Calcium-deficient Apatite Research Articles

Fabrication, characterization, and in vitro studies of Selenium-substituted hydroxyapatite coatings

Abstract The increasing demand for hydroxyapatite (HA) coatings with enhanced functionality have led to novel materials with compositions that are more closely resembling those of natural bone apatites. In the present study, selenium-substituted (Se–HA) powders with various Se quantities were prepared by chemical precipitation. By applying suspension plasma spray (SPS), the surface of Ti substrates was coated with corresponding Se-HA coatings. The microstructural and physicochemical properties of the powders and the coatings were studied. Analysis by x-ray diffraction indicates that SeO3 2− replaced the PO4 3− groups, affecting the crystal structure and crystallinity of HA. As the extent of Se substitution increases, the lattice volume expands and the crystallinity decreases. The synthesized Se-HA powders were confirmed to be calcium-deficient apatite through energy-dispersive x-ray spectroscopy. However, the high temperature of SPS accelerated volatilization of P, increasing the Ca/(P + Se) ratio of the coatings, whereas the chemical valence state of Se remained unchanged. The Se–HA coating exhibited a high bonding strength of >33 MPa, fully meeting the requirement of 15 MPa as coating implant materials. Dissolution behavior tests indicate that the Se–HA coatings had high solubility in comparison to the HA coating. As the substitution degree of Se increased, the dissolution rate also increased, which greatly enhanced the capacity to generate a bone-like apatite layer. In vitro cell experiments indicate that the Se–HA coatings exhibited excellent biocompatibility, and facilitated adhesion and proliferation of osteoblast MC3T3-E1, even in the presence of fluorine. Furthermore, antibacterial properties of Se–HA coatings were also indicated by inhibition of Staphylococcus aureus, which is the main cause of most infections after orthopedic surgeries. Thus, the Se–HA coatings have potential as implant coating materials for orthopedic applications.

Bicalcium Phosphate as an Asset in Regenerative Therapy.

After a loss of a tooth, alveolarbone resorption is immutable, leaving the area devoid of sufficient bone quality and mass for a successful and satisfactory implant or any other dental treatment. To treat this problem of irreversible bone loss, bone grafting is the primary solution and a well-accepted technique. The use of bone grafting procedures has increased in recent years. This review is about the various bone grafting techniques and best-situated material available currently along with their trump cards and limitations. In the thorough discussion regarding bone grafting materials and their substitutes, one alloplastic material has shown unbeaten and the most satisfactory properties than any other material, "bicalcium phosphate" (BCP). BCP is a mixture of hydroxyapatite (HA) and beta-tricalcium phosphate (B-TCP) usually obtained through sintering calcium-deficient apatite (CDA) at or above 700°C or by other methods such as hydrolysis or precipitation. The review also shows comparative studies done to understand the effect, most adequate balance, and impact of ratios of HA/B-TCP on the properties, structure, and success rate of this material. The objective of the review is to enlighten the principal characteristic of the most likely used bone graft material presently, i.e., BCP. The most impeccable characteristic of BCP is its capability to osteointegrate, which results in a superior interface. This interface depicts a dynamic process that includes physicochemical reactions, crystal-protein interactions, cell and tissue colonization, and bone remodeling. BCP has certain essential properties that could be put forth as its advantage over any other substitute. These properties include bioactivity, osteointegration, osteoinduction, osteogenesis, and biodegradation, which are mostly governed by modifying the HA/B-TCP ratio. Other applications of BCP are feasible, such as in drug administration and scaffolds for tissue engineering.

