bluuebunny/crossref_metadata_2025 huggingface dataset:
A low-mass multistage radiator for the passive cooling of X-ray charge-coupled devices in space
Authors: Goodall C V , Butler I G , Mahmoud S M
Published: October 2002

This paper describes the design and construction of a quasi-three-stage radiator as a means of passively cooling an X-ray charge-coupled device (CCD) which was at a distance of about 1 m from a radiating aperture having an unobscured view to cold space. The design was tested through thermal balance measurements which confirmed that a base temperature of —150°C could be achieved at the CCD. The low mass design was essential in ensuring the absence of significant resonant frequencies of vibration below 100 Hz. The system forms part of the EPIC instrument on the European Space Agency (ESA) cornerstone X-Ray Multi-Mirror (XMM) mission which was recently and successfully launched on an Ariane V rocket.
A panel with matched polyvinylidene fluoride volume velocity sensor and uniform force actuator for the active control of sound transmission
Authors: Gardonio P , Lee Y S , Elliott S J , Debost S
Published: October 2002

This paper presents a theoretical and experimental study of a smart panel designed for active structural acoustic control. The system consists of a clamped aluminium panel 1 mm thick with dimensions 414 mm X 314 mm. Polyvinylidene fluoride films 0.5 mm thick with a quadratic electrode shape are bonded to either side of the plate, to form a matched volume velocity sensor and uniform force actuator pair. In this paper the design of the smart panel is described in detail. The main properties of the frequency response from distributed actuator to distributed sensor are then discussed with reference to the requirements for direct velocity feedback control. In particular, three problems encountered in the measurement of the transfer function between the sensor and actuator are addressed: first, the unwanted coupling between the sensor and actuator via in-plane plate vibration; second, the high-frequency effects produced by the non-perfect shaping of the actuator and sensor electrodes; third, the phase delays due to the measurement equipment chain.
Blended wing body airframe mass prediction
Authors: Howe D
Published: October 2002

The blended wing body (BWB) concept is one in which the payload is carried within the inner wing of the aircraft, the local aerofoil sections being deepened to accommodate it. Difficulties, both in design and mass prediction, arise when the payload requires the pressurization of the non-circular cross- sections of the blended wing region. The paper presents a method by which the mass of the BWB airframe may be predicted using an empirically weighted theoretical approach. The ideal wing structure mass is modified by introducing penalties for the secondary structure and, in particular, the payload carrying function. Absolute validation of the method is not possible as no full-size aircraft of this category has been built and flown. Nevertheless, application of the method to several design studies gives reason to believe that it is acceptable for preliminary design purposes.
Wind tunnel experiments on the optimization of distributed suction for laminar flow control
Authors: Wright M C M , Nelson P A
Published: October 2002

It is well known that surface suction can delay boundary layer transition from laminar to turbulent flow, thus reducing drag on the surface in question. In order for laminar flow control by means of suction to be a paying proposition on aircraft, however, it must reduce total energy consumption as well as net drag. The flow control system that will have the best chance of doing this will use the minimum amount of suction pump energy to achieve a given transition position. Previous work has shown how a steepest- descent constrained optimization algorithm in conjunction with a radial basis function gradient estimator is capable of doing this online. In this paper the control strategy is applied to a large (2 m chord, 1.6 m span) aerofoil model in a low turbulence tunnel, with variable incidence and direct force measurement. The effect of pressure gradient over the suction section on the efficacy of the suction can therefore be observed, as can the relationship between transition and drag. The system is shown to converge reliably as long as the desired transition is within its range, and to be capable of maintaining control after a change in aerodynamic conditions without needing to re-identify the gradient estimation coefficients.
Helicopter flight around a ship's' superstructure
Authors: Wakefield N H , Newman S J , Wilson P A
Published: October 2002

A computational fluid dynamics model of a hovering helicopter main rotor is developed to examine air flow in the presence of ship structures and side winds. An illustration of the problem is given. The rotor is modelled by modifying the governing Navier-Stokes equations in the region of the disc. The extra terms added to the governing equations apply a downward force to the fluid; these forces are independent of the flow around the rotor and are equal to the helicopter weight.

The helicopter rotor model and the ship model are combined to yield one flow solution, which, due to the severe non-linearities of the problem, cannot be achieved by superposition. The resultant flow yields valuable data about the induced velocities at the rotor, which ultimately determine the control pitch and power required to maintain the hover in a given location. Indeed, the interactions between the rotor downwash and ship air flow are known to produce unexpected and adverse flight dynamic behaviour of the aircraft.
A validation of the three-dimensional finite element contact method for use with Curvic couplings
Authors: Richardson I J , Hyde T H , Becker A A , Taylor J W
Published: October 2002

Curvic couplings transmit torque between parallel in-line shafts or turbine/compressor discs. They are used extensively within the aero-engine industry but can also be found in industrial gas turbines. The manufacture of Curvic couplings involves the precision cutting and grinding of mating teeth on the adjacent ends of the components; the assembly is then clamped together with bolts.

