ABSTRACT
Using artificially reconstituted membranes based on structurally liquidlike phospholipids, we have performed an experimental study on the mechanical impact of the saponin β-aescin, aka escin, a natural biosurfactant extracted from the seeds of the horse chestnut tree Aesculus hippocastanum. The paper focusses on the modulable interaction of escin with DMPC in model membranes in the form of bilayer vesicles and Langmuir monolayers. As regarding to their dual mechanical membrane behavior being both soft solids and viscoelastic fluids, we have outlined the principal energetic and kinetic features describing the insertion of escin as transversally adsorbed or longitudinally integrated within the model membranes. At connection with the structural phase behavior assessed by dedicated microscopies of surface fluorescence and Brewster angle reflectivity, these hybrid escin / phospholipid membranes have been revealed to possess dual mechanical properties connected to their structural rigidness and fluidity behaving both in one way and another. In particular, we observe a soft glassy rheology typical for liquid-crystalline ordered phases at low temperature, which turns into a fluidlike viscoelasticity characteristic of the disordered phases at high physiological temperature. These original results have been discussed in a physicochemical perspective that may pave new avenues of material engineering and / or pharmacological design exploiting the dual mechanical impact of escin as a mechanical modulator of the cellular membrane.
Competing Interest Statement
LHM is contracted by Maria Zambrano Program from Ministerio de Universidades de Espana for the attraction of international talent under Next Generation European Union funding (grant CT19/22). The work was supported by the Spanish Ministry of Science and Innovation (MICINN Agencia Espanola de Investigacion AEI) under grants PID 2019- 108391RB 100 and TED2021 132296B C52 (to FM), and Comunidad de Madrid under grants S2018/NMT 4389 and Y2018/BIO 5207 (to FM). We also acknowledge the financial support of the German Research Foundation DFG Grant HE 2995/7 1 (to TH), and the Open Access Publication Fund of Bielefeld University for the publication costs. This study was also funded by the REACT-EU program PR38 21 28 ANTICIPA CM, a grant by Comunidad de Madrid and European Union under FEDER program, from European Union in response to COVID-19 pandemics. The funders had no role in the study design, data collection, analysis, preparation of the manuscript, or the decision to publish. We acknowledge Prof. Juan J. Giner-Casares for making available Langmuir troughs and the BAM facility in his laboratory at Universidad de Cordoba, and also for fruitful discussions on the monolayer domain morphologies. LHM gratefully thanks him for hospitality.