Journal of Biomechanical Engineering-Transactions of the Asme最新文献

Robot-assisted gait rehabilitation is an increasingly common therapeutic intervention for enhancing locomotion and improving quality of life for children with lower-limb mobility impairments. However, there are few systems specifically designed for pediatric use, and those that do exist are largely cumbersome, bulky and non-custom devices that ultimately reduce therapy effectiveness. This paper introduces the Cable-Driven Joint System (CDJS), a novel approach for pediatric gait rehabilitation that addresses these shortcomings in a lightweight and compact robotic device using the patient's fitted orthosis. The CDJS consists of a 2.1 kg actuation unit that is held by a clinician which delivers assistive torques through a Bowden cable transmission to a 0.3 kg joint mounted to user-custom bracing. This work details an actuator benchtop evaluation, demonstrating a peak torque of 20 Nm, peak velocity of 7.2 rad/s, bandwidth of 9.7 Hz and a mass moment of inertia of 58.38 kg·cm2. An actuator model was developed and evaluated in simulation, showing a strong correlation with experimental torque data (R-squared = 0.95) and indicating a transmission efficiency of 72%. In-air gait tracking experiments on an emulated subject showed that the CDJS assisted the subject to track a nominal knee trajectory with an average root mean squared error of 2.56° at a continuous torque of 1.37 Nm. These results suggest that the cable-driven actuator meets the design requirements for pediatric gait rehabilitation and is ready for clinical device trials.

Breast reconstruction using tissue expanders is the primary treatment option following mastectomy. Although skin growth in response to chronic supra-physiological stretch is well-established, individual patient factors such as breast shape, volume, skin pre-strain, and mechanical properties, create unique deformation and growth patterns. The inability to predict skin growth and deformation prior to treatment often leads to complications and suboptimal aesthetic outcomes. Personalized predictive simulations offer a promising solution to these challenges. We present a pipeline for predictive computational models of skin growth in tissue expansion. At the start of treatment, we collect 3D photos and create an initial finite element (FE) model. Our framework accounts for uncertainties in treatment protocols, mechanical properties, and biological parameters. These uncertainties are informed by surgeon input, existing literature on mechanical properties, and prior research on porcine models for biological parameters. By collecting 3D photos longitudinally during treatment, and integrating the data through a Bayesian framework, we can systematically reduce uncertainty in the predictions. Calibrated personalized models are sampled using Monte Carlo methods, which require thousands of model evaluations. To overcome the computational limitations of directly evaluating the FE model, we use Gaussian process surrogate models. We anticipate that this pipeline can be used to guide patient treatment in the near future.

Ultrasonically assisted cutting (UAC), a process characterized by high-performance material removal and enhanced surface finish, is widely employed in orthopedic surgery. However, variability in the mechanical properties of cortical bone may lead to unstable fractures and fluctuating cutting force during material removal, particularly under high-frequency vibration cutting. This study introduces a transient shear strength model that utilizes strain rate fluctuations to estimate cutting forces in the UAC process. The impact of varying osteon orientations and strain rate ranges on the yield strength of cortical bone are analyzed to elucidate changes in its mechanical properties under UAC conditions. Additionally, strain rates from conventional cutting (CC) and UAC, measured through digital image correlation (DIC), are compared with model predictions. The results demonstrate that the proposed model accurately predicts cutting forces and associated changes in thrust. This research offers a fresh insight into the dynamics of fluctuating forces during UAC, potentially inspiring advancements in orthopedic surgical instruments.

High Tibial Osteotomy is a common procedure for knee osteoarthritis during which the surgeon opens the tibia and must stop impacting when cortical bone is reached by the osteotome. Surgeons rely on proprioception and fluoroscopy to conduct the surgery. Our group has developed an instrumented hammer to assess the mechanical properties of the material surrounding the osteotome tip. The aim of this study is to determine whether this hammer can be used to detect the transition from cortical to trabecular bone. Osteotomies were performed until rupture in pig tibia using the instrumented hammer. An algorithm was developed to detect both transitions based on the relative variation of an indicator derived from the time variation of the force. The detection by the algorithm of both transitions was compared with the position of the osteotome measured with a video camera and with surgeon proprioception. The difference between the detection of the video and the algorithm (respectively the video and the surgeon; the surgeon and the algorithm) is 1.0 ± 1.5 impacts (respectively 0.5 ± 0.6 impacts; 1.4 ± 1.8 impacts), for the detection of the transition from the cortical to trabecular bone. For the transition from the trabecular to cortical bone, the difference is 3.6 ± 2.6 impacts (respectively 3.9±2.4 impacts; 0.8 ± 0.9 impacts) and the detection by the algorithm was always done before the sample rupture. This ex vivo study demonstrates that this method could prevent impacts leading to hinge rupture.

