Inhibiting Pathological Calcium Phosphate Mineralization: Implications for Disease Progression

Pathological calcifications, especially calcium phosphate microcalcifications (MCs), appear in most early breast cancer lesions, and their formation correlates with more aggressive tumors and a poorer prognosis. Hydroxyapatite (HA) is a key MC component that crystallizes in the tumor microenvironment. It is often associated with malignant breast cancer lesions and can trigger tumorigenesis in vitro. Here, we investigate the impact of additives on HA crystallization and inhibition, and how precancerous breast cells respond to minerals that are deposited in the presence of these additives. We show that nonstoichiometric HA spontaneously crystallizes in a solution simulating the tumor microenvironmental fluids and exhibits lump-like morphology similar to breast cancer MCs. In this system, the effectiveness of poly(aspartic acid) and poly(acrylic acid) (PAA) to inhibit HA is examined as a potential route to improve cancer prognosis. In the presence of additives, the formation of HA lumps is associated with the promotion or only minimal inhibition of mineralization, whereas the formation of amorphous calcium phosphate (ACP) lumps is followed by inhibition of mineralization. PAA emerges as a robust HA inhibitor by forming spherical ACP particles. When precancerous breast cells are exposed to various HA and ACP minerals, the most influential factors on cell proliferation are the mineral phase and whether the mineral is in the form of discrete particles or particle aggregates. The tumorigenic effects on cells, ranging from cytotoxicity and suppression of proliferation to triggering of proliferation, can be summarized as HA particles < HA aggregates < ACP particles < ACP aggregates. The cellular response to minerals can be attributed to a combination of factors, including mineral phase, crystallinity, morphology, surface texture, aggregation state, and surface potential. These findings have implications for understanding mineral-cell interactions within the tumor microenvironment and suggest that, in some cases, the byproducts of HA inhibition can contribute to disease progression more than HA itself.

An experimental teeth bleaching agent containing casein phosphopeptide-amorphous calcium phosphate

OBJECTIVES

This study was aimed to obtain an experimental bleaching agent by adding casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) in order to eliminate the mineral loss on the tooth surface after bleaching and to evaluate the bleaching effectiveness.

MATERIALS AND METHODS

In this study, experimental bleaching agents containing 1%, 3% CPP-ACP and without CPP-ACP were obtained. Bleaching effectiveness (color change), the effect of bleaching agents on mineral content (energy dispersive x-ray spectroscopy), surface morphology (scanning electron microscope), and surface hardness of enamel (Vicker's microhardness) before and after bleaching were evaluated. The obtained data were statistically analyzed.

RESULTS

When the bleaching levels of the groups were compared, no statistically significant difference was observed between the control and 1% CPP-ACP groups (p > 0.05) while the addition of 3% CPP-ACP decreased significantly the effectiveness of the bleaching agent (p < 0.05). When the effects of experimental bleaching agents on surface hardness were examined, while the enamel surface hardness decreased statistically significantly after application in the control group (p < 0.05), no statistically significant change was observed in surface hardness after the application of 1% CPP-ACP containing bleaching agent (p > 0.05). However, a statistically significant increase was observed in surface hardness after the application of 3% CPP-ACP containing bleaching agent (p < 0.05). When the Ca and P ratio of the groups were compared, no statistically significant difference was observed between the control and 1% CPP-ACP groups (p > 0.05), while they increased significantly in 3% CPP-ACP group (p < 0.05).

CONCLUSIONS

The addition of 1% CPP-ACP to the bleaching agent had positive effects on the mineral content and surface hardness of the enamel, and did not negatively affect the whitening effectiveness.

CLINICAL SIGNIFICANCE

Adding CPP-ACP to the bleaching agent at appropriate concentrations can eliminate possible negative effects without compromising the effectiveness of the bleaching agent.

Biomimetic Self-Maturation Mineralization System for Enamel Repair

Enamel repair is crucial for restoring tooth function and halting dental caries. However, contemporary research often overlooks the retention of organic residues within the repair layer, which hinders the growth of dense crystals and compromises the properties of the repaired enamel. During the maturation of natural enamel, the organic matrix undergoes enzymatic processing to facilitate further crystal growth, resulting in a highly mineralized tissue. Inspired by this process, a biomimetic self-maturation mineralization system is developed, comprising ribonucleic acid-stabilized amorphous calcium phosphate (RNA-ACP) and ribonuclease (RNase). The RNA-ACP induces initial mineralization in the form of epitaxial crystal growth, while the RNase present in saliva automatically triggers a biomimetic self-maturation process. The mechanistic study further indicates that RNA degradation prompts conformational rearrangement of the RNA-ACP, effectively excluding the organic matter introduced earlier. This exclusion process promotes lateral crystal growth, resulting in the generation of denser enamel-like apatite crystals that are devoid of organic residues. This strategy of eliminating organic residues from enamel crystals enhances the mechanical and physiochemical properties of the repaired enamel. The present study introduces a conceptual biomimetic mineralization strategy for effective enamel repair in clinical practice and offers potential insights into the mechanisms of biomineral formation.

Preparation of calcium phosphate ion clusters through atomization method for biomimetic mineralization of enamel

Dental enamel is a mineralized extracellular matrix, and enamel defect is a common oral disease. However, the self-repair capacity of enamel is limited due to the absence of cellular components and organic matter. Efficacy of biomimetic enamel mineralization using calcium phosphate ion clusters (CPICs), is an effective method to compensate for the limited self-healing ability of fully developed enamel. Preparing and stabilizing CPICs presents a significant challenge, as the addition of certain stabilizers can diminish the mechanical properties or biosafety of mineralized enamel. To efficiently and safely repair enamel damage, this study quickly prepared CPICs without stabilizers using the atomization method. The formed CPICs were evenly distributed on the enamel surface, prompting directional growth and transformation of hydroxyapatite (HA) crystals. The study revealed that the mended enamel displayed comparable morphology, chemical composition, hardness, and mechanical properties to those of the original enamel. The approach of repairing dental enamel by utilizing ultrasonic nebulization of CPICs is highly efficient and safe, therefore indicating great promise.

Amorphous, Carbonated Calcium Phosphate and Biopolymer-Composite-Coated Si3N4/MWCNTs as Potential Novel Implant Materials

A biodegradable amorphous carbonated calcium phosphate (caCP)-incorporated polycaprolactone (PCL) composite layer was successfully deposited by a spin coater. In this specific coating, the PCL acts as a bioadhesive, since it provides a better adherence of the coatings to the substrate compared to powder coatings. The caCP-PCL coatings were deposited and formed thin layers on the surface of a Si3N4-3 wt% MWCNT (multiwalled carbon nanotube) substrate, which is an emerging type of implant material in the biomedical field. The composite coatings were examined regarding their morphology, structure and biological performance. The biocompatibility of the samples was tested in vitro with MC3T3-E1 preosteoblast cells. Owing to the caCP-PCL thin layer, the cell viability values were considerably increased compared to the substrate material. The ALP and LDH tests showed numerous living cells on the investrigated coatings. The morphology of the MC3T3-E1 cells was examined by fluorescent staining (calcein and DAPI) and scanning electron microscopy, both of which revealed a well-spread, adhered and confluent monolayer of cells. All performed biocompatibility tests were positive and indicated the applicability of the deposited thin composite layers as possible candidates for orthopaedic implants for an extended period.

Small organic molecules containing amorphous calcium phosphate: synthesis, characterization and transformation

As the primary solid phase, amorphous calcium phosphate (ACP) is a pivotal precursor in cellular biomineralization. The intrinsic interplay between ACP and Howard factor underscores the significance of understanding their association for advancing biomimetic ACP development. While organic compounds play established roles in biomineralization, this study presents the synthesis of ACP with naturally occurring organic compounds (ascorbate, glutamate, and itaconate) ubiquitously found in mitochondria and vital for bone remodeling and healing. The developed ACP with organic compounds was meticulously characterized using XRD, FTIR, and solid-state 13C and 31P NMR. The morphological analysis revealed the characteristic spherical morphology with particle size close to 20 nm of all synthesized ACP variants. Notably, the type of organic compound strongly influences true density, specific surface area, particle size, and transformation. The in vitro analysis was performed with MC3T3-E1 cells, indicating the highest cell viability with ACP_ASC (ascorbate), followed by ACP_ITA (itaconate). The lowest cell viability was observed with 10 %w/v of ACP_GLU (glutamate); however, 1 %w/v of ACP_GLU was cytocompatible. Further, the effect of small organic molecules on the transformation of ACP to low crystalline apatite (Ap) was examined in Milli-Q® water, PBS, and α-MEM.

