J. Gallo

In situ measurements of thin films in bovine serum lubricated contacts using optical interferometry

The aim of this study is to consider the relevance of in situ measurements of bovine serum film thickness in the optical test device that could be related to the function of the artificial hip joint. It is mainly focussed on the effect of the hydrophobicity or hydrophilicity of the transparent surface and the effect of its geometry. Film thickness measurements were performed using ball-on-disc and lens-on-disc configurations of optical test device as a function of time. Chromatic interferograms were recorded with a high-speed complementary metal-oxide semiconductor digital camera and evaluated with thin film colorimetric interferometry. It was clarified that a chromium layer covering the glass disc has a hydrophobic behaviour which supports the adsorption of proteins contained in the bovine serum solution, thereby a thicker lubricating film is formed. On the contrary, the protein film formation was not observed when the disc was covered with a silica layer having a hydrophilic behaviour. In this case, a very thin lubricating film was formed only due to the hydrodynamic effect. Metal and ceramic balls have no substantial effect on lubricant film formation although their contact surfaces have relatively different wettability. It was confirmed that conformity of contacting surfaces and kinematic conditions has fundamental effect on bovine serum film formation. In the ball-on-disc configuration, the lubricant film is formed predominantly due to protein aggregations, which pass through the contact zone and increase the film thickness. In the more conformal ball-on-lens configuration, the lubricant film is formed predominantly due to hydrodynamic effect, thereby the film thickness is kept constant during measurement.

Study of film formation in bovine serum lubricated contacts under rolling/sliding conditions

The aim of this study is to perform a detailed experimental analysis of lubricant film thickness of bovine serum within the contact between the artificial metal and ceramic heads (balls) and the glass disc to analyse the effect of proteins on film formation under various rolling/sliding conditions. Lubricant film observation of bovine serum solutions was carried out using an optical test rig. Chromatic interferograms were recorded with a high-speed CMOS digital camera and evaluated with thin film colorimetric interferometry. Film thickness was studied as a function of time. Under pure rolling conditions, film thickness increases with time as well as with rolling distance for all mean speeds and for both materials of the balls; however the metal ball always forms a thicker lubricating film in comparison to the ceramic ball. Under rolling/sliding conditions, when the disc is faster than the ball, the formation of lubricant film thickness is different compared to pure rolling conditions. At first, film thickness increases rapidly with a rolling/sliding distance for all mean speeds. When maximum film thickness is reached, then this effect is lost and film thickness starts to fall and finally, at the end of the measurement, film thickness drops down to a few nanometres. For the metal ball, maximum values of central film thicknesses are proportional to the mean speed; however this is not observed with the ceramic ball. An absolutely different formation of bovine serum film thickness is observed when the ball is faster than the disc. Under this condition, the protein layer is very thin for both materials of balls, and central film thickness reaches only about a few nanometres. Local protein spots are formed in a very small area of the contact zone and reach the thickness between 20 and 25 nm for the metal ball and 5 nm for the ceramic ball. From the performed experiments under rolling/sliding conditions, it is obvious that the formation of lubricant film thickness is markedly dependent on kinematic conditions acting in the contact, especially on the positive and negative slide-to-roll ratio and the mean speed. In addition, the material of the artificial head has a certain influence on the formation of bovine serum lubricating film.

Wear Analysis of Extracted Polyethylene Acetabular Cups Using a 3D Optical Scanner

ABSTRACT Wear analysis of total hip replacements (THRs) is considered one of the most relevant research areas helping to improve the longevity and overall design of THRs. The coordinate machine method (CMM) and Fourier profilometry are the most common methods for measuring THR wear. This article presents optical scanner digitalization as a new method for measuring the wear of polyethylene (PE) acetabular cups. The aim of this article is to explore the potential of this method for the PE wear measurements. Optical scans for the purposes of this study were produced using an ATOS Triple Scan 3D optical scanner. The optical scanner is efficient and it can measure a large number of points for polygonization and for further development of the preworn models. In this study, the scanner first generated point clouds on a sample of 13 retrieved ultra-high-molecular-weight polyethylene (UHMWPE) acetabular cups. Next, volumetric models of the cups were created by polygonizing the point clouds. Reverse engineering was used to develop models of the original acetabular cups using the geometry of the unworn parts of the retrieved cups. A comparison of the two models then showed the total volume of the PE debris. The optical scanning method was validated against the gravimetric method using three new acetabular cups that were worn out on a hip pendulum simulator. Validation shows that the optical scanning method is a valid method for wear analysis of the retrieved UHMWPE acetabular cups.

In situ observation of lubricant film formation in THR considering real conformity: The effect of diameter, clearance and material

The aim of the present study is to provide an analysis of protein film formation in hip joint replacements considering real conformity based on in situ observation of the contact zone. The main attention is focused on the effect of implant nominal diameter, diametric clearance and material. For this purpose, a pendulum hip joint simulator equipped with electromagnetic motors enabling to apply continuous swinging flexion-extension motion was employed. The experimental configuration consists of femoral component (CoCrMo, BIOLOX®forte, BIOLOX®delta) and acetabular cup from optical glass fabricated according to the dimensions of real cups. Two nominal diameters were studied, 28 and 36mm, respectively, while different diametric clearances were considered. Initially, a static test focused on the protein adsorption onto rubbing surfaces was performed with 36mm implants. It was found that the development of adsorbed layer is much more stable in the case of metal head, indicating that the adsorption forces are stronger compared to ceramic. A consequential swinging test revealed that the fundamental parameter influencing the protein film formation is diametric clearance. Independently of implant diameter, film was much thicker when a smaller clearance was considered. An increase of implant size from 28mm to 36mm did not cause a substantial difference in film formation; however, the total film thickness was higher for smaller implant. In terms of material, metal heads formed a thicker film, while this fact can be, among others, also attributed to clearance, which is more than two times higher in the case of ceramic implant.

