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Background:Athletes, especially female athletes, experience high rates of tibial bone stress injuries (BSIs). Knowledge of tibial loads during walking and running is needed to understand injury mechanisms and design safe running progression programs. Purpose:To examine tibial loads as a function of gait speed in male and female runners. Study Design:Controlled laboratory study. Methods:Kinematic and kinetic data were collected on 40 recreational runners (20 female, 20 male) during 4 instrumented gait speed conditions on a treadmill (walk, preferred run, slow run, fast run). Musculoskeletal modeling, using participant-specific magnetic resonance imaging and motion data, was used to estimate tibial stress. Peak tibial stress and stress-time impulse were analyzed using 2-factor multivariate analyses of variance (speed*sex) and post hoc comparisons (α = .05). Bone geometry and tibial forces and moments were examined. Results:Peak compression was influenced by speed ( P < .001); increasing speed generally increased tibial compression in both sexes. Women displayed greater increases in peak tension ( P = .001) and shear ( P < .001) than men when transitioning from walking to running. Further, women displayed greater peak tibial stress overall ( P < .001). Compressive and tensile stress-time impulse varied by speed ( P < .001) and sex ( P = .006); impulse was lower during running than walking and greater in women. A shear stress-time impulse interaction ( P < .001) indicated that women displayed greater impulse relative to men when changing from a walk to a run. Compared with men, women displayed smaller tibiae ( P < .001) and disproportionately lower tibial forces ( P≤ .001-.035). Conclusion:Peak tibial stress increased with gait speed, with a 2-fold increase in running relative to walking. Women displayed greater tibial stress than men and greater increases in stress when shifting from walking to running. Sex differences appear to be the result of smaller bone geometry in women and tibial forces that were not proportionately lower, given the womens’ smaller stature and lower mass relative to men. Clinical Relevance:These results may inform interventions to regulate running-related training loads and highlight a need to increase bone strength in women. Lower relative bone strength in women may contribute to a sex bias in tibial BSIs, and female runners may benefit from a slower progression when initiating a running program. 

Abstract Preventing bone stress injuries (BSI) requires a deep understanding of the condition’s underlying causes and risk factors. Subject-specific computer modeling studies of gait mechanics, including the effect of changes in running speed, stride length, and landing patterns on tibial stress injury formation can provide essential insights into BSI prevention. This study aimed to computationally examine the effect of different exercise protocols on tibial fatigue life in male and female runners during prolonged walking and running at three different speeds. To achieve these aims, we combined subject-specific magnetic resonance imaging (MRI), gait data, finite element analysis, and a fatigue life prediction algorithm, including repair and adaptation’s influence. The algorithm predicted a steep increase in the likelihood of developing a BSI within the first 40 days of activity. In five of the six subjects simulated, faster running speeds corresponded with higher tibial strains and higher probability of failure. Our simulations also showed that female subjects had a higher mean peak probability of failure in all four gait conditions than the male subjects studied. The approach used in this study could lay the groundwork for studies in larger populations and patient-specific clinical tools and decision support systems to reduce BSIs in athletes, military personnel, and other active individuals. 

Abstract Women frequently feel alienated in science, technology, engineering, and mathematics (STEM) environments due to gender biases, ultimately leading them to feel less competent or leave the field altogether. This study utilizes personal statements from a subset of participants from a National Science Foundation (NSF) funded Research Experiences for Undergraduates (REU) Site: Biomedical Engineering in Simulations, Imaging, and Modeling (BME-SIM) to investigate how confidence is shown by participants and how confidence is perceived by faculty reviewers in personal statements. This study compares feedback from faculty reviewers to perceived and self-reported confidence using lexical (i.e., word choices and use) and syntactic (i.e., structures of language segments such as sentences, phrases, and organization of words) features of these personal statements. Women received more negative feedback related to confidence compared to their male counterparts, notably in relation to modesty. Few differences were found between writing styles of genders in their pre- and post-program statements. Overall, writing styles did not seem to correlate with the genders' perceived or self-reported confidence; however, perception of confidence suggested a relationship between genders' pre- and post-program statements when examined by noun and adjective variation. A similar relationship was found between self-reported confidence and noun variation in men and women participants. Findings suggest that writing style perceptions and practices may be influenced by gender norms; however, without looking at the specific diction and content of personal statements, these conclusions cannot be fully established. 

Abstract Undergraduate research continues to serve as an effective strategy for mitigating the effects of a leaky pipeline. Significant funding from institutions and government agencies has increased the number of students participating in undergraduate research. In this paper, we report on the six-year experience of a National Science Foundation funded Research Experiences for Undergraduates (REU) Site: Biomedical Engineering in Simulations, Imaging, and Modeling (BME-SIM). The operation and evaluation of the program are both described. We report on the results from 55 students over six summers from 2014 to 2019. Our program was successful in attracting a diverse group of participants including 46% under-represented minority students and 53% women. Based on evaluation results, students reported significant gains in technical skills, communication skills, and knowledge of graduate school. Our findings indicate baseline gender differences for several learning outcomes, where women and nonbinary students report lower levels of mastery. These gaps are closed by the end of the program except for confidence in skills, which is still significantly lower than those reported by male counterparts. The impact of the experience on ultimate career path is difficult to determine due to underlying biases and other motivating factors; however, 67.6% of graduates have entered graduate programs. Finally, we have provided lessons learned for those who are interested in building a summer research program. In conclusion, we have described the successful implementation of an REU site and the positive learning outcomes of the student participants. 

Hydrogels have gained recent attention for biomedical applications because of their large water content, which imparts biocompatibility. However, their mechanical properties can be limiting. There has been significant recent interest in the strength and fracture toughness of hydrogel materials in addition to their stiffness and time-dependent behavior. Hydrogels can fail in a brittle manner, although they are extremely compliant. In this work, the failure and fracture of hydrogels are examined using a compression test of spherical hydrogel particles. Spheres of commercially available polyacrylamide–potassium polyacrylate were hydrated and tested to failure in compression as a function of loading rate. The spheres exhibited little relaxation when compressed to small fixed displacements. The distributions of strength values obtained were examined in a particle fracture framework previously used for brittle ceramics. There was loading rate dependence apparent in the measured peak force and calculated peak strength values, but the data fell on a single empirical distribution function of strength for the hydrogels regardless of loading rate. Strength values for these hydrogels were mostly in the range of 0.05–0.3 MPa, illustrating the challenges using hydrogels for mechanically demanding applications such as tissue engineering.