Understanding frictional behavior in fascia tissues through tribological modeling and material substitution.

The objective of this study is to develop a reliable tribological model to enable a more thorough investigation of the frictional behavior of fascia tissues connected to non-specific lower back pain. Several models were designed and evaluated based on their coefficient of friction, using a low-frequency, low-load reciprocating motion. The study found that two technical elastomers, layered on PDMS to simulate the fascia and underlying muscle, are suitable substitutes for biological tissue in the model. The influence of tribopair geometry was also examined, and the results showed that greater conformity of contact leads to a lower COF, regardless of the material combination used. Finally, the friction properties of HA of various molecular weights and concentrations were tested.

The effect of albumin and γ-globulin on synovial fluid lubrication: Implication for knee joint replacements.

Total knee arthroplasty has become a routine procedure for patients suffering from joint diseases. Although the number of operations continuously increases, a limited service-life of implants represents a persisting challenge for scientists. Understanding of lubrication may help to suitably explain tribological processes on the way to replacements that become durable well into the third decade of service. The aim of the present study is to assess the formation of protein lubricating film in the knee implant. A developed knee simulator was used to observe the contact of real femoral and transparent polymer tibial component using fluorescent microscopy. The contact was lubricated by various protein solutions with attention to the behaviour of albumin and γ-globulin. In order to suitably mimic a human synovial fluid, hyaluronic acid and phospholipids were subsequently added to the solutions. Further, the change in shape and the migration of the contact zone were studied. The results showed considerable appearance differences of the contact over the swing phase of the simplified gait cycle. Regarding film formation, a strong interaction of the various molecules of synovial fluid was observed. It was found that the thickness of the lubricating layer stabilizes within around 50 s. Throughout the contact zone, protein agglomerations were present and could be clearly visualised using the applied optical technique.

Cell type specific adhesion to surfaces functionalised by amine plasma polymers.

Our previously-obtained impressive results of highly increased C2C12 mouse myoblast adhesion to amine plasma polymers (PPs) motivated current detailed studies of cell resistance to trypsinization, cell proliferation, motility, and the rate of attachment carried out for fibroblasts (LF), keratinocytes (HaCaT), rat vascular smooth muscle cells (VSMC), and endothelial cells (HUVEC, HSVEC, and CPAE) on three different amine PPs. We demonstrated the striking difference in the resistance to trypsin treatment between endothelial and non-endothelial cells. The increased resistance observed for the non-endothelial cell types was accompanied by an increased rate of cellular attachment, even though spontaneous migration was comparable to the control, i.e., to the standard cultivation surface. As demonstrated on LF fibroblasts, the resistance to trypsin was similar in serum-supplemented and serum-free media, i.e., medium without cell adhesion-mediating proteins. The increased cell adhesion was also confirmed for LF cells by an independent technique, single-cell force spectroscopy. This method, as well as the cell attachment rate, proved the difference among the plasma polymers with different amounts of amine groups, but other investigated techniques could not reveal the differences in the cell behaviour on different amine PPs. Based on all the results, the increased resistance to trypsinization of C2C12, LF, HaCaT, and VSMC cells on amine PPs can be explained most probably by a non-specific cell adhesion such as electrostatic interaction between the cells and amine groups on the material surface, rather than by the receptor-mediated adhesion through serum-derived proteins adsorbed on the PPs.

On the observation of lubrication mechanisms within hip joint replacements. Part II: Hard-on-hard bearing pairs.

The present paper represents Part II of the extensive study focused on the lubrication of hip joint replacements. The main goal is to assess the fundamentals of lubrication considering both hard-on-soft (Part I) and hard-on-hard (Part II) bearing pairs. In addition, the effect of individual constituents contained in the model fluid is clarified. For this purpose, multiple model fluids of various composition were employed. In this part of the study, metal-on-glass contact representing hard bearing pairs was observed in situ using pendulum hip joint simulator in combination with thin film colorimetric interferometry method. The designed test consists of initial static loading/unloading phase for the determination of adsorption of molecules on rubbing surfaces. This period is followed by swinging of the pendulum and latest static part under constant load. Three groups of measurements were carried out while fourteen different lubricants were tested. Initially, the experiments were performed with albumin-based model fluid. In that case a substantial positive effect of hyaluronic acid was identified. In contrast, the fluids with γ-globulin as a base constituent showed improved lubrication conditions when phospholipids were added to the solution. Finally, considering the complex fluid, a combined effect of hyaluronic acid and phospholipids caused a better endurance of the lubricant film. The latest part of the paper aims on the comparison of film formation considering hard and soft pairs, highlighting some clear differences. In general, hard pairs exhibit clear decreasing tendency of the film during swinging motion while opposite behaviour was observed for soft pairs.

