Osteoclastic resorption of Ca-P biomaterials implanted in rabbit bone

The Use of Biphasic Calcium Phosphate Substitute (BCP) in Mandibular Defects in Dogs: Use of CBCT to Evaluate Bone Healing

This study aimed to assess the use of cone beam computed tomography (CBCT) to follow-up bone healing of mandibular bone defects in dogs, filled with a combination of autologous blood and millimetric BCP granules. CBCT was performed ≥4 weeks postoperatively. CBCT gray-scale values were measured from multiplanar reconstructions of the defects and compared to that of normal contralateral mandibular bone and to pure BCP/blood composite time 0 (T0) value. Other parameters, determined by affecting grades according to specific criteria included: bone ridge margin restoration; biomaterial homogeneity; bone-biomaterial interface. Results: 8 dogs with 14 defects were included. Median age was 7.2 years (1-15 years). Follow-up CBCT was performed 1 to 7.5 months postoperatively (mean 3.3 months). Defect CBCT gray-scale values at follow-up were significantly greater than T0 (p < 0.05). Ratios of maximum and minimum densities of the defects to contralateral mandibular bone followed a linear correlation with time (p < 0.05). The bone ridge margin was adequately restored in all the defects and significantly correlated with time (p = 0.03). Biomaterial homogeneity was fair to good in 11 defects and significantly correlated with the bone ridge margin parameter (p = 0.05) and time (p = 0.006). There was no significant correlation with the bone-material interface. The latter was satisfactory in 12 defects and significantly correlated with time (p = 0.01) but not with the other parameters. The biomaterial was more homogeneous in smaller defects and with increasing time. CBCT allowed effective assessment of bone healing via the measurement of CBCT gray-scale values and assessment of multiple radiological variables.

Coupling between macrophage phenotype, angiogenesis and bone formation by calcium phosphates

The ability of calcium phosphate (CaP) materials to induce bone formation varies with their physicochemical properties, with surface topography as one of the most crucial triggers. In view of the natural wound healing processes (e.g., inflammation, angiogenesis, tissue formation and remodeling) initiated after surgical implantation, we here comparatively investigated the biological cascades occurring upon ectopic implantation of a tricalcium phosphate with submicron surface topography (TCP-S, osteoinductive) and a tricalcium phosphate with micron-scale topography (TCP-B, non-osteoinductive). In vitro, TCP-S facilitated M2 polarization of macrophages derived from a human leukemic cell line (THP-1) as shown by the enhanced secretion of TGF-β and CCL18. Interestingly, the conditioned media of polarized M2 macrophages on TCP-S enhanced tube formation by human umbilical vein endothelial cells (HUVECs), while had no influence on the osteogenic differentiation of human bone marrow stromal cells (HBMSCs). Following an intramuscular implantation in canines, TCP-S locally increased typical M2 macrophage markers (e.g., IL-10) at week 1 to 3 and enhanced blood vessel formation after week 3 as compared to TCP-B. Bone formation was observed histologically in TCP-S 6 weeks after implantation, and bone formation was inhibited when an angiogenesis inhibitor (KRN633) was loaded onto TCP-S. No bone formation was observed for TCP-B. The data presented herein suggest strong links between macrophage polarization, angiogenesis and CaP-induced bone formation. STATEMENT OF SIGNIFICANCE: The ability of calcium phosphate (CaP) materials to induce bone formation varies with their physicochemical properties, and the key physicochemical properties relevant to CaP-induced bone formation have been outlined in the last two decades. However, the biological mechanism underlying this material-driven osteoinduction remains largely unknown. This manuscript presented demonstrates strong links between surface topography, macrophage polarization, angiogenesis and bone formation in CaP materials implanted in non-osseous sites. The finding may provide new clues for further exploring the possible mechanism underlying osteoinduction by CaP materials.

Guided bone tissue regeneration using a hollow calcium phosphate based implant in a critical size rabbit radius defect

Long bone fractures are common and sometimes difficult to treat. Autologous bone (AB), bovine bone and calcium phosphates are used to stimulate bone growth with varying results. In the present study, a calcium phosphate cement (CPC) that previously showed promising grafting capabilities was evaluated for the first time in a long bone defect. A radius defect of 20 mm was created in twenty rabbits. The defect was filled by either a hollow CPC implant that had been previously manufactured as a replica of a rabbit radius through indirect 3D printing, or by particulate AB as control. Defect filling and bone formation was evaluated after 12 weeks by combining micro computed tomography (μCT) and scoring of 3D images, together with histomorphometry and histology. The μCT and histomorphometric evaluations showed a similar amount of filling of the defect (combining graft and bone) between the CPC and AB group, but the scoring of 3D images showed that the filling in the CPC group was significantly larger. Histologically the AB graft could not be distinguished from the new bone. The AB treated defects were found to be composed of more bone than the CPC group, including reorganised cancellous and cortical bone. Both the CPC and AB material was associated with new bone formation, also in the middle of the defect, which could result in closing of the otherwise critically sized gap. This study shows the potential for an indirectly 3D printed implant in guided bone regeneration in critically sized long bone defects.

Giant cells and osteoclasts present in bone grafted with nacre differ by nuclear cytometry evaluated by texture analysis

Nacre (mother of pearl) is a natural biomaterial used to prepare orthopedic devices. We have implanted screws and plates made with nacre in five sheeps. Bone were harvested after two months and embedded in poly(methyl methacrylate). Blocks were saws and the thick slabs were grinded, polished and surface stained. Sections were photographed at an ×1000 magnification. Giant cells were found in contact with nacre in eroded areas and true osteoclasts were found at distance in the neighboring bone in Howship lacunae. A texture analysis of the nuclei of giant cells and osteoclasts was done using the run-length method of the MaZda freeware. The size of the nuclei was reduced in osteoclast and their mean gray level appeared reduced. Texture analysis revealed that chromatin had a completely different pattern in giant cells when compared to osteoclasts. Giant cells had a fine repartition of the chromatin with large clear areas around prominent nucleoli. On the contrary, osteoclast nuclei had chromatin blocks evenly dispersed in the nuclei. This reflects the different origin of these cells expressing different functions.

Human macrophages and osteoclasts resorb β-tricalcium phosphate in vitro but not mouse macrophages

β-TCP is a resorbable bony biomaterial but its biodegradation mechanisms in vivo remains unclear. Osteoclast can resorb β-TCP but a role for macrophages has also been suggested by in vivo studies. However no in vitro study has clearly evidenced the action of macrophages in the resorption process. We prepared flat β-TCP tablets with a smooth surface to investigate the in vitro capability of murine (RAW 264.7) and human macrophage cells (PBMCs) to resorb the biomaterial. In parallel, these cells were differentiated into multinucleated osteoclasts with M-CSF and RANK-L. The action of these cells was evaluated by scanning electron microscopy and Raman microspectroscopy after a 21 day culture on the tablets. Human macrophages and osteoclasts derived from PBMCs appeared able to resorb β-TCP by forming resorption pits at the surface of the flat tablets. RAW macrophages were unable to resorb β-TCP but they exhibited this possibility when they have been differentiated into osteoclasts. These cells can engulf β-TCP grains in their cytoplasm as evidenced by light and TEM microscopy with production of carbonic anhydrase (revealed by the immunogold technique in TEM). The resorbed areas were characterized by severe degradation of the grains showing speckled and stick-like aspects indicating a chemical corrosion. The effect was maximal at the grain boundaries which have a slightly different chemical composition. Changes in the Raman spectrum were observed between the resorbed and un-resorbed β-TCP suggesting crystal modifications. In contrast, un-differentiated murine macrophages were not able to chemically attack β-TCP and no resorption pit was observed. RAW cell is not a representative model of the macrophage-biomaterial interactions that occur in human. This in vitro study evidences that both human osteoclasts and macrophages represent active cell populations capable to resorb β-TCP.

