Palmitic acid sophorolipid biosurfactant: from self-assembled fibrillar network (SAFiN) to hydrogels with fast recovery

Abstract

Nanofibres are an interesting phase into which amphiphilic molecules can self-assemble. Described for a large number of synthetic lipids, they were seldom reported for natural lipids like microbial amphiphiles, known as biosurfactants. In this work, we show that the palmitic acid congener of sophorolipids (SLC16:0), one of the most studied families of biosurfactants, spontaneously forms a self-assembled fibre network (SAFiN) at pH below 6 through a pH jump process. pH-resolved in situ small-angle X-ray scattering (SAXS) shows a continuous micelle-to-fibre transition, characterized by an enhanced core–shell contrast between pH 9 and pH 7 and micellar fusion into a flat membrane between pH 7 and pH 6, approximately. Below pH 6, homogeneous, infinitely long nanofibres form by peeling off the membranes. Eventually, the nanofibre network spontaneously forms a thixotropic hydrogel with fast recovery rates after applying an oscillatory strain amplitude out of the linear viscoelastic regime: after being submitted to strain amplitudes during 5 min, the hydrogel recovers about 80% and 100% of its initial elastic modulus after, respectively, 20 s and 10 min. Finally, the strength of the hydrogel depends on the medium's final pH, with an elastic modulus fivefold higher at pH 3 than at pH 6. This article is part of the theme issue ‘Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 1)’.

Energy Landscape of the Sugar Conformation Controls the Sol-to-Gel Transition in Self-Assembled Bola Glycolipid Hydrogels

“…For instance, C18:0 derivatives of sophorolipid biosurfactants fibrillate and form hydrogels under slow pH change rates, 23 while gelation of the C16:0 derivative of the same compound is independent of the pH variation rate and is rather affected by the final pH of the gel. 26 Interestingly, the latter is more coherent with the literature on pHdependent LMW gelators, 27,28 while the former followed a path generally observed for temperature-driven LMW hydroand organogelators. 29 In a previous work, we studied the self-assembly of a symmetrical bolaamphiphile sophoroside (SS bola C18:1, Figure 1) in water employing synchrotron small-angle X-ray scattering (SAXS) analysis on freshly prepared samples.…”

“…However, at high q, the data display an oscillation of the form factor, superimposed to a correlation peak at 2.47 nm −1 , which reflects a repeated distance of 2.54 nm. The presence of such a peak in biosurfactants 26,46 and other self-assembled LMW systems 47,48 is generally associated to a semicrystalline order inside the fibers. 48 The fibrillar structure is confirmed using complementary cryo-TEM experiments (Figure 2), showing the presence of twisted ribbons, having a typical width of 20 nm and an internode of about 140 nm (additional pictures are given in Figure S2).…”

From bumblebee to bioeconomy: Recent developments and perspectives for sophorolipid biosynthesis

“…Despite the above, homogeneous fibrillation induces hydrogel formation at concentrations as low as 1 wt% of SL in water (Baccile et al, 2021a(Baccile et al, , 2018Ben Messaoud et al, 2019). Controlled variation of pH and temperature directly controls the nucleation and growth of the SL fibres, thus providing not only pH-responsive, but also tough, hydrogels, with elastic modulus as high as 10 kPa, thus paving the way to the development of biosurfactant-based soft materials (Baccile et al, 2019b).…”

“…x (Yang et al, 2012) Mix with N° 13 pH < ~7 pH> 8 (Baccile et al, 2016b(Baccile et al, , 2011Cuvier et al, 2015b;Dhasaiyan et al, 2017;Penfold et al, 2011;Zhou et al, 2004) Acetylated acidic (C18:1cis) 2 < pH < 7 pH< ~7 (Baccile et al, 2017a;Penfold et al, 2011) Acidic (C18:1-trans) pH > 7.5 3 < pH < 7.5 ## pH> 8 (Dhasaiyan et al, 2018(Dhasaiyan et al, , 2013 Acidic (C18:0) pH > 7.5 3 < pH < 7.5 pH> 8 (Baccile et al, 2016b;Cuvier et al, 2014Cuvier et al, , 2015bDhasaiyan et al, 2018Dhasaiyan et al, , 2013 Acidic (C16:0) pH > 7.5 7.5 < pH < 3 (Baccile et al, 2021a)…”

Bioderived and bioinspired sustainable materials

“…In the first paper, Cranston and co-workers [9] from Chemical and Biological Engineering at the University of British Colombia are exploring how latex film formation and adhesion at the nanoscale correlate to the performance of pressure-sensitive adhesives with cellulose nanocrystals. Finally, Baccile et al [10] from Laboratories de Chime de la Matière Condensée de Paris, Sorbonne Université is exploring the diversity of products that can be obtained from Sophorolipid surfactants in a research paper entitled 'Palmitic acid sophorolipid biosurfactant: from self-assembled fibrillar network (SAFiN) to hydrogels with fast recovery'.…”