ENTROPIC ELASTICITY OF END ADSORBED POLYMER-CHAINS - THE SPECTRIN NETWORK OF RED-BLOOD-CELLS AS C-ASTERISK-GEL

We use Monte Carlo methods to investigate the end-to-end distance dist ribution and entropic elasticity of self-avoiding walks in a three-dim ensional half-space with both ends adsorbed on the limiting surface, T he obtained distributions are well described by the Redner-des Cloizea ux (RdC) ansatz q(x)=Cx(theta) exp(-(Kx)(t)), x being the rescaled len gth. Using the recent solution of the junction affine model for networ ks of RdC springs we apply the results to the cytoskeleton of the red blood cell (RBC), a two-dimensional network of spectrin molecules whic h is attached to the inner surface of the erythrocyte membrane. The sh ear moduli predicted for a noninteracting surface are in close agreeme nt with simulation results by Boal for a bead-spring model of the spec trin network. Moreover, we calculate stress-strain relations for finit e deformations. In particular for a network which is fully adsorbed on the bilayer we find a strongly nonlinear elastic response. Our result s suggest that the elastic properties of RBCs cannot be obtained withi n the usual Gaussian models and depend sensitively on the degree of ad sorption of the spectrin network. (C) 1996 American Institute of Physi cs.