Cross-linked cellulose nanocrystal aerogels as viable bone tissue scaffolds

Chemically cross-linked cellulose nanocrystal (CNC) aerogels possess many properties beneficial for bone tissue scaffolding applications. CNCs were extracted using sulfuric acid or phosphoric acid, to produce CNCs with sulfate and phosphate half-ester surface groups, respectively. Hydrazone cross-linked aerogels fabricated from the two types of CNCs were investigated using scanning electron microscopy, X-ray micro-computed tomography, X-ray photoelectron spectroscopy, nitrogen sorption isotherms, and compression testing. CNC aerogels were evaluatedin vitrowith osteoblast-like Saos-2 cells and showed an increase in cell metabolism up to 7 days while alkaline phosphatase assays revealed that cells maintained their phenotype. All aerogels demonstrated hydroxyapatite growth over 14 days while submerged in simulated body fluid solution with a 0.1 M CaCl₂ pre-treatment. Sulfated CNC aerogels slightly outperformed phosphated CNC aerogels in terms of compressive strength and long-term stability in liquid environments, and were implanted into the calvarian bone of adult male Long Evans rats. Compared to controls at 3 and 12 week time points, sulfated CNC aerogels showed increased bone volume fraction of 33% and 50%, respectively, compared to controls, and evidence of osteoconductivity. These results demonstrate that cross-linked CNC aerogels are flexible, porous and effectively facilitate bone growth after they are implanted in bone defects. STATEMENT OF SIGNIFICANCE: Due to the potential complications associated with autografts, there is a need for synthetic bone tissue scaffolds. Here, we report a new naturally-based aerogel material for bone regeneration made solely from chemically cross-linked cellulose nanocrystals (CNC). These highly porous CNC aerogels were shown to promote the proliferation of bone-like cells and support the growth of hydroxyapatite on their surface in vitro. The first in vivo study on these materials was conducted in rats and showed their osteconductive properties and an increase in bone volume up to 50% compared to sham sites. This study demonstrates the potential of using functionalized cellulose nanocrystals as the basis for aerogel scaffolds for bone tissue engineering.

Maxillary Sinus Lift with Beta-Tricalcium Phosphate (β-TCP) in Edentulous Patients: A Nanotomographic and Raman Study

Sinus lift elevation restores bone mass at the maxilla in edentulate patients before the placement of dental implants. It consists of opening the lateral side of the sinus and grafting beta-tricalcium phosphate granules (β-TCP) under the olfactory membrane. Bone biopsies were obtained in five patients after 60 weeks. They were embedded undecalcified in poly(methyl methacrylate) (pMMA); blocks were analyzed by nanocomputed tomography (nanoCT); specific areas were studied by Raman microspectroscopy. Remnants of β-TCP were osseointegrated and covered with mineralized bone; osteoid tissue was also filling the inner porosity. Macrophages having engulfed numerous β-TCP grains were observed in marrow spaces. β-TCP was identified by nanoCT as osseointegrated particles and as granules in the cytoplasm of macrophages. Raman microspectroscopy permitted to compare the spectra of β-TCP and bone in different areas. The ratio of the ~820 cm^-1 band of pMMA (-CH₂ groups) on the ν1 phosphate band at 960 cm^-1 reflected tissue hydration because water was substituted by MMA during histological processing. In bone, the ratio of the ~960 cm^-1 phosphate to the amide 1 band and the ratio ν2 phosphate band by the 1240-1250 amide III band reflect the mineralization degree. Specific bands of β-TCP were found in osseointegrated β-TCP granules and in the grains phagocytized by the macrophages. The hydration degree was maximal for β-TCP phagocytized by macrophages. Raman microspectroscopy associated with nanoCT is a powerful tool in the analysis of the biomaterial degradation and osseointegration.

Behavior of macrophage and osteoblast cell lines in contact with the β-TCP biomaterial (beta-tricalcium phosphate)

Beta-tricalcium phosphate (β-TCP) is a synthetic ceramic used for filling bone defects. It is a good alternative to autologous grafts since it is biocompatible, resorbable and osteoconductive. Previous in vivo studies have shown that macrophages are one of the first cells coming in contact with the biomaterial followed by osteoclasts and osteoblasts that will elaborate new bone packets. Studies have focused on osteoclast morphology and very few of them have investigated the role of macrophages. The aims of this study were to characterize (i) the biomaterial surface; (ii) the in vitro behavior of macrophages (J774.2 and Raw264.7 cells) using the description of cell morphology by scanning electron microscopy (SEM) at 7 and 14 days; (iii) the behavior of osteoblasts (SaOs-2 and MC3T3-E1 cells) seeded at the surface of the biomaterial 24, 48 and 72hours by SEM and confocal microscopy. Cell proliferation was analyzed by MTT assays. Viability and affinity of the macrophages for β-TCP were found significantly increased after 7 and 14d. MC3T3-E1 cells were anchored and stretched onto the β-TCP surface as early as 24h with a high proliferation rate (+190%) when compared to the surface of a well plate. SaOs-2 exhibited the same morphological profile at 72h. Proliferation became significantly higher compared to the plastic surface at only 72h (+129%). This study emphasises the importance of choice of the cell line used in exploring the osteoconductive and osteoinductive properties of a biomaterial. Additional studies are needed to analyze differentiation of macrophages into giant multinucleated cells and how the biomaterial surface influences osteoblast differentiation.

Beta-tricalcium phosphate for orthopedic reconstructions as an alternative to autogenous bone graft

Autogenous bone graft (autograft) remains the gold standard in the treatment of many orthopedic problems. However, graft harvest can lead to perioperative morbidity and increased cost. We tested the hypothesis that an osteoconductive matrix, beta-tricalcium phosphate (β-TCP), would be a safe and effective alternative to autograft alone. Beta-tricalcium phosphate (β-TCP) is considered as one of the most promising biomaterials for bone reconstruction. This study analyzes the outcomes of patients who received β-TCP as bone substitutes in orthopedic surgery.

METHODS

A total of 50 patients were enrolled in a controlled, non-inferiority clinical trial to compare the safety and efficacy of β-TCP (25 patients) with those of autograft (25 patients) in indications requiring usually autograft. These 50 patients were categorized according to the etiology and morphology of the 54 bone defects resulting from elective surgical procedures, such as 34 open-wedge high tibial osteotomies, and 20 osteonecrosis treatments with core decompression. Radiographic (healing process with or without integration of β-TCP), clinical (no other surgical procedure), functional outcomes and safety (with or without complications) were assessed through fifty-two weeks postoperatively.

RESULTS

With regard to the primary endpoint (radiographic evolution), the fusion rate of the 34 open-wedge osteotomies was 100% (17 among 17) for patients in the group with β-TCP compared with 94% (16 among 17) for patients in the autograft group. For the 20 cavitary defects (osteonecrosis), the radiographic union rates, as determined by the presence of osseous bridging, were 100% for patients in the group with β-TCP and 100% for those in the autograft group. Clinically at one year, all quality-of-life and functional outcome data supported non-inferiority of β-TCP compared with autograft, and patients in the β-TCP group were found to have less pain and an improved safety profile.

CONCLUSIONS

Treatment with β-TCP resulted in comparable fusion rates, less pain and fewer side effects as compared with treatment with autograft. This study established clinical parameters where the β-TCP alone can successfully support the osteogenic process.

