Thermodynamic modelling of acidic collagenous solutions: from free energy contributions to phase diagrams

Abstract

Tropocollagen is considered one of the main precursors in the fabrication of collagen-based biomaterials.

Theoretical Platform for Liquid-Crystalline Self-Assembly of Collagen-Based Biomaterials

“…In our previous validated work [20], we showed that our thermodynamic model of acidic collagen solutions captures two key features: (i) the expected chimney diagram predicted by Flory and found experimentally for many lyotropic rod-like liquid-crystalline polymers [38], and (ii) the parabolic bi-phasic funnel in aqueous acidic collagenous solutions under increasing pH, where cholesteric tactoids (drops) emerge from isotropic phases. Study of cholesteric tactoids is important because of three main reasons: (i) tactoid formation process must occur in to chimney and funnel phase diagrams, which are the fingerprint of rod-like macromolecules.…”

“…Once these functional groups are protonated, the intrachain repulsion causes that, the semi-flexible (worm-like) backbones become uncoiled and essentially rigid rods. The existing interchain repulsion also impedes aggregation, in other words the rods have an effective diameter between two or three times the bare one [20][21][22]. Finally, due to being chargecarrier rigid rod-like molecules, tropocollagen is capable of exhibiting lyotropic cholesteric phase organization.…”

“…Furthermore, to the best of authors' knowledge, theoretic studies of cholesteric selfassembly of aqueous acidic tropocollagen solutions have not been carried out, which also reflects the case of chiral nematic phase ordering in general [24][25][26]. To address this gap, we have recently developed, implemented, and validated a theoretical model tailored for self-assembly of tropocollagen dispersed in acidic aqueous solutions [20]. This thermodynamic theory [20], which is based on the uniaxiality assumption, has integrated microscopic mechanisms of mixing entropy and enthalpy, attraction, repulsion, twisting, excluded-volume, and chirality.…”

“…To address this gap, we have recently developed, implemented, and validated a theoretical model tailored for self-assembly of tropocollagen dispersed in acidic aqueous solutions [20]. This thermodynamic theory [20], which is based on the uniaxiality assumption, has integrated microscopic mechanisms of mixing entropy and enthalpy, attraction, repulsion, twisting, excluded-volume, and chirality. In the present study, we lift the uniaxiality assumption by generalizing the free energy that includes biaxial effects.…”

“…Thus, these cholesteric drops are a crucial element in the validation of thermodynamics of rodshaped rigid macromolecules; (ii) these stable but deformable drops serve a sources of material properties information such as bulk Frank-Oseen-Mermin elasticity [27], novel coupled gradient contributions between nematic order parameter and collagen concentration, and the cholesteric pitch; (iii) characterizing and understanding the emergence, growth, annihilation, and coalescence of tactoids are essential to future developments of collagen-based material processing. To focus on collagen tactoids, as shown in Figure 1, we then target the dynamic of selfassembly through a shallow quench from isotropic phase into the bi-phasic funnel of the previously obtained phase diagram [20]. In contrast to the better known single component monomeric thermotropic tactoids, in the present case concentration is a conserved transport variable that need to be included.…”