Structural and chemical characteristics and maturation of the calcium-phosphate crystals formed during the calcification of the organic matrix synthesized by chicken osteoblasts in cell culture

On the physicochemical properties, setting chemical reaction, and in vitro bioactivity of aragonite–chitosan composite cement as a bone substitute

A chitosan gel additive modulates the initial vaterite dissolution–recrystallisation in injectable aragonite-based composite cement and promotes its in vitro bioactivity.

S. N. SN, Lakshmipathy M, Sagadevan S, Mohammad F, Al-Lohedan HA, Paiman S, Oh WC. Nanoformulations of core–shell type hydroxyapatite-coated gum acacia with enhanced bioactivity and controlled drug delivery for biomedical applications

In this work, nanospherical hydroxyapatite (HAP) was prepared that has combined properties of controlled drug delivery, biocompatibility, and antibacterial activity to have applications in the biomedical sector.

Drug Leaching Properties of Vancomycin Loaded Mesoporous Hydroxyapatite as Bone Substitutes

Infections after bone reconstructive surgery become an authentic therapeutic and economic issue when it comes to a modern health care system. In general; infected bone defects are regarded as contraindications for bone grafting. Since the pathogens develop a biofilm on the inner surface of the bone; local delivery of antibiotics becomes more important. The present work focuses on the synthesis of Mesoporous Hydroxyapatite (MPHAP) loaded with drug Vancomycin (Van) and to investigate its loading and leaching ability in phosphate buffer solution (PBS), to be used for post-operative infections. The effect of pore size on MPHAP was analyzed using different fatty acids as organic modifiers. The impacts of various fatty acids chain length on the morphology and pore size were studied. A simple impregnation technique with optimized conditions ensured a high antibiotic loading (up to 0.476 + 0.0135 mg/mL), with a complete in vitro release obtained within 50 h.

Cellular Processes by Which Osteoblasts and Osteocytes Control Bone Mineral Deposition and Maturation Revealed by Stage-Specific EphrinB2 Knockdown

PURPOSE OF REVIEW

We outline the diverse processes contributing to bone mineralization and bone matrix maturation by describing two mouse models with bone strength defects caused by restricted deletion of the receptor tyrosine kinase ligand EphrinB2.

RECENT FINDINGS

Stage-specific EphrinB2 deletion differs in its effects on skeletal strength. Early-stage deletion in osteoblasts leads to osteoblast apoptosis, delayed initiation of mineralization, and increased bone flexibility. Deletion later in the lineage targeted to osteocytes leads to a brittle bone phenotype and increased osteocyte autophagy. In these latter mice, although mineralization is initiated normally, all processes involved in matrix maturation, including mineral accrual, carbonate substitution, and collagen compaction, progress more rapidly. Osteoblasts and osteocytes control the many processes involved in bone mineralization; defining the contributing signaling activities may lead to new ways to understand and treat human skeletal fragilities.

Intermittent parathyroid hormone 1-34 induces oxidation and deterioration of mineral and collagen quality in newly formed mandibular bone

Intermittent parathyroid hormone (PTH) administration is known to promote bone healing after surgical procedures. However, the mechanism and influence of PTH on the mineral and collagen quality of the jaw are not well understood. Most studies have focused on analyzing the bone density and microstructure of the mandible, and have insufficiently investigated its mineral and collagen quality. Oxidative stress activates osteoclasts, produces advanced glycation end products, and worsens mineral and collagen quality. We hypothesized that PTH induces oxidation and affects the mineral and collagen quality of newly formed mandibular bone. To test this, we examined the mineral and collagen quality of newly formed mandibular bone in rats administered PTH, and analyzed serum after intermittent PTH administration to examine the degree of oxidation. PTH administration reduced mineralization and worsened mineral and collagen quality in newly formed bone. In addition, total anti-oxidant capacity in serum was significantly decreased and the oxidative-INDEX was increased among PTH-treated compared to vehicle-treated rats, indicating serum oxidation. In conclusion, intermittent administration of PTH reduced mineral and collagen quality in newly formed mandibular bone. This effect may have been induced by oxidation.

Cisplatin-Loaded Graphene Oxide/Chitosan/Hydroxyapatite Composite as a Promising Tool for Osteosarcoma-Affected Bone Regeneration

Presently, tissue engineering approaches have been focused toward finding new potential scaffolds with osteoconductivity on bone-disease-affected cells. This work focused on the cisplatin (CDDP)-loaded graphene oxide (GO)/hydroxyapatite (HAP)/chitosan (CS) composite for enhancing the growth of osteoblast cells and prevent the development of osteosarcoma cells. The prepared composites were characterized for the confirmation of composite formation using Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction techniques. A flowerlike morphology was observed for the GO/HAP/CS-3/CDDP composite. UV-vis spectroscopy was used to observe the controlled release of CDDP from the GO/HAP/CS-3/CDDP composite, and 67.34% of CDDP was released from the composite over a time period of 10 days. The GO/HAP/CS-3/CDDP nanocomposites showed higher viability in comparison with GO/HAP/CS-3 on MG63 osteoblast-like cells and higher cytotoxicity against cancer cells (A549). The synthesized composite was found to show enhanced proliferative, adhesive, and osteoinductive effects on the alkaline phosphatase activity of osteoblast-like cells. Our results suggested that the CDDP-loaded GO/HAP/CS-3 nanocomposite has an immense prospective as a bone tissue replacement in the bone-cancer-affected tissues.

Cathepsin K inhibitor causes changes in crystallinity and crystal structure of newly-formed mandibular bone in rats

Cathepsin K inhibitors are new drugs with the potential for the treatment of osteoporosis because they sustain bony remodelling better than bone resorption inhibitors such as bisphosphonates. The treatment of osteoporosis with inhibitors of bony resorption is associated with osteonecrosis of the jaw, as the deterioration in bony quality that they induce is thought to be one of its causes. The quality of bone is delineated by structural and material characteristics (which include the degree and quality of mineralisation, and depends on the content of proteoglycan and the structural integrity of the bony collagen).^1,2 Animal and clinical studies have shown that cathepsin K inhibitors improve the mineral density and structural characteristics of bone, but their effect on the rest remains unknown. We therefore hypothesised that these inhibitors will affect the material characteristics of newly-formed mandibular bone. To verify our hypothesis, we used Raman microspectroscopy to examine such bone in rats that were given a cathepsin K inhibitor, and found unusual crystallinity and an increased substitution of carbonate (CO₃^2-) in its crystal structure.

