Stimulatory effect of zinc-releasing calcium phosphate implant on bone formation in rabbit femora

Although hydroxyapatite (HAP) and tricalcium phosphate (TCP) are currently used as bone graft substitutes or coatings on metallic prostheses because of their excellent biocompatibility and osteoconductivity, they do not stimulate bone formation or inhibit bone resorption. Zinc, an essential trace element in many animals, has a direct specific proliferative effect on osteoblastic cells and has a potent and selective inhibitory effect on osteoclastic bone resorption in vitro. Therefore, zinc-containing beta-tricalcium phosphate (ZnTCP) ceramics and composite ceramics of ZnTCP and HAP (ZnTCP/HAP) were implanted in the femora of New Zealand White rabbits for 4 weeks to promote bone formation. The implants were sintered ceramics with zinc contents of 0 (control), 0.063, 0.316 and 0.633 wt %. Histological and histomorphometrical investigation of the undecalcified sections revealed an increase by 51% (p =.0509) in the area of newly formed bone around the ZnTCP/HAP implants of 0. 316 Zn wt % compared with the control. Plasma zinc concentration was unchanged. An increased bone resorption on the endosteal surface was observed when ZnTCP and ZnTCP/HAP of 0.633 Zn wt % were implanted. To promote bone formation, the optimum zinc content of the calcium phosphate ceramics was therefore 0.316 wt %.     

Preparation, solubility, and cytocompatibility of zinc-releasing calcium phosphate ceramics

Zinc is an essential trace element with stimulatory effects on bone formation. Therefore, zinc was doped into beta-tricalcium phosphate to develop zinc-releasing biomaterials to promote bone formation. The zinc-doped beta-tricalcium phosphate, beta-tricalcium phosphate, and hydroxyapatite powders were mixed at a (Ca+Zn)/P molar ratio of 1.60, followed by sintering into a dense body at 1100 degrees C for 1 h. The sintered body was a composite ceramic consisting of zinc-doped beta-tricalcium phosphate and hydroxyapatite phases. The composite ceramic contained zinc oxide when the zinc content was higher than 1.20 wt %. The composite ceramic released zinc under pseudophysiological conditions. However, the release of calcium and phosphate decreased with an increase in zinc content in a range higher than 0.12 wt % owing to a decrease in solubility of the zinc-doped beta-tricalcium phosphate phase. Proliferation of osteoblastic MC3T3-E1 cells was significantly increased on the composite ceramic with a zinc content from 0.6 to 1.20 wt %, compared with those without zinc. When the zinc content was higher than 1.20 wt %, release of zinc from the zinc oxide caused cytotoxicity. Therefore, the zinc content of the composite ceramic must be <1.20 wt %.     

Comparative study of biphasic calcium phosphate ceramics impregnated with rhBMP-2 as bone substitutes

We investigated pellet-shaped implants prepared from biphasic calcium phosphate (BCP) ceramics with five different ratios of hydroxyapatite (HAP) to beta-tricalcium phosphate (beta-TCP) to evaluate these ceramics as bone substitutes. BCP ceramics impregnated with different doses of recombinant human bone morphogenetic protein 2 (rhBMP-2) (1, 5, and 10 microg) were used for experimental purposes and ceramics without rhBMP-2 were used for control. The pellets were implanted under the pericranium in adult Wistar male rats and were harvested 8 weeks after implantation. The retrieved pellets were then examined radiologically, histologically, and histomorphometrically. The results revealed that the pellets treated with rhBMP-2 exhibited new bone and bone marrow, whereas control pellets produced fibrous connective tissues. The formation of new bone induced by rhBMP-2 was dose dependent. The extent of bone and bone marrow formation and the degree of resorption of the ceramic particles were significantly higher in the pellets composed of 25% HAP-75% TCP. In this study, bioresorption of the ceramic produced favorable conditions for rhBMP-2-induced bone formation.     

