Kunneng Liang

Regeneration of biomimetic hydroxyapatite on etched human enamel by anionic PAMAM template in vitro.

OBJECTIVE To repair the demineralized enamel by biomimetic method, and the effect of Poly (amido amine) (PAMAM) dendrimers on the crystallization of hydroxyapatite on etched enamel surface is investigated. DESIGN PAMAM dendrimers were synthesized step by step following the classical method and modified with the carboxylic acid groups (COOH) on the surface. Demineralized human enamel samples were immersed in 10,000ppm PAMAM-COOH solution for 30min and then in calcium phosphorous solution with or without fluoride under near-clinical conditions for 20h. Other samples without PAMAM-COOH were immersed in calcium phosphorous solution as the control group. After the immersion, the micro structure, morphology and composition of the regrown crystals on the longitudinal and transversal enamel surfaces were investigated by SEM, XRD and FTIR, and the results were compared with etched enamel and intact enamel. RESULTS With the PAMAM-COOH templates, well-arranged rod-like crystals were formed and they were parallel to the long axis of enamel crystals, which was more obvious on the longitudinal enamel surface. Otherwise, irregular flake-like crystals were obtained without PAMAM-COOH. Fluorapatite was not influenced by the PAMAM-COOH but its specific distribution also shown the patterns of the PAMAM-COOH temples XRD spectra showed that the main phase of the obtained crystals with PAMAM-COOH was hydroxyapatite and their morphology and structure were close to the intact enamel. Amide I band and two bands of methylene groups of PAMAM-COOH detected by FTIR demonstrated the presence of PAMAM-COOH within the biomimetic coating. CONCLUSIONS It was concluded that PAMAM-COOH can play as the organic template on the demineralized enamel surface to induce the formation of HAP crystals with the same structure, orientation and mineral phase of the intact enamel in relatively short time.

Triclosan-loaded poly(amido amine) dendrimer for simultaneous treatment and remineralization of human dentine

In order to treat dental caries of damaged dentine, triclosan-loaded carboxyl-terminated poly(amido amine) dendrimer (PAMAM-COOH) is prepared and characterized. While being incubated in artificial saliva, triclosan-loaded PAMAM-COOH formulation can induce in situ remineralization of hydroxyapatite (HA) on etched dentine, and the regenerated HA has a similar crystal structure with natural dentine. It can also release the encapsulated triclosan for a long period. The interesting drug release profiles are controlled by both dendrimer encapsulation capability and the mineralization degree, which are ideal to obtain multifunctional properties of long-term release of anti-bacterial drug for local treatment during the remineralization process. The triclosan-loaded G4-COOH provides a general strategy to cure dental caries and repair damaged dentine at the same time, which forms a potential restorative material for dental repair.

Effective dentin restorative material based on phosphate-terminated dendrimer as artificial protein

In clinic, it calls for effective and simple materials to repair etched dentin. Bioinspired by the natural mineralization process guided by noncollagenous proteins (NCPs), in this work, we synthesized the fourth generation phosphate-terminated polyamidoamine dendrimer (G4-PO3H2) by one-step modification. We used FT-IR and 1H NMR to characterize the structure of G4-PO3H2, and MTT assay to prove its biocompatibility. It was applied as the analog of dentin phosphophoryn (DPP: a type of NCPs) to repair dentin, due to its similar dimensional scale, topological architecture and peripheral functionalities to that of DPP. By the characterization of SEM and XRD, the effective regeneration of human dentin induced by G4-PO3H2 is characterized and illustrated both in vitro (artificial saliva) and in vivo (oral cavity of rats). It is noted that the thickness of the regenerated mineral layers are more than 10 μm both in vitro and in vivo. The design strategy of G4-PO3H2 may be valuable for researchers in the fields of material science, stomatology and medicine to prepare various promising restorative nano-materials for biomineralized hard tissues such as bone and teeth.

Modulated regeneration of acid-etched human tooth enamel by a functionalized dendrimer that is an analog of amelogenin

