Study on injectable and degradable cement of calcium sulphate and calcium phosphate for bone repair

Injectable calcium sulphate/phosphate cement (CSPC) with degradable characteristic was developed by introduction of calcium sulphate (CS) into calcium phosphate cement (CPC). The setting time, compressive strength, composition, degradation, cells and tissue responses to the CSPC were investigated. The results show that the injectable CSPC with optimum L/P ratio exhibited good injectability, and had suitable setting time and mechanical properties. Furthermore, the CSPC had good degradability and its degradation significantly faster than that of CPC in Tris–HCl solution. Cell culture results indicate that CSPC was biocompatible and could support MG63 cell attachment and proliferation. To investigate the in vivo biocompatibility and osteogenesis, the CSPC were implanted in the bone defects of rabbits. Histological evaluation shows that the introduction of CS into CPC enhanced the efficiency of new bone formation, and CSPC exhibited good biocompatibility, degradability and osteoconductivity with host bone in vivo. It can be concluded that the injectable CSPC had a significant clinical advantage over CPC, and might have potential to be applied in orthopedic, reconstructive and maxillofacial surgery, especially for minimally invasive techniques.     

PVA复合磷酸钙骨水泥的制备和性能研究

将含有不同质量分数聚乙烯醇(PVA)的PVA-KH2PO4-Na2HPO4体系缓冲溶液作为骨水泥的调和液,将其与磷酸钙骨水泥粉末混合后成型。将试样在接近生理条件(相对湿度100%,温度(37±1)℃)下养护24h,发现PVA掺入量为1%时的抗压强度达到31.71MPa,比未掺入的提高了将近70%。     

可注射磷酸钙骨水泥及其应用

可注射磷酸钙骨水泥作为一种新型人工骨替代材料,以其良好的生物相容性和骨传导性被广泛应用于临床骨缺损和牙缺损的修复.本文介绍了可注射磷酸钙骨水泥的种类和特性,指出了存在的问题和应用前景.     

Novel calcium phosphate composite bone cement: strength and bonding properties

A new high-strength cement prepared from calcium phosphate and calcium aluminate has been developed and was evaluated for potential use in bone and joint repair applications. Cement specimens were aged under simulated physiological conditions. The compressive strength of the cement was determined at time intervals 1 h after setting up to 52 weeks. A compressive strength of 111.6±12.9 MPa was measured at 4 weeks, with the cement attaining 64% of this maximum strength within 4 h of preparation. Compressive strength greater than 90 MPa was maintained up to 52 weeks. The strength of the cement–prosthesis interface was studied using a pull-out test. Polished, 316L stainless steel rods were implanted in canine cadaver femurs to simulate a cemented hip prosthesis. At 4, 24 h, and 60 days post implantation, the force required to displace the rod was measured. Mean interfacial shear strengths of 1.17±0.25, 1.11±0.21, and 1.11±0.32 MPa were observed at respective time-periods.     

On the development of an apatitic calcium phosphate bone cement

Development of an apatitic calcium phosphate bone cement is reported. 100 μ Particles of tetracalcium phosphate (TTCP) and dicalcium phosphate dihydrate (DCPD) were mixed in equimolar ratio to form the cement powder. The wetting medium used was distilled water with Na₂HPO₄ as accelerator to manipulate the setting time. The cement powder, on wetting with the medium, formed a workable putty. The setting times of the putty were measured using a Vicat type apparatus and the compressive strength was determined with a Universal Testing Machine. The nature of the precipitated cement was analyzed through X-ray diffraction (XRD), fourier transform infrared spectrometry (FTIR) and energy dispersive electron microprobe (EDAX). The results showed the phase to be apatitic with a calcium-to-phosphorous ratio close to that of hydroxyapatite. The microstructure analysis using scanning electron microscopy (SEM) showed hydroxyapatite nano-crystallite growth over particulate matrix surface. The structure has an apparent porosity of ∼ 52%. There were no appreciable dimensional or thermal changes during setting. The cement passed the in vitro toxicological screening (cytotoxicity and haemolysis) tests. Optimization of the cement was done by manipulating the accelerator concentration so that the setting time, hardening time and the compressive strength had clinically relevant values.     