Multinucleated giant cells in the implant bed of bone substitutes are foreign body giant cells-New insights into the material-mediated healing process

In addition to macrophages, multinucleated giant cells (MNGCs) are involved in the tissue reaction to a variety of biomaterials. Especially in the case of bone substitute materials it has been assumed that the MNGCs are osteoclasts, based on the chemical and physical similarity of many materials to the calcified matrix and the bony environment in which they are used. However, many studies indicate that these cells belong to the cell line of the foreign body giant cells (FBGCs), which are of "inflammatory origin", although they have been shown to possess both a pro- and also anti-inflammatory phenotype. Moreover, no information is available about their role in the tissue reaction to bone substitute materials. The present study was conducted to analyze the origin of MNGCs in the implant beds of a synthetic and a xenogeneic bone substitute and focused on the application of immunohistochemical methods. Two antibodies against integrin molecules specific for osteoclasts (β-3 integrin) or FBGCs (β-2 integrin) were used to distinguish both giant cell types. The results of the present study indicate that the MNGCs induced by both kinds of bone substitutes are FBGCs, as they express only β-2 integrin in contrast to the osteoclasts outside of the immediate implantation areas, which only demonstrate β-3 integrin expression. These data give new insight into the tissue reaction to both xenogeneic and synthetic bone substitutes. Based on this new knowledge further research concerning the proteomic profile of the FBGCs especially based on the different physicochemical properties of bone substitutes is necessary. This may show that specific characteristics of bone substitutes may exhibit a substantial influence on the regeneration process via the expression of anti-inflammatory molecules by FBGCs. Based on this information it may be possible to formulate and choose bone substitutes that can guide the process of bone tissue regeneration on the molecular level. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1105-1111, 2017.

In vivo erosion of orthopedic screws prepared from nacre (mother of pearl)

BACKGROUND

Biodegradable biomaterials have been proposed to prepare orthopedic devices. Nacre is a natural aragonitic material made of calcium carbonate and is bioerodible.

WORKING HYPOTHESIS

We postulated that nacre is biodegradable without provoking bone erosion and favors bone apposition.

MATERIAL AND METHODS

We prepared orthopedic screws from nacre of the giant oyster Pinctada maxima. Threaded screws (3.5mm diameter) were implanted in 6 ewes in the upper tibial metaphysis (3 to 4 screws per animal). Their trajectory was transcortical and intramedullary to the opposite cortex. Animals were kept for 3months (n=2) and 6 months (n=4). They did not develop local inflammation. Before euthanasia, they received a double calcein labeling. Bone samples were analyzed by X-ray nanotomography and histology after embedding in poly(methyl methacrylate). The fractal dimension of the screw profiles (measured by the box-counting method) was used to quantify surface erosion.

RESULTS

3D nanotomography showed a gradual erosion of the threads, which was confirmed by a decreased fractal dimension. Histologically, multinucleated cells (non-osteoclastic appearance) were visible at the surface of the screws. No ruffled border was seen in these cells but they had extensions creeping in the organic matter between the aragonite tablets. Bone apposition was noted in the transcortical path of the screws with limited osteoconduction at the endosteum. Mineralization rate was increased in these zones composed of woven bone in contact with the nacre.

DISCUSSION AND CONCLUSION

Screws prepared from nacre have the advantage of an in vivo resorbability by macrophage-derived cells and an osteoconductive apposition in contact with the material without triggering a local inflammatory reaction.

Mechanisms of in Vivo Degradation and Resorption of Calcium Phosphate Based Biomaterials

Calcium phosphate ceramic materials are extensively used for bone replacement and regeneration in orthopedic, dental, and maxillofacial surgical applications. In order for these biomaterials to work effectively it is imperative that they undergo the process of degradation and resorption in vivo. This allows for the space to be created for the new bone tissue to form and infiltrate within the implanted graft material. Several factors affect the biodegradation and resorption of calcium phosphate materials after implantation. Various cell types are involved in the degradation process by phagocytic mechanisms (monocytes/macrophages, fibroblasts, osteoblasts) or via an acidic mechanism to reduce the micro-environmental pH which results in demineralization of the cement matrix and resorption via osteoclasts. These cells exert their degradation effects directly or indirectly through the cytokine growth factor secretion and their sensitivity and response to these biomolecules. This article discusses the mechanisms of calcium phosphate material degradation in vivo.

Histological Comparison in Rats between Carbonate Apatite Fabricated from Gypsum and Sintered Hydroxyapatite on Bone Remodeling

Carbonate apatite (CO₃Ap), the form of apatite found in bone, has recently attracted attention. The purpose of the present study was to histologically evaluate the tissue/cellular response toward the low-crystalline CO₃Ap fabricated using a dissolution-precipitation reaction with set gypsum as a precursor. When set gypsum was immersed in a 100°C 1 mol/L Na₃PO₄ aqueous solution for 24 h, the set gypsum transformed into CO₃Ap. Both CO₃Ap and sintered hydroxyapatite (s-HAp), which was used as a control, were implanted into surgically created tibial bone defects of rats for histological evaluation. Two and 4 weeks after the implantation, histological sections were created and observed using light microscopy. The CO₃Ap granules revealed both direct apposition of the bone matrix by osteoblasts and osteoclastic resorption. In contrast, the s-HAp granules maintained their contour even after 4 weeks following implantation which implied that there was a lack of replacement into the bone. The s-HAp granules were sometimes encapsulated with fibrous tissue, and macrophage polykaryon was occasionally observed directly apposed to the implanted granules. From the viewpoint of bone remodeling, the CO₃Ap granules mimicked the bone matrix, suggesting that CO₃Ap may be an appropriate bone substitute.

Osteoclast resorption of beta-tricalcium phosphate controlled by surface architecture

A resorbable bone graft substitute should mimic native bone in its capacity to support bone formation and be remodeled by osteoclasts (OCl) or other multinucleated cells such as foreign body giant cells (FBGC). We hypothesize that by changing the scale of surface architecture of beta-tricalcium phosphate (TCP), cellular resorption can be influenced. CD14(+) monocyte precursors were isolated from human peripheral blood (n = 4 independent donors) and differentiated into OCl or FBGC on the surface of TCP discs comprising either submicron- or micron-scale surface topographical features (TCPs and TCPb, respectively). On submicrostructured TCPs, OCl survived, fused, differentiated, and extensively resorbed the substrate; however, on microstructured TCPb, OCl survival, TRAP activation, and fusion were attenuated. Importantly, no resorption was observed on microstructured TCPb. By confocal microscopy, OCl formed on TCPs contained numerous actin rings allowing for resorption, but not on TCPb. In comparison, FBGC could not resorb either TCP material, suggesting that osteoclast-specific machinery is necessary to resorb TCP. By tuning surface architecture, it appears possible to control osteoclast resorption of calcium phosphate. This approach presents a useful strategy in the design of resorbable bone graft substitutes.

