Hydroxyapatite Β-tricalcium Phosphate Research Articles

Comparison of the osseointegration of implants placed in areas grafted with HA/TCP and native bone.

This study evaluated the osseointegration of implants in areas grafted with biphasic ceramic based on hydroxyapatite/β-tricalcium phosphate (HA/TCP) and in native bone (NB). Twenty-eight rats were randomly assigned into two groups of 14 animals each: HA/TCP group: implants installed in areas grafted with HA/TCP and NB group: implants installed in areas of native bone. Bone defects were made in both tibiae of the rats belonging to the HA/TCP group and then filled with this bone substitute. After 60 days, the rats were submitted to surgical procedures for implant placement in grafted areas in both tibiae in the HA/TCP group while the implants were installed directly in native bone in the NB group. The animals were euthanized 15 and 45 days, respectively, after the implant placement. Biomechanical (removal torque), microtomographic (volume of mineralized tissues around the implants), and histomorphometric (Bone-Implant contact-%BIC and bone area between the implant threads-%BBT) analyzes were conducted to assess the osseointegration process. The HA/TCP group showed lower values of removal torque, volume of mineralized tissue around the implants, lower %BIC, and %BBT compared to the NB group in both experimental periods. Osseointegration of implants placed in grafted areas with HA/TCP was lower compared to the osseointegration observed in native bone areas. RESEARCH HIGHLIGHTS: The areas grated with HA/TCP presented poor biological conditions. The reduced biological properties for bone formation impaired the osseointegration in HA/TCP grafted areas.

Bone formation around two titanium implant surfaces placed in bone defects with and without a bone substitute material: A histological, histomorphometric, and micro-computed tomography evaluation.

To evaluate the histological and microtomographic response of peri-implant bone tissue around titanium implants with different surface treatments, placed in bone defects filled or not filled with bone substitute materials. Thirty rabbits were divided into two groups according to the implant surface treatment. A bone defect was created in both tibias of all the rabbits, followed by the placement of one implant in each of these defects. On the left tibia, the defect was filled with a blood clot (BC), and on the right tibia, the defect was filled with biphasic hydroxyapatite/β-tricalcium-phosphate (HA/TCP); thus, there were four groups in total: BC-N: bone defect filled with a BC and porous surface titanium implant (control group); BC-A: bone defect filled with a BC and porous-hydrophilic surface titanium implant; HA/TCP-N: bone defect filled with a bone substitute material and porous surface titanium implant; HA/TCP-A: bone defect filled with a bone substitute material and porous-hydrophilic surface titanium implant. The animals were submitted for euthanasia at three distinct periods: 15, 30, and 60 days after implant installation. The samples were evaluated histologically and histometrically, to assess the quantity and quality of cells and the remaining bone substitute material in the grafted areas. The bone quantity was assessed by micro-computed tomography (CT). For both surface types, the presence of a bone substitute material led to higher values in all evaluated micro-CT parameters, except in the bone surface/volume ratio parameter. No significant statistical difference was found for new bone formation between the four groups (P < .05; CI 95%). At all periods, the HA/TCP-A group had a higher percentage of new bone formation. These results suggest that a porous hydrophilic surface in the presence of bone substitute material can accelerate peri-implant bone tissue formation.

Bone tissue formation around two titanium implant surfaces placed in bone defects filled with bone substitute material or blood clot: A pilot study.

The objective of this study was to evaluate the peri-implant bone tissue formation around titanium implants with different surface treatments, placed in bone defects filled or not with bone substitute material (BSM). Ten animals were divided into two groups according to implant surface treatment. In each tibia, a bone defect was created followed by the placement of one implant. On the left tibia, the defect was filled with blood clot (BC), and on the right tibia, the defect was filled with biphasic hydroxyapatite/β-tricalcium-phosphate (HA/TCP) generating four subgroups: BC-N: blood clot and porous surface; BC-A: blood clot and porous-hydrophilic surface; HA/TCP-N: BSM and porous surface; HA/TCP-A: BSM and porous-hydrophilic surface. The animals were submitted to euthanasia 60 days after implant installation. After light-curing resin inclusion, the blocks containing the implant and the bone tissue were stained and evaluated by means of histomorphometry to assess the percentages of bone implant contact (% BIC). Data was normally distributed and the group differences were examined using the parametric tests of Two-Way ANOVA. The BC-A group presented the higher mean value of BIC (46.43%). The HA/TCP-A group presented the higher mean value of BIC. The porous-hydrophilic surfaces presented better results of BIC when compared to the porous surface in both conditions of defect filling. No statistically significant differences were found among all groups (95% confidence interval and P < .05). According to histomorphometric analysis, after 60-days in a rabbit model, hydrophilic and hydrophobic surfaces have the same behavior in the presence or absence of HA/TCP.