Controlled release of gentamicin from calcium phosphate/alginate bone cement

Calcium phosphate cement (CPC) is a good biomaterial for bone defect repair and as a delivery system for active agents. The aim of this study was to explore the physicochemical properties and in vitro soaking and release behaviors of gentamicin-loaded CPC with and without alginate; in particular, for biocompatibility. MTT colorimetric assay and RT-PCR were used to detect U2OS cell viability and level of cyclooxygenase-2 (COX-2), respectively. As a result, the setting time increased after the addition of 0.5% alginate and 5% gentamicin, reaching 19 min—significantly higher than the 8 min taken by the CPC control, demonstrating the adverse effect of alginate and gentamicin on the setting reaction of CPC. Gentamicin might reduce the diametral tensile strength, while alginate did not affect the strength. The rate of gentamicin release from CPC can be extended by the presence of alginate. The addition of gentamicin did not show signs of impaired cell viability, but alginate enhanced the cell viability. COX-2 expression of U2OSs cultured in the alginate-containing cement extract was about one-third level of the cement extract without alginate. Alginate-containing CPC is not only useful as a reservoir for antibiotic delivery but it also helps stimulate bone regeneration.     

Composition and crystal structure of resorbable calcium phosphate thin films

Silicon stabilized tricalcium phosphate (Si-TCP) is formed, among other phases, as a result of sintering hydroxyapatite (HA) in the presence of silica (SiO₂) at >800°C. Calcium phosphate films sintered at 1000°C on quartz substrates are examined with and without additional SiO₂ added to the starting precipitate. Data from transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) separate the undoped film morphology into a surface layer with a monoclinic crystal structure P2₁/a characteristic of α or Si-tricalcium phosphate and grain size in the range 100–1000 nm and a substrate layer with a crystal structure which is predominantly apatitic P6₃/m and grain size in the range 30–100 nm. The silicon content is greatest in the substrate layer. The addition of SiO₂ to the film material during fabrication induces a more uniform grain size of 10–110 nm and a higher Si content. The structural and phase evolution of these films suggests the nucleation of α-TCP by the local formation of Si-TCP at a SiO₂-hydroxyapatite interface. The results are consistent with X-ray diffraction studies and are explained by a model of nucleation and growth developed for bulk powders.     

磷酸钙骨水泥/明胶复合组织工程支架材料的制备及其结构与性能

磷酸钙骨水泥组织工程支架材料具有良好的生物相容性和骨传导性,是一种良好的骨组织工程支架材料,但是这种材料存在力学性能差的缺点,限制了它的应用.本文采用生物相容性良好的可降解明胶材料与磷酸钙骨水泥支架进行复合,制备出的明胶/磷酸钙骨水泥复合支架材料,其压缩强度可达3.7MPa,比复合前磷酸钙支架材料的强度提高了37倍,而且材料具有良好的柔韧性,适合用作为非承重部位骨组织缺损修复用组织工程支架材料.     

Characterization of doxycycline-loaded calcium phosphate cement: implications for treatment of aneurysmal bone cysts

