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.

Injecting hyaluronan in the thoracolumbar fascia: A model study

Hyaluronan (HA) has been recently identified as a key component of the densification of thoracolumbar fascia (TLF), a potential contributor to non-specific lower back pain (LBP) currently treated with manual therapy and systemic or local delivery of anti-inflammatory drugs. The aim of this study was to establish a novel animal model suitable for studying ultrasound-guided intrafascial injection prepared from HA with low and high Mw. Effects of these preparations on the profibrotic switch and mechanical properties of TLF were measured by qPCR and rheology, respectively, while their lubricating properties were evaluated by tribology. Rabbit proved to be a suitable model of TLF physiology due to its manageable size enabling both TLF extraction and in situ intrafascial injection. Surprisingly, the tribology showed that low Mw HA was a better lubricant than the high Mw HA. It was also better suited for intrafascial injection due to its lower injection force and ability to freely spread between TLF layers. No profibrotic effects of either HA preparation in the TLF were observed. The intrafascial application of HA with lower MW into the TLF appears to be a promising way how to increase the gliding of the fascial layers and target the myofascial LBP.

A composite device for viscosupplementation treatment resistant to degradation by reactive oxygen species and hyaluronidase

Osteoarthritis (OA) is one of the most common musculoskeletal disorders in the world. OA is often associated with the loss of viscoelastic and tribological properties of synovial fluid (SF) due to degradation of hyaluronic acid (HA) by reactive oxygen species (ROS) and hyaluronidases. Viscosupplementation is one of the ways how to effectively restore SF functions. However, current viscosupplementation products provide only temporal therapeutic effect because of short biological half-life. In this article we describe a novel device for viscosupplementation (NV) based on the cross-linked tyramine derivative of HA, chondroitin sulfate (CS), and high molecular weight HA by online determination of viscoelastic properties loss during degradation by ROS and hyaluronidase. Rheological and tribological properties of developed viscosupplement were compared with HA solutions with different molecular weights in the range 500-2000 kDa, which are currently commonly used as medical devices for viscosupplementation treatment. Moreover, based on clinical practice and scientific literature all samples were also diluted by model OA SF in the ratio 1:1 (vol/vol) to better predict final properties after injection to the joint. The observed results confirmed that NV exhibits appropriate rheological properties (viscosity, elastic, and viscous moduli) comparable with healthy SF and maintain them during degradation for a significantly longer time than HA solutions with molecular weight in the range 500-2000 kDa and cross-linked material without CS.

Insight into the Lubrication and Adhesion Properties of Hyaluronan for Ocular Drug Delivery

Hyaluronan (HA) is widely used for eye drops as lubricant to counteract dry eye disease. High and low molecular weight HA are currently used in ophthalmology. However, a large portion of the current literature on friction and lubrication addresses articular (joint) cartilage. Therefore, eye drops compositions based on HA and its derivatized forms are extensively characterized providing data on the tribological and mucoadhesive properties. The physiochemical properties are investigated in buffers used commonly in eye drops formulations. The tribological investigation reveals that amphiphilic HA-C12 decreases the friction coefficient. At the same time, the combination of trehalose/HA or HAC12 enhances up to eighty-fold the mucoadhesiveness. Thus, it is predicted a prolonged residence time on the surface of the eye. The incorporation of trehalose enhances the protection of human keratinocytes (HaCaT) cells, as demonstrated in an in-vitro cell-desiccation model. The presence of trehalose increases the friction coefficient. Medium molecular weight HA shows significantly lower friction coefficient than high molecular weight HA. This research represents a first, wide array of features of diverse HA forms for eye drops contributing to increase the knowledge of these preparations. The results here presented also provide valuable information for the design of highly performing HA-formulations addressing specific needs before preclinic.

