Molecular Weight-Dependent Boron Release Effect in PVA/Chitosan Cryogels and In Vitro Mineralization Evaluations by Osteoblast Cells.

Cryogels were fabricated by combining polyvinyl alcohol (PVA) and chitosan of varying molecular weights (Mw). In this study, the effects of chitosan Mw, types of boron-containing molecules on network formation, and boron release rate in resulted cryogels were investigated. The PVA/chitosan blend maintained a constant 4.5% (w/v) polymer content. PVA to chitosan weight ratio of 6:1 was maintained and fixed. Five percent w/w boric acid and borax (sodium tetraborate) crosslinkers were added in PVA and chitosan mixtures to construct cryogels. The freeze-dried specimens underwent crosslinking evaluation, chemical composition analysis by FTIR, and boron release studies by ICP-MS. The pore morphology and the swelling capacity of the cryogel have been assessed by SEM and incubation in water, respectively. Mechanical test was also used to evaluate the effect of borax and Mw of chitosan on cryogels' mechanical properties. It was demonstrated that the types of boron supply had a significant role on the cryogelation capability. For different chitosan Mw, the cryogels made using borax showed stable cryogels. In contrast, even after altering the chitosan Mw, the formula with boric acid was unable to create stable cryogels. In addition, boron release assay showed that the quantity of free boron in the incubation solutions decreased as the Mw of the chitosan component of the cryogel was reduced. Cell culture studies with MC3T3-E1 pre-osteoblast cells in the cryogels indicated that borax-crosslinked samples exhibited sustained cell viability. Alizarin red staining assay was used to study mineralization capacity of boron-containing hydrogels, which confirmed increase of mineralization in low molecular weight chitosan groups.