Carvable calcium phosphate bone substitute material

This study investigated the use of partially set hydroxyapatite forming calcium phosphate cement as a carvable and mechanically stable bone substitute material. Hydroxyapatite-forming cements were made of either mechanically activated alpha-tricalcium phosphate or a mixture of tetracalcium phosphate and dicalcium phosphate anhydrous and setting was arrested up to 4 h post setting. The study showed that these partially set rigid samples of defined geometry could be carved into a desired shape when the degree of reaction was 30-40% and the relative porosity between 40 and 50%; samples are then expected to set completely after implantation in the presence of water or serum, having the same compressive strength as a continuously set calcium phosphate cement (up to 36 MPa). The development of compressive strength, phase composition, and crystallinity when varying production parameters of these partially "preset" bone substitute materials are presented for both cement systems.     

Effects of additives on the rheological properties and injectability of a calcium phosphate bone substitute material

An injectable calcium phosphate bone substitute material has been prepared by mixing amorphous calcium phosphate (ACP) and dicalcium phosphate dihydrate (DCPD) for use in noninvasive surgery, and the influence of additives, such as disodium hydrogen phosphate, polyethylene glycol (PEG), glycerin, and citric acid, on the rheological properties and injectability of the ACP + DCPD cement system have been studied in this work. Novel approach of thixotropy measurement has been used to characterize the stability of the pastes. The results show that the injectability and the setting time can be augmented by the addition of disodium phosphate solution to the paste but reduced by the addition of PEG 200, glycerin, or citric acid to the paste. This study suggests that the injectability and the setting time of the ACP + DCPD bone substitute material can be balanced, and the injectable calcium phosphate bone substitute material with satisfied fluidity and injectability for clinical operation can be prepared by optimizing the additives and their concentrations, according to different clinical requirements.     

The effects of microporosity on osteoinduction of calcium phosphate bone graft substitute biomaterials

The effect of increasing strut porosity on the osteoinductive ability of silicate substituted calcium phosphate (SiCaP) biomaterials was investigated in an ectopic ovine model. Implants with strut porosities of 22.5%, 32.0% and 46.0% were inserted into the parapsinalis muscle. At 8, 12 and 24 weeks histological sections were prepared. Sections were examined using backscattered scanning electron microscopy and un-decalcified histology. Bone area, implant area and bone-implant contact were quantified. At 8 weeks there was no significant difference between the groups in terms of bone area and implant area. However at 12 weeks, the amount of bone formation observed was significantly greater in SiCaP-46 (6.17 ± 1.51%) when compared with SiCaP-22.5 (1.33 ± 0.84%) p=0.035. Results also showed significantly increased amounts of bone-implant contact to the SiCaP-46 scaffold (3.30 ± 1.17%) compared with SiCaP-22.5 (0.67 ± 0.52%, p=0.043) at 8 weeks and 12 weeks; (SiCaP-46 (21.82 ± 5.59%) vs SiCaP-22.5 (3.06 ± 1.89%), p=0.012). At 24 weeks, bone formation and graft resorption had significantly increased in all groups so that the level of bone formation in the SiCaP-46 group had increased 75-fold to 30.05 ± 8.38%. Bone formation was observed in pores <10 μm. Results suggest that bone graft substitute materials with greater strut porosity are more osteoinductive.     