Analysis of Chemisorbed Tribo-Film for Ceramic-on-Ceramic Hip Joint Prostheses by Raman Spectroscopy

To understand the possible lubricant mechanism in ceramic-on-ceramic hip joint prostheses, biochemical reactions of the synovial fluid and the corresponding frictional coefficients were studied. The experiments were performed in a hip joint simulator using the ball-on-cup configuration with balls and cups made from two types of ceramics, BIOLOX^®forte and BIOLOX^®delta. Different lubricants, namely albumin, γ-globulin, hyaluronic acid and three model synovial fluids, were studied in the experiments and Raman spectroscopy was used to analyze the biochemical responses of these lubricants at the interface. BIOLOX^®delta surface was found less reactive to proteins and model fluid lubricants. In contrast, BIOLOX^®forte ball surface has shown chemisorption with both proteins, hyaluronic acid and model fluids imitating total joint replacement and osteoarthritic joint. There was no direct correlation between the measured frictional coefficient and the observed chemical reactions. In summary, the study reveals chemistry of lubricant film formation on ceramic hip implant surfaces with various model synovial fluids and their components.

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.

On the Dependence of Rheology of Hyaluronic Acid Solutions and Frictional Behavior of Articular Cartilage

Hyaluronic acid (HA) injections represent one of the most common methods for the treatment of osteoarthritis. However, the clinical results of this method are unambiguous mainly because the mechanism of action has not been clearly clarified yet. Viscosupplementation consists, inter alia, of the improvement of synovial fluid rheological properties by injected solution. The present paper deals with the effect of HA molecular weight on the rheological properties of its solutions and also on friction in the articular cartilage model. Viscosity and viscoelastic properties of HA solutions were analyzed with a rotational rheometer in a cone-plate and plate-plate configuration. In total, four HA solutions with molecular weights between 77 kDa and 2010 kDa were tested. The frictional measurements were realized on a commercial tribometer Bruker UMT TriboLab, while the coefficient of friction (CoF) dependency on time was measured. The contact couple consisted of the articular cartilage pin and the plate made from optical glass. The contact was fully flooded with tested HA solutions. Results showed a strong dependency between HA molecular weight and its rheological properties. However, no clear dependence between HA molecular weight and CoF was revealed from the frictional measurements. This study presents new insight into the dependence between rheological and frictional behavior of the articular cartilage, while such an extensive investigation has not been presented before.

The Effect of Synovial Fluid Composition, Speed and Load on Frictional Behaviour of Articular Cartilage

Articular cartilage ensures smooth motion of natural synovial joints operating at very low friction. However, the number of patients suffering from joint diseases, usually associated with cartilage degradation, continuously increases. Therefore, an understanding of cartilage tribological behaviour is of great interest in order to minimize its degradation, preserving the reliable function of the joints. The aim of the present study is to provide a comprehensive comparison of frictional behaviour of articular cartilage, focusing on the effect of synovial fluid composition (i), speed (ii), and load (iii). The experiments were realized using a pin-on-plate tribometer with reciprocating motion. The articular cartilage pin was loaded against smooth glass plate while the tests consisted of loading and unloading phases in order to enable cartilage rehydration. Various model fluids containing albumin, γ-globulin, hyaluronic acid, and phospholipids were prepared in two different concentrations simulating physiologic and osteoarthritic synovial fluid. Two different speeds, 5 mm/s and 10 mm/s were applied, and the tests were carried out under 5 N and 10 N. It was found that protein-based solutions exhibit almost no difference in friction coefficient, independently of the concentration of the constituents. However, the behaviour is considerably changed when adding hyaluronic acid and phospholipids. Especially when interacting with γ-globulin, friction coefficient decreased substantially. In general, an important role of the interaction of fluid constituents was observed. On the other hand, a limited effect of speed was detected for most of the model fluids. Finally, it was shown that elevated load leads to lower friction, which corresponds well with previous observations. Further study should concentrate on specific explored phenomena focusing on the detailed statistical evaluation.

The Effect of Kinematic Conditions and Synovial Fluid Composition on the Frictional Behaviour of Materials for Artificial Joints

The paper introduces an experimental investigation of frictional behaviour of materials used for joint replacements. The measurements were performed using a ball-on-disc tribometer, while four material combinations were tested; metal-on-metal, ceramic-on-ceramic, metal-on-polyethylene, and ceramic-on-polyethylene, respectively. The contact was lubricated by pure saline and various protein solutions. The experiments were realized at two mean speeds equal to 5.7 mm/s and 22 mm/s and two slide-to-roll ratios, −150% and 150%. It was found that the implant material is the fundamental parameter affecting friction. In general, the metal pair exhibited approximately two times higher friction compared to the ceramic. In particular, the friction in the case of the metal varied between 0.3 and 0.6 while the ceramic pair exhibited friction within the range from 0.15 to 0.3 at the end of the test. The lowest friction was observed for polyethylene while it decreased to 0.05 under some conditions. It can be also concluded that adding proteins to the lubricant has a positive impact on friction in the case of hard-on-hard pairs. For hard-on-soft pairs, no substantial influence of proteins was observed. The effect of kinematic conditions was found to be negligible in most cases.