On the observation of lubrication mechanisms within hip joint replacements. Part I: Hard-on-soft bearing pairs.

The present study describes the lubrication mechanisms within artificial hip joints considering real conformity of rubbing surfaces. Part I is focused on hard-on-soft material combination, introducing the fundamentals of lubrication performance. These pairs have not been explored in terms of in situ observation before. The contact of metal femoral component articulating with transparent polymer acetabular cup was studied using a hip joint simulator. The film formation was evaluated by fluorescent microscopy method. Various model synovial fluids were employed while the key constituents, i.e. albumin, γ-globulin, and hyaluronic acid were fluorescently stained to determine its role in film formation process. Two types of the tests were performed. The first dynamic test aimed on the development of film thickness under constant load during motor driven swinging motion mimicking flexion-extension. Subsequently, a combined test was designed consisting of the three phases; static part with loading/unloading phase (1), pendulum swinging till spontaneous damping of the motion due to friction (2), and static observation under the constant load (3). The results clearly confirmed that the interaction of constituents of synovial fluid plays a dominant role and substantially influences the lubrication conditions. In particular, the main finding coming from the present study is that γ-globulin together with hyaluronic acid form relatively thin stable boundary layer enabling the enhanced adsorption of albumin, thus increasing the lubricant film. Part II of the present study is focused on hard-on-hard pairs while the main differences in film formation process are highlighted among others.

[Wear and Roughness of Bearing Surface in Retrieved Polyethylene Bicon-Plus Cups]. / Opotrebení a drsnost artikulacního povrhu u extrahovaných polyetylenu jamky Bicon-Plus.

PURPOSE OF THE STUDY By 7th December 2016, 4,755 Bicon-Plus cups in total were implanted in the Czech Republic. Some of them have been continuously re-operated, while the most frequent reason of failure is polyethylene wear and aseptic loosening. The present study is focused on surface analysis of retrieved polyethylene Bicon-Plus cups and the determination of the roughness of their bearing surfaces. MATERIAL AND METHODS In this study, we had 13 high molecular weight polyethylene cups with the average time in situ of 8.11 years (3.6-13.7, SD 3.2) before the retrieval. The study population was composed of 3 men, 10 women, with the mean age of 53.31 years. An optical scanning method, based on the principle of active triangulation, was used to determine wear rate. The rate of wear was identified by means of an obtained scan subsequently processed with the use of the GOM Inspect software. The roughness of surfaces was analysed with the application of Contour GT-X8 profiler using the principle of phase shifting interferometry. Measurements of surface topography of the retrieved cups were performed on the entire bearing surfaces. For the individual surface changes, a typical range of surface roughness, describing the particular wear character, was determined. By means of morphology analysis of the tested implants, three areas were identified: unworn area; area representing the worn part of the cup; and the area roughened by parallel grooving. The total surface roughness was evaluated as an arithmetic mean of the measured values. Subsequently, the values were sorted based on frequency and were classified into categories defining the particular wear mechanisms. RESULTS Wear rate of the retrieved acetabular cups was evaluated based on the wear direction vector and the size of linear wear. The average linear wear was equal to 0.13 mm/year (ranging from 0.26 to 2.29 mm/year), and the mean value of total volumetric material loss was 44.37 mm3/year (the range being from 51.80 to 1,119.7 mm3/year). Using the optical profilometer, a map of roughness distribution of the individual cups was obtained. For each implant, 76 values of roughness were evaluated. With the respect to average roughness, the samples were sorted to various categories describing: surface polishing; abrasiveadhesive wear; surfaces with preserved grooving; substantial plastic deformation. DISCUSSION The results clearly showed an increase of wear depending on implant survival; however, the tendency is not linear. This fact can be attributed to a larger amount of abrasive particles, causing an increase of wear or occurrence of surface wear in terms of micro cracks and oxidation degradation of polyethylene. This study indicates that geometry, positioning, and cup alignment during the implantation have a fundamental impact on the cup durability. Further correlation, which was observed in the case of the cup with prevailing roughness in the range from 0.1 to 0.3 µm, is a relatively wide wear vector angle determined with the use of the optical method. Considering the implants with the longest survival time with no loosening of the acetabular cup, the mean angle of direction vector was 56.8° (SD 2.1°). CONCLUSIONS The present study provides the results of morphology analysis of the retrieved Bicon-Plus cups. In general, relatively high wear rate, mainly of abrasive-adhesive character was identified. The dependence between wear and implant in situ longevity was not clearly linear, which suggests the influence of other parameters on the polyethylene wear rate. An important role of implant positioning on survival was also revealed. Moreover, it seems that it can be a more important parameter than the characteristics of the patient. Key words: total hip arthroplasty, Bicon-Plus cup, retrieval analysis, surface analysis, wear measurement, roughness, deformation, survivorship.

