Enzymatic phosphatization of fish scales-a pathway for fish fossilization.

Phosphatized fish fossils occur in various locations worldwide. Although these fossils have been intensively studied over the past decades they remain a matter of ongoing research. The mechanism of the permineralization reaction itself remains still debated in the community. The mineralization in apatite of a whole fish requires a substantial amount of phosphate which is scarce in seawater, so the origin of the excess is unknown. Previous research has shown that alkaline phosphatase, a ubiquitous enzyme, can increase the phosphate content in vitro in a medium to the degree of saturation concerning apatite. We applied this principle to an experimental setup where fish scales were exposed to commercial bovine alkaline phosphatase. We analyzed the samples with SEM and TEM and found that apatite crystals had formed on the remaining soft tissue. A comparison of these newly formed apatite crystals with fish fossils from the Solnhofen and Santana fossil deposits showed striking similarities. Both are made up of almost identically sized and shaped nano-apatites. This suggests a common formation process: the spontaneous precipitation from an oversaturated solution. The excess activity of alkaline phosphatase could explain that effect. Therefore, our findings could provide insight into the formation of well-preserved fossils.

Injectable macroporous naturally-derived apatite bone cement as a potential trabecular bone substitute.

In this study, we have formulated a novel apatite bone cements derived from natural sources (i.e. eggshell and fishbone) with improved qualities that is, porosity, resorbability, biological activity, and so forth. The naturally-derived apatite bone cement (i.e. FBDEAp) was prepared by mixing hydroxyapatite (synthesized from fishbone) and tricalcium phosphate (synthesized from eggshell) as a solid phase with a liquid phase (a dilute acidic blend of cement binding accelerator and biopolymers like gelatin and chitosan) with polysorbate (as liquid porogen) to get a desired bone cement paste. The prepared cement paste sets within the clinically acceptable setting time (≤20 min), easily injectable (>85%) through hands and exhibits physiological pH stability (7.3-7.4). The pure apatite phased bone cement was confirmed by x-ray diffraction and Fourier transform infrared spectroscopy analyses. The FBDEAp bone cement possesses acceptable compressive strength (i.e. 5-7 MPa) within trabecular bone range and is resorbable up to 28% in simulated body fluid solution within 12 weeks of incubation at physiological conditions. The FBDEAp is macroporous in nature (average pore size ~50-400 µm) with interconnected pores verified by SEM and micro-CT analyses. The FBDEAp showed significantly increased MG63 cell viability (>125% after 72 h), cell adhesion, proliferation, and key osteogenic genes expression levels (up to 5-13 folds) compared to the synthetically derived, synthetic and eggshell derived as well as synthetic and fishbone derived bone cements. Thus, we strongly believe that our prepared FBDEAp bone cement can be used as potential trabecular bone substitute in orthopedics.

Fluoride-Incorporated Apatite Coating on Collagen Sponge as a Carrier for Basic Fibroblast Growth Factor.

Coating layers consisting of a crystalline apatite matrix with immobilized basic fibroblast growth factor (bFGF) can release bFGF, thereby enhancing bone regeneration depending on their bFGF content. We hypothesized that the incorporation of fluoride ions into apatite crystals would enable the tailored release of bFGF from the coating layer depending on the layer's fluoride content. In the present study, coating layers consisting of fluoride-incorporated apatite (FAp) crystals with immobilized bFGF were coated on a porous collagen sponge by a precursor-assisted biomimetic process using supersaturated calcium phosphate solutions with various fluoride concentrations. The fluoride content in the coating layer increased with the increasing fluoride concentration of the supersaturated solution. The increased fluoride content in the coating layer reduced its solubility and suppressed the burst release of bFGF from the coated sponge into a physiological salt solution. The bFGF release was caused by the partial dissolution of the coating layer and, thus, accompanied by the fluoride release. The concentrations of released bFGF and fluoride were controlled within the estimated effective ranges in enhancing bone regeneration. These findings provide useful design guidelines for the construction of a mineralized, bFGF-releasing collagen scaffold that would be beneficial for bone tissue engineering, although further in vitro and in vivo studies are warranted.

