Monitoring the biomechanical response of individual cells under compression: a new compression device.
ABSTRACT Skeletal muscle cells are sensitive to sustained compression, which can lead to the development of pressure sores. Although it is known that this type of tissue breakdown depends on the magnitude and duration of the applied load, the exact relationship between cell deformation and damage remains unclear. To gain more insight into this process, a method has been developed, that incorporates the use of a new loading device and confocal microscopy. The loading device is able to compress individual cells, either statically or dynamically, while measuring the resulting forces. Experiments can be performed under ideal environmental conditions, comparable with those of a CO2 incubator. First compression experiments on C2C12 mouse myoblasts showed the shape changes that cells undergo during static compression by the loading device. Calculations using the three-dimensional confocal images showed no change in volume and an increase in the surface area of the cell as a result of compression. The device presented here provides a useful way to monitor the biomechanical response of skeletal muscle cells during long-term compression experiments. Therefore it will contribute to the knowledge about strain-induced cell damage, as seen in pressure sores and other mechanically induced clinical conditions.
- SourceAvailable from: Ivana Pajić-Lijaković[Show abstract] [Hide abstract]
ABSTRACT: Abstract Various modeling approaches have been applied to describe the rearrangement of immobilized cell clusters within the extracellular matrix. The cell rearrangement has been related with the micro-environmental restrictions to cell growth. Herein, an attempt is made to discuss and connect various modeling approaches on various time scales which have been proposed in the literature in order to shed further light to this complex phenomenon which induces micro-environmental restrictions to cell growth. The rearrangement is driven by internal stress generated within the cluster. The internal stress represents a consequence of the matrix rheological response to cell expansion. The rearrangement includes the interplay between the processes of: (1) single and collective cell migrations, (2) cell deformation and orientation, (3) decrease of cell-to-cell separation distances and (4) cell growth. It has been considered on two time scales: a short time scale (i.e. the rearrangement time) and a long time scale (i.e. the growing time). The results indicate that short and long times cell rearrangement induces energy dissipation. The dissipation provokes biological responses of cells which cause the resistance effects to cell growth. Deeper insight in the anomalous nature of the energy dissipation would be useful for understanding the biological mechanisms which causes the resistance effects to cell growth.Critical Reviews in Biotechnology 03/2014; · 5.10 Impact Factor
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ABSTRACT: Cellular biology takes place inside confining spaces. For example, bacteria grow in crevices, red blood cells squeeze through capillaries, and chromosomes replicate inside the nucleus. Frequently, the extent of this confinement varies. Bacteria grow longer and divide, red blood cells move through smaller and smaller passages as they travel to capillary beds, and replication doubles the amount of DNA inside the nucleus. This increase in confinement, either due to a decrease in the available space or an increase in the amount of material contained in a constant volume, has the potential to squeeze and stress objects in ways that may lead to changes in morphology, dynamics, and ultimately biolog-ical function. Here, we describe a device developed to probe the interplay between confinement and the mechanical properties of cells and cellular structures, and forces that arise due to changes in a structure's state. In this system, the manipulation of a magnetic bead exerts a compressive force upon a target contained in the confining space of a microfluidic channel. This magnetic force microfluidic piston is constructed in such a way that we can measure (a) target compliance and changes in com-pliance as induced by changes in buffer, extract, or biochemical composition, (b) target expansion force generated by changes in the same parameters, and (c) the effects of compression stress on a target's structure and function. Beyond these issues, our system has general applicability to a vari-ety of questions requiring the combination of mechanical forces, confinement, and optical imaging. © 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4864085]Review of Scientific Instruments 02/2014; 8515(85):2370440-23704. · 1.60 Impact Factor
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ABSTRACT: Deep tissue injury (DTI) is a type of pressure ulcer in which tissue breakdown initiates at the bone-muscle interface under intact skin. Excessive deformation in the soft tissue, particularly around bony prominences, is believed to be one of the causes leading to the development of DTI. The main goal of this study was to measure the magnitude and distribution of strains within muscles surrounding the ischial tuberosities, induced by levels of external loading that encompass the range of loading experienced by the soft tissue in seated individuals. The experiments were conducted in adult pigs with intact spinal cords (n = 5) and pigs with partial spinal cord injury (SCI) (n = 2), one of which also had a DTI. A secondary goal was to obtain a preliminary assessment regarding the capacity of intermittent electrical stimulation (IES), an intervention for preventing the formation of DTI, to counteract the muscle compression caused by external loading. In intact animals, muscles subjected to external loads equivalent to 25% of body weight experienced maximal principal strains, minimal principal strains, and shear strains of 0.68, -0.3, and 0.4, respectively. These magnitudes increased by 91.9, 17.6, and 87.5%, respectively, when external loading increased to 50% body weight. Minimal to no further increases in strain magnitudes were seen with the 75% body weight loading level. In one animal with SCI and no DTI, strain magnitudes were on average 9.7% higher than those in the intact animals at the corresponding loading levels. The presence of a DTI in another animal with SCI reduced strain magnitudes by 28% compared to intact animals. The regions in the muscle that underwent the largest deformations were those between the ischial tuberosity and the external surface, and up to 2 cm ventral to the ischial tuberosity (furthest measured). Muscle contractions produced by IES increased the thickness of the tissue between the ischial tuberosities and skin during the period of stimulation by 10-20% for loading levels up to 75% of body weight in both intact and spinal cord injured pigs. This study provides the first measurements of strain around the ischial tuberosities in an animal model that resembles humans.Annals of Biomedical Engineering 03/2012; 40(8):1721-39. · 3.23 Impact Factor