Surface reactions of calcium phosphate ceramics to various solutions

The surface reactions of calcium phosphate ceramics have been thought to play an important role in bonding with living bone. Hydroxyapatite (HA), tricalcium phosphate (TCP), and two kinds of apatite-containing glass ceramics were immersed in three types of solutions with different chemical constituents. The first solution was a physiological saline, the second contained phosphate (PO4), and the third was a balanced salt solution consisting of calcium (Ca), magnesium (Mg), and PO4. After serial incubation periods, changes in the solutions were assessed by measurement of total Ca, Mg, and PO4. The ceramic surfaces were studied using scanning electron spectroscopy, infrared reflection spectroscopy, and thin-film x-ray diffraction. The surface reactions of the ceramics were greatly affected by the chemical compositions of the surrounding media. In the complete solution with both Ca and PO4, a carbonated apatite layer was formed on the surfaces of HA, TCP, and the glass ceramics. In comparison to HA and TCP, the glass ceramics were characterized as Ca-releasing materials, the dissolved Ca creating an apatite layer on the surfaces in a few days, in conjunction with PO4 stock in the surrounding media. The immersion test with various solutions proved to be a simple and effective method of assessing surface conditions of ceramic materials.     

Degradation of calcium phosphate ceramics.

Degradation of three types of sintered calcium phosphate ceramic spheres was investigated in vitro at low pH conditions (LPC) and in an in vivo model, that is, injection into a mouse peritoneal cavity. Degradation was observed under both conditions. The rate of degradation depended on the type of ceramic, with beta-TCP degrading faster than HA and HA degrading faster than FA. Degradation was characterized by dissolution of the necks and the formation of cracks and irregularities in the grains. Intraperitoneal injection of the spheres into a mouse peritoneal cavity led to the formation of foreign body granulomas in which degradation could be observed. The in vivo degradation pattern was similar to that observed in vitro, but longer implantation times resulted in a further degradation. Small fragments rich in Ca and P were present in inclusion bodies. Calcium phosphate crystals sometimes also were observed in mitochondria, many of which were subject to lysis. We observed that ceramic type and implantation period also were related to the number of dead cells in the granulomas. Furthermore, extracellular deposits were seen between cells and ceramic spheres. Ca and P and also Fe were detected in these deposits. The presence of Fe is indicative of a lysosomal origin and thus of exocytotic activity.     

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.     

复合磷酸钙陶瓷人工骨

磷酸钙陶瓷因具有良好的生物相容性和骨传导作用而成为人工骨的常用材料 ,但是 ,它们本身无骨诱导作用。将具有骨诱导作用的物质如 BMP、骨髓、生长因子等与磷酸钙陶瓷复合 ,可以克服磷酸钙陶瓷无骨诱导作用的缺陷     

Comparison of osteoblast-like cell responses to calcium silicate and tricalcium phosphate ceramics in vitro

Calcium silicate ceramics have been proposed as new bone repair biomaterials, since they have proved to be bioactive, degradable, and biocompatible. Beta-tricalcium phosphate ceramic is a well-known degradable material for bone repair. This study compared the effects of CaSiO3 (alpha-, and beta-CaSiO3) and beta-Ca3(PO4)2 (beta-TCP) ceramics on the early stages of rat osteoblast-like cell attachment, proliferation, and differentiation. Osteoblast-like cells were cultured directly on CaSiO3 (alpha-, and beta-CaSiO3) and beta-TCP ceramics. Attachment of a greater number of cells was observed on CaSiO3 (alpha-, and beta-CaSiO3) ceramics compared with beta-TCP ceramics after incubation for 6 h. SEM observations showed an intimate contact between cells and the substrates, significant cells adhesion, and that the cells spread and grew on the surfaces of all the materials. In addition, the proliferation rate and alkaline phosphatase (ALP) activity of the cells on the CaSiO3 (alpha-, and beta-CaSiO3) ceramics were improved when compared with the beta-TCP ceramics. In the presence of CaSiO3, elevated levels of calcium and silicon in the culture medium were observed throughout the 7-day culture period. In conclusion, the results of the present study revealed that CaSiO3 ceramics showed greater ability to support cell attachment, proliferation, and differentiation than beta-TCP ceramic.     