Insight into the interactions of albumin with TiO2 nanomaterials and calcium phosphate-based biomaterials by kinetic adsorption and spectroscopic studies

Among key factors determining the fate of biomaterials in vivo are their interactions with blood serum proteins, which can lead to either successful integration or rejection/encapsulation. Although there are a number of studies investigating the interactions between proteins and bioimplants, comparable data for different types of biomaterials are lacking. To fill this gap, the adsorption kinetics and binding interactions of bovine serum albumin (BSA) with calcium phosphates (CaPs), namely hydroxyapatite (HA) and calcium deficient apatite (CaDHA), different TiO2 nanomaterials (TiNMs) presenting various morphologies such as nanoparticles (TiNPs), nanoplatelets (TiNPls), nanotubes (TiNTs) and nanowires (TiNWs), as well as their composites with CaDHA (CaDHA/TiNMs) were investigated. The kinetics of BSA adsorption on all studied materials was best described by pseudo-second order kinetics. The rate coefficient values obtained for the composites were lower than those for CaDHA and the corresponding TiNMs, while the adsorption density was higher for the composites than for CaDHA, except for the composites with TiNTs. Adsorption on TiNWs, CaDHA and all composites involved intraparticle diffusion, which was the rate-limiting step only for CaDHA/TiNTs. Fluorimetric titration experiments revealed that the number of binding sites was in larger than 1, except for TiNTs and TiNWs, indicating positive binding cooperativity. Interestingly, the values of the binding constants were lower for the TiNMs with a higher adsorption rate coefficient. Overall, BSA adsorption on the studied materials proved to be a complex process, which depended on the different surface properties of the adsorbents. Which property had a dominant role depended on the chemical identity of the adsorbent. The obtained comparable data for different types of materials point to the way of modifying their protein adsorption and binding properties.

Long-Term Fate and Efficacy of a Biomimetic (Sr)-Apatite-Coated Carbon Patch Used for Bone Reconstruction.

Critical bone defect repair remains a major medical challenge. Developing biocompatible materials with bone-healing ability is a key field of research, and calcium-deficient apatites (CDA) are appealing bioactive candidates. We previously described a method to cover activated carbon cloths (ACC) with CDA or strontium-doped CDA coatings to generate bone patches. Our previous study in rats revealed that apposition of ACC or ACC/CDA patches on cortical bone defects accelerated bone repair in the short term. This study aimed to analyze in the medium term the reconstruction of cortical bone in the presence of ACC/CDA or ACC/10Sr-CDA patches corresponding to 6 at.% of strontium substitution. It also aimed to examine the behavior of these cloths in the medium and long term, in situ and at distance. Our results at day 26 confirm the particular efficacy of strontium-doped patches on bone reconstruction, leading to new thick bone with high bone quality as quantified by Raman microspectroscopy. At 6 months the biocompatibility and complete osteointegration of these carbon cloths and the absence of micrometric carbon debris, either out of the implantation site or within peripheral organs, was confirmed. These results demonstrate that these composite carbon patches are promising biomaterials to accelerate bone reconstruction.

Fabrication of chitosan/silica hybrid coating on AZ31 Mg alloy for orthopaedic applications

Biocompatible conversion of chitosan and chitosan/silica hybrid coating were prepared to enhance the biocompatibility and corrosion resistance of biodegradable AZ31 Mg alloy. The coatings were optimized and analysed with potentiodynamic polarization, SEM, ATR-IR and XPS studies. Potentiodynamic polarization studies, revealed that the coatings exhibited high corrosion resistance. The surface morphology of the Ch-3/Si coating showed small globular rough structure. The presence of functional groups was confirmed by ATR-IR. For a better understanding of chitosan/silica hybrid coating, the chemical states were examined by XPS studies. The in-vitro bioactivity of the coated samples was evaluated in Earle's solution, which formed a dense layer of coral-like structure and calcium-deficient apatite with less stoichiometric ratio than the hydroxyapatite. In-vitro cell culture studies exhibited a good cell proliferation rate and the fabricated Ch-3/Si coating was found to be non-hemolytic. The bacterial studies proved that Ch-3/Si coating possessed inherent antibacterial activity.