Characterization of a novel calcium phosphate/sulphate bone cement

Apatitic cements have shown excellent biocompatibility and adequate mechanical properties but have slow resorption in the human body. To assure that new bone tissue grows into the bone defect, a certain porosity is necessary although hard to achieve in injectable cements with suitable mechanical properties. An attempt was made by mixing alpha-tricalcium phosphate (alpha-TCP), calcium sulphate hemihydrate (CSH) and an aqueous solution containing 2.5 wt% of Na(2)HPO(4). The aim was to obtain a material containing two phases: a) one apatitic phase (calcium-deficient hydroxyapatite; CDHA) and b) one resorbable phase (calcium sulphate dihydrate; CSD). alpha-TCP and CSH mixtures were produced at relative intervals of 20 wt%. The liquid-to-powder (L/P) ratio to obtain a paste was 0.32 mLg(-1). The highest compressive strength (34 MPa) was obtained for the pure alpha-TCP sample. The strength was, in a first approximation, directly correlated to the weight proportions of the powders. X-ray diffraction analysis showed that the relative intensity for CDHA increased linearly, and the one for CSD decreased exponentially, when the amount of alpha-TCP increased. Thus, CSH ceased to transform to CSD when the amount of alpha-TCP increased. Observations in environmental scanning electron microscopy confirmed the X-ray diffraction results. CSH-crystals (100 microm) were embedded in the HA-matrix permitting gradual porosity in the material when resorbed.     

The effect of calcium phosphate bone substitute on defect resolution around a rough-surfaced dental implants in dogs

Gap defects often exist around dental implants due to morphological differences between the natural tooth extraction socket and the dental implant. Techniques that can resolve such gap defects include implant surface modification and filling of the defects with bone substitutes. Modified surfaces are generally more effective in this regard than smooth surfaces. Favorable results have also been reported using bone substitutes. This study evaluated the effectiveness of a calcium phosphate (CaP) bone substitute for resolving gap defects around implant surfaces that have been treated with grit blasting and thermal etching. Implants were placed in edentulous areas in four mongrel dogs. Gap defects with a diameter of 2 mm were prepared surgically around the dental implants. These defects were either filled with CaP bone substitute (experimental group) or left unfilled (control group). Defects were evaluated after 8 and 16 weeks of healing. Block specimens were fixed, sectioned, and stained with hematoxylin and eosin. Histometric measurements revealed that healing in gap defects that had been filled with CaP bone substitute proceeded until 16 weeks. Total CaP degradation seemed to occur at between 4 and 8 weeks of healing. In conclusion, a more complete defect resolution was observed in gap defects filled with CaP bone substitute after 16 weeks than after 8 weeks of healing. The beneficial effects of filling in 2-mm gap defects around implants were attributed to the use of CaP bone substitute.     

Structural and material mechanical properties of human vertebral cancellous bone

The structural Young's modulus (i.e. that of the cancellous framework) was determined by non-destructive compressive mechanical testing in the three orthogonal axes of 48 vertebral bone cubes. In addition, the material Young's modulus (i.e. of the trabeculae themselves) was estimated using an ultrasonic technique. Apparent and true density were determined by direct physical measurements. Significant mechanical anisotropy was observed: mean structural Young's modulus varied from 165 MPa in the supero-inferior direction to 43 MPa in the lateral direction. Structural Young's modulus correlated with apparent density, with power-law regression models giving the best correlations (r² = 0.52-0.88). Mechanical anisotropy increased as a function of decreasing apparent density (p < 0.001). Material Young's modulus was 10.0 ± 1.3 GPa, and was negatively correlated with apparent density (p < 0.001). In multiple regression models, material Young's modulus was a significant independent predictor of structural Young's modulus only in the supero-inferior direction. The data suggest the presence of two effects in vertebral bone associated with decreasing apparent density and, by implication, bone loss in general: (a) increased mechanical anisotropy, such that there is relative conservation of stiffness in the axial direction compared with the transverse directions; and (b) increased stiffness of the trabeculae themselves.     

Effect of increased strut porosity of calcium phosphate bone graft substitute biomaterials on osteoinduction