Comparison of the Efficacy of Three Different Bone Regeneration Materials: An Animal Study.

Objective The proposed study aimed to evaluate and compare the bone regeneration between commercially available hydroxyapatite–β-tricalcium phosphate (Ossifi; Equinox, the Netherlands), powdered polylactic acid (powdered PLA; Sigma-Aldrich, United States), and three-dimensionally printed PLA (3D-printed PLA; Cubex, SC, United States) using 3D printer (Cube X trio) in an animal model. Materials and Methods Eighteen New Zealand rabbits were divided into three groups with six animals each. Platelet-rich fibrin (PRF) was collected from the venous blood and preserved. Bone defect (4 mm × 2 mm) without disturbing the bone marrow was created and filled with bone graft material (group 1–Ossifi, group 2–powdered PLA, and group 3–3D-printed PLA), over which PRF membranes were placed. The graft material and the barrier were stabilized using resorbable sutures, and all the animals were maintained for 4, 8, and 12 weeks, after which they were euthanized, and bone samples were retrieved. Retrieved bone samples were subjected to radiological and histological analysis. Results The radiographic and histological changes of 3D-printed PLA in comparison with other two materials (Ossifi and powdered PLA) seemed to have a significant difference. Conclusion 3D-printed PLA scaffolds showed positive signs of bone regeneration around the material in continuity defects. PLA material can be a promising alternative bone regenerative material.

Orthodontic extraction space closure with and without socket preservation: a comparative case analysis.

Preorthodontic socket preservation after tooth extraction is intended to enhance favorable dentoalveolar ridge morphology and architecture, and facilitate orthodontic tooth movement (OTM) and extraction space closure. This 13-year-old skeletal Class II case presents a unique opportunity to evaluate and compare the OTM extraction space closure by means of a split-mouth analysis in a single patient. The comprehensive orthodontic-periodontal treatment included nonsimultaneous extraction of the bilateral periodontally compromised mandibular first molars and the eruption of bilateral impacted mandibular canines. While the right post-extraction space underwent a natural healing process, the left one was grafted using 4BONE BCH (hydroxyapatite β-tricalcium phosphate [HA-β-TCP], HA 60%, and β-TCP 40%). The 3-year multidisciplinary treatment approach resulted in Class I relationships on the right side and Class II on the left side, improved facial appearance, and dento-skeletal jaw relationships. However, a 3-mm residual alveolar space remained unclosed on the grafted left-site, along with an unerupted left third molar. This split-mouth comparative analysis of the orthodontic space closure demonstrated a significant clinical difference in the outcome. Preorthodontic placement of HA-β-TCP grafting material on the left segment, proved to be an obstacle for OTM extraction space closure, hindering the establishment of good occlusion.

Analysis of osseointegration of implants with hydrophilic surfaces in grafted areas: A Preclinical study.

The aim of this study was to evaluate the effect of a hydrophilic surface on the osseointegration in grafted areas with deproteinized bovine bone (DBB) and with biphasic ceramics of hydroxyapatite/β-tricalcium phosphate (HA/TCP). Fifty-six rats were randomly allocated to four groups with 14 animals each: DBB: DBB+Machined surface; HA/TCP: HA/TCP+Machined surface; DBB-H: DBB+Hydrophilic surface; HA/TCP-H: HA/TCP+Hydrophilic surface. The bone defects were performed at the proximal epiphysis of the tibia. Then, the defects were filled with the biomaterials. After 60days, the implants were placed in the grafted areas. The animals were submitted to euthanasia at periods of 15 and 45days after the implants' placement. The osseointegration was assessed by biomechanical, microtomographic, and histometric analyses. In addition, the expression of bone morphogenetic protein-2 (BMP-2), alkaline phosphatase (ALP), and osteocalcin (OCN) was evaluated by immunohistochemistry. The HA/TCP-H group presented higher removal torque values and more mineralized tissue in the vicinity of the implants compared with the HA/TCP group. The DBB-H and HA/TCP-H groups presented higher values of bone-implant contact (at 15 and 45days), of bone between the threads (45days), and expression of BMP-2 (45days) than the DBB and HA/TCP groups. Furthermore, the DBB-H group presented a higher expression of ALP than the DBB group (15days). In conclusion, implants with a hydrophilic surface improve osseointegration in grafted areas compared to implants with machined surfaces in a rat tibia model.

