Cranioplasty with hydroxylapatite ceramic plates that can easily be trimmed during surgery

Summary The author has designed new cranioplastic materials to reconstruct a skull defect of moderate size in both the convexity and the suboccipital region. A domed and elliptic plate measuring 50×75 mm in diameter, 12 mm in the maximum height and 5 mm in thickness was made from hydroxylapatite ceramics. The latter comprise Ca₁₀(PO₄)₆(OH)₂ as mammalian bone minerals and are characterized by an excellent biocompatibility and biostability resulting in bony fusion. Hydroxylapatite ceramic plates can be easily trimmed during surgery to closely fit the skull defect. There were no adverse reactions nor resorption of the implants.     

Influence of disodium (1-hydroxythylidene) diphosphonate on bonding between glass-ceramics containing apatite and wollastonite and mature male rabbit bone

Summary It has been reported that bioactive glass-ceramics containing crystalline oxy- and fluoroapatite [Ca₁₀(PO₄)₆(O,F₂) and wollastonite (CaSiO₃), chemical composition: MgO 4.6, CaO 44.9, SiO₂ 34.2, P₂O₅ 16.3, CaF₂ 0.5 in weight ratio] bond to bone tissue through the formation of an apatite (a calcium and phosphorus-rich layer) on the ceramic surface. In this study, the influence of disodium (1-hydroxythylidene) diphosphonate (DHTD) on the bonding between bone and glass-ceramics containing apatite and wollastonite was investigated. Rectangular ceramic plates (15 mm x 10 mm x 2 mm, abraded with #2000 alumina powder) were implanted into the tibial bone of mature male rabbits. DHTD was administered daily by subcutaneous injection to groups 1–5: group 1–4 at doses of 20, 5.0, 1.0, and 0.1 mg/kg body wt/day for 8 weeks; and group 5 at a dose of 5 mg/kg body wt/day for 4 weeks. Group 6 was given injections of saline as a control. At 8 weeks after implantation, the rabbits were killed. The tibiae containing the ceramics were dissected out and used for a detachment test. The failure load, when an implant became detached from the bone, or when the bone itself broke, was measured. The failure loads for groups 1–6 were 0 kg, 0 kg, 8.08±2.43 kg, 7.28±2.07 kg, 5.56±1.63 kg, and 6.38±1.30 kg, respectively. Ceramic bonding to bone tissue was inhibited by a higher dose of DHTD (groups 1 and 2). In groups 3–6, SEM-EPMA showed a calcium-phosphorus-rich layer (Ca-P-rich layer) at the interface between the ceramic and bone tissue. However, at higher doses (5 and 20 mg), the Ca-P-rich layer was not observed on the surface of the glass-ceramic. DHTD suppressed both the formation of the Ca-P-rich layer on the surface of galss-ceramics and also apatite formation by bone. Thus, bonding between the Ca-P-rich layer of glass-ceramics and the apatite of bone tissue did not occur. This study verified that the apatite crystals in bone tissue bonded chemically to the Ca-P-rich layer on the surface glass-ceramics. The organic matrix (osteoid) did not participate in the bonding between bone and glass-ceramics.     

Carbonate Assignment and Calibration in the Raman Spectrum of Apatite

A series of apatites with varying carbonate levels was prepared in order to assign the carbonate bands and calibrate for Raman analysis of natural materials. Overlap of carbonate bands with phosphate peaks was resolved by curve fitting. A peak at 1,071 cm⁻¹ was assigned to a combination of the carbonate ν₁ mode at 1,070 cm⁻¹ with a phosphate ν₃ mode at 1,076 cm⁻¹. In addition, the carbonate ν₄ mode was identified in apatite samples with >4% carbonate. The carbonate ν₄ bands at 715 and 689 cm⁻¹ identify the samples as B-type carbonated apatite. The carbonate content of apatite was calibrated to a carbonate Raman band, and the method was used to determine the carbonate content of a sample of bovine cortical bone, 7.7 ± 0.4%.     