Molecular alterations of newly formed mandibular bone caused by zoledronate

Bone quality is defined by structural and material characteristics. Most studies on the mandible have focused on the analysis of structural characteristics, with insufficient investigation of material characteristics. This study tested whether zoledronate affects the material characteristics of newly formed mandibular bone. Thirty-six female Wistar rats were assigned to three groups: sham-ovariectomized rats (SHAM, n=12), ovariectomized rats (OVX, n=12), and ovariectomized rats treated with zoledronate (ZOL, n=12). The left side of the mandibular ramus of all rats was drilled bicortically. Twenty-eight days after surgery, all surviving rats were euthanized and all mandibles were removed. Raman microspectroscopy was performed, and five spectra per specimen of newly formed mandibular bone were analysed. Compared with OVX rats, the mineral/matrix ratio in ZOL rats was significantly increased (5.43±1.88 vs. 7.86±2.05), while crystallinity (0.055±0.002 vs. 0.050±0.002), relative proteoglycan content (0.43±0.10 vs. 0.31±0.05), and collagen structural integrity (1.16±0.21 vs. 0.72±0.06) were significantly decreased. These changes in material characteristics may explain why rats that received zoledronate exhibited peculiar biological phenomena such as bisphosphonate-related osteonecrosis of the jaw.

MAPK signaling has stage-dependent osteogenic effects on human adipose-derived stem cells in vitro

OVERVIEW

The use of pro-osteogenic growth factors, such as BMP2, in human adipose-derived stem cell (ASC) osteogenesis is well described. Because these growth factors work via signal transduction pathways, such as the mitogen-activated protein kinase (MAPK) cascade, a study of the relationship between MAPK signaling and ASC osteogenesis was conducted.

MATERIALS AND METHODS

ERK, JNK, and p38MAPK activation were measured in ASCs osteo-induced using either dexamethasone or vitamin D3 and correlated with mineralization. Activation and mineralization were also measured without dexamethasone or using the glucocorticoid, cortisone. The expression of the MAPK phosphatase, MKP1, and its relationship to mineralization was also assessed. The effect of decreasing MAPK activation on mineralization through the use of exogenous inhibitors was examined along with siRNA-knockdown and adenoviral overexpression of ERK1/2. Finally, the effect of ERK1/2 overexpression on ASCs induced on PLGA scaffolds was assessed.

RESULTS

ASC mineralization in dexamethasone or vitamin D3-induced ASCs correlated with both increased ERK1/2 and JNK1/2 activation. ASCs induced without dexamethasone also mineralized, with JNK1/2 signaling possibly mediating this event. No link between cortisone induction and MAPK signaling could be ascertained. ASCs treated with ERK, JNK, or p38MAPK inhibitors showed decreased osteogenic gene expression and diminished mineralization. Mineralization levels were also affected by viruses designed to inhibit or augment ERK1/2 expression and activity. Finally, ASC mineralization appeared to be a balance between the MAPK kinase activity and MKP1.

CONCLUSIONS

It is likely that MAPK signaling plays a significant role in ASC osteogenesis, affecting differentiation in kinase- and stage-specific manners.

Correlations Between Bone Mechanical Properties and Bone Composition Parameters in Mouse Models of Dominant and Recessive Osteogenesis Imperfecta and the Response to Anti-TGF-β Treatment

Osteogenesis imperfecta (OI) is a group of genetic disorders characterized by brittle bones that are prone to fracture. Although previous studies in animal models investigated the mechanical properties and material composition of OI bone, little work has been conducted to statistically correlate these parameters to identify key compositional contributors to the impaired bone mechanical behaviors in OI. Further, although increased TGF-β signaling has been demonstrated as a contributing mechanism to the bone pathology in OI models, the relationship between mechanical properties and bone composition after anti-TGF-β treatment in OI has not been studied. Here, we performed follow-up analyses of femurs collected in an earlier study from OI mice with and without anti-TGF-β treatment from both recessive (Crtap^-/- ) and dominant (Col1a2^+/P.G610C ) OI mouse models and WT mice. Mechanical properties were determined using three-point bending tests and evaluated for statistical correlation with molecular composition in bone tissue assessed by Raman spectroscopy. Statistical regression analysis was conducted to determine significant compositional determinants of mechanical integrity. Interestingly, we found differences in the relationships between bone composition and mechanical properties and in the response to anti-TGF-β treatment. Femurs of both OI models exhibited increased brittleness, which was associated with reduced collagen content and carbonate substitution. In the Col1a2^+/P.G610C femurs, reduced hydroxyapatite crystallinity was also found to be associated with increased brittleness, and increased mineral-to-collagen ratio was correlated with increased ultimate strength, elastic modulus, and bone brittleness. In both models of OI, regression analysis demonstrated that collagen content was an important predictor of the increased brittleness. In summary, this work provides new insights into the relationships between bone composition and material properties in models of OI, identifies key bone compositional parameters that correlate with the impaired mechanical integrity of OI bone, and explores the effects of anti-TGF-β treatment on bone-quality parameters in these models. © 2016 American Society for Bone and Mineral Research.

Nanoanalytical Electron Microscopy Reveals a Sequential Mineralization Process Involving Carbonate-Containing Amorphous Precursors

A direct observation and an in-depth characterization of the steps by which bone mineral nucleates and grows in the extracellular matrix during the earliest stages of maturation, using relevant biomineralization models as they grow into mature bone mineral, is an important research goal. To better understand the process of bone mineralization in the extracellular matrix, we used nanoanalytical electron microscopy techniques to examine an in vitro model of bone formation. This study demonstrates the presence of three dominant CaP structures in the mineralizing osteoblast cultures: <80 nm dense granules with a low calcium to phosphate ratio (Ca/P) and crystalline domains; calcium phosphate needles emanating from a focus: "needle-like globules" (100-300 nm in diameter) and mature mineral, both with statistically higher Ca/P compared to that of the dense granules. Many of the submicron granules and globules were interspersed around fibrillar structures containing nitrogen, which are most likely the signature of the organic phase. With high spatial resolution electron energy loss spectroscopy (EELS) mapping, spatially resolved maps were acquired showing the distribution of carbonate within each mineral structure. The carbonate was located in the middle of the granules, which suggested the nucleation of the younger mineral starts with a carbonate-containing precursor and that this precursor may act as seed for growth into larger, submicron-sized, needle-like globules of hydroxyapatite with a different stoichiometry. Application of analytical electron microscopy has important implications in deciphering both how normal bone forms and in understanding pathological mineralization.