Towards bone regeneration: Understanding the nucleating ability of proline-rich peptides in biomineralisation.

Obtaining rapid mineralisation is a challenge in current bone graft materials, which has been attributed to the difficulty of guiding the biological processes towards osteogenesis. Amelogenin, a key protein in enamel formation, inspired the design of two intrinsically disordered peptides (P2 and P6) that enhance in vivo bone formation, but the process is not fully understood. In this study, we have elucidated the mechanism by which these peptides induce improved mineralisation. Our molecular dynamics analysis demonstrated that in an aqueous environment, P2 and P6 fold to interact with the surrounding Ca2+, PO43- and OH- ions, which can lead to apatite nucleation. Although P2 has a less stable backbone, it folds to a stable structure that allows for the nucleation of larger calcium phosphate aggregates than P6. These results were validated experimentally in a concentrated simulated body fluid solution, where the peptide solutions accelerated the mineralisation process compared to the control and yielded mineral structures mimicking the amorphous calcium phosphate crystals that can be found in lamella bone. A pH drop for the peptide groups suggests depletion of calcium and phosphate, a prerequisite for intrinsic osteoinduction, while S/TEM and SEM suggested that the peptide regulated the mineral nucleation into lamella flakes. Evidently, the peptides accelerate and guide mineral formation, elucidating the mechanism for how these peptides can improve the efficacy of P2 or P6 containing devices for bone regeneration. The work also demonstrates how experimental mineralisation study coupled with molecular dynamics is a valid method for understanding and predicting in vivo performance prior to animal trials.

Characterization, mechanical properties, corrosion behavior and bone-like apatite formation ability of fluorine substituted hydroxyapatite coating.

Hydroxyapatite (HA) is a non-bioceramic commonly used in human implants in the form of coatings, which are limited in their application by mechanical and wear resistance properties, as well as biodegradability. In this study, fluorine substituted hydroxyapatite (FHA) coatings were prepared on Ti-6Al-4V surfaces by plasma spraying method using a mixture of calcium fluoride and hydroxyapatite powders. The prepared coatings were characterized by X-ray diffraction and fourier transform infrared (FTIR) spectroscopy at different levels of calcium fluoride (3 wt%, 6 wt%, 9 wt%, and 12 wt%). The biocompatibility of the coatings was evaluated by in vitro mineralization experiments. Experimental results showed that at 9 wt% of calcium fluoride, the prepared FHA coatings had better mechanical properties, with improved bond strength (28.2 MPa). The X-ray diffraction patterns of the coatings reflect the fluorine substitution during the spraying process and the 9FHA has the highest crystallinity according to the XRD analysis, which is closely related to the biological activity of the coating. In addition, Potentiodynamic polarisation showed that the sample coated with the 9FHA coating had the highest Ecorr and lowest Icorr, indicating the best corrosion resistance. The FHA coating exhibits faster apatite deposition in simulated body fluid, and the efficiency of apatite deposition increases with the increase of CaF2.

Adaptive enhancement of apatite crystal orientation and Young's modulus under elevated load in rat ulnar cortical bone.

Functional adaptation refers to the active modification of bone structure according to the mechanical loads applied daily to maintain its mechanical integrity and adapt to the environment. Functional adaptation relates to bone mass, bone mineral density (BMD), and bone morphology (e.g., trabecular bone architecture). In this study, we discovered for the first time that another form of bone functional adaptation of a cortical bone involves a change in bone quality determined by the preferential orientation of apatite nano-crystallite, a key component of the bone. An in vivo rat ulnar axial loading model was adopted, to which a 3-15 N compressive load was applied, resulting in approximately 440-3200 µÉ› of compression in the bone surface. In the loaded ulnae, the degree of preferential apatite c-axis orientation along the ulnar long axis increased in a dose-dependent manner up to 13 N, whereas the increase in BMD was not dose-dependent. The Young's modulus along the same direction was enhanced as a function of the degree of apatite orientation. This finding indicates that bone has a mechanism that modifies the directionality (anisotropy) of its microstructure, strengthening itself specifically in the loaded direction. BMD, a scalar quantity, does not allow for load-direction-specific strengthening. Functional adaptation through changes in apatite orientation is an excellent strategy for bones to efficiently change their strength in response to external loading, which is mostly anisotropic.

