| Author: | Shah, Parth Bharat |
| Title: | Measurement of pressure thresholds and biomechanical properties of soft tissues in the head region for product design |
| Advisors: | Luximon, Yan (SD) |
| Degree: | Ph.D. |
| Year: | 2021 |
| Subject: | Face -- Measurement Tissues -- Measurement Anthropometry Hong Kong Polytechnic University -- Dissertations |
| Department: | School of Design |
| Pages: | xxi, 203 pages : color illustrations |
| Language: | English |
| Abstract: | The human head comprises of a skull covered by an uneven layer of soft tissue. Skull houses the brain, whereas the facial region has key sensory organs. Hence, the safety of this region is of great priority. Wearable products designed for the head region address the needs for protection, healthcare, or telecommunication. To ensure the proper functioning of these products, they need to be in close contact with the corresponding soft tissue. Consequently, this results in the generation of contact pressure at the site of product-soft tissue interaction. The amount of pressure generated can highly influence user comfort and experience. Hence, it is necessary to evaluate the pressure threshold for discomfort and pain at different regions of the head to have a better understanding for designing ergonomic products. In addition to pressure thresholds, it is also necessary to evaluate the biomechanical properties of the soft tissue in order to achieve a holistic understanding for the design process. Also, the relationship between these parameters and demographic parameters like age, gender, and BMI need to be explored. However, hardly any studies have been conducted in this area. Hence, to address this gap, a research study was conducted. The research aims at measuring pressure discomfort threshold and pressure pain threshold along with biomechanical properties of the soft tissue. Also, the study aims at investigating relationships between different parameters, making the research inherently positivistic in nature. An experimental investigation was conducted following a quantitative methodology to measure the parameters required to address the research gap. A thorough literature review was conducted, followed by a study to identify a technique for the measurement of pressure thresholds and biomechanical properties of soft tissues in different regions of the head. Based on the literature and results of pilot studies, an ultrasound indentation device was considered for this study. A customized software to evaluate the data was also developed using Microsoft VC++. Initial calibration and validation of sensors were performed using silicon phantoms. Pressure thresholds for discomfort and pain were measured for two hundred eighteen participants at seventy-six landmarks, which were identified based on anatomical locations and the region in contact with commonly used head-related products. Three loading and unloading cycles were performed at every landmark using an indentation probe. For two-third of the landmarks, there was a significant difference in the pressure threshold between both genders. Compared to females, male participants had higher pressure threshold values. It was also identified that pressure thresholds were independent of age and BMI. However, at every landmark, the value for pressure thresholds had a high correlation with the value of pressure threshold at every other landmark, showing consistency and symmetry in pressure sensitivity. The data suggested that the skull area was less pressure sensitive, compared to the facial region. The temporal and forehead region had a moderate level of pressure sensitivity. The acquired pressure threshold data was used to develop pressure sensitivity maps. Pressure threshold data is subjective in nature, and hence there was a need to test the consistency of acquired data. Therefore, a study to test the reliability of data was planned, where sixty participants whose pressure thresholds were previously measured were invited again, and their pressure thresholds were measured for the second time. Results of Intraclass correlation analysis showed that the reliability of the pressure threshold data was excellent for the pooled pressure discomfort and pooled pressure pain threshold data. Reliability at individual landmarks was also found to be in the acceptable range (except one for PDT and five for PPT, which were in the marginally acceptable range). Tissue deformation at discomfort and pain threshold was measured using custom-designed Tissue Ultrasound Palpation System (TUPS) software from the ultrasound data acquired at eighteen landmarks for sixty participants. Landmarks were decided based on the results of cluster analysis conducted in the previous study. There was a significant gender-based difference in the measured soft tissue deformation data at discomfort threshold for six landmarks and at seven landmarks for pain threshold. Deformation in the facial region was higher compared to that in the skull and forehead region. Maximum deformation for pressure thresholds was found in the cheek area, whereas minimum deformation was recorded in the forehead region. In addition to soft tissue deformation at discomfort and pain thresholds, biomechanical properties of soft tissue, tissue thickness, elasticity, and deformability were also calculated in five regions of the head. Results of Independent sample t-test suggested significant differences in tissue thickness between both the genders at three locations; however, the values for effective Young's modulus and maximum deformation levels were higher for male participants compared to female participants for most of the landmarks. Also, the results of the correlation analysis showed a relationship pattern between BMI, tissue thickness, effective Young's modulus, and maximum deformation at individual landmarks. With an increase in BMI, tissue thickness and maximum deformation increased, whereas the effective Young's Modulus decreased for individual landmark. The data acquired from this research finds its applications in several fields, including clinical sciences, forensic sciences, diagnostics, and medical sciences. The data from this study can be used for reconstructive surgeries and also to help in planning and simulation of surgeries, and also to identify any morphological changes in the tissue properties due to the onset of any medical condition. In the field of product design, this data can serve as a good reference for designers during the product design process so that the user's comfort and experience can be enhanced. In addition, this data can be used to perform virtual simulation using techniques like Finite Element Analysis (FEA) for product testing. The results from such a study can further help designers come up with a more optimal product design. |
| Rights: | All rights reserved |
| Access: | open access |
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