Comprehensive Review of Adipose Stem Cells and Their Implication in Distraction Osteogenesis and Bone Regeneration

Bone is one of the most dynamic tissues in the human body that can heal following injury without leaving a scar. However, in instances of extensive bone loss, this intrinsic capacity of bone to heal may not be sufficient and external intervention becomes necessary. Several techniques are available to address this problem, including autogenous bone grafts and allografts. However, all these techniques have their own limitations. An alternative method is the technique of distraction osteogenesis, where gradual and controlled distraction of two bony segments after osteotomy leads to induction of new bone formation. Although distraction osteogenesis usually gives satisfactory results, its major limitation is the prolonged duration of time required before the external fixator is removed, which may lead to numerous complications. Numerous methods to accelerate bone formation in the context of distraction osteogenesis have been reported. A viable alternative to autogenous bone grafts for a source of osteogenic cells is mesenchymal stem cells from bone marrow. However, there are certain problems with bone marrow aspirate. Hence, scientists have investigated other sources for mesenchymal stem cells, specifically adipose tissue, which has been shown to be an excellent source of mesenchymal stem cells. In this paper, the potential use of adipose stem cells to stimulate bone formation is discussed.

Extracellular matrix mineralization in murine MC3T3-E1 osteoblast cultures: an ultrastructural, compositional and comparative analysis with mouse bone

Bone cell culture systems are essential tools for the study of the molecular mechanisms regulating extracellular matrix mineralization. MC3T3-E1 osteoblast cell cultures are the most commonly used in vitro model of bone matrix mineralization. Despite the widespread use of this cell line to study biomineralization, there is as yet no systematic characterization of the mineral phase produced in these cultures. Here we provide a comprehensive, multi-technique biophysical characterization of this cell culture mineral and extracellular matrix, and compare it to mouse bone and synthetic apatite mineral standards, to determine the suitability of MC3T3-E1 cultures for biomineralization studies. Elemental compositional analysis by energy-dispersive X-ray spectroscopy (EDS) showed calcium and phosphorus, and trace amounts of sodium and magnesium, in both biological samples. X-ray diffraction (XRD) on resin-embedded intact cultures demonstrated that similar to 1-month-old mouse bone, apatite crystals grew with preferential orientations along the (100), (101) and (111) mineral planes indicative of guided biogenic growth as opposed to dystrophic calcification. XRD of crystals isolated from the cultures revealed that the mineral phase was poorly crystalline hydroxyapatite with 10 to 20nm-sized nanocrystallites. Consistent with the XRD observations, electron diffraction patterns indicated that culture mineral had low crystallinity typical of biological apatites. Fourier-transform infrared spectroscopy (FTIR) confirmed apatitic carbonate and phosphate within the biological samples. With all techniques utilized, cell culture mineral and mouse bone mineral were remarkably similar. Scanning (SEM) and transmission (TEM) electron microscopy showed that the cultures had a dense fibrillar collagen matrix with small, 100nm-sized, collagen fibril-associated mineralization foci which coalesced to form larger mineral aggregates, and where mineralized sites showed the accumulation of the mineral-binding protein osteopontin. Light microscopy, confocal microscopy and three-dimensional reconstructions showed that some cells had dendritic processes and became embedded within the mineral in an osteocyte-like manner. In conclusion, we have documented characteristics of the mineral and matrix phases of MC3T3-E1 osteoblast cultures, and have determined that the structural and compositional properties of the mineral are highly similar to that of mouse bone.

Nanostructural materials increase mineralization in bone cells and affect gene expression through miRNA regulation

We report that several nanomaterials induced enhanced mineralization (increased numbers and larger areas of mineral nests) in MC3T3-E1 bone cells, with the highest response being induced by silver nanoparticles (AgNPs). We demonstrate that AgNPs altered microRNA expression resulting in specific gene expression associated with bone formation. We suggest that the identified essential transcriptional factors and bone morphogenetic proteins play an important role in activation of the process of mineralization in bone cells exposed to AgNPs.

Solid-State P and H NMR Investigations of Amorphous and Crystalline Calcium Phosphates Grown Biomimetically From a Mesoporous Bioactive Glass

By exploiting (1)H and (31)P magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy, we explore the proton and orthophosphate environments in biomimetic amorphous calcium phosphate (ACP) and hydroxy-apatite (HA), as grown in vitro at the surface of a 10CaO-85SiO(2)-5P(2)O(5) mesoporous bioactive glass (MBG) in either a simulated body fluid or buffered water. Transmission electron microscopy confirmed the presence of a calcium phosphate layer comprising nanocrystalline HA. Two-dimensional (1)H-(31)P heteronuclear correlation NMR established predominantly (1)H(2)O↔(31)PO(4) (3-) and O(1)H↔(31)PO(4) (3-) contacts in the amorphous and crystalline component, respectively, of the MBG surface-layer; these two pairs exhibit distinctly different (1)H→(31)P cross-polarization dynamics, revealing a twice as large squared effective (1)H-(31)P dipolar coupling constant in ACP compared with HA. These respective observations are mirrored in synthetic (well-crystalline) HA, and the amorphous calcium orthophosphate (CaP) clusters that are present in the pristine MBG pore walls: besides highlighting very similar local (1)H and (31)P environments in synthetic and biomimetic HA, our findings evidence closely related NMR characteristics, and thereby similar local structures, of the CaP clusters in the pristine MBG relative to biomimetic ACP.

Biomineralization of a self-assembled extracellular matrix for bone tissue engineering

Understanding how biomineralization occurs in the extracellular matrix (ECM) of bone cells is crucial to the understanding of bone formation and the development of a successfully engineered bone tissue scaffold. It is still unclear how ECM mechanical properties affect protein-mineral interactions in early stages of bone mineralization. We investigated the longitudinal mineralization properties of MC3T3-E1 cells and the elastic modulus of their ECM using shear modulation force microscopy, synchrotron grazing incidence X-ray diffraction (GIXD), scanning electron microscopy, energy dispersive X-ray spectroscopy, and confocal laser scanning microscopy (CLSM). The elastic modulus of the ECM fibers underwent significant changes for the mineralizing cells, which were not observed in the nonmineralizing cells. On substrates conducive to ECM network production, the elastic modulus of mineralizing cells increased at time points corresponding to mineral production, whereas that of the nonmineralizing cells did not vary over time. The presence of hydroxyapatite in mineralizing cells and the absence thereof in the nonmineralizing ones were confirmed by GIXD, and CLSM showed that a restructuring of actin occurred only for mineral-producing cells. These results show that the correct and complete development of the ECM network is required for osteoblasts to mineralize. This in turn requires a suitably prepared synthetic substrate for bone development to succeed in vitro.

