Mixed oxides prosthetic ceramic ball heads. Part 1: effect of the ZrO2 fraction on the wear of ceramic on polythylene joints.

Although mixed oxides ceramics have been indicated in the literature as a promising compromise between strength and wear, to the authors' knowledge no reports are available on the influence of the percentage of zirconia in ceramic femoral heads when sliding against polyethylene cups. Two types of mixed oxides ceramic ball heads (alumina plus, respectively, 60 and 80% of zirconia) were compared to pure zirconia and pure alumina heads in terms of wear behaviour against UHMWPE in a hip joint simulator. Polyethylene cups and ceramic femoral heads were fixed on a simulator apparatus with a sinusoidal movement and load in presence of bovine calf serum. The experimental results did not show significant difference between the two experimental ceramic materials or in comparison with pure materials. Considering that all specimens, regardless of the material, had the same level of surface roughness, this roughness factor seems to have a more relevant role than the mix of oxides used to manufacture the ceramic head. Wear tests are conducted on materials used in prosthetic hip implants in order to obtain quality control and to acquire further knowledge of the tribological processes that involve joint prostheses, therefore reducing the risk of implant failure of innovative prostheses.     

Mixed-oxides prosthetic ceramic ball heads. Part 2: effect of the ZrO2 fraction on the wear of ceramic on ceramic joints.

Three different types of mixed-oxides ceramic ball heads have been investigated for their wear behaviour against acetabular cups of the same materials in a hip joint simulator. Mixed-oxides ceramics have been indicated in literature as a promising compromise between strength and wear but no reports are available on the influence of a percentage of zirconia in a ceramic femoral head when sliding against itself. Mixed-oxides ceramic acetabular cups and femoral heads were tested on a simulator apparatus with a sinusoidal load in presence of bovine calf serum. The experimental results did not show any significant difference between the experimental and commercial ceramic material couplings. These results were found to be in accord with those developed in Part 1.     

Advanced nanocomposite materials for orthopaedic applications. I. A long-term in vitro wear study of zirconia-toughened alumina

The use of ceramic-on-ceramic (alumina- and zirconia-based) couplings in hip joint prostheses has been reported to produce lower wear rates than other combinations (i.e., metal-on-polyethylene and ceramic-on-polyethylene). The addition of zirconia into an alumina matrix (zirconia-toughened alumina, ZTA) has been reported to result in an enhancement of flexural strength, fracture toughness, and fatigue resistance. The development of new processing routes in nonaqueous media has allowed to obtain high-density ZTA nanocomposites with a very homogeneous microstructure and a significantly smaller and narrower particle-size distribution of zirconia than conventional powder mixing methods. The aim of the present study was to set up and validate a new ZTA nanocomposite by testing its biocompatibility and wear behavior in a hip-joint simulator in comparison with commercial alumina and experimental alumina specimens. The primary osteoblast proliferation onto ZTA nanocomposite samples was found to be not significantly different from that onto commercial alumina samples. After 7 million cycles, no significant differences were observed between the wear behaviors of the three sets of cups. In this light, it can be affirmed that ZTA nanocomposite materials can offer the option of improving the lifetime and reliability of ceramic joint prostheses.     

Low wear rate of UHMWPE against zirconia ceramic (Y-PSZ) in comparison to alumina ceramic and SUS 316L alloy

Partially stabilized zirconia ceramic is being recognized among ceramics for its high strength and toughness. With this ceramic, is possible to manufacture a 22-mm-size femoral head for low friction arthroplasty of the hip joint in association with an ultra-high-molecular-weight polyethylene socket. Wear-resistant properties of zirconia ceramic were screened on two principally different wear devices. Sterile calf bovine serum, physiological saline, and distilled water were chosen as the lubricant fluid media. Depending on the lubricant medium, the wear factor of polyethylene against zirconia ceramic counterfaces was 40 to 60% less than that against alumina ceramic counterfaces, and 5 to 10 times lower than with the SUS316L metal counterfaces. Polyethylene wear against metal was more susceptible in saline in which it had 2 to 3 times higher wear rate than with serum. On the other hand, different fluid media had little effect on polyethylene wear against ceramic counterfaces. In each set of tests, the wear factor obtained on an unidirectional wear device showed 10 to 15 times higher values, in comparison to the wear factor estimated on a reciprocating wear device.     