Formation and structure of Ca-deficient hydroxyapatite

Summary When amorphous calcium phosphate (ACP) was transformed to crystalline hydroxyapatite (HA) in a series of aqueous slurry concentrations ranging from low to high, the higher slurry concentrations produced more Ca-deficient HA as measured by Ca/P ratio and heat-produced pyrophosphate. We feel that the excess solution phosphate produced in the higher slurry transformations results in lower Ca/P ratio HA. It has been suggested that an ACP is the precursor to bone apatite. Regulation of the in vivo ACP slurry concentration could then control the stoichiometry and, therefore, the metabolic activity of bone apatite. X-ray radial distribution function (RDF) analyses showed that CO ₃ ²⁻ substitution in HA creates far greater structural distortions than do Ca deficiencies. The latter, however, do produce small, but observable, structural distortions when compared to stoichiometric HA. It now seems clear that the RDF of bone apatite can be modeled by a synthetic, Ca-deficient, CO ₃ ²⁻ -containing HA.     

Formation of carbonate-apatite crystals after implantation of calcium phosphate ceramics

Summary The aims of this study were (1) to determine at the crystal level, the nonspecific biological fate of different types of calcium phosphate (Ca−P) ceramics after implantation in various sites (osseous and nonosseous) in animals and (2) to investigate the crystallographic association of newly formed apatitic crystals with the Ca−P ceramics. Noncommercial Ca−P ceramics identified by X-ray diffraction as calcium hydroxylapatite (HA), beta-tricalcium phosphate (β-TCP), and biphasic calcium phosphates (BCP) (consisting of β-TCP/HA=40/60) were implanted under the skin in connective tissue, in femoral lamellar cortical bone, articular spine bone, and cortical mandibular and mastoidal bones of animals (mice, rabbits, beagle dogs) for 3 weeks to 11 months. In humans, HA or β-TCP granules were used to fill periodontal pockets, and biposies of the implanted materials were recovered after 2 and 12 months. Results of this study demonstrated the following: (1) the presence of needle-like microcrystals (new crystals) associated with the Ca−P ceraiic macrocrystals in the microporous regions of the implants regardless of the sites of implantation (osseous or nonosseous), type of Ca−P ceramics (HA, β-TCP, BCP), type of species used (mice, rabbits, dogs, humans), or duration of implantation; (2) decrease in the area occupied by the ceramic crystals and the subsequent filling of the spaces between the ceramic crystals by the new crystals; (3) these new crystals were identified as apatite by electron diffraction and as carbonate-apatite by infrared absorption spectroscopy; (4) high resolution transmission electron microscopy (Hr TEM) revealed one family of apatite lattice fringes in the new crystals in continuity with the lattice planes of the HA of β-TCP ceramic crystals; (5) Hr TEM also demonstrated the presence of linear dislocations at the junction of the new apatite crystals and ceramic crystals. It is suggested that the formation of the CO₃ apatite crystals associated with the implanted Ca−P ceramic is due to dissolution/precipitation and secondary nucleation involving an epitatic growing process and not to an osteogenic property of the ceramic.     

A mechanism for incorporation of carbonate into apatite

Summary Octacalcium phosphate (Ca₈H₂(PO₄)₆·5H₂O) is considered to be a precursor in the formation of apatite in bones and teeth; a crucial step for incorporation of impurities appears to occur during its hydrolysis. The present study examines the role that octacalcium phosphate plays in the process of incorporation of carbonate into apatite. Chemical, X-ray diffraction, and infrared techniques were used. When octacalcium phosphate is hydrolyzed in the presence of sodium and carbonate ions in aqueous media, approximately one sodium and one carbonate ion seem to substitute for a calcium and phosphate ion, respectively, in forming apatite, and thea axis is shortened. The infrared spectrum of the product indicates that the carbonate is in the type B site, which is presumed to be a phosphate site. This mechanism is of particular importance since the presence of carbonate in human enamel appears to be related to caries susceptibility. A structural mechanism for the incorporation of impurities during hydrolysis of octacalcium phosphate is presented.     

Changes in heated and in laser-irradiated human tooth enamel and their probable effects on solubility

