The influence of surface topography on wear debris generation at the cement/bone interface under cyclic loading

The long-term success of a total joint replacement can be undermined by loosening of the implant, generation of wear debris or a combination of both factors. In the present study the influence of the surface morphologies of the bone and cement mantle on loosening of cemented total joint replacements (THJRs) and development of wear debris were studied. Model cemented THJR specimens were prepared in which the femoral canal was textured using specific cutting tools. The specimens were subjected to cyclic loads inducing pure shear fatigue of the cement/bone interface. Changes in both the femoral canal and cement mantle resulting from fatigue were quantified in terms of the surface topography and the volume of wear debris. Loosening occurred with cyclic loading due to degradation of the cement and bone and resulted in the development of cement and bone particles. There was no correlation between the fatigue strength of the interfaces and the volume of wear debris. In general, the change in surface topography of the cement mantle with fatigue decreased with increasing volume of cement interdigitation. Femoral canal surfaces with symmetric profile height distribution (i.e., Gaussian surfaces) resulted in the lowest volume of generated debris.     

The influence of the time-dependent properties of bone cement on stress in the femoral cement mantle of total hip arthroplasty

An empirically determined formula for the creep behavior of bone cement was incorporated into a validated computer model of a cemented femoral total hip arthroplasty component. The stress patterns in the cement mantle were observed over a period of one week, in one instance where the stem–cement interface was rigidly bonded, and in a second, where it was allowed to slip. Principal stresses and maximum shear stresses were shown to decrease rapidly after loading in both situations, suggesting that the stresses generated were not high enough to cause immediate failure, although they may be significant in the long term.     

The prediction of polyethylene wear rate and debris morphology produced by microscopic asperities on femoral heads

Counterface damage in the form of scratches, caused by bone cement, bone or metallic particles, has been cited as a cause of increased wear of ultra-high molecular weight polyethylene (UHMWPE) acetabular cups. It is known that high levels of particulate wear debris lead to osteolysis. Surface damage was characterized in a series of explanted Charnley femoral heads. The heads had a mean scratch height of 1 m with a mean aspect ratio (defined as height divided by half width) of 0.1. Wear discs were artificially scratched using these scratch geometries as a guide. In addition, the scratch geometries were incorporated into a finite element model of a stainless steel asperity repeatedly sliding over UHMWPE under conditions similar to those in an artificial hip joint. Wear tests showed a strong correlation between the average cross-sectional area of the scratch lip above the mean zero line and the measured wear factor. The finite element model predicted increases in the area of UHMWPE suffering plastic strain with increases in the cross-sectional area of the asperity above the mean line. Analysis of the wear debris showed the mode of the particle size was 0.01–0.5 m for all cases. The morphology of the particles varied with aspect ratio of the asperity, with an increased percentage mass of submicrometer-sized debris with increased scratch lip aspect ratio. The finite element results predicted that the maximum surface strains would increase with increasing asperity aspect ratio. Examination of the worn UHMWPE pin surfaces showed an association between increased surface damage, probably due to high surface strains, and increased aspect ratio. The large areas of surface plastic strain predicted for asperities with high cross-sectional areas above the mean line offer an explanation for the positive correlation between wear rate and the average cross-sectional area of the scratch lip material. The higher surface strains predicted for the higher aspect ratios may explain the increased percentage mass of biologically active submicrometer-sized wear particles found for scratch lips with higher aspect ratios. ©©2000 Kluwer Academic Publishers     

The influence of combined alignments on lateral acceleration on mountainous freeways: a driving simulator study

Combined horizontal and vertical alignments are frequently used in mountainous freeways in China; however, design guidelines that consider the safety impact of combined alignments are not currently available. Past field studies have provided some data on the relationship between road alignment and safety, but the effects of differing combined alignments on either lateral acceleration or safety have not systematically examined. The primary reason for this void in past research is that most of the prior studies used observational methods that did not permit control of the key variables. A controlled parametric study is needed that examines lateral acceleration as drivers adjust their speeds across a range of combined horizontal and vertical alignments. Such a study was conducted in Tongji University’s eight-degree-of-freedom driving simulator by replicating the full range of combined alignments used on a mountainous freeway in China. Multiple linear regression models were developed to estimate the effects of the combined alignments on lateral acceleration. Based on these models, domains were calculated to illustrate the results and to assist engineers to design safer mountainous freeways.     