Wear properties of alumina/zirconia composite ceramics for joint prostheses measured with an end-face apparatus

While only alumina is applied to all-ceramic joint prostheses at present, a stronger ceramic is required to prevent fracture and chipping due to impingement and stress concentration. Zirconia could be a potential substitute for alumina because it has high strength and fracture toughness. However, the wear of zirconia/zirconia combination is too high for clinical use. Although some investigations on composite ceramics revealed that mixing of different ceramics was able to improve the mechanical properties of ceramics, there are few reports about wear properties of composite ceramics for joint prosthesis. Since acetabular cup and femoral head of artificial hip joint are finished precisely, they indicate high geometric conformity. Therefore, wear test under flat contact was carried out with an end-face wear testing apparatus for four kinds of ceramics: alumina monolith, zirconia monolith, alumina-based composite ceramic, and zirconia based composite ceramic. Mean contact pressure was 10 MPa and sliding velocity was 40 mm/s. The wear test continued for 72 hours and total sliding distance was 10 km. After the test, the wear factor was calculated. Worn surfaces were observed with a scanning electron micrograph (SEM). The results of this wear test show that the wear factors of the both composite ceramics are similarly low and their mechanical properties are much better than those of the alumina monolith and the zirconia monolith. According to these results, it is predicted that joint prostheses of the composite ceramics are safer against break down and have longer lifetime compared with alumina/alumina joint prostheses.     

Comparison of the cytotoxicity of clinically relevant cobalt-chromium and alumina ceramic wear particles in vitro

Concern over polyethylene wear particle induced aseptic loosening of metal-on-polyethylene hip prostheses has led to renewed interest in alternative materials such as metal-on-metal and alumina ceramic-on-alumina ceramic for total hip replacement. This study compared the effects of clinically relevant cobalt-chromium and alumina ceramic wear particles on the viability of U937 histiocytes and L929 fibroblasts in vitro.Clinically relevant cobalt-chromium wear particles were generated using a flat pin-on-plate tribometer. The mean size of the clinically relevant metal particles was 29.5+/-6.3 nm (range 5-200 nm). Clinically relevant alumina ceramic particles were generated in the Leeds MkII anatomical hip simulator from a Mittelmieier prosthesis using micro-separation motion. This produced particles with a bimodal size distribution. The majority (98%) of the clinically relevant alumina ceramic wear debris was 5-20 nm in size. The cytotoxicity of the clinically relevant wear particles was compared to commercially available cobalt-chromium (9.87 microm+/-5.67) and alumina ceramic (0.503+/-0.19 microm) particles. The effects of the particles on the cells over a 5 day period at different particle volume (microm(3)) to cell number ratios were tested and viability determined using ATP-Lite(TM).Clinically relevant cobalt-chromium particles 50 and 5 microm(3) per cell reduced the viability of U937 cells by 97% and 42% and reduced the viability of L929 cells by 95% and 73%, respectively. At 50 microm(3) per cell, the clinically relevant ceramic particles reduced U937 cell viability by 18%. None of the other concentrations of the clinically relevant particles were toxic. The commercial cobalt-chromium and alumina particles did not affect the viability of either the U937 histiocytes or the L929 fibroblasts.Thus at equivalent particle volumes the clinically relevant cobalt-chromium particles were more toxic then the alumina ceramic particles. This study has emphasised the fact that the nature, size and volume of particles are important in assessing biological effects of wear debris on cells in vitro.     