Consolidation of Spray-Dried Amorphous Calcium Phosphate by Ultrafast Compression: Chemical and Structural Overview

A large amount of research in orthopedic and maxillofacial domains is dedicated to the development of bioactive 3D scaffolds. This includes the search for highly resorbable compounds, capable of triggering cell activity and favoring bone regeneration. Considering the phosphocalcic nature of bone mineral, these aims can be achieved by the choice of amorphous calcium phosphates (ACPs). Because of their metastable property, these compounds are however to-date seldom used in bulk form. In this work, we used a non-conventional "cold sintering" approach based on ultrafast low-pressure RT compaction to successfully consolidate ACP pellets while preserving their amorphous nature (XRD). Complementary spectroscopic analyses (FTIR, Raman, solid-state NMR) and thermal analyses showed that the starting powder underwent slight physicochemical modifications, with a partial loss of water and local change in the HPO42- ion environment. The creation of an open porous structure, which is especially adapted for non-load bearing bone defects, was also observed. Moreover, the pellets obtained exhibited sufficient mechanical resistance allowing for manipulation, surgical placement and eventual cutting/reshaping in the operation room. Three-dimensional porous scaffolds of cold-sintered reactive ACP, fabricated through this low-energy, ultrafast consolidation process, show promise toward the development of highly bioactive and tailorable biomaterials for bone regeneration, also permitting combinations with various thermosensitive drugs.

Journey of Mineral Precursors in Bone Mineralization: Evolution and Inspiration for Biomimetic Design

Bone mineralization is a ubiquitous process among vertebrates that involves a dynamic physical/chemical interplay between the organic and inorganic components of bone tissues. It is now well documented that carbonated apatite, an inorganic component of bone, is proceeded through transient amorphous mineral precursors that transforms into the crystalline mineral phase. Here, the evolution on mineral precursors from their sources to the terminus in the bone mineralization process is reviewed. How organisms tightly control each step of mineralization to drive the formation, stabilization, and phase transformation of amorphous mineral precursors in the right place, at the right time, and rate are highlighted. The paradigm shifts in biomineralization and biomaterial design strategies are intertwined, which promotes breakthroughs in biomineralization-inspired material. The design principles and implementation methods of mineral precursor-based biomaterials in bone graft materials such as implant coatings, bone cements, hydrogels, and nanoparticles are detailed in the present manuscript. The biologically controlled mineralization mechanisms will hold promise for overcoming the barriers to the application of biomineralization-inspired biomaterials.

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.

Lithium isotopes differentially modify mitochondrial amorphous calcium phosphate cluster size distribution and calcium capacity

Lithium is commonly prescribed as a mood stabilizer in a variety of mental health conditions, yet its molecular mode of action is incompletely understood. Many cellular events associated with lithium appear tied to mitochondrial function. Further, recent evidence suggests that lithium bioactivities are isotope specific. Here we focus on lithium effects related to mitochondrial calcium handling. Lithium protected against calcium-induced permeability transition and decreased the calcium capacity of liver mitochondria at a clinically relevant concentration. In contrast, brain mitochondrial calcium capacity was increased by lithium. Surprisingly, 7Li acted more potently than 6Li on calcium capacity, yet 6Li was more effective at delaying permeability transition. The size distribution of amorphous calcium phosphate colloids formed in vitro was differentially affected by lithium isotopes, providing a mechanistic basis for the observed isotope specific effects on mitochondrial calcium handling. This work highlights a need to better understand how mitochondrial calcium stores are structurally regulated and provides key considerations for future formulations of lithium-based therapeutics.

Formation of Hydroxyapatite-Based Hybrid Materials in the Presence of Platelet-Poor Plasma Additive

Biomaterials based on hydroxyapatite with controllable composition and properties are promising in the field of regenerative bone replacement. One approach to regulate the phase composition of the materials is the introduction of biopolymer-based additives into the synthesis process. The purpose of present study was to investigate the formation of hydroxyapatite-based hybrid materials in the presence of 6-24% platelet-poor plasma (PPP) additive, at a [Ca2+]/[PO43-] ratio of 1.67, pH 11, and varying maturing time from 4 to 9 days. The mineral component of the materials comprised 53% hydroxyapatite/47% amorphous calcium phosphate after 4 days of maturation and 100% hydroxyapatite after 9 days of maturation. Varying the PPP content between 6% and 24% brought about the formation of materials with rather defined contents of amorphous calcium phosphate and biopolymer component and the desired morphology, ranging from typical apatitic conglomerates to hybrid apatite-biopolymer fibers. The co-precipitated hybrid materials based on hydroxyapatite, amorphous calcium phosphate, and PPP additive exhibited increased solubility in SBF solution, which defines their applicability for repairing rhinoplastic defects.

Concentration-dependent effect of carboxymethyl chitosan amorphous calcium phosphate on the surface hardness of primary tooth enamel

PURPOSE

To compare the effects of gels containing 2.5% and 5% carboxymethyl chitosan amorphous calcium phosphate (CMC-ACP) on the microhardness of primary tooth enamel.

METHODS

Twenty-four tooth specimens were demineralized with 37% phosphoric acid and divided into four groups: an untreated control group, a positive control group treated with casein phosphopeptide amorphous calcium phosphate, and two groups treated with 2.5% and 5% CMC-ACP gel, respectively. The enamel surface hardness was then measured with a Vickers hardness tester.

RESULTS

In terms of Vickers Hardness Number (VHN), the degree of alteration in tooth surface microhardness was 77.83 ± 13.44 in the 5% CMC-ACP group and 52 ± 6.93 in the 2.5% CMC-ACP group (P = 0.002). The inter-group difference in the surface hardness change was significant (P < 0.05).

CONCLUSION

The 5% CMC-ACP gel increased the hardness of primary tooth enamel to a greater degree than the 2.5% CMC-ACP gel.

Optimizing the biodegradability and osteogenesis of biogenic collagen membrane via fluoride-modified polymer-induced liquid precursor process

Biogenic collagen membranes (BCM) have been widely used in guided bone regeneration (GBR) owing to their biodegradability during tissue integration. However, their relatively high degradation rate and lack of pro-osteogenic properties limit their clinical outcomes. It is of great importance to endow BCM with tailored degradation as well as pro-osteogenic properties. In this study, a fluoride-modified polymer-induced liquid precursor (PILP) based biomineralization strategy was used to convert the collagen membrane from an organic phase to an apatite-based inorganic phase, thus achieving enhanced anti-degradation performance as well as osteogenesis. As a result, three phases of collagen membranes were prepared. The original BCM in the organic phase induced the mildest inflammatory response and was mostly degraded after 4 weeks. The organic-inorganic mixture phase of the collagen membrane evoked a prominent inflammatory response owing to the fluoride-containing amorphous calcium phosphate (F-ACP) nanoparticles, resulting in active angiogenesis and fibrous encapsulation, whereas the inorganic phase induced a mild inflammatory response and degraded the least owing to the transition of F-ACP particles into calcium phosphate with high crystallinity. Effective control of ACP is key to building novel apatite-based barrier membranes. The current results may pave the way for the development of advanced apatite-based membranes with enhanced barrier performances.

Can Differently Stabilized Silver Nanoparticles Modify Calcium Phosphate Precipitation?

Calcium phosphates (CaPs) composites with silver nanoparticles (AgNPs) attract attention as a possible alternative to conventional approaches to combating orthopedic implant-associated infections. Although precipitation of calcium phosphates at room temperatures was pointed out as an advantageous method for the preparation of various CaP-based biomaterials, to the best of our knowledge, no such study exists for the preparation of CaPs/AgNP composites. Motivated by this lack of data in this study we investigated the influence of AgNPs stabilized with citrate (cit-AgNPs), poly(vinylpyrrolidone) (PVP-AgNPs), and sodium bis(2-ethylhexyl) sulfosuccinate (AOT-AgNPs) in the concentration range 5-25 mg dm^-3 on the precipitation of CaPs. The first solid phase to precipitate in the investigated precipitation system was amorphous calcium phosphate (ACP). The effect of AgNPs on ACP stability was significant only in the presence of the highest concentration of AOT-AgNPs. However, in all precipitation systems containing AgNPs, the morphology of ACP was affected, as gel-like precipitates formed in addition to the typical chain-like aggregates of spherical particles. The exact effect depended on the type of AgNPs. After 60 min of reaction time, a mixture of calcium-deficient hydroxyapatite (CaDHA) and a smaller amount of octacalcium phosphate (OCP) formed. PXRD and EPR data point out that the amount of formed OCP decreases with increasing AgNPs concentration. The obtained results showed that AgNPs can modify the precipitation of CaPs and that CaPs properties can be fine-tuned by the choice of stabilizing agent. Furthermore, it was shown that precipitation can be used as a simple and fast method for CaP/AgNPs composites preparation which is of special interest for biomaterials preparation.