Quantitative analysis of polyethylene wear debris, wear rate and head damage in retrieved Charnley hip prostheses

Submicrometer- and micrometer-sized ultra-high molecular weight polyethylene (UHMWPE) wear particles have been associated with osteolysis and failure of total artificial joints. Previous studies have isolated predominantly submicrometer-sized particles at the expense of larger particles (>10 m). This study aimed to isolate and characterize quantitatively all sizes of UHMWPE wear particles generated in 18 Charnley hip prostheses. In addition, to analyze the wear debris with respect to the total volumetric wear of the cup and damage to the femoral head. Particle size distributions ranged from 0.1 to ->1000 m. A significant proportion (3–82%) of the mass of the wear debris isolated was>10 m. The mode of the frequency distribution of the particles was in the range 0.1–0.5 m for all patients. However, analysis of the mass of wear debris as a function of its size allowed differentiation of the wear debris from different patients. Femoral head damage was associated with high volumetric wear and increased numbers of biologically active submicrometer-sized particles.     

Physical simulation of meteoroid and space debris particles influence on spacecraft construction elements

Three methods of physical simulation of collision with barriers of meteoroid particles and space debris are given. The direct method is to accelerate a model particle by means of a gun or a cumulative device. The method of collision simulation by the barrier splinters when the barrier is broken through with a high-speed steel particle, accelerated as before. The method of hydrosimulation is to simulate the particle and the barrier by means of liquid substances. Theoretical foundation of hydrosimulation is given and the results of compairing the crater dimensions obtained by the impact of liquid and solid pairs are discussed. The boundaries of hydrosimulation of high-speed impact according to velocities for solid impact pairs are V = 2 – 12 km/sec and the dimensions ratio are r /r < 3.     

PMMA brush-containing two-solution bone cement: preparation, characterization, and influence of composition on cement properties

Two-solution bone cement consisting of poly (methyl methacrylate) (PMMA) brushes in methyl methacrylate has been developed as an alternative to the traditional two-solution (TSBC) and powder-liquid cements. It was hypothesized that the substitution of brushes, for the entire pre-polymer phase of the cement, would permit a decrease in solution viscosity at higher polymer fractions, and allow for physical entanglements with the cement matrix. Consequently, improved cement exothermal and mechanical properties could be expected with brush addition. PMMA brushes were grafted on the surface of cross-linked PMMA nanospheres following a multi-stage synthetic strategy. Brushes exhibiting optimal molecular weight for preparation of TSBC were used for characterization of cement viscosity, flexural and compressive mechanical properties, exothermal properties and residual monomer content. Interactions between grafts and free polymer formed during free radical polymerization of the cement were evaluated based on molecular weight measurements of the cement matrix and brushes. Brush-containing cements exhibited lower viscosity at significantly higher polymer fractions in comparison to TSBC. Cements with PMMA brushes had significantly lower polymerization temperatures and residual monomer content. Measurements of molecular weight revealed the existence of a dry brush regime when using the brush compositions selected in this study, which led to a reduction in the mechanical properties of some of the compositions tested. The optimal cement viscosity and maintenance of other important cement properties achieved with addition of PMMA brushes is expected to expand the use of the two-solution cements in a range of applications.     

The effects of texting on driving performance in a driving simulator: The influence of driver age