Bone-like apatite formation in biocompatible phosphate-crosslinked bacterial cellulose-based hydrogels for bone tissue engineering applications.

Addressing major bone injuries is a challenge in bone regeneration, necessitating innovative 3D hydrogel-based therapeutic approaches to enhance scaffold properties for better bioactivity. Bacterial cellulose (BC) is an excellent scaffold for bone tissue engineering due to its biocompatibility, high porosity, substantial surface area, and remarkable mechanical strength. However, its practical application is limited due to a lack of inherent osteogenic activity and biomineralization ability. In this study, we synthesized bone-like apatite in biocompatible BC hydrogel by introducing phosphate groups. Hydrogels were prepared using fibrous BC, acrylamide (AM), and bis [2-methacryloyloxy] ethyl phosphate (BMEP) as a crosslinker through free radical polymerization (P-BC-PAM). P-BC-PAM hydrogels exhibited outstanding compressive mechanical properties, highly interconnected porous structures, good swelling, and biodegradable properties. BMEP content significantly influenced the physicochemical and biological properties of the hydrogels. Increasing BMEP content enhanced the fibrous structure, porosity from 85.1 % to 89.5 %, and compressive mechanical strength. The optimized hydrogel (2.0P-BC-PAM) displayed maximum compressive stress, toughness, and elastic modulus at 75 % strain: 221 ± 0.08 kPa, 24,674.2 ± 978 kPa, and 11 ± 0.47 kPa, respectively. P-BC-PAM hydrogels underwent biomineralization in simulated body fluid (SBF) for 14 days, forming bone-like apatite with a Ca/P ratio of 1.75, similar to hydroxyapatite. Confirmed by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and field-emission scanning electron microscopy (FE-SEM), this suggests their potential as scaffolds for bone tissue engineering. MC3T3-E1 osteoblast cells effectively attached and proliferated on P-BC-PAM. In summary, this study contributes insights into developing phosphate-functionalized BC-based hydrogels with potential applications in bone tissue engineering.

Effect of borate, fluoride and strontium ions on biomimetic nucleation of calcium phosphate studied using solid-state nuclear magnetic resonance and X-ray diffraction.

OBJECTIVES: Apatite minerals can have various anions and cations in their crystal structure in addition to phosphate ion (PO4³â») and calcium ion (Ca2+). The aim of this study is to investigate effects of the borate, fluoride and strontium ions on biomimetic nucleation of calcium phosphate. METHODS: Nano-crystalline hydroxyapatite (H-Ap) was obtained from a supersaturated buffered solution containing 4.12 mM HPO42- and 5.88 mM Ca2+ (H-Ap). Four additives were used in solid solution methods: (i) 0.588 mM F- (F-Ap), (ii) 5.88 mM Sr2+ (Sr-Ap), (iii) 4.12 mM BO33- (BO3-Ap), and (iv) a surface pre-reacted glass ionomer (S-PRG) filler eluate that contained 0.17 mM Sr2+, 0.588 mM F-, 11.1 mM BO33-- (SPRG-Ap). Apatite crystallization was investigated using a solid-state magic-angle spinning NMR spectroscopy and X-ray diffraction (XRD) with the Rietveld analysis. RESULTS: A 2D 1H-31P heteronuclear-correlation NMR showed F- ion incorporation in the apatite structure of the F-Ap and SPRG-Ap. The peaks on the 31P axis of the F-Ap, Sr-Ap, and BO3-Ap were different from that of the H-Ap, and the full width at half maximum increased in the following order: H-Ap∼F-Ap∼BO3-Ap< SPRG-Ap< Sr-Ap, suggesting the incorporation of the F-, Sr2+ and BO33-. The incorporation of F and BO3 was further confirmed by 19F and 11B NMR. The XRD revealed that Sr2+ was preferentially incorporated into the CaII site. SIGNIFICANCE: The F-, Sr2+ and BO33-ions might be involved in modifying the crystallization of apatite precipitation, producing a variety of apatite. S-PRG filler that release these ions may have an effect on remineralization, i.e., the reformation of apatite lost due to caries.