Formation of Calcium Phosphate Apatite in System CaO-P2O5-H2O: Equilibrium at 298 K Under a Nitrogen Atmosphere

Aims: The formation of calcium phosphate apatite (hydroxyapatite, carbonate-containing hydroxyapatite, fluorapatite and carbonate-containing fluorapatite) in aqueous systems has been studied for over a century. Background: However, in the region of low concentrations of liquid phases, the question of the nature, composition and region of existence of apatite compounds remains controversial. Objective: The results of studying the phase equilibrium in the system CaO-P2O5-H2O at 298 K in the isotherm region from the invariant point of dicalcium phosphate and monocalcium phosphate monohydrate to the lowest concentrations of the liquid phase components are presented. Method: Chemical analysis, thermogravimetry, IR spectroscopy and optical microscopy were used for the analysis. Result: Long-term monitoring of the establishment of equilibrium (up to 20 months) resulted in the determination of regions of stable solid phases of calcium orthophosphates, calcium-deficient apatites, hydroxyapatite, and apatite with (Ca/P)at >1.67. Two types of calcium-deficient apatite were identified that differ in the (Ca/P)at ratio: the first type is 1.33 < (Ca/P)at ≤ 1.5; the second one is 1.5 ≤ (Ca/P)at < 1.67. Conclusion: The invariant points of calcium orthophosphates and compounds with the apatite structure were determined. The diagram was constructed using the Miller-Kenrick method based on obtained experimental data, which confirms the established regions and invariant points of stable equilibrium solid phases of the studied ternary system. The data obtained can be useful for understanding the processes of formation and change of compounds with apatite structure.

Controlled release of gallium maltolate complex from injectable phosphocalcic cements

Some cancers have tropism for bone: breast, prostate, lung, kidney, and thyroid cancers are the most common. Bone metastases can be treated with surgical resection and the resulting bone defects can be filled with injectable biomaterials. Among these, calcium phosphates may be the biomaterials of choice because of their ability to locally release anticancer active ingredients. Herein, we propose the synthesis of injectable calcium phosphate cement (CPC) loaded with gallium maltolate (GaM). It is an extremely promising anticancer drug with also antibiotic and anti-inflammatory properties. This synthesis was based on commercial cement whose main component was α-tri-calcium phosphate (α-TCP), and the final product obtained after hardening was calcium-deficient apatite (CDA). Two formulations were prepared, containing 3.5% and 7% by mass of GaM (CPC-3.5G and CPC-7G respectively). Powder x-ray diffraction (pXRD), Fourier transform infrared (FTIR) spectroscopy, and magic-angle spinning nuclear magnetic resonance (NMR MAS) 31P analyses showed that the direct incorporation of GaM did not modify the final cement composition. Textural properties, such as setting time, injectability, workability, and cohesiveness, were well preserved or even improved. Additionally, the mechanical strength, although slightly reduced, remained perfectly compatible with surgical use. In vitro kinetics studies of GaM-loaded CPCs showed a controlled release of GaM (49% at 60 days for CPC-3.5G and 58% at 116 days for CPC-7G) following Fick’s law. Raman imaging was used to visualize its diffusion within the cement during in vitro release experiments. Finally, the structural integrity of the gallium complex in the CPC was confirmed using NMR MAS 71Ga.

Improved Corrosion Resistance, Mechanical Stability and Biocompatibility of Functionalized Multiwall Carbon Nanotube Incorporated Calcium-Deficient Apatite for Orthopedic and Dental Applications

This report describes the successful development of functionalized multiwall carbon nanotube (MWCNT) incorporated β-tricalcium phosphate (β-TCP) by typical physical method and its coatings on medical grade 316L SS (316L Stainless Steel) substrate for orthopedic and dental applications. The synthesized material was confirmed by physical and analytical techniques. The improved adhesion property was clearly shown in the field emission scanning electron microscopy (FESEM) cross-sectional view. The Brunauer–Emmett–Teller (BET) analysis reveals the intact nature of the coating on the metal surface with reduced pore size which drastically improves the protective nature of the coating in the aggressive physiological environment the obtained corrosion kinetic parameters also support the observation. The results obtained from the hardness tests and thermogravimetric analysis revealed the information about the mechanical stability (7.1 GPa) and thermal stability of the developed materials. The apatite formation ability tested in the simulated body fluid demonstrates that the developed materials are potential enough to use it as a biomaterial to correct and repair the hard tissue defects.Graphical Abstract

Possibilities of Mechanochemical Synthesis of Apatites with Different Ca/P Ratios

