7 results found
Leopold E, Sopher R, Gefen A, 2011, The effect of compressive deformations on the rate of build-up of oxygen in isolated skeletal muscle cells., Med Eng Phys, Vol: 33, Pages: 1072-1078
In this study we integrated between confocal-based cell-specific finite element (FE) modeling and Virtual Cell (VC) transport simulations in order to determine trends of relationship between externally applied compressive deformations and build-up rates of oxygen in myoblast cells, and to further test how mild culture temperature drops (~3°C) might affect such trends. Geometries of two different cells were used, and each FE cell model was computationally subjected to large compressive deformations. Build-up of oxygen concentrations within the deformed cell shapes over time were calculated using the VC software. We found that the build-up of oxygen in the cells was slightly but consistently hindered when compressive cell deformations were applied. Temperature drops characteristic to ischemic conditions further hinder the oxygen built-up in cells. In a real-world condition, a combination of the deformation and temperature factors should be anticipated, and their combined effect might substantially impair cell respiration functions.
Sopher R, Nixon J, McGinnis E, et al., 2011, The influence of foot posture, support stiffness, heel pad loading and tissue mechanical properties on biomechanical factors associated with a risk of heel ulceration., J Mech Behav Biomed Mater, Vol: 4, Pages: 572-582
Heel ulcers (HU) are the second most common type of pressure ulcers. In this work, we developed the first anatomically-realistic three-dimensional finite element model of the posterior heel for studying the risk for HU in bedridden patients. We specifically simulated a heel that is resting on supports with different stiffnesses at upright and inclined foot postures. Our objective was to examine the effects of foot posture and stiffness of the support on strains and stresses within the fat pad of the resting heel. We found that strains and stresses in the fat pad of the heel are considerably reduced when the foot is positioned so that its lateral aspect is at 90° with respect to the horizon compared to an abducted (60°) foot posture. The study therefore indicates that theoretically, an inclined foot posture puts a bedridden patient at a higher risk for HU with respect to an upright foot posture, which may be explained by the anatomy of the heel that faces a lower curvature and better cushioned region against the support when the foot is upright.
Sopher R, Nixon J, Gorecki C, et al., 2011, Effects of intramuscular fat infiltration, scarring, and spasticity on the risk for sitting-acquired deep tissue injury in spinal cord injury patients., J Biomech Eng, Vol: 133
Sitting-acquired deep tissue injury (DTI) is a severe form of pressure ulcer (PU) often affecting patients with spinal cord injury (SCI) who also tend to suffer from intramuscular fat infiltration, soft tissue scarring (due to previous PU), and/or muscle spasticity in their buttocks. We previously used finite element (FE) modeling to evaluate whether abnormal bodyweight is a risk factor for sitting-acquired DTI. Here we hypothesize that fat infiltration, scarring, or spasms increase internal loads in the gluteus muscles in the vicinity of the ischial tuberosities during sitting, which consequently put SCI patients with these conditions at a higher risk for DTI. Our objective was to determine changes in gluteal strains and stresses and tissue volumes exposed to elevated strains/stresses associated with these factors. Thirty-five FE models of coronal slices through the seated buttocks, simulating these conditions at different severities, were developed. We calculated peak strains and stresses in glutei and percentage volumes of muscle tissue exposed to above-critical strains/stresses (compression strain≥50%, compression/von Mises stress≥2 kPa, and strain energy density≥0.5 kPa). Progressive intramuscular fat infiltration increased all the aforementioned outcome measures. Increase in size of scar patterns that were contained in both muscle and fat tissues similarly elevated the outcome measures. Spasms increased muscle stresses and volumetric exposures to stress, but tissue volumes at risk were ∼1-2% and increases due to spasticity were slight. We conclude that the above potential risk factors can be listed according to the following order of importance: (i) fat infiltration, (ii) scars contained in both muscle and fat tissues, and (iii) spasms. This information should be considered when prioritizing prevention means and resources for patients with SCI.
Sopher R, Gefen A, 2011, Effects of skin wrinkles, age and wetness on mechanical loads in the stratum corneum as related to skin lesions., Med Biol Eng Comput, Vol: 49, Pages: 97-105
Finite element models of skin were developed to determine the effects of wetness, age, and wrinkles on mechanical strains and stresses in the stratum corneum (SC) as related to skin lesions. We modeled two geometries, young (0.12-mm-deep wrinkles) and aged (0.18-mm-deep wrinkles), and for each geometry, three loading conditions were applied (compression in a dry environment, compression and shear in dryness, and compression with shear in wetness). Effects of skin wrinkling were studied independently or while coupled with age-related mechanical property changes. For each simulation, we calculated the peak maximal shear strain and stress in the SC, peak shear stress on the skin surface, and volumetric exposure of the SC to potentially injurious shear stresses (<70 kPa). Compression and shear with wetness produced the highest skin surface loads. Volumetric exposure of aged skin to potentially injurious shear stresses was six times greater than in the young skin for these conditions. Deeper wrinkles caused elevated loads in the SC consistently for all outcome measures and independently of the age factor. Thinning and/or stiffening the SC increased both the surface and internal SC stresses. Our findings indicate that theoretically, wetness, skin aging, and/or skin wrinkling are all risk factors for skin lesions such as superficial pressure ulcers.