Clinical and simulator wear study of alumina ceramic THR to 17 years and beyond

Three THAs with cementless monolithic alumina ceramic sockets and cementless Co-alloy stems were retrieved because of aseptic loosening after 17 and 24 years. At revision heads and cups were marked for orientation. Maps were drawn of wear patterns with the use of light microscopy and surveyed by SEM. In a simulator experiment 28-mm-diameter alumina heads and liners were used. The cups were mounted inverted in a hip simulator and run with calf serum as the lubricant. The hip loads were 2 kN maximum and a 1-Hz frequency for 20 million cycles. Wear severity was classified into five grades. In retrieved implants, SEM analysis showed that the main wear zones (MWZ) had Grade 4 wear. The peripheral wear zones (PWZ) showed grain pull-out regions (Grade 5 wear). These corresponded to neck-socket impingement and head-acetabular cup separation. Gray was due to transferred CoCr particles from the stem. In the simulator study, the MWZ had only localized areas of grain pull out surrounded by polished surface regions (Grade 4 wear) at 20 million cycles; stripe wear was not seen. The alumina ceramic bearings proved excellent up to 22 years in simulator studies and clinical studies. However, microseparation kinematics would be necessary in the simulator to duplicate the more peripheral wear zones.     

Isolation and morphological characterisation of UHMWPE wear debris generated in vitro

Wear tests are generally carried out on materials used in prosthetic hip implants, in order to obtain a better understanding of the tribological processes involved and improve the quality control of joint prostheses, directed towards reducing the risk of implant failure of innovative prostheses. Ceramic femoral heads of mixed alumina-zirconia oxides as well as zirconia and alumina single oxide heads were tested against UHMWPE acetabular cups in a hip joint simulator. Polyethylene cups and ceramic femoral heads were mounted in a simulator apparatus moving according to a sinusoidal function, under load and in the presence of bovine calf serum as lubricant. Wear particles were isolated from the bovine calf serum collected during the wear tests. An easy to follow method was used to separate the wear particles from the lubricant. Chemical digestive methods were used to separate the wear particles from the lubricant and the isolated particles were studied using scanning electron microscopy. The morphologies of the polyethylene debris showed considerable differences, both in size and shape of the particles, as a function of the coupled head material.     

Effects of clinically relevant alumina ceramic wear particles on TNF-alpha production by human peripheral blood mononuclear phagocytes

The recent introduction of microseparation of the components of ceramic-on-ceramic hip prostheses during hip simulations has produced clinically relevant wear rates, wear patterns and wear particles. This provided an opportunity to determine the response of primary human peripheral blood mononuclear cells to clinically relevant alumina ceramic wear particles in vitro. Alumina ceramic wear particles were generated in a hip joint simulator under microseparation conditions. The particles showed a bi-modal size distribution with nanometer sized (5-20nm) and larger particles (0.2->10 micrometer). The particles were cultured with human peripheral blood mononuclear cells obtained from six different donors at particle volume to cell number ratios of 1, 10, 100 and 500 micrometer(3). After 24h incubation the viability of the cells and the levels of TNF-alpha were determined. The response to the microseparation wear particles was compared to that of commercially available alumina powder with a uniform morphology and mean size of 0.5 micrometer. All six Donors PBMNC produced significantly elevated levels of TNF-alpha when stimulated with 100 micrometer(3) of the alumina powder per cell. Volumetric concentrations of 10 and 1.0 micrometer(3) per cell failed to stimulate a significant response by the cells from any of the six donors. Three of the six Donors PBMNC secreted significantly elevated levels of TNF-alpha when stimulated with 100 micrometer(3) of the microseparation wear particles, whereas the other three failed to respond to the wear debris at this concentration. All of the Donors PBMNC produced significantly elevated levels of TNF-alpha when stimulated with 500 micrometer(3) of the microseparation wear particles per cell. Thus, a greater volume of the microseparation wear particles was required to activate the PBMNC than the alumina powder. This was probably due to the microseparation wear particles having fewer particles in the critical size range (0.1-1 micrometer) for macrophage activation compared to the alumina powder. It can be concluded that alumina ceramic wear particles generated under microseparation conditions are capable of inducing osteolytic cytokine production by human mononuclear phagocytes. However, the volumetric concentration of the particles needed to generate this response is extremely high and given the low wear rates (<4mm(3) per million cycles) of ceramic-on-ceramic bearings, even under severe microseparation conditions, it is unlikely that this concentration threshold will be achieved in vivo.     

