Effect of process parameters on the characteristics of porous calcium phosphate ceramics for bone tissue scaffolds

Porous hydroxyapatite (HA) has already been widely used as a bone substitute due to its similarity with the mineral part of the bone. In this work, cylindrical tablets with micro and macro porosity were produced from stoichiometric and deficient hydroxyapatites by using naphthalene as porosifier agent. The influence of the processing parameters such as Ca/P ratio of start material, calcination temperature, and naphthalene content on the characteristics of porous calcium phosphate tablets was evaluated. Three mineral phases-HA, alpha-TCP (alpha tri-calcium phosphate), and beta-TCP (beta tricalcium phos-phate)-with variable contents were identified by x-ray diffraction (XRD) and Fourier-transformed infrared spectroscopy (FT-IR). Image analysis and density measurements were used to characterize sample porosity. As expected, the total porosity of the calcinated material is not dependent on the stoichiometry of the precursor hydroxyapatite. For calcium-deficient hydroxyapatite, the increase in naphthalene content contributes to stabilize alpha-TCP phase, altering the relative phases content.     

Fiber reinforced calcium phosphate cement

The term calcium phosphate cement was introduced by Gruninger et al. (1). This type of cement can be prepared by reacting a calcium phosphate salt with an aqueous solution, which causes it to set by the crossing of the precipitated crystals. These cements offer a series of advantages that allow their use as grafts and substitutes of damaged parts of the bone system. However, these cements have low mechanical strength compared to human bones. This work studied the influence of the use of polyamide fibers in the mechanical properties of a calcium phosphate cement based on alpha-tricalcium phosphate as well as the mechanisms involved in the increase of mechanical strength. The results demonstrate the feasibility of the use of polymeric fibers to increase mechanical strength and the need for coupling agents for the effective performance of the fibers as reinforcement in these materials.     

羟基磷灰石晶体纤维增强磷酸钙骨水泥力学性能及生物相容性研究

目的将高长径比的羟基磷灰石(HA)晶体纤维添加入磷酸钙骨水泥(CPC)中,研究HA晶体纤维对CPC抗压力学性能增强的最佳配方及在体内的生物相容性。方法采用水热合成法制备高长径比HA晶体纤维,并验证其细胞毒安全性。将2.5%、5%及10%(wt%)HA晶体纤维添加入CPC中,分析并获取HA晶体纤维对CPC力学性能增强的最佳配方。使用最佳配方制备CPC+HA晶体纤维复合材料,植入大鼠胫骨近端骨缺损模型,4、8周组织学观察HA晶体纤维添加入CPC的成骨性能及生物相容性。对照组为单纯CPC实验组。结果成功制备高长径比HA晶体纤维,其细胞毒安全性为1级(RGR79%)。与对照组相比,2.5%及5%HA晶体纤维添加入CPC可以增强材料的抗压力学性能(P<0.05),其中5%HA晶体纤维对CPC抗压性能的增强效果最佳,10%HA晶体纤维略降低CPC的抗压性能,但无统计学差异(P>0.05)。大鼠体内研究结果显示:与对照组相比,5%HA晶体纤维添加入CPC复合材料植入后材料周围骨体积分数(BV/TV)无显著性差异(P>0.05),HA晶体纤维添加入CPC后材料周围成骨与材料接触好,生物相容性良好。结论水热合成法制备的HA晶体纤维作为添加剂,具有增强CPC抗压力学性能,减低CPC脆性,生物相容性良好的特点,可用作骨植入生物材料的添加剂。     

