Faculty Publications
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Publications by NITK Faculty
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Item Case study for contact pressure improvisation with graded implant material in articular cartilages of knee joint(Korean Society of Mechanical Engineers, 2021) Raju, V.; Koorata, P.K.; Kamat, Y.In this study, the effect of graded design in comparison to homogeneous cartilage material is investigated for contact pressure distribution in the human knee joint. Knee implants are assumed a homogeneous material. In reality, cartilages are not homogeneous, and to replicate the heterogeneity of cartilages, a graded design is proposed. Simulation results show improved contact pressure distribution in the knee joint due to the graded composition of cartilages. The results are helpful in designing a new class of implant materials. © 2021, The Korean Society of Mechanical Engineers and Springer-Verlag GmbH Germany, part of Springer Nature.Item Design of bypass rotary vane magnetorheological damper for prosthetic knee application(SAGE Publications Ltd, 2021) Saini, R.S.T.; Chandramohan, S.; Sujatha, S.; Kumar, H.Semi-active systems using magnetorheological fluids have been realized in many novel devices such as linear dampers, rotary dampers, brakes, and so on. Rotary vane-type magnetorheological damper is one such device that uses magnetorheological fluid as a hydraulic medium and a controllable magnetorheological valve to generate variable resistance. This device, due to its limited angle motion, lends itself to a natural application for prosthetic knee joint. In this article, a bypass rotary vane-type magnetorheological damper suitable for prosthetic knee device is designed. In the proposed design, the rotary vane chamber and the bypass magnetorheological valve are connected using hydraulic cables and ports. The design of rotary cylinder is implemented based on the largest possible dimensions within the envelope of a healthy human knee, while the magnetorheological valve is designed optimally using a multi-objective genetic algorithm optimization. Off-state braking torque, induced on-state braking torque and mass of the valve are selected as three objectives. The torque and angular velocity requirements of the normal human knee are used as design limits. The optimal solution is chosen from the obtained Pareto fronts by prioritizing the objective of weight reduction of magnetorheological valve. The optimal solution is capable of producing a damping torque of 73 Nm at a design speed of 8.4 rpm and current supply of 1.9 A. Potential benefits offered by this design when compared with multi-plate magnetorheological brake are flow mode operation, large clearance gap, and fewer design components, thus reducing the manufacturing complexity. © The Author(s) 2020.Item Influence of material heterogeneity on the mechanical response of articulated cartilages in a knee joint(SAGE Publications Ltd, 2022) Raju, V.; Koorata, P.K.Structurally, the articular cartilages are heterogeneous owing to nonuniform distribution and orientation of its constituents. The oversimplification of this soft tissue as a homogeneous material is generally considered in the simulation domain to estimate contact pressure along with other physical responses. Hence, there is a need for investigating knee cartilages for their actual response to external stimuli. In this article, impact of material and geometrical heterogeneity of the cartilage is resolved using well known material models. The findings are compared with conventional homogeneous models. The results indicate vital differences in contact pressure distribution and tissue deformation. Further, this study paves way for standardizing material models to extract maximum information possible for investigating knee mechanics with variable geometry and case specific parameters. © IMechE 2022.Item Computational assessment on the impact of collagen fiber orientation in cartilages on healthy and arthritic knee kinetics/kinematics(Elsevier Ltd, 2023) Raju, V.; Koorata, P.K.Background: The inhomogeneous distribution of collagen fiber in cartilage can substantially influence the knee kinematics. This becomes vital for understanding the mechanical response of soft tissues, and cartilage deterioration including osteoarthritis (OA). Though the conventional computational models consider geometrical heterogeneity along with fiber reinforcements in the cartilage model as material heterogeneity, the influence of fiber orientation on knee kinetics and kinematics is not fully explored. This work examines how the collagen fiber orientation in the cartilage affects the healthy (intact knee) and arthritic knee response over multiple gait activities like running and walking. Methods: A 3D finite element knee joint model is used to compute the articular cartilage response during the gait cycle. A fiber-reinforced porous hyper elastic (FRPHE) material is used to model the soft tissue. A split-line pattern is used to implement the fiber orientation in femoral and tibial cartilage. Four distinct intact cartilage models and three OA models are simulated to assess the impact of the orientation of collagen fibers in a depth wise direction. The cartilage models with fibers oriented in parallel, perpendicular, and inclined to the articular surface are investigated for multiple knee kinematics and kinetics. Findings: The comparison of models with fiber orientation parallel to articulating surface for walking and running gait has the highest elastic stress and fluid pressure compared with inclined and perpendicular fiber-oriented models. Also, the maximum contact pressure is observed to be higher in the case of intact models during the walking cycle than for OA models. In contrast, the maximum contact pressure is higher during running in OA models than in intact models. Additionally, parallel-oriented models produce higher maximum stresses and fluid pressure for walking and running gait than proximal-distal-oriented models. Interestingly, during the walking cycle, the maximum contact pressure with intact models is approximately three times higher than on OA models. In contrast, the OA models exhibit higher contact pressure during the running cycle. Interpretation: Overall, the study indicates that collagen orientation is crucial for tissue responsiveness. This investigation provides insights into the development of tailored implants. © 2023 IPEMItem Feasibility study of a 4-DOF cable-driven exosuit for elbow and wrist rehabilitation(Springer Science and Business Media B.V., 2025) Alapati, S.; Seth, D.; Nakka, S.; Aoustin, Y.Cable-driven exosuits are emerging as an effective solution for upper limb rehabilitation, offering lightweight, flexible, and customizable assistance. While prior research for upper limb rehabilitation has primarily focused on single-joint actuation or systems with up to 2 degrees of freedom (DOF), the combined actuation of the elbow and wrist, including forearm pronation-supination, within an exosuit remains largely unexplored. Addressing this gap, this study investigates the feasibility of a 4-DOF cable-driven exosuit designed to assist these joints, which are essential for rehabilitation exercises and activities of daily living (ADLs) such as eating and object manipulation. A torque-tension model is developed to establish the relationship between joint torques and cable tensions. An optimization framework is implemented to determine optimal tension values. Motion capture data from six healthy subjects performing rehabilitation and daily tasks are used to analyze tension variations and validate the model. The results confirm that the proposed exosuit can provide effective assistance for the elbow and wrist while maintaining cable tensions optimized between 5 N to 50 N for ADLs. Furthermore, workspace analysis confirms that the exosuit maintains 100% feasibility across the rehabilitation range of motion. These insights lay the groundwork for an adaptive, personalized exosuit capable of assisting multi-DOF upper limb movements. © The Author(s), under exclusive licence to Springer Nature B.V. 2025.Item 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.Item Effect of trunk angle on lower limb joint moment in different strategies of sit-to-stand-to-sit motion with healthy subjects(Springer Science and Business Media Deutschland GmbH, 2025) Suman, S.K.; Verma, K.Patients with lower limb impairments often face sit-to-stand-to-sit motion challenges. The patients utilize a greater trunk flexion angle at seat-off time to mitigate knee moment. Alternative methods of STSTS motion strategies are required to study and understand the various patterns to guide physical rehabilitation programs in clinical practice. Four different STSTS strategies—Natural, Full Flexion, Pelvis-spine alignment, and Frame-Assisted—were experimented with twenty healthy subjects in a 3D motion capture lab, and inverse kinematics and dynamics methods were used for motion analysis in Visual 3D. At seat-off time in full flexion, the maximum trunk flexion angle is 58.77(± 17.92) degrees, duration is 1.63 s, 27% of the cycle, which reduces knee moment by -0.466(± 0.2) N.m/kg, increased hip moment by 0.67(± 0.312) N.m/kg, and ankle moment by 0.225(± 0.09) N.m/kg for the compensation. The compensatory movement also occurred while sitting down. Frame-assisted STSTS motion reduced knee moments without increases in hip and ankle moments at the maximum of trunk flexion angle while standing and sitting, and its motion patterns are similar to pelvis-spine alignment and natural strategies. These findings provide valuable insights for physiotherapists to predict the current stage of the patient for clinical assessment and guide in the design and development of medical devices. © International Federation for Medical and Biological Engineering 2025.