Abstract
Poly(vinyl alcohol) (PVA) hydrogels produced using the freeze-thaw method have attracted attention for a long time since their first preparation in 1975. Due to the importance of polymer intrinsic features and the advantages associated with them, they are very suitable for biomedical applications such as tissue engineering and drug delivery systems. On the other hand, there is an increasing interest in the use of biobased additives such as cellulose nanocrystals, CNC. This study focused on composite hydrogels which were produced by using different concentrations of PVA (5 and 10%) and CNC (1 and 10 wt.%), also, pure PVA hydrogels were used as references. The main goal was to determine the impact of both components on mechanical, thermal, and water absorption properties of composite hydrogels as well as on morphology and initial water content. It was found that PVA had a dominating effect on all hydrogels. The effect of the CNC addition was both concentration-dependent and case-dependent. As a general trend, addition of CNC decreased the water content of the prepared hydrogels, decreased the crystallinity of the PVA, and increased the hydrogels compression modulus and strength to some extent. The performance of composite hydrogels in a cyclic compression test was studied; the hydrogel with low PVA (5) and high CNC (10) content showed totally reversible behavior after 10 cycles.
Highlights
A great number of studies were devoted to the structure and properties of Poly(vinyl alcohol) (PVA) hydrogels
The dense package of the polymer chain in the P10C10 composite makes relaxation after the withdrawal of load more difficult. The effect of both PVA polymer and cellulose nanocrystals on various properties of composite hydrogels produced by using the freeze-thaw method was investigated
We were interested to study the P5C1 and P5C10 composite hydrogels, due to the fact that most referred studies on PVA hydrogels were produced with PVA concentration of 10% or higher, and it was expected that cellulose nanocrystals (CNCs) would have a reinforcing effect
Summary
A great number of studies were devoted to the structure and properties of PVA hydrogels. These were obtained by freeze-thawing techniques, first prepared by Peppas (1975). Despite first being prepared nearly half a century ago and commercial PVA cryogel material (SalubriaTM) being readily available, the study on PVA hydrogels prepared by the freeze-thawing method is still in an early stage of research. The authors are aware that there are plenty of other publications on PVA-based materials produced by techniques other than freeze-thawing (e.g., injection molding, film casting, etc.) as well as methods, which include the usage of chemical cross-linking agents (for example, glutaraldehyde). The key interest of the authors was freeze-thaw as a method, which allows the production of three dimensional porous structures with the possibility to modify the network structure by a changing of freezing and/or thawing parameters
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