Authors: Susana M. Ramalhete | Karol P. Nartowski | Hayley Green | Jesús Angulo | Dinu Iuga | L. Fábián | Gareth O. Lloyd | Yaroslav Z. Khimyak
Source: Faraday Discussions (article, 2024-05-23)
Field: Materials Science — Biomaterials

Probing assembly/disassembly of ordered molecular hydrogels Supramolecular hydrogels have a wide range of applications in the biomedical field, acting as scaffolds for cell culture, matrices for tissue engineering and vehicles for drug delivery. L-Phenylalanine (Phe) is a natural amino acid that plays a significant role in several physiological and pathophysiological processes (phenylketonuria and assembly of fibrils linked to tissue damage). Since Myerson <i>et al.</i> [<i>Chem. Eng. Commun.</i>, 2002, <b>189</b>(8), 1079-1090] reported that Phe forms a fibrous network <i>in vitro</i>, Phe's self-assembly processes in water have been thoroughly investigated. We have reported structural control over gelation by introduction of a halogen atom in the aromatic ring of Phe, driving changes in the packing motifs, and therefore, dictating gelation functionality. The additional level of control gained over supramolecular gelation <i>via</i> the preparation of multi-component gel systems offers significant advantages in tuning functional properties of such materials. Gaining molecular-level information on the distribution of gelators between the inherent structural and dynamic heterogeneities of these materials remains a considerable challenge. Using multicomponent gels based on Phe and amino-L-phenylalanine (NH<sub>2</sub>-Phe), we will explore the patterns of ordered/disordered domains in the gel fibres and will attempt to come up with general trends of interactions in the gel fibres and at the fibre/solution interfaces. Phe and NH<sub>2</sub>-Phe were found to self-assemble in water into crystalline hydrogels. The determined faster dynamics of exchange between the gel and solution states of NH<sub>2</sub>-Phe in comparison with Phe were correlated with weaker intermolecular interactions, highlighting the role of head groups in dictating the strength of intermolecular interactions. In the mixed Phe/NH<sub>2</sub>-Phe systems, at a low concentration of NH<sub>2</sub>-Phe, disruption of the network was promoted by interference of the aliphatics of NH<sub>2</sub>-Phe with the electrostatic interactions between Phe molecules. At high concentrations of NH<sub>2</sub>-Phe, multiple-gelator hydrogels were formed with crystal habits different from those of the pure gel fibres. NMR crystallography approaches combining the strengths of solid- and solution-state NMR proved particularly suitable to obtain structural and dynamic insights into the "ordered" fibres, solution phase and fibre/solution interfaces in these gels. These findings are supported by a plethora of experimental (diffraction, rheology, microscopy and thermal analysis) and computational methods. Self-healing hydrogels ; Intermolecular force ; Chemistry ; Phenylalanine ; Chemical engineering ; Nanotechnology ; Materials science ; Polymer chemistry ; Amino acid ; Molecule ; Organic chemistry ; Biochemistry Supramolecular Self-Assembly in Materials ; Polydiacetylene-based materials and applications ; Lipid Membrane Structure and Behavior