Apatite is widely used in medicine as a biomaterial for bone tissue restoration. Properties of apatite depend on its composition, including the Ca/P ratio. This paper shows what range of Ca/P ratio can be attained in apatite by the mechanochemical method of synthesis, providing fast formation of a single-phase product. The synthesis was carried out from a reaction mixture of CaHPO4 and CaO at different Ca/P ratios in the range of 1.17–2.10. The products were studied by PXRD, FTIR and NMR spectroscopy, HRTEM, and STA. In mixtures with a low initial Ca/P ratio (1.17–1.48), directly in the mill, the formation of calcium orthophosphate with whitlockite structure containing an HPO42− group and structural water is shown for the first time. This phosphate has structure similar to that of whitlockites of hydrothermal origin and differs from high-temperature β-tricalcium phosphate that has composition Ca3(PO4)3. A series of samples of apatite was obtained with varied composition, which depends on the initial Ca/P ratio. At Ca/P < 1.67, the formation of two types of calcium-deficient apatite was documented. At Ca/P > 1.67, the existence of two types of calcium-rich apatite is confirmed.

Modulation of 3D Printed Calcium-Deficient Apatite Constructs with Varying Mn Concentrations for Osteochondral Regeneration via Endochondral Differentiation.

Osteochondral regeneration remains a vital problem in clinical situations affecting both bone and cartilage tissues due to the low regeneration ability of cartilage tissue. Additionally, the simultaneous regeneration of bone and cartilage is difficult to attain due to their dissimilar nature. Thus, fabricating a single scaffold for both bone and cartilage regeneration remains challenging. Biomaterials are frequently employed to promote tissue restoration, but they still cannot replicate the structure of native tissue. This study aims to create a single biomaterial that could be used to regenerate both bone and cartilage. This study focuses on synthesizing calcium-deficient apatite (CDA) with the gradual addition of manganese. The phase stability and the effect of heat treatment on manganese-doped CDA were studied using X-ray diffraction (XRD) and Rietveld refinement. The obtained powders were tested for their 3-dimensional (3D) printing ability by fabricating cuboidal 3D structures. The 3D printed scaffolds were examined for external topography using field-emission scanning electron microscopy (FE-SEM) and were subjected to compression testing. In vitro biocompatibility and differentiation studies were performed to access their biocompatibility and differentiation capabilities. Reverse transcription-quantitative PCR (RT-qPCR) analysis was done to determine the gene expression of bone- and cartilage-specific markers. Mn helps in stabilizing the β-TCP phase beyond its sintering temperature without being degraded to α-TCP. Mn addition in CDA improves the compressive strength of the fabricated scaffolds while keeping them biocompatible. The concentrations of Mn in the CDA ceramic were found to influence the differentiation behavior of MSCs in the fabricated scaffolds. Mn-doped CDA is a promising candidate to be used as a substitute material for bone, cartilage, and osteochondral defects to facilitate repair and regeneration via endochondral differentiation. 3D printing can assist in the fabrication of a multifunctional single-unit scaffold with varied Mn concentrations, which might be able to generate the two tissues in situ in an osteochondral defect.

Synthesis, Structural, and Mechanical Behavior of β-Ca3(PO4)2-ZrO2 Composites Induced by Elevated Thermal Treatments.

Biocompatible β-Ca3(PO4)2 and mechanically stable t-ZrO2 composites are currently being combined to overcome the demerits of the individual components. A series of five composites were synthesized using an aqueous precipitation technique. Their structural and mechanical stability was examined through X-ray diffraction, Rietveld refinement, FTIR, Raman spectroscopy, high-resolution scanning electron microscopy, and nanoindentation. The characterization results confirmed the formation of β-Ca3(PO4)2–t-ZrO2 composites at 1100 °C. Heat treatment above 900 °C resulted in the degradation of the composites because of cationic interdiffusion between Ca2+ ions and O−2 vacancy in Zr4+ ions. Sequential thermal treatments correspond to four different fractional phases: calcium-deficient apatite, β-Ca3(PO4)2, t-ZrO2, and m-ZrO2. The morphological features confirm in situ synthesis, which reveals abnormal grain growth with voids caused by the upsurge in ZrO2 content. The mechanical stability data indicate significant variation in Young’s modulus and hardness throughout the composite.