Lateral packing of mineral crystals in bone collagen fibrils

Combined small-angle x-ray scattering and transmission electron microscopy studies of intramuscular fish bone (shad and herring) indicate that the lateral packing of nanoscale calcium-phosphate crystals in collagen fibrils can be represented by irregular stacks of platelet-shaped crystals, intercalated with organic layers of collagen molecules. The scattering intensity distribution in this system can be described by a modified Zernike-Prins model, taking preferred orientation effects into account. Using the model, the diffuse fan-shaped small-angle x-ray scattering intensity profile, dominating the equatorial region of the scattering pattern, could be quantitatively analyzed as a function of the degree of mineralization. The mineral platelets were found to be very thin (1.5 nm approximately 2.0 nm), having a narrow thickness distribution. The thickness of the organic layers between adjacent mineral platelets within a stack is more broadly distributed with the average value varying from 6 nm to 10 nm, depending on the extent of mineralization. The two-dimensional analytical scheme also leads to quantitative information about the preferred orientation of mineral stacks and the average height of crystals along the crystallographic c axis.

The associations between mineral crystallinity and the mechanical properties of human cortical bone

It is well known that the amount of mineralization renders bone its stiffness. However, besides the mere amount of the mineral phase, size and shape of carbonated apatite crystals are postulated to affect the mechanical properties of bone tissue as predicted by composite mechanics models. Despite this predictive evidence, there is little experimental insight on the relation between the characteristics of mineral crystals and hard tissue mechanics. In this study, Raman spectroscopy was used to provide information on the crystallinity of bone's mineral phase, a parameter which is an overall indicator of mineral crystal size and stoichiometric perfection. Raman scans and mechanical tests (monotonic and fatigue; n=64 each) were performed on the anterior, medial, lateral and posterior quadrant sections of 16 human cadaveric femurs (52 y.o.-85 y.o.). The reported coefficient of determination values (R(2)) were adjusted for the effects of age to bring out the unbiased contribution of crystallinity. Crystallinity was able to explain 6.7% to 48.3% of the variation in monotonic mechanical properties. Results indicated that the tissue-level strength and stiffness increased with increasing crystallinity while the ductility reduced. Crystallinity explained 11.3% to 63.5% of the variation in fatigue properties. Moduli of specimens with greater crystallinity degraded at a slower rate and, also, they had longer fatigue lives. However, not every anatomical quadrant displayed these relationships. In conclusion, these results acknowledge crystal properties as an important bone quality factor and raise the possibility that aberrations in these properties may contribute to senile osteoporotic fractures.

The compositional and physicochemical homogeneity of male femoral cortex increases after the sixth decade

The temporal and spatial fluctuations in the dynamics of secondary osteonal remodeling impart heterogeneity to the compositional quality of bone. Bone mineral density (BMD) fails to reflect this heterogeneity as being a single score, and thus it cannot resolve the overlap between healthy individuals and those who experience fractures. Such information on tissue heterogeneity is lacking in the literature. In the current study, specimens were prepared from mid-diaphyseal portions of human femora (N=16, age range 52-85 years old) and grouped based on the anatomical location (anterior, lateral, medial and posterior quadrants). Raman microscopy was used to obtain multiple measurements from each specimen which allowed the construction of histograms of mineralization, crystallinity and carbonation. The coefficient of variation (COV) and skewness were extracted from histograms as measures of heterogeneity. Results demonstrated that average mineralization of the medial quadrant and the data pooled over quadrants significantly increased with age. The mean carbonation increased within the observed age range for the pooled data. The variations of values about the mean became tighter for mineralization, crystallinity and type-B carbonation with age, indicating an overall reduction in compositional heterogeneity of aging femoral cortex. Skewness values indicated that the distributions of histograms were not Gaussian. We conclude that age-related changes in mean tissue composition are confounded with changes in the variation of tissue make-up about the mean. Future studies will establish as to whether compositional heterogeneity correlates with the mechanical strength of bone.

Raman spectroscopic evidence for octacalcium phosphate and other transient mineral species deposited during intramembranous mineralization

To understand early mineralization events, we studied living murine calvarial tissue by Raman spectroscopy using fibroblast growth factor 2 (FGF2)-soaked porous beads. We detected increased levels of a transient phase resembling octacalcium phosphate in sutures undergoing premature suture closure.

INTRODUCTION

Several calcium phosphates have been postulated as the earliest inorganic precursors to bone mineral. They are unstable and have not been previously detected in tissue specimens. Whether the same intermediates are formed in sutures undergoing premature closure is also unknown.

METHODS

Six coronal suture tissue specimens from fetal day 18.5 B6CBA F1/J wild-type mice were studied. Three sutures specimens were treated with FGF2-soaked heparin acrylic beads to induce accelerated mineralization and premature suture closure. Three control specimens were treated with empty heparin acrylic beads. All sutures were maintained as organ cultures to permit repeated spectral analyses at 12-24 h intervals over a 72-h period.

RESULTS

During the first 24 h, the spectra contained bands of octacalcium phosphate (OCP) or an OCP-like mineral. The main phosphorus-oxygen stretch was at 955 cm(-1), instead of the 957-959 cm(-1) seen in bone mineral, and there was an additional band at 1010-1014 cm(-1), as expected for OCP. A broad band was found at 945 cm(-1), characteristic of a highly disordered or amorphous calcium phosphate. An increased amount of mineral was observed in FGF2-treated sutures, but no qualitative differences in Raman spectra were observed between experimental and control specimens.

CONCLUSIONS

Inorganic mineral deposition proceeds through transient intermediates, including an OCP-like phase. Although this transient phase has been observed in purely inorganic model systems, this study is the first to report OCP or an OCP-like intermediate in living tissue. Raman microspectroscopy allows observation of this transient mineral and may allow observation of other precursors as well.

Chemical makeup of microdamaged bone differs from undamaged bone

Microdamage naturally occurs in bone tissue as a result of cyclic loading placed on the body from normal daily activities. While it is usually repaired through the bone turnover process, accumulation of microdamage may result in reduced bone quality and increased fracture risk. It is unclear whether certain areas of bone are more susceptible to microdamage than others due to compositional differences. This study examines whether areas of microdamaged bone are chemically different than undamaged areas of bone. Bone samples (L3 vertebrae) were harvested from 15 dogs. Samples were stained with basic fuchsin, embedded in poly-methylmethacrylate, and cut into 5-microm-thick sections. Fuchsin staining was used to identify regions of microdamage, and synchrotron infrared microspectroscopic imaging was used to determine the local bone composition. Results showed that microdamaged areas of bone were chemically different than the surrounding undamaged areas. Specifically, the mineral stoichiometry was altered in microdamaged bone, where the carbonate/protein ratio and carbonate/phosphate ratio were significantly lower in areas of microdamage, and the acid phosphate content was higher. No differences were observed in tissue mineralization (phosphate/protein ratio) or crystallinity between the microdamaged and undamaged bone, indicating that the microdamaged regions of bone were not over-mineralized. The collagen cross-linking structure was also significantly different in microdamaged areas of bone, consistent with ruptured cross-links and reduced fracture resistance. All differences in composition had well-defined boundaries in the microcrack region, strongly suggesting that they occurred after microcrack formation. Even so, because microdamage results in an altered bone composition, an accumulation of microdamage might result in a long-term reduction in bone quality.