Improved bone anchorage of hydroxypatite coated implants compared with tricalcium-phosphate coated implants in trabecular bone in dogs

Tricalcium phosphate (TCP) and hydroxyapatite (HA) ceramic coatings are bioactive coatings that have been shown to stimulate bone apposition onto ceramic-coated implants. TCP and HA ceramics have well-documented differences in physical properties, but both types of ceramics are used for stimulation of bone ongrowth to cementless endo-prosthetic components clinically. However, little is known about the difference in osteoconductive properties between these coatings when inserted into trabecular bone in a controlled experimental situation. Unloaded cylindrical gritblasted titanium (Ti-6A1-4V) implants (6 x 10 mm) coated with either hydroxyapatite (HA) or tricalcium phosphate (TCP) ceramic were inserted into the proximal humerus of 20 skeletally mature dogs. The implants were initially surrounded by a 2 mm gap. Each animal received one HA-coated implant and one TCP-coated implant. All dogs were sacrificed 6 weeks after surgery. Results were evaluated by histomorphometry and mechanical push-out test. Push-out tests demonstrated that HA-coated implants were 10-fold stronger fixated in comparison to TCP-coated implant. Bone ongrowth was significantly higher for HA-coated implants compared to TCP-coated implants. Bone volume in the gap showed a tendency to less bone volume around HA-coated implants compared to TCP-coated implants but this difference was insignificant. As expected almost all of the TCP coating were resorbed after 6 weeks and almost none of the HA coating. HA-coated implants with a grit-blasted surface provide a favorable early mechanical implant anchorage most likely due to superior ceramic stability compared to TCP-coated implants.     

Osteogenic differentiation of cultured rat and human bone marrow cells on the surface of zinc-releasing calcium phosphate ceramics

Rat and human bone marrow cells (BMCs) were cultured on a composite ceramic of zinc-containing beta-tricalcium phosphate and hydroxyapatite (ZnTCP/HAP) with a (Ca+Zn)/P molar ratio of 1.60 and varying zinc contents. After a 2-week culture of the BMCs in the presence of beta-glycerophosphate and dexamethasone, many macroscopic mineralized areas with high alkaline phosphatase (ALP) activity were seen on the ZnTCP/HAP ceramic disks. The ALP activity increased with increasing zinc content in the ceramics. The highest ALP activity was observed when the BMCs were cultured on the ceramics with 1.26 wt % zinc, and the ceramics released zinc ions at concentrations from 2.2 to 7.2 microg/mL into the culture medium. Zinc ions were incorporated into mineralized areas produced by BMCs. BMCs also were directly cultured onto the culture dish surface, and the addition of 100 microM of free ZnCl(2) (6.5 microg/mL) to the culture medium significantly increased the ALP activity of the BMCs relative to the culture medium without the ZnCl(2)addition. The maximum zinc concentration required to enhance mineralization was higher in human BMCs than in rat BMCs. The present study demonstrates the superiority of ZnTCP/HAP ceramics over TCP/HAP in supporting the osteogenic differentiation of BMCs, and thus these ceramics are safe and useful in clinical settings, such as for bone reconstructive surgery.     

Solubilization of hydroxyapatite crystals by murine bone cells, macrophages and fibroblasts

Calcium phosphate ceramic is widely used as implant material. It is made up of hydroxyapatite, beta-tricalcium phosphate or various combinations of both. In the present study, we use an in vitro model to examine the role of cell-mediated resorption of calcium phosphate ceramic implant material. We compare the abilities of two sequential enzymatic released populations of bone cells from murine calvaria (Population II and Population V), macrophages and dermal fibroblasts to solubilize 45Ca-labelled hydroxyapatite crystals. These crystals were incubated with each of the cell types for 24 h in the presence or absence of parathyroid hormone, prostaglandin E2, calcitonin, and 1,25-dihydroxyvitamin D3. The amount of cell-mediated hydroxyapatite solubilization was determined by measuring the radioactivity in an aliquot of the supernatant after centrifugation. Using dermal fibroblasts as a baseline, relative abilities of macrophages, Population II and Population V to degrade crystals were 10.5, 5 and 2 times that of fibroblasts. Crystal-cell contact was required. While none of the bone resorption agents tested had any effect on this process, crystal dissolution by bone cells was inhibited by two lysosomotropic agents, NH4Cl and chloroquine.     

Micro-architecture of calcium phosphate granules and fibrin glue composites for bone tissue engineering

Calcium phosphate ceramics are currently used as bone graft substitutes in various types of clinical applications. Fibrin glue is also used in surgery due to its haemostatic, chemotactic and mitogenic properties. By combining these two biomaterials, new composite scaffolds were prepared. In this study, we attempt to analyse whether thrombin concentration in the fibrin glue could influence the properties of the composite. The association between fibrin glue and calcium phosphate ceramic granules was characterized at the ultra structural level. Micro and macroporous biphasic calcium phosphate ceramic granules with a diameter of 1-2mm composed of hydroxyapatite and beta-tricalcium phosphate (60/40) were associated to fibrin glue. The composites were observed by scanning and transmission electron microscopy and microcomputed tomography. Fibre thickness, porosity and homogeneity of the fibrin clot were modified by increased the thrombin concentration. Mixing fibrin glue with calcium phosphate granules (1:2) did not modify the microstructure of the fibrin clot in the composite. Nevertheless, thrombin interacted with the bioceramic by inducing the nucleation of crystalline precipitate at the ceramic/fibrin glue interface. Combining fibrin sealant and calcium phosphate ceramics could lead to new scaffolds for bone tissue engineering with the synergy of the properties of the two biomaterials.     