Dickkopf-related protein 3 negatively regulates the osteogenic differentiation of rat dental follicle cells.

The present study aimed to investigate the effect of Dickkopf-related protein 3 (DKK3) on osteogenic differentiation of rat dental follicle cells (DFCs). A PCR array analysis of Wnt pathway activation in DFCs identified genes dysregulated by mineral induction. Among them, DKK3expression levels were decreased, and further experiments were conducted to investigate its role in DFC osteogenesis. By comparing DFCs grown in normal growth and mineral-induction media for 4 weeks, the present study confirmed that DKK3 was a potential target gene of osteogenesis through reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blotting (WB). A short hairpin RNA (shRNA) was introduced into DFCs using a lentiviral vector to inhibit DKK3 expression. An alkaline phosphatase (ALP) activity assay and Alizarin Red staining were performed to observe the DKK3-shRNA DFCs. In addition, the osteogenic differentiation of DKK3-shRNA DFCs was analyzed by RT-qPCR and WB. In vivo, DKK3-shRNA DFCs seeded on hydroxyapatite/β-tricalcium phosphate (HA/TCP) scaffolds were transplanted into the subcutaneous tissue of mice with severe combined immunodeficiency, followed by hematoxylin-eosin and Masson staining. The results confirmed that DKK3 expression was downregulated during mineral induction in rat DFCs. Lentivirus-mediated expression of DKK3 shRNA in DFCs promoted calcified-nodule formation, ALP activity and the expression of β-catenin, runt-related transcription factor 2 and osteocalcin, compared with control cells. In vivo, the implanted section presented the majority of newly formed osteoid matrices and collagen, with limited space between the HA/TCP scaffolds and matrices. In conclusion, DKK3 expression negatively regulates the osteogenic differentiation of DFCs and, conversely, downregulation of DKK3 may enhance DFC osteogenesis.

Synergistic effect of nanomaterials and BMP-2 signalling in inducing osteogenic differentiation of adipose tissue-derived mesenchymal stem cells

The lack of complete understanding in the signalling pathways that control the osteogenic differentiation of mesenchymal stem cells hinders their clinical application in the reconstruction of large bone defects and non-union bone fractures. The aim of this study is to gain insight into the interactions of bone morphogenetic protein-2 (BMP-2) and bone biomimetic scaffolds in directing osteogenic differentiation of adipose tissue-derived mesenchymal stem cells (ASCs) and the underlying signalling pathways involved. We demonstrated that bioactive glass nanoparticles (nBG) incorporated polycaprolactone (PCL) coating on hydroxyapatite/β-tricalcium phosphate (HA/TCP) scaffold exerted a synergistic effect with 3days of BMP-2 treatment in promoting osteogenic gene expression levels (Runx-2, collagen I, osteopontin and bone sialoprotein) and alkaline phosphatase activity in ASCs. Furthermore, we revealed that the synergistic effect was mediated through a mechanism of activating β1-integrin and induction of Wnt-3a autocrine signalling pathways by nBG incorporated scaffold. From the Clinical EditorThe aim of this study was to gain insight into the interactions of bone morphogenetic protein-2 and bone biomimetic scaffolds in directing osteogenic differentiation of adipose tissue-derived mesenchymal stem cells and the underlying signaling pathways involved.

Biomaterial scaffolds in cartilage–subchondral bone defects influencing the repair of autologous articular cartilage transplants

