Smart Nanosacrificial Layer on the Bone Surface Prevents Osteoporosis through Acid-Base Neutralization Regulated Biocascade Effects.

Osteoporosis is a global chronic disease characterized by severe bone loss and high susceptibility to fragile fracture. It is widely accepted that the origin acidified microenvironment created by excessive osteoclasts causes irreversible bone mineral dissolution and organic degradation during osteoclastic resorption. However, current clinically available approaches are mainly developed from the perspective of osteoclast biology rather than the critical acidified niche. Here, we developed a smart "nanosacrificial layer" consisting of sodium bicarbonate (NaHCO3)-containing and tetracycline-functionalized nanoliposomes (NaHCO3-TNLs) that can target bone surfaces and respond to external secreted acidification from osteoclasts, preventing osteoporosis. In vitro and in vivo results prove that this nanosacrificial layer precisely inhibits the initial acidification of osteoclasts and initiates a chemically regulated biocascade to remodel the bone microenvironment and realize bone protection: extracellular acid-base neutralization first inhibits osteoclast function and also promotes its apoptosis, in which the apoptosis-derived extracellular vesicles containing RANK (receptor activator of nuclear factor-κ B) further consume RANKL (RANK ligand) in serum, achieving comprehensive osteoclast inhibition. Our therapeutic strategy for osteoporosis is based on original and precise acid-base neutralization, aiming to reestablish bone homeostasis by using a smart nanosacrificial layer that is able to induce chemically regulated biocascade effects. This study also provides a novel understanding of osteoporosis therapy in biomedicine and clinical treatments.

ACP-Mediated Phase Transformation for Collagen Mineralization: A New Understanding of the Mechanism.

Despite significant efforts utilizing advanced technologies, the contentious debate surrounding the intricate mechanism underlying collagen fibril mineralization, particularly with regard to amorphous precursor infiltration and phase transformation, persists. This work proposes an amorphous calcium phosphate (ACP)-mediated pathway for collagen fibril mineralization and utilizing stochastic optical reconstruction microscopy technology, and has experimentally confirmed for the first time that the ACP nanoparticles can infiltrate inside collagen fibrils. Subsequently, the ACP-mediated phase transformation occurs within collagen fibrils to form HAP crystallites, and significantly enhances the mechanical properties of the mineralized collagen fibrils compared to those achieved by the calcium phosphate ion (CPI)-mediated mineralization and resembles the natural counterpart. Furthermore, demineralized dentin can be effectively remineralized through ACP-mediated mineralization, leading to complete restoration of its mechanical properties. This work provides a new paradigm of collagen mineralization via particle-mediated phase transformation, deepens the understanding of the mechanism behind the mineralization of collagen fibrils, and offers a new strategy for hard tissue repair.

Reversion of ACP Nanoparticles into Prenucleation Clusters via Surfactant for Promoting Biomimetic Mineralization: A Physicochemical Understanding of Biosurfactant Role in Biomineralization Process.

Amphiphilic biomolecules are abundant in mineralization front of biological hard tissues, which play a vital role in osteogenesis and dental hard tissue formation. Amphiphilic biomolecules function as biosurfactants, however, their biosurfactant role in biomineralization process has never been investigated. This study, for the first time, demonstrates that aggregated amorphous calcium phosphate (ACP) nanoparticles can be reversed into dispersed ultrasmall prenucleation clusters (PNCs) via breakdown and dispersion of the ACP nanoparticles by a surfactant. The reduced surface energy of ACP@TPGS and the electrostatic interaction between calcium ions and the pair electrons on oxygen atoms of C-O-C of D-α-tocopheryl polyethylene glycol succinate (TPGS) provide driving force for breakdown and dispersion of ACP nanoparticles into ultrasmall PNCs which promote in vitro and in vivo biomimetic mineralization. The ACP@TPGS possesses excellent biocompatibility without any irritations to oral mucosa and dental pulp. This study not only introduces surfactant into biomimetic mineralization field, but also excites attention to the neglected biosurfactant role during biomineralization process.

