Interpenetrated Biosurfactant-Biopolymer Orthogonal Hydrogels: The Biosurfactant's Phase Controls the Hydrogel's Mechanics

Cytotoxicity evaluation of microbial sophorolipids and glucolipids using normal human dermal fibroblasts (NHDF) in vitro

Fibroblasts are considered a key player in the wound healing process. Although this cellular family is constituted by several distinct subtypes, dermal fibroblasts are crucial thanks to their ability to secrete pro-regenerative growth factors, extracellular matrix (ECM) proteins and their immune and anti-inflammatory role. Sophorolipids (SL), sophorosides (SS) and glucolipids (G), mono-unsaturated (C18:1) or saturated (C18:0), glycolipids derived from microbial fermentation of wild type or engineered yeast Starmerella bombicola, constitute a novel sustainable class of bio-based chemicals with interesting physicochemical characteristics, which allow them to form soft diverse structures from hydrogels to vesicles, micelles or complex coacervates with potential interest in skin regeneration applications. In this study, we first tested the cytocompatibility of a broad set of molecules from this family on normal human dermal fibroblasts (NHDF). Our results show that, up to an upper threshold (0.1 % w/v), the microbial glycolipids (SL-C18:1, G-C18:1, SSbola-C18:1, SL-C18:0 and G-C18:0) under study were able to sustain cell growth. Furthermore, we selected the least cytotoxic glycolipids (SL-C18:1, SSbola-C18:1, SL-C18:0) to study their potential to promote wound healing by measuring the gene expression of several key skin regeneration markers (i.e. collagen, elastin, transforming growth factor β, fibroblast growth factor …) using qPCR. Unfortunately, none of these glycolipids modulated the gene expression of molecules involved in tissue repair. However, this study aims to encourage the community to test this novel class of molecules for novel high-end biomedical applications.

Importance

Biosurfactants prepared by microbial fermentation are natural amphiphiles of growing importance, with the goal of replacing synthetic surfactants in commercial formulations. However, their cytotoxicity profile is still poorly known, especially for new molecules like single-glucose lipids or bolaform sophorolipids. This wants to contribute to all those applications, which could be developed with biosurfactants in contact with the skin (cosmetics, wound healing). We test the cytotoxicity of five structurally-related molecules (C18:1 and C18:0 sophorolipids, C18:1 and C18:0 single-glucose lipids, C18:1 di-sophoroside) against normal human dermal fibroblasts (NHDF) and evaluate the metabolic activity of the least toxic among them. To the best of our knowledge, cytotoxicity of these molecules, and of microbial biosurfactants in general, was never tested against NHDF.

Manipulating supramolecular gels with surfactants: Interfacial and non-interfacial mechanisms

Gel is a class of self-supporting soft materials with applications in many fields. Fast, controllable gelation, micro/nano structure and suitable rheological properties are essential considerations for the design of gels for specific applications. Many methods can be used to control these parameters, among which the additive approach is convenient as it is a simple physical mixing process with significant advantages, such as avoidance of pH change and external energy fields (ultrasound, UV light and others). Although surfactants are widely used to control the formation of many materials, particularly nanomaterials, their effects on gelation are less known. This review summarizes the studies that utilized different surfactants to control the formation, structure, and properties of molecular and silk fibroin gels. The mechanisms of surfactants, which are interfacial and non-interfacial effects, are classified and discussed. Knowledge and technical gaps are identified, and perspectives for further research are outlined. This review is expected to inspire increasing research interest in using surfactants for designing/fabricating gels with desirable formation kinetics, structure, properties and functionalities.

In Situ Stimulation of Self-Assembly Tunes the Elastic Properties of Interpenetrated Biosurfactant-Biopolymer Hydrogels

Hydrogels are widespread soft materials, which can be used in a wide range of applications. The control over the viscoelastic properties of the gel is of paramount importance. Ongoing environmental issues have raised the consumer's concern toward the use of more sustainable materials, including hydrogels. However, are greener materials compatible with high functionality? In a safe-by-design approach, this work demonstrates that functional hydrogels with in situ responsivity of their elastic properties by external stimuli can be developed from entirely "sustainable" components, a biobased amphiphile and biopolymers (gelatin, chitosan, and alginate). The bioamphiphile is a stimuli-responsive glycolipid obtained by microbial fermentation, which can self-assemble into fibers, but also micelles or vesicles, in water under high dilution and by a rapid variation of the stimuli. The elastic properties of the bioamphiphile-/biopolymer-interpenetrated hydrogels can be modulated by selectively triggering the phase transition of the glycolipid and/or the biopolymer inside the gel by mean of temperature or pH.