Liposomal clodronate inhibition of osteoclastogenesis and osteoinduction by submicrostructured beta-tricalcium phosphate

Bone graft substitutes such as calcium phosphates are subject to the innate inflammatory reaction, which may bear important consequences for bone regeneration. We speculate that the surface architecture of osteoinductive β-tricalcium phosphate (TCP) stimulates the differentiation of invading monocyte/macrophages into osteoclasts, and that these cells may be essential to ectopic bone formation. To test this, porous TCP cubes with either submicron-scale surface architecture known to induce ectopic bone formation (TCPs, positive control) or micron-scale, non-osteoinductive surface architecture (TCPb, negative control) were subcutaneously implanted on the backs of FVB strain mice for 12 weeks. Additional TCPs samples received local, weekly injections of liposome-encapsulated clodronate (TCPs + LipClod) to deplete invading monocyte/macrophages. TCPs induced osteoclast formation, evident by positive tartrate resistant acid phosphatase (TRAP) cytochemical staining and negative macrophage membrane marker F4/80 immunostaining. No TRAP positive cells were found in TCPb or TCPs + LipClod, only F4/80 positive macrophages and foreign body giant cells. TCPs stimulated subcutaneous bone formation in all implants, while no bone could be found in TCPb or TCPs + LipClod. In agreement, expression of bone and osteoclast gene markers was upregulated in TCPs versus both TCPb and TCPs + LipClod, which were equivalent. In summary, submicron-scale surface structure of TCP induced osteoclastogenesis and ectopic bone formation in a process that is blocked by monocyte/macrophage depletion.

Deproteinized bovine bone functionalized with the slow delivery of BMP-2 for the repair of critical-sized bone defects in sheep

As an alternative to an autologous bone graft, deproteinized bovine bone (DBB) is widely used in the clinical dentistry. Although DBB provides an osteoconductive scaffold, it is not capable of enhancing bone regeneration because it is not osteoinductive. In order to render DBB osteoinductive, bone morphogenetic protein 2 (BMP-2) has previously been incorporated into a three dimensional reservoir (a biomimetic calcium phosphate coating) on DBB, which effectively promoted the osteogenic response by the slow delivery of BMP-2. The aim of this study was to investigate the therapeutic effectiveness of such coating on the DBB granules in repairing a large cylindrical bone defect (8 mm diameter, 13 mm depth) in sheep. Eight groups were randomly assigned to the bone defects: (i) no graft material; (ii) autologous bone; (iii) DBB only; (iv) DBB mixed with autologous bone; (v) DBB bearing adsorbed BMP-2; (vi) DBB bearing a coating but no BMP-2; (vii) DBB bearing a coating with adsorbed BMP-2; and (viii) DBB bearing a coating-incorporated depot of BMP-2. 4 and 8 weeks after implantation, samples were withdrawn for a histological and a histomorphometric analysis. Histological results confirmed the excellent biocompatibility and osteoconductivity of all the grafts tested. At 4 weeks, DBB mixed with autologous bone or functionalized with coating-incorporated BMP-2 showed more newly-formed bone than the other groups with DBB. At 8 weeks, the volume of newly-formed bone around DBB that bore a coating-incorporated depot of BMP-2 was greatest among the groups with DBB, and was comparable to the autologous bone group. The use of autologous bone and BMP-2 resulted in more bone marrow formation. Multinucleated giant cells were observed in the resorption process around DBB, whereas histomorphometric analysis revealed no significant degradation of DBB. In conclusion, it was shown that incorporating BMP-2 into the calcium phosphate coating of DBB induced strong bone formation around DBB for repairing a critical-sized bone defect.

Preparation and properties of calcium phosphate cements incorporated gelatin microspheres and calcium sulfate dihydrate as controlled local drug delivery system

To develop high macroporous and degradable bone cements which can be used as the substitute of bone repairing and drug carriers, cross-linked gelatin microspheres (GMs) and calcium sulfate dihydrate (CSD) powder were incorporated into calcium phosphate bone cement (CPC) to induce macropores, adjust drug release and control setting time of α-TCP-liquid mixtures after degradation of GMs and dissolution of CSD. In this study, CSD was introduced into CPC/10GMs composites to offset the prolonged setting time caused by the incorporation of GMs, and gentamicin sulphate (GS) was chosen as the model drug entrapped within the GMs. The effects of CSD amount on the cement properties, drug release ability and final macroporosity after GMs degradation were studied in comparison with CPC/GMs cements. The resulting cements presented reduced setting time and increased compressive strength as the content of CSD below 5 wt%. Sustained release of GS was obtained on at least 21 days, and release rates were found to be chiefly controlled by the GMs degradation rate. After 4 weeks of degradation study, the resulting composite cements appeared macroporous, degradable and suitable compressive strength, suggesting that they have potential as controlled local drug delivery system and for cancellous bone applications.

A glass-reinforced hydroxyapatite and surgical-grade calcium sulfate for bone regeneration: In vivo biological behavior in a sheep model

A glass-reinforced hydroxyapatite (HA) composite (Bonelike®) was developed for bone grafting. This biomaterial is composed of a modified HA matrix with α- and β-tricalcium phosphate secondary phases, resulting in higher solubility than single HA type of materials. Several in vitro and in vivo studies demonstrated that Bonelike® has a highly bioactive behavior, which was also confirmed by employing granular forms of this biomaterial in orthopedics and dental applications. However, a fast consolidation vehicle was needed to promote the fixation of Bonelike® granules if applied in larger defects or in unstable sites. Surgical-grade calcium sulfate (CS), which is widely recognized as a well-tolerated and inexpensive bone graft material, was the chosen vehicle to improve the handling characteristics of Bonelike® as it can be used in the form of a powder that is mixed with a liquid to form a paste that sets in situ. After application in non-critical monocortical defects in sheep, histological, and scanning electron microscopy evaluations demonstrated that Bonelike® associated to CS functioned as a very satisfactory scaffold for bone regeneration as it achieved synchronization of the ingrowing bone with biomaterial resorption and subsequent preservation of the bone graft initial volume. Therefore, our results indicate that CS is an effective vehicle for Bonelike® granules as it facilitates their application and does not interfere with their proven highly osteoconductive properties. In the opposite way, the incorporation of Bonelike® improves the bone regeneration capabilities of CS.

Octacalcium phosphate: osteoconductivity and crystal chemistry

Octacalcium phosphate (OCP), which is structurally similar to hydroxyapatite (HA), is a possible precursor of bone apatite crystals. Although disagreement remains as to whether OCP comprises the initial mineral crystals in the early stage of bone mineralization, the results of recent biomaterial studies using synthetic OCP indicate the potential role of OCP as a bone substitute material, owing to its highly osteoconductive and biodegradable characteristics. OCP tends to convert to HA not only in an in vitro environment, but also as an implant in bone defects. Several lines of evidence from both in vivo and in vitro studies suggest that the conversion process could be involved in the stimulatory capacity of OCP for osteoblastic differentiation and osteoclast formation. However, the osteoconductivity of OCP cannot always be secured if an OCP with distinct crystal characteristics is used, because the stoichiometry and microstructure of OCP crystals greatly affect bone-regenerative properties. Osteoconductivity and stimulatory capabilities may be caused by the chemical characteristics of OCP, which allows the release or exchange of calcium and phosphate ions with the surrounding of this salt, and its tendency to grow towards specific crystal faces, which could be a variable of the synthesis condition. This paper reviews the effect of calcium phosphates on osteoblastic activity and bone regeneration, with a special emphasis on OCP, since OCP seems to be performing better than other calcium phosphates in vivo.

Sinus lift augmentation and beta-TCP: a microCT and histologic analysis on human bone biopsies

Sinus lift elevation is an interesting method to restore bone mass at the maxilla in edentulated patients. We have investigated the histological effects of beta tricalcium phosphate (beta-TCP) combined with autograft bone for sinus lift elevation. A series of 14 patients who were candidate for dental implantation were grafted with beta-TCP granules and morcellized autograft bone harvested at the chin. beta-TCP was characterized by scanning electron microscopy and optical profilometry. Before implant placement, a small bone biopsy (2mm in diameter) was done. The amount of residual material and newly formed bone were determined by microcomputed tomography. Histological analysis was done on undecalcified sections stained by Goldner's trichrome and osteoclast identification (TRAcP). beta-TCP served as a template for bone apposition by osteoblasts onto the granules' surface. The material was simultaneously resorbed by TRAcP positive osteoclasts and macrophages. Fragments of the material remained buried in bone trabeculae as long as 12 months post-graft but the formed bone onto the granules surface had a lamellar texture. beta-TCP combined with autograft bone appears a suitable biomaterial for sinus lift augmentation before the placement of bone implants. The material favors the apposition of lamellar bone by osteoblasts and is simultaneous resorbed by two types of cells.