Bioactive CaTiO3 film prepared on the biomedical porous Ti–15Mo alloy by one-step hydrothermal treatment

The bioactive CaTiO 3 film was grown on the surface of the microwave sintered porous Ti–15Mo alloy by one-step hydrothermal process in supersaturated Ca(OH) 2 solution. The microstructures of the film and apatite-forming ability and cytocompatibility of the hydrothermally treated porous Ti–15Mo alloy were then investigated. The results show that the hydrothermally treated sample has a thickness of approximately 250 nm and is mainly composed of CaTiO 3 phase with some –OH groups except the α-Ti and β-Ti phases. The porous structure of the Ti–15Mo alloy has no significant change after hydrothermal treatment. When immersed in SBF solution, the hydroxyapatite preferentially nucleates and grows on the inner surface and the pore sites, forming a layer of the calcium-deficient apatite on the surface of the hydrothermally treated porous Ti–15Mo alloy finally. The hydrothermal treatment is demonstrated to facilitate the proliferation of MG-63 cells over the porous Ti–15Mo alloy surface ( p < 0.01), and promote the alloy from Grade 1 of non-toxic material to Grade 0.

Precipitation at Room Temperature as a Fast and Versatile Method for Calcium Phosphate/TiO2 Nanocomposites Synthesis.

The constantly growing need for advanced bone regeneration materials has motivated the development of calcium phosphates (CaPs) composites with a different metal or metal-oxide nanomaterials and their economical and environmentally friendly production. Here, two procedures for the synthesis of CaPs composites with TiO2 nanoplates (TiNPl) and nanowires (TiNWs) were tested, with the immersion of TiO2 nanomaterials (TiNMs) in corrected simulated body fluid (c-SBF) and precipitation of CaP in the presence of TiNMs. The materials obtained were analyzed by powder X-ray diffraction, spectroscopic and microscopic techniques, Brunauer–Emmett–Teller surface area analysis, thermogravimetric analysis, dynamic and electrophoretic light scattering, and their hemocompatibility and ability to induce reactive oxygen species were evaluated. After 28 days of immersion in c-SBF, no significant CaP coating was formed on TiNMs. However, the composites with calcium-deficient apatite (CaDHA) were obtained after one hour in the spontaneous precipitation system. In the absence of TiNMs, CaDHA was also formed, indicating that control of the CaP phase formed can be accomplished by fine-tuning conditions in the precipitation system. Although the morphology and size of crystalline domains of CaDHA obtained on the different nanomaterials differed, no significant difference was detected in their local structure. Composites showed low reactive oxygen species (ROS) production and did not induce hemolysis. The results obtained indicate that precipitation is a suitable and fast method for the preparation of CaPs/TiNMs nanocomposites which shows great potential for biomedical applications.

α-tricalcium phosphate synthesis from amorphous calcium phosphate: structural characterization and hydraulic reactivity

In the present study, amorphous tricalcium phosphate (TCP) has been synthetized by a wet route to obtain low temperature α-TCP at 650 °C (LT-αTCP) and compare its structural, physical–chemical and thermal properties with those of α-TCP obtained by the conventional solid-state reaction method at 1400 °C (HT-αTCP). Even if no significant differences were observed concerning the values of lattice parameters measured by Rietveld refinement, LT-αTCP presented lower crystallinity and higher crystal strains than HT-αTCP. The reactivity in water of the α-TCP obtained by the two different routes was assessed. Both raw samples appeared relatively inert in solution and did not favour the nucleation of calcium deficient apatite (CDA); the LT-αTCP and HT-αTCP were converted into apatite only after milling. The mechanical process leads to a decrease in crystallinity and the formation of an amorphous phase, which is supported in this work by Raman spectroscopy. The faster rate of conversion of milled LT-αTCP compared to HT-αTCP can be assigned to its higher specific surface area, lower crystallinity and higher residual crystal strain; these favour the dissolution of the α-TCP phase. Finally, the setting properties of α-TCP-based bone cements were compared regarding their synthesis route. Although the synthesis route does not significantly affect the setting times, the kinetic of conversion into CDA was faster for LT-αTCP than for HT-αTCP. Thus, the modulation of the dissolution rate of α-TCP-based cement determined by the preparation route and the grinding process allows control of the overall setting reaction.