Alumina-alumina artificial hip joints. Part II: characterisation of the wear debris from in vitro hip joint simulations

Until recently it was not possible to reproduce clinically relevant wear rates and wear patterns in in vitro hip joint simulators for alumina ceramic-on-ceramic hip prostheses. The introduction of microseparation of the prosthesis components into in vitro wear simulations produced clinically relevant wear rates and wear patterns for the first time. The aim of this study was to characterise the wear particles generated from standard simulator testing and microseparation simulator testing of hot isostatically pressed (HIPed) and non-HIPed alumina ceramic-on-ceramic hip prostheses, and compare these particles to those generated in vivo. Standard simulation conditions produced wear rates of approximately 0.1 mm3 per million cycles for both material types. No change in surface roughness was detected and very few wear features were observed. In contrast, when microseparation was introduced into the wear simulation, wear rates of between 1.24 (HIPed) and 1.74 mm3 per million cycles (non-HIPed) were produced. Surface roughness increased and a wear stripe often observed clinically on retrieved femoral heads was also reproduced. Under standard simulation conditions only nanometre-sized wear particles (2-27.5 nm) were observed by TEM, and it was thought likely that these particles resulted from relief polishing of the alumina ceramic. However, when microseparation of the prosthesis components was introduced into the simulation, a bi-modal distribution of particle sizes was observed. The nanometre-sized particles produced by relief polishing were present (1-35nm). however, larger micrometre-sized particles were also observed by both transmission electron microscopy (TEM) (0.021 microm) and scanning electron microscopy (SEM) (0.05-->10 microm). These larger particles were thought to originate from the wear stripe and were produced by trans-granular fracture of the alumina ceramic. In Part I of this study, alumina ceramic wear particles were isolated from the periprosthetic tissues from around Mittelmeier ceramic-on-ceramic hip prostheses. Characterisation of the particles by TEM and SEM revealed a bi-modal size distribution. SEM analysis revealed particles in the 0.05-3.2 microm size range. and TEM revealed particles in the 5-90 nm size range, indicating that microseparation of the prosthesis components may be a common event in vivo. This study (Part II) has revealed that the introduction of microseparation of the prosthesis components during the swing phase of the wear simulation reproduced clinically relevant wear rates, wear patterns and wear particles in in vitro hip joint simulators.     

The wear of a polyethylene socket articulating with a zirconia ceramic femoral head in canine total hip arthroplasty.

Wear of yttria-zirconia (zirconia) in the femoral head was investigated in mature mongrel dogs weighing 10 to 13 kg. Two dogs, which were used as a control group, were sacrificed 18 months after implantation of the uncemented modular hip system with an alumina ceramic (alumina) femoral head. A zirconia femoral head was implanted in five dogs: one was sacrificed 12 months after implantation, two at 18 months, and two at 24 months. In each femoral head and polyethylene (PE) socket, the surface was observed by means of scanning electron microscopy (SEM); the mean articulation surface roughness on the femoral head and PE socket and the thickness of the PE socket were measured. Wear was not seen on the surface of either the zirconia or the alumina heads. In both groups, minute white spots on the smooth surface of the PE socket were visible by SEM. In the alumina and zirconia groups the mean roughness was 0.1 microm. The mean thickness of the PE socket was reduced by 0.2 mm in the alumina group. In the zirconia group it was reduced by 0.2 to 0.3 mm. However, the mechanical strength of zirconia is known to be greater than that of alumina and it may be possible to reduce the diameter of the femoral head. The smaller zirconia head may contribute to the reduction of the wear of the PE socket in an uncemented modular total hip system.     

Combining ageing and wear to assess the durability of zirconia-based ceramic heads for total hip arthroplasty

The degradation of zirconia-based ceramic components for total hip arthroplasty (head and cup) has been the topic of many works. However, the correlation between what is measured in vivo and what is expected from in vitro simulations on hip simulators may be sometimes feeble, especially where zirconia component are concerned, mainly due to a lack of representativeness of in vitro experiments. The present study seeks to explore the combined effects of hydrothermal ageing and wear on zirconia components. It shows that hydrothermal ageing increases the roughness of zirconia components, which in turn might increase the wear rate of the polyethylene counterparts. Moreover, the friction during hip simulation increases the ageing rate of the zirconia components. This auto-accelerating degradation may explain some of the poor long-term in vivo results of zirconia hip prostheses reported in the literature. Finally, it is shown that zirconia-toughened alumina components may be free from this combined degradation.     

