Beta-tricalcium Phosphate Research Articles

Effects of teriparatide on bone formation in novel unidirectional porous beta-tricalcium phosphate.

This study aimed to evaluate the effect of intermittent teriparatide treatment on changes in bone formation using unidirectional porous beta-tricalcium phosphate in a rabbit bone defect model. Twel...

Effects of micro-porosity and local BMP-2 administration on bioresorption of \u03b2-TCP and new bone formation

BackgroundIt has been reported that the microporous structure of calcium phosphate (CaP) ceramics is important to osteoconduction. Bone morphogenetic protein-2 (BMP-2) has been shown to be a promising alternative to bone grafting and a therapeutic agent promoting bone regeneration when delivered locally. The aim of this study was to evaluate the effects of micro-porosity within beta-tricalcium phosphate (β-TCP) cylinders and local BMP-2 administration on β-TCP resorption and new bone formation.MethodsBilateral cylindrical bone defects were created in rabbit distal femora, and the defects were filled with β-TCP. Rabbits were divided into 3 groups; defects were filled with a β-TCP cylinder with a total of approximately 60% porosity (Group A: 13.4% micro- and 46.9% macropore, Group B: 38.5% micro- and 20.3% macropore, Group C: the same micro- and macro-porosity as in group B supplemented with BMP-2). Rabbits were sacrificed 4, 8, 12, and 24 weeks postoperatively.ResultsThe number of TRAP-positive cells and new bone formation in group B were significantly greater than those in group A at every period. The amount of residual β-TCP in group C was less than that in group B at all time periods, resulting in significantly more new bone formation in group C at 8 and 12 weeks. The number of TRAP-positive cells in group C was maximum at 4 weeks.ConclusionsThese results suggest that the amount of submicron microporous structure and local BMP-2 administration accelerated both osteoclastic resorption of β-TCP and new bone formation, probably through a coupling-like phenomenon between resorption and new bone formation.

Angiogenesis and new bone formation in novel unidirectional porous beta-tricalcium phosphate: a histological study.

Affinos® (Kuraray Co., Ltd., Tokyo, Japan) is a beta-tricalcium phosphate (TCP) artificial bone comprising a novel unidirectional porous structure with 57% porosity. This study examined angiogenesis and bone formation over time with unidirectional porous beta-TCP (UDPTCP). Ten Japanese White rabbits were used in this study. A 5 × 8-mm rectangular area of periosteum was resected, followed by preparation of a cortical bone defect using a high-speed bur. UDPTCP was embedded in the defect in the direction of the pores, parallel to the axis of the tibia. Tissue samples were harvested at 2weeks (n = 3) and 6weeks (n = 7) after implantation. Just before euthanasia, the vasculature of the lower limb was perfused with saline from the femoral artery and filled with MICROFIL® (Flow Tech, Inc., Carver, MA) to create a vascular cast. The tibia was cut longitudinally at the center of the material. Decalcified sagittal sections treated with hematoxylin and eosin staining, undecalcified sagittal sections treated with Villanueva-Goldner staining, and axial unstained sections were used for histological evaluation. The lengths of the largest vessels and newly formed bone at the material border were measured in a sagittal section. Both lengths were significantly larger at 6weeks than at 2weeks. In the axial sections at 2weeks, newly formed vessels filled with blue dye grew along the pores of the UDPTCP. Mature bone tissue with a lamellar structure was observed at 6weeks. Our histological findings demonstrated that angiogenesis and bone formation occur over time in UDPTCP.

Synthesis and growth mechanism of calcium phosphate layer on SiC-coated carbon/carbon composites with surface pre-oxidation

Substrates surface containing with polar components has a great influence on the synthesis of sol-gel derived calcium phosphate coatings. This paper reports the synthesis of calcium phosphates coatings on native and pre-oxidated C/C-SiC (SiC-coated carbon/carbon) substrates, and compares their differences in composition, structure and in vitro bioactivity. C/C-SiC composites were prepared by CVD (chemical vapor deposition) at 1100 °C for 25 h and modified with aqua regia (HCl/HNO3) for 2 h. Then the coatings were manufactured by sol-gel combined with dip-coating technique. It is shown that the pre-oxidation promotes the formation of dispersed beta-tricalcium phosphate (β-TCP) particles, and the conversion of calcium phosphates coatings from hydroxyapatite (HA) to BCP (HA/β-TCP). The formed β-TCP is composed of hexagonal and orthorhombic systems, and HA is mainly hexagonal crystal. Additionally, the BCP coating on C/C-SiC exhibits better bioactivity compared to pure HA coating during immersion in simulated body fluid (SBF), which is result from the negatively functional groups OH and COOH formed on pre-oxidated surface. These groups disturb the stability of sol via electrostatic interaction and induce the nucleation of β-TCP. Hence, the BCP coating with preferential dissolution of β-TCP phases reveals better apatite formation capability.