In the bioinspired repair process of tooth enamel, it is important to simultaneously mimic the organic-matrix-induced biomineralization and increase the binding strength at the remineralization interface. In this work, a fourth-generation polyamidoamine dendrimer (PAMAM) is modified by dimethyl phosphate to obtain phosphate-terminated dendrimer (PAMAM-PO3H2) since it has a similar dimensional scale and peripheral functionalities to that of amelogenin, which plays important role in the natural development process of enamel. Its phosphate group has stronger affinity for calcium ion than carboxyl group and can simultaneously provide strong hydroxyapatite (HA)-binding capability. The MTT assay demonstrates the low cytotoxicity of PAMAM-PO3H2. Adsorption tests indicate that PAMAM-PO3H2 can be tightly adsorbed on the human tooth enamel. Scanning electron microscopy and X-ray diffraction are used to analyze the remineralization process. After being incubated in artificial saliva for 3weeks, there is a newly generated HA layer of 11.23μm thickness on the acid-etched tooth enamel treated by PAMAM-PO3H2, while the thickness for the carboxyl-terminated one (PAMAM-COOH) is only 6.02μm. PAMAM-PO3H2 can regulate the remineralization process to form ordered new crystals oriented along the Z-axis and produce an enamel prism-like structure that is similar to that of natural tooth enamel. The animal experiment also demonstrates that PAMAM-PO3H2 can induce significant HA regeneration in the oral cavity of rats. Thus PAMAM-PO3H2 shows great potential as a biomimetic restorative material for human tooth enamel.

Effective dentinal tubule occlusion induced by polyhydroxy-terminated PAMAM dendrimer in vitro

In recent years, poly (amido amine) (PAMAM) dendrimers have become a research focus in biomineralization fields. In this study, polyhydroxy-terminated PAMAM dendrimers (PAMAM-OH) were used to induce dentinal tubule occlusion. Demineralized dentin samples were coated with the second generation or the fourth generation PAMAM-OH solutions (G2-PAMAM-OH or G4-PAMAM-OH, 1 mg mL−1). The binding capacity of PAMAM-OH to demineralize dentin was tested by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Then the G4-PAMAM-OH-treated samples were immersed in artificial saliva for different periods. The remineralized samples were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). 6 wt% citric acid (pH 1.5) solutions were used to evaluate the effect of dentinal tubule occlusion. Cytotoxicity assay on dental pulp cells was carried out to examine the biocompatibility of G4-PAMAM-OH. The results of ATR-FTIR showed that G4-PAMAM-OH had a stronger binding capacity towards demineralized dentin than G2-PAMAM-OH did. After the remineralization, the G4-PAMAM-OH-treated samples showed obvious remineralization compared to the control group and the dentinal tubule occlusion was effective even after acid attack. The results of EDS and XRD confirmed that the regenerated minerals induced by G4-PAMAM-OH were hydroxyapatite (HA). Cytotoxicity assay showed that G4-PAMAM-OH had hardly any cytotoxicity towards dental pulp cells. In conclusion, G4-PAMAM-OH has great potential to be used in the treatment of dentin hypersensitivity in the future.

8DSS-promoted remineralization of demineralized dentin in vitro

Dentin phosphoprotein (DPP) plays an extremely important role in the biomineralization of human tooth. The repetitive nucleotide sequence of aspartate-serine-serine (DSS) is the fundamental unit within DPP, and peptides containing 8 repeats of DSS (8DSS) have been shown to possess the ability to induce remineralization of the demineralized enamel. In this work, we coated the 8DSS peptide on the completely demineralized dentin to evaluate the effect of 8DSS peptide coating on dentin remineralization. Human dentin samples were demineralized with 37% phosphoric acid for 2 min, and then the 8DSS peptide (1 mg mL-1) was coated and the binding strength of the 8DSS peptide to demineralized dentin was examined using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Then the coated dentin samples were immersed in artificial saliva for 3 weeks. After that, the remineralized dentin samples were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) analysis and ATR-FTIR. The mechanical properties of the remineralized surfaces were determined by nano-indentation and atomic force microscopy (AFM). The results showed that the 8DSS peptide had good binding strength to demineralized dentin and could induce nano-crystals precipitation both on the surfaces and within the dentinal tubules. The mechanical properties of the 8DSS-coated samples were significantly improved. In contrast, there were hardly any newly generated minerals deposited on the samples without 8DSS peptide coating. In conclusion, the 8DSS peptide may be a promising biomaterial for restoring the demineralized human dentin.

Biomimetic mineralization of collagen fibrils induced by amine-terminated PAMAM dendrimers – PAMAM dendrimers for remineralization

Objective: Achieving biomimetic mineralization of collagen fibrils by mimicking the role of non-collagenous proteins (NCPs) with biomimetic analogs is of great interest in the fields of material science and stomatology. Amine-terminated PAMAM dendrimer (PAMAM-NH2), which possesses a highly ordered architecture and many calcium coordination sites, may be a desirable template for simulating NCPs to induce mineralization of collagen fibrils. In this study, we focused on the ability of PAMAM-NH2 to mineralize collagen fibrils. Design: Type-I collagen fibrils were reconstituted over 400-mesh formvar-and-carbon-coated gold grids and treated with a third-generation PAMAM-NH2 (G3-PAMAM-NH2) solution. The treated collagen fibrils were immersed in artificial saliva for different lengths of time. The morphologies of the mineralized reconstituted type-I collagen fibrils were characterized by transmission electron microscopy. Results: No obvious mineralized collagen fibrils were detected in the control group. On the contrary, collagen fibrils were heavily mineralized in the experimental group. Most importantly, intrafibrillar mineralization was achieved within the reconstituted type-I collagen fibrils. Conclusions: In this study, we successfully induced biomimetic mineralization within type-I collagen fibrils using G3-PAMAM-NH2. This strategy may serve as a potential therapeutic technique for restoring completely demineralized collagenous mineralized tissues.