Synergistic remineralization of enamel white spot lesions using mesoporous bioactive glasses loaded with amorphous calcium phosphate

Objectives: The purpose of this study was to create a new delivery system that can synergistically remineralize enamel white spot lesions (WSLs). Materials and methods: The delivery system (PAA-ACP@aMBG) was prepared by using aminated mesoporous bioactive glasses (aMBG) as the carrier loaded with polyacrylic-stabilized amorphous calcium phosphate (PAA-ACP). The materials were characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), inductively coupled plasma-optical emission spectrometry (ICP-OES), and so on. Forty-eight artificial WSLs enamel samples were randomized to four groups: artificial saliva (negative control, NC), casein phosphopeptide-amorphous calcium phosphate (CPP-ACP), PAA-ACP@aMBG, and MBG. The effects of demineralization and remineralization of the enamel surface were compared by means of surface microhardness (SMH) measurements, surface color change measurements, fluorescence microscopy (FM), X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). Results: There was no significant difference in the surface microhardness recovery rate (SMHRR) or color recovery rate (CRR) among the CPP-ACP group, PAA-ACP@aMBG group and MBG group (P>0.05), but these values were significantly higher than those in the NC group (p < 0.01). FM demonstrated that the remineralization depth in the PAA-ACP@aMBG group was significantly greater than that of the remaining three groups (p < 0.01). SEM analysis indicated that the enamel demineralization marks in the PAA-ACP@aMBG group, CPP-ACP group, and MBG group were obscured by mineral deposition. Conclusions: PAA-ACP@aMBG showed good mineralization properties, implying its great potential for clinical application.

Changes in the C-terminal, N-terminal, and histidine regions of amelogenin reveal the role of oligomer quaternary structure on adsorption and hydroxyapatite mineralization

Adsorption interactions between amelogenin and calcium phosphate minerals are believed to be important to amelogenin's function in enamel formation, however, the role of specific amino acid residues and domains within the protein in controlling adsorption is not well known. We synthesized "mechanistic probes" by systematically removing charged regions of amelogenin in order to elucidate their roles. The probes included amelogenin without the charged residues in the N-terminus (SEKR), without two, three, or eight histidines (H) in the central protein region (H2, H3, H8), or without the C-terminal residues (Delta). In-situ atomic force microscopy (AFM) adsorption studies onto hydroxyapatite (HAP) single crystals confirmed that the C-terminus was the dominant domain in promoting adsorption. We propose that subtle changes in protein-protein interactions for proteins with histidines and N-terminal residues removed resulted in changes in the oligomer quaternary size and structure that also affected protein adsorption. HAP mineralization studies revealed that the oligomer-HAP binding energy and protein layer thickness were factors in controlling the amorphous calcium phosphate (ACP) to HAP induction time. Our studies with mechanistic probes reveal the importance of the oligomer quaternary structure in controlling amelogenin adsorption and HAP mineralization.

Ultrastructural Characterization of Human Gingival Fibroblasts in 3D Culture

Cell spheroids are applied in various fields of research, such as the fabrication of three-dimensional artificial tissues in vitro, disease modeling, stem cell research, regenerative therapy, and biotechnology. A preclinical 3D culture model of primary human gingival fibroblasts free of external factors and/or chemical inducers is presented herein. The ultrastructure of the spheroids was characterized to establish a cellular model for the study of periodontal tissue regeneration. The liquid overlay technique was used with agarose to generate spheroids. Fibroblasts in 2D culture and cell spheroids were characterized by immunofluorescence, and cell spheroids were characterized by optical and scanning electron microscopy, energy-dispersive X-ray spectroscopy, backscattered electrons, and Fourier transform infrared spectroscopy. Ostegenic related genes were analyzed by RT-qPCR. Gingival fibroblasts formed spheroids spontaneously and showed amorphous calcium phosphate nanoparticle deposits on their surface. The results suggest that human gingival fibroblasts have an intrinsic potential to generate a mineralized niche in 3D culture.

Bioactive Inorganic Materials for Dental Applications: A Narrative Review

Over time, much attention has been given to the use of bioceramics for biomedical applications; however, the recent trend has been gaining traction to apply these materials for dental restorations. The bioceramics (mainly bioactive) are exceptionally biocompatible and possess excellent bioactive and biological properties due to their similar chemical composition to human hard tissues. However, concern has been noticed related to their mechanical properties. All dental materials based on bioactive materials must be biocompatible, long-lasting, mechanically strong enough to bear the masticatory and functional load, wear-resistant, easily manipulated, and implanted. This review article presents the basic structure, properties, and dental applications of different bioactive materials i.e., amorphous calcium phosphate, hydroxyapatite, tri-calcium phosphate, mono-calcium phosphate, calcium silicate, and bioactive glass. The advantageous properties and limitations of these materials are also discussed. In the end, future directions and proposals are given to improve the physical and mechanical properties of bioactive materials-based dental materials.

Remineralization of human dentin type I collagen fibrils induced by carboxylated polyamidoamine dendrimer/amorphous calcium phosphate nanocomposite: an in vitro study

Intrafibrillar mineralization of type I collagen fibrils is of great significance in dental remineralization, which is the key of caries prevention and treatment. Herein, two substances that have the remineralization ability, carboxylated polyamidoamine dendrimer (PAMAM-COOH) and nano-sized amorphous calcium phosphate (n-ACP) were combined to synthesize a novel nanomaterial, carboxylated polyamidoamine dendrimer/amorphous calcium phosphate nanocomposite (PAMAM-COOH/ACP). This article aims to evaluate the remineralization effect of PAMAM-COOH/ACP of dentin type I collagen fibrils in vitro. Fluorescence labeling technique was innovatively used to observe and evaluate the remineralization effect. PAMAM-COOH/ACP showed superior remineralization ability of human dentin type I collagen fibrils, especially the intrafibrillar remineralization. Therefore, the novel nanomaterial PAMAM-COOH/ACP is promising to prevent and treat various diseases caused by dentin demineralization and to improve various dental materials.

Multifunctional Nanomachinery for Enhancement of Bone Healing

The visionary idea that RNA adopts nonbiological roles in today's nanomaterial world has been nothing short of phenomenal. These RNA molecules have ample chemical functionality and self-assemble to form distinct nanostructures in response to external stimuli. They may be combined with inorganic materials to produce nanomachines that carry cargo to a target site in a controlled manner and respond dynamically to environmental changes. Comparable to biological cells, programmed RNA nanomachines have the potential to replicate bone healing in vitro. Here, an RNA-biomineral nanomachine is developed, which accomplishes intrafibrillar and extrafibrillar mineralization of collagen scaffolds to mimic bone formation in vitro. Molecular dynamics simulation indicates that noncovalent hydrogen bonding provides the energy source that initiates self-assembly of these nanomachines. Incorporation of the RNA-biomineral nanomachines into collagen scaffolds in vivo creates an osteoinductive microenvironment within a bone defect that is conducive to rapid biomineralization and osteogenesis. Addition of RNA-degrading enzymes into RNA-biomineral nanomachines further creates a stop signal that inhibits unwarranted bone formation in tissues. The potential of RNA in building functional nanostructures has been underestimated in the past. The concept of RNA-biomineral nanomachines participating in physiological processes may transform the nanoscopic world of life science.

Polyzwitterion Manipulates Remineralization and Antibiofilm Functions against Dental Demineralization

Biomineralization technology has become a trend for the arrest and prevention of dental caries. In particular, the bioactivity and ability to release large amounts of Ca²⁺ and PO₄^3- ions make amorphous calcium phosphate (ACP) for hard tissue remineralization are highly desired. However, the instability of ACP limits its clinical application. Under continuous bacterial challenge in the oral cavity, the currently developed ACP-based remineralization system lacks the ability to inhibit bacterial adhesion and biofilm formation. Here, a dual-functional nanocomposite with antibiofilm and remineralization properties was designed by combining zwitterionic poly(carboxybetaine acrylamide) (PCBAA) and ACP. The resulting nanocomposite was stable in solution for at least 3 days without any aggregation. The PCBAA/ACP nanocomposite exerted a significant inhibitory effect on the adhesion and biofilm formation of Streptococcus mutans and exhibited bactericidal activities under acidic conditions resulting from bacteria. Moreover, compared with fluoride, this nanocomposite demonstrated superior effects in promoting the remineralization of demineralized enamel and the occlusion of exposed dentinal tubules in vivo and in vitro. The present work provides a theoretical and experimental basis for the use of the PCBAA/ACP nanocomposite as a potential dual-functional agent for arresting and preventing caries.

