Swelling and mechanical properties of physically crosslinked poly(vinyl alcohol) hydrogels

Abstract

Physically crosslinked poly(vinyl alcohol) gels are versatile biomaterials due to their excellent biocompatibility. In the past decades, physically crosslinked poly(vinyl alcohol) and poly(vinyl alcohol)-based hydrogels have been extensively studied for biomedical applications. However, these materials have not yet been implemented due to their mechanical strength. Physically crosslinked poly(vinyl alcohol) gels consist of a swollen amorphous network of poly(vinyl alcohol) physically crosslinked by microcrystallites. Although the mechanical properties can be improved to some extent by controlling the distribution of microcrystallites on the nano- and micro-scales, enhancing the mechanical properties while maintaining high water content remains very difficult. It may be technologically impossible to significantly improve the mechanical properties while keeping the gel's high water absorbance ability using conventional fabrication methods. Physical and chemical understandings of the swelling and mechanical properties of physically crosslinked poly(vinyl alcohol) gels are considered here; some promising strategies for their practical applications are presented. This review focuses more on the recent studies on swelling and mechanical properties of poly(vinyl alcohol) hydrogels, prepared using only poly(vinyl alcohol) and pure water with no other chemicals, as potential biomedical materials.

Silver hydroxyapatite reinforced poly(vinyl alcohol)—starch cryogel nanocomposites and study of biodegradation, compressive strength and antibacterial activity

“…However, beyond the 9 th freeze thaw cycle, the much enhanced crystallites tend to oppose the elastic response of the nanocomposite and the compressive strength decreases. In a study by Suzuki and Sasaki the Young's modulus of PVA cryogel was found to increase constantly with increasing number of freeze thaw cycles, however, no such observation was found in our case. Similar type of increase in mechanical properties of PVA hydrogel with increasing number of thermal cycles has also been reported by Millon and co‐workers .…”

Swelling Resistance and Mechanical Performance of Physical Crosslink‐Based Poly(Vinyl Alcohol) Hydrogel Film with Various Molecular Weight

“…The highest crystallinity, Young's modulus, and swelling degree were 36%, 1.46 GPa, and 470%, respectively . In recent decades, the physically crosslinked gels have attracted more attention, to avoid using chemical crosslinking agents and reagents …”

Tensile Fatigue of Poly(Vinyl Alcohol) Hydrogels with Bio‐Friendly Toughening Agents

“…[ 80,81 ] In addition, crystallinity of a swollen gel is not always proportional to that of a dried gel. [ 82 ] As a result, any change in the crystallinity degree could not be appropriately assigned to the presence of starch, as it would be unclear what role a particular drying process may have played. X‐ray diffraction was then pursued to study the crystalline nature of the hydrogel samples in their as‐prepared state, as seen in Figure a.…”

“…The PVA‐based hydrogels consist of a swollen, amorphous network of PVA molecular chains that are physically crosslinked together with small, highly ordered pockets of PVA known as microcrystallites. [ 82 ] These microcrystallite regions develop from the freezing of water at very cold temperatures, giving way to small regions of minimal molecular motion that are highly concentrated with PVA. [ 87 ] With the PVA molecular chains in close proximity to one another, crystallite formation begins and it continues to progress during subsequent freezing cyles.…”