Enhanced expression of the inorganic phosphate transporter Pit-1 is involved in BMP-2-induced matrix mineralization in osteoblast-like cells

Pi handling by osteogenic cells is important for bone mineralization. The role of Pi transport in BMP-2-induced matrix calcification was studied. BMP-2 enhances Pit-1 Pi transporters in osteogenic cells. Experimental analysis suggest that this response is required for bone matrix calcification.

INTRODUCTION

Bone morphogenetic proteins (BMPs) are produced by osteogenic cells and play an important role in bone formation. Inorganic phosphate (Pi) is a fundamental constituent of hydroxyapatite, and its transport by osteogenic cells is an important function for primary calcification of the bone matrix. In this study, we investigated the role of Pi transport in BMP-2-induced matrix mineralization.

MATERIALS AND METHODS

Confluent MC3T3-E1 osteoblast-like cells were exposed to BMP-2 for various time periods. Pi and alanine transport was determined using radiolabeled substrate, Pit-1 and Pit-2 expression by Northern blot analysis, cell differentiation by alkaline phosphatase activity, matrix mineralization by alizarin red staining, and the characteristics of mineral deposited in the matrix by transmission electron microscopy, electron diffraction analysis, and Fourier transformed infrared resolution (FTIR).

RESULTS

BMP-2 time- and dose-dependently stimulated Na-dependent Pi transport in MC3T3-E1 cells by increasing the V(max) of the transport system. This effect was preceded by an increase in mRNA encoding Pit-1 but not Pit-2. BMP-2 also dose-dependently enhanced extracellular matrix mineralization, an effect blunted by either phosphonoformic acid or expression of antisense Pit-1. Enhanced Pi transport and matrix mineralization induced by BMP-2 were blunted by a specific inhibitor of the c-Jun-N-terminal kinase (JNK) pathway.

CONCLUSIONS

Results presented in this study indicate that, in addition to its well-known effect on several markers of the differentiation of osteoblastic cells, BMP-2 also stimulates Pi transport activity through a selective increase in expression of type III Pi transporters Pit-1. In MC3T3-E1 cells, this effect is mediated by the JNK pathway and plays an essential role in bone matrix calcification induced by BMP-2.

Mineralization of decalcified bone occurs under cell culture conditions and requires bovine serum but not cells

The purpose of this study was to develop an in vitro model system for bone matrix mineralization in the absence of cells. For this model, we utilized EDTA-decalcified new-born rat tibias with the cartilaginous ends intact, allowing us to visually determine the specificity of mineralization within the bone. Our results show that supplementation of DMEM culture medium with 10mM beta-glycerophosphate and 15% fetal bovine serum (FBS) results in non-physiological mineral percipitation in the tibia because of the generation of supraphysiological (5mM) levels of inorganic phosphate in the medium. The same medium supplemented only with inorganic phosphate to a final concentration of 2mM failed to mineralize a decalcified tibia matrix. However, additional supplementation of this medium with as little as 5% FBS resulted in mineralization of those regions of the type I collagen where mineral was found prior to decalcification, with no evidence for mineralization in the cartilage at the bone ends or in the periosteum. Analysis of the mineral by Fourier-transform infrared spectroscopy and powder X-ray diffraction shows that tibias that have been decalcified and then remineralized contain an apatitic mineral that is strikingly similar to the mineral in normal bone. Tendon, a type I collagen matrix not normally mineralized in vivo, also mineralizes when incubated in DMEM containing 2mM Pi and as little as 1.5% FBS, but not when incubated in DMEM without serum. These data indicate that serum contains a nucleator of type I collagen matrix mineralization, and that mineralization of type I collagen under cell culture conditions requires serum but not living cells.

Strategies for directing the differentiation of stem cells into the osteogenic lineage in vitro

A major area in regenerative medicine is the application of stem cells in bone reconstruction and bone tissue engineering. This will require well-defined and efficient protocols for directing the differentiation of stem cells into the osteogenic lineage, followed by their selective purification and proliferation in vitro. The development of such protocols would reduce the likelihood of spontaneous differentiation of stem cells into divergent lineages on transplantation, as well as reduce the risk of teratoma formation in the case of embryonic stem cells. Additionally, such protocols could provide useful in vitro models for studying osteogenesis and bone development, and facilitate the genetic manipulation of stem cells for therapeutic applications. The development of pharmokinetic and cytotoxicity/genotoxicity screening tests for bone-related biomaterials and drugs could also use protocols developed for the osteogenic differentiation of stem cells. This review critically examines the various strategies that could be used to direct the differentiation of stem cells into the osteogenic lineage in vitro.

Osteoblastic cell response to thin film of poorly crystalline calcium phosphate apatite formed at low temperatures

The response of osteoblastic cells to a thin film of poorly crystalline calcium phosphate apatite crystals (PCA) was examined in vitro. The PCA thin film was prepared on polystyrene culture dishes using highly metastable calcium phosphate ion solution at low temperatures. The PCA thin film was formed through fusion and transformation of granular calcium phosphate particles, which had initially formed on the surface, into a film of calcium phosphate apatite crystal. The PCA thin film was used for cell culture without additional surface treatment. The osteoblastic cell behaviors including adhesion, proliferation, expression of the marker genes, and calcified matrix formation were examined on the PCA thin film using primary osteoblasts or MC3T3-E1 cells. The cells were well attached and had spread in a slender shape over the PCA thin film. The extent of cell proliferation on the PCA thin film is as much as on the plain dishes. In addition, a much larger number of calcified nodules had formed on the PCA thin film than on the plain dish. The expression of the marker genes such as alkaline phosphatase, osteocalcin, osteopontin, osteonectin was apparent. These results demonstrate that the osteoblasts exhibit a full spectrum of cellular activity including the adequate differentiation on the PCA thin film. Therefore, a PCA thin film can be used as a coating material for biomaterials where the surface is not adequate for inducing the full activity of bone cells.

Compression-induced changes on physical structures and calcification of the aromatic polyether polyurethane composite

It is generally accepted that stress causes calcification in both bio-prosthetic and polyurethane heart valves. However, simple uni-axially- and bi-axially-stretched samples did not yield a feasible model for the elaboration of the stress-induced calcification. In this study, heat compaction combined with the incorporation of polyethylene has been explored. Specimens of polyurethane were solution cast onto a porous bi-axially-drawn ultra-high-molecular-weight polyethylene film and then heat compacted under a pressure of 18 MPa at a chosen temperature for 1.5 h. The heat-compaction-induced calcification and physical changes of the polyurethane composite were evaluated using a 28-day in vitro calcification model and Attenuated Total Reflection-Fourier Transform-Infrared (ATR-FT-IR) spectroscopy. The calcification results indicated that heat-compaction-induced calcification was double that achieved without heat compaction. Heat-compacted polyurethane composite showed higher affinity to calcium ions than the non-heat compacted sample. The ATR-FT-IR results showed that the heat-compaction-induced physical changes include distortions of polymeric molecules and permanent changes of microstructures. The distortions of polymeric molecules could be deteriorated in contact with different media. The relaxation of the stressed structures of the polyether moiety might serve as a calcium trap and a heterogeneous nucleation site for calcification. The permanent changes of microstructures resulted from high distortions also served as affinity sites attracting calcification.