Novel strategy for toughening robocast bioceramic scaffolds using polymeric cores

Abstract A novel method for the fabrication of hybrid polymer/ceramic porous scaffolds with core/shell struts is developed. Robocasting with coaxial needles is used to deposit beta-tricalcium phosphate scaffolds with hollow rods, which are subsequently filled with a polycaprolactone melt by suction. The polymeric core provides outstanding improvement of the toughness of the structure in bending, with strain energy density increasing nearly two orders of magnitude and continuous polymeric fibres holding the structure together even after large deflections. Moreover, flexural strength is not significantly reduced compared to dense-strut structures; and the macroporosity of the scaffold and osteoconductivity of bioceramic surfaces are preserved.

Recombinant Human Platelet-Derived Growth Factor BB in Combination With a Beta-Tricalcium Phosphate (rhPDGF-BB/β-TCP)-Collagen Matrix as an Alternative to Autograft.

Joint arthrodesis often employs autograft to promote union; graft harvesting can lead to perioperative morbidity. A Canadian randomized controlled trial (RCT) demonstrated that recombinant human platelet-derived growth factor BB homodimer (rhPDGF-BB) combined with beta-tricalcium phosphate (β-TCP)-collagen was a safe, effective alternative to autograft. This multicenter North American RCT compared the safety and efficacy of rhPDGF-BB/β-TCP-collagen with autograft for ankle and hindfoot fusion. Subclassification using propensity scores (PS) incorporated patients from previous trials for enhanced statistical power for noninferiority testing and broader review of treatments. Patients requiring ankle or hindfoot arthrodesis and supplemental bone graft were treated with rhPDGF-BB/β-TCP-collagen (n = 69) or autograft (n = 35). Outcomes included joint fusion on computed tomography (24 weeks), clinical healing status, visual analog scale (VAS) pain, Short-Form 12 (SF-12), American Orthopaedic Foot & Ankle Society (AOFAS) Ankle-Hindfoot Scale, and Foot Function Index (FFI) scores over 52 weeks. PS methodology addressed potential selection bias arising from pooling data among these patients and 2 previous RCTs with similar inclusion criteria, surgical techniques, graft harvest techniques, and outcomes. All 132 rhPDGF-BB/β-TCP-collagen-treated patients and 167 of 189 candidate autograft-treated controls were selected for comparison by an independent statistician blinded to outcomes. In the PS subclassification, 68.1% treatment patients and 68.4% controls achieved >50% osseous bridging at fusion sites. Clinical healing status was achieved in 84.8% of treated patients and 90.7% of controls at 52 weeks. Clinical, functional, and quality of life results demonstrated noninferiority of rhPDGF-BB/β-TCP-collagen to autograft. Safety-related outcomes were equivalent. PS subclassification analysis of 3 RCTs demonstrated that rhPDGF-BB/β-TCP-collagen was as effective as autograft for ankle and hindfoot fusions, with less pain and morbidity than treatment with autograft. Level I, prospective randomized study.

A unidirectional porous beta-tricalcium phosphate material (Affinos®) for reconstruction of bony defects after excision of fibular bone for spinal surgery graft

