42 answers to life, the universe, and everything

01 Even simple mechanics can give a lot of insight...
02 ... but different cell types can have totally different mechanical characteristics!
03 Most cells consist of a cytoskeleton and organelles embedded in a membrane.
04 And as always, energy minimization rulez...
05 ... but the free energy can consist of an energetic and an entropic contribution!
06 For jiggly filaments, the entropic term dominates the energetic term.
07 Biofilament entropy can be modeled by the statistics of long chain molecules.
08 Based on the chain shape uncorrelated or correlated chain models can be used.
09 Correlated chains can be characterized through the persistence length.
10 Polymerization governs the dynamic assembly and disassembly of filaments.
11 Cell movement is driven by filament assembly at the leading edge.
12 Treadmilling is the simultaneous growth and shrinkage at opposite filament ends.
13 Filament growth is limited by buckling when pushing the envelope.
14 The Euler buckling modes explain filopodia buckling and filament crosslinking.
15 The interaction with the environment lowers the critical buckling length.
16 Homogenization can relate subcellular and cellular mechanical properties.
17 The flexible membrane of red blood cells can be modeled as a spring network.
18 Six fold networks explain the rigidity of red blood cells, four fold networks don’t.
19 The cytoskeleton is made of microtubules, intermediate filaments and actin.
20 Cytoskeletal filaments possess a highly organized hierarchical mircostructure.
21 Tensegrity models view the cell as trusses tied together by pre-stressed ropes.
22 Lightweight engineering structures use tensegrity concepts similar to some cells.
23 Membrane phospholipids consist of hydrophilic heads and hydrophobic tails.
24 The lipid bilayer is the energetically favorable configuration of phospholipids.
25 The Law of Laplace can describe both soap bubbles and cell membranes.
26 Surface tension is important in thin membranes and in micropipette aspiration.
27 Depending on their stiffness, cells can act as elastic solid or liquid drop.
28 Structural elements display in plane tension and shear and out-of-plane bending.
29 The tension and shear equation is of 2nd order, the bending equation of 4th order.
30 Mechanotransduction is the conversion of forces into biochemical signals.
31 Its complex cascades of biochemical events are illustrated in funny figures.
32 To improve understanding, it is usually probed in tension, compression, or shear.
33 The cell membrane is selectively permeable.
34 Membrane transport is passive along and active against concentration gradients.
35 Cells consist mainly of water with charged sodium, potassium, and chloride ions.
36 At the resting state, cells are negatively charged.
37 At rest, concentration gradient and membrane potential are balanced.
38 Action potentials are responsible for an all-or-none response of excitable cells.
39 Pacemaker cells continuously re-excite themselves, muscle cells usually don’t.
40 Stem cells differentiate according to their mechanical environment.
41 Cell mechanics uses weird super large and super small units.
42 Cell mechanics still faces lots of exciting open problems that will be fun to solve!