Differentiation of activated monocytes into osteoclast-like cells on a hydroxyapatite substrate: an in vitro study

BACKGROUND

Hydroxyapatite surface coatings of dental implants have been introduced to obtain more rapid and complete osteointegration. A possible complication associated with hydroxyapatite implant surface is the release of particles. Those particles may be phagocytosed by monocytes, the first cells to colonize the inflammatory sites. The activated monocytes produce cytokines that could cause osteoclast activation.

METHODOLOGY

In order to establish the biological effect of particles released on monocyte differentiation to an osteoclast phenotype, we have used the murine monocyte/macrophage cell line, RAW 264.7 clone CRL-2278 cultured on a hydroxyapatite substrate. The direct action of hydroxyapatite on monocyte differentiation was examined using tartrate-resistant acid phosphatase (TRAP), immunohistochemistry and transmission electron microscopy (TEM) and Western Blot analysis.

RESULTS

The present study demonstrated that hydroxyapatite substrate might be able to induce a self-production of RANKL cytokine that directly stimulates a different behaviour in terms of phenotype expression from monocyte/macrophage lineage to mature and functional osteoclasts without the addition of exogenous factors.

CONCLUSIONS

These studies were designed to test a model in which osteoclasts could be formed from HA-activated monocytes via positive feedback elicited by RANKL, allowing for identification of innovative targets for therapeutic approaches.

The efficacy of Biobon and Ostim within metaphyseal defects using the Göttinger Minipig

INTRODUCTION

To compare bio, osteocompatibility, rate of resorption and remodeling dynamics of two clinically used bone substitutes.

MATERIALS AND METHODS

In a randomized fashion Biobon and Ostim were implanted bilaterally into the proximal metaphyseal tibiae of 18 Göttinger Minipigs in a direct right versus left "intra-individual" comparison. Fluorescent labelling was used. Microradiographic, histological and morphometric evaluation was carried out at 6, 12 and 52 weeks.

RESULTS

Both bone substitutes showed good biocompatibility, bioactivity and osteoconductivity. The degradation dynamics of both materials differed. Degradation of Ostim stopped after 6 weeks postoperatively, whereas Biobon was degraded slowly but evenly over the time intervals. Only at 6 weeks a significant (P < 0.05) difference in resorption rate was detected. Both Biobon and Ostim showed incomplete resorption after a year.

CONCLUSION

After 1 year no "restitutio ad integrum" could be observed in either group. Similar to ceramics, a thorough osseous incorporation seemed to inhibit further degradation of both bone substitute materials.

Creation of macroporous calcium phosphate cements as bone substitutes by using genipin-crosslinked gelatin microspheres

Macroporous calcium phosphate cements (CPCs) were developed using genipin-crosslinked gelatin microspheres (GMs) with two weight ratios (2.5 wt% and 5 wt%). The initial setting time of the composite was prolonged by GMs. After GMs/CPCs were soaked in phosphate-buffered saline (PBS) for several weeks, macropores appeared as a result of the degradation of GMs. The presence of GMs accelerated the setting reaction and improved the structure of the composite. The compressive strength increased up to 12 MPa (2.5 wt% GMs/CPCs) and 14 MPa (5 wt% GMs/CPCs) after one week of PBS soaking, then gradually decreased to 9 MPa (2.5 wt% GMs/CPCs) and 7 MPa (5 wt% GMs/CPCs) after three weeks of soaking, and further to 6 MPa (2.5 wt% GMs/CPCs) and 2 MPa (5 wt% GMs/CPCs) after five weeks of soaking. CPCs with 2.5 wt% GMs were the most favorable composite in the tested samples. Cell experiments showed that rat osteoblasts displayed normal morphologies when exposed to the 2.5 wt% GMs/CPCs, and proliferation of the cells was also enhanced. An in vivo study showed that new bone tissue was able to grow into the pores that resulted from GM degradation. This study suggests that the new composite could be a promising candidate for use as a bone substitute under non-compression-loaded circumstances.

Electron microscopic study on bone formation and bioresorption after implantation of beta-tricalcium phosphate in rabbit models

BACKGROUND

The role of bone formation and bioresorption in an early stage after implantation of beta-tricalcium phosphate (beta-TCP) was investigated using scanning and transmission electron microscopy (SEM, TEM).

METHODS

The ceramic beta-TCP cylinders were implanted into cavities drilled in the femoral condyles of eight NZW rabbits. Four of the rabbits were sacrificed at 2 weeks and four at 4 weeks after implantation, respectively. The femoral condyles were excised to prepare the specimens for SEM and TEM.

RESULTS

SEM showed giant cells of more than 20 mum in diameter were observed on the surface of beta-TCP at 2 weeks after implantation. TEM demonstrated that collagen fibrils secreted from the monocytic cells invaded beta-TCP micropores at 2 weeks. Multinucleated giant cells (MNGCs) were in contact with the surface of beta-TCP at 2 weeks. Some of them had a ruffled border (RB) at the cell-substrate interface, characteristic of osteoclasts.

CONCLUSIONS

These findings suggest that cell-mediated disintegration by osteoclasts played a role in the bioresorption of beta-TCP at an early stage after implantation. In addition, the micropores of beta-TCP ceramic may provide an environment for collagen formation, leading to the deposition of apatite crystals. Therefore, the micropores facilitate bone ingrowth as well as ceramic resorption.

Histological findings of long-term healing of the experimental defects by application of a synthetic biphasic ceramic in rats

Calcium phosphate ceramics are generally biocompatible and can develop interactions with human recipient bone. Therefore, they can be widely used in the field of periodontology and dentistry. The purpose of this investigation was to assess the long-term histological bone healing results of experimentally created critical size parietal bone defects in rats. Twelve Wistar rats were used in this investigation. Two 6-mm wide, symmetrical, and circular critical size defects were created in each parietal bone of the animals. While the right defects filled with granular implant (Ceraform), the symmetrical defects were taken as controls. Eighteen months after implantation, rats were killed and defects including the biomaterial with surrounding bone was taken for histological examination. Serial histological sections were cut across the defects and stained for the histological analysis. Both control and Ceraform implanted regions contained dense collagenous tissue. In the implantation site, multinuclear giant cells were observed around the material. On the other hand, there were no necrosis, tumour, and infection in the implantation region. There was no statistical difference between the control and ceraform implanted groups when the bone formation results were compared (p > 0.05). In conclusion, the results revealed that this material is biocompatible and does enhance the new bone building despite the long-term observation period. Although this biphasic ceramic shows within the limits of the study as a less resorptive and not osteoconductive properties, it can be considered as a biocompatible bone defect filling material having a limited application alternative in dentistry and medicine.