Summary Enamel of intact human teeth laser irradiatedin vitro under certain conditions is known to have less subsurface demineralization than unirradiated enamel on exposure to acid; consequently, the potential use of laser irradiance to reduce caries is apparent. The laser-induced physical and/or chemical changes that cause this reduced subsurface demineralization are not known. A laser-irradiated tooth enamel surface will have a temperature gradient that decreases towards the dentin junction. Dependent on irradiant conditions, the temperature may range from >1400°C at the surface to near normal at the dentin-pulp junction. Along this steep temperature gradient, different compositional, structural, and phase changes in the tooth enamel are to be expected. Identification of changes occurring along this gradient has bearing on understanding the dissolution reduction mechanism and, in turn, optimizing its effect. Changes in laser-irradiated material from the highest temperature region have been characterized, but those occurring in sequential layers of decreasing temperatures have not. Since the laser-induced changes are expected to primarily arise from localized heating, previously reported theramlly induced changes in tooth enamel on heating in conventional furnaces were utilized to infer corollary changes along the gradient in laser-irradiated tooth enamel. These thermally inferred changes which resulted in modifications in the tooth enamel apatite and/or newly formed phases were correlated with their probable effects on altering solubility. A temperature gradient range from 100–1600°C was considered with subdivisions as follows: I, 100–650°C; II, 650–1100°C; and III,>1100°C. Two of the products formed in range III, α-Ca₃(PO₄)₂ and Ca₄(PO₄)₂O, and also identified in the fused-melted material from laser-irradiated tooth enamel, are expected to markedly increase solubility in those regions that contain considerable amounts of these compounds. Products and changes occurring in range II, separate phases of α- and/or β-Ca₃(PO₄)₂, and a modified phase of apatite, may increase or decrease the solubility depending on the Ca/P ratio and the resultant amounts of α-, β-Ca₃(PO₄)₂ formed. Modifications in tooth enamel apatite effected in range I are expected to decrease its solubility; the formation of pyrophosphate in this range may have a substantial effect on reducing the solubility rate. It appears that laser-irradiant conditions that produce localized temperatures above about 650°C may have a deleterious effect on tooth enamel solubility unless calcium is introduced to increase the Ca/P ratio to near that of hydroxyapatite. Other important considerations of laser-irradiant treatment and interactions of tooth enamel, including enhanced uptake of fluoride, more effective irradiant wavelengths, selective reactions, directional absorption in crystals, and threshold irradiant conditions are briefly discussed and/or reviewed.     

Experimental data regarding macroporous biphasic calcium phosphate ceramics

Summary Macroporous biphasic calcium phosphate ceramics are biocompatible. Their physico-chemical structure is close to the mineral phase of the bone and provides bioactivity. Shortly after implantation in osseous area, dissolution appears with precipitation and formation of apatite crystals. Soon after osteoclastic resorption begins osteoconduction inside the macropores. Mechanical studies reveal a significant improvement in the mechanical properties due to the growth of the trabecular bone. Animal experiments in the spine have demonstrated bone penetration which allows a postero-lateral fusion. The rigidity of the fusion is equivalent to that obtained with bone graft. Macroporous biphasic calcium phosphate can be applied to fill bone defects and for postero-lateral spine fusion.     

Age-related changes in mineral of rat and bovine cortical bone

Summary The mineral of cortical bones has been studied in newborn, growing, and adult rats and in the calf and cow, using X-ray diffraction and infrared spectroscopy during the thermal decomposition of bones and by microassay of carbonate. The mineral of all the bone samples, regardless of species or age, was found to be a calcium-deficient apatite containing both CO₃ ²⁻ and HPO₄ ²⁻ ions in the crystal lattice. The crystal size, Ca/P molar ratio, and CO₃ ²⁻ ion content of cortical bone all increased with increasing age in both the rat and the bovine. The Ca/P ratio varied from 1.51 in newborn rats to 1.69 in adults but remained that of Ca-deficient apatite even though its value was close to that of stoichiometric hydroxyapatite (1.67). Both the carbonate ion and the hydrogenophosphate ion contents varied from one animal species to another and with age within a given species. Maturation was correlated with an increase in carbonate ion content, which replaced the HPO₄ ²⁻ ions. In contrast, the calcium ion number per unit formula did not vary during maturation. Cortical bone mineral, in both species, regardless of age, can therefore be represented by the following formula: Ca_8.3(PO₄)_4.3(CO₃)_x(HPO₄)_y(OH)_0.3; y decreased and x increased with increasing age, (x+y) being constant, equal to 1.7.     

Tissue compatibility of different intracranial implant materials: In-vivo and in-vitro studies

Summary Tissue compatibility of different intracranial implant materials was studied by a tissue culture method using fibroblasts. The same materials were implanted in the crania of rabbits for two months. Undecalcified sections of rabbit crania, including the materials, were stained with Fuchsin and Methylene Blue and Masson-Goldner methods. Soft X-ray was used to detect new bone formation. The materials used were alumina ceramics, hydroxy apatite ceramics, titanium, methylmethacrylate, Sugita aneurysm clip, silicon shunt tube and lyophilized human dura mater (Lyo-dura). Both alumina ceramics and hydroxy apatite ceramics showed an excellent tissue compatibility in-vivo experiments. Although alumina ceramics showed an excellent tissue compatibility in in-vitro experiments, hydroxy apatite ceramics showed less compatibility. Methylmethacrylate prepared one week before the experiment showed excellent compatibility, but the same material prepared at the time of experiment showed only fair compatibility. The titanium and silicon shunt tube showed excellent compatibility. The Sugita aneurysm clip, made from elgiloy, showed fair compatibility, while Lyo-dura showed excellent compatibility in in-vitro experiments, but less compatibility in in-vivo experiments. The reasons for the differences between the results of in-vivo and in-vitro experiments are discussed.     