The aim of this study was to elucidate the bone regeneration-inducing capability of Affinos®, a newly developed, high-porosity unidirectional porous β-TCP artificial bone. We compared the ability of Affinos® and OSferion®, a commercially available β-TCP product, to induce bone regeneration following implantation into bony defects left after fibula harvesting for spinal fusion surgery.Study subjects underwent surgery to harvest non-vascularized fibula grafts for spinal fusion surgery and were implanted with either Affinos® (19 patients) or OSferion® (15 patients, control group) at the defect site. The minimal and mean follow up periods were 6 and 11 months after surgery, respectively. X-rays of the lower leg taken 1–2 weeks after surgery and at the final follow-up visit were used to evaluate fibular-β-TCP continuity and fibula defect filling ratio.There was no significant difference in radiographic continuity in the fibula between the two groups. The fibula defect filling ratio for the Affinos® group decreased from 0.94 ± 0.17 at 1–2 weeks to 0.77 ± 0.14 at 10 months. For the OSferion® control group, the fibula defect filling ratio decreased from 0.94 ± 0.14 at 1–2 weeks to 0.52 ± 0.27 at final follow-up. The Affinos® group showed a significantly higher fibula defect filling ratio compared to that for the OSferion® group (p = 0.003).These results indicate that Affinos® has slow absorption rates and significant defect filling activity compared with OSferion®. Thus, Affinos® could be a suitable substitute to fill bony defects induced by fibula harvesting for spinal reconstruction surgery.

Beta-Tricalcium Phosphate Block for Donor Site Morbidity of the Patella in Anterior Cruciate Ligament Reconstruction Using Bone-Patellar Tendon-Bone Graft.

PurposeThis study aimed to investigate anterior knee symptoms in patients who underwent anterior cruciate ligament (ACL) reconstruction using bone-patellar tendon-bone (BPTB) graft followed by implantation of a beta-tricalcium phosphate (β-TCP) block as a bone void filler.Materials and MethodsWe retrospectively reviewed 84 cases of synthetic bone grafting using a β-TCP block for the patellar bone defect in ACL reconstruction with a BPTB autograft. Computed tomography of the operated knee was performed immediately after the surgery to evaluate whether the grafted β-TCP block protruded forward from the anterior surface of the patella. On the basis of the results, the cases were divided into a protrusion group (n=31) and a non-protrusion group (n=53). Anterior knee symptoms at 12 months postoperatively and absorption of the grafted β-TCP block were compared between the two groups.ResultsExcept for patellofemoral crepitus, there was no significant difference in anterior knee symptoms between the two groups (p>0.05). The incidence of patellofemoral crepitus was significantly lower in the protrusion group than in the non-protrusion group (p=0.027). The groups showed no significant difference in β-TCP absorption.ConclusionsThe present study demonstrated that the protrusion of β-TCP that was used as a bone void filler had no adverse effects.

Effect of calcium phosphate heparinization on the in vitro inflammatory response and osteoclastogenesis of human blood precursor cells.

The immobilization of natural molecules on synthetic bone grafts stands as a strategy to enhance their biological interactions. During the early stages of healing, immune cells and osteoclasts (OC) modulate the inflammatory response and resorb the biomaterial, respectively. In this study, heparin, a naturally occurring molecule in the bone extracellular matrix, was covalently immobilized on biomimetic calcium-deficient hydroxyapatite (CDHA). The effect of heparin-functionalized CDHA on inflammation and osteoclastogenesis was investigated using primary human cells and compared with pristine CDHA and beta-tricalcium phosphate (β-TCP). Biomimetic substrates led to lower oxidative stresses by neutrophils and monocytes than sintered β-TCP, even though no further reduction was induced by the presence of heparin. In contrast, heparinized CDHA fostered osteoclastogenesis. Optical images of stained TRAP positive cells showed an earlier and higher presence of multinucleated cells, compatible with OC at 14days, while pristine CDHA and β-TCP present OC at 21-28days. Although no statistically significant differences were found in the OC activity, microscopy images evidenced early stages of degradation on heparinized CDHA, compatible with osteoclastic resorption. Overall, the results suggest that the functionalization with heparin fostered the formation and activity of OC, thus offering a promising strategy to integrate biomaterials in the bone remodelling cycle by increasing their OC-mediated resorption.

