Interpenetrated biosurfactant-biopolymer orthogonal hydrogels: the biosurfactant's phase controls the hydrogel's mechanics

TL;DR

This study develops biobased hybrid hydrogels using biopolymers and biosurfactants, demonstrating how the biosurfactant's phase behavior controls the hydrogel's mechanical properties through pH and ion interactions.

Contribution

It introduces a new method to tune hydrogel mechanics by controlling biosurfactant phases, combining biopolymers with microbial glycolipids for customizable properties.

Findings

Fiber phase enhances hydrogel strength by forming interpenetrated networks.

Micellar and vesicular phases reduce hydrogel elasticity.

Hydrogel mechanics can be modulated via pH and calcium ions.

Abstract

Controlling the viscoelastic properties of hydrogels is a challenge for many applications. Low molecular weight gelators (LMWG) like bile salts and glycolipids, and biopolymers like chitosan and alginate, are good candidates for developing fully biobased hybrid hydrogels that combine the advantages of both components. Biopolymers lead to enhanced mechanics while LMWG add functionality. In this work, hybrid hydrogels are composed of biopolymers (gelatin, chitosan, alginate) and microbial glycolipid bioamphiphiles, known as biosurfactants. Besides their biocompatibility and natural origin, bioamphiphiles can present chameleonic behavior, as pH and ions control their phase diagram in water around neutrality under strongly diluted conditions (< 5 wt%). The glycolipid used in this work behaves like a surfactant (micellar phase) at high pH or like a phospholipid (vesicle phase) at low pH. Moreover, at neutral-to-alkaline pH in the presence of calcium, it behaves like a gelator (fiber phase). The impact of each of these phases on the elastic properties of biopolymers is explored by means of oscillatory rheology, while the hybrid structure is studied by small angle X-ray scattering. The micellar and vesicular phase reduce the elastic properties of the hydrogels, while the fiber phase has the opposite effect, it enhances the hydrogel's strength by forming an interpenetrated biopolymer-LMWG network.