Distracted driving is a significant contributor to motor vehicle accidents and fatalities, and texting is a particularly significant form of driver distraction that continues to be on the rise. The present study examined the influence of driver age (18–59 years old) and other factors on the disruptive effects of texting on simulated driving behavior. While ‘driving’ the simulator, subjects were engaged in a series of brief text conversations with a member of the research team. The primary dependent variable was the occurrence of Lane Excursions (defined as any time the center of the vehicle moved outside the directed driving lane, e.g., into the lane for oncoming traffic or onto the shoulder of the road), measured as (1) the percent of subjects that exhibited Lane Excursions, (2) the number of Lane Excursions occurring and (3) the percent of the texting time in Lane Excursions. Multiple Regression analyses were used to assess the influence of several factors on driving performance while texting, including text task duration, texting skill level (subject-reported), texting history (#texts/week), driver gender and driver age. Lane Excursions were not observed in the absence of texting, but 66% of subjects overall exhibited Lane Excursions while texting. Multiple Regression analysis for all subjects (N = 50) revealed that text task duration was significantly correlated with the number of Lane Excursions, and texting skill level and driver age were significantly correlated with the percent of subjects exhibiting Lane Excursions. Driver gender was not significantly correlated with Lane Excursions during texting. Multiple Regression analysis of only highly skilled texters (N = 27) revealed that driver age was significantly correlated with the number of Lane Excursions, the percent of subjects exhibiting Lane Excursions and the percent of texting time in Lane Excursions. In contrast, Multiple Regression analysis of those drivers who self-identified as not highly skilled texters (N = 23) revealed that text task duration was significantly correlated with the number of Lane Excursions. The present studies confirm past reports that texting impairs driving simulator performance. Moreover, the present study demonstrates that for highly skilled texters, the effects of texting on driving are actually worse for older drivers. Given the increasing frequency of texting while driving within virtually all age groups, these data suggest that ‘no texting while driving’ education and public service messages need to be continued, and they should be expanded to target older drivers as well.     

Simple isolation method for the bulk isolation of wear particles from metal on metal bearing surfaces generated in a hip simulator test

Isolation and characterization of metal-on-metal (MoM) wear particles from simulator lubricants is essential to understand wear behaviour, ion release and associated corrosive activity related to the wear particles. Substantial challenges remain to establish a simple, precise and repeatable protocol for the isolation and analysis of wear particles due to their extremely small size, their tendency to agglomerate and degrade. In this paper, we describe a simple and efficient method for the bulk isolation and characterisation of wear particles from MoM bearings. Freeze drying was used to remove the large volume of water from the serum lubricant, enzymes used to digest the proteins and ultracentrifugation to finally isolate and purify the particles. The present study involved a total of eight steps for the isolation process and a wear particle extraction efficiency of 45% was achieved.     

Impact of wear debris on striated muscle‐ a comparative in‐vivo study with titanium and stainless steel

Wear debris and corrosion products of metal implants induce biological events that may have severe consequences for skeletal muscle microcirculation. We therefore studied in vivo leukocyte‐endothelial cell interaction and leukocyte transmigration in skeletal muscle after confrontation with characterised titanium and stainless steel fretting corrosion particles, and compared these results with those of the bulk materials. Using the hamster dorsal skinfold chamber preparation and intravital microscopy, we could demonstrate in 30 animals that stainless steel induces a more pronounced inflammatory answer in contrast to the implant material titanium. However we were not able to show a general benefit of bulk vs. debris. Overall the study suggests that not only the bulk properties of orthopaedic implants but also the microcirculatory implications of inevitable wear debris may play a role in determining biocompatibility and ultimately longlivety of an implant. The skinfold chamber is a feasible and versatile model for observation of the dynamic process of microvascular response after foreign‐body implantation, and offers much perspective. With a minimum of adverse host reaction, our results indicate that titanium still represents the gold standard in metallic implant material, even in the case of generated wear debris, which shows a comparatively low inflammatory potential.     

The mechanical properties of recovered PMMA bone cement: A preliminary study

Samples of polymethylmethacrylate (PMMA) bone cement, used in the fixation of hip prostheses, have been recovered from 11 patients after in service life spans of between 15 and 24 years. Eighteen samples in total have been recovered from the acetabular and/or femoral cement. Samples were subjected to three point bending tests, their density, porosity and microhardness determined and all specimens were examined using EDX and X-ray techniques. Since the porosity of many of the samples is very high, the continuous matrix properties are inferred from the performance of individual specimens. No evidence has been found to suggest that the PMMA has deteriorated whilst in-vivo and the mechanical properties of the cement matrices appear to be comparable to freshly made PMMA.     

