Behaviour of the model antibody fluid constrained by rigid spherical obstacles: effects of the obstacle-antibody binding

Abstract

We study a simplified model of monoclonal antibodies confined in a patchy random porous medium. Antibodies are represented as Y-shaped particles composed of seven tangential hard spheres with attractive patches on the terminal beads, while the matrix consists of randomly distributed hard-sphere obstacles bearing adhesive sites. The model captures antibody behavior in crowded biological environments with strong short-range antibody-matrix attractions. The theoretical approach combines Wertheim's multidensity thermodynamic perturbation theory, the Flory-Stockmayer theory of polymerization, and scaled particle theory for fluids in porous media. We analyze thermodynamic properties, percolation thresholds, and phase behavior, and compare the selected results with new computer simulations. The interplay between antibody-antibody and antibody-matrix interactions produces a complex phase behavior, including re-entrant phase separation with a closed-loop coexistence region at higher temperatures and conventional liquid-gas separation at lower temperatures.

Figures (8)

• Figure 1: (Colour online) Coarse-grained model of antibody molecules (blue) confined within a matrix of rigid spherical obstacles (yellow), both decorated with attractive patches (red). The left-hand panel shows an example of an individual antibody molecule built from seven tangentially connected beads.
• Figure 2: (Colour online) Fractions of $i$-times bonded particles vs density $\rho^*_1$ for the system with $\epsilon^*_{11}=1$, $n_1=3$, $n_0=0$, $\eta_0=0.1$, $\sigma_0/\sigma_1=3$, at temperatures $T^*=0.085$ (panel a) and $T^*=0.1$ (panel b). Here, $x_1^{(1)}$, $x_2^{(1)}$, and $x_3^{(1)}$ are shown by black, red, and blue lines, respectively. Symbols represent simulation results.
• Figure 3: (Colour online) Fractions of $i$-times bonded molecules vs density $\rho^*_1$ for the system with $\epsilon^*_{11}=1$, $\epsilon^*_{01}=1$, $n_1=3$, $n_0=1$, $\eta_0=0.1$, $\sigma_0/\sigma_1=3$, at temperature $T^*=0.085$. In panel a, $x_1^{(1)}$, $x_2^{(1)}$, and $x_3^{(1)}$ are shown by black, red, and blue lines, respectively, while in panel b $x_1^{(0)}$ is shown by a black line. Symbols represent simulation results.
• Figure 4: (Colour online) The same as in figure \ref{['f2']}, but at temperature $T^*=0.1$.
• Figure 5: (Colour online) Fractions of $i$-times bonded molecules vs density $\rho^*_1$ for the system with $\epsilon^*_{11}=1$, $\epsilon^*_{01}=1$, $n_1=3$, $n_0=3$, $\eta_0=0.1$, $\sigma_0/\sigma_1=3$, at temperature $T^*=0.085$. In panel a, $x_1^{(1)}$, $x_2^{(1)}$, and $x_3^{(1)}$ are shown by black, red, and blue lines, respectively, and in panel b $x_1^{(0)}$, $x_2^{(0)}$, and $x_3^{(0)}$ are shown by black, red, and blue lines, respectively. Symbols represent simulation results.