Mineralization of developing mouse calvaria as revealed by Raman microspectroscopy

Raman microspectroscopy is a nondestructive vibrational spectroscopic technique that permits the study of organic and mineral species at micron resolution, offers the ability to work with hydrated and dehydrated specimens in vivo or in vitro, and requires minimal specimen preparation. We used Raman microspectroscopy to determine the composition of the mineral environments present in mouse calvaria, the flat bones that comprise the top of the skull. We have acquired Raman transects (lines of point spectra) from mouse calvaria during a developmental time course ranging from embryonic day 13.5 (E13.5; 6 days before birth) to 6 months of age. Exploratory factor analysis (FA) reveals the presence of a variety of apatitic mineral environments throughout the tissue series. The earliest mineral is observed in the fetal day 15.5 (F15.5) mice and is identified as a carbonated apatite. The presence of a heterogeneous mineralized tissue in the postnatal specimens suggests that ionic incorporation and crystal perfection in the lattice yary as the mouse develops. This variation is indicative of the presence of both recently deposited mineral and more matured remodeled mineral. Band area ratios reveal that the mineral/matrix ratio initially increases, reaches a plateau, and then increases again. The carbonate/phosphate band area ratio remains constant from F18.5 to postnatal day 3 (PN3) and then increases with age. Insights into the chemical species, the degree of mineralization, and the multiple mineral environments that are present in normal calvarial tissue will enable us to better understand both normal and abnormal mineralization processes.

Hydroxyapatite crystals as a local delivery system for cisplatin: adsorption and release of cisplatin in vitro

This study describes the characteristics of the in vitro binding and release of the anti-tumor drug cisplatin by slurries of synthetic hydroxyapatite crystals carried out in aqueous media. The adsorption of cisplatin by slurries of hydroxyapatite and its release were found to depend significantly on the ionic composition of the aqueous media used. At a constant pH of 7.4, significantly more cisplatin is adsorbed by the hydroxyapatite crystals in the slurry from a chloride-free phosphate buffered solution or a Tris buffered solution than from a buffered phosphate solution containing chloride ions. The amount of hydroxyapatite-bound cisplatin desorbed into solution was also progressively increased as a function of the increasing concentration of chloride in the equilibrating solution. Very little hydroxyapatite-bound cisplatin was released from the crystals in either a Tris or phosphate buffer. These results suggest that it is the hydrated derivatives of cisplatin which are involved in the adsorption of cisplatin by hydroxyapatite crystals. The adsorption data can be expressed as a Freundlich isotherm from which the association constant can be calculated. The rate of release of cisplatin bound to crystals of hydroxyapatite is relatively slow even at the maximum concentration of chloride ions in the phosphate buffer. Approximately 33% of the total cisplatin bound to the crystals of hydroxyapatite was released after 4.25 days. An additional 15% of the remaining cisplatin bound to the hydroxyapatite cyrstals was released after an additional equilibration with fresh buffer for two weeks (58% of the total cisplatin originally bound). These findings suggest that cisplatin bound to slurries of hydroxyapatite crystals may be useful in the local treatment of malignant tumors.

Microstructural investigations of strain-related collagen mineralization

Distraction osteogenesis in rabbit mandibles after osteotomy can be used as an experimental model to study the microstructural features of mineralization of callus under defined mechanical loads. Our aim was to study the relation between the micromotions in the gap and the resulting features of mineralization of the matrix. We found that assembly of collagen and formation of crystals depended on the magnitude of the mechanical stress applied. At physiological bone strains (2000 microstrains), the callus had collagen type I in a mature bone-like extracellular arrangement, whereas at 20000 microstrains bundles were orientated predominantly towards the tension vector. Maximum loads (200000 microstrains) resulted in disorganized assembly of the collagen. Quantitative energy-dispersive analysis by X-rays confirmed that high strains were associated with substantially lower concentrations of calcium and phosphate. In contrast to bone-like apatitic formation of crystals at physiological strains, significantly fewer but larger crystals were detected by electron diffraction analysis in samples exposed to high strains. We suggest that mechanical stress regulates the assembly and mineralization of collagen during distraction osteogenesis.

Study of the maturation of the organic (type I collagen) and mineral (nonstoichiometric apatite) constituents of a calcified tissue (dentin) as a function of location: a Fourier transform infrared microspectroscopic investigation

Fourier transform infrared microspectroscopy (FTIRM) was used to investigate the organic and mineral phases of a calcified tissue (dentin) as a function of its location from predentin toward enamel. Thin dentin slices (decalcified or not) were fixed in formaldehyde and embedded in glycolmethylmethacrylate (GMA). Fixation did not denature collagen, and GMA did not interact with organic or mineral constituents of dentin. The v1v3 PO4 domain was studied in particular in order to estimate mineral maturity and amide I, II, A, and B to obtain data on protein conformation. The results showed that dentin apatite became increasingly mature (stoichiometric) from the mineralization front toward the enamel, especially through loss of HPO4(2-) groups and vacancies. Moreover, collagen fibrils became less and less hydrated, suggesting that intrafibrillar mineralization partially dehydrated the collagen. Combined study of the organic and mineral fractions of calcified tissues may help clarify their relationships in physiological and pathological tissues.

Structure, composition, and maturation of newly deposited calcium-phosphate crystals in chicken osteoblast cell cultures

Characterization of the very early calcium phosphate (CaP) crystals deposited in bone or in osteoblast cell cultures has been hampered by the overwhelming presence of organic matrix components and cells that obscure spectral analyses. We have overcome this problem using isolated protein-free crystals and have obtained new data including 31P nuclear magnetic resonance (NMR) spectra for the first time from mineral crystals deposited during osteoblast calcification in culture. Crystals were isolated from cultures at two time points: (a) at first calcium accumulation (day 8-10) and (b) after 60 days of culture, to assess maturational changes. The analyses show that the chemical composition overall and short range order of the early and mature crystals are characteristic of the apatite crystals found in young embryonic chick bone in vivo. No mineral phase other than apatite was detected by any of the methods used. 31P NMR spectroscopy identified the HPO4 groups as those present in bone apatite. Similar to bone apatites, no OH groups were detected by Fourier transform infrared (FTIR) spectroscopy. The temporal maturational changes in composition and structure of the mineral phase were difficult to assess because of the continuous deposition of crystals throughout culturing. The pathway of the maturational changes observed were similar to those occurring in chick bone in vivo and synthetic apatite crystals in vitro although to a much smaller extent.