Verification of abrasion measurement of juncture implants using Fourier profilometry

Three dimensional measurements have great use today and it is quite large and important part of the experimental physics. These methods are also used in biomedicine for measuring the abrasion of juncture implants, coxal cotyles and knees. These implants are under stress in the patients body and therefore they change their shape and waste some material. This waste is a key parameter for examination of quality of the given type of implant. The surface of the used implant is measured and compared with unused one. This comparison gives possibility to enumerate the waste of material of implant. One of the three dimensional optic measurement methods is Fourier profilometry, based on the analysis of harmonic structure projected on the surface of the measured object. It is profilometric method; it means that the surface of measured object is specified in every point of result. Fundamentals of Fourier profilometry, its features and used experimental setup are described in the beginning of the paper. The results of such measurement lead to enumerate the waste of material of implant. The purpose of this contribution is the verification of used method to measure the waste of material of implant. Its principle lies in artificial abrasion made by cutting tool, so the abrasion is defined and known. The surface of the implant is measured before and after this machining and the waste of material of implant is enumerated. This value is compared with an actual waste of material.

Content of distinct metals in periprosthetic tissues and pseudosynovial joint fluid in patients with total joint arthroplasty: DISTINCT METALS IN PERIPROSTHETIC TISSUES AND PSEUDOSYNOVIAL JOINT FLUID

This prospective study examined the content of metals released from total joint arthroplasty into joint fluid, whole blood and periprosthetic tissues. We determined the levels of Ti, V, Nb, Co, Cr, and Mo, using inductively coupled plasma mass spectrometry, in samples from patients who underwent reoperation of total hip or knee arthroplasty. All of the patients (n = 117) included in the study had either metal on polyethylene or ceramic on polyethylene-bearing pairs. First, our results conclusively showed that the majority of released metals were deposited in periprosthetic tissues. In this context, the bloodstream turned out to be an ineffective biomarker of the effects occurring in local tissues. Second, there was a clear time-dependent nature of metallic accumulation. Based on our extensive dataset, we found significantly elevated levels of the released metals in joint fluid and periprosthetic tissues originating from loosened implants compared to stable ones, as well as recognizable differences between the groups with stable implants and aseptic loosening. Finally, it was proved that the concentrations of metals decreased dependent on the distance of the tissue from the implant.

Effect of Contact Condition on Film Thickness Formation in Artificial Joints

Total hip replacement is the most effective method for treating severe degenerative, post-traumatic and other diseases of the hip joint. Nevertheless wear of artificial implants remains a serious health issue especially for metal-on-metal hip components where the formation of metallic wear debris has been linked to adverse tissue necrosis and increased of metal ions in the blood. Wear in MOM joints is essentially dependent on interfacial lubrication processes, which are subjected to the complex research work at the present time. The aim of this study is to analyze formation of lubrication film and experimental mapping of the lubricating film thickness of bovine serum within the contact between an artificial metal or ceramic femoral head and a glass disc and analyze effect of proteins on the film formation under rolling/sliding conditions. The film thickness was studied experimentally using film colorimetric interferometry. This study showed that protein formation plays an important role in the lubrication processes of artificial joints of the human. Due to challenging of this study the more complex research work is carried out at the present time.

Optical Non-contact In-vitro Measurement of Total Hip Arthroplasty Wear

Total hip arthroplasty significantly improves the quality of life in majority of patients with osteoarthritis. However, prosthetic wear is a problem because of inducing the development of aseptic loosening and periprosthetic osteolysis which needs the revision surgery. Thus, the polyethylene wear measurement is the central to contemporary orthopaedics. Various in vivo methods have been developed offering the ability to determine and study the prosthetic cup linear wear before the revision surgery. The radiological methods are the most available but the accuracy and related relationship between measured linear wear and true value of volumetric wear is the problem. As the “golden” standard the in vitro methods can be employed. This contribution gives the review of previously published study concerned with the accuracy of three radiological techniques (Livermore, Charnley, and Dorr methods) based on the using the universal-type measuring microscope in vitro method. Moreover, this paper introduces the comparison of results obtained by the previously used microscope method and the newly developed optical scanning profilometry in vitro method. Results of the comparison shows the using of this optical method can specify and spread the mentioned study.

Sensor for Measurement of Wear in Total Hip Arthroplasty

This article treats of measurements of the total deformation of polyethylen cotyles ABG I of coxa by means of the optical topography method. The total deformation is considered as a combination of the plastic deformation and the real diminution of the artificial cotyle material due to usage of a hip replacement. We use 3D scanning topography to measure surface geometry of cotyle. The sensor consists of optical source, digital camera, rotating stage and linear stage. We use LabView to control the measurement and Matlab to compute the result. We want to measure the set of more then 200 cotyle samples.

Potentialities of Wear Measurement in Total Knee Arthroplasty

The contribution describes two optical and one contact measuring method used to measure the wear of polyethylene insert of knee implants. These implants are under stress in patient body and therefore they suffer from wear. The purpose of these measurements is the creation of sensor intended to measure a statistic file of damaged implants and compare this file with way of life and other parameters of patients, who used them.