Experimental study of apatite cement containing antibiotics

Long-term systemic administration of high concentrations of antibiotics may have adverse effects on local osmolality and on various organs; the potential for such effects provides a rationale for the direct administration of such drugs to local sites. The ideal material for this purpose should contain adequate amounts of antibiotics and be biocompatible, and be capable of filling bone defects. We used an implant material called apatite cement. Compounded with gentamyicin (GM) and poly-l-lactic acid (PLA), this material has excellent biocompatibility. In vitro and in vivo studies of this new compound (52 Japanese white house rabbits) showed that the release of antibiotic was gradual and that an effective drug concentration was maintained for 2 months. Histologic findings revealed new bone formation from 2 weeks after implantation. Thereafter, new bone formation sequentially increased in volume. Within 24 weeks, new bone was identified even inside cracked implants. The implant we developed was composed of bioactive material and delivered antibiotic at a level that exceeded the minimal inhibitory concentration ofStaphylococcus aureus. Our implant appears to stimulate satisfactory bone formation. An abstract of this paper was presented at the 9th International Symposium on Ceramics in Medicine and the 9th Basic Research Session of the Japanese Society of Orthopedic Surgery     

Utilising solid models for preoperative shaping of HAP-TCP ceramic bone substitute: application for craniomaxillofacial surgery

Summary Recently, the use of a three-dimensional solid model prepared by laser stereolithography have become widely used to simulate cranio-maxillofacial surgery. Moreover, development of high-strength apatite ceramics, composed of hydroxyapatite and tricalciumphosphate (HAP-TCP), has made it possible for us to preoperatively prepare a bone substitute material. A total of 27 models have been produced in 21 patients with craniofacial tumors, trauma, and congenital deformities who required preoperative simulation. In 12 of these cases, the HAP-TCP ceramic implant was made preoperatively, designing them directly on the models. Three representative cases are presented.     

Ultrastructural and Electron Diffraction of the Bone-Ceramic Interfacial Zone in Coral and Biphasic CaP Implants

We investigated the influence of natural coral implants used as a bone substitute on the quality of bone ingrowth in rabbits 2, 3, and 6 weeks after implantation. Explants were characterized by transmission electron microscopy and electron diffraction. Bone ingrowth has been previously demonstrated by light microscopy, however, few have been performed in electron microscopy to compare mineralized tissue ingrowth in coral implants which occurs at the expense of calcium carbonate to that of calcium phosphate (CaP) implants. The interface between coral aragonite and mineralized tissue or bone was abrupt, with no invasion of the aragonite structure by newly formed crystals, as occurs in micropores when biphasic CaP (BCP) ceramics were used. The restoring process appears to be different from that induced by BCP implants. Precipitation of needle-like apatite crystals on the CaCO₃ implant surface was not observed. Instead, apatitic smooth-shaped crystals formed in aggregates. The coral dissolution process does not release phosphate and so precipitation of apatite does not occur in the micropores of the coral implant, thereby limiting the formation of an apatite layer and hence bone bonding to the outer surface of the implant. In addition, on the outer surface of the implant, close to bone and a phosphorus source, the CaP crystals that do form are in aggregates presumably due to the carbonate and mismatch between the aragonite and the apatite. This seems to result in a delayed bone attachment or weaker bone bonding than CaP implants which encourage an epitaxial biological crystal deposition. Received: 21 July 1995 / Accepted: 7 August 1997     

MicroRaman Spectral Study of the PO4 and CO3 Vibrational Modes in Synthetic and Biological Apatites