Evaluation of an injectable bone substitute (betaTCP/hydroxyapatite/hydroxy-propyl-methyl-cellulose) in severely osteopenic and aged rats

The use of injectable biomaterials is of interest in osteoporotic patients to locally restore bone mass in sites at risk of fracture. An injectable bone substitute (IBS1 made of betaTCP/hydroxyapatite as a calcium phosphate substitute and hydroxy-propyl-methyl-cellulose as a polymer carrier) was used in a severely osteopenic rat model obtained by combining orchidectomy (ORX) and disuse (paralysis induced by botulinum toxin - BTX). Fifty-six aged male rats were randomized into three groups: 18 were SHAM operated; 38 were ORX and BTX injected in the right hindlimb; they constituted the OP (osteoporotic) group. One month after ORX-BTX surgery, 20 of these OP rats received a IBS1 injection in the right femur (OP-IBS1 rats). Animals were studied at the time of IBS1 injection 1 month post ORX-BTX (M1), 1 month (M2) and 2 months (M3) after IBS1 injection. Bone mass (BV/TV) and microarchitectural parameters were measured by microCT. BV/TV was decreased after ORX-BTX; ORX and BTX had cumulative effects on bone loss (differences maximized on the right femur). BV/TV (combining the volume of both bone and material in OP-IBS1 rats) was elevated at M1 but decreased at M2. Marked bone formation was found onto the biomaterial granules but bone had a woven texture. A marked increase in the number of nonosteoclastic TRAcP+ cells was found in the implanted area. IBS1 induced new bone formation shortly after implantation but both IBS1 and woven bone were resorbed without inducing lamellar bone. Biomaterial trials must be conducted with long-term implantation periods, in aged osteoporotic animals.

First histological observations on the incorporation of a novel nanocrystalline hydroxyapatite paste OSTIM in human cancellous bone

Background:

A commercially available nanocrystalline hydroxyapatite paste Ostim^® has been reported in few recent studies to surpass other synthetic bone substitutes with respect to the observed clinical results. However, the integration of this implantable material has been histologically evaluated only in animal experimental models up to now. This study aimed to evaluate the tissue incorporation of Ostim^® in human cancellous bone after reconstructive bone surgery for trauma.

Methods:

Biopsy specimens from 6 adult patients with a total of 7 tibial, calcaneal or distal radial fractures were obtained at the time of osteosynthesis removal. The median interval from initial operation to tissue sampling was 13 (range 3–15) months. Samples were stained with Masson-Goldner, von Kossa, and toluidine blue. Osteoid volume, trabecular width and bone volume, and cortical porosity were analyzed. Samples were immunolabeled with antibodies against CD68, CD56 and human prolyl 4-hydroxylase to detect macrophages, osteoblasts, and fibroblasts, respectively. TRAP stainings were used to identify osteoclasts.

Results:

Histomorphometric data indicated good regeneration with normal bone turnover: mean osteoid volume was 1.93% of the trabecular bone mass, trabecular bone volume – 28.4%, trabecular width – 225.12 μm, and porosity index – 2.6%. Cortical and spongious bone tissue were well structured. Neither inflammatory reaction, nor osteofibrosis or osteonecrosis were observed. The implanted material was widely absorbed.

Conclusion:

The studied nanocrystalline hydroxyapatite paste showed good tissue incorporation. It is highly biocompatible and appears to be a suitable bone substitute for juxtaarticular comminuted fractures in combination with a stable screw-plate osteosynthesis.

Biocompatibility and degradation of poly(DL-lactic-co-glycolic acid)/calcium phosphate cement composites

Injectable calcium phosphate (Ca-P) cement materials exhibit favorable osteocompatible behavior but are resorbed slowly because of a lack of a bone ingrowth-enabling macroporosity. In this study, poly(DL-lactic-co-glycolic acid) (PLGA) microparticles (average size 66 +/- 25 microm) were incorporated into Ca-P cement to obtain a macroporous Ca-P cement scaffold after PLGA hydrolysis in vivo. Preset PLGA/Ca-P cement composite discs of various weight ratios (0/100, 15/85, 30/70, and 50/50) were implanted subcutaneously and in cranial defects in rats for 12 weeks. Histological analysis revealed that all macropores in the PLGA-containing composites (average pore size 73 +/- 27 microm) were filled with fibrous tissue and blood vessels (subcutaneous implants) and/or bone (cranial implants). Histologically, bone formation appeared most abundant and most consistent in the 30/70 PLGA/Ca-P cement composites. Histomorphometrical evaluation revealed a significant increase in defect fill in the 15/85 and 30/70 PLGA/Ca-P cement composites. Finally, subcutaneous and cranial 50/50 PLGA/Ca-P cement composites had degraded to a large extent, without adequate replacement by bone in the cranial implants. Therefore, we conclude that PLGA/Ca-P cement composites enable tissue ingrowth and show excellent osteocompatibility in weight ratios of 15/85 and 30/70 PLGA/Ca-P cement. In this model, 30/70 PLGA/Ca-P cement composites showed the most favorable biological response.

In vivo biological performance of composites combining micro-macroporous biphasic calcium phosphate granules and fibrin sealant

INTRODUCTION

Fibrin glues are currently used by surgeons and can facilitate the handling of biomaterials. Combining fibrin glue with calcium phosphate bioceramics gives a mouldable composite that cements the granules into the implantation site. In addition to the mechanical aspect of the composite, it has been suggested that the mixture also promotes wound healing. These human blood derivatives contain natural (aprotinin) or synthetic (tranexamic acid) antifibrinolytic substances. We compared the bioactivity of two composites combining calcium phosphate granules with two different types of fibrin glue, one with aprotinin and the other with tranexamic acid.

MATERIALS AND METHODS

The composite was composed of fibrin glue (Tissucol) and 1 to 2 mm granules of biphasic calcium phosphate granules (MBCP) with a volume ratio of 1 for 2. Bone cavities were drilled in 12 New Zealand rabbits and filled with a composite with aprotinin-fibrin glue on the right condyle and one with tranexamic acid-fibrin glue on the left condyle. The rabbits were randomized into two groups: 3 and 6 weeks of delay. Light microscopy, scanning electron microscopy and image analysis were performed.

RESULTS

No adverse reactions were observed in either sample. Bony ingrowth associated with bioceramic resorption by osteoclastic TRAP-positive cells was noted. No significant difference was observed between the two composites. The bony ingrowth and ceramic resorption were qualitatively and quantitatively similar with both composites.

CONCLUSION

This study demonstrated that the choice of a natural (aprotinin) or synthetic (tranexamic acid) antifibrinolytic agent in the fibrin sealant associated with calcium phosphate granules and used as a bone substitute had no effect on the bioactivity of the composite. It remained efficient in bone reconstruction, no adverse effects were observed, and the bony ingrowth was qualitatively and quantitatively equivalent with the two types of fibrin sealant.

MBCP biphasic calcium phosphate granules and tissucol fibrin sealant in rabbit femoral defects: the effect of fibrin on bone ingrowth

An ageing population implies an increase in bone and dental diseases, which are in turn a source of numerous handicaps. These pathologies are an expensive burden for the European health system. As no specific bioactive materials are efficient enough to cope with this burden, we have to develop an injectable, mouldable, self-hardening bone substitute to support bone tissue reconstruction and augmentation. New, highly bioactive and suitable biomaterials have been developed to replace bone grafts in orthopedic revision and maxillofacial surgery for bone augmentation. These mouldable, self-hardening materials are based on the association of MBCP Biphasic Calcium Phosphate Granules and Tissucol Fibrin Sealant. The in vivo evaluation of ingrowth in relation to the composite was made in an experiment on rabbits. The results indicate that in the presence of fibrin sealant, newly-formed bone developed at a small distance from the surface of the calcium phosphate ceramic. Two different bone apposition processes were identified. Without the fibrin component (MBCP group), bone rested directly on the surface of the granules. This observation is commonly described as osteoconduction in calcium phosphate materials. On the contrary, the presence of the fibrinogen component seemed to modify this standard osteoconduction phenomenon: the newly-formed bone essentially grew at a distance from the surface of the granules, on the fibrillar network, and could be considered as an inductive phenomenon for osteogenic cell differentiation from mesenchymal stem cells.

