mechanical-mapping-of-spheroids-using-brillouin-spectroscopy

Mechanical Mapping of Spheroids Using Brillouin Spectroscopy

Brillouin spectroscopy, an emerging technique gaining significant interest in biomedical science, allows researchers to gather information related to ...

University of Glasgow

Mixing low molecular weight gelators (LMWGs) can be used to combine favorable properties of the individual components within a multifunctional gel. Such multicomponent systems are complex enough in themselves but the method of combining components is not commonly considered something to influence self-assembly. Herein, two multicomponent systems comprising of a naphthalene-based dipeptide hydrogelator and one of two modified naphthalene diimides (NDIs), one of which forms gels, and the other does not, are investigated. These systems are probed, examining the structures formed and their gel properties (when preparing a solution from either a mixed powder of both components or by mixing pre-formed solutions of each component) using rheology, small angle neutron scattering (SANS), and absorbance spectroscopy. It is found that by altering the method of preparation, it is can either induce self-sorting or co-assembly within the fibers formed that underpin the gel network.

Process Dependent Complexity in Multicomponent Gels.

pH dependence on water soluble aggregates is well-known in the field of low molecular weight gelators (LMWGs), with different aggregates sometimes having very different properties depending on their final pH. This aggregation determines their applications and performance. Here, we investigate the pH dependence of perylene bisimide gels; initially solutions are formed at a high pH and gels form as the pH is decreased. We find it is not only the final pH but also the starting pH that can impact the resulting gel. We use small angle neutron scattering (SANS), rheology,  H NMR spectroscopy and absorption spectroscopy to examine the effect of starting pH on gelation kinetics and final gel properties. Adjusting the solution from pH 9 (where there are few or no aggregates) to pH 6 results in the formation of different worm-like micelles than the ones directly formed at pH 6, leading to again gels with different mechanical properties. This work highlights the importance of controlling the pH of solutions before gelation, but also opens up more possible morphologies and therefore more properties from the same molecule.

Using Solution History to Control Hydrogel Properties of a Perylene Bisimide.

Preparation of multicomponent systems provides a method for changing the properties of low molecular weight gelator (LMWG)-based systems. Here we have prepared a variety of multicomponent systems where both components are -functionalised dipeptide-based LMWGs that may either co-assemble or self-sort when mixed. We exemplify how varying the concentration ratio of the two components can be used to tune the properties of the multicomponent systems pre-gelation, during gelation and in the gel state using viscosity and rheology measurements, circular dichroism, NMR and small angle neutron scattering. We also investigate the effect of changing the chirality of a single component on the properties of these systems. While predicting the outcome of multicomponent assembly is a challenge, the preparation of a variety of systems allows us to probe the factors affecting their design. This work provides insights into how the properties of multicomponent systems composed of two gelators with the same basic structural design can be tuned by varying the chirality and the concentration ratio of the two components and considering the behaviour of the two components when alone.

Investigating multigelator systems across multiple length scales.

By using different salts as a method to achieve gelation of two different amino-acid-functionalised perylene bisimides, we were able to tune reduction potentials while maintaining the mechanical and optical properties of the system all at pH 7.4.

Tuning conductivity while maintaining mechanical properties in perylene bisimide hydrogels at physiological pH.

Understanding the key parameters that control the self-assembly process is critical to predict self-assembly modes in multi-component systems, which will lead to the development of nanofibrous materials with tuneable properties. Enantiomeric amino acid-based low-molecular-weight gelators (LMWGs) were mixed in polar (polar protic) and aromatic apolar (aromatic) solvents and compared to their individual counterparts to probe the effect of solvent polarity on the self-assembly process. Scanning electron microscopy (SEM) reveals that xerogels of individual components display hollow needles in polar protic solvents, while chiral coils are observed in aromatic solvents. In contrast, the multi-component gel displays hollow needle morphologies in both solvents, indicating similar morphologies in polar protic solvents but an entirely different nanostructure for the individual gel networks in aromatic solvents. PXRD experiments performed on the dried gels showed that the nature of the solvents plays a vital role in the co-assembly process of multi-component gels. The self-assembly modes and the gel state structure of the gels are analysed by wide-angle X-ray diffraction (WAXS) and small-angle neutron diffraction (SANS), which reveals that the mixed gel undergoes different co-assembly modes depending on the nature of the solvent systems. This study shows that different co-assembly modes can be achieved for structurally similar components by varying the solvent polarity, demonstrating the importance of solvent choice in the self-assembly process of multi-component gels.

Nanoscale assembly of enantiomeric supramolecular gels driven by the nature of solvents.

Low molecular weight gels continue to attract notable interest, with many potential applications. However, there are still significant gaps in our understanding of these systems and the correlation between the pre-gel and final gel states. The kinetics of the gelation process plays a crucial role in the bulk properties of the hydrogel and presents an opportunity to fine-tune these systems to meet the requirements of the chosen application. Therefore, it is possible to use a single gelator for multiple applications. This review discusses four ways to modify the pre-gelled structures before triggering gelation. Such modifications can enhance the material's intended performance, which may result in significant advancements in high-tech areas, such as drug delivery, cell culturing, electronics, and tissue engineering.

Methods of changing low molecular weight gel properties through gelation kinetics.

The 3D printing of hydrogels from low molecular weight gelators (LMWGs) continues to attract notable interest, with many potential applications. One of the main issues with 3D printing is the difficulty characterising these gels after printing. Currently, the understanding of whether these bulk rheological properties are maintained upon printing is limited. To address this, we have developed a series of rheological and scattering methods to characterise these materials before, during, and after printing. We have used rheology and small-angle neutron scattering (SANS) to gain a deeper understanding of the impact printing has on the bulk properties of the hydrogels. We have determined that printing impacts the resulting gel fibril structure, which consequently changes the stiffness and strength of the gel. We hope that through this work, we have provided advances to the field of 3D printing of LMWGs, as well as showing the versatility of this fabrication technique to create gels with different properties.

Article	Year
Process Dependent Complexity in Multicomponent Gels. Macromolecular rapid communications\| PubMed ID: 36177680	2023
Using Solution History to Control Hydrogel Properties of a Perylene Bisimide. Chemistry (Weinheim an der Bergstrasse, Germany)\| PubMed ID: 37067953	2023
Investigating multigelator systems across multiple length scales. Soft matter\| PubMed ID: 37345406	2023
Tuning conductivity while maintaining mechanical properties in perylene bisimide hydrogels at physiological pH. Chemical communications (Cambridge, England)\| PubMed ID: 38385307	2024
Nanoscale assembly of enantiomeric supramolecular gels driven by the nature of solvents. Nanoscale\| PubMed ID: 38591601	2024
Methods of changing low molecular weight gel properties through gelation kinetics. Soft matter\| PubMed ID: 38691131	2024
Can we mimic 3D printing of low molecular weight gels using a rheometer? - a characterisation toolkit for extrusion printed gels. Faraday discussions\| PubMed ID: 40365669	2025

Rebecca E. Ginesi

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