Cytomechanics 432/532

1. Cytomechanics432/532 • Tuesday, January 18, 2005: Introduction • WebCT syllabus, book, resources, posting. • Office : BME 124 Weds, Thurs: 1-4 PM • Grading: HW + Exams + Project • Craelius@rci

2. Learning objectives • 1. To learn the structural/mechanical components of cells, specifically: biophysics and material properties of the cytoskeleton (CSK), membrane, and matrix. • 2. To learn about experimental tools for evaluating cell mechanical properties, specifically: mechanical testing, imaging with immunocytochemisty and knock-out methods.

3. Learning Objectives • 3. To learn kinematics and dynamics of cells, specifically, interactions among CSK, cytosol, matrix, and nucleus, mechanotransduction, and motility • 4. To learn statistical mechanics of cell polymers and CSK assembly. • 5. To learn tools for modelling cell mechanics, specifically simulations with matlab and simulink.

4. Topics in Cytomechanics • A cell is a “cytoplasmic structural element.” • Tensegrity holds it together -’centripetally.’ • Structural components include lipids, and 3 separate filament systems. • No cell is an island- interactions with others and the ECM shape and regulate it. • Trans-skeletal molecules regulate the cell. • Rxns in solid-state versus enzyme solution.

5. Questions • How do cells • maintain and change shape? • Move? • Grow and maintain a size? • Anchor to substrate or stick together or not? • Transport materials inside? • Form tissues? • Sense force and deformation?

6. Medical Stress-Growth Hypothesis Mechanoelectrical Feedback Tumor-Endothelium Wound Healing Edema Bone & Cartilage Control Cellular signalling Technological Gas structural elements Motility of Gels Microtubular nanostructures Bioprocess optimization Plant Growth & Production Microgravity Effects Applications of Cytomechanics?

7. How are cells put together? Not nice and regular Varied and irregular 200 different types

8. The generic cell

10. Tension + compression hold the cell together Green fluorescent dye for Actin

11. Basic Cell Components • A membrane, skeleton, and internal structures. • All serve both as structural and functional elements. • Simplified basic building blocks

12. Geodesic- Buckminster Fuller A geodesic dome uses a pattern of self-bracing triangles in a pattern that gives maximum structural advantage, thus theoretically using the least material possible. (A "geodesic" line on a sphere is the shortest distance between any two points.)

13. Stick Geodesic Domes : Ingber

14. Tensegrity structures • Body stands upright by compression due to gravity counteracted by tension from muscles • Same for bridges and many other structures.

15. 100 nM Tensegrity Neurofilaments Cross-linked In frog axon Spectrin In RBC

16. the CSK: smart design • orienting along stress lines, filaments size themselves according to strength requirements: a conservative architectural practice. Thin supporting struts connecting thick beams

17. Underneath the hood • Lipid shell • Actin network • Cytosol • Filaments • Organelles • Nucleus

18. Lipid vesicles are ghost-like • pipets suck up the vesicles • Miscibility allows intermingling

19. Plasma membrane • Lipid bilayer 30 A° • Dielectric - capacitor • Amphiphile • Semi-permeable • No tensile but some shear strength

20. The cytoskeleton Decorated actin

21. Tensegrity Malines, Belgium Fibroblast

22. Major Filaments • Filaments: • Actin : 8 nM • Intermediate 10nM • Microtubules:25 nM

23. 3 types of filaments

24. Cellular Rods and Ropes

25. Filaments have different functions Spectrin bends Microtubules are stiff

26. Cell Crawling

28. Visualizing actin-myosin motion

29. Types of motors

30. How does the CSK provide structure? Signals travel at speed of sound. Some results are not compatible with tensegrity model

31. Structure by light & immunofluorescence PMT

32. Fibroblasts are stained with Phallacidin green for F actin, Texas red for microtubules, and DAPI for nucleic acid. F actin microtubules

33. F actin is green with Phalloidin, G actin is red with Texas red. Nucleus has fewer stress fibers, but is thicker than rest of cell, so red is diffuse. F actin G actin

34. Fibroblast dividing

35. Cells are Wiggly and Soft New ways to describe softness- difference between cooked and uncooked noodles. thermal fluctuations Of lipid vesicle:

36. Types of Loading

37. 50% Swelling and Lysis to measure membrane strength • RBCs 3% Muscle Frog

39. Pipet Aspiration Neutrophils are WBCs involved in immune response. The source of cortical tension is unknown, but may be from actin tangential to surface.

40. Unwinding of rubber Rubber Elasticity s 1 mm e Collagen

41. Stress-strain varieties liquid s J Curve Rubber unwinding e

42. Micropipette Solutes

43. Elasticity and safety at high strains Mesangial cell area expansivity Rubber-like

44. Common Quantities in Cytomechanics

45. Where we are going • Feedback Regulation: Bioelectricity- eg. Heart, bone, cartilage • Optics of cytoskeleton; immunofluoresc. • Micromotors; Gels; piezo- & ferro-electric • Cell shape regulation, eg. Edema, tumors • Tissue morphogenesis; osseointegration • Endothelial regulation • Wound healing

46. Common quantities

48. The cytoskeleton is both internal and external

49. Fibroblast-myocyte interactions Fibroblasts Myocytes

50. Growth patterns vary in myocytes