The dynamic viscoelastic characterisation and magnetic resonance imaging of poly(vinyl alcohol) cryogel: identifying new attributes and opportunities

Poly(vinyl alcohol) (PVA) cryogel is a biocompatible, synthetic hydrogel, compatible with magnetic resonance (MR) imaging. It is widely used as a biomaterial in tissue scaffolds and mimics to test various diagnostic techniques. The aim of this study is to characterise the effect of varying PVA concentration, molecular weight (MW) and manufacturing protocol on the viscoelastic mechanical properties and MR T₂ relaxation time. Further to this MR imaging (MRI) was investigated as a method to quantify material homogeneity. Cylindrical samples of PVA, of varying MW, concentration and number of freeze thaw cycles (FTCs), were manufactured. Dynamic mechanical analysis was performed to evaluate the storage and loss moduli between frequencies of 0.5 and 10 Hz. MR T₂ relaxation maps were imaged using a 7 T MRI instrument. Storage and loss moduli were shown to increase with MW, concentration, or the number of FTCs; with storage modulus ranging from 55 kPa to 912 kPa and loss modulus ranging from 6 kPa to 103 kPa. MR T₂ relaxation time was shown to increase linearly with PVA concentration. The qualitative and quantitative heterogeneity of the PVA sample were identified through MR T₂ relaxation time maps. Excitingly, PVA demonstrated a composition-dependent casual correlation between the viscoelastic mechanical properties and MR T₂ relaxation time. In conclusion, this research thoroughly characterised the viscoelastic mechanical properties of PVA to support its extensive use as a biomaterial, and demonstrated the use of MRI to non-invasively identify sample heterogeneity and to predict the composition-dependent viscoelastic properties of PVA.