The focus of this research is on the development of an Orthotic device for the human knee joint by implementing the compliant properties of flexible 3D Printed mechanisms. The main purpose of this study is to address the aspects of customization and especially in the low-budget solutions where currently there is a lack of wearable options due to the cost limitations. Additionally, there is an existing gap for devices with not only personalized flexibility but with adjustable one, controllable during the rehabilitation process of the patients. After the knee injury occurs, a surgical intervention might be needed to replace the damaged ligaments. After that, the patient’s lower limb is fixed, and they are required to move by using crutches. The next phase of the recovery is using orthotic devices. Currently there are solid supportive devices on the market for the initial stage of the healing. Later, when the condition improves, and these supportive devices are being replaced by soft fabric type wearables and supplemented with low impact rehabilitation exercises. The problem with that solution is the lack of a middle supportive devices t that makes the transition during the recovery smoother. The missing transitioning pieces can be serious issue amongst athletes who wish to accelerate their recovery process and start practicing on the field as soon as possible. The knee joint is especially vulnerable during those periods of transition between the hard hinge type devices and the soft sleeves, and usually this is the time when many people get injured again. Therefore, it can be assumed that there is a gap on the current market for an Orthotic device with an adjustable elasticity based on the stage of the rehabilitation process, individual requirements of the patients and their lifestyle. This necessity is even more present among the budget solutions for supportive device realization. In addition, this works is focused on ACL (Anterior Cruciate Ligament) injuries since, as explored in the literature below, they occur 10 times more often than the PCL complications, and in general, from all ligament injuries, half are at the ACL. The ACL usually tears during sports. Some of the main questions this research tries to answer can be formulated as: Is there an actual need for such solution? What are the current solutions and how this problem has been addressed? Who are the targeted groups experiencing this problem? What are the main advantages and disadvantages of the proposed concepts? Lastly, is the implementation on its own a possible task? In this work a more “unconventional” techniques, suitable for the purposes of Orthotic device design and fabrication is introduced and analyzed. The problem has been approached from a different perspective. Instead of looking for ways to improve the existing solutions, the findings of another field – 3D Printing and in particular, soft 3D Printing of compliant mechanisms were implanted and adapted according to the requirements of the above stated problem. At first, a definition of a compliant mechanism is “a flexible mechanism that transmits force and motion through elastic body deformation”. Simply put, a mechanism that relays on the deformation caused by an external loading to perform the motion. From this notion is clear that compliant mechanisms have possible applications for Orthotic purposes. This, combined with the fact that these mechanisms are a good fit for 3D Printing, makes them strong candidate for the development and fabrication of supportive devices designed regarding the individual specificities. In this thesis, several models of compliant flexible 3D Printed mechanisms implemented in Orthotic devices for the knee joint have been presented and investigated. The models of the Orthotic device were verified by non-linear Finite Element Analysis due to the anisotropic nature of the 3D Printing materials and the occurring large deformations. Additionally, some of the proposed models were confirmed in an experimental environment by using a robotic arm and an artificial leg to measure the relationship between the force and the displacements of the samples. A rehabilitation protocol for athletes with ACL complications was developed and proposed. To take full advantage of the capabilities of the additive manufacturing processes and to better optimize the samples, the cellular solid model was implemented to describe the 3D Printing structure from inside and explore the parameters important for controlling the stiffness/flexibility of the mechanisms. Three different infill types and seven infill densities were explored. It was established that flexible 3D Printing can fulfil the criteria of fabricating compliant supportive devices with adjustable resistance and deformation depending on the required parameters. Also was found the relation between the relative density and the moduli of elasticity, and relative density and stress of 3D Printed parts with different infill density and infill geometry. This can be valuable tool throughout the design phase in order to optimize the compliant supportive device, its stiffness and strength to weight ratio. Finally, it can be concluded, 3D Printing by using flexible filaments is suitable manufacturing process for custom-made supportive wearables, especially for low-cost options. It gives extra levels of personalization unavailable to the traditional technologies with removing material. Implementation of compliant mechanisms allows for deeper control on the parameters related with the flexibility, ergonomics, and reliability of the Orthotic device. In the context of the Forth Industrial Revolution, Additive Manufacturing technologies emerge as better and better alternatives as toolless methods with minimal material waste drastically decreasing the prototyping costs and time and only limited by the imagination of the designers and makers, to shape our new perspectives of what is possible.九州工業大学博士学位論文 学位記番号：生工博甲第450号 学位授与年月日：令和4年9月26日1 Introduction|2 Literature Review|3 Methodology|4 Results|5 Discussion|6 Conclusion九州工業大学令和4年
