Wrinkling of thin films and membranes can occur due to various mechanisms such as growth and/or mismatch between the mechanical properties of the film and substrate. However, the physical origins of dynamic wrinkling in soft membranes are still not fully understood. Here we use milk skin as a tractable experimental system to investigate the physics of wrinkle formation in a thin, poroelastic film. Upon heating milk, a micron-thick hydrogel of denatured proteins and fat globules forms at the air-water interface. Over time, we observe an increase in the total length of wrinkles. By confocal imaging and profilometry, we determine that the composition and thickness of the milk skin appears to be homogeneous over the length scale of the wrinkles, excluding differences in milk skin composition as a major contributor to wrinkling. To explain the physical origins of wrinkle growth, we describe theory that considers the milk skin as a thin, poroelastic film where pressure is generated by the evaporative-driven flow of solvent across the film; this imparts in-plane stresses in the milk skin, which cause wrinkling. Viscous effects can explain the time-dependent growth of wrinkles. Our theoretical predictions of the effects of relative humidity on the total length of wrinkles over time are consistent with our experimental results. Our findings provide insight into the physics of the common phenomenon of milk skin wrinkling, and identify hydration gradients as another physical mechanism that can drive morphological instabilities in soft matter.
IntroductionPrevious studies have claimed gap year clinical experiences before medical school matriculation increase student self-efficacy and clinical confidence. At the University of Central Florida College of Medicine, 41 first-year medical students participated in a new certification course to become emergency medical responders before beginning their coursework. This study describes the results of a follow-up study that aims to investigate the impact the course had on student competency, self-efficacy, and clinical efficacy and if the course would prepare students similarly to previous clinical experience. MethodsFirst-year medical students completed a 30-question survey consisting of a Likert scale and free-response questions. Questions were based on the Accreditation Council for Graduate Medical Education core competencies: medical knowledge, practice-based learning and improvement, systems-based practice, patient care, professionalism, and interpersonal and communication skills. Questions on the perceived benefit of the emergency medical responder course and previous clinical experiences were also included. Responses were separated based on participation in the emergency medical responder course and prior clinical experience. Two-tail Welch's t-tests were performed on the data to determine significance. ResultsOf 98 responses: 20.4% (20/98) of participants of the emergency medical responder course had previous clinical experience, 21.5% (21/98) of participants of the course had no clinical experience, 26.5% (26/98) did not participate in the course but had previous clinical experience, and 31.6% (31/98) did not participate in the course nor had previous clinical experience. Students with previous clinical experience reported the emergency medical responder course improved both their patient care skills and performance in courses that emphasized patient interviewing and physical exams. Students with clinical experience had significantly higher medical knowledge (p < 0.1) and professionalism (p < 0.1) Likert scores. Eighty-seven percent of students agreed the course had a positive impact on their patient care skills. ConclusionLarger sample size is needed to make stronger conclusions; however, the responses show the emergency medical responder course had a positive subjective impact on students with previous medical experience. Previous clinical experience leads to the most positive subjective reporting of competencies such as medical knowledge and professionalism. Early clinical exposure, such as an emergency medical responder certification course, may improve self-efficacy and patient care skills for medical students with no previous clinical experience.
Truong et al. This is an open access article distributed under the terms of the Creative Commons Attribution License CC-BY 4.0., which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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