Synthesis and characterization of bioscaffolds using freeze drying technique for bone regeneration

Abstract Bioscaffolds composed of polymeric biomaterials must be bio-compatible, absorbable and biodegradable upon implantation into humans. The aim of the current study is to synthesize highly porous bioscaffold that provides the appropriate environment for the regeneration of bone tissue. To accomplish this, bioscaffold was prepared by Freeze drying method using Beta-tricalcium phosphate, chitin and gelatin. The Scaffold was characterized by X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), and Field emission scanning electron microscopy (FESEM). The in-vitro bioactivity was tested by calcium phosphate rich layer on surface of soaked scaffold in different pH. FESEM demonstrated that the prepared scaffold had interconnected pores with a pore size of 50–60 nm. The XRD showed the composite structure and FTIR revealed the incorporation of Beta-tricalcium phosphate into chitin and gelatin. Porosity calculated by Archimedes principles was 76%. The degradation of scaffold biomaterial was pH dependent. The acidic pH had high weight loss initially ranging from 35% to 40% compared to neutral pH. However, the degradation rate was slowed down after 10 h. Thus, our study preliminarily concludes that Beta-tricalcium phosphate, chitin and gelatin incorporated bio-scaffolds could be an ideal scaffold for bone regeneration. However, further research is needed to confirm the use of synthesized scaffold for bone tissue engineering or bone defects.

Characterization and in vitro evaluation of gelatin–chitosan scaffold reinforced with bioceramic nanoparticles for bone tissue engineering

Abstract

Effect of Baghdadite Substitution on the Physicochemical Properties of Brushite Cements.

Brushite cements have been clinically used for irregular bone defect filling applications, and various strategies have been previously reported to modify and improve their physicochemical properties such as strength and injectability. However, strategies to address other limitations of brushite cements such as low radiopacity or acidity without negatively impacting mechanical strength have not yet been reported. In this study, we report the effect of substituting the beta-tricalcium phosphate reactant in brushite cement with baghdadite (Ca3ZrSi2O9), a bioactive zirconium-doped calcium silicate ceramic, at various concentrations (0, 5, 10, 20, 30, 50, and 100 wt%) on the properties of the final brushite cement product. X-ray diffraction profiles indicate the dissolution of baghdadite during the cement reaction, without affecting the crystal structure of the precipitated brushite. EDX analysis shows that calcium is homogeneously distributed within the cement matrix, while zirconium and silicon form cluster-like aggregates with sizes ranging from few microns to more than 50 µm. X-ray images and µ-CT analysis indicate enhanced radiopacity with increased incorporation of baghdadite into brushite cement, with nearly a doubling of the aluminium equivalent thickness at 50 wt% baghdadite substitution. At the same time, compressive strength of brushite cement increased from 12.9 ± 3.1 MPa to 21.1 ± 4.1 MPa with 10 wt% baghdadite substitution. Culture medium conditioned with powdered brushite cement approached closer to physiological pH values when the cement is incorporated with increasing amounts of baghdadite (pH = 6.47 for pure brushite, pH = 7.02 for brushite with 20 wt% baghdadite substitution). Baghdadite substitution also influenced the ionic content in the culture medium, and subsequently affected the proliferative activity of primary human osteoblasts in vitro. This study indicates that baghdadite is a beneficial additive to enhance the radiopacity, mechanical performance and cytocompatibility of brushite cements.

Combustion synthesis and characterization of Mg-based Fe-doped biphasic calcium phosphate ceramics

Mg-based (0.35 at.%) biphasic calcium phosphates (BCPs) doped with Fe at various amounts (e.g., 0.35, 0.70 and 1.05 at.%) were prepared by the combustion method. The X-ray diffraction (XRD) analysis confirmed the biphasic structure, composed of hydroxyapatite (HAp) and beta-tricalcium phosphate (β-TCP) for each sample. While β-TCP content increases, HAp content decreases with increasing Fe levels. The crystallinity decreased with the addition of Fe. The unit cell parameters and crystallite size were affected by Fe content. The existence of both phosphate and hydroxyl groups in the samples was verified by the Fourier transform infrared (FTIR). A mass gain was observed for each BCP. The formation of the rod-shaped particles was observed.