磷酸钙骨水泥复合去甲万古霉素后理化性质改变及药物释放规律的研究

目的研究磷酸钙骨水泥(calcium phosphate cement，CPC)复合抗生素后理化性质的改变及体外药物释放规律。方法将CPC中复合1％、3％、50h，的去甲万古霉素，观察水泥的固化时间，测试固化强度，通过X线衍射(XRD)及傅立叶变换红外光谱分析(FTIR)检测固化产物，将抗生素骨水泥浸泡于生理盐水中，定期取浸泡液，用紫外分光光度计测定抗生素浓度，观察抗生素释放特点。结果随着加入去甲万古霉素浓度的增加，骨水泥固化时间缩短，固化强度降低，含量为5％时，抗压强度最低为20．1MPa，但仍高于正常松质骨强度。XRD与FTIR显示固化产物仍为碳酸化羟基磷灰石(carbonated hydroxyapatite，CHA)。抗生素在初期释放很快，48h后释放速度减慢并长时间维持。结论CPC具有原位固化特性，固化反应温和，不产生高热，不影响药物活性，体外实验证明可以维持很长的药物释放时间，是一种理想的抗生素载体，用于骨髓炎的治疗。     

In vivo degradation and new bone formation of calcium phosphate cement-gelatin powder composite related to macroporosity after in situ gelatin degradation

Calcium phosphate cement (CPC) is reported to have excellent biocompatibility and osteoconductivity. However, its biodegradability must be improved to promote bone regeneration. We have mixed gelatin powder with CPC to create a composite containing macropores with interconnectivity. Sixty rabbits were grouped as follows: 85 wt% CPC to 15 wt% gelatin powder (C15), 90 wt% CPC to 10 wt% gelatin powder (C10), 100 wt% CPC (C0) as control group and Sham group. Trabecular bone defects of distal femurs were made and implanted with the composites. The femurs were harvested for histomorphometry at 4, 12, 24 weeks after implantation, and mechanical testing at 3 days, 1, 4, 12, 24 weeks. Compared with C0, X-ray and micro-CT results of the composites revealed a progressive increase in the amount of CPC-gelatin powder composite which was replaced by trabeculae. New bone area increased from 3.8 to 18% in C10, and 4.2 to 22% in C15, residual composite area decreased from 65 to 31% in C10, and 70 to 20% in C15. The compressive strength of C15 was 9.2 MPa, which was inferior to 14.6 MPa (normal cancellous bone), but was 27.4 MPa in C10 at 1 week. Further improvement of this composite may make a suitable scaffold for bone regeneration.     

磷酸钙骨水泥可注射性的研究进展

目的 了解磷酸钙骨水泥注射性能的改性研究的进展。方法广泛查阅近年来的相关文献，对磷酸钙骨水泥的评价方法、可注射性评测方法及改性方法进行综述。结果提高磷酸钙骨水泥的注射性能是其改性研究的重要内容之一。常用的注射性能评价方法包括测定注射能力系数、推力和注射压力三种。可以通过提高液／固比、调整固相或液相成分，以及加入各种添加剂的方法提高磷酸钙骨水泥的注射性能。结论提高磷酸钙骨水泥的注射性能，适于临床应用需要，使其应用范围更加广泛。     

Self-hardening calcium phosphate composite scaffold for bone tissue engineering.

Calcium phosphate cement (CPC) sets in situ to form solid hydroxyapatite, can conform to complex cavity shapes without machining, has excellent osteoconductivity, and is able to be resorbed and replaced by new bone. Therefore, CPC is promising for craniofacial and orthopaedic repairs. However, its low strength and lack of macroporosity limit its use. This study investigated CPC reinforcement with absorbable fibers, the effects of fiber volume fraction on mechanical properties and macroporosity, and the cytotoxicity of CPC-fiber composite. The rationale was that large-diameter absorbable fibers would initially strengthen the CPC graft, then dissolve to form long cylindrical macropores for colonization by osteoblasts. Flexural strength, work-of-fracture (toughness), and elastic modulus were measured vs. fiber volume fraction from 0% (CPC Control without fibers) to 60%. Cell culture was performed with osteoblast-like cells, and cell viability was quantified using an enzymatic assay. Flexural strength (mean+/-SD; n=6) of CPC with 60% fibers was 13.5+/-4.4 MPa, three times higher than 3.9+/-0.5 MPa of CPC Control. Work-of-fracture was increased by 182 times. Long cylindrical macropores 293+/-46 microm in diameter were created in CPC after fiber dissolution, and the CPC-fiber scaffold reached a macroporosity of 55% and a total porosity of 81%. The new CPC-fiber formulation supported cell adhesion, proliferation and viability. The method of using large-diameter absorbable fibers in bone graft for mechanical properties and formation of long cylindrical macropores for bone ingrowth may be applicable to other tissue engineering materials.     