Percutaneous doxycycline for treatment for aneurysmal bone cysts (ABCs) has been shown to decrease recurrence rates, however, this requires multiple procedures, includes the risks soft tissue necrosis, and does not provide structural support. We propose utilizing curettage with doxycycline-loaded calcium phosphate cement. This study aimed to evaluate the elution profile of doxycycline from calcium phosphate cement. Calcium phosphate cement underwent an in vitro elution protocol evaluating doxycycline concentrations of 0, 5, 10, and 15?mg/mL. Eluted concentrations were quantified utilizing high performance liquid chromatography at predetermined time points over 96?h. Compressive strength was evaluated both pre- and post-elution and micro-computed tomography was utilized to assess changes in cement porosity. Cement with 15?mg/mL of doxycycline maintained a higher average concentration (mean, 95% confidence intervals) (14.5?µg/mL [9.2–19.9?µg/mL]) compared to both 5?mg/mL (5.8?µg/mL [3.1–8.6?µg/mL]; P?<?0.001) and 10?mg/mL (8.4?±?µg/mL [6.0–10.9?µg/mL]; P?<?0.001). Ultimate stress significantly decreased between pre- and post-elution samples for 10?mg/mL (P=?0.001) and 15?mg/mL (P?=?0.004) groups. This study demonstrated a dose-dependent response in ultimate strength and compressive modulus with addition of doxycycline to calcium phosphate cement.     

Air-foamed calcium aluminate phosphate cement for geothermal wells

Air-foamed low-density calcium aluminate phosphate (CaP) cement slurry was prepared by mixing it with chemical foaming reagent at room temperature without any pressure, followed by autoclaving at 200 °C. When the porosity, compressive strength, and water permeability of the autoclaved CaP foam cement made from a 1.22 g/cc slurry density was compared with those of N₂ gas-foamed Class G cement made from a slurry of similar density under high pressure and hydrothermal temperature at 288 °C, the CaP cement revealed some advanced properties, such as a higher compressive strength and lower porosity. These advanced properties were due to the hybrid formation of three crystalline hydrothermal reaction products; hydroxyapatite, boehmite, and hydrogarnet phases. However, one shortcoming was an increase in water permeability because of the formation of an undesirable continuous porous structure caused by coalesced air bubble cells, suggesting that an appropriate lesser amount of foaming reagent be used to create a conformation in which fine discrete air-bubble cells are uniformly dispersed throughout the slurry. For non-foamed cement, three major factors contributed to protecting carbon steel against corrosion: (1) good adherence to steel, reflecting a high extent of coverage by the cement layer over the steel’s surfaces; (2) retardation of cathodic corrosion reactions; and, (3) minimum conductivity of corrosive ionic electrolytes. However, adding an excessive amount of foaming reagent did not offer as effective corrosion protection as that of non-foamed cement.     

In situ study on the curing process of calcium phosphate bone cement

The aim of this study was to follow the entire curing process of modified alpha-TCP cement, and to explore how the liquid phase affects the curing reaction. Two calcium phosphate bone cements (CPCs) with a variety of aqueous solution were studied for comparison. In situ X-ray diffraction analysis and pH testing were employed to follow the chemical reaction, while quantitative ultrasonic measurement (QUS) was carried out to monitor the physical change. Results showed that CPC powders were completely consumed after 72 h. Two steps were presented in apatite formation. The first step was the precipitation of carbonated hydroxyapatite (CHA), and in the second step, conversion of calcium deficient hydroxyapatite (CDHA) was the dominant reaction. Finally, CPCs were fully converted to apatite except the cement with NaH2PO4 as liquid phase, because acidic environment inhibited the conversion of apatite. The pH increased linearly after mixing, when supersaturation was reached, it decreased to pH approximately 6.0 gradually. Ultrasound measurement indicated that the variation of speed of sound (SOS) was related to both apatite formation and microstructural evolution. Ultrasonic attenuation coefficient (UAC) was able to quantitatively describe the curing process from viscous paste to elastic solid as a function of curing time. Moreover, the curing reaction conformed to classical dissolution-precipitation mechanism.     

Injectable iron-modified apatitic bone cement intended for kyphoplasty: cytocompatibility study

In this study, the cytocompatibility of human ephitelial (HEp-2) cells cultured on new injectable iron-modified calcium phosphate cements (IM-CPCs) has been investigated in terms of cell adhesion, cell proliferation, and morphology. Quantitative MTT-assay and scanning electron microscopy (SEM) showed that cell adhesion and viability were not affected with culturing time by iron concentration in a dose-dependent manner. SEM-cell morphology showed that HEp-2 cells, seeded on IM-CPCs, were able to adhere, spread, and attain normal morphology. These results showed that the new injectable IM-CPCs have cytocompatible features of interest to the intended kyphophasty application, for the treatment of osteoporotic vertebral compression fractures.     