The effect of increasing strut porosity on the osteoinductivity of porous calcium phosphate (CaP) and silicate-substituted calcium phosphate (SiCaP) bone substitute materials was investigated in an ovine ectopic model. One to two millimeter-sized granules or block implants with strut porosities of 10, 20, or 30% were inserted into the left and right paraspinalis muscle. At 12 weeks, histological sections were prepared through the center of each implant and bone contact, bone area and implant area quantified. Backscattered scanning electron microscopy (bSEM) was used to visualize bone within small pores in the struts of the scaffolds. Increased bone formation was measured in the SiCaP with 30% strut porosity (5.482% ± 1.546%) when compared with the nonsilicate CaP with the same morphology (1.160% ± 0.502%, p = 0.02), indicating that silicate substitution may increase osteoinduction. Greater bone formation was seen in scaffolds with increased strut porosity. No bone growth was found in any of the SiCaP scaffold with 10% porosity. There was no significant difference between block and granule specimens. Scanning electron microscopy and EDX in combination with histology demonstrated bone formation within pores <5 μm in size. The use of silicate-substituted CaP material with increased strut porosity may further augment repair and regeneration in bony sites.     

A novel hydroxyapatite ceramic bone substitute transformed by ostrich cancellous bone: characterization and evaluations of bone regeneration activity

Various biomaterials have been used for bone repair and reconstruction of bone defects. Inorganic xenogenic bone substitutes have been intensively studied because they possesses favorable regenerative properties. The purpose of this study was to evaluate the properties of a novel inorganic xenogenic bone substitute, sintered ostrich cancellous bone (SOCB). Bone regeneration capability was also comparing to that of other bone substitutes in rabbit calvarial defects. Biochemical and biomechanical properties of the SOCB ceramic closely resembled those of human bone. Bone regeneration was evaluated by radiograph, histology, and histomorphometry. Bone regeneration was significantly enhanced in defects treated with SOCB when compared with other bone substitutes. The biochemical and biomechanical properties of SOCB are favorable for bone regeneration. SOCB might be a promising biomaterial for the repair of bone defects.     

Histological osseointegration of a calciumphosphate bone substitute material in patients

The aim of this study was to evaluate histological and radiological osseointegration characteristics of implanted di-/tri-calciumphosphate in patients bone substitute material in opening-wedge osteotomies patients. Up to now the hypothesis of bioresorption and replacement with vital bone bases on numerous animal studies showing complete remodelling within 12-26 weeks. Histological patient studies hardly exist. In this study 13 patient biopsies were collected 16 months after tibial osteotomy. Unlike animal studies the results showed mainly incorporated avital cement residues (38%) as well as new bone formation (61%). Radiological scoring confirmed increasing signs of osseointegration and an incomplete resorption. In conclusion degradation and replacement of di-/tri-calciumphosphate seems to be less accelerated in patients than prior animal studies indicated. Nevertheless, it shows excellent biocompatibility, good osteoconductive characteristics and may represents a useful alternative to autogenous graft.     

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

Journal of Artificial Organs - Affinos® (Kuraray Co., Ltd., Tokyo, Japan) is a beta-tricalcium phosphate (TCP) artificial bone comprising a novel unidirectional porous structure with 57%...     

新型大孔隙磷酸钙骨水泥作为骨组织工程支架的相关研究

目的 探讨新型大孔隙磷酸钙骨水泥(CPC)材料支架的细胞毒性和对细胞黏附、生长和增殖的影响.方法 通过添加甘露醇制孔剂和应用磷酸钠溶液作为CPC固化液的方法合成新型CPC材料.通过CCK8法检测细胞在新型CPC材料浸提液中的生长增殖情况;通过电子扫描电镜测试材料孔径和细胞在材料表面上黏附生长情况;应用力学三点弯曲实验测试新型CPC的生物力学性能.结果 新型CPC材料的孔径值达到(267.43±118.01)μm,孔隙率为(66.15±6.91)％.新型CPC材料的最大负荷、抗弯强度和坚韧度较传统CPC均增加了约1倍(P＜0.05).新型CPC材料浸提液与细胞共培养2、4、6、8d后CCK8法测试吸光度(OD)值与阴性对照组比较其差异无统计学意义(P＞0.05).结论 新型CPC材料具有强大的生物力学性能、大孔隙、高孔隙率和良好的生物相容性,有望成为理想的骨组织工程支架.     

