Modeling Mechanical Stimulus

Intro Activity -(Outline Activity Once Determined) -(Questions, etc.)

Module Objectives Understand how cells respond to different types of mechanical signals. Calibrate a syringe pump to perform better analysis. Examine the effect of flow on a model scaffold. Compare simulated bone and vessel properties.

Stiffness -Stiffness is now much a material deforms when a force is applied. -Bone is very stiff -Ligaments are less stiff -Neural tissue has very little stiffness

Stresses -Stress is the amount of force in a unit area. -When an external force is applied to an object, it experiences internal stresses. -Plastic -Metal -CELLS

Normal Stresses -Normal stress result from forces that act through the center of an object. -Compression -Tension Picture Here

Shear Stresses -Shear stresses occur when forces are applied that are parallel to the surface of an object. -Fluid Flow Picture Here

Stresses and Cells -Muscles experience tension and compression during movement. -Bones develop to provide resistance to compressive forces. -Vessels experience shear as blood flows within them.

Tissue engineers are now looking to mimic the mechanical environment of a cell type to encourage growth.

Stiffness-Based Differentiation -Stem cells can differentiate based on matrix stiffness. -Neurons develop on a soft matrix. -Bone cells develop on a very rigid matrix. -(PICTURE?)

Strain-Based Differentiation -Muscle cells grow best when they alternate between tension and compression. -Bone growth is encouraged by uniform tensile strain. -Compression encourages chondrocyte growth, leading to increased cartilage in joints.

Shear-Based Differentiation -Shear stresses resulting from fluid flow encourage cellular activity. -Increased extracellular matrix formation. -Better cell proliferation on scaffolds.

Mechanical Signal Transduction -Though researchers have yet to determine how mechanical signals are transduced in the cell, proteins in the cytoskeleton have been shown to be important.

Activities 1.) Calibrating the syringe pump 2.) Measuring the effect of flow on ‘cellular growth’ 3.) Problems with scaffold wash out

Operating the Syringe Pump -Check the pump to make sure it is in working order. -Fill the syringe with the proper amount of water. -Attach the catheter to the syringe and centrifuge tube. -Place the syringe in the pump. -Apply weight to depress syringe. -Remove weight when fully depressed.

Activity 1 - Objectives -Familiarize operation of the gravity-powered syringe pump. -Determine the relation between weight and flow rate for the pump.

Activity 1 - Procedure -Time how long the syringe pump takes to depress weights of 2.5, 5, 7.5, 10, 12.5, and 15 pounds. -Calculate the average flow rate for each weight.

Activity 1 - Procedure -Create a calibration curve for the syringe pump. Sample Calibration Curve

Activity 2 - Objectives -Prepare scaffolds by adding ‘cell culture’ and ‘growth differentiation factor.’ -Test the effect of flow rate to see how much ‘flow- dependent growth factor’ is released for different ‘cell’ types. -Use the spectrophotometer to determine ‘growth factor’ concentration.

Activity 2 - Procedure -Prepare ‘scaffold’ by adding 5 mL ‘cell culture’ -Add 1 mL ‘differentiation growth factor’ -Run water through the scaffold after thirty seconds Diagram

Activity 2 - Procedure -Use a spectrophotometer to measure the concentration of ‘growth factor’ released -Compare the two ‘tissue’ types Diagram

Activity 3 - Objectives -Understand the hazards of excessive flow in tissue engineering. -Count ‘cells’ that are washed away from a scaffold at various flow rates.

Activity 3 - Procedure -Students will create ‘cells by adding ‘cell culture’ to ‘growth factor.’ Visualize process here

Activity 3 - Procedure -Populate the scaffold -Flow water through the system. -Count the number of cells washed out. -Repeat the procedure ad different flow rates. Diagram