The repair of articular cartilage typically involves the repair of cartilage-subchondral bone tissue defects. Although various bioactive materials have been used to repair bone defects, how these bioactive materials in subchondral bone defects influence the repair of autologous cartilage transplant remains unclear. The aim of this study was to investigate the effects of different subchondral biomaterial scaffolds on the repair of autologous cartilage transplant in a sheep model. Cylindrical cartilage-subchondral bone defects were created in the right femoral knee joint of each sheep. The subchondral bone defects were implanted with hydroxyapatite-β-tricalcium phosphate (HA-TCP), poly lactic-glycolic acid (PLGA)-HA-TCP dual-layered composite scaffolds (PLGA/HA-TCP scaffolds), or autologous bone chips. The autologous cartilage layer was placed on top of the subchondral materials. After 3 months, the effect of different subchondral scaffolds on the repair of autologous cartilage transplant was systematically studied by investigating the mechanical strength, structural integration, and histological responses. The results showed that the transplanted cartilage layer supported by HA-TCP scaffolds had better structural integration and higher mechanical strength than that supported by PLGA/HA-TCP scaffolds. Furthermore, HA-TCP-supported cartilage showed higher expression of acid mucosubstances and glycol-amino-glycan contents than that supported by PLGA/HA-TCP scaffolds. Our results suggested that the physicochemical properties, including the inherent mechanical strength and material chemistry of the scaffolds, play important roles in influencing the repair of autologous cartilage transplants. The study may provide useful information for the design and selection of proper subchondral biomaterials to support the repair of both subchondral bone and cartilage defects.

A comparison between the efficacy of Bio-Oss, hydroxyapatite tricalcium phosphate and combination of mesenchymal stem cells in inducing bone regeneration

Recently, tissue engineering has been introduced as a regenerative treatment for bone defects. There is some evidence showing bone regeneration from mesenchymal stem cells (MSC) loaded on hydroxyapatite β-tricalcium phosphate (HA/TCP) as a scaffold in large defects. This study aimed to compare the quality and quantity of regenerated bone using Bio-Oss, HA/TCP and MSC loaded HA/TCP scaffolds. Mesenchymal stem cells were aspirated from iliac crest bone marrow after extracting the first, second and third premolars and the first molar in five mature hybrid dogs. The cells were cultured and their osteogenic differentiation potential was evaluated after the third cell passage using Alizarin red staining in experimental conditions. The HA/TCP scaffold (3 × 3 × 3 mm) was loaded with undifferentiated mesenchymal stem cells. Bilateral bone defects were then prepared in the jaws using trephine burs. The defects were randomly filled with HA/TCP, Bio-Oss, or HA/TCP + MSCs. One defect served as a control and was left as an empty cavity. All defects except the control defect were covered with an absorbable membrane. Histological and histomorphometric evaluations were conducted after 6 weeks and data were subjected to analysis of variance (ANOVA) (p < 0.05). The empty cavity demonstrated more bone formation (60.80%) than the HA/TCP (44.93%) and Bio-Oss (40.60%) (p < 0.05) groups. However, the difference from the HA/TCP + MSCs group was not significant (46.38%) (p > 0.05). An MSC-loaded HA/TCP scaffold is a more effective alternative than Bio-OSS or HA/TCP in inducing bone regeneration.

The effect of Emdogain® and platelet-derived growth factor on the osteoinductive potential of hydroxyapatite tricalcium phosphate

The aim of this study was to determine whether hydroxyapatite β-tricalcium phosphate (HA-TCP) either alone or coated with Emdogain (EMD) or recombinant human platelet-derived growth factor-BB (rhPDGF-BB) becomes osteoinductive in the murine thigh muscle model for osteoinduction. Twenty CD1 adult male mice had gelatin capsules implanted into the thigh muscle of both hind limbs. The capsules were either empty or contained one of the following: uncoated particulate HA-TCP, EMD-coated HA-TCP or rhPDGF-BB-coated HA-TCP. The implant sites were assessed histologically at 4 and 8 weeks. A semi-quantitative histological examination was performed to assess the inflammatory changes, reparative processes and osteoinduction within the graft site. At both 4 and 8 weeks, histological analysis failed to demonstrate any osteoinductive activity in any of the specimens from the experimental groups. A minimal chronic inflammatory response and foreign body reaction around the implanted materials was seen which reduced over time. The HA-TCP particles were embedded within fibrous connective tissue and were encapsulated by a dense cellular layer consisting of active fibroblasts and occasional macrophages with the thickness of this layer decreasing over time. The results of this study suggest that the use of commercially available HA-TCP alone or in combination with EMD or rhPDGF-BB is biocompatible but not osteoinductive in the murine thigh muscle model of osteoinduction. Coating HA-TCP with EMD or rhPDGF-BB does not enhance its osteoinductive potential.

