The use of uncemented stems in hip arthroplasty has been increasing, even in osteoporotic patients. The major concerns of uncemented hip-stems, however, are peri-prosthetic fracture, thigh pain, and proximal femoral stress-/strain-shielding. In this study, a novel design of uncemented hip-stem is proposed that will reduce such concerns, improve osseointegration, and benefit both osteoporotic and arthritic patients. The stem has a central titanium alloy core surrounded by a set of radial buttresses that are partly porous titanium, as is the stem tip. The aim of the study was to investigate the mechanical behaviour of the proposed partly-porous design, examining load transfer in the short-term, and comparing its strain-shielding behaviour with a solid metal implant. The long-term effect of implant-induced bone remodelling was also simulated. Computed tomography based three-dimensional finite element models of an intact proximal femur, and the same femur implanted with the proposed design, were developed. Peak hip contact and major muscle forces corresponding to level-walking and stair climbing were applied. The proposed partly-porous design had approximately 50% lower strain-shielding than the solid-metal counterpart. Results of bone remodelling simulation indicated that only 16% of the total bone volume is subjected to reduction of bone density. Strain concentrations were observed in the bone around the stem-tip for both solid and porous implants; however, it was less prominent for the porous design. Lower strain-shielding and reduced bone resorption are advantageous for long-term fixation, and the reduced strain concentration around the stem-tip indicates a lower risk of peri-prosthetic fracture.

In this letter, an adaptive trajectory synchronization controller is developed that synchronizes the robot joint trajectory to the human joint trajectory in the presence of communication time delay and uncertainty in robot model parameters including nonlinear-in-parameter friction term. The controller synchronizes to the human trajectory by accounting for time delays that arise in human-robot collaboration tasks such as, estimating the human trajectory using image processing, or sensor fusion for trajectory intent estimation, or computational limitations. The developed adaptive time-delayed synchronization controller utilizes a new integral concurrent learning (ICL)-based parameter update law for Neural Network parameter estimation. Uniformly ultimately bounded stability of the synchronization and parameter estimation errors are proved using a Lyapunov-Krasovskii functional analysis. Results of the Monte Carlo simulations are presented to validate the performance of the proposed synchronization controller using a human-robot synchronization example.

In this paper, a data-driven modeling and control framework is developed for task space control of a soft robot gripper which consists of four individual soft fingers. Each of the four fingers is modeled as a manipulator with high degrees of freedom. The corresponding task space dynamics of the manipulator are derived using a rigid-link approximation of the continuum manipulator. A neural network approach is used to learn the derived dynamics in State Dependent Coefficient (SDC) form. Using the learned SDC matrices, an asymptotically stable optimal closed-loop tracking controller which is based on solving the State Dependent Riccati Equation (SDRE) is derived. The model learning and trajectory tracking controller is implemented on an open source Soft Motion (SoMo) platform simulating the soft gripper motion and corresponding tracking results are presented.

Joint replacements are prevalent surgical procedures performed for treating various skeletal disorders and injuries. In this procedure, the damaged part of the joints is replaced with an artificial design called an implant. Various biomaterials are commonly used in manufacturing orthopedic implants. "Ultra-high molecular weight polyethylene (UHMWPE)" has found extensive applications in various joint replacements as a bearing material at the articulating surface of the replaced joints. The overall clinical performance of polyethylene has been reported to be good; however, some concerns remain associated with its use. Wear particles generated from the polyethylene causes osteolysis, affecting the longevity of the implant. To improve its wear properties, polyethylene has undergone several development stages over the last five decades, including cross-linking and incorporation of vitamin E. In this article, a summary of the use of different grades of UHMWPE in various joint replacements is presented. Historical development of UHMWPEs and their state-of-the-art processing techniques are highlighted. The evaluation of both clinical and pre-clinical performances of UHMWPE used in major orthopedic implants, correlation of material properties with the failure mechanisms, and the limitations and the future scope of improvement of UHMWPE have been discussed.