Correlation between hydroxyapatite osseointegration and Young's Modulus

From the standpoint of hard tissue response to implant materials, calcium phosphate is probably the most compatible of materials known. During the last few years, much attention has been paid to hydroxyapatite and beta-tricalcium phosphate as potential biomaterials for a bone substitute. Good implantation of biomaterials in the skeleton is evidenced by an ability to reach full integration of the non-living implant with living bone. The aim of this study is to correlate hydroxyapatite osseointegration with Young's Modulus. Cylinders (5-6 mm in diameter) of these ceramics were packed into holes made in the femur diaphysis of a mature sheep. At 2, 4, 8, 12, 16, 20, 28, 36 and 48 weeks after the operation, samples of the bone/implant interface were embedded in polymethylmethacrylate. We used the PIXE method (Particles Induced X-rays Emission) to measure the distribution of mineral elements (Ca, P, Sr, Zn, Mn and Fe) at the bone/implant interface. At 4, 8, 12, 16, 20, 28, 36 and 48 weeks after implantation we studied Young's Modulus on a biopsy of the ceramic. Young's Modulus increased with time after implantation and is linked with biomaterials integration into cortical bone.     

Resorption of apatite-wollastonite containing glass-ceramic and beta-tricalcium phosphate in vivo

Apatite-wollastonite containing glass ceramic is considered to be difficult to resorb, but we experienced the disappearance of the porous type of Apatite-wollastonite glass ceramic particles . In this study, the resorption of porous apatite-wollastonite glass-ceramic implanted in the femurs of rabbits was investigated, and the process was compared with beta-tricalcium phosphate, a resorbable ceramics. Porous apatite-wollastonite glass-ceramic (70, 80, and 90% porosity) and beta-tricalcium phosphate (75% porosity) were implanted in the femurs of Japanese white rabbits. Samples were harvested and examined 0, 4, 8, 12, 24 and 36 weeks after implantation. Quantitative analysis of the radiographic and histologic findings was performed with NIH Image software. Radiographic examination demonstrated that the radiopacity and size of the porous apatite-wollastonite glassceramic cylinders decreased gradually after implantation. Histologic examination revealed that the surface area of the apatite-wollastonite glass-ceramic cylinders decreased continuously, and approached 20% of the original area 36 weeks after implantation. However, the resorption rate of porous apatite-wollastonite glass-ceramic was slower than that of beta-tricalcium phosphate. Toluidine blue staining showed abundant new bone formation on the surface of the apatite-wollastonite glassceramic matrix. Considering its mechanical strength, gradual resorption characteristics, and good osteochonductive activity, porous apatite-wollastonite glass-ceramic appears to be a suitable artificial bone substitutes.     

The most appropriate (Ca+Zn)/P molar ratio to minimize the zinc content of ZnTCP/HAP ceramic used in the promotion of bone formation

The (Ca+Zn)/P molar ratio of zinc-containing tricalcium phosphate and hydroxyapatite composite ceramics (ZnTCP/HAP) was investigated in the range from 1.50 to 1.66 to reveal the minimum zinc content possible in ceramics used in the promotion of osteoblastic cell proliferation and bone formation. The release rate of zinc increased with an increase in the (Ca+Zn)/P molar ratio up to 1.64 (ZnTCP/HAP1.64) and then decreased over 1.64 even when the zinc content of ZnTCP/HAP was the same. The zinc release rate of ZnTCP/HAP1.64 with a 0.21 Zn wt % nearly coincided with that of ZnTCP/HAP1.60 with a 0.316 Zn wt %, which was found be the most effective for promoting bone formation in rabbit femora. This means that the zinc content needed to promote bone formation can be reduced by 34% when the (Ca+Zn)/P molar ratio is increased to 1.64. The relative growth rate of MC3T3-E1 cells cultured on ZnTCP/HAP1.64 had a maximum value of 1.3 at a zinc content of 0.51 wt %; however, a 1.20 Zn wt % is required to attain the same value in relative growth rate in the case of ZnTCP/HAP1.60. A reduction in zinc content at a certain zinc release rate results from an increase in zinc content of the ZnTCP phase in ZnTCP/HAP. The ZnTCP/HAP1.64 would be better than any other ZnTCP/HAP relative to material safety because the risk of an accidental burst of zinc from the material is minimized due to the low zinc content.     