Microstructure and mineral components of the outer dentin of Chimaera phantasma tooth plates.

Tooth plates are a unique dental organ found in holocephalan fishes and lungfish. The chimaeroid tooth plates are atypical in terms of biomineralization, due to the hard tissue composition of whitlockite and apatite, while those of lungfish and other vertebrates are composed of apatite. The tooth plates are overlaid by a thin veneer-outer dentin-whose composition and role are not known. We aimed to test whether the outer dentin is composed of whitlockite or apatite, and whether it protects the osteodentin from abrasion and supports its overall strength. For this purpose, the mineral components and microstructure of outer dentin were studied. Our analyses of the outer dentin from the anterior (vomerine) tooth plates of Chimaera phantasma revealed that the mineral component is magnesium- and carbonate-containing calcium-deficient apatite and that the outer dentin has a three-zone structure. The main body is sandwiched between thin zones, which are less mineralized than the main body. Furthermore, in the outer zone and the main body, a higher-order structure was formed in accordance with the organization of wide and narrow fibers. Mineralization made the main body a composite of bundles of fibers and apatite. Transmission electron microscopy showed a structural relationship between apatite and the fibrous component on which the apatite was formed. Such a structure of the main body could be highly effective as a framework to resist abrasion and support the overall strength of the tooth plate.

Influences of strontium on the phase composition and lattice structure of biphasic calcium phosphate

Hydroxyapatite (HAp) and β-tricalcium phosphate (β-TCP) are widely used in bone graft materials, because they have excellent biocompatibility. However, the degradation rates of HAp and β-TCP do not match the rate of osteogenesis, which limits their clinical applications. Therefore, forming biphasic calcium phosphate (BCP) is a promising method to control the biodegradation rate of the material. In addition, strontium (Sr) is an important element that promotes osteogenesis and inhibits bone absorption. Therefore, this study focused on the effects of Sr in the as-synthesized BCP with varied Sr concentrations of 1, 5, and 15 mol%, which are synthesized by chemical precipitation and a high-temperature calcination method. In this study, we assume that Sr is doped into Ca(5) of β-TCP and Ca(1) & Ca(2) of HAp during the Rietveld refinement. On the basis of the Rietveld refinement results obtained from X-ray diffraction (XRD) patterns, with increasing Sr concentration, the mass percentage of HAp decreases first, which is due to the distortion of the HAp structure, resulting in a decrease in HAp stability and phase variation from HAp to β-TCP. However, when the concentration of Sr reaches 15 mol%, the mass percentage of HAp increases, which may be because of the phase transformation from β-TCP to calcium-deficient apatite by the diffusion of Ca. In addition, the increase in the lattice constants and volumes indicates that Sr has been successfully doped into the crystal lattices of both β-TCP and HAp, since the ion radius of Sr2+ (0.113 nm) is larger than the ion radius of Ca2+ (0.099 nm). As shown in the X-ray photoelectron spectroscopy (XPS) results, the intensities of Sr3d and Sr3p increase with increasing Sr concentrations, which indicates that Sr is not only on the surface of the sample but also in the crystalline structures of both β-TCP and HAp.

Microstructure, degradation properties and cytocompatibility of micro-arc oxidation coatings on the microwave sintered Ti-15Mg metal-metal composite

The micro-arc oxidation (MAO) coatings were fabricated on the surface of the microwave sintered Ti-15Mg metal-metal composite (MMC). The surface morphologies, phase composition, degradation properties and cytocompatibility of the MAO treated Ti-15Mg MMC were investigated. The XRD and XPS results show that the MAO coatings are mainly composed of anatase and rutile TiO2 crystal phases and amorphous MgO and SiO2 with some –OH groups. There are some differences between MAO pore structure in Ti region and Mg region, but both of the pore sizes increase and the number of pores decreases with increasing the applied voltages. The degradation rate of Ti-15Mg MMC is reduced by the MAO coatings, and with increasing the applied voltages, the degradation rates of the MAO treated samples decrease first, reaching the minimum value at 300 V, and then increase. After immersed in SBF solution for 250 h, the calcium-deficient apatite containing CO32− is detected on the surface of the MAO treated and untreated Ti-15Mg MMC. The results of cell viability and alkaline phosphatase activity show that the MAO treated Ti-15Mg MMCs are more conducive to the proliferation and differentiation of MG-63 cells.