Mechanochemical synthesis of cerium chlorapatite from a mixture of cerium chloride heptahydrate, dicalcium phosphate dihydrate, and calcium hydroxide for biomedical application.

BACKGROUND: Cerium ions promote osteoclastogenesis and activate bone metabolism, while cerium oxide nanoparticles exhibit potent anti-inflammatory properties, making them promising for biomedical applications. OBJECTIVE: The purpose of this study was to develop and evaluate a synthesis method for sustained-release cerium-ion bioceramics containing apatite. Substituted apatite was found to be an effective biomaterial. METHODS: Cerium-containing chlorapatite was synthesized using a mechanochemical method employing dicalcium phosphate, cerium chloride heptahydrate, and calcium hydroxide as raw materials. The synthesized samples were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Raman spectroscopy. RESULTS: Cerium chlorapatite was successfully synthesized in the 10.1% and 20.1% samples. However, at Ce concentrations higher than 30.2%, the samples consisted of three or more phases, indicating the instability of a single phase. CONCLUSION: The method used in this study was found to be more efficient and cost-effective than the precipitation method for producing substituted apatite and calcium phosphate-based biomaterials. This research contributes to the development of sustained-release cerium-ion bioceramics with potential applications in the field of biomedicine.

One-Pot Synthesis of Bioinspired Peptide-Decorated Apatite Nanoparticles for Nanomedicine.

Hybrid organic-inorganic bio-inspired apatite nanoparticles (NPs) are attractive for biomedical applications and especially in nanomedicine. Unfortunately, their applications in nanomedicine are limited by their broad particle size distributions and uncontrolled drug loading due to their multistep synthesis process.  Besides, very few attempts at exposing bioactive peptides on apatite NPs are made. In this work, an original one-pot synthesis of well-defined bioactive hybrid NPs composed of a mineral core of bioinspired apatite surrounded by an organic corona of bioactive peptides is reported. Dual stabilizing-bioactive agents, phosphonated polyethylene glycol-peptide conjugates, are prepared and directly used during apatite precipitation i) to form the organic corona during apatite precipitation, driving the size and shape of resulting hybrid NPs with colloidal stabilization and ii) to expose peptide moieties (RGD or YIGSR sequences) at the NPs periphery in view of conferring additional surface properties to enhance their interaction with cells. Here, the success of this approach is demonstrated, the functionalized NPs are fully characterized by Fourier-transform infrared, Raman, X-ray diffraction, solid and liquid state NMR, transmission electron microscopy, and dynamic light scattering, and their interaction with fibroblast cells is followed, unveiling a synergistic proliferative effect.

Bone implant substitutes from synthetic polymer and reduced graphene oxide: Current perspective.