Progress on Biomimetic Mineralization and Materials for Hard Tissue Regeneration.

Biomineralization is a process in which natural organisms regulate the crystal growth of inorganic minerals, resulting in hierarchical structured biominerals with excellent properties. Typical biominerals in the human body are the bones and teeth, and damage to these hard tissues directly affect our daily lives. The repair of bones and teeth in a biomimetic way, either by using a biomimetic mineralization strategy or biomimetic materials, is the key for hard tissue regeneration. In this review, we briefly introduce the structure of bone and tooth, and highlight the fundamental role of collagen mineralization in tissue repair. The recent progress on intra-/extrafibrillar collagen mineralization by a biomimetic strategy or materials is presented, and their potential for tissue regeneration is discussed. Then, recent achievements on bone and tooth repair are summarized, and these works are discussed in the view of materials science and biological science, providing a broader vision for the future research of hard tissue repair techniques. Lastly, recent progress on hard tissue regeneration is concluded, and existing problems and future directions are prospected.

The effect of calcium phosphate ion clusters in enhancing enamel conditions versus Duraphat and Icon.

This study aimed to evaluate and compare the remineralisation, mechanical, anti-aging, acid resistance and antibacterial properties of calcium phosphate ion clusters (CPICs) materials with those of Duraphat and Icon. The remineralisation and mechanical properties were investigated using scanning electron microscopy, Fourier-transform infrared (FTIR) spectroscopy and nanoindentation. CPICs induced epitaxial crystal growth on the enamel surface, where the regrown enamel-like apatite layers had a similar hardness and elastic modulus to natural enamel (p > 0.05). Acid resistance and anti-aging properties were tested based on ion dissolution and surface roughness. CPICs exhibited similar calcium and phosphate ion dissolution to the control (p > 0.05), and its roughness decreased after thermocycling (p < 0.05), thereby decreasing the risk of enamel surface demineralisation. The minimum inhibitory concentration was 0.1 mg/ml, and the minimum bactericidal concentration ranged from 0.05 to 0.1 mg/ml. Overall, this biomimetic CPICs is a promising alternative to dental demineralisation.

In-Depth Occlusion of Dentinal Tubules and Rapid Remineralization of Demineralized Dentin Induced by Polyelectrolyte-Calcium Complexes.

Dentin hypersensitivity (DH) is triggered by external stimuli irking fluid flow through exposed dentinal tubules (DTs). Three commercially available desensitizing agents as control in this study only achieve limited occlusion depths of ≈10 µm in the DTs as well as scarce remineralization of demineralized dentin matrix. Herein, polyelectrolyte-calcium complexes pre-precursor (PCCP) process is proposed for managing DH that demineralized dentin with exposed DTs is rubbed with ultrahighly concentrated polyelectrolyte-calcium suspension (4 g L-1 -5.44 m) followed by phosphate solution (3.25 m), each 10 min, leading to heavy remineralization of demineralized dentin and compact occlusion of the DTs over 200 µm after 1 day of in vitro and in vivo incubation. For the first time, it is demonstrated that the PCCP process relies on the pH-dependent electrostatic attraction between electropositive polyelectrolyte-calcium complexes and electronegative inwalls of DTs comprised of collagen fibrils and hydroxyapatite crystals under alkaline condition. The PCCP process might shed light on a promising dentin desensitizing strategy for DH management via rapid in-depth DT occlusion and remineralization of demineralized dentin.

Promotion of collagen mineralization and dentin repair by succinates.

