Serum Lubricant Research Articles

Enhanced Tribological Performance of UHMWPE Composites Reinforced With Wollastonite: Biocompatibility and Wear Behavior

Abstract Ultra-high molecular weight polyethylene (UHMWPE) is often limited by poor tribological properties in artificial joints, leading to high wear-rates compared to metals and ceramics. This study explores the use of wollastonite, a natural mineral, as a filler to enhance the tribological performance of UHMWPE composites. X-ray diffraction (XRD) analysis revealed that wollastonite content and particle size inversely affected the crystallinity of the composite due to heterogeneous nucleation and stress concentration. The incorporation of wollastonite significantly improved the tribological performance, with wear-rate reductions of 71%, 69.81%, and 50.73% under dry friction, normal saline (NS) lubricant, and new-born calf serum (NBCS) lubricant conditions, respectively. The wear mechanisms in the composite were predominantly slight fatigue and abrasive wear, contrasting with the extrusion deformation and severe fatigue wear observed in neat UHMWPE. Additionally, simulated body fluid (SBF) immersion tests demonstrated the composite's ability to form a surface apatite-like deposition. These findings suggest that wollastonite reinforcement effectively enhances both mechanical and tribological properties of UHMWPE.

In-Vitro Investigation on the Tribological Properties of Nickel-Titanium (NiTi) Alloy Used in Braided Vascular Stents

The integration of diverse weaving angles in vascular stent design proves beneficial for addressing complex applications such as bending, branching, and load-bearing. However, the weaving process may introduce frictional corrosion issues among threads, necessitating further investigation into frictional behaviors at different weaving angles. This study simplifies the contact between nickel-titanium (NiTi) alloy threads in woven stents as line-to-line contact between rods. A proposed in vitro experiment, based on weaving angles of 30°, 45°, 60°, 75°, and 90°, systematically analyzes friction and wear characteristics, including friction coefficients, wear parameters, and morphology. Findings indicate significant impacts of weaving angles on tribological behaviors, with 30° weaving angle stents exhibiting the lowest wear rate. The study identifies four developmental stages in the life cycle of line-to-line contact wear: breaking-in wear, steady wear, severe wear, and post-stable wear. Under 25% calf serum lubrication, lower friction coefficients and wear rates are observed, validating NiTi alloy suitability for lubricated human environments. The investigation reveals a nonlinear correlation between weaving angles, friction cycles, and wear rates, offering insights for the tribological design of woven instruments.

Polyethylene wear testing of a nonmechanically linked total elbow replacement

The objective of this study was to perform a polyethylene wear test on a nonmechanically linked total elbow arthroplasty implant using a clinically relevant in-vitro elbow wear test methodology that simulated 10 years of use in the light to moderate activity of daily living range. The test protocol applied an 80° arc of ulnohumeral motion beginning at 30° shy of full extension and progressing to 110° of flexion. Force was applied at 7° to recreate a valgus load on the elbow. A variable joint load profile at a frequency of 0.5Hz was employed. The implants were tested for 5 million cycles (mc) in a bovine serum lubricant. Implant component failure was characterized and polyethylene wear was determined gravimetrically. After 5 mc, the small polyethylene bushing wear rate was 0.56mg/mc. The medium size wear rate was 0.28mg/mc. Three large sizes were tested and the average wear rate was 0.39±0.07mg/mc. No implant failure was identified. The test recreated an invivo loading environment and measured polyethylene wear rates at specified cycle counts. The test demonstrated less wear than other joint replacements. Further clinical evaluation is necessary to determine if this translates into reduced complications of total elbow replacement associated with wear.

Titanium Nitride Coatings on CoCrMo and Ti6Al4V Alloys: Effects on Wear and Ion Release

While titanium nitride (TiN) coatings are well known for their biocompatibility and excellent mechanical properties, their wear particle and debris release in orthopedic implants remains a matter of active investigation. This study addresses the efficacy of TiN coatings on CoCrMo and Ti6Al4V alloys to enhance wear resistance and reduce ion release from prosthetic implants. Three different coating variants were utilized: one variant deposited using arc evaporation (Arc) followed by post-treatment, and two variants deposited using high-power impulse magnetron sputtering (HiPIMS) with or without post-treatment. The coatings’ performance was assessed through standard wear testing against ultra-high-molecular-weight polyethylene (UHMWPE) in bovine serum lubricant, and in the presence of abrasive PMMA bone cement particles in the lubricant. The results indicated that Arc and HiPIMS with post-treatment significantly reduced wear and eliminated detectable metal ion release, suggesting that these coatings could extend implant longevity and minimize adverse biological responses. Further long-term simulator and in vivo studies are recommended to validate these promising findings.