Comparison of the Bone Regenerative Capacity of Three-Dimensional Uncalcined and Unsintered Hydroxyapatite/Poly-d/l-Lactide and Beta-Tricalcium Phosphate Used as Bone Graft Substitutes

This study compared the in vivo applicability of three-dimensional uncalcined and unsintered hydroxyapatite/poly-d/l-lactide (3D-HA/PDLLA) with beta-tricalcium phosphate (β-TCP). 3D-HA/PDLLA is a newly developed bioactive, osteoconductive, bioresorbable bone regenerative composite. We performed critical-defect surgery on the mandible body of rats; the defects were filled with one of two bone graft substitutes. After a 4-week follow-up period, the mandibular specimens were examined using hematoxylin and eosin (H&E) staining, immunohistochemistry (IHC) staining and micro-computed tomography (micro-CT). The H&E staining showed an increase in newly formed bone in both groups from week 1 to 4. The difference in the Runx2 IHC optical density (OD) scores of 3D-HA/PDLLA and β-TCP was not statistically significant (p > 0.05); however, the osteocalcin IHC OD scores of the groups differed significantly (p < 0.05). Micro-CT demonstrated a similar trabecular thickness, trabecular spacing, and bone volume per total volume in the two groups (p > 0.05), indicating that bone formation in the two groups was nearly the same from a macro-perspective of bone regeneration. These results demonstrated that a different bone regeneration pattern and earlier osteoblast differentiation occurred in 3D-HA/PDLLA compared with β-TCP. In conclusion, our study demonstrates that 3D-HA/PDLLA is feasible for clinical application as a new bioactive, osteoconductive/bioresorbable bone graft substitute for maxillofacial surgery.

Alternatif Kemik Grefti Olarak Üretilen Yeni Biyogreftlerin Mikroyapılarının ve Mekanik Özelliklerinin Araştırılması

In this study, alternative biografts used for orthopedic applications were produced by sol gel method. The effects of boric acid, MgO and SrBr 2 compounds on the morphological structure and mechanical properties of the produced biografts were investigated. For these purposes, the morphological effects of biografts were examined by FTIR, XRD and SEM-EDX analyzes and their mechanical properties were investigated by hardness and compression tests. As a result of FTIR and XRD investigations on all biografts, it was observed that the additive materials decreased the crystallinity and formed the HA (Hydroxyapatite), β-TCP (Beta tricalcium phosphate), Ca 3 (Si 3 O 9 ), Ca 2 H 4 O 9 P 2 phase structures. In addition, as a result of the SEM-EDX and mechanical tests, it has been determined that different sizes of grain structure in all biografts are formed and boric acid, MgO and SrBr 2 additives increase the compressive strength and hardness values.

Metallic ion doped tri-calcium phosphate ceramics: Effect of dynamic loading on in vivo bone regeneration

The present study was carried out to evaluate the effect of dynamic loading on bone regeneration performance of different doped β-tri-calcium phosphate ceramics. We have developed porous beta tri-calcium phosphate (β-TCP), 5%zinc doped, 5% magnesium doped and 5% titanium doped β-TCP by aqueous solution combustion technique. All the synthesized β-TCP powders showed pore size of 21–146 μm (pure β-TCP), 16–142 μm (Zn-β-TCP), 28–156 μm (Mg- β-TCP) and 14–173 μm (Ti-β-TCP) while their apparent porosity 17.89%, 28.09%, 26.54% and 25.87% respectively. The pure and doped samples were implanted in femoral bone defect model (rabbit) to assess bone regeneration under dynamic loading. Bone regeneration was assessed after 1 and 2 month post-implantation on the basis of clinical radiological, histological, fluorochrome labelling, micro computed tomography (μ-CT) and scanning electron microscopy (SEM). Radiological and fluorochrome labelling study showed reduced size of 5%Ti-β-TCPimplant vis-à-vis more new bone formation as compared to other groups. Micro-CT of the implanted bone sample showed a significant amount of newly formed bony tissue surrounding the Ti-β-TCP implant as compared to other samples. Similar findings of less interfacial gap between the implant and bone were also observed in SEM study. However, all the doped materials are suitable as bone grafting material and have potential for application in bone tissue engineering.

In vitro and in vivo assessment of CaP materials for bone regenerative therapy. The role of multinucleated giant cells/osteoclasts in bone regeneration.