Biomineralization of collagen fibers is regulated by non-collagenous proteins and small biomolecules, which are essential in bone and teeth formation. In particular, small biomolecules such as succinic acid (SA) exist at a high level in hard tissues, but their role is yet unclear. Here, our work demonstrated that SA could significantly promote intrafibrillar mineralization in two- and three-dimensional collagen models, where the relative mineralization rate was 16 times faster than the control group. Furthermore, the FTIR spectra and isothermal experimental results showed that collagen molecules could interact with SA via a hydrogen bond and that the interaction energy was about 4.35 kJ mol-1. As expected, the SA-pretreated demineralized dentin obtained full remineralization within two days, whereas it took more than four days in the control group, and their mechanical properties were considerably enhanced compared with those of the demineralized one. The possible mechanism of the promotion effect of SA was ultimately illustrated, with SA modification strengthening the capacity of the collagen matrix to attract more calcium ions, which might create a higher local concentration that could accelerate the mineralization of collagen fibers. These findings not only advance the understanding of the vital role of small biomolecules in collagen biomineralization but also facilitate the development of an effective strategy to repair hard tissues.

Deep and compact dentinal tubule occlusion via biomimetic mineralization and mineral overgrowth.

Dentinal tubule (DT) occlusion by desensitizing agents has been widely applied to inhibit the transmission of external stimuli that cause dentin hypersensitivity (DH). However, most desensitizing agents merely accomplish porous blocking or the formation of a superficial tubular occlusion layer, resulting in a lack of mechanical and acid resistance and long-term stability. Herein, combining biomimetic mineralization and mineral overgrowth of the dentinal matrix was shown to effectively occlude DTs, resulting in the formation of a compact and deep occluding mineral layer that is strongly bound to the organic matrix on tubule walls. This DT occlusion method could achieve both mechanical resistance and acid resistance, demonstrating the potential of an inexpensive, long-term, and efficient therapy for treating DH.

Effect of aspartic acid on the crystallization kinetics of ACP and dentin remineralization.

Type I collagen and non-collagen proteins are the main organic components of dentin. This study aimed to investigate the biomimetic remineralization of demineralized dentin by aspartic acid (Asp), which is abundant in non-collagenous proteins (NCPs). Asp was added to a mineralizing solution containing polyacrylic acid (PAA) to explore the mechanism of Asp regulating the pure amorphous calcium phosphate (ACP) phase transition process. The remineralization process and superstructure of the remineralized layer of demineralized dentin were evaluated and analyzed by transmission electron microscope (TEM) and scanning electron microscope (SEM), and the biological stability of the remineralized layer was investigated by collagenase degradation experiment. It demonstrated that Asp promoted the crystallization kinetics of PAA-stabilized amorphous calcium phosphate to hydroxyapatite (HAP), and shortened the remineralization time of demineralized dentin from 7 days to 2 days. The newly formed remineralized dentin had similar morphology and biological stability to the natural dentin layer. The presence of a large number of Asp residues in NCPs promoted the phase transformation of ACP, and further revealed the mechanism of action of NCPs in dentin biomineralization. This experiment also showed that Asp promoted the biomimetic remineralization of dentin; the morphology and hierarchical structure of remineralized layer was similar to that of natural teeth, and had good biological properties.

Effect of saliva contamination and decontamination on bovine enamel bond strength of four self-etching adhesives.

OBJECTIVE: This study evaluated the effect of saliva contamination on the bovine enamel microtensile bond strengths (microTBS) of four self-etching adhesives. MATERIALS AND METHODS: The labial enamel surfaces of extracted non-carious bovine incisors were serially wet ground. The enamel surfaces were not contaminated (Group A), contaminated with saliva before/after priming (Groups B/C) or they were water-sprayed after salivary contamination occurred before/after priming (Groups D/E). Four self-etching adhesives and the corresponding resin composites from the same manufacturer (Clearfil SE Bond + Clearfil AP-X, Kuraray Co; Xeno III + Ceram X, Densply; Frog + Ice, SDI; FL Bond H + Beautifil II, Shofu Inc) were applied onto the enamel surfaces. The microTBS tests were performed with a micro tester (BISCO, Inc). The enamel surface was analyzed with AFM (Atomic Force Microscopy) before/after salivary contamination occurred or after the saliva-contaminated enamel was water-sprayed. The data were analyzed using one-way ANOVA, factorial design ANOVA and post hoc Tukey's HSD multiple comparisons. RESULTS: Salivary contamination significantly reduced the microTBS of all the adhesives in the current study (p < 0.001). Thorough water-spraying could significantly restore the microTBS of saliva-contaminated enamel to some degree (p < 0.05) or fully restore it for Clearfil SE Bond, but it could not remove some proteins adsorbed on the enamel surface. CONCLUSION: Hydrophilic self-etching adhesives are negatively influenced by salivary contamination. Thorough water-spraying could significantly improve the microTBS of the saliva-contaminated enamel. Proper isolation should be performed before and during application of the adhesives and during placement of the resin composite.