Acrylic bone—cement: Influence of mixer design and unmixed powder

The effects of hand mixing with two different mechanical mixing systems (fixed versus rotating central axis) on unmixed powder content, macroporosity, density, and bending strength of acrylic bone—cement are compared. The effects of voids and unmixed powder on cement bending strength are also evaluated. In acrylic cement, both unmixed powder monomer and voids 1 mm and larger can be easily visualized and analyzed on radiographs of 3-mm-thick samples. Image analysis allowed demonstration of a significant increase in unmixed powder content (P < .0001), in cement prepared using a vacuum mixing system with a fixed central axis compared with both the rotating axis system and hand mixing. The rotating-axis system produced cement of higher density compared with hand mixing only (P = .004). There was a significant correlation between the number of voids measured per square centimeter and cement bending strength (P < .0001), as well as an independent and significant correlation between unmixed powder content and cement bending strength (P < .0001). Mechanical mixing using a fixed central axis produced significantly weaker cement compared with both hand mixing (P < .015) and the rotating-central-axis system (P < .0001). A 15% drop in strength between the two mechanical mixing systems was observed. It is therefore concluded that the use of different rotating systems in mechanical mixers can influence void and unmixed powder content and, consequently, the mechanical properties of acrylic cement, and that unmixed powder is an independent factor affecting the bending strength of the cement.     

Experimental increase in resistance of the osteoporotic distal radius with a calcium phosphate cement

Diagnosis and treatment of osteoporosis are focused on demineralisation but bone mineral density is not directly correlated with bone strength. As with every material, the mechanical strength of bone depends upon its Young's modulus and its cross-sectional moment of inertia. In the clinical situation, bone strength can be quantified using peripheral quantitative computed tomography imaging (pQCT), a non-invasive imaging method, which allows calculation of a strength index. In this study, we tried to increase the fracture threshold of the distal radius by directly increasing bone strength rather than density. Twenty wrists in 10 cadavers were filled percutaneously with a calcium phosphate cement. Fluoroscopy and pQCT were performed twice, once before cementing and again 24 h after cement crystallisation to hydroxyapatite. We obtained measurements of trabecular and total bone density, and also stress strain index (SSI). Our results showed that trabecular bone density increased by a factor of 2.85, whereas total bone density increased by 1.61 and SSI by 1.99. Fluoroscopy showed two small leaks of cement at the point of injection. This study demonstrated that percutaneous injection of calcium phosphate cement increased distal radius strength, and consequently its fracture threshold. This technique could be employed in the future to prevent the occurrence of fractures in osteoporotic patients.     

Elution characteristics and mechanical properties of calcium sulfate-loaded bone cement containing teicoplanin

Background Acrylic bone cement is the most widely used drug delivery system clinically. It has already been shown that antibiotic release is significantly increased when calcium sulfate-loaded acrylic bone cement is used. However, there is no information yet about the mechanical responses of these composite materials. Thus, the purpose of this study was to investigate the effect of calcium sulfate on the elution characteristics and mechanical behavior of teicoplanin-loaded acrylic bone cement. Methods Four groups of acrylic bone cements (GI, GII, GIII, GIV) were prepared using the same liquid/powder ratios. After mixing, the bone cement and additive mixtures were packed into different-type molds to prepare the specimens for the elution and mechanical tests. All of the specimens were tested for two conditions (dry and human plasma solution). The mechanical tests included the setting time (hardness) and tensile, bending, and compression strengths. The fracture surfaces of the failed samples were also examined by scanning electron microscopy. Results Teicoplanin release in the calcium sulfate powder added groups (GIII and GIV) was higher than that of GII. When the calcium sulfate and teicoplanin were added on acrylic bone cement, the compressive, bending and tensile strength, hardness values, and elastic modulus decreased. Also, further reductions were evident in human plasma solution. Conclusions Although mechanical properties of tested specimens decreased, all of the results obtained were higher than those required by the American Society for Testing and Materials Standards, but further investigations are necessary before making definitive statements for clinical applications.     

