Abstract
Water has a key role in the functioning of all biological systems, it mediates many biochemical reactions, as well as other biological activities such as material biocompatibility. Water is often considered as an inert solvent, however at the molecular level, it shows different behavior when sorbed onto surfaces like polymeric implants. Three states of water have been recognized: non-freezable water, which does not freeze even at −100 °C; intermediate water, which freezes below 0 °C; and, free water, which freezes at 0 °C like bulk water. This review describes the different states of water and the techniques for their identification and quantification, and analyzes their relationship with hemocompatibility in polymer surfaces. Intermediate water content higher than 3 wt % is related to better hemocompatibility for poly(ethylene glycol), poly(meth)acrylates, aliphatic carbonyls, and poly(lactic-co-glycolic acid) surfaces. Therefore, characterizing water states in addition to water content is key for polymer selection and material design for medical applications.
Highlights
Water is considered to be the most important compound of life and is the most abundant compound on earth
The weight percentages of the different states of water can be calculated based on nuclear magnetic resonance (NMR) data, though not many studies base their calculations on this technique
Water and its states influence polymer hemocompatibility. In polymers such as Poly(ethylene glycol) (PEG), aliphatic carbonyls, poly(meth)acrylates, poly(lactic-co-glycolic acid) (PLGA), and poly(vinyl alcohol) (PVA), intermediate water content of at least 3 wt % relates to low platelet adhesion and higher hemocompatibility than those with less or none, which is due to the better stability that this state of water has in comparison to free water, preventing platelets contacting non-freezable water and activating it
Summary
Water is considered to be the most important compound of life and is the most abundant compound on earth. Over 70% of the surface of the planet is covered by water, in the form of solid, liquid, and vapor [1]. It is the main component of biological systems, being essential for many chemical reactions. Water is often regarded as the universal solvent because of its great versatility: it can dissolve proteins, ions, sugars, gases, organic liquids, and lipids. Compared to other common liquids, water is characterized by having high boiling, melting, and critical temperatures, large specific heat, and high surface tension, among other properties [2]. In the first section of the review, general aspects of water and its behavior in biological systems and surfaces are described
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