Extracellular DNA: A Missing Link in the Pathogenesis of Ectopic Mineralization

Although deoxyribonucleic acid (DNA) is the genetic coding for the very essence of life, these macromolecules or components thereof are not necessarily lost after a cell dies. There appears to be a link between extracellular DNA and biomineralization. Here the authors demonstrate that extracellular DNA functions as an initiator of collagen intrafibrillar mineralization. This is confirmed with in vitro and in vivo biological mineralization models. Because of their polyanionic property, extracellular DNA molecules are capable of stabilizing supersaturated calcium phosphate solution and mineralizing 2D and 3D collagen matrices completely as early as 24 h. The effectiveness of extracellular DNA in biomineralization of collagen is attributed to the relatively stable formation of amorphous liquid droplets triggered by attraction of DNA to the collagen fibrils via hydrogen bonding. These findings suggest that extracellular DNA is biomimetically significant for fabricating inorganic-organic hybrid materials for tissue engineering. DNA-induced collagen intrafibrillar mineralization provides a clue to the pathogenesis of ectopic mineralization in different body tissues. The use of DNase for targeting extracellular DNA at destined tissue sites provides a potential solution for treatment of diseases associated with ectopic mineralization.

Nanostructured Zn-Substituted Monetite Based Material Induces Higher Bone Regeneration Than Anorganic Bovine Bone and β-Tricalcium Phosphate in Vertical Augmentation Model in Rabbit Calvaria

The capacity of a nanostructured multicomponent material composed of Zn-substituted monetite, amorphous calcium phosphate, hydroxyapatite and silica gel (MSi) to promote vertical bone augmentation was compared with anorganic bovine bone (ABB) and synthetic β-tricalcium phosphate (β-TCP). The relation between biological behavior and physicochemical properties of the materials was also studied. The in vivo study was conducted in a vertical bone augmentation model in rabbit calvaria for 10 weeks. Significant differences in the biological behavior of the materials were observed. MSi showed significantly higher bone regeneration (39%) than ABB and β-TCP (24%). The filled cylinder volume was similar in MSi (92%) and ABB (91%) and significantly lower in β-TCP (81%) implants. In addition, β-TCP showed the highest amount of non-osteointegrated particles (17%). MSi was superior to the control materials because it maintains the volume of the defect almost full, with the highest bone formation, the lowest number of remaining particles, which are almost fully osteointegrated and having the lowest amount of connective tissue. Besides, the bone formed was mature, with broad trabeculae, high vascularization and osteogenic activity. MSi resorbs gradually over time with an evident increment of the porosity and simultaneous colonization for vascularized new bone. In addition, the osteoinductive behavior of MSi material was evidenced.

Effects of NanoAg-ACP Microparticles as Bioactive Fillers on the Mechanical and Remineralization Properties of Dental Resin Cement

PURPOSE

To investigate the potential of adding silver-nanoparticle-containing amorphous calcium phosphate microparticles as bioactive fillers into commercially available non-bioactive dental resin cement.

MATERIALS AND METHODS

Experimental cement was formulated by adding 7.5% silver-nanoparticle-containing amorphous calcium phosphate microparticles to Multilink Automix resin cement (Ivoclar Vivadent). The experimental cement was evaluated for shear bond strength (N=11 per group) and demineralization/remineralization (N=16 per group), with BioCem^® Universal BioActive cement (NuSmile) as the positive control and Multilink Automix cement as the negative control. One-way analysis of variance and post hoc tests were used to assess the significance of differences among or between the groups RESULTS: : The addition of silver-nanoparticle-containing amorphous calcium phosphate microparticles at the level of 7.5% by weight into Multilink Automix did not have a statistically significant effect on the shear bond strength (p>0.05), but statistically significantly increased the depth of remineralization on both dentin and enamel (p=0.01 and p<0.001, respectively.) when compared to Multilink Automix alone. The experimental cement prepared in the present study was comparable to BioCem^® on the depths of remineralization on both dentin and enamel (p=0.59 and p=0.99, respectively).

CONCLUSION

When incorporated into non-bioactive commercial dental resin cements as bioactive fillers at the level of 7.5% by weight, silver-nanoparticle-containing amorphous calcium phosphate microparticles could provide remineralization potential without affecting the shear bond strength. This article is protected by copyright. All rights reserved.

Composite Drug Delivery System Based on Amorphous Calcium Phosphate-Chitosan: An Efficient Antimicrobial Platform for Extended Release of Tetracycline

One major warning emerging during the first worldwide combat against healthcare-associated infections concerns the key role of the surface in the storage and transfer of the virus. Our study is based on the laser coating of surfaces with an inorganic/organic composite mixture of amorphous calcium phosphate–chitosan–tetracycline that is able to fight against infectious agents, but also capable of preserving its activity for a prolonged time, up to several days. The extended release in simulated fluids of the composite mixture containing the drug (tetracycline) was demonstrated by mass loss and UV–VIS investigations. The drug release profile from our composite coatings proceeds via two stages: an initial burst release (during the first hours), followed by a slower evolution active for the next 72 h, and probably more. Optimized coatings strongly inhibit the growth of tested bacteria (Enterococcus faecalis and Escherichia coli), while the drug incorporation has no impact on the in vitro composite’s cytotoxicity, the coatings proving an excellent biocompatibility sustaining the normal development of MG63 bone-like cells. One may, therefore, consider that the proposed coatings’ composition can open the prospective of a new generation of antimicrobial coatings for implants, but also for nosocomial and other large area contamination prevention.

Effect of Temperature on Electrochemically Assisted Deposition and Bioactivity of CaP Coatings on CpTi Grade 4

Calcium phosphate (CaP) coatings are able to improve the osseointegration process due to their chemical composition similar to that of bone tissues. Among the methods of producing CaP coatings, the electrochemically assisted deposition (ECAD) is particularly important due to high repeatability and the possibility of deposition at room temperature and neutral pH, which allows for the co-deposition of inorganic and organic components. In this work, the ECAD of CaP coatings from an acetate bath with a Ca:P ratio of 1.67, was developed. The effect of the ECAD conditions on CaP coatings deposited on commercially pure titanium grade 4 (CpTi G4) subjected to sandblasting and autoclaving was presented. The physicochemical characteristics of the ECAD-derived coatings was carried out using SEM, EDS, FTIR, 2D roughness profiles, and amplitude sensitive eddy current method. It was showed that amorphous calcium phosphate (ACP) coatings can be obtained at a potential −1.5 to −10 V for 10 to 60 min at 20 to 70 °C. The thickness and surface roughness of the ACP coatings were an increasing function of potential, time, and temperature. The obtained ACP coatings are a precursor in the process of apatite formation in a simulated body fluid. The optimal ACP coating for use in dentistry was deposited at a potential of −3 V for 30 min at 20 °C.

Suspension of Amorphous Calcium Phosphate Nanoparticles Impact Commitment of Human Adipose-Derived Stem Cells In Vitro

Amorphous calcium phosphate (aCaP) nanoparticles may trigger the osteogenic commitment of adipose-derived stem cells (ASCs) in vitro. The ASCs of three human donors are investigated using basal culture medium DMEM to either 5 or 50 µg/mL aCaP nanoparticles suspension (control: no nanoparticles). After 7 or 14 days, stem cell marker genes, as well as endothelial, osteogenic, chondrogenic, and adipogenic genes, are analyzed by qPCR. Free calcium and phosphate ion concentrations are assessed in the cell culture supernatant. After one week and 5 µg/mL aCaP, downregulation of osteogenic markers ALP and Runx2 is found, and averaged across the three donors. Our results show that after two weeks, ALP is further downregulated, but Runx2 is upregulated. Endothelial cell marker genes, such as CD31 and CD34, are upregulated with 50 µg/mL aCaP and a 2-week exposure. Inter-donor variability is high: Two out of three donors show a significant upregulation of ALP and Runx2 at day 14 with 50 µg/mL aCaP compared to 5 µg/mL aCaP. Notably, all changes in stem cell commitment are obtained in the absence of an osteogenic medium. While the chemical composition of the culture medium and the saturation status towards calcium phosphate phases remain approximately the same for all conditions, gene expression of ASCs changes considerably. Hence, aCaP nanoparticles show the potential to trigger osteogenic and endothelial commitment in ASCs.