The geometry and motility of the stomach play a critical role in the digestion of ingested liquid meals. Sleeve gastrectomy, a common type of bariatric surgery used to reduce the size of the stomach, significantly alters the stomach?s anatomy and motility, which impacts gastric emptying and digestion. In this study, we use an imaging data-based computational model, StomachSim, to investigate the consequences of sleeve gastrectomy. The pre-operative stomach anatomy was derived from imaging data and the post-sleeve gastrectomy shapes were generated for different resection volumes. We investigate the effect of sleeve sizes and motility patterns on gastric mixing and emptying. Simulations were conducted using an immersed-boundary flow solver, modeling a liquid meal to analyze changes in gastric content mixing and emptying rates. The results reveal that different degrees of volume reduction and impaired gastric motility have complex effects on stomach's mixing and emptying functions, which are important factors in gastric health of the patient. Specifically, the total gastric liquid emptying rates increased by 21% with a 30% volume reduction and by 51% with reductions exceeding 50%, due to altered intragastric pressure. Additionally, impaired motility functions resulted in slower mixing, leading to delayed food emptying. These findings provide insights into the biomechanical effects of sleeve gastrectomy on gastric digestion and emptying functions, highlighting the potential of computational models to inform surgical planning and post-operative management.

This paper presents a novel Hip Trajectory Error (HTE) framework for designing prosthetic feet specifically for people with an above-knee amputation. Finding a high-performance prosthetic foot for people with an above-knee amputation can greatly improve mobility and prosthesis satisfaction of a user and provide a predictable interaction with the knee prosthesis. The HTE framework accounts for the lack of early and mid-stance knee flexion, a common gait deviation in people with above-knee amputation compared to people with a below-knee amputation and able-bodied subjects. The goal of the HTE framework is to design prosthetic feet that closely replicate able-bodied hip motion, a kinematic target that is correlated with sufficient shock absorption lost due to the lack of knee flexion during early and mid-stance. This paper presents a design process to optimize HTE prosthetic feet and shows that the performance of the foot is not constrained by ankle height determined by the prosthetic knee choice. In simulation, HTE feet also demonstrate a closer replication of able-bodied hip motion compared to Lower Leg Trajectory Error framework, which designs prosthetic feet specifically for people with a below-knee amputation. The HTE framework may provide the above-knee amputee population around the world with high-performance prosthetic feet designed specifically for their needs, which could improve the overall function of the prosthetic limb and user satisfaction.

A systematic literature search and meta-analysis were performed to evaluate the variability in biomechanical testing of murine long bones, specifically focused on point-bending tests of mice femora. Due to the lack of standardized protocols for these tests, the assessment quantifies the heterogeneity in reported mechanical properties across existing literature. This study followed PRISMA and STROBE guidelines to search publicly available databases for relevant studies. After title and abstract screening, full-text reviews identified 73 articles meeting the inclusion criteria. Data were extracted from these studies, including stiffness, maximum load, modulus, and ultimate stress values for both 3-point and 4-point bending tests. The data were analyzed through ANOVA and meta-regression to assess variability caused by age, sex, and genetic strain. The reviewers also assessed the quality of the included studies. The meta-analysis revealed significant heterogeneity in reported mechanical properties, with I2 values ranging from 72% to 100% in the 3 point-bending test of pooled genetic strains. This heterogeneity persisted even after accounting for age, sex, and genetic strain differences. The review concludes that nonstandardized testing setups are the likely major source of the observed variability in reported data more than the population characteristics of the mice, highlighting the need for more consistent testing methodologies in future studies.