BMP-2 incorporated in a tricalcium phosphate bone substitute enhances bone remodeling in sheep

Bone morphogenetic protein-2 (BMP-2) is a well-known osteoinductive protein, which requires a carrier for local application. As an alternative to the previously described carriers, an in situ hardening, resorbable, and osteoconductive beta-tricalcium phosphate cement (TCP) is tested. Trepanation defects in the bovine distal femoral epiphysis are filled with a composite consisting of TCP and 200 microg rhBMP-2 per cm3 TCP, autologous bone graft, pure TCP, or left empty. A radiological follow-up is performed after 7 weeks and 3 months. The sheep are euthanized and bone samples are analyzed by microradiography, histology, and histomorphometry. Microradiography and histology show similar results for pure TCP and the composite. The defects are filled with trabecular bone and newly formed bone is in close contact with the remaining TCP-particles. The majority of the cement is resorbed, in the composite group the amount of remaining cement particles is reduced. Defects treated with autologous bone graft are filled completely, while untreated defects shows only a small amount of bone originating from the rim of the defect. Histomorphometry of the defects treated with pure TCP shows a significantly increased bone content in comparison to defects treated with the composite or autologous bone graft. Analysis of the remaining cement particles shows significantly less cement in the TCP/rhBMP-2 group in comparison to pure TCP. The sum of bone and cement content in the rhBMP-2 group shows amounts comparable to the calcified structures found following autologous bone grafting. The addition of rhBMP-2 to the TCP leads to faster remodeling of the defect comparable to autologous bone graft, while defects treated with pure TCP are not completely remodeled.     

Development of calcium phosphate cement using chitosan and citric acid for bone substitute materials.

We developed a calcium phosphate cement that could be molded into any desired shape due to its chewing-gum-like consistency after mixing. The powder component of the cement consists of alpha-tricalcium phosphate and tetracalcium phosphate, which were made by decomposition of hydroxyapatite ceramic blocks. The liquid component consists of citric acid, chitosan and glucose solution. In this study, we used 20% citric acid (group 20) and 45% citric acid (group 45). The mechanical properties and biocompatibility of this new cement were investigated. The setting times of cements were 5.5 min, in group 20 and 6.4 min, in group 45. When incubated in physiological saline, the cements were transformed to hydroxyapatite at 3, and 6 weeks, the compressive strengths were 15.6 and 20.7 MPa, in group 45 and group 20, respectively. The inflammatory response around the cement implanted on the bone and in the subcutaneous tissue in rats was more prominent in group 45 than in group 20 at 1 week after surgery. After 4 weeks, the inflammation disappeared and the cement had bound to bone in both groups. These results indicate that this new calcium phosphate cement is a suitable bone substitute material and that the concentration of citric acid in the liquid component affects its mechanical properties and biocompatibility.     

Use of a novel bone graft substitute in peri-articular bone tumours of the knee

We treated three patients with aneurysmal bone cysts and seven with giant cell tumours who presented with a large osteolytic lesion in peri-articular areas of the knee. The patients age ranged from 8 to 49 years (mean 25 years). The average tumour volume was measured at 39.8 cm³ (range 18 to 65 cm³). The tumour cavities were treated with curettage, phenolisation and application of a composite bone graft substitute containing 35% calcium-sulphate hemihydrate and 65% hydroxyapatite granules. All patients were followed up for 4.0 to 5.2 years (mean 4.5 years). Tumour recurrence was noted in two cases. In the remaining patients consolidation of the lesion was considered complete at a mean of 4.5 months (3–6.5 months). During follow-up no deformities developed and no radiological signs of joint degeneration were noted. All patients regained close to normal function, with a mean Musculoskeletal Tumour Society Rating Score of 95.1%.

Due to their good osteoconductive abilities, composite synthetic bone graft substitute combining porous hydroxyapatite with calcium-sulphate appears to be an effective alternative to autologous cancellous bone graft in the treatment of large osteolytic lesions in peri-articular areas around the knee joint. They bear major advantages through ubiquitous availability and the avoidance of morbidity associated with iliac crest harvest. Concerns remain as the radio-opaque appearance of the bone graft substitute may potentially delay the detection of tumour recurrence.     