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.

Lubrication within hip replacements - Implication for ceramic-on-hard bearing couples.

The objective of the present study is to clarify the lubrication processes within artificial joints considering the ceramic femoral heads focusing on the role of particular proteins. Two optical methods were employed; colorimetric interferometry and fluorescent microscopy. The experiments were conducted in ball-on-disc configuration, where the ball is made from ceramic (Sulox(TM), BIOLOX(®)delta) and the disc from optical glass. The measurements were realized under pure rolling, partial negative and partial positive sliding, to get a complex information about the protein film behaviour under various conditions. Moreover, two different speeds were investigated; 5.7 and 22 mm/s, respectively. The contact was lubricated by saline solutions containing albumin and γ-globulin in a ratio 2:1, while the total protein concentration was 10.5 mg/ml. Under pure rolling conditions, the film thickness gradually increases with time/rolling distance independently of material and rolling speed, while the dominant fluid constituent is albumin. In the case of negative sliding, the film formation is time/distance/speed dependent. At lower speed, both proteins contribute to film thickness; at higher speed, the effect of γ-globulin is not substantial. When the disc is faster, the character of film formation is similar to the metal component in the case of Sulox ceramic. Biolox ceramic shows a different behaviour, while for both materials, the contribution of γ-globulin increases with increasing speed. As most of the results can be well explained in terms of specific proteins, it can be concluded that the experimental approach is suitable for the investigation of protein film formation considering the ceramic materials.

[Determination of a Friction Coefficient for THA Bearing Couples]. / Stanovení soucinitele trení hlavic a jamek TEP kycle.

PURPOSE OF THE STUDY: The wear of articular surfaces is considered one of the most important factors limiting the life of total hip arthroplasty (THA). It is assumed that the particles released from the surface of a softer material induce a complex inflammatory response, which will eventually result in osteolysis and aseptic loosening. Implant wear is related to a friction coefficient which depends on combination of the materials used, roughness of the articulating surfaces, internal clearance, and dimensions of the prosthesis. MATERIAL AND METHODS: The selected parameters of the bearing couples tested were studied using an experimental device based on the principle of a pendulum. Bovine serum was used as a lubricant and the load corresponded to a human body mass of 75 kg. The friction coefficient was derived from a curve of slowdown of pendulum oscillations. Roughness was measured with a device working on the principle of interferometry. Clearance was assessed by measuring diameters of the acetabular and femoral heads with a 3D optical scanner. The specimens tested included unused metal-on-highly cross-linked polyethylene, ceramic-on-highly cross-linked polyethylene and ceramic-on-ceramic bearing couples with the diameters of 28 mm and 36 mm. For each measured parameter, an arithmetic mean was calculated from 10 measurements. RESULTS: 1) The roughness of polyethylene surfaces was higher by about one order of magnitude than the roughness of metal and ceramic components. The Protasul metal head had the least rough surface (0.003 µm). 2) The ceramic-on-ceramic couples had the lowest clearance. Bearing couples with polyethylene acetabular liners had markedly higher clearances ranging from 150 µm to 545 µm. A clearance increased with large femoral heads (up to 4-fold in one of the couple tested). 3) The friction coefficient was related to the combination of materials; it was lowest in ceramic-on-ceramic surfaces (0.11 to 0.12) and then in ceramic-on-polyethylene implants (0.13 to 0.14). The friction coefficient is supposed to increase with a decreasing femoral head diameter. However, in the bearing couples with polyethylene liners manufactured by one company, paradoxically, the friction coefficient slightly increased with an increase in femoral head size from 28 mm to 36 mm. 4) The lowest friction moment (< 3.5 Nm) was found for ceramic-on-ceramic implants 28 mm in diameter; the highest values were recorded in metal-on-polyethylene bearing couples 36 mm in diameter (> 7 Nm). DISCUSSION: Although our study confirmed that the bearing couples produced by different manufacturers varied to some extent in the parameters studied, in our opinion, this variability was not significant because it was not within an order of magnitude in any of the tests. CONCLUSIONS: The study showed that both the friction coefficient and the friction moment are affected more by the combination of materials than by the diameter of a femoral head. The best results were achieved in ceramic-on-ceramic implants.