Browsing by Author "Mathew, M."

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Development, optimization, and prototyping of a simplified sit-stand mechanism for lower limb impairments
(Springer Science and Business Media Deutschland GmbH, 2025) George, S.P.; Thomas, M.J.; Mathew, M.; Gangadharan, N.; Varghese, A.K.
A sit-stand device for rehabilitation should be simple in its design, easy to manufacture, and convenient for individuals with mobility impairments to use. This paper proposes a design framework and prototyping process for developing an assisted sit-to-stand mechanism tailored to the specific limitations faced by individuals with lower limb impairments. The study incorporates a functional kinematic and kinetic design to ensure the mechanism’s usability across a diverse range of individuals. Recognizing the critical challenges faced by individuals with spinal cord injuries (SCI) and subsequent paralysis, the design philosophy integrates considerations specifically aimed at this population. A simplified circular design trajectory is presented for individuals with muscle paralysis, focusing on the synthesis of an electrically actuated mechanism. A four-bar linkage is modeled to represent the mechanism in the sagittal plane. The functional attributes of the device are determined, and kinematic synthesis is performed to ensure comfort during the sit-to-stand motion. This is achieved by minimizing the actuator’s travel distance during the lift. The velocity and acceleration profiles of the linear actuator are determined after applying boundary conditions. An optimal configuration is selected based on minimizing the displacement of the electric actuator. A human body model based on a 50th percentile male was developed to simulate a motion study of the sit-stand and validate the trajectory using the motion study module in SOLIDWORKS™. An optimum sit-to-stand linkage design was synthesized, and the corresponding prototype was fabricated. The independent anthropometric dimensions on which the design depends are the thigh length and the weight. The sagittal linkages for lifting were calculated and tested through simulation with a human body model to replicate the sit-to-stand movement. The prototype was evaluated on an able-bodied individual. A key design feature was the repositioning of support from the armpit to the hip, thereby reducing user discomfort and improving ergonomics. The motion study revealed that the trajectory of the hip joint (H-point) followed a nearly circular curvature. Stability analysis using a mannequin confirmed a static stability margin of 1 and showed that the device would tip forward only if the deceleration exceeded 35.8 m/s2, which is significantly higher than typical human-induced accelerations—indicating safe operation during use. The prototype fabricated demonstrated the intended sit-to-stand functionality and validated the design approach. The motion analysis confirmed ergonomic hip support and smooth joint trajectories. While the initial testing was successful on an able-bodied subject, further evaluation involving individuals with spinal cord injuries is recommended for final adjustments. This work presents a cost-effective and customizable framework for manufacturing sit-to-stand assistive devices, scalable for variations in body weight and thigh length. © International Federation for Medical and Biological Engineering 2025.
Flexural strength of hydrogen plasma-treated polypropylene fiber-reinforced polymethyl methacrylate denture base material
(2018) Mathew, M.; Shenoy, K.; Ravishankar, K.
Objectives: The present study aimed to evaluate flexural strength of hydrogen plasma-treated polypropylene fibers-reinforced polymethyl methacrylate (PMMA) polymer composite. Materials and Methods: One control group with no fiber reinforcement and 9 polymer composite test groups with varying fiber weight percentage (2.5, 5, and 10 Wt%) and aspect ratio (3/220, 6/220, and 12 mm/220 ?m) were prepared. Flexural strength was measured using Instron. Results: All hydrogen plasma-treated polypropylene fiber-reinforced test groups obtained significantly higher flexural strength characteristics. Among the test groups, 6 mm long fibers reinforced in 10 Wt% showed superior flexural strength. Conclusion: Hydrogen plasma treatment on polypropylene fiber has a significant role in enhancing the adhesion between PMMA polymer matrix and the polypropylene fibers and thereby the flexural strength. 2018 The Journal of Indian Prosthodontic Society | Published by Wolters Kluwer - Medknow.
Flexural strength of hydrogen plasma-treated polypropylene fiber-reinforced polymethyl methacrylate denture base material
(Wolters Kluwer Medknow Publications B9, Kanara Business Centre, off Link Road, Ghatkopar (E) Mumbai 400 075, 2018) Mathew, M.; Shenoy, K.; Ravishankar, K.
Objectives: The present study aimed to evaluate flexural strength of hydrogen plasma-treated polypropylene fibers-reinforced polymethyl methacrylate (PMMA) polymer composite. Materials and Methods: One control group with no fiber reinforcement and 9 polymer composite test groups with varying fiber weight percentage (2.5, 5, and 10 Wt%) and aspect ratio (3/220, 6/220, and 12 mm/220 ?m) were prepared. Flexural strength was measured using Instron. Results: All hydrogen plasma-treated polypropylene fiber-reinforced test groups obtained significantly higher flexural strength characteristics. Among the test groups, 6 mm long fibers reinforced in 10 Wt% showed superior flexural strength. Conclusion: Hydrogen plasma treatment on polypropylene fiber has a significant role in enhancing the adhesion between PMMA polymer matrix and the polypropylene fibers and thereby the flexural strength. © 2018 The Journal of Indian Prosthodontic Society | Published by Wolters Kluwer - Medknow.