Amelogenin Affects Brushite Morphology and Promotes Phase Transformation to Monetite

Objectives: Amelogenin protein has been applied in a variety of systems to prepare enamel-like materials. Brushite crystals have been used as a precursor to synthesize apatitic enamel-like structures through phase transformation. To study the effect of amelogenin on brushite crystal morphology and phase transformation, and to understand the mechanisms underlying these effects. Our long-term goal is to develop a novel approach of synthesizing enamel-like biomimetic materials with the prismatic structure.
Methods: Brushite was produced by titrating Na₂HPO₄ into a mixture of KH₂PO₄ and CaCl₂ at room temperature. The pH was adjusted to 5.5 and 0.1 mg/ml amelogenin was added into the solution, alongside a control group without protein. We used: FTIR and TGA to study amelogenin adsorption; SEM and AFM to study crystal morphology; XRD and TGA to analyze crystal phase transformation. We characterized the amelogenin adsorption on the brushite crystal surface, which led to morphological changes. The abnormal crystal phase transformation caused by amelogenin was deduced to derive from specific bonding between amelogenin and crystalline water on the brushite (010) crystal faces.
Results: Amelogenin had a strong affinity to the brushite (010) face, leading to changes in brushite crystal morphology. SEM revealed that new layers and sub-layers appeared in the presence of amelogenin. Brushite-monetite phase transformation occurred faster in the presence of amelogenin. The morphological change was retained even after phase transformation to monetite, creating a structure similar to the “rod-interrod” pattern seen in natural enamel.
Conclusions: Amelogenin adsorbed onto the brushite (010) surface, a) significantly affecting brushite crystal morphology and b) promoting brushite-monetite phase transformation by interacting with the crystalline water layers on the (010) face. Remarkably, crystal shape was preserved even after phase transformation, producing a structure similar to the prismatic structure of dental enamel.