The carbonate and phosphate vibrational modes of different synthetic and biological carbonated apatites were investigated by Raman microspectroscopy, and compared with those of hydroxyapatite. The ν₁ phosphate band at 960 cm⁻¹ shifts slightly due to carbonate substitution in both A and B sites. The spectrum of type A carbonated apatite exhibits two ν₁ PO₄ ³⁻ bands at 947 and 957 cm⁻¹. No significant change was observed in the ν₂ and ν₄ phosphate mode regions in any carbonated samples. The ν₃ PO₄ ³⁻ region seems to be more affected by carbonation: two main bands were observed, as in the hydroxyapatite spectrum, but at lower wave numbers. The phosphate spectra of all biominerals apatite were consistent with type AB carbonated apatite. In the enamel spectrum, bands were observed at 3513 and at 3573 cm⁻¹ presumably due to two different hydroxyl environments. Two different bands due to the carbonate ν₁ mode were identified depending on the carbonate substitution site A or B, at 1107 and 1070 cm⁻¹, respectively. Our results, compared with the infrared data already reported, suggest that even low levels of carbonate substitution induce modifications of the hydroxyapatite spectrum. Increasing substitution ratios, however, do not bring about any further alteration. The spectra of dentine and bone showed a strong similarity at a micrometric level. This study demonstrates the existence of acidic phosphate, observable by Raman microspectrometry, in mature biominerals. The HPO₄ ²⁻ and CO₃ ²⁻ contents increase from enamel to dentine and bone, however, these two phenomena do not seem to be correlated. Received: 5 January 1998 / Accepted: 12 May 1998     

Effect of carbonate content on the ESR spectrum near g=2 of carbonated calciumapatites synthesized from aqueous media

Summary The ESR spectrum of X-irradiated carbonated apatites synthesized at low temperature was studied as a function of their carbonate content. Using¹³C-enriched samples, four different carbonate-derived radicals and a surface O⁻ ion could be identified. Isotropic CO ₃ ⁻ and CO ₂ ⁻ ions are present at a B site in the apatite lattice, and anisotropic CO ₃ ⁻ and CO ₂ ⁻ radicals are located at the surface of the crystallites. Only the isotropic ESR signals increase with increasing carbonate content. The anisotropic signal ascribed to a surface CO ₂ ⁻ radical is mainly responsible for the so-called asymmetric ESR signal near g=2. It is argued that this surface signal may still be composite and caused by several very similar CO ₂ ⁻ ions. The consequences for phenomenological ESR studies of calcified tissues are discussed.     

Local delivery of zoledronate from a poly (d,l‐lactide)‐coating increases fixation of hydroxy‐coated implants

Initial secure implant fixation predicts long‐term survival. Bisphosphonates are anti‐resorptive agents. They have been shown to increase implant fixation. We investigated whether local delivery of zoledronate from a poly‐d ,l ‐lactide (PDLLA)‐coating could improve fixation and osseointegration of hydroxy‐apatite coated implants. Cylindrical hydroxy‐apatite coated implants were bilaterally inserted press‐fit into the proximal tibiae of 10 dogs. On one side the implant was coated with PDLLA containing zoledronate. The PDLLA coating was applied upon the hydroxy‐apatite coating. We used the contralateral implant as control. This implant was not coated with a poly‐d ,l ‐lactide. Observation period was 12 weeks. We evaluated implant fixation with histomorphometry and biomechanical push‐out test. Zoledronate resulted in an approximately threefold increase in all biomechanical parameters when comparing data with their respective controls. We found that zoledronate increased preservation of old lamellar bone and increased formation of new woven bone. This study indicates that local delivery of zoledronate from a PDDLA coating has the potential to increase implant fixation. Studies investigating different doses of zoledronate and longer follow‐up are needed. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:974–979, 2017.

     

Structural Water in Carbonated Hydroxylapatite and Fluorapatite: Confirmation by Solid State 2H NMR

Water is well recognized as an important component in bone, typically regarded as a constituent of collagen, a pore-filling fluid in bone, and an adsorbed species on the surface of bone crystallites. The possible siting and role of water within the structure of the apatite crystallites have not been fully explored. In our experiments, carbonated hydroxyl- and fluorapatites were prepared in D₂O and characterized by elemental analysis, thermal gravimetric analysis, powder X-ray diffraction, and infrared and Raman spectroscopy. Two hydroxylapatites and two fluorapatites, with widely different amounts of carbonate were analyzed by solid state ²H NMR spectroscopy using the quadrupole echo pulse sequence, and each spectrum showed one single line as well as a low-intensity powder pattern. The relaxation time of 7.1 ms for 5.9 wt% carbonated hydroxylapatite indicates that the single line is likely due to rapid, high-symmetry jumps in translationally rigid D₂O molecules, indicative of structural incorporation within the lattice. Discrimination between structurally incorporated and adsorbed water is enhanced by the rapid exchange of surface D₂O with atmospheric H₂O. Moreover, a ²H resonance was observed for samples dried under a variety of conditions, including in vacuo heating to 150°C. In contrast, a sample heated to 500°C produced no deuterium resonance, indicating that structural water had been released by that temperature. We propose that water is located in the c-axis channels. Because structural water is observed even for apatites with very low carbonate content, some of the water molecules must lie between the monovalent ions.     

