We demonstrate that composite envelopes of nucleated cells exhibit pronounced short wavelength ($\le 0.5\mu \mathrm{m}$) bending excitations of $\sim 10\mathrm{nm}$ root mean square amplitudes at physiological temperatures, which impede strong adhesion due to entropic repulsion forces. Quantitative microinterferometric analysis of the dynamic cell surface roughness of macrophages in terms of the theory of statistical surfaces suggests that the membrane excitations are mainly thermally driven Brownian motions (although active driving forces may contribute substantially). We determine the effective bending modulus of the cell envelope ($\sim 1000k_{\mathrm{B}}T$), the cortical tension ($\sim {10}^{-4}\mathrm{N}{\mathrm{m}}^{-1}$), and the work of adhesion ($\sim {10}^{-5}\mathrm{J}{\mathrm{m}}^{-2}$).

• Received 4 August 2005

DOI:https://doi.org/10.1103/PhysRevLett.96.048103