An injectable,biodegradable calcium phosphate cement containing poly lactic-co-glycolic acid as a bone substitute in ex vivo human vertebral compression fracture and rabbit bone defect models

Purpose/Aim of the study: To evaluate the biomechanical characteristics and biocompatibility of an injectable, biodegradable calcium phosphate cement (CPC) containing poly lactic-co-glycolic acid (PLGA). Materials and methods: A vertebral compression fracture model was established using 20 human cadaveric vertebrae (T11-L3) divided into CPC/PLGA composite versus PMMA groups for biomechanical testing. In addition, 35 New Zealand rabbits were used to evaluate biodegradability and osteoconductive properties of CPC/PLGA using a bone defect model. In vitro cytotoxicity was evaluated by culturing with L929 cells. Results: The CPC/PLGA composite effectively restored vertebral biomechanical properties. Compared with controls, the maximum load and compression strength of the CPC/PLGA group were lower, and stiffness was lower after kyphoplasty (all p <.05). Degradation was much slower in the control CPC compared with CPC/PLGA group. The bone tissue percentage in the CPC/PLGA group (44.9 ± 23.7%) was significantly higher compared with control CPC group (25.7 ± 10.9%) (p <.05). The viability of cells cultured on CPC/PLGA was greater than 70% compared with the blanks. Conclusions: Our biodegradable CPC/PLGA composite showed good biomechanical properties, cytocompatibility, and osteoconductivity and may represent an ideal bone substitute for future applications.     

Effect of the calcium to phosphate ratio of tetracalcium phosphate on the properties of calcium phosphate bone cement

Six different tetracalcium phosphate (TTCP) products were synthesized by solid state reaction at high temperature by varying the overall calcium to phosphate ratio of the synthesis mixture. The objective was to evaluate the effect of the calcium to phosphate ratio on a TTCP-dicalcium phosphate dihydrate (DCPD) cement. The resulting six TTCP-DCPD cement mixtures were characterized using X-ray diffraction analysis, scanning electron microscopy, and pH measurements. Setting times and compressive strength (CS) were also measured. Using the TTCP product with a Ca/P ratio of 2.0 resulted in low strength values (25.61 MPa) when distilled water was used as the setting liquid, even though conversion to hydroxyapatite was not prevented, as confirmed by X-ray diffraction. The suspected CaO presence in this TTCP may have affected the cohesiveness of the cement mixture but not the cement setting reaction, however no direct evidence of CaO presence was found. Lower Ca/P ratio products yielded cements with CS values ranging from 46.7 MPa for Ca/P ratio of 1.90 to 38.32 MPa for Ca/P ratio of 1.85. When a dilute sodium phosphate solution was used as the setting liquid, CS values were 15.3% lower than those obtained with water as the setting liquid. Setting times ranged from 18 to 22 min when water was the cement liquid and from 7 to 8 min when sodium phosphate solution was used, and the calcium to phosphate ratio did not have a marked effect on this property.     

Resorbable calcium phosphate particles as a carrier material for bone marrow in an ovine segmental defect

Resorbable calcium phosphate ceramics are only osteoconductive; therefore, their combination with osteogenic substances may lead to stimulation of bone healing. In the present study this combination, using autologous bone marrow, was investigated. In 31 sheep, a 3-cm tibial segmental defect was created and stabilized with an intramedullary nail. The animals were divided into four groups: empty defects (group 1, n = 7), and defects filled with 10-mL dense resorbable calcium phosphate particles (group 2, n = 8), with 10-mL particles soaked in bone marrow (group 3, n = 8), or with 10-mL autologous bone (group 4, n = 8). On evaluation after 12 weeks, significantly higher values were seen in group 3 than in group 2 for callus volume (p = .016), bone mineral density ratio (p = .03), bone mineral content ratio (p = .04), torsional strength (p = .005), and torsional stiffness (p = .01). For all end points, the outcome of group 3 was lower than that of group 4. In the histology, there was direct contact between newly formed bone and remnants of the particles. There were no signs of inflammatory reactions. Although a stimulatory effect of bone marrow was seen, the combination of resorbable calcium phosphate particles with bone marrow does not provide an alternative for autologous bone grafting.     

