title: Tuning, understanding and evaluating the mechanical properties of peptide-based low molecular weight hydrogels over different length scales
Creators: name: Fuentes Caparrós, Ana María
Publisher: name: University of Glasgow
Year: 2021
Subjects: subject: gel, hydrogel, multicomponent, rheology, 3D-printing.

description: We report the ability to tune and characterise the mechanical properties of low molecular weight hydrogels over different length scales. These materials have been investigated due to their potential for use in a wide range of biomedical applications including drug delivery, tissue engineering, cell culture and wound healing. As such, it is really important to not only being able to characterise the properties of this class of materials at different length scales, but also to find new approaches that will open up new opportunities to control gel networks on demand to provide tuneable, triggerable materials. We describe a multicomponent system of two gelators that forms a gel via a solvent-trigger approach. After gelation, thermal annealing leads to a self-sorted network which interestingly exhibits significantly different mechanical properties to the as-prepared gel. The changes in the mechanical properties affect the stiffness of the resulting gel system, which will also impact on the diffusion and transport within the gel network. Furthermore, we demonstrate that it is also possible to selectively anneal only one component within the mixture. This also leads to a change in the final gel properties, but in a different manner than when both gelators were annealed. We also describe the use of cavitation rheology to characterise the linear elastic modulus of a range of hydrogels at a different scale that traditional shear rheology cannot access. We investigate a quantitative relationship, ksc, between the gel modulus determined using both cavitation and traditional shear rheology, that will allow to interconvert between both techniques. We show that the data from the cavitation rheology correlates with the underlying microstructure within the gels, which allows a greater degree of understanding of the gel systems than can be obtained from the bulk measurements using traditional shear rheology, as well as allowing information to be gathered on a local environment, which can be used to determine gel homogeneity. Finally, we successfully developed new rheological protocols to characterise the mechanical properties of multi-layered hydrogels prepared in situ and post 3D-printing with a high degree of control. From rheological analysis, we show that not only a high control of the measured mechanical properties of the individual layers within the multi-layered constructions can be achieved, but also the contribution of each layer on the resulting properties being measured can be assessed. We also emphasise the importance of using different measuring systems for rheological measurements, as these impact heavily on the resulting properties being measured. We present this study as a tool for assessing the mechanical properties of 3D printed gels and we hope this will open up new opportunities to characterise new biomaterials on demand.