Comparative histocompatibility testing of seven calcium phosphate ceramics

Five hydroxyapatite and two tricalcium phosphate ceramics were implanted in rat femora for one to six months. They were compared with each other in regard to faiocompatibility and bone induction. After one month hone had grown directly on to the surface of all implants. After six months the on-growth of bone had increased with the exception of two dense HA materials. In these materials some bio-degradation had occurred with subsequent formation of a wide macrophage interlayer. Bio-degradation and biocompatibility of calcium phosphate ceramics seem to depend not only on density but also on other factors. Induction of bone could not be observed in soft tissue environment.     

骨诱导性磷酸钙陶瓷材料修复牙槽突裂

BACKGROUND: In our previous studies, we had prepared calcium phosphate ceramics with better ectopic osteogenesis. OBJECTIVE: To explore the effect of novel osteoinductive calcium phosphate ceramics in the repairing of alveolar cleft. METHODS: Bilaterl alveolar defects were created in nine immature beagles. Three months later, osteoinductive calcium phosphate ceramics with high modular surface (experimental group) and smooth surface (control group) were randomly implanted in each side of the defect. Meanwhile, the corresponding material was implanted into the thigh muscle. New bone formation in the implanted region, osteogenesis in the implanted region and muscle, and respair results were respectively observed by fluorescence microscope, light microscope and CT at 4, 8 and 12 weeks after implantation. RESULTS AND CONCLUSION: (1) Fluorescence microscope observation: A circular permutation of red, yellow and green fluorescent strip could be observed in both two groups. (2) Light microscope observation: At 12 weeks after implantation, in the experimental group, the bone reconstruction was obvious, the implant material was decomposed gradually, the gap was filled with a large number of mature bone that combined with the rest material closely, and numerous Haversian canals appeared; the control group was similar but slightly inferior to the experimental group in the quality of new bone. The experimental group material successfully induced heterotopic osteogenesis in muscle, while the control did not. (3) CT examination: The two group materials restored the appearance and continuity of the alveolar ridge, and made no effect on the eruption of permanent teeth in both sides of the defect. To conclude, our findings suggest that the novel osteoinductive calcium phosphate ceramic exhibits advantages in alveolar cleft repair with earlier osteogenesis activation, faster osteogenesis rate and more bone formation than those traditional materials.     

Osteogenicity of biphasic calcium phosphate ceramics and bone autograft in a goat model

The aim of this work was to compare the osteogenicity of calcium phosphate ceramic granules with autologous bone graft in ectopic and orthotopic sites. Biphasic calcium phosphate (BCP) granules composed of hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP) in a 60/40 ratio were sintered at 1050, 1125 and 1200 degrees C, producing different microporosities. Either BCP ceramic granules or autologous bone chips (n=7) were implanted into paraspinal muscles. Osteoinduction was not observed in either the BCP implants or autologous bone chips after 6 or 12 weeks in the ectopic sites. Hollow and bored polytetrafluoroethylene (PTFE) cylinders were filled with autologous bone, BCP granules or left empty, then implanted into critical-sized defects in femoral epiphyses. The PTFE cylinders left empty contained marrow and blood vessels but not mineralized bone, indicating that this model prevented bone ingrowth (0.56+/-0.43% at 12 weeks). Bone formation was observed in contact with the BCP1050 and BCP1125 granules in the femoral sites after 6 weeks. The amount of bone after 12 weeks was 5.6+/-7.3 and 9.6+/-6.6% for BCP1050 and BCP1125, respectively. Very little bone formation was observed with the BCP1200 implants (1.5+/-1.3% at 12 weeks). In both the ectopic and orthotopic sites, autologous bone chips were drastically resorbed (from 19.4+/-3.7% initially to 1.7+/-1.2% at 12 weeks). This study shows that synthetic bone substitutes may have superior stability and osteogenic properties than autologous bone grafts in critical-sized bone defects.     

Biphasic calcium phosphate: a comparative study of interconnected porosity in two ceramics

Interconnection, one of the main structural features of macroporous calcium-phosphate ceramics, contributes to the biological and physicochemical properties of bone substitutes. As no satisfactory method exists for evaluating this feature, analysis was performed to determine the permeability, tortuosity, and equivalent diameter of interconnecting channels, that is the parameters that appear to be representative of the way pores are linked. The testing of two ceramics with similar porosity levels revealed important differences in all three interconnection parameters. One ceramic showed poor permeability, corresponding to a small equivalent diameter for interconnecting channels in conjunction with a high tortuosity factor, while the other displayed high permeability, a large diameter for interconnecting channels, and a low tortuosity factor. The methodology used, which can be applied to the quantification of interconnection in all calcium-phosphate ceramics, constitutes the first step in a complete study of the role of this feature in cellular colonization of the ceramic, matrix dissolution, and drug release from the calcium-phosphate matrix.     