预混合磷酸钙骨水泥研究进展

磷酸钙骨水泥以其良好的生物相容性、骨传导性及可塑性被作为骨缺损重要的修复材料,其性能的改进研究仍然是生物医学骨组织工程领域的热点课题。预混合磷酸钙骨水泥较传统原位即时混合型磷酸钙骨水泥具有方便临床手术操作、节约手术时间、便于保存等优点,克服了即时混合不均匀、不充分的缺点,并能根据缺损部位形状不同而随意塑形,因而预混合磷酸钙骨水泥也成为该领域研究热点之一。     

新型复合纤维蛋白胶的磷酸钙骨水泥的生物安全性研究

目的 研究新型复合纤维蛋白胶的磷酸钙骨水泥的生物相容性和生物安全性,探讨其用于临床修复骨缺损的可行性。方法 制备新型复合纤维蛋白胶的磷酸钙骨水泥,获取材料浸提液。选择急性毒性试验、溶血试验、微核试验、细胞毒性试验,对新型复合人工骨材料进行生物相容性和安全性评价。结果 该磷酸钙骨水泥材料浸提液未引起小鼠急性毒性反应;各实验组肉眼下未见明显溶血反应,溶血率0.05);浸提液对小鼠MC3T3成骨细胞的生长分化无明显影响,细胞毒性分级为Ⅰ级。结论新型复合纤维蛋白胶的磷酸钙人工骨材料具有良好的生物相容性和生物安全性。     

磷酸钙骨水泥复合物/脐带间充质干细胞凝胶构建组织工程骨

目的构建新型可注射强化型磷酸钙骨水泥复合物/脐带间充质干细胞凝胶组织工程骨,探讨其力学性能,细胞活性和成骨作用。方法选用第四代hUCMSCs,1.2%海藻酸钠水凝胶构建hUCMSCs水凝胶微球。高温煅烧钙/磷比约为1.9的磷酸氢钙和碳酸钙混合物,按摩尔质量比以1：1混合制备CPC粉末。15%Chitosan,8mm长度可吸收纤维用于提高CPC复合物力学强度。实验组分为四组：（1）单纯hUCMSCs微球;（2）CPC＋hUCMSCs微球;（3）CPC＋chitosan＋hUCMSCs微球;（4）CPC＋chitosan＋可吸收纤维＋hUCMSCs微球,分别检测力学性能,细胞活性和成骨作用。结果新型组织工程骨力学性能显著增强,抗弯曲强度提高到（11.7±2.1）MPa,弹性模量提高到（2.0±0.4）GPa,断裂功提高到（1.65±0.66）kj/m2（P〈0.05）。hUCMSCs的ALP活性第7天时明显增高,第14天时达峰,第21天时有所减弱,各组间比较无明显统计学差异（P〉0.1）。第7天时,所有实验组中的hUCMSCs均见少量矿物合成。第14天和第21天时,矿物合成数量明显增多。hUCMSCs中ALP基因表达培养第1天最低,第4天达峰,第8天时稍减弱。OC基因表达第8天达峰。结论构建完成新型可注射强化型磷酸钙骨水泥/脐带间充质干细胞凝胶构建组织工程骨。水凝胶微球中hUCMSCs在CPC中具有良好的成骨作用。CPC-chitosan-可吸收纤维组织工程骨力学性能满足松质骨力学要求,支持水凝胶微球中hUCMSCs的细胞活性和成骨作用。为组织工程骨研究和临床应用提供新思路和新方法。     

