| AVS 57th International Symposium & Exhibition | |
| Biomaterial Interfaces | Tuesday Sessions |
| Session BI-TuM |
| Session: | Cells on Surfaces |
| Presenter: | B. Müller, University of Basel, Switzerland |
| Authors: | B. Müller, University of Basel, Switzerland J. Köser, University of Applied Sciences, Switzerland |
| Correspondent: | Click to Email |
Mechanical properties of substrates have been shown to be crucial factors for cell behavior, which includes the differentiation of stem cells or the malignant transformation into cancerogeneous cells (Engler et al. (2006) Cell 126, 677 and Cross et al. (2007) Nature Nanotechnol 2, 780). There have been published several techniques to measure contractile forces of cells, exerted onto the underlying substrate, since 1980. These approaches, however, only rely on compliant substrates and not on rigid ones as well known from load-bearing implants and culture dishes.
We present an approach to quantify the contractile forces of an ensemble of cells growing on rigid substrates based on nanomechanical cantilever sensors. In particular, we measured the relaxation of micro-cantilevers as the result of trypsin-release of about 100 fibroblasts. The optically measured change in cantilever bending, detected by means of the Cantisens Research system (Concentris GmbH, Basel), together with the number of fibroblasts counted was converted to the contractile cell force using the STONEY formula.
For the measurement of the contractile cell forces the selected cells were cultured on silicon cantilever arrays. The arrays consist of 8 micro-cantilevers each 500 µm long, 100 µm wide and 1 μm thin that enables us to detect stresses as small as 0.01 mN/m. Following adhesion and contractile force generation over night, the cantilever arrays were introduced into the Cantisens Research system to monitor the cantilever relaxations upon trypsin-mediated release of the cells from the substrate.
When rat2 fibroblasts are seeded on the silicon cantilevers they adhere and develop the morphology indistinguishable from that on standard culture dishes. Upon trypsin-induced release of the cells from the silicon substrate bending, the free end of the cantilever changes its position according to the following function D = 0.5D0 (1-tanh(t/τ)), where D0 corresponds to the deflection amplitude and τ the time constant of the cell release. While τ is apparatus and process specific, D0 directly relates to the contractile forces of an ensemble of cells. The contractile force of an individual rat2 fibroblast on silicon corresponds to (17±7) µN. This value is reasonable, but high compared to the contractile forces of fibroblasts exerted on compliant substrates, a behavior expected from the studies on differently stiff compliant substrates. The contractile cell forces are strongly dependent on the state of the cell that explains the rather large error bar.
The method will support the fundamental understanding of cell-materials interactions with implications for cell-based biosensing and implant design.