Premixed macroporous calcium phosphate cement scaffold

Calcium phosphate cement (CPC) sets in situ to form resorbable hydroxyapatite and is promising for orthopaedic applications. However, it requires on-site powder-liquid mixing during surgery, which prolongs surgical time and raises concerns of inhomogeneous mixing. The objective of this study was to develop a premixed CPC scaffold with macropores suitable for tissue ingrowth. To avoid the on-site powder-liquid mixing, the CPC paste was mixed in advance and did not set in storage; it set only after placement in a physiological solution. Using 30% and 40% mass fractions of mannitol porogen, the premixed CPC scaffold with fibers had flexural strength (mean ± sd; n = 5) of (3.9 ± 1.4) MPa and (1.8 ± 0.8) MPa, respectively. The scaffold porosity reached (68.6 ± 0.7)% and (74.7 ± 1.2)%, respectively. Osteoblast cells colonized in the surface macropores of the scaffold and attached to the hydroxyapatite crystals. Cell viability values for the premixed CPC scaffold was not significantly different from that of a conventional non-premixed CPC known to be biocompatible (P > 0.1). In conclusion, using fast-dissolving porogen and slow-dissolving fibers, a premixed macroporous CPC scaffold was developed with strength approaching the reported strengths of sintered porous hydroxyapatite implants and cancellous bone, and non-cytotoxicity similar to a biocompatible non-premixed CPC. Official contribution of the National Institute of Standards and Technology; not subject to copyright in the United States.     

The optimum zinc content in set calcium phosphate cement for promoting bone formation in vivo

The final aim of our study is to develop a novel calcium phosphate cement based on zinc-containing α-tricalcium phosphate (αZnTCP) and evaluate its potential as bonegraft material in vivo. In the present study, in vivo efficacy of zinc in hardened bodies of αZnTCP was explored. The hardened bodies prepared from αZnTCP with zinc content of 0.00, 0.04, 0.08, 0.11 and 0.19 wt % were prepared by mixing pure αTCP or αZnTCP powder with 12 wt% sodium succinate solution at a solid-to-liquid ratio of 2.0. Due to the release of zinc ions into the physiological salt solution during curing, the zinc content in the hardened bodies was calculated to be 0.00, 0.03, 0.06, 0.10 and 0.18 wt%, respectively. The hardened bodies were implanted in the femora and tibia of white rabbits for 4 weeks. Histological and histomorphometric evaluation showed that the hardened body containing 0.03 wt% zinc, significantly promoted more new bone formation without evoking adverse tissue reactions than that without zinc. The hardened bodies containing 0.06 and 0.10 wt% zinc also resulted in the increase in numbers of active osteoblasts surrounding the new bone but caused inflammation at the implant sites. Results of this study indicate that the hardened body prepared with αZnTCP is superior to that prepared with αTCP in promoting new bone formation due to the release of zinc ions. This study also indicates that the optimum amount of zinc in the hardened body is about 0.03 wt % to avoid inflammatory reaction.     

