Do hydrogels contain different classes of water?

Area of Science:

• Materials Science
• Physical Chemistry
• Biophysics

Background:

• Poly (hydroxy ethyl methacrylate) (PHEMA) hydrogels are widely studied.
• Previous calorimetric studies showed irregular melting curves, interpreted as evidence for distinct water populations within the hydrogels.
• The nature of water in hydrogels remains a topic of scientific interest.

Purpose of the Study:

• To investigate the cause of irregular melting curves observed in calorimetric studies of PHEMA hydrogels.
• To determine if the observed melting behavior indicates different types of water or other phenomena.
• To provide a more accurate interpretation of calorimetric data for hydrogel systems.

Main Methods:

• Calorimetric studies were performed on poly (hydroxy ethyl methacrylate) (PHEMA) hydrogels during freezing and thawing.
• Nuclear Magnetic Resonance (NMR) relaxation measurements were used to assess water molecule mobility within the hydrogels.
• Data were compared with findings from fundamental freeze-drying studies.

Main Results:

• Calorimetric studies indicate that the irregular melting behavior of PHEMA hydrogels is likely caused by a glass transition phenomenon during freezing.
• NMR relaxation measurements revealed rapid interchange between water molecules in the hydrogels.
• These findings suggest that the observed calorimetric irregularities do not necessarily imply the existence of different classes of water.

Conclusions:

• The irregular melting curves in calorimetric studies of PHEMA hydrogels are attributed to the glass transition, not distinct water types.
• NMR data support the conclusion that water molecules in hydrogels exhibit rapid exchange, refuting the multiple water classes hypothesis.
• The interpretation of calorimetric data for hydrogels should consider the influence of the glass transition and water mobility.