Investigation of postnatal stem cells from canine dental tissue and bone marrow

Purpose: The aim of this study was to evaluate the stemness of cells from canine dental tissues and bone marrow. Methods: Canine periodontal ligament stem cells (PDLSC), alveolar bone stem cells (ABSC) and bone marrow stem cells(BMSC) were isolated and cultured. Cell differentiations (osteogenic, adipogenic and chondrogenic) and surface antigens (CD146, STRO-1, CD44, CD90, CD45, CD34) were evaluated in vitro. The cells were transplanted into the subcutaneous space of nude mice to assess capacity for ectopic bone formation at 8 weeks after implantation. Results: PDLSC, ABSC and BMSC differentiated into osteoblasts, adipocytes and chondrocytes under defined condition. The cells expressed the mesenchymal stem cell markers differently. When transplanted into athymic nude mice, these three kinds of cells with hydroxyapatite / β - tricalcium phosphate (HA/TCP) carrier showed ectopic bone formation. Conclusions: This study demonstrated that canine dental stem cells have stemness like bone marrow stem cells. Transplantation of these cells might be used as a therapeutic approach for dental stem cell-mediated periodontal tissue regeneration. (J Korean Acad Periodontol 2009;39:119-128)

Synthesis and characterization of calcium phosphate/collagen biocomposites doped with Zn2+

Composites were developed using calcium phosphate (CaP)/collagen (COL) doped with Zn+2 to attempt the materials association with adequate properties for biological applications in the recovery of the bone tissue by trauma or pathogenies. Hydroxyapatite (HAP) and hydroxyapatite-βtricalcium phosphate (HAPβTCP) were synthesized and doped with zinc nitrate. High purity grade type I collagen was extracted and purified from bovine pericardium. CaP doped and undoped with Zn+2 were produced with COL and the composites were developed using a simple mixture process. All samples were characterized by Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction analysis (XRD. In addition, biocompatibility and cell viability were assessed by MTT assay (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide) using osteoblast cell culture. The results have indicated that both morphological and structural features and chemical composition of the composites were very similar to their precursors, collagen and calcium phosphate components. Also, the biocomposites presented a homogeneous aspect with the calcium phosphate particles aggregated to the collagen fibers. The biological evaluation of the composites in vitro showed cellular viability, presenting proliferation of the osteoblasts compared to the control cells (P<0.05). The composites showed appropriate physical and biological properties creating more biologically active scaffolds that may support bone growth. Therefore, the novel developed biocomposites have high potential to be used for rebuilding small lesions in bone tissue engineering.

A comparative study of biphasic calcium phosphate ceramics for human mesenchymal stem-cell-induced bone formation

For the repair of bone defects, a tissue engineering approach would be to combine cells capable of osteogenic (i.e. bone-forming) activity with an appropriate scaffolding material to stimulate bone regeneration and repair. Human mesenchymal stem cells (hMSCs), when combined with hydroxyapatite/ β-tricalcium phosphate (HA/TCP) ceramic scaffolds of the composition 60% HA/40% TCP (in weight %), have been shown to induce bone formation in large, long bone defects. However, full repair or function of the long bone could be limited due to the poor remodeling of the HA/TCP material. We conducted a study designed to determine the optimum ratio of HA to TCP that promoted hMSC induced bone formation yet be fully degradable. In a mouse ectopic model, by altering the composition of HA/TCP to 20% HA/80% TCP, hMSC bone induction occurred at the fastest rate in vivo over the other formulations of the more stable 100% HA, HA/TCP (76/24, 63/37, 56/44), and the fully degradable, 100% TCP. In vitro studies also demonstrated that 20/80 HA/TCP stimulated the osteogenic differentiation of hMSCs as determined by the expression of osteocalcin.

Development and In Vivo Test of Sol-Gel Derived Bone Grafting Materials

A novel bioceramic derived via sol gel method was developed and very good resorption properties in long term period of implantation were established. Calcium phosphate materials are bioactive, osteoconductive materials used as guides for bone regeneration. An identical sequence of events apparently occurred at the contact of the ceramics when implanted in vivo. Two kinds of calcium phosphate ceramics have been produced in a form of threads with 1 mm in diameter: hydroxyapatite SiO2-containing ceramic and hydroxyapatite—β-tricalcium phosphate SiO2-containing ceramic. Above mentioned calcium phosphate ceramic established an interconnecting macroporous structure, which is responsible for growth of bone and for replacement of ceramic by bone. Three ranges of pores were designed. Viscosity measurements were made to control the point of gelation and production phase of transplant material. In vivo experiments were carried out for 5 weeks and 8 months. The results after the short period of examination have shown the early stage of bone formation and material dissolution. Within 6 months nearly 100% of implanted ceramic was resorpted and new bone around place of intervention was formed.