For single ventricle congenital heart patients, Fontan surgery is the final stage in a series of palliative procedures, bypassing the heart to enable passive flow of deoxygenated blood from the inferior vena cava (IVC) to the pulmonary arteries. This circulation leads to severely elevated central venous pressure, diminished cardiac output, and thus numerous sequelae and high mortality rates. To address these issues, we propose a bioprinted pulsatile conduit providing a secondary power source for Fontan circulation. A multiphysics computational framework was developed to predict conduit performance and provide design guidance prior to printing. Physics components included electrophysiology, cardiomyocyte contractility, and fluid-structure interaction coupled to a closed-loop lumped parameter network representing Fontan physiology. A range of myocardial contractility values was considered and simulated. The initial conduit design with adult ventricular cardiomyocyte contractility values coupled to a Purkinje network demonstrated potential to reduce liver (IVC) pressure from 16.4 to 9.3 mmHg and increase cardiac output by 29%. After systematically assessing the impacts of contraction duration, fiber direction, and valve placement on conduit performance, we identified a favorable design that successfully reduces liver pressure to 7.3 mmHg and increases cardiac output by 38%, almost normalizing adverse hemodynamics in the lower venous circulation. Valves at the input and output of the conduit are essential to achieve these satisfactory results; without valves, performance is degraded. However, a potential drawback of the design is the elevation of superior vena cava (SVC) pressure, which varies linearly with liver pressure reduction.

Multiscale coupling between cell scale biology and tissue-scale mechanics is a promising approach for modeling disease growth. In such models, tissue-level growth and remodeling (G&R) is driven by cell-level signaling pathways and systems biology models, where each model operates at different scales. Herein, we generate multiscale G&R models to capture the associated multiscale connections. At the cell-scale, we consider systems biology models in the form of systems of ordinary differential equations (ODEs) and partial differential equations (PDEs) representing the reactions between the biochemicals causing the growth based on mass-action or logic-based Hill-type kinetics. At the tissue-scale, we employ kinematic growth in continuum frameworks. Two illustrative test problems (a tissue graft and aneurysm growth) are examined with various chemical signaling networks, boundary conditions, and mechano-chemical coupling strategies. We extend two open-source software frameworks - FEBio and FEniCS - to disseminate examples of multiscale growth and remodeling simulations. One-way and two-way coupling between the systems biology and the growth models are compared and the effect of biochemical diffusivity and ODE vs. PDE based systems biology modeling on the G&R results are studied. The results show that growth patterns emerge from reactions between biochemicals, the choice between ODEs and PDEs systems biology modeling, and the coupling strategy. Cross-verification confirms that results for FEBio and FEniCS are nearly identical. We hope that these open-source tools will support reproducibility and education within the biomechanics community.

Multidirectional load transmission ability by Annulus Fibrosus (AF) require substantial mechanical stability. Additionally, AF exhibits a unique biochemical concentration gradient with outer AF (OA) dominated by type I collagen (COL-I) and inner AF dominated by type II collagen (COL-II) with higher water and proteoglycan concentration. This indicates an intricate relationship between biochemistry and mechanical stability, which remains unclear. This study uses molecular dynamics simulations to investigate the impact of water, COL-I and COL-II, concentration gradients on mechanical stability of AF's Collagen-Hyaluronan nanointerfaces during tensile and compressive deformation. For this, COL-HYL atomistic models are created by increasing COL-II concentrations from 0% to 75%, and water from 65% to 75%. Additional simulation is conducted by increasing water concentration of COL-I-HYL interface (0% COL-II) to 75% to segregate water concentration variation effects. Results show increasing water concentration to 75% results in marginal changes in local hydration indicating increase in bulk water. This enhances HYL and COL segment sliding - leading to reduction in mechanical stability in tension, indicated by drop in stress-strain characteristics. Additionally, increase in bulk water shifts load bearing characteristics towards water - leading to reduction in modulus from 3.7 GPa to 1.9 GPa. Conversely, increasing COL-II and water concentration facilitates stable water bridge formation which impede sliding in HYL and COL - enhancing mechanical stability. These water bridges improve compressive load sustenance leading to lower reduction in compressive modulus from 3.7 GPa to 2.8 GPa.