Deciphering the Relevance of Bone ECM Signaling.

Bone mineral density, a bone matrix parameter frequently used to predict fracture risk, is not the only one to affect bone fragility. Other factors, including the extracellular matrix (ECM) composition and microarchitecture, are of paramount relevance in this process. The bone ECM is a noncellular three-dimensional structure secreted by cells into the extracellular space, which comprises inorganic and organic compounds. The main inorganic components of the ECM are calcium-deficient apatite and trace elements, while the organic ECM consists of collagen type I and noncollagenous proteins. Bone ECM dynamically interacts with osteoblasts and osteoclasts to regulate the formation of new bone during regeneration. Thus, the composition and structure of inorganic and organic bone matrix may directly affect bone quality. Moreover, proteins that compose ECM, beyond their structural role have other crucial biological functions, thanks to their ability to bind multiple interacting partners like other ECM proteins, growth factors, signal receptors and adhesion molecules. Thus, ECM proteins provide a complex network of biochemical and physiological signals. Herein, we summarize different ECM factors that are essential to bone strength besides, discussing how these parameters are altered in pathological conditions related with bone fragility.

The Influence of Different Classes of Amino Acids on Calcium Phosphates Seeded Growth

Amino acids (AAs) attract attention for elucidating the role of proteins in biomineralization and the preparation of functionalized biomaterials. The influence that AAs exert on calcium phosphate (CaP) mineralization is still not completely understood, as contradictory results have been reported. In this paper, the influence of the addition of different classes of AAs, charged (L-aspartic acid, Asp; L-lysine, Lys), polar (L-asparagine, Asn; L-serine, Ser; L-tyrosine, Tyr), and non-polar (L-phenylalanine, Phe), on CaP growth in the presence of octacalcium phosphate (OCP) and calcium hydrogenphosphate dihydrate (DCPD) seeds was investigated. In control systems (without AAs), a calcium-deficient apatite (CaDHA) layer was formed on the surface of OCP, while a mixture of CaDHA and OCP in the form of spherical aggregates was formed on the surface of DCPD crystals. Charged and non-polar promoted, while polar AAs inhibited CaDHA formation on the OCP seeds. In the case of DCPD, Lys, Asp, and Phe promoted CaP formation, while the influence of other AAs was negligible. The most efficient promotor of precipitation in both cases was non-polar Phe. No significant influence of AAs on the composition and morphology of precipitates was observed. The obtained results are of interest for understanding biomineralization processes and additive controlled material synthesis.

XRD and FTIR Analysis of Magnesium Substituted Tricalcium Calcium Phosphate Using a Wet Precipitation Method

The incorporation of magnesium (Mg) in tricalcium phosphate (TCP) was prepared through a precipitation method followed by calcination at 850 °C in air. Calcium hydroxide, (Ca(OH)2), phosphoric acid, (H3PO4), and magnesium chloride (MgCl2.6H2O) with a Ca/P ratio of 1.5, were mixed as the precursor materials. The concentration of added Mg was varied with respect to calcium (Ca) precursor molarity as such Mg/(Ca +Mg) molar ratio was 0.05, 0.10, and 0.15, while the (Ca+Mg)/P ratio was maintained at 1.50 throughout the experiment. The influence of Mg-doped TCP on phase composition, chemical structure, and a functional group at different weight percentages were accomplished through X-ray diffraction (XRD), inductively coupled plasma optical emission spectroscopy (ICP-OES) and Fourier Transform Infrared Spectroscopy (FTIR) analyses. Based in the results of this research, the presence of magnesium led to the formation of Mg-doped calcium-deficient apatite (MgCDA) at 80°C and Mg-doped β-TCP at 850°C; the incorporation of Mg into the TCP phase causing an expansion of the lattice and increase in the lattice parameter. This result could be considered rather unusual.