Effects of hydroxyapatite particulate debris on the production of cytokines and proteases in human fibroblasts

Cytokines and proteases are secreted by fibroblasts in response to particulate wear debris, and these proteins are felt to play an important role in the development of osteolysis and implant loosening. Although metallic and polyethlyene debris have been studied extensively, little is known about the cellular responses to hydroxyapatite, despite the wide clinical use of these materials. Therefore, the effects of hydroxyapatite (HA) and hydroxyapatite/β-tricalciumphosphate (HA/TCP) on cellular proliferation, cytokine gene expression and protein secretion, protease synthesis, and gelatinolytic activity were investigated in human fibroblasts. HA and HA/TCP particles were synthesized, and their effects were compared to the responses elicited by titanium and cobalt chromium. Sample characterization by scanning electron microscopy and Coulter Counter demonstrated that the materials had a mean particle size of less than 10 μm, and all of the particles were compared using the same concentration ranges. Aliquots of particle suspensions were added to human fibroblasts maintained in tissue culture, and dose–response and time-course experiments were performed. Effects of the particles on fibroblast proliferation were assessed, and alterations in cytokine levels were determined by specific enzyme linked immunosorbent assays (ELISA). Cytokines that were evaluated included interleukin-1 (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α), all of which have been demonstrated to enhance bone resorption and are associated with osteolysis and implant loosening. Gene expression was determined using Northern blot analysis with cytokine-specific probes, while secretion of the proteases collagenase and stromelysin was determined by Western blot analysis. Functional gelatinolytic assay was assessed using zymogram gels. The particles were evaluated in a concentration range from 0.000021 to 0.021 vol%. All of the particles produced increases in cellular proliferation up to 0.0021 vol%, with the largest increases being seen at 0.021 vol% with HA/TCP and titanium. At the highest concentration, both cobalt chromium and HA samples decreased cellular proliferation relative to lower doses, possibly representing cytotoxicity. Hydroxyapatite particles yielded a 30-fold increase in interleukin-6 secretion compared to unstimulated controls, which was also greater than three times the levels produced by cobalt chromium, titanium, or HA/TCP. HA particles also tripled the secretion of IL-1β at 0.00021 vol%, and doubled TNF-α secretion at 0.021 vol%. Addition of conditioned media prepared by incubation of the particles in culture medium in the absence of cells did not alter the secretion of any of the cytokines. Northern blot analysis using IL-6 probes also demonstrated strong increases with HA compared to the other materials, suggesting that the action of the HA particles was at the level of transcription. Secretion of the protease collagenase was increased by all of the samples including HA when compared to unstimulated controls. Stromelysin secretion into the culture medium was decreased by cobalt chromium, but increased by titanium, HA, and HA/TCP. All of the particles including HA increased the gelatinolytic activity of the fibroblasts. These findings demonstrate that HA and HA/TCP particles are capable of stimulating the expression and secretion of cytokines and proteases that enhance bone resorption, and suggest that particulate debris from implants using these coatings may also increase osteolysis and loosening.

The early host and material response of hydroxyapatite/?-tricalciumphosphate porous ceramics after implantation into the femur of rats

The early responses of host and hydroxyapatite/β-tricalciumphosphate (HA-TCP) porous ceramic implants were studied using light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) at 3, 7, 14, 21, and 28 days after implantation into the femur of rats. Micropores (<5 μm) and macropores of the implant surface provided effective structures for anchoring of various tissue components. Mineralization started directly on the implant surface and was observed in macropores and micropores, suggesting bone-bonding by epitaxis. Bone-bonding was observed with and without an amorphous intervening interface layer. The composition of this layer and the mechanisms guiding its production are not yet fully understood. Extracellular matrix filled up the clefts between HA-TCP crystal grain clusters. These processes contributed to the mechanical stabilization of the interface. Slight changes of implant grain surface morphology were observed which were explained by leaching of impurities, such as TCP and/or by dissolution acting on single grains. Diameters of pores and HA-TCP grains did not change in a period up to 28 days, which seems to be related to the relatively short periods of insertion and the material properties. Leaching and degradation were observed and loose particles of implant origin were phagocytosed by macrophages and multinuclear giant cells which dominated at non-bonding interfaces.