Long-term implantation of zinc-releasing calcium phosphate ceramics in rabbit femora

Zinc is an essential trace element that has stimulatory effects on bone formation. Recently, we developed zinc-releasing calcium phosphate ceramics in order to add the pharmacologic effect of zinc to calcium phosphate ceramics. In our previous study, we showed that the optimum zinc content for promoting bone formation was 0.316 wt %. Therefore a zinc composite ceramic of zinc-containing beta-tricalcium phosphate and hydroxyapatite, with a zinc content of 0.316 wt %, was chosen for long-term implantation. Cylindrical rods of the zinc composite ceramic were implanted in rabbit femora for 2 to 60 weeks. Using computer-aided image analysis, a histomorphometric study was carried out to investigate bone formation and resorption around the implants. The control was a composite ceramic of beta-tricalcium phosphate and hydroxyapatite without zinc. The addition of zinc to the implant demonstrated both favorable and unfavorable effects on bone remodeling. The favorable effect was enhanced bone apposition to the implant surface, demonstrated by a significant increase in intramedullary bone apposition rate at 6 weeks and in cortical bone apposition rate at 24 and 60 weeks (p < 0.05). The unfavorable effect was increased bone resorption, demonstrated by a significant increase in medullary cavity area at 60 weeks (p < 0.05). In order to utilize the favorable effect and avoid the unfavorable effect of zinc, either a reduction in zinc content in the zinc composite ceramic or the selection of implantation sites that do not have excessive exposure to bone marrow are required.     

Synthesis of carbonated calcium phosphate ceramics using microwave irradiation

Carbonated hydroxyapatites (CHA) were synthesized by the substitution of calcium carbonate for calcium hydroxide during the reaction with diammonium phosphate under microwave irradiation. The X-ray powder diffraction analysis indicates the decrease of alpha-axis up to 20 mol% of carbonate substitution confirming the formation of the B-type CHA. Further increase of carbonate content shows the presence of tricalcium phosphate (TCP) in addition to CHA. Reaction of substituted magnesium carbonate instead of calcium carbonate in the above process results in the formation of biphasic calcium phosphate (BCP) ceramics consisting of both CHA and TCP phases. Fourier transform infrared spectroscopic study also confirmed the carbonate substitution in HA and BCP formation. The in vitro solubility study in phosphate buffer of pH 7.2 at 37 degrees C showed the resorbable nature of the BCP samples. The present study thus indicates the feasibility of in situ formation of BCP ceramics using microwave irradiation.     

结构特征对磷酸钙陶瓷骨诱导活性的影响

背景：目前关于磷酸钙陶瓷诱导成骨的机制尚不完全清楚,许多学者试图从材料的结构特征方面去阐明磷酸钙陶瓷诱导成骨的机制。 目的：综述结构特征如何影响磷酸钙陶瓷的骨诱导活性。 方法：使用计算机检索PubMed和谷歌学术数据库中1997年1月至2015年3月关于磷酸钙骨组织工程的文献,排除观点陈旧和重复的文章,最后对60篇文章进行归纳总结。 结果与结论：磷酸钙陶瓷的结构可分宏观结构和微观结构,宏观结构包括宏孔、孔洞或管道及颗粒间的间隙等;微观结构包括微孔、颗粒大小、表面粗糙度、比表面积等。结构特征的中各个参数都以一定的方式影响磷酸钙陶瓷的生物活性,使其诱导成骨能力发生着从无到有、从弱到强的变化。但是骨诱导活性的优化并非仅仅依靠结构设计就能达到目的,因为磷酸钙陶瓷的物理化学性质同样也会影响其在体内的生物活性。因此,磷酸钙陶瓷结构设计需要“因地制宜”地与其自身的物理化学性质“完美契合”,以获得最佳的骨诱导活性。 中国组织工程研究杂志出版内容重点：生物材料;骨生物材料; 口腔生物材料; 纳米材料; 缓释材料; 材料相容性;组织工程     

Long-term craniofacial osteoblast culture on a sodium phosphate and a calcium/sodium phosphate glass