The design objectives for aerospace transmissions, and hence the Curvic coupling, are to reduce manufacturing cost, weight and size. The experimental testing of Curvic couplings within an aero-engine environment is time consuming and expensive. The objective of this paper is to justify confidence in the results from three-dimensional finite element (F E) contact analyses when investigating Curvic couplings. The accuracy of the FE analyses requires a fine mesh in the contact region and the capability to deal with stick-slip behaviour in multiple three-dimensional contact surfaces. A comparison of the results from a photoelastic test with the results from an FE analysis provides a validation of the FE contact method for use with Curvic couplings. The results presented in this paper indicate that the photoelastic results agree reasonably well with results of the FE method analyses.
The internal bevel gear and its applications
Authors: Molyneux W G
Published: October 2002

Information on bevel gears and their applications is comprehensive where external bevel gears are concerned but proves to be more scarce when related to internal bevel gears, despite the fact that there are isolated practical examples of the use of such gears that have demonstrated their effectiveness in demanding transmission situations.

In what follows a unique family of transmissions is examined, based solely on a particular layout of internal and external bevel gear combinations, that aims to demonstrate the wide ranging, largely unexploited, potential of transmission systems of this kind.
Developments in adhesively bonding the wings of the SAAB 340 and 2000 aircraft
Authors: Hart-Smith L J , Strindberg G
Published: October 2002

The development of the adhesive bonding of the wing of the SAAB 340 and 2000 aircraft is traced from the development of the technology during the Primary Adhesively Bonded Structure Technology (PABST) research programme performed at Douglas Aircraft under contract to the US Air Force Wright Laboratories in the late 1970s through initial fabrication by Fairchild in America in the early 1980s to series production by SAAB in Sweden and, today, also by CASA in Spain. The saga of solving a processing problem encountered in America before the first aircraft was delivered is recounted as an object lesson in how to approach problems and in the benefits derived by doing so promptly and thoroughly. Every aspect of the problem was identified and replicated in the laboratory where, because it was understood properly, it could be duplicated and prevented at will. The lessons learned about bonding tool designs from this investigation and during the manufacture of the PABST fuselage were implemented during the transfer of production of the wing from America to Sweden. The use of a floating caul plate, rather than a traditional rigid bonding tool, is explained. The justification for doing so is the virtual elimination of all fit problems and the production of a far more uniform void-free bond line. In addition, the evolution of progressively simpler, yet more effective, bagging procedures is also described, culminating in a refinement of a technique pioneered by Fokker in Holland. Today, all breather and bleeder layers have been eliminated. This reduces costs and the need for disposal of costly expendable materials and also permits a positive check of the fit of the details by visual examination through the transparent bag once the vacuum is drawn before the assembly is inserted into the autoclave, giving an opportunity to correct any misfits while it is still possible to do so. Consequently, there is also no need for traditional verifilm operations. The tooling technology developed during the PABST programme did not die when the contract was completed with no follow-on production programme for large transport aircraft in the United States. It is alive and flourishing in Sweden. In addition, as the paper describes, the transfer of the technology was so complete that it has since been improved upon. Today, the bonding of the stiffened wing skins for these two aircraft is probably the most advanced and simultaneously the most forgiving production application of large-scale metal bonding the world has yet seen.
Implications of NOy emissions from subsonic aircraft at cruise altitude
Authors: Lee S H , Le Dilosquer M , Singh R , Hobbs S E , Giannakopoulos C , Plantevin P H , Law K S , Pyle J A , Rycroft M J
Published: October 2002

The exhaust emissions from civil subsonic aircraft at cruise altitude are important man-made sources that pollute the upper troposphere and the lower stratosphere (8-12 km). The formation of NO y species from NO x, both before and after the exit nozzle, have created increasing environmental concerns. Flight histories of Boeing 747-400 aircraft during the cruise stage between selected city pairs have been simulated using a computer program developed at Cranfield University. The passive distribution of NO x and HNO3 is calculated using the UGAMP three-dimensional chemical transport model. The sink of NO x, which is HNO3, is parameterized using an exponential decay process with an altitude-dependent lifetime. The model also includes transport by advection, vertical diffusion and convection. These simulations for January and July are analysed in terms of the resulting mean volume mixing ratios for both NO x and HNO3.
Grid adaptation for unsteady flow computations
Authors: Allen C B
Published: October 2002

