Towards Wearable Tremor Suppression Orthoses

We use our hands to interact with our surroundings. We execute many varying tasks with the hands of which many are basic activities of daily life. Movement disorders in the upper limb can limit the execution of those tasks and impair the quality of life. One of the most common movement disorders is tremor, affecting 5.6% of the population aged over 65 with Parkinson’s Disease or Essential Tremor. In the overall population, approximately 2.2% are affected by Essential Tremor. More than 65% of those suffering from tremor in the upper limb present serious difficulties in performing activities of daily life. Currently, neither Essential Tremor nor Parkinson’s Disease is curable, and therefore, treatment is focused on relieving the symptoms to increase the quality of life of the patients. Medication is the most commonly used treatment, while deep brain stimulation is the most effective treatment but is reserved for advanced cases as it is highly invasive. As a large fraction of patients is either refractory to medication, drug intolerant, or not qualified for surgical treatment, alternative treatments are needed. Even with optimal medical or surgical intervention in tremor, patients will still require physical and occupational therapy interventions to promote full social participation. An alternative non-invasive symptom treatment is the mechanical suppression of the oscillation movement with tremor suppression orthoses. In wearables, including tremor suppression orthoses, the functionality contradicts the comfort and needs to be balanced. The use of a tremor suppression orthosis brings the dilemma of low comfort for the wearer due to non-optimized wearability. In the philosophy of technology, this trade-off between tremor suppression and wearability is called the dilemma of assistance and acceptance, whereas acceptance is defined as a combination of wearability and social factors. The objective of this thesis was to tackle the dilemma by maximizing wearability without reducing the tremor suppression efficacy of such tremor suppression orthoses. Therefore, two user groups were identified to tailor approaches to their needs. The intermittent user group requires a tremor suppression orthosis for activities of daily living occurring infrequently during the day. The continuous user group needs a tremor suppression orthosis for a variety of complex tasks performed consecutively throughout the entire day. In the first step, I conducted a systematic literature review to identify the weaknesses of current wearable tremor suppression orthoses for the upper limb and to identify the need for further research and developments. I identified 21 different orthoses concepts and prototypes, of which most of them concentrated on the wrist and elbow flexion and extension. They mainly relied on rigid structures and actuators while having tremor suppression efficacies for tremor affected people of 63% on average. I showed that most of the orthoses had low wearability by being bulky and heavy, with a non-adapted human-machine interface. For the intermittent user group, infrequently in need of tremor suppression, I developed a lightweight, textile-integrated orthosis. With a passive element in this orthosis, I modified the human wrist impedance. The working principle of the orthosis was based on a task adjustable, air-filled structure placed on the dorsal side of the wrist. I characterized the stiffness and damping properties of the orthosis with which the wrist impedance was modified. Furthermore, I evaluated the efficacy of the developed passive orthosis by analyzing the suppression of involuntary movements in the wrist of a tremor affected patient during different activities of daily living. I demonstrated that the soft orthosis reduced tremor power for daily living activities, such as drinking from a cup, pouring water, and drawing a spiral, between 74% and 82%. In the next step, I developed a controlled suppression orthosis for the continuous user group, continuously in need of tremor suppression. This semi-active orthosis relied on a decentralized two-state electromagnetic brake coupled via rope to the wrist flexion-extension movement. Using a computer model and a test bench, the controlled brake parameter, brake duration, and offset in the tremor cycle were optimized for a combination of the highest tremor suppression with the highest voluntary movement preservation. I evaluated the computer model and test bench with a proof-of-concept study with tremor affected people. With the optimized parameter, a tremor suppression of 79% and 67% were determined for the computer model and the test bench. The voluntary movement, determined by the trajectory offset, was suppressed by 24% and 32%. In the proof-of-concept study, I preserved all voluntary movements and suppressed tremor by 41%, 55%, and 26% for the tasks Drinking, Pouring, and Drawing-Spiral, determined with the power spectral density. To further improve the wearability of the semi-active tremor orthosis, I developed a method with which electro-mechanical systems as the clutch can be integrated into textiles. A new metal textile laser welding method was presented for rapid one-step, stable and cost-efficient manufacturing of electrically conductive textiles. This method is a direct on-textile approach for customized 2D metal coatings in the nanometer range with a flexible design. Investigating the mechanical durability, I showed that the coating resisted up to 10 000 abrasion cycles using the standardized Martindale test and up to 42 000 flexion cycles using the standardized Schildknecht test. This technology presents properties and variabilities for a wide range of applications in E-textiles and wearable devices. Furthermore, to improve the wearability of physical human-robot interaction, I developed a new air-filled padding for wearable devices such as tremor suppression orthoses. The tactile and thermal comfort of the new padding was compared to a foam padding using the MyoSuit as a testing platform. The tactile and thermal comfort of the padding was investigated in isolated setups as well as in a use-case scenario (n=6). The mean pressure at the shin padding, measured with a thin foil sensor with 44x44 sensels, was reduced by 59%, while pressure peaks were reduced by 72%. Wearing the pneumatic padding significantly reduced the shear force chafing and pain rating compared to the foam padding. In the use-case scenario, using a questionnaire, the pneumatic padding significantly improved tactile comfort while not compromising the thermal comfort compared to the foam padding. Thus, this new pneumatic padding has the potential to improve the wearability of wearable devices by providing an individual fit. With this work, I contributed to the field of tremor suppression orthosis by improving several aspects of wearability. I proposed and validated two new suppression concepts with special emphasis on wearability. Additionally, I proposed two methods with which the wearability can further be improved. I re-centered the design focus of tremor suppression orthoses by improving their wearability and promoting a wider adaptation for the future. Furthermore, this advancement in wearability can also be translated to other wearable devices. In summary, with this work, the gap between tremor suppression and wearability was diminished, and the field got closer to solving the dilemma of assistance and acceptance