The aim of this study was to determine the characteristics of human craniofacial osteoblasts cultured on sodium phosphate glass and calcium-sodium phosphate glass in a long-term culture of up to 28 days. The characteristics studied were attachment, proliferation, alkaline phosphatase activity, collagen-1 production, and mineralization. A comparison of the degradation rate, measured by mass loss of the glasses, which are intended for use as a component of a novel degradable composite for craniofacial bone repair, was also performed. It was our hypothesis that the glass would be degradable with a change in degradation rate observed by calcium addition and support osteoblast proliferation and expression of the above characteristics. The inclusion of calcium into the reaction mixture significantly decreased the degradation rate, and it is suggested that the slower degradation is the result of pseudo crosslinking (ionic crosslinks rather than covalent bonding) of the polyphosphate chains by the calcium ions. Therefore, twice as many P-O bonds will need to be hydrolyzed for dissolution of the metal phosphate to occur, therefore greatly reducing the rate of hydrolysis. Osteoblasts were able to attach, spread, and proliferate in a manner comparable with the positive control, as shown by analysis of variance. Formation of a collagen-rich mineralized matrix was also observed. The results presented here suggest that a biocompatible soluble glass has been produced, which has potential to be included in a novel biodegradable craniofacial implant.     

Substrate geometry directs the in vitro mineralization of calcium phosphate ceramics

Repetitive concavities on the surface of bone implants have recently been demonstrated to foster bone formation when implanted at ectopic locations in vivo. The current study aimed to evaluate the effect of surface concavities on the surface mineralization of hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) ceramics in vitro. Hemispherical concavities with different diameters were prepared at the surface of HA and β-TCP sintered disks: 1.8 mm (large concavity), 0.8 mm (medium concavity) and 0.4 mm (small concavity). HA and β-TCP disks were sintered at 1100 or 1200 °C and soaked in simulated body fluid for 28 days at 37 °C; the mineralization process was followed by scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction and calcium quantification analyses. The results showed that massive mineralization occurred exclusively at the surface of HA disks treated at 1200 °C and that nucleation of large aggregates of calcium phosphate started specifically inside small concavities instead of on the planar surface of the disks. Regarding the effect of concavity diameter size on surface mineralization, it was observed that small concavities induce 124- and 10-fold increased mineralization compared to concavities of large or medium size, respectively. The results of this study demonstrated that (i) in vitro surface mineralization of calcium phosphate ceramics with surface concavities starts preferentially within the concavities and not on the planar surface, and (ii) concavity size is an effective parameter to control the spatial position and extent of mineralization in vitro.     

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.     

Comparison of calcium phosphate glass ceramics with apatite ceramics implanted in bone. An interface study--II

In order to study bone tissue interaction on calcium phosphate glass ceramics and on apatite ceramics, cylinders of standard size were implanted in the tibiae of rabbits. The materials were evaluated by radiography, light microscopy and microradiography. Apatite ceramics gave rise to a very close contact with new bone. Glass with an apatite surface evoked bone growth similar to that for apatite ceramics but with a loose contact while glass without an apatite surface gave rise to porous remodelling of new bone without close contact to the implant.     

In vivo degradation of low temperature calcium and magnesium phosphate ceramics in a heterotopic model

Bone replacement using synthetic and degradable materials is desirable in various clinical conditions. Most applied commercial materials are based on hydroxyapatite, which is not chemically degradable under physiological conditions. Here we report the effect of a long-term intramuscular implantation regime on the dissolution of various low temperature calcium and magnesium phosphate ceramics in vivo. The specimens were analysed by consecutive radiographs, micro-computed tomography scans, compressive strength testing, scanning electron microscopy and X-ray diffractometry. After 15months in vivo, the investigated materials brushite (CaHPO(4)·2H(2)O), newberyite (MgHPO(4)·3H(2)O), struvite (MgNH(4)PO(4)·6H(2)O) and hydroxyapatite (Ca(9)(PO(4))(5)HPO(4)OH) showed significant differences regarding changes of their characteristics. Struvite presented the highest loss of mechanical performance (95%), followed by newberyite (67%) and brushite (41%). This was accompanied by both a distinct extent of cement dissolution as well as changes of the phase composition of the retrieved cement implants. While the secondary phosphate phases (brushite, newberyite, struvite) completely dissolved, re-precipitates of whitlockite and octacalcium phosphate were formed in either particulate or whisker-like morphology. Furthermore, for the first time the possibility of a macropore-free volume degradation mechanism of bioceramics was demonstrated.     