In vivo mechanisms of hydroxyapatite ceramic degradation by osteoclasts: fine structural microscopy

In the present study the in vivo mechanism of calcium-phosphate (CaP) ceramic degradation has been investigated by means of transmission electron microscopy. The results revealed osteoclast-mediated degradation of hydroxyapatite ceramic implanted into sheep bone by simultaneous resorption and phagocytosis. After 6 weeks of implantation, osteoclasts were localized immediately beneath the ceramic surface. They had formed resorption lacunae and exhibited typical ultrastructural features, such as the ruffled border, the clear zone, and the dorsal microvilli. Their resorption capacity also had become evident by alterations of the electron density and the shape of the CaP crystals localized within the acidic microenvironment of the ruffled border. Moreover, the osteoclasts simultaneously were capable of phagocytosing the resorbed CaP crystals. The formation of endophagosomes was performed (1) by the uptake of particles into large intracellular vacuoles, which were generated by deep invagination of the membranes of the osteoclastic ruffled border, and (2) by the encircling of particles due to the development of pseudopodia-like plasmaprotrusions of the ruffled border. The formation of endophagosomes was followed by the in situ fragmentation of the inclusion material, which subsequently was released into the extracellular space and phagocytosed by macrophages.

Effects of topography and composition of titanium surface oxides on osteoblast responses

To investigate the roles of composition and characteristics of titanium surface oxides in cellular behaviour of osteoblasts, the surface oxides of titanium were modified in composition and topography by anodic oxidation in two kinds of electrolytes, (a) 0.2 M H(3)PO(4), and (b) 0.03 M calcium glycerophosphate (Ca-GP) and 0.15 M calcium acetate (CA), respectively. Phosphorus (P: ca.10at%) or both calcium (Ca: 1-6at%) and phosphorus (P: 3-6at%) were incorporated into the anodized surfaces in the form of phosphate and calcium phosphate. Surface roughness was slightly decreased or enhanced (R(a) in the range of 0.1-0.5 microm) on the anodized surfaces. The geometry of the micro-pores in the anodized surfaces varied with diameters up to 0.5 microm in 0.2 M H(3)PO(4) and to 2 microm in 0.03 M Ca-GP and 0.15 M CA, depending on voltages and electrolyte. Contact angles of all the anodic oxides were in the range of 60-90 degrees. Cell culture experiments demonstrated absence of cytotoxicity and an increase of osteoblast adhesion and proliferation by the anodic oxides. Cells on the surfaces with micro-pores showed an irregular and polygonal growth and more lamellipodia, while osteoblasts on the titanium surface used as a control or on anodic oxides formed at low voltages showed many thick stress fibres and intense focal contacts. Alkaline phosphatase (ALP) activity of the cells did not show any correlation with surface characteristics of anodic oxides.

Small-animal models for testing macroporous ceramic bone substitutes

The aim of this study was to compare the bone colonization of a macroporous biphasic calcium phosphate (MBCP) ceramic in different sites (femur, tibia, and calvaria) in two animal species (rats and rabbits). A critical size defect model was used in all cases with implantation for 21 days. Bone colonization in the empty and MBCP-filled defects was measured with the use of backscattered electron microscopy (BSEM). In the empty cavities, bone healing remained on the edges, and did not bridge the critical size defects. Bone growth was observed in all the implantation sites in rats (approximately 13.6-36.6% of the total defect area, with ceramic ranging from 46.1 to 51.9%). The bone colonization appeared statistically higher in the femur of rabbits (48.5%) than in the tibia (12.6%) and calvaria (22.9%) sites. This slightly higher degree of bone healing was related to differences in the bone architecture of the implantation sites. Concerning the comparison between animal species, bone colonization appeared greater in rabbits than in rats for the femoral site (48.5% vs. 29.6%). For the other two sites (the tibia and calvaria), there was no statistically significant difference. The increased bone ingrowth observed in rabbit femurs might be due to the large bone surface area in contact with the MBCP ceramics. The femoral epiphysis of rabbits is therefore a favorable model for testing the bone-bonding capacity of materials, but a comparison with other implantation sites is subject to bias. This study shows that well-conducted and fully validated models with the use of small animals are essential in the development of new bone substitutes.

Evaluation of a resorbable,in situ setting bone substitute in a sheep model

The gold standard for bone substitution is the autologous bone graft, but because of its limited supply and the associated morbidity, the search for synthetic alternatives is necessary. A new in situ setting tricalcium phosphate cement was implanted in a trepanation defect (9.4 mm diameter, 10 mm depth) in the distal femoral epiphysis of sheep. Empty cavities and autologous bone graft were used as controls. Histologic and histomorphometric examinations were carried out after 12 weeks. Nearly 90% of the implanted cement was resorbed and replaced by ingrown bone with close contact between surrounding bone, new bone, and remaining cement particles. The amount of bone in the defect area was significantly higher in defects filled with cement relative to defects filled with autologous bone graft (mean 27 vs. 21%, 95% confidence intervals 23 to 31 and 18 to 23, p = 0.026). In conclusion, this new in situ setting cement is bioactive, resorbable, and osteoconductive. It will be useful as an alternative to autologous bone graft to fill stable defects.

Calcium-deficient apatite: a first in vivo study concerning bone ingrowth

Biphasic calcium phosphate (BCP) materials are increasingly used to restore bone loss in surgery. Calcium-deficient apatites (CDA), the precursors of BCP, are closer in structure to biological apatites and can be associated with therapeutic agents to form drug-delivery systems. The purpose of this first in vivo study of CDA was to evaluate the osteoconductive properties of two composites, consisting of 40-80 microm granules carried by a cellulose-derived polymer, used to fill critical size bone defects in rabbit femoral ends. Animals were sacrificed 2 or 3 weeks after implantation. Histomorphometric analysis of scanning electron microscopy implant surface files was performed using gray level threshold that distinguish between bone or materials (white) and noncalcified tissue (black). Quantitative results for new bone formation showed no significant differences between the composites or the implantation periods. However, nearly all of the CDA disappeared early while supporting more extensive bone colonization than biphasic calcium phosphates implanted in the same conditions.

Tissue responses to nacreous implants in rat femur: an in situ hybridization and histochemical study

The interface of bone and aragonite nacre (Margaritifera, fresh water pearl mussel) was studied by in situ hybridization and a tartrate-resistant acid phosphatase (TRAP) histochemical assay. Columnar implants were inserted into rat femora for 4, 7, 14, 28 and 56 days. In medullary region, a burst of transient bone formation was observed, which propagated from the periphery towards the nacre implant. A fused interface of bone and nacre was observed at 14 days. Later, the new medullary bone was resorbed and bone marrow was re-established while a thin layer of bone tissue remained covering the implant surface. Expressions of collagen alpha1(I), osteocalcin, osteopontin mRNAs and TRAP in the surrounding tissue were monitored. Correlated with the histology events, a strong transient induction of collagen alpha1(I) and osteocalcin mRNAs as well as TRAP expression, exhibiting a peak signal intensity on day 7 and subsequent down-regulation after day 14 was observed. Osteopontin mRNA, in contrast, was expressed continuously. The degrading nacre surface appeared in direct contact with macrophages and multinucleated giant cells at both days 14 and 28. These cells expressed osteopontin mRNA intensively and some TRAP enzyme activity occasionally.

A synthetic porous ceramic as a bone graft substitute in the surgical management of scoliosis: a prospective, randomized study

STUDY DESIGN

A prospective randomized study.