A grid adaptation procedure suitable for use during unsteady flow computations is described. Transfinite interpolation is used to generate structured grids for the computation of steady and unsteady Euler flows past aerofoils. This technique is well suited to unsteady flows, since instantaneous grid positions and speeds required by the flow solver are available directly from the algebraic mapping. A different approach to grid adaptation is described, wherein adaptation is performed by redistributing the interpolation parameters, instead of the physical grid positions. This results in the adapted grid positions, and hence speeds, still being available algebraically. Grid adaptation during an unsteady computation is performed continuously by imposing an ‘adaptation velocity’ on grid points, thereby applying the adaptation over several time steps and avoiding the interpolation of the solution from one grid to another, which is associated with instantaneous adaptation. For both steady and unsteady flows the adapted grid technique is shown to produce sharper shock resolution for a very small increase in CPU (central processing unit) requirements.
The development and validation of a model for the electron beam welding of aero-engine components
Authors: Reed R C , Stone H J , Roberts S M , Robinson J M
Published: October 2002

Electron beam welding is used to manufacture high-integrity structures, for example compressor assemblies, for the latest generation of Rolls-Royce aero-engines. For such applications, the welding variables (for example welding current, voltage, beam focusing parameters) must be optimized, such that any distortion induced by the process is insignificant when compared to the dimensional tolerances allowed by the designers. Furthermore, the residual stresses induced by the process must be described and characterized, since these are required for estimates of component life. A model for such electron beam welding processes is described, along with the strategy adopted during its development. The basis of the model is a coupled thermal-mechanical finite element analysis. Particular attention is paid to (a) modelling of the heat source, (b) the frame of reference for the analysis, and (c) choice of finite element mesh. For the purposes of calibration and verification, a number of validatory experiments have been carried out. Typical results are presented and practical benefits are discussed.
A method for identification of non-linear multi-degree-of-freedom systems
Authors: Dimitriadis G , Cooper J E
Published: October 2002

System identification methods for non-linear aeroelastic systems could find uses in many aeroelastic applications such as validating finite element models and tracking the stability of aircraft during flight flutter testing. The effectiveness of existing non-linear system identification techniques is limited by various factors such as the complexity of the system under investigation and the type of non-linearities present. In this work, a new approach is introduced which can identify multi-degree-of-freedom systems featuring any type of non-linear function, including discontinuous functions. The method is shown to yield accurate identification of three mathematical models of aeroelastic systems containing a wide range of structural non-linearities.
A study of unsteady wake-induced boundary-layer transition with thermochromic liquid crystals
Authors: Zhong S , Kittichaikan C , Hodson H P , Ireland P T
Published: October 2002

A method of using thermochromic liquid crystals has been developed to visualize the thermal footprints of artificially created turbulent spots as they propagate downstream in an otherwise laminar boundary layer. In the present study, this technique was employed to study the turbulent events, which were generated spontaneously by turbulent wakes of circular cylinders convecting in a laminar boundary layer over a heated flat plate. The experiment was conducted in a water tunnel at a free-stream velocity of 0.2 m/s. The purpose of the experiment was to simulate the unsteady wake-induced boundary-layer transition typically occurring in multistage turbomachines. The location of the onset of transition and the turbulent spot formation rate were obtained by processing the recorded colour change of thermochromic liquid crystals for the first time. The results were compared with those predicted from standard correlations.
Mass-averaging pseudo-shock model in a straight flow passage
Authors: Matsuo K , Miyazato Y , Kim H D
Published: October 2002

Pseudo-shock is often encountered in a variety of internal flows, almost always entailing an increase in total pressure loss, hence leading to deterioration of the flow system performance. This pseudo-shock is a very complex process still requiring a good deal of elucidation. In spite of the recent rapid progress that has been made in numerical computation methods, there is as yet no quantitative prediction of pseudo-shock flow. The present paper describes a simple pseudo-shock flow model using a mass-weighted averaging technique. The flow quantities across pseudo-shock were analysed for different Mach numbers, flow confinements and turbulent boundary layer Reynolds numbers. The analytical results agree well with the previous experimental data. The flow model presented can be used to estimate the important features of pseudo-shocks in engineering practice.
Liquid sheet radiators for space power systems
Authors: Tagliafico L A , Fossa M
Published: October 2002

Liquid sheet radiators offer a promising technological solution to the problem of disposing of large heat fluxes in space. The present paper describes the fluid-dynamic and thermal characteristics of a liquid sheet radiator (LSR) and presents a design method aimed at establishing the optimal design parameters of the radiator system from the point of view of reducing the mass, radiating surfaces and electrical energy required to circulate the refrigeration fluid. The algorithm is used to analyse various LSR designs combined with a power conversion unit for the production of electricity in given working conditions in space. When compared with the performance of a liquid droplet radiator (LDR), the results reveal the differences in design and functioning of the two systems, as well as the effect of variations in the thermal load on the performance of the LSR. Finally, the possible developments of this type of radiator and the most promising solutions in terms of performance and efficient coupling with the energy conversion system are discussed.
Development of artificial articular cartilage
Authors: Oka M , Ushio K , Kumar P , Ikeuchi K , Hyon S H , Nakamura T , Fujita H
Published: October 2002

Attempts have been made to develop an artificial articular cartilage on the basis of a new viewpoint of joint biomechanics in which the lubrication and load-bearing mechanisms of natural and artificial joints are compared. Polyvinyl alcohol hydrogel (PVA-H), ‘a rubber-like gel’, was investigated as an artificial articular cartilage and the mechanical properties of this gel were improved through a new synthetic process.