The influence of cruise control and adaptive cruise control on driving behaviour--a driving simulator study

Although Cruise Control (CC) is available for most cars, no studies have been found which examine how this automation system influences driving behaviour. However, a relatively large number of studies have examined Adaptive Cruise Control (ACC) which compared to CC includes also a distance control. Besides positive effects with regard to a better compliance to speed limits, there are also indications of smaller distances to lead vehicles and slower responses in situations that require immediate braking. Similar effects can be expected for CC as this system takes over longitudinal control as well. To test this hypothesis, a simulator study was conducted at the German Aerospace Center (DLR). Twenty-two participants drove different routes (highway and motorway) under three different conditions (assisted by ACC, CC and manual driving without any system). Different driving scenarios were examined including a secondary task condition. On the one hand, both systems lead to lower maximum velocities and less speed limit violations. There was no indication that drivers shift more of their attention towards secondary tasks when driving with CC or ACC. However, there were delayed driver reactions in critical situations, e.g., in a narrow curve or a fog bank. These results give rise to some caution regarding the safety effects of these systems, especially if in the future their range of functionality (e.g., ACC Stop-and-Go) is further increased.     

Preparation and characterization of a novel bioactive bone cement: Glass based nanoscale hydroxyapatite bone cement

A novel type of glass-based nanoscale hydorxypatite (HAP) bioactive bone cement (designed as GBNHAPC) was synthesized by adding nanoscale hydroxyapatite (HAP) crystalline (20–40 nm), into the self-setting glass-based bone cement (GBC). The inhibition rate of nanoscale HAP and micron HAP on osteosarcoma U2-OS cells was examined. The effects of nanoscale HAP on the crystal phase, microstructure and compressive strength of GBNHAPC were studied respectively. It was concluded that nanoscale HAP could inhibit the cell proliferation, while micron HAP could not, and that nanoscale HAP could be dispersed in the cement evenly and the morphology did not change significantly after a longer immersion time. XRD and FTIR results show nanoscale HAP did not affect the setting reaction of the cement. Furthermore, GBNHAPC had a higher compressive strength (92 MPa) than GBC. It was believed that GBNHAPC might be a desirable biomaterial that could not only fill bone defects but also inhibit cancer cell growth.     

The influence of wear on stresses in PCD inserts

The paper addresses the behavior of maximum stresses on the tool face and flank and the tool failure probability with increasing wear. The maximum tool life is calculated from the wear rate diagram. The authors provide some research findings on the influence of a Ni-resist cast iron embedded in the piston on the wear resistance of a PCD insert.     

The influence of Sr and H3PO4 concentration on the hydration of SrCaHA bone cement

Sr-contained calcium hydroxyapatite (SrCaHA) cement is a potential biomaterial for in vivo bone repair and surgery fixation due to its excellent biodegradability, bioactivity, biocompatibility, easily shaping and self-hardening. We had ever reported the in vitro physiochemical properties, biocompatibility and in vivo degradability of the SrCaHA cement obtained by mixing a cement powder of Ca(4)(PO(4))(2)O/CaHPO(4)/SrHPO(4) and a cement liquid of diluted H(3)PO(4) aqueous solution. In the present study, we intensively studied the influences of both Sr content and H(3)PO(4) concentration in diluted phosphoric acid aqueous solution on the setting time, hydration heat-liberation behaviours, and real-time microstructure and phase evolutions of the SrCaHA cement. The results show that both PO(4)(3-) and H(+) ions in PA solution attended the hydration reaction as reactants, and thus the increase of the PA concentration not only promoted the dissolution of Ca(4)(PO(4))(2)O but also pushed the hydration progress of SrCaHA bone cement. Sr content exhibits a remarkable retardation role on the apatite transformation of the SrCaHA cement pastes which probably attributed to its higher degree of supersaturation for yielding apatite crystals and lower transformation rate when exposed to the Sr(2+)-containing hydration system. This present results contribute to a better understanding on the hydration mechanism of the new SrCaHA cement and help to the more precisely controlling of its hydration process.     

The influence of tool wear particles scattering in the contact zone on the workpiece surface microprofile formation in polishing quartz

The paper describes the interaction and scattering of wear particles in the tool-workpiece contact zone in the course of polishing and explains the oscillatory structure of scatter of the tool wear particles on debris particles and on wear particles. The differential cross-section of scattering of the wear particles on the debris particles as well as on the wear particles is shown to be maximum in the case of forward scattering on the central segments of the contact zone. We have calculated the coordinate dependence of the differential cross-section of scattering of tool wear particles and the dependence of the polished surface microprofile height on the radius of circular zones. The theoretical curve of polished surface profile microirregularities is shown to fit well the experimental one for a quartz workpiece.     