注射式磷酸钙骨水泥在胫骨平台骨折中的应用

目的采用回顾性分析方法,对注射式β-磷酸三钙骨水泥作为植骨材料在胫骨平台骨折中的临床疗效进行评估。方法对23例胫骨平台骨折复位后骨缺损区采用可注射式磷酸钙骨水泥进行填充。结果全部病例平均随访15.4个月,均获得骨性愈合,无骨不连和感染情况发生,内固定无松动及脱落现象。注射式β-磷酸三钙骨水泥术后10～12周开始出现吸收,20～24周大部分吸收,28～32周基本全部吸收。术后6个月和1年膝关节功能良好。结论注射式β-磷酸三钙骨水泥具有安全、方便、副作用小、填充效果确实等优点。固化后具有较强的支撑作用,可提高患者膝关节早期功能锻炼的安全性,促进了骨折的愈合过程,是治疗和填充胫骨骨折骨缺损区的较佳方法之一。     

用于骨质疏松脊柱压缩骨折的新型可降解材料的体外实验研究

目的 研发一种用于治疗骨质疏松椎体压缩骨折的新型复合生物玻璃的磷酸钙骨水泥,并观察其体外材料学及生物学活性。方法 将不同质量百分比的生物玻璃（bioglass,BG）与磷酸钙（calcium phosphate cement,CPC )球磨后物理共混获得一种具有可注射、自固化、可降解的椎体成型替代材料。分别对该替代材料的凝固时间、流动性、力学强度进行测定并行材料体外成骨细胞粘附实验、增殖实验,观察其生物相容性。结果 随着新型替代材料中BG组分含量的增加,替代材料的凝固时间逐渐延长,同时,流动性较磷酸钙骨水泥改善明显。随着凝固时间的延长,替代材料固化后的抗压强度显著高于实验组CPC骨水泥。此外,与CPC相比,替代材料更有利于细胞的粘附、增殖及分化,具有良好的生物相容性。结论新型复合生物玻璃的磷酸钙的生物材料不仅具有可注射性和较高的力学强度,同时骨传导性能更好,有希望成为临床治疗骨质疏松椎体压缩骨折的一种新型椎体成形材料。     

骨质疏松致椎体压缩性骨折PVP治疗中CPC填充物的应用研究进展

经皮椎体成形术(PVP)可增加椎体强度、解除疼痛,在脊柱疾病治疗中有着广泛的应用,临床研究已证实采用磷酸钙骨水泥(CPC)作为骨填充物是种安全、可靠、生物相容性高的替代材料。但单纯CPC作骨填充物仍不理想,文章从现阶段磷酸钙骨水泥的临床应用出发,总结分析出磷酸钙骨水泥的常用方式及最新的改性研究进展,以期为临床应用提供参考。     

Mechanical augmentation of the vertebral body by calcium phosphate cement injection

The effectiveness of transpedicular calcium phosphate cement (CPC) injection as a new treatment for osteoporotic compression fracture of vertebrae was evaluated by measuring the compressive strength and the mode of failure in vertebrae experimentally injected with CPC. Forty-five human cadaver vertebrae were divided into three groups: a control group; group A, in which CPC was injected into the upper half of the vertebral body; and group B, in which CPC was injected into the whole vertebra. The load-displacement curve characteristically had two peaks in group A, and decreased rapidly after failure in group B. The failure site was the cancellous bone immediately below the cranial endplate in the control group, cancellous bone immediately below the CPC injection area in group A, and in the CPC injection area in group B. Although mechanical strength was greatest in those vertebrae in which the entire cancellous bone was replaced with CPC, the compressive strength of the vertebrae was also increased by partial replacement of cancellous bone with CPC injection. In terms of mode of failure and mechanical gradient with adjacent vertebrae, there were several advantages for those vertebrae in which the cranial half of the cancellous bone was replaced with CPC. Received: May 29, 2000 / Accepted: September 20, 2000     

