CELL BIOMECHANICS

Cell Biomechanics

Cell Biomechanics

25µM

100µM

250µM

1000µM

PBS µM

Water µM

1

45

40

28

30

29

54

Diameter

2

43

40

27

34

24

40

3

39

38

22

31

25

50

4

41

40

22

25

25

55

5

43

32

27

25

26

53

6

40

38

26

25

28

55

7

48

34

20

27

30

43

8

47

37

22

19

27

51

9

38

38

31

25

30

55

10

43

42

34

22

25

43

Averagre

42.7

37.9

25.9

26.3

26.9

49.9

Average Radius

21.35

18.95

12.95

13.15

13.45

24.95

AverageVolume

40743.8

28490.23

9092.382

9520.1906

10186.74

65024.95114

V/V0

3.99959

2.796725

0.892548

0.9345431

0.9999745

6.383130573

?C

25

100

250

1000

225

1

?p

122573

490290

1225725

4902900

1103152.5

4902.9

By observing the results from above table we conclude that, it is of importance to biomodify the pillars in such a way that they gain an extracellular substrate appealing cell adhesion. In this context, it should be noted that biomodification should not prevent from direct conclusions of the environmental biomechanics on cell behaviour.

Results & Discussion

Consistent with previous studies (Steinberg et al., 2007; Mussig et al., 2008), polymerisation of PDMS in the silicon wafer yielded micropillar interfaces of constant height (15 µm) and diameter (5 µm) as revealed by scanning electron microscopy. Concerning the biomechanical properties of the extracellular environment of the periodontal cells, pillars were configured with variable, but distinct micropatterns. This vario-patterning can be demonstrated best in the SEM-overview provided in Fig. 1B. Beginning from the down-left to the top-right, pillar arrays of 5 and 11 µm were fabricated. In addition to the micropattern, environmental biomechanics can be changed by the pillar's stiffness, i.e. its elasticity. In preliminary experiments, we have achieved differential elasticity moduli (E-moduli) by either adding distinct volumes of silicone oil to the PDMS mixture or by selective PDMS-baking using exclusive times and temperatures during the baking process. In this study, selective baking was the means of choice, since compared to adding oil it yielded highly reproducible E-moduli. The baking conditions comprising a period of 4 h at 65 °C resulted in a pillars' E-modulus of 0.6 Mega Pascal (MPa), while durations of 16 h at 65 °C lead to an E-modulus of 1.0, and 14 h at 65 °C followed by a 2 h period at 180 °C to a 3.5 MPa E-modulus, respectively. Despite this generation of variable but defined biomechanics, the naked pillars per se render an unfavourable environment for cell adhesion, due to their silicone-based nature.

Fig. 1. Micropillar interfaces and biofunctionalisation with fibronectin (FN). SEM images of (A) single PDMS micropillars aslope from the top, illustrating the morphology of single pillars with a height of 15 µm and a diameter of 5 µm. (B) A pillar field from top view, displaying the vario-patterning with pillar distances of 5 (B1), 7 (B2), 9 (B3) and 11 µm (B4), and a pillar head diameter of 5 µm. (C) Indirect immunofluorescence (IIF) indicates FN- biofunctionalised pillar “heads” in an array of 9 µm pillar distances.

Thus, the biomimetic concept of FN-biofunctionalisation of the pillars should address only the apical pillar surface. As proven in many in vitro studies, the extracellular matrix constituent fibronectin FN is a suitable molecule for cell adhesion (Cai et al., 2008). To ensure adhesion of the periodontal cells under study only on the pillar tops, we exerted biofunctionalisation of the pillars exclusively on the pillar tops. This is shown in Fig. 1C, where indirect immunofluorescence proves the FN-immobilisation only at apical pillar sites.

Successful adhesion to FN-biofunctionalised pillar tops is exemplified for a gingival fibroblast by SEM in Fig. 2, spanning approximately 18 pillars (Fig. 2A).

Fig. 2. Adhesion of a gingival fibroblast on micropillar heads with pillar distances of 5 µm. (A) Gingival fibroblasts were seeded on a micropillar surface at a density of 7×103 cells/ml, and ...