Anodizing/Anaphoretic Electrodeposition of Nano-Calcium Phosphate/Chitosan Lactate Multifunctional Coatings on Titanium with Advanced Corrosion Resistance, Bioactivity, and Antibacterial Properties

The aim of this work was to investigate corrosion resistivity, bioactivity, and antibacterial activity of novel nano-amorphous calcium phosphate (ACP) potentially multifunctional composite coatings with and without chitosan oligosaccharide lactate (ChOL), ACP + ChOL/TiO₂ and ACP/TiO₂ ACP + ChOL/TiO₂, respectively, on the titanium substrate. The coatings were obtained by new single-step in situ anodization of the substrate to generate TiO₂ and the anaphoretic electrodeposition process of ACP and ChOL. The obtained coatings were around 300 ± 15 μm thick and consisted of two phases, namely, TiO₂ and hybrid composite phases. Both ACP/TiO₂ and ACP + ChOL/TiO₂ have improved corrosion stability, whereas the ACP + ChOL/TiO₂ coating showed better corrosion stability. It was shown that at the very start of the deposition process, the formation of the ChOL/TiO₂ layer takes place predominantly, which is followed by the inclusion of ChOL into ACP with simultaneous growth of TiO₂. This deposition mechanism resulted in the formation of strongly bonded uniform stable coating with high corrosion resistance. In vitro bioactivity was investigated by immersion of the samples in simulated body fluid (SBF). There is in-bone-like apatite formation on both ACP/TiO₂ and ACP + ChOL/TiO₂ surfaces upon immersion into SBF, which was proven by X-ray diffraction and Fourier transform infrared spectroscopy. While ACP/TiO₂ shows no antibacterial activity, ACP + ChOL/TiO₂ samples exhibited three- to fourfold decreases in the number of Staphylococcus aureus and Pseudomonas aeruginosa, respectively, after 420 min. The probable mechanism is binding ChOL with the bacterial cell wall, inhibiting its growth, altering the permeability of the cell membrane, and leading to bacterial death.

Citrate Stabilizes Hydroxylapatite Precursors: Implications for Bone Mineralization

Mineralization of hydroxylapatite (HAp), the main inorganic phase in bone, follows nonclassical crystallization routes involving metastable precursors and is strongly influenced by organic macromolecules. However, the effect of small organic molecules such as citrate on the formation of HAp is not well constrained. Using potentiometric titration experiments and titration calorimetry, in combination with a multianalytical approach, we show that citrate stabilizes prenucleation species as well as a liquid-like calcium phosphate precursor formed before any solid phase nucleates in the system. The stabilization of a liquid-like precursor phase could facilitate infiltration into the cavities of the collagen fibrils during bone mineralization, explaining the enhancement of collagen-mediated mineralization by citrate reported in previous studies. Hence, citrate can influence bone mineralization way before any solid phase (amorphous or crystalline) is formed. We also show that HAp formation after amorphous calcium phosphate (ACP) in the absence and presence of citrate results in nanoplates of about 5-12 nm thick, elongated along the c axis. Such nanoplates are made up of HAp nanocrystallites with a preferred c axis orientation and with interspersed ACP. The nanoplatelet morphology, size, and preferred crystallographic orientation, remarkably similar to those of bone HAp nanocrystals, appear to be an intrinsic feature of HAp formed from an amorphous precursor. Our results challenge current models for HAp mineralization in bone and the role of citrate, offering new clues to help answer the long-standing question as to why natural evolution favored HAp as the mineral phase in bone.

Mechanisms of Enamel Mineralization Guided by Amelogenin Nanoribbons

The nanofibrous nature and its intricate structural organization are the basis for the extraordinary ability of sound enamel to outlive masticatory forces at minimal failure rates. Apatite nanofibers of several hundreds of micrometers to possibly millimeters in length originate during the secretory stage of amelogenesis as 2-nm-thin and 15-nm-wide ribbons that develop and grow in length under the guidance of a dynamic mixture of specialized proteins, the developing enamel matrix (DEM). A critical role in the unidirectional and oriented growth of enamel mineral ribbons has been attributed to amelogenin, the major constituent of the DEM. This review elaborates on recent studies on the ability of ribbon-like assemblies of amelogenin to template the formation of an amorphous calcium phosphate precursor that transforms into apatite mineral ribbons similar to the ones observed in developing enamel. A mechanistic model of the biological processes that drive biomineralization in enamel is presented in the context of a comparative analysis of enamel mouse models and earlier structural data of the DEM emphasizing a regulatory role of the matrix metalloproteinase 20 in mineral deposition and the involvement of a process-directing agent for the templated mineral growth directed by amelogenin nanoribbons.

Long-Term Assessment of the In Vitro Corrosion Resistance of Biomimetic ACP Coatings Electrodeposited from an Acetate Bath

Calcium phosphate coatings are able to improve the osseointegration process due to their chemical composition, which is similar to that of bone tissues. In this work, to increase the long-term corrosion resistance and to improve the osseointegration process of commercially pure titanium Grade 4 (CpTi G4), biomimetic amorphous calcium phosphate (ACP) coatings were electrodeposited for the first time from an acetate bath with a pH level of 7.0 and a Ca:P ratio of 1.67. ACP coatings were obtained on CpTi G4 substrate subjected to sandblasting and autoclaving using electrochemically assisted deposition at a potential of -3 V relative to the open circuit potential for 30 min at room temperature. SEM, EDS, 2D roughness profiles, amplitude-sensitive eddy current method, and Kelvin scanning probe were used for the surface characterization of the biomaterial under study. In vitro corrosion resistance tests were conducted for 21 days in artificial saliva using open circuit potential, polarization curves, and electrochemical impedance spectroscopy measurements. The passive-transpassive behavior was revealed for the obtained ACP coatings. The long-term corrosion resistance test showed a deterioration of the protective properties for CpTi G4 uncoated and coated with ACP with immersion time. The mechanism and kinetics of the pitting corrosion on the CpTi G4|TiO2|ACP coating system are discussed in detail.

Oxidized Low-Density Lipoprotein Promotes In Vitro Calcification

Calcification plays an important role in the human body in maintaining homeostasis. In the human body, the presence of a high amount of oxidized low-density lipoprotein (ox-LDL) is a consistent feature of the local areas that are common sites of ectopic calcification, namely dental calculus, renal calculus, and the areas affected by arteriosclerosis. Hence, ox-LDL may have some effect on calcification. Scanning electron microscopy (SEM) observation revealed a high amount of amorphous calcium phosphate (ACP) when ox-LDL was included in the solution. In the in vitro experiment, the highest amount of precipitation of calcium phosphate was observed in the solution containing ox-LDL compared to the inclusion of other biomaterials and was 4.2 times higher than that of deionized water for 4.86 mM calcium and 2.71 mM phosphate. The morphology of calcium phosphate precipitates in the solution containing ox-LDL differed from that of the precipitates in solutions containing other biomaterials, as determined by transmission electron microscopy (TEM). Through the time course observation of the sediments using TEM, it was observed that the sediments changed from spherical or oval shape to a thin film shape. These results indicate that sediments acquired a long-range order array, and the phase transitioned from non-crystalline to crystalline with an increased time and density of ACP. Thus, it is concluded that ox-LDL promoted ACP precipitation and it plays an important role in ectopic calcification.

Amorphous Calcium Magnesium Phosphate Particles for Treatment of Dentin Hypersensitivity: A Mode of Action Study

Occlusion of exposed dentin tubules may eliminate or reduce dentin hypersensitivity by hindering fluid movements within the tubules. In this study, the mode of action of spherical particles of amorphous calcium magnesium phosphate (180-440 nm in diameter) was studied. A degradation study of the particles in Tris-HCl buffer showed that the particles continuously released Ca²⁺, Mg²⁺, and phosphate, and XRD analysis revealed the formation of hydroxyapatite (HA) after 1 week. The occluding effect and efficacy of the spherical particles as an occluding agent were evaluated in an in vitro study. The ACMP particles were incorporated in a gel intended for at-home use and tested on extracted human molars. Application of the particles followed by incubation in artificial saliva resulted in occlusion of exposed tubules, and examination with SEM showed that the particles could penetrate the tubules down to 100 μm from the dentin surface. Transformation of the particles into nanocrystalline HA-structures (nanoHA) was initiated at the dentin surface within 12 h of application, and tubule penetration of the particles, accompanied by further ion release and diffusion of ions, resulted in deep intratubular occlusion in the majority of the tubules within 3 days from application. NanoHA was tightly adhered to the tubule walls, filling the entire tubule volume after 7 days. The results of this study demonstrate the mode of action of the amorphous calcium magnesium phosphate particles in occluding exposed dentin tubules. Interaction with saliva and transformation of the particles within the tubules inducing further mineralization indicate that the particles may be used as an effective treatment to reduce dentin hypersensitivity.

