Dynamics of Biomineralization and Biodemineralization

Effect of a new modified polyamidoamine dendrimer biomimetic system on the mineralization of type I collagen fibrils: an in vitro study

We evaluate the effects of the new Dentine matrix protein 1 (DMP-1) biomimetic system composed of phosphorylated polyamidoamine dendrimer (PAMAM-PO₃H₂) and carboxylated polyamidoamine dendrimer (PAMAM-COOH) on the mineralization of type I collagen fibrils. PAMAM-PO₃H₂ and PAMAM-COOH were observed to have the ability to induce internal and external mineralization of type I collagen fibrils in vitro through non-classical mineralization crystallization pathway, which has become a hopeful biomimetic system of biomimetic remineralization and demineralization of dentin type I collagen fibrils and has great potential in inducing biomimetic remineralization of demineralized dentin.

Intraosseous Injection of Calcium Phosphate Polymer-Induced Liquid Precursor Increases Bone Density and Improves Early Implant Osseointegration in Ovariectomized Rats

PURPOSE

Osteoporosis, due to bone loss and structural deterioration, is a risk factor for dental implant failure, as it impedes initial stability and osseointegration. We aim to assess the effects of calcium phosphate polymer-induced liquid precursor (CaP-PILP) treatment, which significantly increases bone density and improves early implant osseointegration in ovariectomized rats.

METHODS

In this study, CaP-PILP was synthesized and characterized through TEM, FTIR and XRD. A rat model of osteoporosis was generated by ovariectomy. CaP-PILP or hydroxyapatite (HAP, negative control) was injected into the tibia, and the resulting changes in bone quality were determined. Further, implants were installed in the treated tibias, and implantation characteristics were assessed after 4 weeks.

RESULTS

The CaP-PILP group had superior bone repair. Importantly, CaP-PILP had excellent properties, similar to those of normal bone, in terms of implant osseointegration. In vivo experiment displayed that CaP-PILP group had better bone contact rate (65.97±3.176) than HAP and OVX groups. Meanwhile, a mound of mature and continuous new bone formed. Moreover, the values of BIC and BA showed no significant difference between the CaP-PILP group and the sham group.

CONCLUSION

In summary, CaP-PILP is a promising material for application in poor-quality bones to improve implant success rates in patients with osteoporosis. This research provides new perspectives on the application of nano-apatite materials in bone repair.

Pro-angiogenic and osteogenic composite scaffolds of fibrin, alginate and calcium phosphate for bone tissue engineering

Due to the limitations of bone autografts, we aimed to develop new composite biomaterials with pro-angiogenic and osteogenic properties to be used as scaffolds in bone tissue engineering applications. We used a porous, cross-linked and slowly biodegradable fibrin/alginate scaffold originally developed in our laboratory for wound healing, throughout which deposits of calcium phosphate (CaP) were evenly incorporated using an established biomimetic method. Material characterisation revealed the porous nature and confirmed the deposition of CaP precursor phases throughout the scaffolds. MC3T3-E1 cells adhered to the scaffolds, proliferated, migrated and differentiated down the osteogenic pathway during the culture period. Chick chorioallantoic membrane (CAM) assay results showed that the scaffolds were pro-angiogenic and biocompatible. The work presented here gave useful insights into the potential of these pro-angiogenic and osteogenic scaffolds for bone tissue engineering and merits further research in a pre-clinical model prior to its clinical translation.

Fourier transform infrared spectroscopy of developing bone mineral: from amorphous precursor to mature crystal

Bone mineral development has been described to proceed through an amorphous precursor prior to apatite crystallization. However, further analytical approaches are necessary to identify specific markers of amorphous mineral components in bone. Here, we establish an original Fourier transform infrared (FTIR) spectroscopy approach to allow the specific identification of the amorphous and/or crystalline nature of bone mineral. Using a series of standards, our results demonstrate that obtaining the second derivative of the FTIR spectra could reveal a peak specifically corresponding to amorphous calcium phosphate (ACP) at ∼992 cm-1. The intensity of this peak was strongly correlated to ACP content in standard mixtures. The analysis of a variety of bones showed that a clear ACP peak could be identified as a specific marker of the existence of an amorphous mineral component in developing bones. In contrast, the ACP peak was not detected in the mature bones. Moreover, subjecting developing bones to ex vivo crystallization conditions led to a clear reduction of the ACP peak, further substantiating the conversion of amorphous mineral precursor into mature apatite crystals. Analysis of mineralization in osteogenic cell cultures corroborated our observations, showing the presence of ACP as a major transient component in early mineralization, but not in the mature matrix. Additionally, FTIR imaging revealed that ACP was present in areas of matrix development, distributed around the edges of mineralizing nodules. Using an original analytical approach, this work provides strong evidence to support that bone mineral development is initiated by an amorphous precursor prior to apatite crystallization.