OBJECTIVES

To assess the clinical and radiologic performances of a synthetic ceramic as a bone graft substitute in scoliosis surgery.

SUMMARY OF BACKGROUND DATA

Surgery on the skeleton frequently requires harvesting of autogenous bone grafts from the pelvis, but this procedure often is complicated by problems.

METHODS

Fifty-eight patients with idiopathic scoliosis, ages 13 to 25 years, were treated by posterior correction and arthrodesis using Cotrel-Dubousset instrumentation. Posterior spinal fusion was performed using local bone grafts combined with autogenous iliac bone grafts in 30 patients, and combined with porous biphasic calcium phosphate ceramic blocks comprising hydroxyapatite and tricalcium phosphate in another 28 patients. The patients were observed for a minimum of 24 months after surgery, with a mean postoperative observation time of 48 months. The results were assessed clinically and radiographically.

RESULTS

Patients in the ceramic group had a lower average blood loss than those in the iliac graft group. They also were free from postoperative local complications in the iliac region, which were experienced by a significantly high proportion of patients belonging to the iliac graft group. Radiography demonstrated successful incorporation of the ceramic blocks within 12 months. The correction of the deformity was maintained similarly and satisfactorily in both groups.

CONCLUSIONS

These results justify and favor the use of calcium phosphate ceramics as bone graft substitutes for instrumented posterior spinal fusion in teenagers and young adults. Potentially hazardous harvesting of pelvic bone is no longer necessary for such operations.

Kinetic study of bone ingrowth and ceramic resorption associated with the implantation of different injectable calcium-phosphate bone substitutes

This study investigated the in vivo performance of two composite injectable bone substitutes (IBS), each with different calcium-phosphate particles granulometries [40-80 (IBS 40-80) and 200-500 microm (IBS 200-500)]. These biomaterials were obtained by associating a biphasic calcium-phosphate (BCP) ceramic mineral phase with a 3% aqueous solution of a cellulosic polymer (hydroxy-propyl-methyl-cellulose). Both materials were injected for periods of 2, 3, 8, or 12 weeks into bone defects at the distal end of rabbit femurs. Quantitative results on new bone formation, BCP resorption, and staining for tartrate-resistant acid phosphatase (TRAP) activity were studied for statistical purposes. Measurements with scanning electron microscopy and image analysis showed that the final rates of newly formed bone were similar for both tested IBS after 12 weeks of implantation. Bone colonization occurred more extensively during early implantation times for IBS 40-80 than for IBS 200-500. For the latter, BCP degradation occurred regularly throughout the implantation period, whereas it was very intensive during the first 2 weeks for IBS 40-80. Positive TRAP-stained degradation cells were significantly more numerous for IBS 40-80 than for IBS 200-500 regardless of implantation time. With the granulometry of either mineral phase, both tested IBS supported extensive bone colonization, which was greater than that previously reported for an equivalent block of macroporous BCP. The resorption-bone substitution process seemed to occur earlier and faster for IBS 40-80 than for IBS 200-500. Both tested IBS expressed similar biological efficiency, with conserved in vivo bioactivity and bone-filling ability.

Interaction of a plasma-sprayed hydroxyapatite coating in contact with human osteoblasts and culture medium

The loss of calcium from plasma-sprayed calcium phosphate ceramics (CPCs) on bioinert metal substrate (Ti-6Al-4V) immersed in cell culture medium with or without human osteoblast culture was measured. The ceramics were a CPC and a duplex system composed of a CPC layer on an alumina coating. The dissolution of calcium compounds was monitored by measuring the calcium leaked from the coatings into the culture medium in 15 days. Calcium was measured by flame photometry. The surfaces of the ceramics exposed to the culture medium and in contact with osteoblasts were analysed by X-ray diffraction (XRD). The dissolution process occurred in the first 6 days of contact, but the calcium released into the culture medium was only a small fraction of the calcium content of the coatings. The presence or absence of osteoblasts on the surface of the ceramics did not make significant difference for the calcium release. The XRD spectra of the ceramics before and after immersion and in contact with cells did not show a significant change in the compounds of the coatings.

Short-term effects of mineral particle sizes on cellular degradation activity after implantation of injectable calcium phosphate biomaterials and the consequences for bone substitution

This in vivo study investigated the influence of two calcium phosphate particle sizes (40-80 microm and 200-500 microm) on the cellular degradation activity associated with the bone substitution process of two injectable bone substitutes (IBS). The tested biomaterials were obtained by associating a biphasic calcium phosphate (BCP) ceramic mineral phase and a 3% aqueous solution of a cellulosic polymer (hydroxypropylmethylcellulose). Both were injected into osseous defects at the distal end of rabbit femurs for 2- and 3-week periods. Quantitative results for tartrate-resistant acid phosphatase (TRAP) cellular activity, new bone formation, and ceramic resorption were studied for statistical purposes. Positive TRAP-stained degradation cells were significantly more numerous for IBS 40-80 than IBS 200-500, regardless of implantation time. BCP degradation was quite marked during the first 2 weeks for IBS 40-80, and bone colonization occurred more extensively for IBS 40-80 than for IBS 200-500. The resorption-bone substitution process occurred earlier and faster for IBS 40-80 than IBS 200-500. Both tested IBS displayed similar biological efficiency, with conserved in vivo bioactivity and bone-filling ability. Differences in calcium phosphate particle sizes influenced cellular degradation activity and ceramic resorption but were compatible with efficient bone substitution.

Role of the osteoclast at the bone-implant interface

A thorough understanding of the processes of healing, repair, and remodeling of bone is critical for the establishment and maintenance of osseointegration of dental implants. In this regard, much attention has been paid to the anabolic aspects of bone remodeling, including the cell biology of the osteoblast and the various cytokines and growth factors which regulate these processes. In contrast, there is little information on the bone-resorptive activity that occurs around implants during osseointegration, and of the role of osteoclasts, macrophages, and stromal cells in those catabolic processes associated with bone remodeling. This paper reviews osteoclast cell biology, the interaction of osteoclasts and biomaterials, and the information available on osteoclasts and dental implants, and poses some questions for future research.

A new injectable calcium phosphate biomaterial for immediate bone filling of extraction sockets: a preliminary study in dogs

BACKGROUND

Many different bone substitutes, such as autografts, allografts or synthetic biomaterials have been proposed to restore alveolar bone loss and support efficient placement of dental implants. This experimental study evaluated the osteoconductive properties of an injectable bone substitute (IBS) composed of a polymeric carrier and a calcium phosphate mineral phase, used to fill mandibular and maxillary canine extraction sockets.

METHODS

The polymer was a cellulose derivative (methyl-hydroxy-propyl-cellulose, MHPC), and the mineral phase consisted of granules of biphasic calcium phosphate (BCP) ceramics 200 to 500 microm in diameter. Mandibular and maxillary premolars extracted from 3 dogs (a total of 60 extraction sites) were immediately treated with the IBS or left unfilled as control sites. Animals were sacrificed 3 months after implantation and all extraction sockets were prepared for histological evaluation.

RESULTS

Qualitative histological studies showed that the IBS was able to support the extensive apposition of well-mineralized newly formed lamellar bone over the entire socket surface and appeared to prevent alveolar ridge bone loss in treated extraction sites. Quantitative evaluation showed that the amount of newly formed bone was significantly higher in mandibular than maxillary extraction sockets for both treated and control sites.

CONCLUSIONS

An injectable bone substitute composed of a polymeric carrier and calcium phosphate was effective in enhancing the bone fill of extraction sockets. This approach may prove promising for periodontal lesions. The material expressed osteoconductive capacities, and the biological properties of the mineral phase were conserved.