In this article the biocompatibility and various mechanical properties of the new improved PVA-H is reported from the perspective of its usefulness as an artifical articular cartilage. As regards lubrication, the changes in thickness and fluid pressure of the gap formed between a glass plate and the specimen under loading were measured and it was found that PVA-H had a thicker fluid film under higher pressures than polyethylene (PE) did. The momentary stress transmitted through the specimen revealed that PVA-H had a lower peak stress and a longer duration of sustained stress than PE, suggesting a better damping effect. The wear factor of PVA-H was approximately five times that of PE. Histological studies of the articular cartilage and synovial membranes around PVA-H implanted for 8–52 weeks showed neither inflammation nor degenerative changes. The artificial articular cartilage made from PVA-H could be attached to the underlying bone using a composite osteochondral device made from titanium fibre mesh.

In the second phase of this work, the damage to the tibial articular surface after replacement of the femoral surface in dogs was studied. Pairs of implants made of alumina, titanium or PVA-H on titanium fibre mesh were inserted into the femoral condyles. The two hard materials caused marked pathological changes in the articular cartilage and menisci, but the hydrogel composite replacement caused minimal damage. The composite osteochondral device became rapidly attached to host bone by ingrowth into the supporting mesh.

The clinical implications of the possible use of this material in articular resurfacing and joint replacement are discussed.
Analytical modelling of the elastomeric layer in soft layer hip replacements
Authors: Strozzi A
Published: October 2002

A mechanical analysis is carried out for a flat deformable layer, firmly anchored to a rigid substrate, and frictionlessly compressed by a rigid spherical indenter, with reference to the design of hip replacements whose cup is covered by an elastomeric layer. An available perturbation solution of differential character, developed for a layer subject to plane strain conditions, indented by a cylinder approximated as parabolic in shape and valid for high contact widths, is here extended to the axisymmetric problem of a layer compressed by a paraboloidal indenter. In addition to the paraboloidal idealization, an accurate mathematical description of the indenter spherical profile is incorporated into the modelling of this contact problem. Perturbed solutions up to the second order are developed for both compressible and incompressible layers. Selected numerical examples addressing actual joint geometries are included to assess the validity of the proposed analytical modelling, to explore the accuracy in describing the spherical profile and to compare the contact pressure profiles activated by paraboloidal and spherical indenters.
Wear of ultra-high molecular weight polyethylene (UHMWPE) in total knee prostheses: A review of key influences
Authors: McGloughlin T M , Kavanagh A G
Published: October 2002

The formation and development of wear is now widely accepted as one of the major concerns in the long-term survivorship of contemporary knee prostheses in vivo. This review examines the role of surface topography, third-body debris, load, contact mechanics and material quality in the wear process. Some of the kinematic and physiological issues that need to be modelled in the development of wear testing regimes for evaluation of material combinations and geometrical combinations in total knee implant designs are considered. Wear testing procedures and some of the results from wear tests are discussed and the need to consider the impact of rolling and sliding in the study of wear in total knee components is highlighted. The dominant wear mechanisms that occur in vivo are identified and the role of these mechanisms is currently being examined experimentally at the University of Limerick wear testing machine.
Evaluation of bone strength: Correlation between measurements of bone mineral density and drilling force
Authors: Ong F R , Bouazza-Marouf K
Published: October 2002

Bone drilling is a major part of modern orthopaedic surgery which involves the internal fixation of fractured bones. The investigation of bone drilling described in this paper demonstrates the contribution of automation technology towards the study of bone strength. The aim of this preliminary investigation is to establish a relationship between bone drilling forces and measurements of bone mineral density (BMD) by dual energy X-ray absorptiometry (DXA). A linear relationship with a high coefficient of correlation has been found between average drilling forces and BMD measurements at both the greater trochanter and the femoral head of porcine femurs when drilling in the anterior-posterior (AP) direction (i.e. the direction of the DXA scan). It has also been found that in the normal drilling direction (i.e. in the cervical axis direction), which is orthogonal to the DXA scanning direction, there are similar trends between the drilling forces and BMD levels in regions where bone density is more consistent (e.g. the femoral head). The findings of this investigation indicate that analysis of bone drilling forces has the potential to provide useful information about the strength of bone.
An investigation of three-dimensional scanning of human body surfaces and its use in the design and manufacture of prostheses
Authors: Bibb R , Freeman P , Brown R , Sugar A , Evans P , Bocca A
Published: October 2002

The capture of highly accurate data describing the complex surfaces of the human body may prove extremely useful in many medical situations. The data provide a method of measuring and recording changes to the surface of a patient's soft tissue. The data may be applied to computer-controlled manufacturing techniques, such as rapid prototyping (RP). This enables accurate physical replicas of the patient topography to be produced. Such models may be used as an aid in the design and manufacture of prostheses.