Experimental study of calcium phosphate cement impregnated with dideoxy-kanamycin B

Background The present study was undertaken to examine whether antibiotic-impregnated calcium phosphate cement (CPC) would provide a valid means of treating osteomyelitis. Methods The antibiotic used for the impregnation was dideoxy-kanamycin B (DKB), which is available in two forms (powder and liquid). Columnar test specimens (diameter 7 mm, height 14 mm) were prepared by adding the liquid or powdered DKB. Group A: Three types (6.25-titer, 12.5-titer, 25-titer) of test specimen were prepared by mixing the setting solution and DKB solutions into cement. Group B: Three types (25-titer, 50-titer, 100-titer) of test specimen were prepared by mixing the setting solution and DKB powder into cement. Group C: A control specimen was prepared by mixing the setting solution into the cement. The study included a consistency test, setting-time test, compressive strength test, porosity test, and elution test. Results The value for the consistency test was >23 mm in all test groups. The results of the setting-time test showed that the setting time became significantly longer as the DKB content increased for groups A group B. Compressive strength decreased as the antibiotic content increased, although all specimens remained sufficiently strong for clinical application. In group A the porosity did not differ significantly depending on the antibiotic content, whereas in group B the porosity increased significantly as the antibiotic content increased. In the elution test using specimens with the same titer (25 titer), the elution efficiency was higher in group A than in group B, and the duration of elution was longer in group A. Conclusions Although polymethylmethacrylate (PMMA) has been conventionally used as a drug-delivery system (DDS), the results of the present study indicate that CPC shows better elution efficiency than PMMA. It is thus a promising DDS for the treatment of osteomyelitis.     

Ultrastructural Study of Apatite Precipitation in Implanted Calcium Phosphate Ceramic: Influence of the Implantation Site

Macroporous biphasic calcium phosphate (MBCP) blocks were implanted into rabbit trabecular bone and muscle, recovered 18 weeks later, and then observed and analyzed by transmission electron microscopy (TEM), electron diffraction, and electron microprobes. The results showed that (1) apatitic microcrystals appeared by secondary nucleation in both bone and muscle sites; (2) precipitated microcrystals were aggregated around ceramic crystals in bone sites but distributed randomly and without orientation in micropores in muscle sites; (3) the ratio of calcium to phosphorus was higher for microcrystals in bone than muscle sites; and (4) precipitated microcrystals around β-tricalcium phosphate (β-TCP) crystals were less aggregated and dense than those around hydroxyapatite (HA). These findings suggest that microenvironmental parameters such as fluid circulation and the interaction of ceramics with proteins or cells affect the physicochemical dissolution/reprecipitation process. Epitaxic growth of apatitic microcrystals seems more favorable from HA than β-TCP. Received: 18 October 1996 / Accepted: 20 November 1997     

Grafting of tibial bone defects in knee replacement using Norian skeletal repair system

Introduction: The authors have been using Norian skeletal repair system (SRS) to repair cancellous bone defects in knee replacements since 1999. Norian SRS is injectable, biocompatible calcium phosphate cement with a high mechanical strength. This product is similar to the mineral phase of bone and should undergo gradual remodeling with time. We present our experience with this bone substitute in a total of 13 knee replacement surgeries. Materials and methods: This included three unicompartmental knee replacements (UKR), two bilateral UKR following tibial plateau fractures, five revisions of UKR to total knee replacements (TKR), two TKR revisions and one hinged knee prosthesis for significant deformity. Full weight bearing was permitted as soon as tolerated in all patients. Patients were evaluated at the latest follow-up using both the Knee Society Score (KSS) and GIUM (Italian UKR Users Group) knee scores. Results: At the latest follow-up, no poor results were seen with an improvement between pre-operative and post-operative knee scores in all cases. There was no evidence of bone loss or post-operative deformity. Complete compound resorption was seen in the first 4 cases. Conclusions: The authors state that Norian SRS is a practical alternative as bone grafting in knee replacement surgery for type 1 and 2 bone defects.