Polydopamine Promotes Dentin Remineralization via Interfacial Control.

Biomineralization has intrigued researchers for decades. Although mineralization of type I collagen has been universally investigated, this process remains a great challenge due to the lack of mechanistic understanding of the roles of biomolecules. In our study, dentine was successfully repaired using the biomolecule polydopamine (PDA), and the remineralized dentine exhibited mechanical properties comparable to those of natural dentine. Detailed analyses of the collagen mineralization process facilitated by PDA showed that PDA can promote intrafibrillar mineralization with a decreased heterogeneous nucleation barrier for hydroxyapatite (HAP) by reducing the interfacial energy between collagen fibrils and amorphous calcium phosphate (ACP), resulting in the conversion of an increasing amount of nanoprecursors into collagen fibrils. The present work highlights the importance of interfacial control in dentine remineralization and provides profound insight into the regulatory effect of biomolecules in collagen mineralization as well as the clinical application of dentine restoration.

Nanoengineering of a biocompatible organogel by thermal processing.

The formation of most organogels requires the compatibility of both the gelator and solvent. It is very desirable if the rheological properties of a gel can be manipulated to achieve the desired performance. In this paper, a novel organogel was developed and its rheological properties and fiber network were engineered by controlling the thermal processing conditions. The gel was formed by the gelation of 12-hydroxystearic acid as a gelator in benzyl benzoate. It was observed that the degree of supercooling for gel formation has a significant effect on the rheological properties and fiber network structure. By increasing supercooling, the elasticity of the gel was enhanced, and the correlation length of the fibers was shortened, leading to the formation of denser fiber networks. The good biocompatibility of both the gelator and solvent makes this gel a promising vehicle for a variety of bioapplications such as controlled transdermal drug release and in vivo tissue repair.

Therapeutic Management of Demineralized Dentin Surfaces Using a Mineralizing Adhesive To Seal and Mineralize Dentin, Dentinal Tubules, and Odontoblast Processes.

Dentin hypersensitivity is attributable to the exposed dentin and its patent tubules. We proposed the therapeutic management of demineralized dentin surfaces using a mineralizing adhesive to seal and remineralize dentin, dentinal tubules, and odontoblast processes. An experimental self-etch adhesive and a mineralizing adhesive consisting of the self-etch adhesive and 20 wt % poly-aspartic acid-stabilized amorphous calcium phosphate (PAsp-ACP) nanoparticles were prepared and characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and scanning electron microscopy. After 60 acid-etched midcoronal dentin disks were treated with distilled water (control), a desensitizing agent (Gluma), the experimental self-etch adhesive, and the mineralizing adhesive, dentin permeability was measured and mineralization was evaluated by Raman, FTIR, XRD, TEM, and selected-area electron diffraction, irrespective of abrasive and acidic challenges. In vitro cytotoxicity of the adhesive and the mineralizing adhesive was assessed by Cell Counting Kit-8. The mineralizing adhesive possessed excellent biocompatibility. We proposed a hybrid mineralization layer composed of the light-cured mineralizing adhesive and the mineralized dentin surfaces, as well as interiorly mineralized resin tags and odontoblast processes inside of the dentinal tubules. This hybrid mineralization not only reduced dentin permeability but also resisted abrasive and acidic attacks.