Influence of biphasic calcium phosphate granulometry on bone ingrowth, ceramic resorption, and inflammatory reactions: preliminary in vitro and in vivo study.

Calcium-phosphate ceramics used in surgery, as bone-bonding materials, are currently available in different forms (blocks, granules, etc.). However, progress in noninvasive surgery has favored the development of injectable composite materials associating a polymeric and a dusty mineral phase. The purpose of this study was the in vivo evaluation of biphasic calcium phosphate of various grains sizes, to elucidate the role of granulometries in ceramic degradation/resorption, bone ingrowth, and inflammatory reactions. Three particle sizes were compared: 10-20, 80-100, and 200-400 microm. The 10-20-microm powders provided the best bone ingrowth, with a higher resorption/degradation rate in conjunction with stronger early inflammatory reactions. The 200-400-microm powders showed higher bone ingrowth than 80-100-microm ones, indicating that properties of cell recruitment for osseous apposition and mechanical support for bone bonding may both play a role in both ingrowth mechanisms. Our results suggest that the strong inflammatory reaction in 10-20-microm granulated powders was due to a faster reversal of the resorption/apposition sequence in bone. This may have resulted from massive release of bone ingrowth factors, which implies that the brief inflammatory process observed in the early stages of implantation was favorable to the osteoconduction process.     

Bone in-growth induced by biphasic calcium phosphate ceramic in femoral defect of dogs

Biphasic calcium phosphate (BCP) ceramics consisting of hydroxyapatite (HA) and tricalcium phosphate (TCP) has been used as a bone graft material during the last decade. In this paper, we report the bone in-growth induced by BCP ceramic in the experimentally created circular defects in the femur of dogs. This BCP ceramic consists of 55% hydroxyapatite (HA) and 45% b-tricalcium phosphate (TCP) prepared in situ by the microwave method. The defects were created as 4-mm holes on the lateral aspect of the femur of dogs and the holes were packed with the implant material. The defective sites were radiographed at a period of 4, 8, and 12 weeks postoperatively. The radiographical results showed that the process of ossification started after 4 weeks and the defect was completely filled with new woven bone after 12 weeks. Histological examination of the tissue showed the formation of osteoblast inducing the osteogenesis in the defect. The collageneous fibrous matrix and the complete Haversian system were observed after 12 weeks. The blood serum was collected postoperatively and biochemical assays for alkaline phosphatase activity were carried out. The measurement of alkaline phosphatase activity levels also correlated with the formation of osteoblast-like cells. This microwave-prepared BCP ceramic has proved to be a good biocompatible implant as well as osteoconductive and osteoinductive materials to fill bone defects.     

Inhibitory effect of Zn2+ in zinc-containing beta-tricalcium phosphate on resorbing activity of mature osteoclasts

Long term effect of the growing instability of the bone-implant interface due to bone resorption at the interface is a problem for the implants, including bioactive ceramics. Zn2+ -containing tricalcium phosphate (ZnTCP) is a material which may overcome this problem. The present study aims to clarify whether Zn2+ -containing tricalcium phosphate (ZnTCP) ceramics with a Zn2+ content of 0.316 (ZnTCP316) and 0.633 (ZnTCP633) wt % suppress resorption by mature osteoclasts in vitro. Suppression would be due to an increase in the number of apoptotic osteoclasts and the inhibition of the resorbing activity of osteoclasts, the latter being the major mechanism of the suppression. The number of apoptotic osteoclasts was significantly 6.3 times higher with ZnTCP633 than with tricalcium phosphate ceramic (TCP) after 24-h culture. The net contribution to resorption of this change in apoptotic cell numbers is much smaller than that of the change in resorbing activity. The osteoclasts cultured on ZnTCP formed fewer actin rings than those cultured on the TCP. The mRNA expression of CAII and cathepsin K/OC2 in the osteoclasts on ZnTCP633 was downregulated 0.5-fold and 0.6-fold, respectively, compared with that on the TCP. The volume of resorption pits was downregulated 0.4-fold in the ZnTCP633 than that in TCP. These results suggest that ZnTCPs suppressed the resorbing activity of mature osteoclasts probably through a local increase in the level of Zn2+. Bone substitutes or coating layers containing ZnTCP would be promising biomaterials from the viewpoint of counteracting osteoclastic bone resorption at the bone-implant interface.     