Natural diatomite particles: Size-, dose- and shape- dependent cytotoxicity and reinforcing effect on injectable bone cement

Natural diatomite(DT) is the ancient deposit of diatom skeleton with many regular pores of 50–200 nm and also an abundant source of biogenic silica. Although silica is considered biologically safe and there is an increasing interest of using natural diatomite for biomedical applications, the toxicity information about natural diatomite is still missing. Here, cytotoxicity of natural diatomite on osteoblasts and fibroblasts were compared to hydroxyapatite and the relationships between cytotoxicity and diatomite sizes, dose, geometry or impurity were systematically investigated. Cell adhesion and interaction with diatomite particles were also fluorescently observed. The results clearly suggested a size-, dose-and shape-dependent cytotoxicity of natural diatomite. Disk-shaped diatomite particles with average size of30 um in diameter revealed the least toxicity, while the diatomite particles with irregular shapes and sizes less than 10 um were remarkably toxic. Diatomite particles with proper sizes were then selected to investigate the reinforcing effect on injectable calcium phosphate bone cement. Results showed that diatomite significantly improved the compressive strength of bone cement but did not alter the injectability of the cement. This work provided important biocompatibility information of natural diatomite and demonstrated the feasibility of using selected diatomite as bone implant material.     

Biological activity and migration of wear particles in the knee joint: an in vivo comparison of six different polyethylene materials

Wear of polyethylene causes loosening of joint prostheses because of the particle mediated activity of the host tissue. It was hypothesized that conventional and crosslinked polyethylene particles lead to similar biological effects around the knee joint in vivo as well as to a similar particle distribution in the surrounding tissues. To verify these hypotheses, particle suspensions of six different polyethylene materials were injected into knee joints of Balb/C mice and intravital microscopic, histological and immunohistochemical evaluations were done after 1 week. Whereas the biological effects on the synovial layer and the subchondral bone of femur and tibia were similar for all the polyethylenes, two crosslinked materials showed an elevated cytokine expression in the articular cartilage. Furthermore, the distribution of particles around the joint was dependent on the injected polyethylene material. Those crosslinked particles, which remained mainly in the joint space, showed an increased expression of TNF-alpha in articular cartilage. The data of this study support the use of crosslinked polyethylene in total knee arthroplasty. In contrast, the presence of certain crosslinked wear particles in the joint space can lead to an elevated inflammatory reaction in the remaining cartilage, which challenges the potential use of those crosslinked polyethylenes for unicondylar knee prostheses.     

Biocompatibility of calcium phosphate bone cement with optimised mechanical properties: an in vivo study

This work establishes the in vivo performance of modified calcium phosphate bone cements for vertebroplasty of spinal fractures using a lapine model. A non-modified calcium phosphate bone cement and collagen-calcium phosphate bone cements composites with enhanced mechanical properties, utilising either bovine collagen or collagen from a marine sponge, were compared to a commercial poly(methyl methacrylate) cement. Conical cement samples (8?mm height?×?4?mm base diameter) were press-fit into distal femoral condyle defects in New Zealand White rabbits and assessed after 5 and 10 weeks. Bone apposition and tartrate-resistant acid phosphatase activity around cements were assessed. All implants were well tolerated, but bone apposition was higher on calcium phosphate bone cements than on poly(methyl methacrylate) cement. Incorporation of collagen showed no evidence of inflammatory or immune reactions. Presence of positive tartrate-resistant acid phosphatase staining within cracks formed in calcium phosphate bone cements suggested active osteoclasts were present within the implants and were actively remodelling within the cements. Bone growth was also observed within these cracks. These findings confirm the biological advantages of calcium phosphate bone cements over poly(methyl methacrylate) and, coupled with previous work on enhancement of mechanical properties through collagen incorporation, suggest collagen-calcium phosphate bone cement composite may offer an alternative to calcium phosphate bone cements in applications where low setting times and higher mechanical stability are important.