Paper BI-TuP2
Flash Networking Poster: Characterising Hydrogel Chemistry Through Low Temperature ToF-SIMS

Tuesday, October 20, 2015, 6:30 pm, Room Hall 3

Over the last decade the beneficial properties of hydrogels as artificial cell culture supports have been extensively investigated¹. Certain synthetic hydrogels have been proposed to be similar in composition and structure to the native extracellular matrix of the stem cell niche, their in vivo cell habitat, which is a powerful component in controlling stem cell fate². The stem cell differentiation pathway taken is influenced by a number of factors. When culturing cells within or upon hydrogels this choice can be strongly dependent on the underlying 3D hydrogel chemistry which strongly influences hydrogel-cell interactions³. The interrelationship between hydrogel chemistry and that of biomolecules in controlling cellular response ideally requires analysis methods to characterise the chemistry without labels and often in 3D. Time-of-flight secondary ion mass spectrometry (ToF SIMS) has the potential to be utilised for through thickness characterisation of hydrogels. The frozen-hydrated sample format is well suited to minimise changes associated with dehydration or the chemical complexity of ‘fixation’, a challenging aspect in vacuum analysis conditions⁴. Frost formation can occur in the ambient atmosphere preventing ready depth profiling of the frozen hydrogels. We develop a simple method to remove this frost by blowing with gas prior to entry into the instrument which is shown to produce remarkably good profiles on a poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogel film where a model protein, lysozyme, is incorporated to demonstrated how biomolecule distribution within hydrogels can be determined. A comparison of lysozyme incorporation is made between the situation where the protein is present in the polymer dip coating solution and lysozyme is a component of the incubation medium. It is shown that protonated water clusters H(H₂O)_n⁺ where n=5-11 that are indicative of ice are detected through the entire thickness of the pHEMA and the lysozyme distribution through the pHEMA hydrogel films can be determined using the intensity of characteristic fragment secondary ions. Early stage data from more complex gel systems will be presented to determine the limitation of this approach.