Biomineralization Precursor Carrier System Based on Carboxyl-Functionalized Large Pore Mesoporous Silica Nanoparticles

Bone and teeth are derived from intrafibrillarly mineralized collagen fibrils as the second level of hierarchy. According to polymer-induced liquid-precursor process, using amorphous calcium phosphate precursor (ACP) is able to achieve intrafibrillar mineralization in the case of bone biomineral in vitro. Therefore, ACP precursors might be blended with any osteoconductive scaffold as a promising bone formation supplement for in-situ remineralization of collagens in bone. In this study, mesoporous silica nanoparticles with carboxyl-functionalized groups and ultra large-pores have been synthesized and used for the delivery of liquid like biomimetic precursors (ACP). The precursor delivery capacity of the nanoparticles was verified by the precursor release profile and successful mineralization of 2D and 3D collagen models. The nanoparticles could be completely degraded in 60 days and exhibited good biocompatibility as well. The successful translational strategy for biomineralization precursors showed that biomineralization precursor laden ultra large pore mesoporous silica possessed the potential as a versatile supplement in demineralized bone formation through the induction of intrafibrillar collagen mineralization.

Novel Bioactive and Therapeutic Root Canal Sealers with Antibacterial and Remineralization Properties

According to the American Dental Association Survey of Dental Services Rendered (published in 2007), 15 million root canal treatment procedures are performed annually. Endodontic therapy relies mainly on biomechanical preparation, chemical irrigation and intracanal medicaments which play an important role in eliminating bacteria in the root canal. Furthermore, adequate obturation is essential to confine any residual bacteria within the root canal and deprive them of nutrients. However, numerous studies have shown that complete elimination of bacteria is not achieved due to the complex anatomy of the root canal system. There are several conventional antibiotic materials available in the market for endodontic use. However, the majority of these antibiotics and antiseptics provide short-term antibacterial effects, and they impose a risk of developing antibacterial resistance. The root canal is a dynamic environment, and antibacterial and antibiofilm materials with long-term effects and nonspecific mechanisms of action are highly desirable in such environments. In addition, the application of acidic solutions to the root canal wall can alter the dentin structure, resulting in a weaker and more brittle dentin. Root canal sealers with bioactive properties come in direct contact with the dentin wall and can play a positive role in bacterial elimination and strengthening of the root structure. The new generation of nanostructured, bioactive, antibacterial and remineralizing additives into polymeric resin-based root canal sealers are discussed in this review. The effects of these novel bioactive additives on the physical and sealing properties, as well as their biocompatibility, are all important factors that are presented in this article.

The Injectable Woven Bone-Like Hydrogel to Perform Alveolar Ridge Preservation With Adapted Remodeling Performance After Tooth Extraction

Grafting bone substitute is paramount to prevent the alveolar ridge resorption after tooth extraction and facilitate the subsequent implant treatment. An ideal bone substitute should acquire the excellent osteogenic property, more importantly, possess the suitable remodeling rate in balance with bone formation and desirable clinical manageability. However, none of bone substitute is simultaneously characterized by these features, and currently, the limited remodeling property leads to the excessive waiting time before implantation. Enlightened by woven bone, the transitional tissue that is able to induce osteogenesis during bone healing could be easily remodeled within a short period and depend on the favorable injectability of hydrogel, an injectable woven bone-like hydrogel (IWBLH) was constructed in this study to address the above problems. To mimic the component and hierarchical structure of woven bone, amorphous calcium phosphate (ACP) and mineralized collagen fibril were synthesized and compounded with alginate to form IWBLHs with various ratio. Screened by physiochemical characterization and in vitro biological assays, an optimal IWBLH was selected and further explored in rat model of tooth extraction. Compared with the most widely used bone substitute, we showed that IWBLH could be easily handled to fully fill the tooth socket, perform a comparable function to prevent the alveolar bone resorption, and completely remodeled within 4 weeks. This IWBLH stands as a promising candidate for alveolar ridge preservation (ARP) in future.

Characterization of Phosphorus Species in Human Dentin by Solid-State NMR

The rat has been considered as an appropriate animal model for the study of the mineralization process in humans. In this work, we found that the phosphorus species in human dentin characterized by solid-state NMR spectroscopy consist mainly of orthophosphate and hydrogen phosphate. Some orthophosphates are found in a disordered phase, where the phosphate ions are hydrogen-bonded to structural water, some present a stoichiometric apatite structure, and some a hydroxyl-depleted apatite structure. The results of this study are largely the same as those previously obtained for rat dentin. However, the relative amounts of the various phosphorus species in human and rat dentin are dramatically different. In particular, stoichiometric apatite is more abundant in human dentin than in rat dentin, whereas the converse is true for disordered-phase orthophosphates. Furthermore, spatial proximity among all phosphorus species in human dentin is identical within experimental error, in contrast to what observed for rat dentin. Although it is not clear how these spectroscopic data could relate to the hierarchical structure or the mechanical properties of teeth, our data reveal that the molecular structures of human and rat dentin at different growth stages are not exactly the same.

Highly Porous Amorphous Calcium Phosphate for Drug Delivery and Bio-Medical Applications

Amorphous calcium phosphate (ACP) has shown significant effects on the biomineralization and promising applications in bio-medicine. However, the limited stability and porosity of ACP material restrict its practical applications. A storage stable highly porous ACP with Brunauer-Emmett-Teller surface area of over 400 m2/g was synthesized by introducing phosphoric acid to a methanol suspension containing amorphous calcium carbonate nanoparticles. Electron microscopy revealed that the porous ACP was constructed with aggregated ACP nanoparticles with dimensions of several nanometers. Large angle X-ray scattering revealed a short-range atomic order of <20 Å in the ACP nanoparticles. The synthesized ACP demonstrated long-term stability and did not crystallize even after storage for over 14 months in air. The stability of the ACP in water and an α-MEM cell culture medium were also examined. The stability of ACP could be tuned by adjusting its chemical composition. The ACP synthesized in this work was cytocompatible and acted as drug carriers for the bisphosphonate drug alendronate (AL) in vitro. AL-loaded ACP released ~25% of the loaded AL in the first 22 days. These properties make ACP a promising candidate material for potential application in biomedical fields such as drug delivery and bone healing.

Six-month evaluation of novel bioabsorbable scaffolds composed of poly-L-lactic acid and amorphous calcium phosphate nanoparticles in porcine coronary arteries

Objective Using coronary angiography and intravascular ultrasound methods to evaluate the performance of the novel fully bioabsorbable scaffold (NFBS) composed of poly-L-lactic acid/amorphous calcium phosphate (PLLA/ACP) at six-month follow-up by comparing with PLLA scaffolds Methods Twelve PLLA/ACP scaffolds and 12 PLLA scaffolds were implanted into the coronary arteries of 12 miniature pigs. Quantitative coronary angiography (QCA) was used to measure the reference vessel diameter (RVD), mean lumen diameter (MLD) and late lumen loss (LLL). According to IVUS images, we calculated the strut malapposition rate (SMR) at post implantation, strut overlap rate (SOR), reference vessel area (RVA), mean stent area (MSA), mean lumen area (MLA) and luminal patency rate (LPR) at six-month follow-up. The radial strength of the scaffold was evaluated using a catheter tensile testing machine. Results QCA results indicated that, at six month, MLD of PLLA/ACP scaffolds was greater than those of PLLA scaffolds (2.47 ± 0.22 mm vs. 2.08 ± 0.25 mm, P < 0.05); LLL of PLLA/ACP scaffolds was less than those of PLLA scaffolds (0.42 ± 0.20 mm vs. 0.75 ± 0.22 mm, P < 0.05). IVUS results showed the SMR and SOR were all significantly less with the PLLA/ACP scaffolds than the PLLA scaffolds (5.84% ± 3.56% vs. 17.72% ± 4.86%, P < 0.05) (6.17% ± 4.63% vs. 17.65% ± 4.29%, P < 0.05). MSA, MLA and LPR of the PLLA/ACP scaffolds were all greater than those of PLLA scaffolds (6.35 ± 0.45 mm² vs. 5.35 ± 0.51 mm², P < 0.05) (4.76 ± 0.46 mm² vs. 3.77 ± 0.46 mm², P < 0.05) (78.01% ± 12.29% vs. 61.69% ± 9.76%, P < 0.05). Radial strength of PLLA/ACP scaffold at six month was greater than that of PLLA scaffold (76.33 ± 3.14 N vs. 67.67 ± 3.63 N). Conclusion The NFBS had less stent recoil, better lumen patency rate and greater radial strength than PLLA scaffolds. The results suggest the NFBS scaffolds can maintain the structural strength and functional performance, which are effective for up to six months when implanted in porcine coronary arteries.

