This study is an investigation into methods of developing ergonomic guidelines for automotive assembly tasks involving insertion of small parts. The study was conducted in four major parts: 1) a method of determining and evaluating subjective exertion limits was modified and tested, 2) a large dataset was collected from an industrial population in 10 simulated assembly line tasks, 3) a smaller dataset was collected from a student population to assess hand dominance effects, and 4) strength data obtained was compared with a strength prediction model to determine if the model could predict manual insertion forces. The traditional method of psychophysical data collection requires participants to extrapolate sensations from a relativity short session to judge if the task could be done for a much longer period. Maximum acceptable limits (MALs) are typically derived from having participants adjust a weight, resistance, or frequency to an acceptable level. The present study evaluated a relatively new method of collecting MAL data for simple, single-digit exertions where participants were asked to determine an MAL by self-adjusting and then regulating to maintain the exertion level. Results showed that MAL values obtained from a series of self-regulated exertions were independent of both analysis method and duration (5 minutes vs. 25 minutes) used for evaluation, and that the method was repeatable both within and between sessions. Ergonomic guidelines are often obtained from the strength capacity for a certain task, as it is important to ensure that workers possess sufficient strength to accomplish a task. As task demands increase, however, a larger percentage of a worker's strength capability in required, and other factors, such as performance and worker comfort, tend to be compromised. In this work, both strength capacity and subjective limits were obtained for a variety of simulated tasks to facilitate development of guidelines for the specific tasks. The relationship between these two measures (maximum force, acceptable force) was determined, and acceptable limits were found to be approximately 55% of population strength capacity, with correlations (R2) ranging from 0.40 to 0.60 depending on the task, suggesting the subjective limits and strength capacity are related in these tasks. Hand dominance was found to have a small (5%), but significant (p = 0.006) effect on strength capability, and no significant effect on subjective limit. Biomechanical strength prediction models can be used to assess loads placed on the human performing various tasks. One of the more popular models, Three-Dimensional Static Strength Prediction Program, is often used for heavy material handling tasks, such as lifting or pushing. The tasks studied presently, however, are manual insertions, requiring localized force application rather than whole body exertion. The prediction capabilities of this strength prediction model were compared with strength values obtained from the simulated assembly tasks. Results indicated that the model was not successful when predicting localized force, accounting for only 40% of the observed variance in strength (R2 = 0.4) / Master of Science

Transdermal drug delivery (TDD) is limited by high resistance of the outer layer of the skin, namely stratum corneum which blocks any molecule that is larger than 500 Da. Research on TDD has become very active in recent years and various technologies have been developed to overcome the resistance of the stratum corneum. In particular, researchers have started to consider the possibility of combining the TDD technologies in order to achieve further increment for drug permeability. Microneedles (MNs) and sonophoresis are both promising technologies that can perform notable enhancement in drug permeation via different mechanisms and therefore give a good potential for combining with each other. We discuss the possible ways to achieve this combination as well as how this combination would increase the permeability. Some of the undeveloped (weaker) research areas of MNs and sonophoresis are also discussed in order to understand the true potential of combining the two technologies when they are developed further in the future. We propose several hypothetical combinations based on the possible mechanisms of MNs and sonophoresis.

Needles are commonly used to reach target locations inside of the human body for various medical interventions such as drug delivery, biopsy, and brachytherapy cancer treatment. The success of these procedures is highly dependent on whether the needle tip reaches the target. One of the most significant contributors to the target accuracy is the needle insertion force that causes needle-tip deflection, tissue deformation, and tissue damage. Recently there has been tremendous interest in the medical community to develop innovative surgical needles using biologically-inspired designs. It is well known that insects such as honeybee and mosquito steer their stingers effortlessly to a specific target and release their venom in a certain path through the skin with minimal force. These unique traits inspire this dissertation work to develop bioinspired needles and to study the insertion mechanics of these needles for reducing the insertion force, needle-tip deflection, tissue deformation, and tissue damage. In this work, the insertion mechanics of honeybee-inspired needles with applied vibration in polyvinyl chloride (PVC) tissue phantom and chicken breast tissues was first investigated. It was observed that the insertion force was decreased by 43% and the needle tip deflection was minimized by 47% using honeybee-inspired needles. Furthermore, the insertion mechanics of mosquito-inspired needles in PVC tissue phantom and bovine liver tissues were studied. Design parameters such as maxilla design on the needle body, labrum-tip, vibration, and insertion velocity were considered. It was found that the insertion force was reduced by 60% in PVC tissues and 39% in bovine liver tissues using mosquito-inspired needles. To validate the developed bioinspired needle prototypes, a size scale study was performed using insertion test in a PVC tissue phantom. It was confirmed that the insertion force was decreased by 38% using different needle sizes. An analytical LuGre friction model was used to explain the insertion mechanics and to confirm the experimental results. Lastly, to investigate the effect of the insertion force reduction, the tissue deformation and the tissue damage studies were performed. Using a novel magnetic sensing system, it was observed that the tissue deformation caused by mosquito-inspired needles was decreased by 48%. A histological study was performed to quantify the tissue damage in bovine liver tissues. It was observed that the tissue damage of mosquito-inspired needles was reduced by 27% compared to standard needles. In conclusion, this dissertation study shows that applying bioinspired needle designs and vibration during insertion into tissues reduces the insertion force, the needle-tip deflection, the tissue deformation, and the tissue damage. The outcome of this study will benefit medical communities to advance the bioinspired needles for vibration-assisted clinical procedures. / Mechanical Engineering

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