Cellular fluid shear stress on implant surfaces-establishment of a novel experimental set up

Abstract

Background: Mechanostimuli of different cells can affect a wide array of cellular and inter-cellular biological processes responsible for dental implant healing. The purpose of this in vitro study was to establish a new test model to create a reproducible flow-induced fluid shear stress (FSS) of osteoblast cells on implant surfaces.

Methods: As FSS effects on osteoblasts are detectable at 10 dyn/cm², a custom-made flow chamber was created. Computer-aided verification of circulation processes was performed. In order to verify FSS effects, cells were analysed via light and fluorescence microscopy.

Results: Utilising computer-aided simulations, the underside of the upper plate was considered to have optimal conditions for cell culturing. At this site, a flow-induced orientation of osteoblast cell clusters and an altered cell morphology with cellular elongation and alteration of actin fibres in the fluid flow direction was detected.

Conclusions: FSS simulation using this novel flow chamber might mimic the peri-implant situation in the phase of loaded implant healing. With this FSS flow chamber, osteoblast cells' sensitivity to FSS was verified in the form of morphological changes and cell re-clustering towards the direction of the flow. Different shear forces can be created simultaneously in a single experiment.

Keywords: Bioengineering; Biomechanics; Cell biology; Dental implant materials; Implant healing; Osteoblast; Stress analysis.

Fig. 1

Three-dimensional illustration (a–e) and photography (f) of the experimental setup with the components marked numerical. a 1 Lower petri dish (s’ bottom serving as the lower plate); 2 Rotating glass panel [60 mm diameter (cell bearing)]; 3 Titanium axis. b 4 Liquid medium (red). c 5 Reversed upper petri dish. d 6 Gearwheel with set screw. e 7 Closing; 8 Electronic motor device and adjusting ring with additional set screw

Fig. 2

Side view of a computerized simulation, showing the flow chambers’ lower compartment and the flow profile in between the two plates; shearing gap and bottom plate are shown on the left side; rotation speed = 200 rpm; colour code bar (left edge) showing shear force values [Pa] [1 Pa = 10 dyn/cm²]; flow direction presented by arrows

Fig. 3

Diagram for visualisation of the calculation of shear stress rates taking into account the centrifugal force and the glass plates’ dimensions. For example, at a distance of 25 mm from the centre of the upper plate, the shear forces’ value is 8.33 dyn/cm², together with an additional centrifugal force that has a value of 0.55 dyn/cm²

Fig. 4

Randomly orientated osteoblasts without influence of rotation (phallacidin fluorescence staining). On the left side with 200× and on the right side with 400× magnification. The white X on the coloured circle marks the location upon the plate where the osteoblasts were located. The red X marks the centre of the plate

Fig. 5

Osteoblasts with an orientation tendency after 24 h of rotation (phallacidin fluorescence staining). On the left side with 200× and on the right side with 400× magnification. The yellow arrows show the orientation of the cells. The red arched arrow within the coloured circle shows the direction of rotation. The dashed white line oriented to the right stands for the resulting centrifugal force. The dashed white line pointing upwards shows the direction of the resulting flow resistance. The solid white arrow stands for the vectorial sum of the abovementioned forces