Composites of polyvinyl alcohol (PVA) hydrogel and calcium and magnesium phosphate formed by enzymatic functionalization

In this study, polyvinyl alcohol (PVA) hydrogels designed for osteochondral regeneration were mineralized with calcium phosphate (CaP) and magnesium phosphate (MgP) by incorporation of the enzyme alkaline phosphatase (ALP) and incubation in solutions of 0.1 M calcium or magnesium glycerophosphate (CaGP, MgGP). Hydrogels incubated in water served as controls. Dry mass percentage, i.e. the percentage consisting of polymer and mineral and not water, was markedly higher for samples incubated in CaGP and MgGP and decreased in the order: CaGP>MgGP>water. CaP and MgP formation was confirmed by FTIR. SEM revealed spherical deposits characteristic for apatite in samples incubated in CaGP and plate-like crystals of the magnesium phosphate bobierrite in samples incubated in MgGP, while samples incubated in water were devoid of deposits. Rheometric testing showed that storage modulus of hydrogels incubated in CaGP and MgGP was markedly higher and decreased in the order: CaGP>MgGP>water. The results prove the principle of enzymatic mineralization of PVA with CaP and MgP to improve their suitability for bone regeneration applications.