Microseparation and stripe wear in alumina-on-alumina hip implants

The combination of materials that still has highest wear resistance for total hip replacement is ceramic-on-ceramic. However, brittleness is a major concern for ceramics: in vivo and in vitro studies on ceramic hip prostheses correlate microseparation with hip noise, ceramic wear, or ceramic liner damage. Ceramic microseparation can lead to edge load, ceramic head wear, and squeaking. The aim of this in vitro study was to investigate whether different angles of inclination influence the wear pattern of alumina-on-alumina hip joints with micro-separation during the swing phase. We also evaluated the wear rate obtained from this in vitro investigation with retrieval specimens obtained at 13 years' mean follow-up. The study was performed using a 12-station hip joint wear simulator (Shore Western, Monrovia, CA, USA) under bovine calf serum used as lubricant. Wear was evaluated by the gravimetric method and the test length was set at two million cycles. After two million cycles, a volumetric loss of 0.11 ±0.03 mm3 and 0.12 ±0.06 mm3 was observed, respectively, for 23° and 63° angles of inclination. In particular, the results obtained in this work revealed an increase of about 12-fold compared to previous results without microseparation conditions. No significant differences were observed between the two different inclinations on the wear patterns of the acetabular cups with a level of significance of a = 0.5. The location and general shape of the stripes wear were similar for the retrieved and simulator balls.     

An in vitro investigation of diamond-like carbon as a femoral head coating

Wear of polyethylene acetabular components of hip implants is a significant clinical problem. In prosthetic hip surgery, polyethylene wear is identified as a factor that limits the life of the implant; it is known that the production of debris can cause adverse tissue reactions that may lead to extensive bone loss around the implant, and consequently loosening of the fixation. A new class of so-called Diamond-Like Carbon coatings, applied to titanium femoral heads was compared to ceramic and metallic heads in terms of wear behavior against UHMWPE using a hip joint simulator with a bovine calf serum lubricant. A thin film of Diamond-Like Carbon was deposited directly onto titanium (Ti6Al4V) head using chemical vapor deposition. The wear of polyethylene coupled with Diamond-Like Carbon coated femoral heads was comparable to that obtained with the polyethylene coupled with commercial alumina femoral heads.     

Volumetric determination of the wear of ceramics for hip joints.

Osteolysis relating to the reaction cascade to wear debris is the main cause of the failure of arthroprostheses. New materials are still under development to minimise the wear of joints and to improve in this way the performance of total joint replacements. Testing the wear performance of very low wear materials is a rather sophisticated technique. Currently, the worn volume is calculated from the weight variations of the sample, observed from wear testing. This method may be limited especially when very low weight differences are to be evaluated on high hardness, high-density materials like CoCr alloys or ceramics like alumina or zirconia. In the present work, the tribological behaviour of ceramic biomaterials like alumina, Y-TZP and alumina-zirconia composites was evaluated by a pin-on-disc apparatus under different testing conditions. The worn volume was calculated by the use of 3-D (three-dimensional) optical profilometry data. Comparison between 3-D optical profilometry and gravimetric wear data shows the better accuracy of the profilometric method in the determination of wear rate in the range of 10(-7) mm3 (mN(-1)) or lower.     

Severe wear from retrieved alumina-on-alumina coupled implant: a case report.

This study details the in vivo wear behavior of an alumina acetabular cup and a femoral head on a retrieved non-cemented hip prosthesis. A commercial alumina ceramic-on-ceramic prosthesis was retrieved from a patient previously treated for bilateral hip arthrosis in "coxa profunda". Massive wear was found on the retrieved alumina ceramic head and acetabular cup. The total measured penetration depth was 1.9 mm while the total calculated weight loss for the acetabular cup was 6.06 g. The study underlines the head-cup instability caused by cup loosening as major cause of severe ceramic wear.     