可缓释药物的明胶/磷酸钙骨水泥复合组织工程支架材料

采用向孔隙中灌注含聚乳酸聚乙醇酸共聚物（PLGA）载药微球的明胶溶液的方法制备了具有药物缓释功能的明胶/磷酸钙骨水泥复合组织工程支架。用扫描电子显微镜观察了微球和支架的形貌特征,用万能材料试验机测定了支架材料的抗压强度,用紫外-可见分光光度计分析了复合支架的释药率。结果表明,灌注明胶对多孔磷酸钙骨水泥支架起到显著的增强作用,抗压强度达2.42 MPa。复合支架携载硫酸庆大霉素, 具有良好的药物缓释功能,缓释时间可达30天以上,使支架在修复骨缺损的同时能消除炎症反应,成为一种集骨修复和治疗于一体的新型组织工程支架材料,具有良好的应用前景。      

Crystallization mechanisms of calcium phosphate cement for biological uses

Self-setting calcium phosphate cement for dental or surgical applications can be prepared by the addition of a liquid to a mixture of acidic and basic calcium phosphate. After hardening, the final compound becomes hydroxyapatite. Using an orthogonal central composite plan, the main factors which control the setting and the final hardness of the cement were defined and models are proposed. The mechanisms of crystallization, the role of free and linked water, and the nature of the final and intermediate compounds are described.This paper was accepted for publication after the 1995 Conference of the European Society of Biomaterials, Oporto, Portugal, 10–13 September.     

Physicochemical properties and release characteristics of growth factor‐modified calcium phosphate bone cement

The addition of growth factors, such as recombinant human transforming growth factor‐β1 (rhTGF‐β1) to calcium phosphate cements (CPCs) may improve bone regeneration. Previously we have shown that the differentiation of pre‐osteoblastic cells from adult rat long bones was stimulated by rhTGF‐β1 in CPC. CPC that was intermixed with rhTGF‐β1 and then applied in rat calvarial defects enhanced bone growth around the cement and increased the degradation of the cement. It is still unknown however whether the addition of rhTGF‐β1 changes the material properties of the CPC, and what the release characteristics are of rhTGF‐β1 from the CPC. We therefore determined here the release of rhTGF‐β1 in vitro from the cement pellets as implanted in the rat calvariae. The possible intervening effects of rhTGF‐β1‐intermixing on clinical compliance of CPC were studied by assessing its compressive strength and setting time, as well as crystallinity, calcium to phosphorus ratio, porosity and microscopic structure. CPC was prepared by mixing calcium phosphate powder (58% α‐tricalcium‐phosphate, 25% dicalcium‐phosphate anhydrous, 8.5% calcium‐carbonate and 8.5% hydroxyapatite), with liquid (3 g/ml). The liquid for standard CPC consisted of water with 4% sodium hydrogen phosphate, while the liquid for modified CPC, was mixed with an equal amount of 4 mM hydrochloride with 0.2% bovine serum albumin. The hydrochloride liquid contained the rhTGF‐β1 in different concentrations for the release experiments. Most of the incorporated rhTGF‐β1 in the cement pellets was released within the first 48 hr. Approximately 0.5% rhTGF‐β1 (intermixed at 100 ng to 2.5 mg/g CPC) was released within the first 4 hr increasing to 1% after 48 hr. rhTGF‐β1 release continued at 0.1% up to at least 8 weeks. Modification of CPC slightly increased the initial setting time at 20°C from 2.6 to 5 min, but did not affect the final setting time of the CPC at 20°C, nor the initial and final setting time at 37°C. The compressive strength was increased from 18 MPa (standard CPC) to 28 MPa (modified CPC) only at 4 hr after mixing. The compressive strength diminished in the modified CPC between 24 hr and 8 weeks from 55 to 25 MPa. X‐ray diffraction revealed that both standard and modified CPC changed similarly from the basic components, alpha‐tri‐calcium phosphate and dicalcium phosphate anhydrous, into an apatite cement. The calcium to phosphorus ratio as determined by an electron microprobe did not differ for standard CPC and modified CPC. Standard and modified CPC became a dense and homogeneous structure after 24 hr, but the modified CPC contained more crystal plaques compared to the standard CPC, as observed by scanning electron microscopy (SEM). SEM and back scattered electron images revealed that after 8 weeks both cements showed an equally and uniform dense structure with microscopic pores (less than 1 μm). Both CPCs showed fewer crystal plaques at 8 weeks than at 24 hr. This study shows that the calcium phosphate cement was not severely changed by modification of the CPC for rhTGF‐β1. Clinical handling may be affected by the prolonged setting time of modified cement, but it is still within preferable limits. Compressive strength was for both standard and modified cements within the range of thin trabecular bone, and therefore both CPCs can withstand equal mechanical loading. The faster diminishing compressive strength of modified cement (from 24 hr to 8 weeks) likely results in early breakdown, and therefore might be favourable for bone regeneration. Together with our previous studies showing the beneficial effects of adding rhTGF‐β1 to CPC on bone regeneration, we conclude that the envisaged applications for CPC in bone defects are upgraded by intermixing of rhTGF‐β1. Therefore the combination of CPC with rhTGF‐β1 forms a promising synthetic bone graft.     