In the present work, bone implant materials (BIM) were produced, in sheet form which comprises epoxy resin (synthetic polymer) (ER), calcium carbonate (CaCO3), and reduced graphene oxide (R-GO), by open mold method, for the possibility uses in bone tissue engineering. The developed BIM was analyzed for its physico-chemical, mechanical, bioactivity test, antimicrobial study, and biocompatibility. The BIM had excellent mechanical properties such as tensile strength (194.44 + 0.21 MPa), flexural strength (278.76 + 0.41 MPa), and water absorption (02.61 + 0.24%). A pore size distribution study using the HR-SEM has proved the 180 and 255 µm average pore was observed in the BIM structure. The Bioactivity test of BIM was examined after being immersed in a simulated body fluids (SBF) solution. The result of BIM formed an excellent deposition of bone tube apatite crystals. High-resolution scanning electron microscopy (HR-SEM) morphology of the bone tube apatite crystals revealed the diameter size in the range from 100 ± 159 to 210 ± 188 nm. BIM has excellent antimicrobial characteristics against E. coli (8.75 + 0.06 mm) and S. aureus (9.82 + 0.08 mm). The biocompatibility of the study MTT (3-(4, 5-dimethyl) thiazol-2-yl-2, 5-dimethyl tetrazolium bromide) assay using the MG-63 (human osteoblast cell line) has proven to be the 78% viable cell presence in BIM. After receiving the necessary approval, the scaffold with the required strength and biocompatibility could be tested as a bone implant material in large animals.

Bioactive apatite-wollastonite glass ceramics coating on metallic titanium for biomedical applications: effect of boron.

Metallic titanium (Ti) implant surfaces need improvement for bioproperties and antibacterial behavior. For this purpose, a new boron-doped bioactive apatite-wollastonite (AW) coating was successfully developed on the Ti plate surface. The effects of boron addition on the microstructure, mechanical properties, and bioproperties of the AW coating were investigated. With the addition of boron (B), the AW coating morphology became less porous and compact. In terms of bio properties, the rate of apatite formation increased with the addition of B, and the cell viability rate increased from approximately 66-81%. B addition increased the elastic modulus of the AW coating from about 24-46 GPa and increased its hardness about 2.5 times. In addition, while no antibacterial activity was observed in the AW coating, the addition of boron slightly introduced antibacterial properties. The novel AW/B composite coating obtained is promising for Ti implant surfaces.

Contribution to Knowledge on Bioapatites: Does Mg Level Reflect the Organic Matter and Water Contents of Enamel?

The matter constituting the enamels of four types of organisms was studied. The variability of the ions was presented in molar units. It was proven that the changes in water contents of the enamel are significantly positively related to changes in Mg; inversely, there is also a strong connection with changes in Ca and P, the main components of bioapatite. The variability in the organic matter has the same strong and positive characteristics and is also coupled with changes in Mg contents. Amelogenins in organic matter, which synthesize enamel rods, likely have a role in adjusting the amount of Mg, thus establishing the amount of organic matter and water in the whole enamel; this adjustment occurs through an unknown mechanism. Ca, P, Mg, and Cl ions, as well as organic matter and water, participate in the main circulation cycle of bioapatites. The selection of variations in the composition of bioapatite occurs only along particular trajectories, where the energy of transformation linearly depends on the following factors: changes in the crystallographic d parameter; the increase in the volume, V, of the crystallographic cell; the momentum transfer, which is indirectly expressed by ΔsinΘ value. To our knowledge, these findings are novel in the literature. The obtained results indicate the different chemical and crystallographic affinities of the enamels of selected animals to the human ones. This is essential when animal bioapatites are transformed into dentistic or medical substitutes for the hard tissues. Moreover, the role of Mg is shown to control the amount of water in the apatite and in detecting organic matter in the enamels.

Crystalline Micro-Sized Carbonated Apatites: Chemical Anisotropy of the Crystallite Surfaces, Biocompatibility, Osteoconductivity, and Osteoinductive Effect Enhanced by Poly(ethylene phosphoric acid).