Fabrication of collagen membranes with different intrafibrillar mineralization degree as a potential use for GBR.

The process of biomineralization in dentin and bone tissue repair has been extensively studied. In vitro, biomineralization can be stimulated via a polymer-induced liquid precursor (PILP) process. Guided bone regeneration using a barrier membrane and bone substitute materials is widely used in implantology in cases where there is insufficient bone volume. Herein, we applied a homologous PILP processes to fabricate collagen films with a varying degree of mineralization and tested their performance. The results showed that the prepared biomineralized membranes are biocompatible, have a high stress strength and can promote MC3T3-e1 cell proliferation. This indicated that the membranes can be potentially applied in guided bone regeneration, with membranes containing a higher degree of mineralization achieving the best results.

Repair of tooth enamel by a biomimetic mineralization frontier ensuring epitaxial growth.

The regeneration of tooth enamel, the hardest biological tissue, remains a considerable challenge because its complicated and well-aligned apatite structure has not been duplicated artificially. We herein reveal that a rationally designed material composed of calcium phosphate ion clusters can be used to produce a precursor layer to induce the epitaxial crystal growth of enamel apatite, which mimics the biomineralization crystalline-amorphous frontier of hard tissue development in nature. After repair, the damaged enamel can be recovered completely because its hierarchical structure and mechanical properties are identical to those of natural enamel. The suggested phase transformation-based epitaxial growth follows a promising strategy for enamel regeneration and, more generally, for biomimetic reproduction of materials with complicated structure.

Anisotropic demineralization and oriented assembly of hydroxyapatite crystals in enamel: smart structures of biominerals.

It is interesting to note that the demineralization of natural enamel does not happen as readily as that of the synthesized hydroxyapatite (HAP), although they share a similar chemical composition. We suggest that the hierarchical structure of enamel is an important factor in the preservation of the natural material against dissolution. The anisotropic demineralization of HAP is revealed experimentally, and this phenomenon is understood by the different interfacial structures of HAP-water at the atomic level. It is found that HAP {001} facets can be more resistant against dissolution than {100} under acidic conditions. Although {100} is the largest surface of the typical HAP crystal, it is {001}, the smallest habit face, that is chosen by the living organisms to build the outer surface of enamel by an oriented assembly of the rodlike crystals. We reveal that such a biological construction can confer on enamel protections against erosion, since {001} is relatively dissolution-insensitive. Thus, the spontaneous dissolution of enamel surface can be retarded in biological milieu by such a smart construction. The current study demonstrates the importance of hierarchical structures in the functional biomaterials.

Citrate Improves Collagen Mineralization via Interface Wetting: A Physicochemical Understanding of Biomineralization Control.

Biological hard tissues such as bones always contain extremely high levels of citrate, which is believed to play an important role in bone formation as well as in osteoporosis treatments. However, its mechanism on biomineralization is not elucidated. Here, it is found that the adsorbed citrate molecules on collagen fibrils can significantly reduce the interfacial energy between the biological matrix and the amorphous calcium phosphate precursor to enhance their wetting effect at the early biomineralization stage, sequentially facilitating the intrafibrillar formation of hydroxyapatite to produce an inorganic-organic composite. It is demonstrated experimentally that only collagen fibrils containing ≈8.2 wt% of bound citrate (close to the level in biological bone) can reach the full mineralization as those in natural bones. The effect of citrate on the promotion of the collagen mineralization degree is also confirmed by in vitro dentin repair. This finding demonstrates the importance of interfacial controls in biomineralization and more generally, provides a physicochemical view about the regulation effect of small biomolecules on the biomineralization front.

A novel fluorescent adhesive-assisted biomimetic mineralization.