口腔氧化锆陶瓷的粘接方法

背景：氧化锆陶瓷因具有良好的理化性能和生物相容性在口腔修复重建领域被广泛应用,但如何对氧化锆陶瓷表面进行改性,以提高修复体与牙体组织的粘接强度成为目前临床工作中的难点。 目的：综述口腔氧化锆陶瓷的粘接方法。 方法：应用计算机检索PubMed 数据库,检索关键词为“zirconia, silane coupling agent, resin cement, bonding”。 结果与结论：通过化学摩擦硅涂层系统结合新型混合非功能性硅烷偶联剂对氧化锆瓷进行表面处理,利用小粒径(50 µm)的含硅颗粒氧化铝粉末对氧化锆进行喷砂,形成含硅粒子的粗糙覆盖表层,此系统可降低传统喷砂对瓷边缘薄弱部位的损伤,提高修复体边缘密合度;新型混合非功能性硅烷偶联剂与陶瓷表面可形成稳定且高强度的硅氧烷键,其水解稳定性远高于传统的硅烷偶联剂,利用硅氧烷在界面处与聚合物交联形成的互穿网络体系,可更有效地将树脂共价接枝到硅烷表面,有效提高氧化锆陶瓷与树脂的粘接强度,为修复体提供足够的固位力,提高临床修复成功率。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;组织工程全文链接：     

Crack growth resistance of alumina, zirconia and zirconia toughened alumina ceramics for joint prostheses.

Mono-phase bio-ceramics (alumina and zirconia) are widely used as femoral heads in total hip replacements (THR) as an alternative to metal devices. Unfortunately, the orthopaedic community reports significant in-vivo failures. Material scientists are already familiar with composites like alumina zirconia. Since both are biocompatible, this could prove to be a new approach to implants. This paper deals with a new generation of alumina-zirconia nano-composites having a high resistance to crack propagation, and as a consequence may offer the option to improve lifetime and reliability of ceramic joint prostheses. The reliability of the above mentioned three bio-ceramics (alumina, zirconia and zirconia toughened alumina) for THR components is analysed based on the study of their slow crack-growth behaviour. The influence of the processing conditions on the microstructure development, of the zirconia toughened alumina composites and the effect of these microstructures, on its mechanical properties, are discussed.     

Hemocompatibility of high strength oxide ceramic materials: an in vitro study

High strength oxide ceramic materials like alumina and zirconia are frequently used for artificial joints because of their biocompatibility and high wear resistance. Their suitability as materials for implants and biomedical devices with direct blood contact, such as cardiovascular implants or components for blood pumps and dialyzers, has not been confirmed to date. The objective of this study was to investigate whether oxide ceramics show sufficient hemocompatibility. Dense specimens were made out of alumina, zirconia, titanium oxide, and aluminum titanate. Polyvinylchloride and silicone were additionally tested as reference materials. Interactions of human blood with the surfaces were studied by investigating partial thromboplastin time (PTT), thrombin antithrombin III complex (TAT), free plasma hemoglobin concentration, complete blood count, complement factor 5a, and protein adsorption. The results from the PTT and TAT tests clearly indicated higher blood activation by the ceramic materials when compared to the two polymer materials. However, alumina and zirconia showed lower C5a concentrations and less protein adsorption than the reference materials. Our results revealed that oxide ceramic materials alone cannot be used for implants in direct blood contact without modification of the ceramic surface, for example, by made-to-measure inert nanocoatings.     

Long-term wear of ceramic matrix composite materials for hip prostheses under severe swing phase microseparation

The purpose of this study was to evaluate the long-term wear performance of alumina matrix composite (AMC) heads against alumina matrix composite inserts and alumina matrix composite heads against alumina (Al) inserts with the use of a hip-joint simulator incorporating severe swing phase joint microseparation. The wear of AMC on Al produced an average wear rate of 0.61 mm3/million cycles over the 5-million-cycle test duration. The wear of AMC on AMC produced an average wear rate of 0.16 mm3/million cycles over the 5-million-cycle test duration. Both the AMC on alumina and AMC on AMC produced significantly lower wear than previously tested HIPed alumina, where an average wear rate of 1.84 mm3/million cycles was reported over 5 million cycles. The wear mechanisms and wear debris of AMC on AMC and AMC on Al were similar to those observed in previous alumina retrieval studies with stripe wear caused by intragranular fracture and wear debris consisting of predominantly uniform 10-20-nm-sized particles and a few irregular particles up to 3 microm in size.