Faniry carried out her research in the IDeAS team at the Softmat laboratory.
On 18th of November, she defended her thesis entitled: “Shaping supramolecular gels of N-alkyl-D-galactonamides in aqueous-only media: 3D Printing, wet Spinning, and molybdate complexes”
N-alkyl-D-galactonamides are small molecules derived from galactose which have the property of self-assembling into supramolecular fibers in an aqueous medium. This results in the formation of white hydrogels where the aqueous phase is stabilised inside a network of entangled fibers. The objective of the thesis was to explore different methods of injection and 3D printing of these hydrogels.
As these are fragile gels, which are neither shear thinning nor thixotropic, it is not possible to inject them directly through a needle, as this process would break the gels irreversibly. As a result, she has developed a method which allows the gel to be formed during its injection and which respects the integrity of the gels. This is a wet spinning technique which consists of injecting the gelling agent solubilised in a good solvent, dimethyl sulfoxide, into a water bath. On contact with water, the gelling agent self-assembles very quickly into supramolecular fibers, allowing, through their entanglement, the formation of continuous and well-formed gel filaments. This technique was then adapted to 3D printing. It has been shown that it is possible to construct small, well-resolved structures at the millimeter scale using 3D printing, formed solely from N-alkyl-D-galactonamides. Some of these N-alkyl-D-galactonamides were also used in this process as sacrificial inks to generate channels in printed architectures.
To transpose this mode of gelation into a green chemistry context, she then explored two other methods of wet spinning and 3D printing of N-alkyl-D-galactonamides using only aqueous media, avoiding the use of dimethysulfoxide. As N-alkyl-D-galactonamides are very poorly soluble in water, since they self-assemble, it was necessary to find ways to temporarily solubilise these molecules in a suitable aqueous medium.
The first method consisted of solubilizing N-heptyl-D-galactonamide in a very concentrated basic medium. Because sugar hydroxyls are more acidic than regular hydroxyls, they can be deprotonated under these strongly basic conditions, which ionises the molecule and makes it soluble in water. Then, the injection of this basic gelator solution into an acid bath makes it possible to reform the neutral molecule which self-assembles to form gel filaments. The base-acid transition was followed by pH-indicator dyes and the distance at which this transition occurs during injection was modeled by applying the laws of acid-base neutralization to the injected volumes. It was shown that these new conditions can be easily transposed to 3D printing.
The second method in aqueous medium only consisted of using and studying the complexation of N-alkyl-D-galactonamides with molybdenum VI. N-heptyl-D-galactonamide reacts with ammonium molybdate to form complexes that are soluble in neutral water. The molecular structure of the main complex was analysed by 1H, 13C, 95Mo NMR and mass spectrometry. Although complexation makes the molecule more hydrophilic and charged, the presence of a hydrophilic part and a hydrophobic chain does not make the molecule surface-active, as demonstrated by tensiometry. In an acidic environment, molybdates formed clusters which cause the complexes to assemble into supramolecular fibers and triggered gelation. The resulting gels were very different from N-heptyl-D-galactonamide gels alone. They are transparent and rheological analysis highlighted their thixotropic behavior. Injecting the neutral solution of the complex into a bath of moderately acidic bath facilitated the shaping of these gels into filaments.
Highlights of the thesis:
- Faniry was awarded the prize for best oral paper (ex-aequo) at the Journées du GFP Sud-Ouest 2022;
- She has been accepted for an oral presentation at the European Congress ECIS 2022;
- An illustration of the process used in her thesis has been selected for the cover of an issue of the journal Colloids and Surfaces A “Physicochemical and Engineering aspects” in 2023.
Congratulations to Faniry for the quality of her work!