Release of gentamicin from bone regenerative materials: an in vitro study

Antibiotic loading of bone regenerative materials is a promising way to protect augmentation procedures from infection during the resorption phase of bone substitutes. Especially in the early stage of implantation, it should protect the grafted site against microbiological pathogens. The present study reports the release kinetics of gentamicin after loading from two synthetic bone filling materials. The first, BONITmatrix, is a biphasic calcium phosphate silica composite obtained by the sol-gel route consisting of 13% silicon dioxide (w/w) and calcium phosphates (hydroxyapatite/beta-tricalcium phosphate 60/40 w/w). The second, Synthacer, is a sintered hydroxyapatite ceramic. Gentamicin was loaded by dipping and by vacuum coating. Release kinetics of the loaded Gentamicin was investigated by fluorescence polarization immunoassay and by staphylococcus aureus assay. By dipping, loading failed for Synthacer, and it was 12.7 mg gentamicin per gram bone substitute for BONITmatrix. By vacuum coating, loading was 11.3 mg gentamicin per gram bone substitute for Synthacer and 7.4 mg gentamicin per gram bone substitute for BONITmatrix. Distinct release kinetics were measured. For Synthacer, a high initial release was followed by a lower protracted release level up to 28 days. For BONITmatrix release was continuous over the investigated 70-day period. The present data suggest that the porosity properties at the nano- and microscopic levels, or the composition are responsible for antibiotic loading and subsequent release.     

Bone regeneration of porous beta-tricalcium phosphate (Conduit TCP) and of biphasic calcium phosphate ceramic (Biosel) in trabecular defects in sheep

In this study bone regeneration between porous beta-tricalcium phosphate (Conduit TCP) and biphasic calcium phosphate ceramic (Biosel), with a hydroxyapatite/beta-TCP ratio of 75/25, was compared. The ceramic particles were implanted in sheep trabecular bone for 3, 12, and 26 weeks. Histomorphometrical analysis revealed that Conduit degraded significantly during time and only 36% of the material was left at 26 weeks implantation time. Biosel, in contrast, remained nearly intact. The degradation of Conduit was due to dissolution as well as cell-mediated. Biosel showed a high cellular intervention, although this material did not degrade. Both materials were osteoconductive. The amount of newly formed bone appeared greater in the Conduit group after 26 weeks (46% +/- 8% as compared to 37% +/- 8% for Biosel), but this difference was not significant. Bone distribution over the defect was homogeneous in Conduit, whereas Biosel showed significantly more bone in the periphery of the defect after 26 weeks in comparison to the center. In conclusion, both ceramics are biocompatible and osteoconductive. Degradation showed a difference in amount and in cellular events, with more degraded Conduit TCP with less cellular intervention as compared to Biosel.     

The material science of calcium phosphate ceramics

Tricalcium, tetracalcium phosphate and hydroxyapatite ceramics exhibit distinct differences in their chemical and structural composition. Only hydroxyapatite ceramic is identical with the original bone mineral. Different preparation methods lead to compact hydroxyapatite ceramic or to porous material with interconnecting macropores as structural equivalents of the spatial structure of cancellous bone. Concerning the behaviour in a biological environment, high crystallinity and large material density result in resistance to dissolution and long lasting stability. Amorphous ultrastructure and porous formation enhance interface activity and bone ingrowth, but also biological degradation of the ceramic implant material.     

Bioactivity and osseointegration study of calcium phosphate ceramic of different chemical composition

Synthetic hydroxyapatite (HA) and tricalcium phosphate (TCP) are promising bone-substitute materials in the orthopaedic and dental fields, as their chemical composition is similar to that of bone. This study investigated the osseointegration performance of carbonated biphasic calcium phosphate (CBCP) ceramics containing carbonated hydroxyapatite and tricalcium phosphate prepared by microwave irradiation, in femoral defects of dogs. The defects were created as 3-mm holes on the lateral aspect of femur and filled with the implant material. The serum was collected postoperatively and biochemical assays for alkaline phosphatase activity levels were carried out. The animals' defective sites were radiographed at 4, 8, and 12 weeks. The radiographic results showed that the process of ossification started after 4 weeks and the defect was completely filled with new bone after 8 weeks. Histological examination of the tissue showed the osteoblastic activity inducing the osteogenesis in the defect. The complete haversian system with osteoblastic and osteoclastic activity and bone remodelling process were observed after 12 weeks. The alkaline phosphatase activity levels also correlated with the formation of osteoblast cells. This calcium phosphate ceramic has proved to work well as a biocompatible implant and as an osteoconductive and osteoinductive material for the filling of bone defects.     