Synthesis of titanium carbide coating on Ti15Mo alloy and its tribological behaviour

AbstractTi15Mo alloy has been regarded as one of the most potential biomedical materials due to its excellent performance. However, the low hardness and poor wear resistance of titanium alloy limit the further application. Therefore, high temperature solid carburising technology was performed on the surface of Ti15Mo alloys to prepare titanium carbide (TiC) coating with graphene (G) as the carburising agent. The microstructure, mechanical properties, and tribological properties of TiC coating under different lubricants were investigated. Results showed that TiC coating was closely bonded to the titanium substrate. The maximum thickness of TiC coating treated with 1150°C was approximately 184.02 μm, and the microhardness of alloys treated with 1100°C can achieve 1221.5 HV. All modified Ti15Mo alloys showed improved tribological performance compared to the original samples. The wear mechanisms of modified Ti15Mo alloys were abrasive wear and adhesive wear under the SBF lubricant, and the TiC coating was slightly peeled off. The overall friction coefficient and wear rate under 25% calf serum lubricant were lower than the SBF lubricant, and surface scratches were almost absent, and slight abrasive wear and adhesive wear occurred on the surface.

The occurrence of squeaking under wear testing standards for ceramic on ceramic total hip replacements

Ceramic on ceramic total hip replacement clinical reports may on occasion note a noise or squeaking. There is much debate on whether this is an actual concern, but some medical centres want to avoid any possible negative impact on the patients’ wellbeing due to the noise generated.The aim of this study was to determine what sound frequencies can be picked up from hip testing standards for ceramic on ceramic under different lubrication conditions. The ISO-14242-1 (35° cup angle) and ISO-14242-4 (55° cup angle with a 4 mm translational mismatch) standards were used for testing with dry, water and serum lubrication conditions up to 10000 cycles.No sound was detected for water and serum conditions under standard walking (ISO-14242-1) testing. An audible noise with a frequency range of 0.4–0.8 kHz was picked up within 600 cycles under water and edge loading (ISO-14242-4) conditions. All dry testing produced a high pitch squeak when the frequency was higher than 2 kHz. One sample under dry edge loading conditions had an audible noise of 0.8 kHz, considered not as squeaking, as it was not high pitch. Dry testing for both, standard walking (ISO-14242-1) and edge loading (ISO-14242-4) conditions, which resulted in a high pitch noise, had a frequency range of 2–8 kHz and 5–9 kHz respectively. One sample tested with edge loading and serum produced a faint squeak noise after 6000 cycles with a frequency of 7 kHz.Edge loading due to ISO-14242-4 conditions had an increased torque which may be playing a role in increased friction leading to noise. Edge loading conditions were more prone to the generation of audible noise and squeaking whilst under lubricated conditions.

An investigation on tribological behavior of methacrylated κ-carrageenan and gellan gum hydrogels as a candidate for chondral repair.

Natural polysaccharides have recently attracted attention as structural biomaterials to replace focal chondral defects. In the present study, in-vitro tribological performance of methacrylated κ-carrageenan and gellan gum hydrogels (KA-MA and GG-MA) was evaluated under physiological conditions. Coefficient of friction (COF) was continuously recorded over testing whilst worn area was measured post-testing. The findings help improve our understanding of KA-MA-H and GG-MA-H tribological performance under various physiological conditions. The friction and wear performance of the hydrogels improved in bovine calf serum lubricant at lower applied loads. Adhesion was the dominant wear mechanism detected by SEM. Among the proposed hydrogels GG-MA-H found robust mechanical properties, increased wear resistance and considerably low COF, which may suggest its potential usage as a cartilage substitute.

Effect of Sliding Velocity on UHMWPE and VEXLPE Friction Against CoCr in Multidirectional, Serum Lubricated Conditions

Abstract The recently introduced four-station friction RandomPOD device was utilized in multidirectional, circular translation pin-on-disk (CTPOD) tests. The effect of sliding velocity on friction with orthopaedic bearing materials was studied. The tests included UHMWPE and VEXLPE pins against polished CoCr disks in serum lubrication at 37 °C. In the constant velocity tests, the sliding velocities used were from 5 to 50 mm/s at intervals of 5 mm/s. The test length with each velocity was 24 h. In the constant acceleration tests, the velocity steadily increased from 0 to 50 mm/s in 24 h. In all tests, the sample size was 4. No strong effect of velocity on friction was observed. This indicated a boundary lubrication mechanism. With sliding velocities above 10 mm/s, VEXLPE showed significantly lower friction than UHMWPE. The finding was in agreement with earlier dynamic RandomPOD tests. Clinically, the use of VEXLPE may result in lower frictional heating.

