The Biomimetic Regeneration Of Enamel Via Nano Calcium Phosphate And Active Bioglass

The development of biomineralization and biomaterials has demonstrated that nano-sized calcium phosphate particles play an essential role in the formation of hard tissues in biomatiarials. There is a general agreement that the basic building blocks in both bone and enamel are nano-sized apatite particles, although their hierarchical structures and functions are different. These nano building blocks can self-assemble into calcified tissue under the control of an organic matrix during biomineralization process. In our previous work, we demonstrated the remarkable role of nano apatite in enamel repair. The research includes:enamel repair by using nano apatite particles with the similar size as natural enamel blocks; a simple and effective biomimetic way to regenerate enamel structure with nano apatite particles; constructing enamel-like apatite layer on enamel surface by using bioglass under near-physiological conditions. The thesis is composed of five chapters:In chapter1, we introduce the conception of biomineralization, the formation process and structure of the hard tissues formed by of calcium phosphate, the concept of biomimetic mineralization, the development of enamel demineralization and caries. Then we review the common restoration materials and the recent development of enamel regeneration or repair. The basic problems in enamel repair are summarized based on these above knowledge and the research concerning these problems is proposed at the end of this chapter briefly.In chapter2, we study the role of nano apatite (HAP) particles which have the similar size and morphology with the natural enamel building blocks in enamel repair. Different from the conventional HAP and amorphous calcium phosphate (ACP), the nano HAP particles can tightly absorb on enamel surface and tend to array along the direction of natural enamel rod structure. Our previous studies have already revealed that the natural enamel building blocks are20-40nm calcium phosphate particles. And these building blocks can resist dissolution in acidic conditions. The CLSM (confocal laser scanning microscopy) results indicate that the demineralization of enamel surface was inhibited with the prevention of these nano particles. Thus the caries or second cries can be prevented significantly by the restoration. The results suggest the importance of size effect of calcium phosphate materials for their application in biomedical engineering.In chapter3, we develop an effective and simple approach to enamel regeneration. In our previous work, we have revealed that the nano calcium phosphate particles can self-assemble into enamel-like and bone-like structure with the control of amino acids. In this study, we immerse the enamel surface pre-absorbed20nm calcium phosphate particles into SBF solutions (simulated body fluid) containing100mM glutamic acid for72h. The results show that a repaired layer with enamel-like structure is formed on enamel surface in the combined effects of nano particles and glutamic acid. Besides, the regenerated layer has comparable mechanical prooerties with natual enamals. In previous works, various addtives are used in enamel remineralization including proteins, polymers, surfactants and fluoride ions. However, they hardly provide a simple, safe and economic strategy to enamel regeneration. Herein we report that a bio-inspired cooperative effect of glutamic acid and nano HAP can result in the effective regeneration of enamel-like structure under physiological conditions. Importantly, the mechanical characteristics of the repaired enamel are similar as the natual enamal. The study emphasizes the importance of co-reactions between the nano basic building blocks and organic molecules in the calcifications process and the study of biomedical biomaterials.Based on these above achievements, a more simple and practical method to regenerate enamel is shown in chapter4. Althoughthe method by using nano HAP and glutamine together has remarkable effect in enamel repair, the complex synthesis and purification of20nm HAP particles limite on its further application. Thus, a althernative substance which can replace the role of HAP nanoparticles are in great demand. Bio-glass can be appropriate candidate due to its excellent bio-compatibility and mineralization ability. Herein, the similar HAP layer with enamellike structure is well regenerated on enamel surface with the presence of bioglass and glutamic in SOF (simulated oral fluid). Again, the repaired layer formed on enamel surface shares the similar mechanical properties with that of natural enamel. Besides, glutamic acid can also accelerate the crystallization process from amorphous calcium phosphate to HAP. The promotion effect of Glu in enamel repair could not be achieved with fluoride which is now wildly used in dental products. Our current achievment provides a practical application to repair enamel clinically and highlight the biomimetic strategy in the regeneration of hard tissues.In chapter5, we emphasize the biomimetic strategy for hard tissue repair or regeneration. Our attempts about the enamel reconstruction may contribute to the development of biomaterials for the hard tissues regeneration. Some important but unsolved issues are also suggested in this chapter.