Correlating the mass and mechanical property changes during the degradation of PEG-based adhesive

Change in mechanical property of a degrading adhesive is critical to its performance. However, characterization of degradation behavior is often limited to tracking its mass loss. 4-armed PEG end modified with dopamine (PEG-DA) was used as a model bioadhesive to correlate its change in mass with change in mechanical property. Shear modulus (G) was calculated based on the mass and average molecular weight between crosslinks $$ of PEG-DA, while the storage modulus (G') was determined by oscillatory rheometry. G decreased slowly within the first week of degradation (10% reduction by week 2), while G' decreased by 60% during the same period. This large discrepancy is due to the partially disconnected and elastically ineffective PEG polymer, which is trapped within the adhesive network. This resulted in minimal mass change and higher calculated G value during the earlier time points. Therefore, tracking mass loss profile alone is inadequate to completely describe the degradation behavior of an adhesive. Additionally, PEG-DA was coated onto magnetoelastic (ME) sensors, and the change in the resonance amplitude of the sensor corresponded well with dry mass loss of PEG-DA. ME sensing provide a non-destructive method to track the mass loss of the coated adhesive.