Molecular level and microstructural characterisation of thermally sensitive chitosan hydrogels

Chitosan–glycerophosphate (GP) is a physiological pH solution at room temperature which forms a physical hydrogel upon heating to 37 °C. The hydrogel is suitable for biomedical applications and in particular as a biodegradable scaffold for tissue engineering. Since the structure of the hydrogel is critical to cell–material interactions, small angle neutron scattering (SANS) and ultra SANS (USANS) were used to examine the molecular conformation of chitosan chains and the larger scale microstructure. On the nanoscale, the hydrogel is described in terms of a static component (characteristic length, Ξ) which accounts for the physical cross-links, and a dynamic component (correlation length, ξ) which accounts for solution-like properties. Over the range 0.25–1.5 w/v% chitosan concentration the molecular structure is dependent on concentration with the characteristic length decreasing from ∼450 Å to ∼300 Å, and the correlation length increasing from ∼110 Å to ∼130 Å. The chitosan chains were arranged at a larger scale into polymer-rich aggregates of 1–2 µm diameter which decreased in size as the chitosan concentration increased. Such structural information is important for tailoring the hydrogel for specific applications.