Biomimetic Remineralization of Human Enamel in the Presence of Polyamidoamine Dendrimers in vitro

Poly(amidoamine) (PAMAM) dendrimers, known as artificial proteins, have unique and well-defined molecular size and structure. It has previously been used to mimic protein-crystal interaction during biomineralization. In this study, generation 4.5 (4.5G) PAMAM with carboxylic acid (PAMAM-COOH) was synthesized and utilized to remineralize the surface of etched enamel in vitro. Using confocal laser scanning microscopy, Fourier transform infrared spectroscopy, X-ray diffraction analysis and scanning electron microscopy we observed that 4.5G PAMAM-COOH can be absorbed on the etched enamel surface and that it can induce the formation of hydroxyapatite crystals with the same orientation as that of the enamel prisms on longitudinal and transversal enamel surfaces. The self-assembly behavior of PAMAM in the mineralization solution was also investigated and the result showed that 4.5G PAMAM can assemble to microribbon structure similar to the behavior of amelogenins. Therefore, we concluded that 4.5G PAMAM-COOH assemblies can act as the organic template on enamel surface and in mineralization solution to control the nucleation site and morphology of new-grown crystals to form the biomimetic structure of human enamel, which may open a new way for repairing damaged enamel.

Bio-inspired peptide decorated dendrimers for a robust antibacterial coating on hydroxyapatite

Bacterial colonization on implanted biomaterials remains a clinically significant problem. In order to achieve relatively long-term antibacterial activity and reduce the incidence of infections associated with the use of biomaterials, a salivary statherin protein (SSP) inspired poly(amidoamine) dendrimer (SSP-PAMAM-NH2) was synthesized and characterized. PAMAM-NH2 has numerous peripheral amino groups, and thus possesses effective antibacterial activity. The SSP bio-inspired peptide sequence DDDEEKC was conjugated to PAMAM-NH2 since it has a strong capability of adsorbing on hydroxyapatite (HA). Moreover, SSP-PAMAM-NH2 is a zwitterionic polymer possessing cationic amino groups and anionic carboxylic groups, thus it can form aggregates by intermolecular electrostatic interactions, thereby promoting its adsorption on HA. Adsorption tests by ATR-IR, UV, QCM-D, and CLSM, all indicated that SSP-PAMAM-NH2 can tightly adsorb on the HA surface. We found that even after being incubated in PBS for 4 weeks, the SSP-PAMAM-NH2 treated HA disks still retained stable antibacterial activity, while the inhibitory impact of PAMAM-NH2 treated disks had disappeared. Animal experiments also demonstrated that SSP-PAMAM-NH2 could significantly reduce infection of HA implanted into the medullary cavity of rats.

8DSS peptide induced effective dentinal tubule occlusion in vitro

OBJECTIVE Eight repetitive nucleotide sequences of aspartate-serine-serine (8DSS) derived from dentin phosphoprotein (DPP) has been proved to be a good remineralization agency. In this study, 8DSS peptide was employed to induce dentinal tubule occlusion. METHODS Dentin samples were acid-etched, and then the samples were coated with 8DSS solution. The binding capacity of 8DSS to acid-etched dentin was tested by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Subsequently, the 8DSS-treated dentin samples were immersed in artificial saliva for 1, 2 and 4 weeks. After 4 weeks, the remineralized dentin was treated with 6wt% citric acid (pH 1.5) solution for 1min. Dentin permeability measurement and scanning electron microscopy (SEM) were carried out after different periods. Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were used to identify the mineral phase of the regenerated minerals. RESULTS The results showed that 8DSS had a good binding capacity to the acid-etched dentin, and significantly reduced the dentin permeability by inducing minerals deposited within the dentinal tubules. After 4 weeks, all the dentinal tubules were occluded by large bulk of regenerated minerals, which largely decreased the diameters of the tubules. The regenerated minerals deposited with a deep depth within the dentinal tubules, ensuring an effective occlusion even after an acid challenge. The results of XRD and EDS confirmed that the regenerated minerals were mainly hydroxyapatite (HA). SIGNIFICANCE 8DSS peptide induced strong dentinal tubule occlusion. 8DSS have a great potential to be used in the treatment of dentin hypersensitivity in the future.