Carbonated hydroxyapatites (CAp) are very close to natural bone apatite in chemical composition and are regarded as a prospective bone mineral substitute for bone surgery and orthopedics. However, until now, the studies and applications of CAp were limited because of the amorphous nature of the synthetic CAp. In the present work, microsized highly crystalline carbonated apatites with uniform hexagonal (hCAp) or platelike (pCAp) morphology have been studied for the first time in vitro and in vivo, comparing against commercial hydroxyapatite (HAp) and ß-tricalcuim phosphate (ßTCP). In vitro experiments on dissolution of those calcium phosphate ceramics (CPCs) in acetate (pH 5.5) and Tris (pH 7.3) buffer solutions showed the following rank order of the dissolution rates: ßTCP > hCAp > pCAp > HAp. The higher dissolution rate of hCAp in comparison with pCAp is explained by chemical anisotropy of the crystallite surfaces, which was proven by SEM studies of the changes in the morphology of hCAp and pCAp crystallites during hydrolysis. A 5-week experiment on subcutaneous implantation of CPC species showed the following rank order of bioresorption rates: ßTCP > pCAp > hCAp > HAp. pCAp matrixes exhibited the highest biocompatibility, confirmed by histomorphological analysis. Three-month bone regeneration experiments involving a rat tibial defect model were conducted with 250-500 µm granules of pCAp and pCAp-PEPA [pCAp, pretreated with 2 wt % poly(ethylene phosphoric acid)]. Notably, pCAp-PEPA implants were resorbed at higher rates and induced the formation of more mature osseous tissue, a compact bone with Haversian systems.

Biomineralization of mantis shrimp dactyl club following molting: Apatite formation and brominated organic components.

The stomatopod Odontodactylus scyllarus uses weaponized club-like appendages to attack its prey. These clubs are made of apatite, chitin, amorphous calcium carbonate, and amorphous calcium phosphate organized in a highly hierarchical structure with multiple regions and layers. We follow the development of the biomineralized club as a function of time using clubs harvested at specific times since molting. The clubs are investigated using a broad suite of techniques to unravel the biomineralization history of the clubs. Nano focus synchrotron x-ray diffraction and x-ray fluorescence experiments reveal that the club structure is more organized with more sub-regions than previously thought. The recently discovered impact surface has crystallites in a different size and orientation than those in the impact region. The crystal unit cell parameters vary to a large degree across individual samples, which indicates a spatial variation in the degree of chemical substitution. Energy dispersive spectroscopy and Raman spectroscopy show that this variation cannot be explained by carbonation and fluoridation of the lattice alone. X-ray fluorescence and mass spectroscopy show that the impact surface is coated with a thin membrane rich in bromine that forms at very initial stages of club formation. Proteomic studies show that a fraction of the club mineralization protein-1 has brominated tyrosine suggesting that bromination of club proteins at the club surface is an integral component of the club design. Taken together, the data unravel the spatio-temporal changes in biomineral structure during club formation. STATEMENT OF SIGNIFICANCE: Mantis shrimp hunt using club-like appendages that contain apatite, chitin, amorphous calcium carbonate, and amorphous calcium phosphate ordered in a highly hierarchical structure. To understand the formation process of the club we analyze clubs harvested at specific times since molting thereby constructing a club formation map. By combining several methods ranging from position resolved synchrotron X-ray diffraction to proteomics, we reveal that clubs form from an organic membrane with brominated protein and that crystalline apatite phases are present from the very onset of club formation and grow in relative importance over time. This reveals a complex biomineralization process leading to these fascinating biomineralized tools.

Host bone microstructure for enhanced resistance to bacterial infections.

Postoperative bacterial infection is a serious complication of orthopedic surgery. Not only infections that develop in the first few weeks after surgery but also late infections that develop years after surgery are serious problems. However, the relationship between host bone and infection activation has not yet been explored. Here, we report a novel association between host bone collagen/apatite microstructure and bacterial infection. The bone-mimetic-oriented micro-organized matrix structure was obtained by prolonged controlled cell alignment using a grooved-structured biomedical titanium alloy. Surprisingly, we have discovered that highly aligned osteoblasts have a potent inhibitory effect on Escherichia coli adhesion. Additionally, the oriented collagen/apatite micro-organization of the bone matrix showed excellent antibacterial resistance against Escherichia coli. The proposed mechanism for realizing the antimicrobial activity of the micro-organized bone matrix is by the controlled secretion of the antimicrobial peptides, including ß-defensin 2 and ß-defensin 3, from the highly aligned osteoblasts. Our findings contribute to the development of anti-infective strategies for orthopedic surgeries. The recovery of the intrinsically ordered bone matrix organization provides superior antibacterial resistance after surgery.

