cell mechanobiology

• The direction of a quantum system becomes nearly uncorrelated when it is in a state known as the vacuum.
• Physical forces influence cell behaviour such as growth, differentiation, metabolism, secretion, movement and gene expression, and hence influence the function and architecture of all living tissues.
• The cell response to mechanical forces results in functional adaption, damage or pathologies.
• Tissues recognize forces which are then transmitted to cell level, for example growth of muscle tissue as response to exercise.
• Positive responses to mechanical forces include endothelium reorganisation, muscle adaption, bone remodelling.
• Negative responses to mechanical forces include atherosclerosis, hearing disorders, pressure ulcers, cardiac overload.
• Pressure ulcer: when person lies down or sits down for long time due to disability, constant pressure on certain area.
• Pressure is a mechanical cue for cells, leading to pressure ulcers which leads to further degeneration of tissue.
• Chronic hypertension (hemodynamic overload) induces increased cell volume, specific signal transduction pathways and altered gene expression in myocytes.
• Emery Dreyfuss muscle dystrophy is associated with abnormalities in nuclear organisation, which may result in decreased nuclear stiffness and strength and early nuclear damage.
• Pompe’s disease results in impaired force transmission in muscle fibers.
• Alterations in the mechanical properties of cells or the interactions between the cell and its environment may cause changes in cell and tissue behaviour and architecture eventually leading to functional adaption or pathological conditions.
• Mobility of cancer cells, survival of cells, treatment of mechanical diseases in skeletal and heart muscle, bone structure rearrangement, ciliar movement diseases, intracellular molecular transport, gene therapy are examples of applications of cell mechanics.
• The nucleus stores genetic information of cell and is a mechanical, physical entity within the cell.
• The nucleus can sense mechanical signals, transduce these mechanical signals to biochemical signals inside the cells, resulting in cell response and behaviour.
• The cell membrane is dynamic and the lipid bilayer has some kind of tension as it does not like to be stretched, with right underneath this layer is the actin cortex.
• Cells differ in many details according to function, evolution and environment, with over 200 cell types in humans.
• Nucleus deformability is limiting in cancer cell migration, it is too stiff.
• The nucleus is the stiffest component of the cell and underneath the nuclear envelope there is a scaffold called the nuclear lamina, which provides structural integrity for the nucleus.
• This governs cell blebbing: when a part of the cell cortex is damaged, then there is pressure difference between inside of cell and outside so that area bubbles up.
• The cell can recognize that there is a pressure difference and it can recognize that there is a part of the cell cortex that is damaged.
• The cell membrane exhibits inherent resistance to stretch but no inherent resistance for bending.
• The cell maintains its structure using a reinforced membrane strategy, with a thin layer of cytoskeleton called the actin cortex right underneath the cell membrane.
• The mechanical properties of the whole cell are dependent on what the whole cell is composed of, especially important for determining mechanics of cell: nucleus, cell membrane, cytoplasm, cytoskeleton.
• The nucleus senses mechanical signals and modulates the transcription machinery by changing chromosome positions, chromatin arrangements and transport of molecules across the nuclear membrane.
• The cell membrane physically separates the aqueous extracellular environment and the aqueous cytoplasm.
• The lipid bilayer on the cells are ruffled where a lot of lipid molecules are stored, serving as a reservoir of lipid molecules such that if necessary for a cell to expand in volume, the cell membrane does not get ruptured.
• The cell membrane is a lipid bilayer composed of fatty acids and phospholipids.
• Lipid molecules are mobile within the lipid bilayer, resulting in no inherent resistance to membrane bending.
• The natural SI unit for force at level of the cell is μN, nN or pN, depending on what you are looking at.
• The natural SI unit for length at level of the cell is μm.
• A higher viscosity indicates that a medium is thick flowing, a lower viscosity that it is thin flowing.
• Cytoplasm contains cytosol and the cytoskeleton, is something in between water and gel, and is viscoelastic.
• Over 8% of the human genome encodes for the cytoskeleton.
• If you heat up water and put spaghetti in, it changes from stiff to flexible, allowing particles to move around.
• Persistence length is a reliable measure to quantify how stiff something is.
• Intermediate filaments are skeletal proteins that are 7-11 nm in diameter.
• G’ is higher at low frequency when deformation is applied slowly, indicating that the material acts more as an elastic material.
• The natural SI unit for (protein) concentration micomolar
• Persistence length is used to describe the stiffness or flexibility of a rod.