous bio-scaffold are unable to realise a precise architecture, thus the inability to mimic the cells natural micro-environment found within the body. Bio-printing approaches are the current state of the art with the ability to accurately mimic the complex 3D hierarchical structure of tissue. However, a functional construct also requires high strength to provide adequate support in load bearing applications such as bone and cartilage tissue engineering, and to maintain the open geometry of a large intricate channel network, which is crucial for the transport of nutrients and wastes. Typical approaches utilise materials which have processing parameters more amendable for cell incorporation, thus they can be simultaneously deposited with scaffolding material. However, the resulting construct is typically of low strength. This thesis explores the automation of a printing and “tissue assembly” process with the ability to incorporate delicate cell aggregates or spheroids within a high strength bio-scaffold requiring harsh processing parameters, at precise locations. The 3D printed bio-scaffold has a lattice architecture which enables a frictional fit to be formed between the particle and scaffold, thus preventing egress. To achieve this the pore must be expanded before the delivery of a single 1mm particle. Novel subsystems were developed to automate this process and provide the ability to achieve scalable, flexible, complex constructs with accurate architecture. A system architecture employing the benefits of modularity was devised. The main subsystems developed were the singulation device, to ensure the separation of a single particle; the injection device, to deliver and seed particles into the scaffold, and the control system, to facilitate the operation of the devices. Three generations of singulation devices have been developed ranging from mechanical to fluid manipulation methods alone. The first prototype utilised mechanical methods, with simple control methods. However the inability to correctly position the lead particle within the singulation chamber, resulted in damage to the test alginate particles. In the second prototype a fully fluidics based device utilised two trapping sites to capture the leading particles. Singulation success rates of up to 88% was achieved. Higher rates were limited by the trapped particle’s interaction with the lagging particles during capture. In a similar concept to the second prototype, the third prototype utilised only a single trapped particle, and achieved much higher throughput, and 100% singulation accuracy. The injection device, utilised a conical expanding rod within a thin outer sheath. It was able to expand the pore, with minimal damage to the scaffold, providing an unobstructed path for the delivery of the particle into the pore. A decentralised control system was devised to integrate the process operation for the electro-mechanical devices. Separate microcontrollers were able to sense, interact and communicate with one another, and the master control PC, to execute specific tasks to automate the process. The development of systems to automate the process has addressed the ability to accurately incorporate delicate cells with a high strength bio-scaffold, and will enable the realisation and investigation of intricate complex constructs, unachievable with current manual processes. Thus features found within the body may be more closely mimicked and functionalised, which may provide the necessary signals, micro-environment and infrastructure to correctly regulate the formation of complex functional tissue, supported by the adequate mass transport of nutrients and wastes. This may one day lead to 3D printing or assembly of viable replacement tissue, accurate in vitro model systems for laboratory testing, or even whole organs.