This paper describes an investigation aimed at identifying problems that may be encountered when scanning patients and describes the application of the resulting data in the design and manufacture of facial prostheses. The results of the experiment are presented together with a discussion of the accuracy and potential advantages afforded by this approach.
Finite element analysis of bone stress and strain around a distal osseointegrated implant for prosthetic limb attachment
Authors: Xu W , Crocombe A D , Hughes S C
Published: October 2002

Direct skeletal attachment techniques have recently been identified as an alternative method for percutaneous attachment of prosthetic limbs. Osseointegrated implants for prosthetic attachments are subjected to a complex load condition. This finite element study investigates the effect of varying geometries of the implant on the stress and strain distribution in the area of the bone/implant interface. Simplified three-dimensional axisymmetric models of the femur and seven implants with different core diameters, external diameters, implant lengths and thread pitches were derived. The resulting stress and strain distributions were compared. The significance of each implant geometry was identified for improving implant design in the light of benefit to the bone/implant osseointegration and the bone remodelling of the femur.
Development of a computer model to predict pressure generation around hip replacement stems
Authors: Dunne N J , Orr J F
Published: October 2002

Cemented fixation of hip replacements is the elective choice of many orthopaedic surgeons. The cement is an acrylic polymer which grouts the prostheses into the medullary cavity of the femur. Cement pressure is accepted as a significant parameter in determining the strength of cement/bone interfaces and hence preventing loosening of the prostheses.

The aim of this work was to allow optimal design of the intramedullary stem of a hip prosthesis through knowledge of the flow characteristics of curing bone cement which can be used to predict pressures achieved during insertion of the femoral stem. The viscosity of the cement is a vital property determining the cement flow and hence cement interdigitation into bone. The apparent viscosities, ηa, of three commercial bone cements were determined with respect to time by extrusion of the curing cement through a parallel die of known geometry under selected pressures.

Theoretical models were developed and implemented in a computer program to describe cement flow in three models each of increasing complexity: (a) a simple parallel cylinder, (b) a tapered conical mandrel and (c) an actual femoral prosthesis, the latter models being complicated by extensional effects as annular areas increase.

Predicted pressures were close to those measured experimentally, maximum pressures being in the range 10-160 kPa which may be compared with a threshold of 76 kPa proposed for effective interdigitation with cancellous bone.

The theoretical model allows the prosthesis/bone geometry of an individual patient to be evaluated in terms of probable pressure distributions in the medullary cavity during cemented fixation and can guide stem design with reference to preparation of the medullary canal. It is proposed that these models may assist retrospective studies of failed components and contribute to implant selection, or to making informed selection from options in custom hip prosthesis designs to achieve optimum cement pressurization.
Fluid absorption study in ultra-high molecular weight polyethylene (UHMWPE) sterilized and unsterilized acetabular cups
Authors: Affatato S , Vandelli C , Bordini B , Toni A
Published: October 2002

The weight gain due to fluid absorption was measured in γ-sterilized, ethylene oxide (ETO) gas-sterilized, and unsterilized ultra-high molecular weight (UHMW) polyethylene acetabular cups. After about 2 months the total average fluid absorption gain of the polyethylene cups was: 1.76 ± 0.45 mg (average ± standard deviation) for the unsterilized polyethylene cups, 2.81 ± 0.95 mg for the γ-sterilized polyethylene cups and 1.51 ± 0.34 for the ETO gas-sterilized polyethylene cups. There was little difference in fluid absorption between the sterilized and unsterilized specimens. In particular, the γ-sterilized acetabular cups absorbed more than the ETO gas-sterilized and the unsterilized cups. However, the weight gain was higher in serum compared with that in water.
The effect on the fatigue strength of bone cement of adding sodium fluoride
Authors: Minari C , Baleanil M , Cristofolini L , Baruffaldi F
Published: October 2002

New bone cements that include several additives are currently being investigated and tested. One such additive is sodium fluoride (NaF), which promotes bone formation, facilitating implant integration and success. The influence of NaF on the fatigue performance of the cement as used in biomedical applications was tested in this paper. In fact fatigue failure of the cement mantle is a major factor limiting the longevity of a cemented implant.