晶须化磷酸钙多孔生物活性陶瓷修复犬股骨髁缺损

BACKGROUND: Previous studies have demonstrated that the internal microstructure of porous calcium phosphate ceramics after the whiskering process has some changes, and obtain good mechanical properties. OBJECTIVE: To further investigate the effect of whisker-covered porous calcium phosphate ceramics in repair of canine femoral condyle defects. METHODS: Highly interconnected porous calcium phosphate ceramics was prepared by placeholder method. The whiskering of the materials was finished by hydrothermal process. Fifteen healthy adult beagle dogs were selected in this study. A 10 mm×10 mm cylindrical inclusive bone defect was made bilaterally on the lateral femoral condyle with a drill. The porous calcium phosphate ceramics after the whiskering process was implanted onto the right femoral condyle as experiment group. The porous calcium phosphate ceramics without the whiskering process was implanted onto the left femoral condyle as control group. At 2, 4, 8, and 12 weeks after implantation, X-ray and dual-energy X-ray test were conducted in the bone defect area respectively. RESULTS AND CONCLUSION: (1) X-ray: With the increase of time, the interface between bone defect and normal bone of two groups gradually blurred, disappeared, and completely fused at 12 weeks. The material in the control group was partially dissolved, while there was no obvious dissolution in the experiment group. No significant difference in the X-ray scores was found between two groups at different time points. (2) Dual-energy X-ray: With the increase of time, the bone mineral density of the two groups both increased gradually, but there was no significant difference in the bone mineral density at different time points between these two groups. These results demonstrate that the porous calcium phosphate ceramics after the whiskering process has good ability to repair the defects of femoral condyle.       

Effect of nanostructure on osteoinduction of porous biphasic calcium phosphate ceramics

In order to evaluate the effect of the nanostructure of calcium phosphate ceramics on osteoinductive potential, porous biphasic calcium phosphate (BCP) ceramics with a nano- or submicron structure were prepared via microwave sintering and compared to conventional BCP ceramics. The selective protein adsorption of bovine serum albumin and lysozyme (LSZ) and the osteogenic differentiation of human mesenchymal stem cells in vitro was investigated. Porous BCP nanoceramics showed higher ability to adsorb proteins, especially low molecular weight protein of LSZ, than conventional BCP ceramics, and the BCP nanoceramics promoted bone sialoprotein expression more than conventional BCP did. Further in vivo study to investigate ectopic bone formation and bone repair efficiency proved the highly osteoinductive potential of nanostructured BCP ceramics. The results suggest that nanostructured BCP ceramics have the potential to become a new generation of bioceramics for bone tissue engineering grafts.     

Fabrication and cellular biocompatibility of porous carbonated biphasic calcium phosphate ceramics with a nanostructure

Microwave heating was applied to fabricate interconnective porous structured bodies by foaming as-synthesized calcium-deficient hydroxyapatite (Ca-deficient HA) precipitate containing H(2)O(2). The porous bodies were sintered by a microwave process with activated carbon as the embedding material to prepare nano- and submicron-structured ceramics. By comparison, conventional sintering was used to produce microstructured ceramics. The precursor particles and bulk ceramics were characterized by transmission electron microscopy (TEM), dynamic light scattering, scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FTIR) and mechanical testing. TEM micrographs and assessment of the size distribution showed that the needle-like precursor particles are on the nanoscale. SEM observation indicated that the ceramics formed by microwave sintering presented a structure of interconnective pores, with average grain sizes of approximately 86 and approximately 167nm. XRD patterns and FTIR spectra confirmed the presence of carbonated biphasic calcium phosphate (BCP), and the mechanical tests showed that the ceramics formed by microwave sintering had a compressive strength comparable to that obtained by conventional methods. Rat osteoblasts were cultured on the three kinds of BCP ceramics to evaluate their biocompatibility. Compared with the microscale group formed by conventional sintering, MTT assay and ALP assay showed that nanophase scaffolds promoted cell proliferation and differentiation respectively, and SEM observation showed that the nanoscale group clearly promoted cell adhesion. The results from this study suggest that porous carbonated biphasic calcium phosphate ceramics with a nanostructure promote osteoblast adhesion, proliferation and differentiation. In conclusion, porous carbonated BCP ceramics with a nanostructure are simple and quick to prepare using microwaves and compared with those produced by conventional sintering, may be better bone graft materials.