Femtosecond laser induced fixation of calcium alkali phosphate ceramics on titanium alloy bone implant material

Femtosecond lasers provide a novel method of attaching bioceramic material to a titanium alloy, thereby improving the quality of bone implants. The ultrashort 30 fs laser pulses (790 nm wavelength) penetrate a thin dip-coated layer of fine ceramic powder, while simultaneously melting a surface layer of the underlying metal. The specific adjustment of the laser parameters (pulse energy and number of pulses per spot) avoids unnecessary melting of the bioactive calcium phosphate, and permits a defined thin surface melting of the metal, which in turn is not heated throughout, and therefore maintains its mechanical stability. It is essential to choose laser energy densities that correspond to the interval between the ablation fluences of both materials involved: about 0.1–0.4 J cm^?2. In this work, we present the first results of this unusual technique, including laser ablation studies, scanning electron microscopy and optical microscope images, combined with EDX data.     

Mechanism of bone incorporation of beta-TCP bone substitute in open wedge tibial osteotomy in patients

A histological study was performed of bone biopsies from 16 patients (17 biopsies) treated with open wedge high tibial osteotomies for medial knee osteoarthritis. The open wedge osteotomies were filled with a wedge of osteoconductive beta tricalcium phosphate (beta-TCP) ceramic bone replacement. At the time of removal of the fixation material, core biopsies of the area where the beta-TCP was located were taken at different follow-up periods (6-25 months). beta-TCP resorption, bone ingrowth and bone remodelling were studied. We hypothesized that the incorporation and remodelling process occurs similarly as in animals. Histology showed a good resorption of the beta-TCP with complete incorporation and remodelling into new bone. The different phases as described in animal studies were found. A correlation was found between histological findings and radiological assessment. In conclusion, beta-TCP appeared to be a bone replacement material with optimal biocompatibility, resorption characteristics and bone conduction properties for the clinical use.     

Architecture of the cancellous bone of the human talus

The trabeculae of the cancellous bone are formed along the direction of the lines of stresses to which a bone is subjected. The talus sustains the weight of the body and transmits the weight in different directions (i.e., the calcaneus and navicular). The aim of the present study was to investigate the architecture of the cancellous bone of the talus to understand the mechanism of transmission of force within the bone. Twenty-five dry, macerated tali of adult male humans were used to study the trabecular architecture. In a few bones, serial longitudinal (parasagittal), transverse (coronal), and horizontal sections were cut; in other bones, the trabecular bone was exposed by removal of cortical bone. Trabecular architecture was studied by dissection microscope and by taking radiographs of the slices. The body of the talus consisted of vertical, parallel plates arranged posteroanteriorly. This kind of orientation of the plates facilitates the transmission of weight, when the tibia rolls posteroanteriorly on the trochlear surface during walking. The trabecular architecture in the head of talus consisted of semiarched plates running parallel to each other. The vertical limb of these semiarched plates were situated above the middle and anterior calcaneal facets on the plantar surface of the head, whereas the horizontal limbs of the arches were deep to the navicular articular surface of the head. The vertical plates of the body and semiarched plates of the head were interconnected by a meshwork of irregularly arranged trabecular bone of the neck. The architecture of this meshwork was such that it could facilitate the change in the direction and nature of force. In conclusion, the part of compressive force, acting vertically downward on the body of the talus during standing, was converted to tensile force in the neck, and its direction was made perpendicular to enable this force to go toward the head of the talus. In a similar manner, the semiarched pattern of plates in the head facilitated the change in the direction of the force, at the end of the stance phase, from the downward (toward calcaneus) to the forward (toward navicular) direction. Anat. Rec. 252:185–193, 1998. © 1998 Wiley-Liss, Inc.