Creating a characterisation toolkit for extrusion printed hydrogels

, by CeMi Team

Dr. Rebecca Ginesi shares her development of advanced techniques to characterise printed supramolecular hydrogels, uncovering how the 3D printing process impacts their microstructure and mechanical behaviour.

Printable hydrogels are gaining interest in a wide variety of fields, from precision medicine to optoelectronics. One challenge in 3D printing is characterising these hydrogels post-printing. Furthermore, most reported examples of printable hydrogels have been discovered through serendipity. Therefore, the link between the microstructure of the gel network and its printability is poorly understood.  

During my PhD in the School of Chemistry (UoG), one of my research projects focused on 3D printing supramolecular hydrogels, and specifically finding the best way to characterise them. Often, only the pre-printed gel is characterised, with little (if any) characterisation done post-printing. Therefore, it is assumed that the mechanical properties of the printed gel are unaffected by the printing process, which seems unlikely due to the processes involved (FIGURE 1). Our latest publication (Ginesi, R. E., Doutch, J., & Draper, E. R. (2025). Can we mimic 3D printing of low molecular weight gels using a rheometer? – a characterisation toolkit for extrusion printed gels. Faraday Discuss.) focused on creating new methods of comparing printed and extruded gels with gels that had been sheared on a rheometer.

FIGURE 1. CARTOON SHOWING HOW PRINTING CAN IMPACT THE PROPERTIES OF GELS AND THE TYPES OF RHEOLOGICAL CHARACTERISATIONS THAT ARE IMPORTANT DURING THE DIFFERENT STAGES OF THE PRINTING PROCESS.

FIGURE 1: CARTOON SHOWING HOW PRINTING CAN IMPACT THE PROPERTIES OF GELS AND THE TYPES OF RHEOLOGICAL CHARACTERISATIONS THAT ARE IMPORTANT DURING THE DIFFERENT STAGES OF THE PRINTING PROCESS. 

To address these challenges, we developed a series of rheological methods to characterise the properties of hydrogels before, during, and after printing to better understand the impact of the printing process and the effect on the bulk properties. Rheology showed that printing made the gels stiffer but weaker, likely due to shear-induced energy dissipation. To explore nanoscale structural changes, we used small-angle neutron scattering (SANS). Here, neutrons are directed at a sample, and how these neutrons scatter at small angles due to interactions with atomic nuclei is measured. This scattering provides information about the size, shape, and arrangement of the structures present in the sample. Therefore, this technique was used to determine whether the gel fibres are altered by extrusion. We found that the fibres became more tape-like when printed and could explain the increase in stiffness observed in the rheological data. We then applied in situ RheoSANS (simultaneous rheology and small-angle neutron scattering) to monitor structural and mechanical changes during printing. This approach, not previously applied to printed hydrogels, enabled direct correlation between stiffness and fibre structure. 

I am excited to bring the knowledge I have gained from this project to my role at CeMi. In a few days, I am conducting an experiment at ISIS Neutron and Muon source to do a RheoSANS experiment where I will mimic cell movement in our polymer-based hydrogels to better understand how the cells interact within these systems.