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First published online 18 May 2004
doi: 10.1242/jcs.01119

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Dynamic changes in traction forces with DC electric field in osteoblast-like cells

¹ Department of Experimental Orthopedics and Biomechanics, Philipps-University Marburg, Baldingerstr., 35033 Marburg, Germany
² Department of Biomedical Engineering, Boston University, 44 Cummington Street, Boston, MA 02215, USA

View larger version (20K): [in a new window]   Fig. 1. The leading edge of a Mg63 cell on a polyacrylamide substrate (YM=4320 N/m2). Total traction force in rest (A) and after 30 seconds of electric-field application (B). Differential vectors for the change between A and B are displayed in C. The scale bar represents 10 µm. The scale vector represents 300 N/m2 for A and B and 20 N/m2 for C.

View larger version (93K): [in a new window]   Fig. 2. Phase-contrast light micrographs showing the alignment processes of osteoblasts. Cells were subjected to 10 V/cm for 80 minutes. A, cells resting; B, after 30 minutes; C, 60 minutes; D, 100 minutes; E, 150 minutes; and F, 180 minutes of exposure. Signs (+/–) show the polarity of the field.

View larger version (26K): [in a new window]   Fig. 3. (A) The x dimension (along the electric field lines) of a bounding box around every cell as a function of the length of time of electric field application at 10 V/cm. (B) The y dimension (perpendicular to the electric field) of the bounding boxes as in Fig. 3 around every cell as a function of the length of time of electric field application. (C) Ratio (x/y) of both sides of the bounding boxes from Fig. 3 and Fig. 4. (D) Ratio (x/y) as in Fig. 5, but for all cells from 12 independent experiments with an electric field of 10 V/cm.

View larger version (17K): [in a new window]   Fig. 4. The strength of the electric field applied to primary osteoblasts was altered. Time taken for cellular elongation, a clear noticeable orientation and the maximal time under electric-field exposure for cellular re-spreading is shown.

View larger version (13K): [in a new window]   Fig. 5. (A) Voltage is correlated to the time for the visible retraction. The graph shows results for 12, 15, 18 and 20 V/cm. (B) Change in average traction force for 15 cells within 300 seconds (A) and for 15 cells under the influence of a 10-V/cm electric field (B). Forces are in N/m2; error bars show the s.e.m.

View larger version (44K): [in a new window]   Fig. 6. Differential traction forces visualized in pseudocolor according to the intensity and the force vectors in N/m2. Traction force changes after an application of a 10-V/cm electric field for 30 seconds on a substrate with a stiffness of 4317 N/m2 compared to the cell in rest before application are shown. Total traction force is not shown. The vectors show almost the same orientation as the electric field, where +/– labeled scale vectors indicate orientation of the electric field. Scale bar represents 10 µm; scale vector represents 50 N/m2. Increased inward-pointing traction forces with same orientation as the electric field appear at margins facing the poles.

View larger version (40K): [in a new window]   Fig. 7. Differential traction forces during cellular alignment as a result of a 10-V/cm electric field in a primary bovine osteoblast on a substrate with a stiffness of 6000 N/m2. +/– labeled scale vectors indicate orientation of the electric field. A, the phase of increasing force. After 5 minutes (E and F) the loss of the normally inward-pulling traction forces occur at sides where the cell will start to elongate a few minutes later (d and e). The bar scale represents 10 µm; the scale vector represents 10 N/m2. Retraction between E and F is visible at area labeled a and b.

View larger version (44K): [in a new window]   Fig. 8. Differential traction forces during cellular alignment in a 10-V/cm electric field in a MG63 cell on a substrate with a stiffness of 4000 N/m2. +/– labeled scale vectors indicate orientation of the electric field. Tractions increase in some cellular regions up to the 300th second. Scale bar represents 10 µm; scale vector represents 10 N/m2 for A to E and 50 N/m2 for F.

View larger version (37K): [in a new window]   Fig. 9. Screen shot showing intracellular free-calcium measurement of 6 cells (A-F) exposed to a 10-V/cm electric field. The field was applied at 25.76 seconds (first bar). Times for the onset of calcium rise were 34 seconds for A, 61 seconds for B, 37 seconds for C, 196 seconds for D, 65 seconds for E and 76 seconds for F.