Apatite-coated outer layer eggshell membrane: A novel osteoinductive biohybrid composite for guided bone/tissue regeneration.

Hybrid biomimetic materials aim to replicate the organic-inorganic constructs of mineralized tissues. During eggshell formation, the outer surface of the eggshell membrane (ESM) promotes calcium carbonate nucleation, while the inner one prevents mineralization toward the egg white and yolk. In the current study, the outer surface of the ESM acted as a heteronucleant in calcium phosphate precipitation by the vapor diffusion sitting drop method, while the inner one remained unmineralized. The aim was to fabricate a 2D biomaterial with dual functions, osteoinductive on one side and protective against cell invasion on the other side. The microstructural, physicochemical, morphological, and mechanical properties of the mineralized ESM were characterized by XRD, TGA, XPS, FTIR/Raman, HR-SEM, and mechanical testing techniques. The cytocompatibility and osteoinductive ability were assessed by biological assays of cell viability, proliferation, and osteogenic differentiation on human mesenchymal stromal cells (hMSCs). Results indicate that the outer surface of the ESM induces the heterogeneous precipitation of carbonate-apatite phase depicting biomimetic features. In addition, the apatite/ESM shows a much higher cytocompatibility than the pristine ESM and promotes the osteogenic differentiation of hMSCs more efficiently. Overall, the apatite/ESM composite exhibits compositional, crystalline, mechanical, and biological properties that resemble those of mineralized tissues, rendering it an approachable and novel material especially useful in guided tissue/bone regeneration.

Quantitative Description of Isomorphism in the Series of Simple Compounds.

The introduction of the notion of energy change resulting from the ion exchange in apatites leads to the question: how can some simple isomorphic series be described using the mentioned idea? We concentrated on the simple isomorphic series of compounds: apatite, bioapatite, calcite, aragonite, celestine, K-, Zn- and Cu-Tutton's salts. It was demonstrated in all the series, except Tutton's salts, that the change in energy and the change in the crystal cell volume are, in a simple way, dependent on the change in the ionic radii of the introduced ions. The linear relationships between the variations in energy and in the universal crystallographic dimension d were derived from the earlier equations and proven based on available data. In many cases, except the Tutton's salts, linear dependence was discovered between the change in energy and the sinus of universal angle Θ, corresponding to the change in momentum transfer. In the same cases, linear dependencies were observed between the energy changes and the changes in the volumes of crystallographic cells, and mutually between changes in the crystallographic cell volume V, crystallographic dimension d, and diffraction angle Θ.

Biogenic apatite in carbonate concretions with and without fossils investigated in situ by micro-Raman spectroscopy.

Micro-Raman spectra of concretions with and without fossils were measured in a nondestructive manner. The band position and full width at half maximum height (FWHM) of ν1-PO43- of apatite in the concretions were analyzed to investigate the origin of apatite. The analyzed concretions were derived from the Kita-ama Formation of the Izumi Group, Japan. The micro-Raman analysis showed that the apatites in the concretions were divided into two groups: Group W (wide FWHM group) and Group N (narrow FWHM group). The apatite belonging to Group W is suggested to be biogenic apatite originating from the soft body tissues of organisms because the Sr content is high and the FWHM is similar to that of apatite in bones and teeth of present-day animals. The other apatite belonging to Group N is considered affected by the diagenetic process because of its narrow FWHM and F substitution. These features of both groups were observed regardless of the presence of fossils or absence of fossils in the concretions. This Raman spectroscopic study suggests that the apatite at the time of concretion formation belonged to Group W but was changed to Group N by the substitution of F during the diagenesis process.