Mechanisms of Modulation of Calcium Phosphate Pathological Mineralization by Mobile and Immobile Small-Molecule Inhibitors

Potential pathways for inhibiting crystal growth are via either disrupting local microenvironments surrounding crystal-solution interfaces or physically blocking solute molecule attachment. However, the actual mode of inhibition may be more complicated due to the characteristic time scale for the inhibitor adsorption and relaxation to a well-bound state at crystal surfaces. Here we demonstrate the role of citrate (CA) and hydroxycitrate (HCA) in brushite (DCPD, CaHPO₄·2H₂O) crystallization over a broad range of both inhibitor concentrations and supersaturations by in situ atomic force microscopy (AFM). We observed that both inhibitors exhibit two distinct actions: control of surface crystallization by the decrease of step density at high supersaturations and the decrease of the [1̅00]_Cc step velocity at high inhibitor concentration and low supersaturation. The switching of the two distinct modes depends on the terrace lifetime, and the slow kinetics along the [1̅00]_Cc step direction provides specific sites for the newly formed dislocations. Molecular modeling shows the strong HCA-crystal interaction by molecular recognition, explaining the AFM observations for the formation of new steps and surface dissolution along the [101]_Cc direction due to the introduction of strong localized strain in the crystal lattice. These direct observations highlight the importance of the inhibitor coverage on mineral surfaces, as well as the solution supersaturation in predicting the inhibition efficacy, and reveal an improved understanding of inhibition of calcium phosphate biomineralization, with clinical implications for the full therapeutic potential of small-molecule inhibitors for kidney stone disease.

Dissolution mechanism of calcium apatites in acids: A review of literature

Eight dissolution models of calcium apatites (both fluorapatite and hydroxyapatite) in acids were drawn from the published literature, analyzed and discussed. Major limitations and drawbacks of the models were conversed in details. The models were shown to deal with different aspects of apatite dissolution phenomenon and none of them was able to describe the dissolution process in general. Therefore, an attempt to combine the findings obtained by different researchers was performed which resulted in creation of the general description of apatite dissolution in acids. For this purpose, eight dissolution models were assumed to complement each other and provide the correct description of the specific aspects of apatite dissolution. The general description considers all possible dissolution stages involved and points out to some missing and unclear phenomena to be experimentally studied and verified in future. This creates a new methodological approach to investigate reaction mechanisms based on sets of affine data, obtained by various research groups under dissimilar experimental conditions.

Amorphous calcium phosphate and its application in dentistry

Amorphous Calcium Phosphate (ACP) is an essential mineral phase formed in mineralized tissues and the first commercial product as artificial hydroxyapatite. ACP is unique among all forms of calcium phosphates in that it lacks long-range, periodic atomic scale order of crystalline calcium phosphates. The X-ray diffraction pattern is broad and diffuse with a maximum at 25 degree 2 theta, and no other different features compared with well-crystallized hydroxyapatite. Under electron microscopy, its morphological form is shown as small spheroidal particles in the scale of tenths nanometer. In aqueous media, ACP is easily transformed into crystalline phases such as octacalcium phosphate and apatite due to the growing of microcrystalline. It has been demonstrated that ACP has better osteoconductivity and biodegradability than tricalcium phosphate and hydroxyapatite in vivo. Moreover, it can increase alkaline phosphatase activities of mesoblasts, enhance cell proliferation and promote cell adhesion. The unique role of ACP during the formation of mineralized tissues makes it a promising candidate material for tissue repair and regeneration. ACP may also be a potential remineralizing agent in dental applications. Recently developed ACP-filled bioactive composites are believed to be effective anti-demineralizing/remineralizing agents for the preservation and repair of tooth structures. This review provides an overview of the development, structure, chemical composition, morphological characterization, phase transformation and biomedical application of ACP in dentistry.