We propose a novel fluorescent adhesive-assisted biomimetic mineralization strategy, based on which 1 wt% of sodium fluorescein and 25 wt% of polyacrylic acid stabilized amorphous calcium phosphate (PAA-ACP) nanoparticles were incorporated into a mild self-etch adhesive (Clearfil S3 Bond) as a fluorescent mineralizing adhesive. The characterization of the PAA-ACP nanoparticles indicates that they were spherical particles clustered together, each particle with a diameter of approximately 20-50 nm, in a metastable phase with two characteristic absorption peaks (1050 cm-1 and 580 cm-1). Our results suggest that the fluorescent mineralizing adhesive was non-cytotoxic with minimal esthetic interference and its fluorescence intensity did not significantly decrease within 6 months. Our data reveal that the fluorescent mineralizing adhesive could induce the extra- and intra-fibrillar remineralization of the reconstituted type I collagen, the demineralized enamel and dentin substrate. Our data demonstrate that a novel fluorescent adhesive-assisted biomimetic mineralization strategy will pave the way to design and produce anti-carious materials for the prevention of dental caries.

Self-Etch Adhesive as a Carrier for ACP Nanoprecursors to Deliver Biomimetic Remineralization.

Lab biomineralization should be carried out in an actual clinical practice. This study evaluated self-etch adhesive as a carrier for amorphous calcium phosphate (ACP) nanoprecursors to continuously deliver biomimetic remineralization of self-assembly type I collagen and demineralized dentin. Si-containing ACP particles (Si-ACP) stabilized with polyaspartic acid (PAsp) were synthesized and characterized by transmission electron microscopy (TEM), scanning electron microscopy-energy-dispersive X-ray spectroscopy, Fourier transform infrared analysis, X-ray powder diffractometry, and X-ray phototelectron spectroscopy. The biomimetic remineralization of single-layer reconstituted type I collagen fibrils and demineralized dentin was analyzed by using two one-bottle self-etch dentin adhesives (Clearfil S3 Bond (S3), Kurraray-Noritake; Adper Easy One (AEO), 3 M ESPE) as a carrier loaded (or not, in the case of the control) with 25 wt % of Si-ACP particles. In vitro cytotoxicity assessed by the Cell Counting Kit-8 indicated that the Si-ACP particles had no adverse effect on cell viability. The capacity for Ca and P ions release from cured Si-ACP-containing adhesives (S3, AEO) was evaluated by inductively coupled plasma-atomic emission spectrometry, revealing the successively increasing release of Ca and P ions for 28 days. The intra- and extrafibrillar remineralization of type I collagen and demineralized dentin was confirmed by TEM and selected-area electron diffraction when the adhesives were used as a carrier loaded with Si-ACP particles. Therefore, we propose self-etch adhesive as a novel carrier for ACP nanoprecursors to continuously deliver biomimetic remineralization.

Glutaraldehyde-induced remineralization improves the mechanical properties and biostability of dentin collagen.

The purpose of this study was to induce a biomimetic remineralization process by using glutaraldehyde (GA) to reconstruct the mechanical properties and biostability of demineralized collagen. Demineralized dentin disks (35% phosphoric acid, 10s) were pretreated with a 5% GA solution for 3min and then cultivated in a calcium phosphate remineralization solution. The remineralization kinetics and superstructure of the remineralization layer were evaluated by Raman spectroscopy, transmission electron microscopy, scanning electron microscopy and nanoindentation tests. The biostability was examined by enzymatic degradation experiments. A significant difference was found in dentin remineralization process between dentin with and without GA pretreating. GA showed a specific affinity to dentin collagen resulting in the formation of a cross-linking superstructure. GA pretreating could remarkably shorten remineralization time from 7days to 2days. The GA-induced remineralized collagen fibrils were well encapsulated by newly formed hydroxyapatite mineral nanocrystals. With the nano-hydroxyapatite coating, both the mechanical properties (elastic modulus and hardness) and the biostability against enzymatic degradation of the collagen were significantly enhanced, matching those of natural dentin. The results indicated that GA cross-linking of dentin collagen could promote dentin biomimetic remineralization, resulting in an improved mechanical properties and biostability. It may provide a promising tissue-engineering technology for dentin repair.