Or-Tzadikario S, Sopher R, Gefen A, 2010, Quantitative monitoring of lipid accumulation over time in cultured adipocytes as function of culture conditions: toward controlled adipose tissue engineering., Tissue Eng Part C Methods, Vol: 16, Pages: 1167-1181
Adipose tissue engineering is investigated for native fat substitutes and wound healing model systems. Research and clinical applications of bioartificial fat require a quantitative and objective method to continuously measure adipogenesis in living cultures as opposed to currently used culture-destructive techniques that stain lipid droplet (LD) accumulation. To allow standardization, automatic quantification of LD size is further needed, but currently LD size is measured mostly manually. We developed an image processing-based method that does not require staining to monitor adipose cell maturation in vitro nondestructively using optical micrographs taken consecutively during culturing. We employed our method to monitor LD accumulation in 3T3-L1 and mesenchymal stem cells over 37 days. For each cell type, percentage of lipid area, number of droplets per cell, and droplet diameter were obtained every 2-3 days. In 3T3-L1 cultures, high insulin concentration (10 microg/mL) yielded a significantly different (p < 0.01) time course of all three outcome measures. In mesenchymal stem cell cultures, high fetal bovine serum concentration (12.5%) produced significantly more lipid area (p < 0.01). Our method was able to successfully characterize time courses and extents of adipogenesis and is useful for a wide range of applications testing the effects of biochemical, mechanical, and thermal stimulations in tissue engineering of bioartificial fat constructs.
Nottbohm CT, Sopher R, Heilemann M, et al., 2010, Fluorescently labeled 1 nm thin nanomembranes., J Biotechnol, Vol: 149, Pages: 267-271
Fluorescent labeling of self-assembled monolayers (SAMs) has a great potential for chemical and biotechnological sensing. However, its use is limited by the quenching of the fluorescence in the proximity of the conducting substrates. We show that this quenching can be overcome by the labeling of a cross-linked aromatic SAM (nanosheet) and its subsequent transfer onto a non-conducting substrate. We demonstrate the successful labeling of nanosheets with a fluorophore (tetramethylrhodamine) and its subsequent transfer to oxidized silicon, where they are detected by optical as well as fluorescence microscopy. Fluorescently labeled freestanding nanosheets, i.e. nanomembranes were obtained by a similar transfer of the nanosheets to TEM grids.
Sopher R, Nixon J, Gorecki C, et al., 2010, Exposure to internal muscle tissue loads under the ischial tuberosities during sitting is elevated at abnormally high or low body mass indices., J Biomech, Vol: 43, Pages: 280-286
Deep tissue injury (DTI) is a severe pressure ulcer characteristic of chairfast or bedfast individuals, such as those with impaired mobility or neurological disorders. A DTI differs from superficial pressure ulcers in that the onset of DTI occurs under intact skin, in skeletal muscle tissue overlying bony prominences, and progression of the wound continues subcutaneously until skin breakdown. Due to the nature of this silently progressing wound, it is highly important to screen potentially susceptible individuals for their risk of developing a DTI. Abnormally low and high values of the body mass index (BMI) have been proposed to be associated with pressure ulcers, but a clear mechanism is lacking. We hypothesize that during sitting, exposure to internal muscle tissue loads under the ischial tuberosities (IT) is elevated at abnormally high or low body mass indices. Our aims in this study were: (a) to develop biomechanical models of the IT region in the buttocks that represent an individual who is gaining or losing weight drastically. (b) To determine changes in internal tissue load measures: principal compression strain, strain energy density (SED), principal compression stress and von Mises stress versus the BMI. (c) To determine percentage volumes of muscle tissue exposed to critical levels of the above load measures, which were defined based on our previous animal and tissue engineered model experiments: strain>or=50%, stress>or=2 kPa, SED>or=0.5 kPa. A set of 21 finite element models, which represented the same individual, but with different BMI values within the normal range, above it and below it, was solved for the outcome measures listed above. The models had the same IT shape, size, distance between the IT, and (non-linear) mechanical properties for all soft tissues, but different thicknesses of gluteus muscles and fat tissue layers, corresponding to the BMI level. The resulted data indicated a trend of progressive increase in internal tissue loadin
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