Material-dependent bone induction by calcium phosphate ceramics: a 2.5-year study in dog

Bone induction by different calcium phosphate biomaterials has been reported previously. With regard to (1) whether the induced bone would disappear with time due to the absence of mechanical stresses and (2) whether this heterotopically formed bone would give rise to uncontrolled growth, a long-time investigation of porous hydroxyapatite ceramic (HA), porous biphasic calcium phosphate ceramic (TCP/HA, BCP), porous alpha-tricalcium phosphate ceramic (alpha-TCP) and porous beta-tricalcium phosphate ceramic (beta-TCP) was performed in dorsal muscles of dog, for 2.5 years. Histological observation, backscattered scanning electron microscopy observation and histomorphometric analysis were made on thin un-decalcified sections of retrieved samples. Normal compact bone with bone marrow was found in all HA implants (n = 4) and in all BCP implants (n = 4), 48 +/- 4% pore area was filled with bone in HA implants and 41 +/- 2% in BCP implants. Bone-like tissue, which was a mineralised bone matrix with osteocytes but lacked osteoblasts and bone marrow, was found in all beta-TCP implants (n = 4) and in one of the four alpha-TCP implants. Both normal bone and bone-like tissues were confined inside the pores of the implants. The results show that calcium phosphate ceramics are osteoinductive in muscles of dogs. Although the quality and quantity varied among different ceramics, the induced bone in both HA and BCP ceramics did neither disappear nor grow uncontrollably during the period as long as 2.5 years.     

Early weight bearing of porous HA/TCP (60/40) ceramics in vivo: a longitudinal study in a segmental bone defect model of rabbit

Porous interconnected hydroxyapatite (HA) and HA/tricalcium phosphate (TCP) (60/40) ceramics are promising materials for hard tissue repair. However, the mechanical properties of these materials have not been accurately determined under weight-bearing conditions. In this study, newly developed HA and HA/TCP (60/40) ceramics were used with intramedullary fixation in segmental bone defects of rabbits. Early radiological, histological, densitometric and biomechanical changes were evaluated. The mean radiological grade of healing and bonding to bone was higher in HA/TCP (60/40) ceramics than that of pure HA ceramics but the difference was not statistically significant. The densities of both implanted ceramics improved with time, supported by the histological evaluation of bone matrix ingrowth into ceramic pores, whereas the densities at the bone–ceramic interface decreased gradually. Flexural resonant frequencies and three-point bending strength increased, revealing an increase in mechanical stability during this early critical time interval where implant and/or bone–implant interface failures occur frequently. It can be concluded that both HA and HA/TCP (60/40) ceramics have a limited application in the treatment of load-bearing segmental bone defects but did not fail at the early stages of implantation.     

Ectopic bone formation associated with mesenchymal stem cells in a resorbable calcium deficient hydroxyapatite carrier

Bone substitute materials can induce bone formation in combination with mesenchymal stem cells (MSC). The aim of the current study was to examine ectopic in vivo bone formation with and without MSC on a new resorbable ceramic, called calcium deficient hydroxyapatite (CDHA). Ceramic blocks characterized by a large surface (48 m2/g) were compared with beta-tricalcium phosphate (beta-TCP), hydroxyapatite (HA) ceramics (both ca. 0.5 m2/g surface) and demineralized bone matrix (DBM). Before implantation in the back of SCID mice carriers were freshly loaded with 2x10(5) expanded human MSC or loaded with cells and kept under osteogenic conditions for two weeks in vitro. Culture conditions were kept free of xenogenic supplements. Deposits of osteoid at the margins of ceramic pores occurred independent of osteogenic pre-induction, contained human cells, and appeared in 416 MSC/CDHA composites compared to 216 MSC/beta-TCP composites. ALP activity was significantly higher in samples with MSC versus empty controls (p<0.001). Furthermore, ALP was significantly (p<0.05) higher for all ceramics when compared to the DBM matrix. Compared to previous studies, overall bone formation appeared to be reduced possibly due to the strict human protocol. Ectopic bone formation in the novel biomaterial CDHA varied considerably with the cell pool and was at least equal to beta-TCP blocks.