Acceleration of calcium phosphate formation on bioactive PMMA-based bone cement by controlling spatial design

Polymethylmethacrylate (PMMA)-based bone cement is widely used for the fixation of artificial joints. However, it is not considered a bioactive material because it lacks the ability to induce a direct bond with bone. In order to improve the long-term stability of cemented fixations, the development of bioactive bone cements is desirable. An essential requirement of a bioactive material includes the induction of bone-like apatite on its surface within the in vivo environment. Previously, we prepared bioactive PMMA-based bone cements by a modification with water-soluble calcium salts and alkoxysilane. Because spatial design may enhance apatite formation on bioactive material surfaces in vivo, we aimed to evaluate the effect of spatial design on apatite formation on modified PMMA-based bone cements in simulated body fluid (SBF). We found that an appropriate spatial design shortened the induction period for the apatite deposition on the modified bone cements. It is expected that osteoconduction would be enhanced in spontaneously created gap between the cement and the host bone leading to tight integration.     

Study of a hydraulic calcium phosphate cement for dental applications

Calcium phosphate-based cements (CPCs) have attracted much interest because of their good osteoconductivity for bone reconstruction. We obtained CPCs by mixing calcium bis-dihydrogenophosphate monohydrate (MCPM) and calcium oxide with water or sodium phosphate buffers (NaP) as liquid phase. Cement samples with different calcium-to-phosphate ratios (Ca/P), liquid-to-powder ratios (L/P) and liquid phases were analyzed by X-rays diffraction (XRD), pH-metry, extensometry and calorimetry. Antibacterial activity on two bacterial strains (Streptococcus mutans, Lactobacillus acidophilus) and a polycontaminated bacterial inoculum was also studied using the agar diffusion method. The best mechanical properties (25 MPa) corresponded to Ca/P ratios between 1.67 and 2.5, a 1 M sodium phosphate buffer pH 7, as liquid phase and a L/P ratio of 0.6 ml g^-1. The final setting time increased with the Ca/P ratio. The setting expansion, around 1–2%, depended on the Ca/P and L/P ratios. The inner temperature of the cements rose to 45° during setting then decreased rapidly. The injectability was 100% up to 3.5 min and then decreased. It increased with increasing the L/P ratio but to the detriment of the compressive strength and setting time. XRD analysis indicated that the setting reaction led to a mixture of calcium hydroxide and calcium-deficient hydroxyapatite even for a Ca/P ratio of 1.67. Consequently, the pH of the surrounding fluids rose to 11.5–12 during their dissolution. Bacterial growth inhibition was only clearly observed for Ca/P2. This bioactive calcium phosphate cement can potentially be employed for pulp capping and cavity lining as classical calcium hydroxide-based cements, but it is not usable, in the present formulation, for root canal filling because of its short setting time.     

磷酸钙骨水泥化学活性及机械性能研究

在研究磷酸四钙制备方法的基础上,讨论其化学活性,发现该物质在高温时热稳定性不好,易于向能量更低的羟基磷灰石转化;在室温下又容易吸附空气中的水分子,发生缓慢水解.因此最好真空保存.