Evaporative Drying Induced Self-Assembly of Epicuticular Wax: A Biomimetic Approach in Tuning Surface Roughness.

Epicuticular wax is an example of a naturally created functional material that forms a layer on the outermost surface of plants with the objective to protect them from adverse environmental conditions, such as UV-solar radiation, uncontrolled water loss, microbial attacks, and so forth. Their functionalities are often attributed to the chemical composition of the wax as well as the physical structuration formed by the wax crystals on the surface. With this work, we present a simple, one-step biomimetic approach to replicate similar surface structures, on model substrate, using wax extracted from Euphorbia Cerifera (Candelilla wax). First, we describe formation of structured wax due to self-assembly induced by evaporative drying on quartz plates. Subsequently, we highlight the fundamental physical parameters required to tune the surface morphology. Our experiments reveal that it is possible to achieve considerably diverse surface morphologies depending on the solvent properties and deposition temperature. This diversity is due to the kinetics of recrystallization of wax during evaporation of solvent which, in turn, is primarily driven by the solubility of wax as well as evaporation rate of the solvent. Thus, the final morphology that we obtain is an interplay between recrystallization kinetics and solvent evaporation. Additionally, the degree of crystallinity of the structured films could also be tuned by solvent polarity. Surprisingly, X-ray diffraction indicates that the crystalline structure at the molecular level remains similar to that of bulk Candelilla wax. Our results provide fundamental insights into the replication of epicuticular wax films and identification of tuning parameters to obtain different surface morphologies with the same wax material for potential bioinspired multifunctional coatings in cosmetic applications.

Effect of molecular structure of eco-friendly glycolipid biosurfactants on the adsorption of hair-care conditioning polymers.

Pseudo-binary mixtures of different glycolipids, four different rhamnolipids (RL) and an alkyl polyglucoside (APG), with poly(diallyl-dimethylammonium chloride) (PDADMAC) have been studied in relation to their adsorption onto negatively charged surfaces to shed light on the impact of the molecular structure of surfactants from natural sources (instead of synthetic surfactant, such as sodium laureth sulfate) on the adsorption of hair-conditioning polymers. For this purpose, the self-assembly of such mixtures in aqueous solution and their adsorption onto negatively charged surfaces mimicking the negative charge of damaged hair fibres have been studied combining experiments and self-consistent field (SCF) calculations. The results show that the specific physico-chemical properties of the surfactants (charge, number of sugar rings present in surfactant structure and length of the hydrocarbon length) play a main role in the control of the adsorption process, with the adsorption efficiency and hydration being improved in relation to conventional sulfate-based systems for mixtures of PDADMAC and glycolipids with the shortest alkyl chains. SCF calculations and Energy Dispersive X-Ray Spectroscopy (EDS) analysis on real hair confirmed such observations. The results allow one to assume that the characteristic of the surfactants, especially rhamnolipids, conditions positively the adsorption potential of polyelectrolytes in these model systems. This study provides important insights on the mechanisms underlying the performance of more complex but eco-friendly washing formulations.

An optimized biotechnological system for the production of centellosides based on elicitation and bioconversion of Centella asiatica cell cultures.

Centella asiatica is a herbaceous plant of Asian traditional medicine. Besides wound healing, this plant is recommended for the treatment or care of various skin conditions such as dry skin, leprosy, varicose ulcers, eczema, and/or psoriasis. Triterpene saponins, known as centellosides, are the main metabolites associated with these beneficial effects. Considering the interest in these high value active compounds, there is a need to develop biosustainable and economically viable processes to produce them. Previous work using C. asiatica plant cell culture technology demonstrated the efficient conversion of amyrin derivatives into centellosides, opening a new way to access these biomolecules. The current study was aimed at increasing the production of centellosides in C. asiatica plant cell cultures. Herein, we report the application of a new elicitor, coronatine, combined with the addition of amyrin-enriched resins as potential sustainable precursors in the centelloside pathway, for a positive synergistic effect on centelloside production. Our results show that coronatine is a powerful elicitor for increasing centelloside production and that treatments with sustainable natural sources of amyrins enhance centelloside yields. This process can be scaled up to an orbitally shaken CellBag, thereby increasing the capacity of the system for producing biomass and centellosides.

An improvement of surfactin production by B. subtilis BBG131 using design of experiments in microbioreactors and continuous process in bubbleless membrane bioreactor.

Culture medium elements were analysed by a screening DoE to identify their influence in surfactin specific production by a surfactin constitutive overproducing Bacillus subtilis strain. Statistics pointed the major enhancement caused by high glutamic acid concentrations, as well as a minor positive influence of tryptophan and glucose. Successively, a central composite design was performed in microplate bioreactors using a BioLector®, in which variations of these impressive parameters, glucose, glutamic acid and tryptophan concentrations were selected for optimization of product-biomass yield (YP/X). Results were exploited in combination with a RSM. In absolute terms, experiments attained an YP/X 3.28-fold higher than those obtained in Landy medium, a usual culture medium used for lipopeptide production by B. subtilis. Therefore, two medium compositions for enhancing biomass and surfactin specific production were proposed and tested in continuous regime in a bubbleless membrane bioreactor. An YP/X increase of 2.26-fold was observed in bioreactor scale.