Abstract
Casein is a micellar protein rich in glutamic and aspartic acids as well as in phosphoserine. Considering its native affinity for calcium and the connection of sub-micelles through calcium phosphate nanoclusters, this protein holds promise for stimulating biomimetic mineralisation phenomena and direct binding with the mineral phase of hard tissues. In this work we prepared new hybrids based on casein embedded in a poly(2-hydroxyethyl methacrylate)-polyethyleneglycol diacrylate (PHEMA-PEGDA) hydrogel. The resulting materials were investigated structurally by Fourier transform infrared (FT-IR). Casein modified the water affinity and the rheological properties of the hybrids. The microstructure was explored by scanning electron microscopy (SEM) and the distribution of the protein was established by combined SEM micrographs and elemental mapping considering the casein-specific elements (P, N and S) not contained by the synthetic hydrogel matrix. The effect of casein on the mineralisation potential and stability of the mineral phase was investigated by FT-IR and SEM when alternating incubation in Ca/P solutions is performed. Increasing casein content in the hybrids leads to improved mineralisation, with localised formation of nanoapatite phase on the protein areas in the richest sample in protein. This behaviour was proved microstructurally by SEM and through overlapping elemental distribution of Ca and P from the newly formed mineral and P, S and N from the protein. This study indicates that nanoapatite-casein-PHEMA-PEGDA nanocomposites may be developed for potential use in bone repair and regeneration.
Highlights
Introduction published maps and institutional affilThe development of hybrid materials incorporating casein is gaining increasing attention considering the high availability and low cost of this protein and its interesting properties
This study aimed, in the first step, to obtain new hybrid hydrogels based on casein embedded into a synthetic HP matrix, further denoted H1P1C hydrogels
We previously explored casein-poly(2-hydroxyethyl methacrylate) (PHEMA) hybrids for their mineralisation potential in synthetic body fluid, the hybrid hydrogels being obtained by network-forming polymerisation in the presence of commercial PHEMA macromolecules and protein dissolved in NaOH solution, through crosslinking of HEMA with 3% molar tetraethylene glycol dimethacrylate [1]
Summary
Introduction published maps and institutional affilThe development of hybrid materials incorporating casein is gaining increasing attention considering the high availability and low cost of this protein and its interesting properties. The combination of synthetic hydrogels such as polyacrylamide (PAAm), poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(sodium methacrylate) (PMANa) with casein has been performed to obtain hydrogels with added value when compared to individual ones [1,2,3,4,5,6] This micellar protein is rich in glutamic and aspartic acids as well as in phosphoserine, these aminoacids presenting high affinity for calcium [3,4,5,6]. The sub-micelles are connected through calcium phosphate nanoclusters [3,7] Such a native proteic microstructure holds promise for stimulating biomimetic mineralisation and direct binding with the mineral phase of hard tissues.
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