In this work, bone formation/remodeling/maturation was correlated with the presence of multinucleated giant cells (MGCs)/osteoclasts (tartrate-resistant acid phosphatase [TRAP]-positive cells) on the surface of beta-tricalcium phosphate (β-TCP), sintered deproteinized bovine bone (sDBB), and carbonated deproteinized bovine bone (cDBB) using a maxillary sinus augmentation (MSA) in a New Zealand rabbit model. Microtomographic, histomorphometric, and immunolabeling for TRAP-cells analyses were made at 15, 30, and 60 days after surgery. In all treatments, a faster bone formation/remodeling/maturation and TRAP-positive cells activity occurred in the osteotomy region of the MSA than in the middle and submucosa regions. In the β-TCP, the granules were rapidly reabsorbed by TRAP-positive cells and replaced by bone tissue. β-TCP enabled quick bone regeneration/remodeling and full bone and marrow restoration until 60 days, but with a significant reduction in MSA volume. In cDBB and sDBB, the quantity of TRAP-positive cells was smaller than in β-TCP, and these cells were associated with granule surface preparation for osteoblast-mediated bone formation. After 30 days, more than 80% of granule surfaces were surrounded and integrated by bone tissue without signs of degradation, preserving the MSA volume. Overall, the materials tested in a standardized preclinical model led to different bone formation/remodeling/maturation within the same repair process influenced by different microenvironments and MGCs/osteoclasts. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 108B:282-297, 2020.

Preparation of beta-tricalcium phosphate microsphere-hyaluronic acid-based powder gel composite as a carrier for rhBMP-2 injection and evaluation using long bone segmental defect model

The specific objective of this study was to evaluate whether rhBMP-2-loaded bio-scaffolds can be used as effective rhBMP-2 carriers in the implantation of bone defect sites or poor bone quality in host bone. The rhBMP-2 release pattern test showed slow results in both groups, and a 1:9 ratio composition with a high water-absorption rate was selected for in vivo study. All animals euthanized after 9 weeks. The new bone formation and bone quantity and quality of fibular samples were examined. The results showed that the rhBMP-2 powder gel composite improved the new bone formation in the cortical bone and the marrow space. The length of new bone formation ratio of the rhBMP-2 loaded composite group was significantly higher than the powder gel group. The composite of powder gel seems to be a nice carrier, and slow release of rhBMP-2 can promote new bone formation in a segmental cortical bone defect after implantation.

Beta-tricalcium phosphate ceramic triggers fast and robust bone formation by human mesenchymal stem cells.

Due to their osteoconductive and inductive properties, a variety of calcium phosphate (CaP) scaffolds are commonly used in orthopaedics as graft material to heal bone defects. In this study, we have used two CaP scaffolds with different hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) ratios (MBCP®; 60/40 and MBCP+ ®; 20/80) to investigate their intrinsic capacity to favour human bone marrow stem cells (hBMSCs) osteogenic differentiation capacity. We report that MBCP+ ® showed in in vitro culture model a higher rate of calcium ion release in comparison with MBCP®. In two defined coculture systems, the hBMSC seeded onto MBCP+ ® presented an increased amount of VEGF secretion, resulting in an enhanced endothelial cell proliferation and capillary formation compared with hBMSC seeded onto MBCP®. When both ceramics combined with hBMSC were implanted in a nude mouse model, we observed a faster osteogenic differentiation and enhancement mature bone deposition sustained by the presence of a vast host vasculature within the MBCP+ ® ceramics. Bone formation was observed in samples highly positive to the activation of calcium sensing receptor protein (CaSr) on the surface of seeded hBMSC that also shown higher BMP-2 protein expression. With these data we provide valuable insights in the possible mechanisms of ossification and angiogenesis by hBMSC that we believe to be primed by calcium ions released from CaP scaffolds. Evidences could lead to an optimization of ceramic scaffolds to prime bone repair.

Preparation of ex-situ Mixed Sintered Biphasic Calcium Phosphate Ceramics from Its Co-Precipitated Precursors and Their Characterization

ABSTRACTBiphasic calcium phosphate (BCP) ceramics was synthetically prepared by ex-situ method using hydroxyapatite (HAp) and beta tricalcium phosphate (β-TCP) powders. Both HAp and β-TCP were prepared by wet chemical co-precipitation and calcination method and were then mixed at two different weight ratios of 60:40 and 70:30. The mixed BCPs were then pressed and sintered at 1200o and 1250oC. Sintered pure HAp and β-TCP were also prepared for comparison purpose. Sintered products were then characterized for various properties. Higher density and strength values were found for the composition with higher HAp content and also the bioactivity on immersion in SBF (simulated body fluid) solution was found to be higher for HAp containing composition.