Thin film of low-crystalline calcium phosphate apatite formed at low temperature

Surface modification of biomaterials to improve biocompatibility without changing their bulk properties is desired for many clinical applications and has become an emerging technology in biomaterial research and industry. In the present study, a simple method of coating the solid surfaces of metals, organic tissue matrices, glasses, inorganic ceramics as well as organic polymers with a thin film of low-crystalline apatite crystals (LCA) was developed. Acidic solution containing calcium and phosphate ions was neutralized with alkaline solution to form calcium phosphate precipitates at low temperature. Precipitates of solid calcium phosphate particles were, then, removed by filtration. Concentration of free ions in the filtered ion solution which were not involved in the formation of calcium phosphate precipitate was high enough to induce the heterogeneous nucleation on the solid surfaces at low temperature. Thin layers of calcium phosphate crystals were formed on the surfaces of metals, glasses, inorganic ceramics, organic polymers including hydrophobic ones, and biological tissue matrices with this solution. The thin layer of crystals consisted of poorly crystalline calcium phosphate apatite crystals which contain high amount of labile ions like bone crystals and did not dissolve in the physiologic solutions. Various cells attached to this crystal layer and proliferated well.

Matrix GLA protein is a developmental regulator of chondrocyte mineralization and, when constitutively expressed, blocks endochondral and intramembranous ossification in the limb

Matrix GLA protein (MGP), a gamma-carboxyglutamic acid (GLA)-rich, vitamin K-dependent and apatite-binding protein, is a regulator of hypertrophic cartilage mineralization during development. However, MGP is produced by both hypertrophic and immature chondrocytes, suggesting that MGP's role in mineralization is cell stage-dependent, and that MGP may have other roles in immature cells. It is also unclear whether MGP regulates the quantity of mineral or mineral nature and quality as well. To address these issues, we determined the effects of manipulations of MGP synthesis and expression in (a) immature and hypertrophic chondrocyte cultures and (b) the chick limb bud in vivo. The two chondrocyte cultures displayed comparable levels of MGP gene expression. Yet, treatment with warfarin, a gamma-carboxylase inhibitor and vitamin K antagonist, triggered mineralization in hypertrophic but not immature cultures. Warfarin effects on mineralization were highly selective, were accompanied by no appreciable changes in MGP expression, alkaline phosphatase activity, or cell number, and were counteracted by vitamin K cotreatment. Scanning electron microscopy, x-ray microanalysis, and Fourier-transform infrared spectroscopy revealed that mineral forming in control and warfarin-treated hypertrophic cell cultures was similar and represented stoichiometric apatite. Virally driven MGP overexpression in cultured chondrocytes greatly decreased mineralization. Surprisingly, MGP overexpression in the developing limb not only inhibited cartilage mineralization, but also delayed chondrocyte maturation and blocked endochondral ossification and formation of a diaphyseal intramembranous bone collar. The results show that MGP is a powerful but developmentally regulated inhibitor of cartilage mineralization, controls mineral quantity but not type, and appears to have a previously unsuspected role in regulating chondrocyte maturation and ossification processes.

Elastin calcification and its prevention with aluminum chloride pretreatment

Elastin, an abundant structural protein present in the arterial wall, is prone to calcification in a number of disease processes including porcine bioprosthetic heart valve calcification and atherosclerosis. The mechanisms of elastin calcification are not completely elucidated. In the present work, we demonstrated calcification of purified elastin in rat subdermal implants (Ca(2+) = 89.73 +/- 9.84 microgram/mg after 21 days versus control, unimplanted Ca(2+) = 0.16 +/- 0.04 microgram/mg). X-ray diffraction analysis along with resolution enhanced FTIR spectroscopy demonstrated the mineral phase to be a poorly crystalline hydroxyapatite. We investigated the time course of calcification, the effect of glutaraldehyde crosslinking on calcification, and mechanisms of inhibition of elastin calcification by pretreatment with aluminum chloride (AlCl(3)). Glutaraldehyde pretreatment did not affect calcification (Ca(2+) = 89.06 +/- 17.93 microgram/mg for glutaraldehyde crosslinked elastin versus Ca(2+) = 89.73 +/- 9.84 microgram/mg for uncrosslinked elastin). This may be explained by radioactive ((3)H) glutaraldehyde studies showing very low reactivity between glutaraldehyde and elastin. Our results further demonstrated that AlCl(3) pretreatment of elastin led to complete inhibition of elastin calcification using 21-day rat subdermal implants, irrespective of glutaraldehyde crosslinking (Ca(2+) = 0.73-2.15 microgram/mg for AlCl(3) pretreated elastin versus 89.73 +/- 9.84 for untreated elastin). The AlCl(3) pretreatment caused irreversible binding of aluminum ions to elastin, as assessed by atomic emission spectroscopy. Moreover, aluminum ion binding altered the spatial configuration of elastin as shown by circular dichroism (CD), Fourier transform infrared (FTIR), and (13)C nuclear magnetic resonance (NMR) spectroscopy studies, suggesting a net structural change including a reduction in the extent of beta sheet structures and an increase in coil-turn conformations. Thus, it is concluded that purified elastin calcifies in rat subdermal implants, and that the AlCl(3)-pretreated elastin completely resists calcification due to irreversible aluminum ion binding and subsequent structural alterations caused by AlCl(3).

Heterotopic implantation of mouse bone-marrow cells: an in vivo model allowing analysis of mineral phases during mineralization processes

Heterotopic calcification induced after implantation of bone-marrow cells under the murine kidney capsule was used to study the mineral phases occurring during the mineralization process. Ossicles were found to contain numerous osteoblastic cells that produced an organic matrix closely associated with active hematopoietic tissue. During implantation of bone marrow, needle-shaped microcrystals were progressively deposited on collagen fibers. The mineral formed in the heterotopic calcification consisted mainly of calcium phosphate. The distribution and density of the microcrystals were heterogeneous after 6 weeks of implantation but became homogeneous and well-crystallized after 10 weeks. The Fourier transform infrared microspectroscopy provided important spatial data on the nature of the mineral formed and the changes in the mineral environment. Similarities were noted between young bone (bone callus) and 6-week heterotopic ossicles, and between adult bone and 10- or 12-week heterotopic ossicles. The study demonstrated that murine heterotopic calcification under the renal capsule can be a very useful model for studying bone apatite formation during the mineralization process.