[Wear and Roughness of Bearing Surface in Retrieved Polyethylene Bicon-Plus Cups]

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.

Towards near-permanent CoCrMo prosthesis surface by combining micro-texturing and low temperature plasma carburising

An advanced surface engineering process combining micro-texture with a plasma carburising process was produced on CoCrMo femoral head, and their tribological properties were evaluated by the cutting-edge pendulum hip joint simulator coupled with thin film colorimetric interferometry. FESEM and GDOES showed that precipitation-free C S-phase with a uniform case depth of 10μm was formed across the micro-textures after duplex treatment. Hip simulator tests showed that the friction coefficient was reduced by 20% for micro-metre sized texture, and the long-term tribological property of microtexture was enhanced by the C-supersaturated crystalline microstructure formed on the surface of duplex treated CoCrMo, thereby enhancing biotribological durability significantly. In-situ colorimetric interferometry confirmed that the maximum film thickness around texture area was 530nm, indicating that the additional lubricant during sliding motion might provide exceptional bearing life.

A novel tribological study on DLC-coated micro-dimpled orthopedics implant interface

This study investigates a tribological performance of diamond like carbon (DLC) coated micro dimpled prosthesis heads against ceramic cups in a novel pendulum hip joint simulator. The simulator enables determining friction coefficient and viscous effects of a concave shaped specimen interface (conformal contact). Two types of DLC such as hydrogenated amorphous carbon (a-C:H) and tetrahedral amorphous carbon (Ta-C) and one set of micro dimple (diameter of 300µm, depth of 70µm, and pitch of 900µm) were fabricated on metallic prosthesis heads. The experiment results reveal a significant friction coefficient reduction to the 'dimpled a-C:H/ceramic' prosthesis compared to a 'Metal (CoCr)/ceramic' prosthesis because of their improved material and surface properties and viscous effect. The post-experiment surface analysis displays that the dimpled a-C:H yielded a minor change in the surface roughness, and generated a larger sizes of wear debris (40-200nm sized, equivalent diameter), a size which could be certainly stored in the dimple, thus likely to reducing their possible third body abrasive wear rate. Thus, dimpled a:C-H can be used as a 'metal on ceramic hip joint interface', whereas the simulator can be utilized as an advanced bio-tribometer.

[Determination of a Friction Coefficient for THA Bearing Couples]

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.

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.

[What should an orthopaedic surgeon know about biotribology of total hip arthroplasty]

The objective of this paper is to briefly review the engineering biotribology of total hip arthroplasty (THA). At present the issue of lubrication, wear and friction within a THA is being studied in detail and the results have been published in a number of papers. The reason is obvious since the rate at which the articulating surfaces wear off affects the longevity of a THA to a great extent. Seeking an optimal biotribological configuration remains an important task for both the researchers and orthopaedic surgeons. In order to enable the orthopaedic community to think over THA biotribology and, at the same time, communicate with the representatives of technical professions, knowledge of the basic principles of biotribology and their understanding is necessary.

Stress and strain analysis of the hip joint using FEM

Many disorders of the hip can be treated with a suitable osteotomy based on the improvement of mechanical conditions in the hip joint. These operations, such as osteotomies are very complex. The surface replacement has also been developed as an alternative to a total hip replacement for young and more active people. It is up-to-date to concern with biomechanics of pathological hips and it is necessary to supplement the existing clinical findings with the results of mechanical analyses. Several finite element (FE) models are presented in this paper. The first one offers solutions to the strain-stress analysis of the physiological hip. The second one represents dysplastic hip joint. Another two computational models of both hips of a young patient were created (FE model of physiological hip and pathological hip affected by Perthes disease with a deformed shape of the femoral head). Also a computational model is presented, which enables us to investigate strain and stress parameters in the hip joint with applied surface replacement. The strain and stress analysis was performed by means of finite element method (FEM) in ANSYS system.