An experimental bone cement with added NaF (12wt%) was investigated. The fatigue strength of the novel bone cement was evaluated in comparison with the cement without additives; fatigue tests were conducted according to current standards. The load levels were arranged based on a validated, statistically based optimization algorithm. The curve of stress against number of load cycles and the endurance limit were obtained and compared for both formulations. The results showed that the addition of NaF (12 wt %) to polymethylmethacrylate (PMMA) bone cement does not affect the fatigue resistance of the material. Sodium fluoride can safely be added to the bone cement without altering the fatigue performance of the PMMA bone cement.
Reciprocating gait prosthesis for the bilateral hip disarticulation amputee
Authors: Spence W D , Fowler N K , Nicol A C , Murray S J
Published: October 2002

This paper describes the design, manufacture and use of a new prosthesis which produced reciprocating gait for a bilateral hip disarticulation amputee. A special mechanism used the hip extension moment during weight bearing to drive the contralateral limb through the swing phase. The user rapidly attained efficient and safe reciprocating gait, together with simple donning and doffing. The success of this project has major implications for hip disarticulation amputees in terms of profound improvements of their independence and self-esteem.
The application of the neural network on Morse code recognition for users with physical impairments
Authors: Yang C-H , Yang C-H , Chuang L-Y , Truong T-K
Published: October 2002

Morse code is a simple, speedy and low cost means of communication composed of a series of dots, dashes and space intervals. Each tone element (either a dot, dash or space interval) is transmitted by sending a signal for a defined length of time. This poses a challenge as the automatic recognition of Morse code is dependent upon maintaining a stable typing rate. In this paper, a suitable adaptive automatic recognition method, combining the least-mean-square (LMS) algorithm with a neural network, was applied to this problem. The method presented in this paper is divided into five modules: space recognition, tone recognition, learning process, adaptive processing and character recognition. Statistical analyses demonstrated that the proposed method elicited a better recognition rate in comparison with other methods in the literature.
The effect of socket design, materials and liner thickness on the wear of the porous coated anatomic total hip replacement
Authors: Elfick A P D , Hall R M , Pinder I M , Unsworth A
Published: October 2002

The wear of joint replacement prostheses represents the greatest challenge to their continued development. Parameters such as polyethylene quality, liner thickness and metal backing have all been implicated as potential detractors in the search for the lowest-wearing socket. This study examined the effect of these parameters through an extensive study of the two versions of the porous coated anatomic (PCA) hip prosthesis (one-piece socket and snaplock socket). For the whole cohort the wear rate was found to be 88 (SE 10) mm3/year and the clinical wear factor was 2.00 (SE 0.28) × 10−6mm3/Nm. When the two socket types were investigated individually, the wear factors found were 2.39 (SE 0.44) × 10−6mm3/Nm and 0.99 (SE 0.25) × 10−6mm3/Nm for the one-piece and snaplock, respectively. This illustrates that the metal backing per se does not predispose these sockets to rapid wear. The good wear performance of the snaplock liner may be attributed to the high quality of the ultra-high molecular weight polyethylene (UHMWPE) used and the shorter implantation period compared to that for the one-piece design. No correlation was found between the thickness of the liner and the clinical wear factor. Within the range of thicknesses tested here, UHMWPE thickness is not an influential parameter for the hip prosthesis and this is confirmed by theory.
Disc hydration measured by magnetic resonance imaging in relation to its compressive stiffness in rat models
Authors: Han S-M , Lee S-Y , Cho M-H , Lee J-K
Published: October 2002

The in vivo effects of body dehydration on the water content and compressive stiffness of rat intervertebral disc (IVD) and vertebral body were investigated. Thirty-one rats were divided into three dietary groups: water restricted (WR), pair fed (PF) and ad libitum (AL). The in vivo water content of L4-5 IVD was measured using magnetic resonance imaging (MRI). Water contents of L4-5 IVD were also determined using the wet/dry weight method after killing. Compressive stiffness of the L5 vertebral body and the L3-4 motion segment were determined. Results showed that the water content of L4-5 IVD was significantly less in the WR group than in the PF and AL groups as measured by the wet/dry weight method; likewise, MRI water content was also less in the WR group. The material stiffness of the IVD was significantly greater in the WR than in the PF and AL groups. However, there was no significant difference in material stiffness of the L5 vertebral body for the WR group in comparison with the PF and AL groups. It was also found that the stiffness of the IVD was significantly lower than that of the vertebral body. This study suggests that the dehydrated matrix of the IVD may be responsible for a stiffer disc that may lead to a less flexible spine.
The wear of metal-on-metal total hip prostheses measured in a hip simulator
Authors: Scholes S C , Green S M , Unsworth A
Published: October 2002