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.

A new method for in situ structural investigations of nano-sized amorphous and crystalline materials using mixed-flow reactors

Structural investigations of amorphous and nanocrystalline phases forming in solution are historically challenging. Few methods are capable of in situ atomic structural analysis and rigorous control of the system. A mixed-flow reactor (MFR) is used for total X-ray scattering experiments to examine the short- and long-range structure of phases in situ with pair distribution function (PDF) analysis. The adaptable experimental setup enables data collection for a range of different system chemistries, initial supersaturations and residence times. The age of the sample during analysis is controlled by adjusting the flow rate. Faster rates allow for younger samples to be examined, but if flow is too fast not enough data are acquired to average out excess signal noise. Slower flow rates form older samples, but at very slow speeds particles settle and block flow, clogging the system. Proper background collection and subtraction is critical for data optimization. Overall, this MFR method is an ideal scheme for analyzing the in situ structures of phases that form during crystal growth in solution. As a proof of concept, high-resolution total X-ray scattering data of amorphous and crystalline calcium phosphates and amorphous calcium carbonate were collected for PDF analysis.

Insights into the kinetics of thermally induced crystallization of amorphous calcium phosphate

Transformations between amorphous and crystalline apatite mechanistically govern some of the most essential processes in bone metabolism, including biomineralization and bone remodeling. Fundamental understanding of this phase transition can help us gain control over the formation and dissolution of boney tissues in vivo and utilize that knowledge for various therapeutic ends. Crystallization of hydroxyapatite (HAp) and two tricalcium phosphate (TCP) polymorphs from the metastable precursor, amorphous calcium phosphate (ACP) was here studied kinetically and mechanistically using thermal analyses, X-ray diffraction and Fourier-transform infrared spectroscopy. Crystallization was detected in the differential thermal analysis as the exothermic peak at 639.5 °C at the slowest heating regimen of 5 °C min-1, while a combination of different kinetics models, including Augis-Bennett, Borchardt-Daniels, Johnson-Mehl-Avrami, Kissinger, Ozawa and Piloyan, yielded activation energies in the 435-450 kJ mol-1 range. Dehydrated ACP required a significant energy input to transform to HAp, thus indirectly proving the key role that structural water plays in this process in a biological setting. The phase transformation at high temperatures involved preformed nuclei and was solely due to their 3D growth, contrasting the edge-controlled nucleation derived earlier as the mechanism of growth in the solution. Crystallization was in both cases accompanied by the formation of needle-shape crystals of HAp through aggregation of ultrafine spherical units of ACP. Relationship between crystallinity and the heating rate was detected only for the initially amorphous structure, indicating a more intense and coherent lattice ordering process in annealed ACP than in HAp. Despite that, crystallization disobeyed the rule of inverse proportionality between the thermal energy required for the relaxation of defects and the level of strain, as the recovery rate of the initially poorly crystalline HAp was higher than that of ACP.

Plaque Accumulation and Inflammation Adjacent to Restorations of Amorphous Calcium Phosphate-containing Composite in Early Childhood Caries

PURPOSE

To evaluate the clinical, biochemical, and microbiological reactions to nanocomposite containing amorphous calcium phosphate (ACP) in comparison to a traditional composite restorative material in early childhood caries.

MATERIALS AND METHODS

Eighteen teeth were restored with the test material (ACP-containing resin) and 18 teeth were restored with the control material (traditional composite, TC) in fourteen paediatric patients using a split-mouth design. One caries- and restoration-free intact tooth in each patient was selected as the healthy control. Gingival crevicular fluid (GCF) and supragingival plaque samples were collected at baseline before the treatment and also on days 1, 7, 14 and 30 after treatment. Unstimulated whole saliva samples were obtained from each patient at baseline, and 1 and 6 months after restoration. GCF and saliva samples were assayed for IL-17A, IL-17F IL-17A/F, IL-17E, OPG and RANKL levels by ELISA, and plaque composition was assessed using RT-PCR.

RESULTS

Clinical evaluation indicated no statistically significant differences between the two restorative materials according to the FDI criteria surface lustre, material retention and marginal adaptation properties. Pro-inflammatory IL-17 levels decreased statistically significantly at 6 months compared to baseline and 1-month values (p < 0.05). The baseline pro-inflammatory IL-17 cytokine levels in GCF samples around the carious teeth were higher than those obtained around the healthy teeth (p < 0.05), but similar in GCF from the ACP-test and TC teeth. Microbiological findings were similar in the ACP and T groups.

CONCLUSION

It may be suggested that both ACP-containing and traditional resin composites show similar antimicrobial and biochemical effects in early childhood caries.

The effect of polyaspartate chain length on mediating biomimetic remineralization of collagenous tissues

Formation of hydroxyapatite (HAP) within collagen fibrils, as found in bone, dentine and cementum, is thought to be mediated by proteins rich in aspartate (Asp) and glutamate such as osteopontin and bone sialoprotein, respectively. Indeed polyaspartate (pAsp), a homopolymer analogue of such proteins, has been shown to induce intrafibrillar mineralization of collagen from solutions of calcium and phosphate that are supersaturated with respect to HAP. To elucidate the role of pAsp in mineralization of collagen, we explored the effect of pAsp chain length on in vitro HAP deposition in demineralized mouse periodontal tissue sections. Through characterization of both tissue sections and mineralizing solution, we show that chain length contributes to the effectiveness of pAsp in mediating intrafibrillar mineralization. This function appears to be associated with inhibition of otherwise kinetically favoured crystallization in the bulk solution, which allows for intrafibrillar crystallization, though this does not preclude the possibility of a more active role for pAsp in addition. Inhibition of crystallization in solution by pAsp occurs by slowing the growth of amorphous calcium phosphate and stabilization of this phase, rather than by sequestration of Ca²⁺ ions. These results suggest that the length of Asp-rich sequences of mineralizing proteins may be essential to their function, and could also be useful in optimization of mineralized tissue replacement synthesis.

Effects of Amorphous Calcium Phosphate Administration on Dental Sensitivity during In-Office and At-Home Interventions

Background. Tooth bleaching is the most frequently employed whitening procedure in clinics. The major side effect of tooth bleaching is dental sensitivity during and after the treatment. Here, we evaluated whether the administration of amorphous calcium phosphate (ACP), during in-office and at-home procedures may impact on dental sensitivity. Methods. Eighty patients, responding to the study requirements were enrolled according to the following criteria. Group 1 (n = 40), received in-office, 10% ACP prior to 30% professional hydrogen peroxide application. The whitening procedure continued at home using 10% carbamide peroxide with 15% ACP for 15 days. Group 2 (n = 40) received only 30% hydrogen peroxide application and continued the whitening procedures at home, using 10% carbamide hydroxide, without ACP- Casein phosphopeptides (CPP), for 15 days. Dental sensitivity was recorded with a visual analogue scale (VAS) at baseline, immediately after, and at 15 days after treatment in the two groups. Results. We observed that patients receiving ACP in the bleaching mixture experienced decreased dental sensitivity (* p ≤ 0.05), as detected by VAS scale analysis immediately following the procedures. Patients receiving ACP-CPP during at-home procedures showed a statistically significant (*** p ≤ 0.0001) reduction of dental sensitivity. Conclusions. We demonstrated that ACP-CPP administration, while exerting the same whitening effects as in control subjects receiving potassium fluoride (PF), had an impact on the reduction of dental sensitivity, improving patient compliance.

Contribution of Mitophagy to Cell-Mediated Mineralization: Revisiting a 50-Year-Old Conundrum

Biomineralization in vertebrates is initiated via amorphous calcium phosphate (ACP) precursors. These precursors infiltrate the extracellular collagen matrix where they undergo phase transformation into intrafibrillar carbonated apatite. Although it is well established that ACP precursors are released from intracellular vesicles through exocytosis, an unsolved enigma in this cell-mediated mineralization process is how ACP precursors, initially produced in the mitochondria, are translocated to the intracellular vesicles. The present study proposes that mitophagy provides the mechanism for transfer of ACP precursors from the dysfunctioned mitochondria to autophagosomes, which, upon fusion with lysosomes, become autolysosomes where the mitochondrial ACP precursors coalesce to form larger intravesicular granules, prior to their release into the extracellular matrix. Apart from endowing the mitochondria with the function of ACP delivery through mitophagy, the present results indicate that mitophagy, triggered upon intramitochondrial ACP accumulation in osteogenic lineage-committed mesenchymal stem cells, participates in the biomineralization process through the BMP/Smad signaling pathway.