Effects of leukemia inhibitory factor and oncostatin M on bone mineral formed in in vitro rat bone-marrow stromal cell culture: physicochemical aspects

Leukemia inhibitory factor (LIF) and oncostatin M (OSM), two pleiotropic cytokines involved in bone remodeling, have both anabolic and catabolic activities. This study analyzed the effects of LIF and OSM on the physicochemical characteristics of mineral phases formed in a rat bone-marrow stromal cell culture model. Stromal cells were cultured for three weeks in the presence of 10(-8) M dexamethasone, 50 microgram/mL ascorbic acid and 10 mM Na beta-glycerophosphate with or without 10 ng/ml LIF or OSM. Subsequently, the physicochemical characteristics of the mineralization nodules formed were analyzed by energy dispersive X ray microanalysis (EDX) and Fourier transform-infrared (FT-IR) and FT-Raman spectroscopy. EDX and FT-IR spectroscopy revealed the influence of LIF and OSM on the physicochemical characteristics of mineral phases. FT-Raman spectroscopy showed modifications of the main vibrational modes of the organic matrix. These alterations induced by growth factors could help define new strategies for the prevention and treatment of skeletal disorders.

Matrix mineralization in MC3T3-E1 cell cultures initiated by beta-glycerophosphate pulse

MC3T3-E1 cells, grown in the presence of serum and ascorbate, express alkaline phosphatase and produce an extensive collagenous extracellular matrix that can be mineralized by the addition of beta-glycerophosphate (beta-GP). In the present work, we study the influence of concentration and duration of beta-GP treatment on the mineralization pattern in 4-week-old cell cultures. Amount and structure of mineral deposition were monitored by von Kossa staining, light, and electron microscopy, as well as small-angle X-ray scattering (SAXS) of unstained specimens. SAXS measures the total surface of the mineral phase and is therefore preferentially sensitive to very small crystals (typically <50 nm). It was used to determine the ratio (M) of small crystals to collagen matrix. A variety of mineralization patterns was observed to occur simultaneously, some associated with collagen within nodules or in deeper layers of the cultures and some independent of it. At a beta-GP concentration of 10 mmol, mineralization was initiated after about 24 h and continued to increase, irrespective of whether the high level of beta-GP was maintained or reduced to 2 mmol. With shorter pulses (<24 h), no significant mineralization was observed in the week following beta-GP pulse. With continuous treatment at 5 mmol beta-GP, the first signs of mineralization were detected 14 days after the beginning of treatment in the 4-week-old cultures, but no mineralization at all occurred at lower beta-GP concentrations. When cells were grown without ascorbic acid for 4 weeks, only two cell layers without collagen matrix were found. In these cultures, no mineralization detectable by SAXS could be induced with beta-GP. These data indicate that, in viable cells, high doses of beta-GP are essential for the nucleation of mineral crystals, but not for the progression of mineralization once crystals had been nucleated. In contrast, when 4-week-old cell cultures were devitalized, M was found to increase immediately, even at 2 mmol beta-GP. These results suggest that, in MC3T3-E1 cell cultures, cell viability is essential for prevention of spontaneous mineralization of the extracellular matrix.

Leukemia inhibitory factor and oncostatin M influence the mineral phases formed in a murine heterotopic calcification model: a Fourier transform-infrared microspectroscopic study

The study of bone mineralization processes is of considerable interest in understanding bone diseases and developing new therapies for skeletal disorders, particularly since bone homeostasis requires numerous cell types and a large cytokine network. Cell culture models of mineralization have often been used to study the cellular mechanisms of mineralization, but few data have been reported concerning the influence of extracellular matrix components and cytokines on the physicochemical properties of mineral. The purpose of this study was to analyze the effects of two cytokines, leukemia inhibitory factor (LIF) and oncostatin M (OSM), involved in bone metabolism on the physicochemical properties of bone mineral formed in a murine in vivo mineralization model. Murine bone marrow cells implanted under the kidney capsule in the presence or absence of cytokines led to heterotopic ossicle formation. A scanning electron microscopic microprobe revealed that heterotopic calcification had a lower (approximately 20%) Ca/P ratio after cytokine treatment as compared with the control without cytokine. Transmission electron microscopic analysis of cytokine-treated ossicles showed numerous areas with low mineral density, whereas electron diffraction pattern revealed an apatitic phase. These areas were not observed in the absence of cytokine. Moreover, Fourier transform-infrared microspectroscopy showed at the molecular level that the presence of either cytokine induced many microscopic areas in which short-range order organization, such as incorporation of carbonate and crystallinity/maturity of ossicle mineral, were modified. LIF and OSM influenced mineral phase formation in the present model and may thus be key protagonists in bone mineral development and skeletal diseases.

Application of FT-IR microspectroscopy to the study of an injectable composite for bone and dental surgery

Hydroxypropylmethylcellulose (HPMC) of high-viscosity grade is used as a ligand for a bioactive calcium phosphate ceramic (the filler) in a ready-to-use injectable sterilized biomaterial for bone and dental surgery. Application of physico-chemical methods such as XPS, NMR, or Raman spectroscopy encounters difficulties when used to study such a multiphased material. This paper reports on the application of FT-IR microspectroscopy (FT-IRM) for the investigation of inorganic and organic phases of the rough composite and separated phases obtained by mechanical or chemical extraction methods. A comparison of FT-IRM with the conventional KBr pellet method was made and indicates that the macro and micro FT-IR methods are complementary: the former revealed new chemical groups not visualized with the KBr method whereas the latter detected the major compound of the blend. FT-IR microspectroscopy was revealed to be a powerful method of analysis that is complementary to other existing spectroscopic methods. Moreover, it is expected to be a useful tool in the study of biomaterials in biological samples.

Characterization of the apatite crystals of bone and their maturation in osteoblast cell culture: comparison with native bone crystals

Calcium phosphate crystals deposited in the organic matrix synthesized by chick bone osteoblasts in culture were studied by x-ray and electron diffraction, Fourier transform infrared spectroscopy and chemical composition. The amounts of mineral phase deposited with time and the extent of calcification (% of mineral phase in the tissue) were also determined as a function of time, as were the nature of the changes in the short range order of the crystals. The amount of mineral deposited and the extent of calcification increased with time; the tissue not only contained more crystals of apatite, but the extent of calcification also increased with time as it does in vivo. After 30 days of culture the extent of calcification in the cell culture matrix was similar to that in late chick embryonic and early postnatal chick tibiae. The nature of the CO3 and HPD4 environments were similar to those found in vivo although the concentrations of these ions and the changes in their concentrations with time appeared to develop more slowly in cell culture than they do in vivo. However, the general overall pathway of maturation was similar in cell culture to that observed in vivo.