New generation metal-on-metal prostheses have been introduced to try and overcome the problem of osteolysis often attributed to the wear particles of the polyethylene component of conventional metal-on-ultra-high molecular weight polyethylene (UHMWPE) joints. The wear rates of four metal-on-metal joints (two different clearances) were assessed along with that of a conventional metal-on-UHMWPE joint. Friction measurements of the metal-on-metal joints were taken before and after the wear test and compared. Two distinct wear phases were discernible for all the metal-on-metal joints: an initial wear phase up to 0.5 × 106 cycles and then a lower steady state wear phase. The steady state wear rate of the 22 μUm radial clearance metal-on-metal joint was lower than that for the 40 μUm radial clearance joint, although this difference was not found to be significant ( p > 0.15). The wear rates for all the joints tested were consistent with other simulator studies. The friction factors produced by each joint were found to decrease significantly after wear testing ( p < 0.05).
An infant reciprocal walking orthosis: Engineering development
Authors: Stallard J , Woollam P J , Miller K , Farmer I R , Jones N , Poiner R
Published: October 2002

The growing trend of prescription of reciprocal walking orthoses for children under the age of 5 years has created a requirement for a new design of orthosis in this category. In response to this new demand, a prototype orthosis for infants, incorporating a specially developed hip joint and manufactured as a rehabilitation engineering device within the provisions of the EC Medical Devices Directive, has been produced and tested. A design feature that strongly influences the efficiency of walking is the rigidity of the body brace structure. Monitoring the specific structural performance of the body brace intended for infants showed that it would equal or improve the stiffness achieved in an orthosis for adults. Additionally its strength was comparable with the adult design, which has proven to be safe and reliable in many years of routine prescription. Incorporation of the infant body brace within a complete orthosis provided a structure of more acceptable physical dimensions for these more diminutive patients. The orthosis showed no incipient sign of failure after 100 000 cycles of representative service loading equivalent to that imposed by a 20 kg (5-year-old) patient. The results of structural assessment and cyclic load testing confirm that the design of the orthosis sufficiently satisfies the statutory requirements for devices that are safe and fit for purpose to permit field trials with patients.
Arch-shaped versus flat arthrodesis of the ankle joint: Strength measurements using synthetic cancellous bone
Authors: Lauge-Pedersen H , Aspenberg P , Ryd L , Tanner K E
Published: October 2002

The aim of this study was to see if preservation of the arch shape of the ankle at arthrodesis contributes to stability. The ankle joint was simulated by paired blocks of a synthetic material corresponding to rheumatoid cancellous bone with low stiffness and strength. Flat end constructs with and without subchondral bone were compared with arch-shape constructs with and without subchondral bone. The pairs were fixed with two screws simulating an arthrodesis. These constructs were then tested to failure in four-point bending and torque. In four-point bending the subchondral bone increased the strength, regardless of shape. Stiffness was higher in the arch-shaped specimens but was not influenced by the subchondral bone. In torque, both arch-shape and subchondral bone increase the strength. Stiffness was increased by arch-shape but not subchondral bone. The results imply that the arch-shape and subchondral bone should be preserved when performing an ankle arthrodesis, especially in weak rheumatoid bone.
A test procedure for artificial finger joints
Authors: Joyce T J , Unsworth A
Published: October 2002

This paper highlights the lack of an agreed testing standard for artificial finger joints. It reviews the anatomy, pathology and biomechanics of finger joints as well as the various designs of finger prostheses and the machines used to test them. While pre-implantation testing should be fundamental, increasing regulation of the biomedical engineering industry will further demand testing of prostheses to pre-agreed standards. Standards relating to the testing of other artificial joints are reviewed before possible parameters for testing finger prostheses are offered.
Comparison of wear, wear debris and functional biological activity of moderately crosslinked and non-crosslinked polyethylenes in hip prostheses
Authors: Endo M , Tipper J L , Barton D C , Stone M H , Ingham E , Fisher J
Published: October 2002

The wear, wear debris and functional biological activity of non-crosslinked and moderately crosslinked ultrahigh molecular weight polyethylene (UHMWPE) acetabular cups have been compared when articulating against smooth and intentionally scratched femoral heads. Volumetric wear rates were determined in a hip joint simulator and the debris was isolated from the lubricant and characterized by the percentage number and volumetric concentration as a function of particle size. The volumetric concentration was integrated with the biological activity function determined from in vitro cell culture studies to predict an index of specific biological activity (SBA). The product of specific biological activity and volumetric wear rate was used to determine the index of functional biological activity (FBA).