Remineralization Efficacy of an Amelogenin-Based Synthetic Peptide on Carious Lesions

Objective: The aim of this study was to evaluate the remineralization efficacy of an amelogenin-based peptide on initial enamel carious lesions in vitro. Furthermore, we attempted to provide insights into the possible mechanism of the remineralization, including determining the calcium-binding properties of the peptide and its effects on calcium phosphate mineralization.

Methods: The peptide comprising the N-terminus and the C-terminus of porcine amelogenin was synthesized by Synpeptide Co., Ltd. Fifty specimens were randomly assigned to five immersing treatment groups for 12 days: remineralizing medium only; 12.5 μg/mL peptide + remineralizing medium; 25 μg/mL peptide + remineralizing medium; 50 μg/mL peptide + remineralizing medium; fluoride + remineralizing medium. After immersion, mean mineral loss before and after remineralization of each specimen was determined using micro-CT. Mean mineral gain after remineralization was calculated. Calcium binding properties were measured by Isothermal titration calorimetry (ITC). TEM and Fourier transform-infrared were used to determine the effects of the peptide on calcium phosphate mineralization.

Results: A significant decrease in mineral loss after remineralization process in all groups was observed (p < 0.05). Treatment in remineralizing medium resulted in the lowest mineral gain while the fluoridated treatment exhibited the highest mineral gain among all groups. Inclusion of synthetic peptide in the remineralizing medium exhibited a higher mineral gain and the gain of 50 μg/mL group was greater than that of the 25 μg/mL group. No significant difference in mineral gain was observed between the remineralizing medium only group and the 12.5 μg/mL peptide group (p > 0.05). ITC values showed that the Ca²⁺-binding affinity of the peptide is about 9.914 × 10⁴M⁻¹. Furthermore, the peptide was found to inhibit calcium phosphate precipitation and stabilize amorphous calcium phosphate formation for more than 2 h and finally transform into ordered hydroxyapatite crystals.

Conclusion: Specific concentrations of the amelogenin-based synthetic peptide promoted in vitro remineralization, with higher concentrations exhibiting significantly greater remineralization. This study presented evidence suggesting that the peptide may act as a Ca²⁺carrier as well as a regulating factor. When the stabilizing calcium and phosphorus ions bind with the peptide they become biologically available for the remineralization of deeper carious lesions, while also regulated by the peptide to transform into ordered hydroxyapatite crystals.

On Grounds of the Memory Effect in Amorphous and Crystalline Apatite: Kinetics of Crystallization and Biological Response

Memory effects, despite being intrinsic to biological systems, are rarely potentiated in biomaterials. By exploring the transition between amorphous calcium phosphate (ACP) and hydroxyapatite (HAp) from different empirical angles, here, we attempt to set the basis for elicitation of structural memory effects in CPs. Two CPs precipitated under different degrees of saturation (DS), yielding HAp at a low DS and ACP at a high DS, were shown to evolve into structures with a high level of crystallographic similarity after their prolonged aging in the solution and served as the basis for this study. Amorphous-to-crystalline transition was abrupt in both precipitates, indicating an autocatalytic process preceded by considerable nucleation lag times, but it was more dynamic and proceeded in multiple stages in the precipitate formed at a higher DS, involving a greater degree of lattice rearrangements. ACP was found to exist in one of the two stoichiometrically and crystallographically different forms, one of which, amounting to ≥60 wt %, resembled tricalcium phosphate and transformed to HAp through the surface dissolution/reprecipitation mechanism and the other one, amounting to ≤20 wt %, was apatitic, enabling the transformation of ACP to HAp via martensitic, bulk lattice reordering phenomena. Large density of stacking faults was responsible for the comparatively high lattice strain, the property to which biogenic apatite owes its ability to accommodate foreign ions and act as a mineral reservoir for the body. Being the precursor for biogenic apatite during biomineralization and a thermodynamically logical intermediate in the ripening of HAp per the Ostwald law of stages, ACP proved to be more prone to structural transformation than the final and the most stable of the CP phases in this sequence of events: HAp. Amorphized upon gelation, two CPs transformed into HAp, albeit at different rates, which were higher for the material that had been crystalline prior to amorphization than for the one that had initially been amorphous, indicating the presence of a definite memory effect. The two HAp powders with different histories of formation also elicited different biological responses, including a Runx2 transcription factor expression in MC3T3-E1 osteoblasts, cell uptake efficiency, and antibacterial activity, extending the memory effect in HAp to the biological domain. The biological response was typically indistinct between the final products and their respective precursors but markedly different between the two products obtained by following different formation paths, confirming the presence of the given memory effect. It is suggested that the key to explaining the difference in the response between the materials differing in their route of formation lies in the direct dependence between the DS at which precipitation occurs and the rate of exchange of hydrated ions and ionic clusters across the particle surface in contact with a solution.

Amorphous calcium phosphate (ACP) in tissue repair process

Synthetic biomaterials submitted to new structural technologies have become ideal for the recovery of traumatized bone tissues and some bone substitutes such as bioactive glass, β-Tricalcium phosphate (β-TCP) and amorphous calcium phosphate (ACP) are being used in areas of tissue defects. For this study, ACP was produced in the form of fibers and then submitted to cytotoxicity testing. A sample of ACP was inserted into the mandibular region of a patient with a lost implant so after removal and curettage, the remaining bone site was filled with the ACP biomaterial. Preliminary cytotoxicity test was negative. After 15 weeks of healing, a titanium implant was inserted at the site. Clinical and radiographic follow-up was conducted for 12 months and sequential radiographic analyses revealed tissue formation resembling spongy bone. Images under immunohistochemistry demonstrated efficient deposition and osteoconduction of the newly deposited tissue. Residual portion of the CaO:P₂ O₅ outer layers served as a substrate for osteoid matrix deposition, aiding growth, and the results of fiber absorption favored maturation of the new bone tissue.

Antimicrobial Monomers for Polymeric Dental Restoratives: Cytotoxicity and Physicochemical Properties

A trend for the next generation of polymeric dental restoratives is to incorporate multifunctional capabilities to regulate microbial growth and remineralize tooth surfaces. Polymerizable 2-(methacryloyloxy)-N-(2-(methacryloyloxy)ethyl)-N,N-dimethylethan-1-aminium bromide (IDMA1) and N,N′-([1,1′-biphenyl]-2,2′-diylbis(methylene))bis(2-(methacryloyloxy)-N,N-dimethylethan-1-aminium) bromide (IDMA2), intended for utilization in bi-functional antimicrobial and remineralizing composites, were synthesized, purified with an ethanol-diethyl ether-hexane solvent system, and validated by nuclear magnetic resonance (¹H and ¹³C NMR) spectroscopy, mass spectrometry, and Fourier-transform infrared spectroscopy. When incorporated into light-curable urethane dimethacrylate (UDMA)/polyethylene glycol-extended UDMA (PEG-U)/ethyl 2-(hydroxymethyl)acrylate (EHMA) (assigned UPE) resins, IDMAs did not affect the overall resins’ hydrophilicity/hydrophobicity balance (water contact angle: 60.8–65.5°). The attained degrees of vinyl conversion (DVC) were consistently higher in both IDMA-containing copolymers and their amorphous calcium phosphate (ACP) composites (up to 5% and 20%, respectively) reaching 92.5% in IDMA2 formulations. Notably, these high DVCs values were attained without an excessive increase in polymerization stress. The observed reduction in biaxial flexure strength of UPE-IDMA ACP composites should not prevent further evaluation of these materials as multifunctional Class V restoratives. In direct contact with human gingival fibroblasts, at biologically relevant concentrations, IDMAs did not adversely affect cell viability or their metabolic activity. Ion release from the composites was indicative of their strong remineralization potential. The above, early-phase biocompatibility and physicochemical tests justify further evaluation of these experimental materials to identify formulation(s) suitable for clinical testing. Successful completion is expected to yield a new class of restoratives with well-controlled bio-function, which will physicochemically, mechanically, and biologically outperform the conventional Class V restoratives.