Correction of Skull Defects Using Hydroxyapatite Cement (HAC) – Evidence Derived from Animal Experiments and Clinical Experience

Summary. Summary. Background: The development of satisfactory cranioplasty material and technique has been a continuing bio-engineering challenge. Cranial defects resulting from trauma, tumour or infection are most frequently reconstructed with nonviable alloplastic materials. At present, all synthetic or biological materials in the use for human cranioplasty are more or less ideal. Methods: The in vivo properties of a fully resorbable bony substitute – hydroxyapatite cement (HAC, BoneSource^?) are described in clinical investigations and animal experiments. HAC is prepared from calcium phosphate precursors which are hydrated and harden endothermically at 37 ^°C to form hydroxyapatite. Bone formation and resorption characteristics of HAC are examined in an adult minipig cranial defect model. Findings: Cranial bone integrity has been restored in ten of eleven patients. Radiographic examination 6 months after surgery reveal a successful reconstruction of the skull defects. Sections of the cranial defect site from animals sacrificed at 12, 18 and 40 weeks demonstrate that new bone formation proceeds in HAC filled osseous defects. Histomorphological evaluation of HAC resorption and new bone formation indicates that HAC is nearly completely resorbed within 40 weeks and replaced by new bone with no loss in size or volume. Interpretation: Hydroxyapatite cement (HAC) has an excellent biocompatibility (non-immunogenic and non-toxic), seems to be an optimal implant for cranial reconstruction and provides a biological scaffold for bone formation. However, further studies need to be conducted to determine the long-term stability of HAC.     

Crystallographic nature of fluoride in enameloids of fish

Summary X-ray diffraction studies on calcified tissues (teeth and/or scales) of fish and of shark showed that the presence of fluoride affects the crystallite size and lattice parameters of the apatite phase. An inverse correlation between F contents (ranging from 0.2 to 3.8 wt% F) anda-axis dimensions (9.441 to 9.375±0.003A) exists for both synthetic and enameloid apatites and is consistent with the F-for-OH substitution in the apatite, idealized as Ca₁₀(PO₄)₆(OH)₂ and Ca₁₀(PO₄)₆F₂, for fluoride-free and maximum fluoride-substituted apatite, respectively. In synthetic systems, the incorporation of F is found to be dependent on the F concentration of the media from which the apatite formed. This dependency is also observed between F content of the dentine apatites and the F concentration of the water from which the fish came (i.e., less than 0.08 ppmF in fresh water, about 1.3 ppm in seawater). However, no such dependency was observed between the F incorporation in fish enameloid apatite and the F concentration in the water of origin. In some cases, the F incorporated in the enameloid apatite is much in excess of what can be expected from the F concentration of water. These observations suggest that in some fish, a fluoride-concentrating mechanism is operative during the formation of the enameloid but not during the formation of the dentine, and this mechanism appears to be specie-related.     

Evidence of hydroxyl-ion deficiency in bone apatites: an inelastic neutron-scattering study

The novelty of very large neutron-scattering intensity from the nuclear-spin incoherence in hydrogen has permitted the determination of atomic motion of hydrogen in synthetic hydroxyapatite and in deproteinated isolated apatite crystals of bovine and rat bone without the interference of vibrational modes from other structural units. From an inelastic neutron-scattering experiment, we found no sharp excitations characteristic of the vibrational mode and stretch vibrations of OH ions around 80 and 450 meV (645 and 3630 cm⁻¹), respectively, in the isolated, deproteinated crystals of bone apatites; such salient features were clearly seen in micron- and nanometer-size crystals of pure hydroxyapatite powders. Thus, the data provide additional definitive evidence for the lack of OH⁻ ions in the crystals of bone apatite. Weak features at 160–180 and 376 meV, which are clearly observed in the apatite crystals of rat bone and possibly in adult mature bovine bone, but to a much lesser degree, but not in the synthetic hydroxyapatite, are assigned to the deformation and stretch modes of OH ions belonging to HPO₄-like species.