Re-entrant phase diagram and pH effects in cross-linked gelatin gels

Abstract

Experimental results have shown that the kinetics of bond formation in chemical cross-linking of gelatin solutions are strongly affected not only by gelatin and reactant concentrations but also by the solution pH. We present an extended numerical investigation of the phase diagram and of the kinetics of bond formation as a function of the pH, via Monte Carlo simulations of a lattice model for gelatin chains and reactant agent in solution. We find a re-entrant phase diagram, namely, gelation can be hindered either by loop formation at low reactant concentrations, or by saturation of chain active sites via formation of single bonds with a cross-linker at high reactant concentrations. The ratio of the characteristic times for the formation of the first and the second bond between the cross-linker and an active site of a chain is found to depend on the reactant reactivity, in good agreement with experimental data.

Gelation kinetics of crosslinked gelatin

“…As a small remark, we notice that at very low C r , corresponding to the sol phase, $n_l$ decreases with C over the whole observed range following a power‐law decay $n_l \sim C^{ - 0.8}$ [4, 5]. For increasing C r , the same power law decay is recovered at higher C .…”

“…We have performed Monte Carlo simulations on a cubic lattice of a system made of bifunctional monomers [4, 5]. Each monomer represents a unit on the linear chain or else a reactant.…”

“… Phase diagram, obtained plotting the percolation probability $P$ as a function of chain and reactant concentration, C and C r , respectively, using a gray scale (adapted from ref 5…”

“…In this article, we present results from a detailed numerical study of the kinetics of the bond formation as a function of the pH, and of the gelatin and reactant concentrations. By means of Monte Carlo simulations on the cubic lattice of a simple model, we analyze the kinetics of bond formation in chemical crosslinking of a gelatin solution [4, 5]. We consider a solution of polymer chains at different concentrations where reactant monomers can diffuse forming bonds with the active sites along the chains, producing the crosslinking.…”

Potential doxorubicin delivery system based on magnetic gelatin microspheres crosslinked with sugars

“…Therefore, we decided to modify the pH in order to change the equilibrium between cyclic and open fructose forms and thus provide more ketone available for the formation of crosslinks. According to the literature, the kinetics of bond formation in chemical crosslinking of gelatin solutions is strongly affected by the solution's pH [28] , but at pH values higher than 9 and lower than 5 the denaturation enthalpy decreases, indicating that the triple helix amount is reduced [29] . Thus, gelatin microspheres were produced by varying the pH.…”