On smooth femoral heads the crosslinked UHMWPE had a 30 per cent lower wear rate, but it had a greater percentage volume of smaller, more biologically active particles, which resulted in a similar index of FBA compared with the non-crosslinked material. On the scratched femoral heads the volumetric wear rate was three times higher for the moderately crosslinked UHMWPE and two times higher for the non-crosslinked UHMWPE compared with the smooth femoral heads. This resulted in a higher wear rate for the moderately crosslinked material on the scratched femoral heads. All the differences in wear rate were statistically significant. There were only small differences in particle volume concentration distributions, and this resulted in similar indices of FBA which were approximately twice the values of those found on the smooth femoral heads. Both materials showed lower wear and FBA than for previously studied aged and oxidized UHMWPE gamma irradiated in air. However, this study did not reveal any advantage in terms of predicted FBA for moderately crosslinked UHMWPE compared with non-crosslinked UHMWPE.
Effects of the sample preparation temperature on the nanostructure of compression moulded ultrahigh molecular weight polyethylene
Authors: Ho S P , Riester L , Drews M , Boland T , LaBerge M
Published: October 2002

In this study, the effects of the sample sectioning temperature on the surface nanostructure and mechanical response of compression moulded ultrahigh molecular weight polyethylene (UHMWPE) at a nanometer scale (nanomechanical properties) have been characterized. The primary focus of this work was to determine if the sample sectioning temperature significantly changed the nanostructure of UHMWPE, while the secondary focus was to characterize the effect on the mechanical response due to the changes in the sectioned surface nanostructure. The goals of this study were:

to investigate the potential possibility of creating surface artefacts by the sample preparation technique by sectioning at different temperatures relative to the published range of glass transition temperatures, Tg, for PE (−12, −80 and −25°C); to determine the possibility of molecular orientation induced by plastic deformation of the UHMWPE sample during the process of sample preparation; to measure the relative difference in nanomechanical properties owing to evolution of different nanostructures as a function of sample sectioning temperature.

Field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and nanoindentation were used to demonstrate that the sectioning temperature caused a change in nanostructure of the compression moulded UHMWPE sectioned surface, explaining the change in mechanical response to indentation at a nanoscale. In this study, it was demonstrated that significant plastic deformation occurs when a shear stress is applied between the glass or diamond blade and the UHMWPE during sample preparation under ambient conditions at a temperature of 22°C. These results also suggest that an optimum sample sectioning temperature should definitely be below the measured Tg of the polymer.
Flexible tubular replicas of abdominal aortic aneurysms
Authors: Berry E , Marsden A , Dalgarno K W , Kessel D , Scott D J A
Published: October 2002

The aim of this study was to manufacture life-size, flexible, tubular replicas of human abdominal aortic aneurysms and the associated vasculature, suitable for use in a training simulator for endovascular procedures. Selective laser sintering was used to create a geometrically correct master model for each of ten anatomical variations. The masters were used to generate flexible latex replicas. The use of the replicas in the training simulator was demonstrated. In total ten silicone rubber models were produced. When connected into the training simulator and perfused at arterial pressure it was possible to deploy an endovascular stent under fluoroscopic control and to perform angiography. The study has shown that conventional rapid prototyping technology can be used to manufacture flexible, radiolucent replicas which provide a realistic training environment for endovascular procedures.
Bone registration method for robot assisted surgery: Pedicle screw insertion
Authors: Abdel-Malek K , McGowan D P , Goel V K , Kowalski D , Smith S B
Published: October 2002

A registration method that identifies bone geometry with respect to a robotic manipulator arm is presented. Although the method is generally applicable to many orthopaedic internal fixation procedures, it was only demonstrated for the insertion of pedicle screws in vertebral bodies for spine fixation. The method relies upon obtaining an impression of the vertebral bodies. Computerized tomography (CT) scans of both vertebrae and mould are reconstructed using a computer aided engineering (CAE) system. From the reconstructions, the surgeon is able to do preoperative planning including selection of pedicle screw diameter, direction of screw through pedicle, point of entry and length of engagement. The three-dimensional models are then meshed to determine positions of the surgeon's preoperative plan relative to the mould. Intra-operative positions are defined in space by a mechanical fixture rigidly attached to the mould and designed to allow a manipulator end-effector to recognize the global coordinates of the in vivo spine. The theory and methodology were validated using a five-axis manipulator arm. This initial presentation assumes and allows no relative motion between vertebrae in vivo.
Wear of ultra-high molecular weight polyethylene acetabular cups in a physiological hip joint simulator in the anatomical position using bovine serum as a lubricant
Authors: Bigsby R J A , Hardaker C S , Fisher J
Published: October 2002

The Leeds physiological anatomical (PA) hip joint simulator was developed to apply three axes of loading and a complex three-dimensional motion so that the forces and motions can reproduce exactly the walking cycles defined by Paul. This paper presents the results of a study using the Leeds PA hip joint simulator to determine the wear of 32 mm ultra-high molecular weight polyethylene (UHMWPE) acetabular cups against stainless steel and zirconia ceramic heads, using bovine serum as lubricant. These results have been compared with the results of a previous study that used water as the lubricant, which led to UHMWPE transfer film being formed on the stainless steel head. Comparisons are also made with clinical results and results from other simulators. The study indicates that it is preferable to use bovine serum in simulator studies. In addition, the results indicate that if the surface roughness of the metallic and femoral heads are similar, and they remain undamaged during the tests, the wear rates of the UHMWPE cups are likely to be similar.