Mechanical properties and bio-tribological performance of PVD (Ta/ZrN)n multilayer coatings on UHMWPE in bovine serum lubrication

Mechanical properties and bio-tribological performance of PVD (Ta/ZrN)n multilayer coatings on UHMWPE in bovine serum lubrication

Bio‐tribological characterisation of ultra‐high molecular weight polyethylene against different metal counterparts

Excessive wear is a key issue affecting the performance of ultra-high molecular weight polyethylene (UHMWPE)-based artificial prosthesis. This work is focussed on the bio-tribology behaviours of UHMWPE when mating with different metal counterparts (iron-based 316L, Co-based Stellite-S21 and Stellite-S22). According to the ASTM F732 standard, two million cycles comparative wear tests were carried out under bovine serum lubrication. When coupled with S21, S22, and 316L metal counterparts, the obtained average wear factors of UHMWPE were 1.333 ± 0.192, 1.360 ± 0.160, and 1.190 ± 0.177 × 10−6 mm3/N · m, respectively. Initial surface roughness of the metal counterpart has shown an important role in controlling the volume of UHMWPE wear, especially the first one million cycles. Compared with 316L, CoCrMo-based counterparts possessed relative higher hardness and exhibited less rise in surface roughness caused by wear. For UHMWPE-on-metal bearings, random scratch, surface pit, and wear debris attachment were commonly seen, which suggested the coexistence of abrasion, third-body abrasion, and adhesion-based wear. In contrast, the metal counterpart was slightly scratched with no polymer transfer film formation. The work conducted in the present study gives useful knowledge regarding the UHMWPE-on-metal bearing design. With an intention to minimise wear, surface roughness of metal counterpart should be carefully controlled.

Fabrication and tribological behavior of novel UHMWPE/vitamin-C/graphene nanoplatelets based hybrid composite for joint replacement

PurposeThis study aims to fabricate and investigate the tribological performance of ultra-high molecular weight polyethylene (UHMWPE)-based composite materials reinforced with 0.5, 1 and 2 weight percentage of graphene nanoplatelets (GNPs) while keeping the weight percentage of vitamin C constant at 2% for each composite.Design/methodology/approachIn this paper, the composites were fabricated using hot pressing, and the dispersion of GNP/vitamin C/UHMWPE hybrid composite was investigated by X-ray diffraction. Experimental trials were performed according to ASTM F732 on a reciprocating sliding tribometer (pin-on-disc) at human body temperature of 37 ± 1 °C, for a load of 52 N, to assess the role of these fillers on the tribological properties of UHMWPE against Ti6Al4V counter body material under dry and lubricating (human serum) environment.FindingsIn this study, it has been observed that friction and wear behavior of the developed composites improve with increase in weight percentage of GNP, and human serum adheres to the surface of the composite pins upon sliding, resulting in the formation of a film, which results in better wear resistance of the composite pins under human serum lubrication than dry sliding. Scanning electron microscope was used to investigate the worn surface morphological examination of the composite materials. Specific wear rate of 0.76 × 10−7 mm3/Nm was attained for 2 Wt.% GNP-filled composite under human serum lubrication.Practical implicationsThe results indicate the compatibility of the composite material used in this study and suggested the in vitro implant application.Originality/valueThe presented work includes novel study of synergistic effect of GNP (which acts as a solid lubricant) and vitamin C (added as an antioxidant) on the tribological performance of UHMWPE under dry and human serum lubrication.

Quantitative analysis and degradation mechanisms of different protein degradation methods.

The abrasive debris produced by wear test of artificial joints in vitro is encapsulated by proteins in serum lubricants, which hinder the characterization of debris analysis. One of the key issues of isolating wear debris from serum is degrading the proteins wrapping the wear debris. In this article, the proteins in calf serum were degraded by a strong alkali, a strong acid, and an enzyme. The residual concentration of proteins in calf serum was detected by UV absorption. Quantitative analysis of protein degradation and the protein degradation rate was proposed, following treatment with different degradation reagents and different incubation times. The results showed that when 10 mL of 25% volume calf serum was added with 40 mL of NaOH and incubated at 65°C for 24 h, the protein degradation rate reached a maximum of 95.52%. The protein degradation rate in the solution ranged from 31.86% to 71.64% when a different volume of 37% HCl was added and incubated at 60°C. The highest protein degradation rate was 94.98% in the protease degradation solution. When the protein degradation rate is less than 70%, the particles were coated by protein. When the protein degradation rate was more than 95%, there was no protein coating around the particles. The three protein degradation methods have different processes and protein degradation rates. A suitable method for protein degradation can be selected according to these practical applications.

Effect of temperature on UHMWPE and VEXLPE friction and wear against CoCr in noncyclic tests

In prosthetic joints, frictional heating may cause protein denaturation in synovial fluid which may affect its lubrication properties. In arthroplasty, conventional ultra-high molecular weight polyethylene (UHMWPE) is being gradually replaced by vitamin E stabilized, extensively cross-linked UHMWPE (VEXLPE) with a superior combination of wear and oxidation resistance. There is scarcity of literature on UHMWPE vs.VEXLPE friction. A noncyclic, single-station friction measurement device, the Friction RandomPOD, was recently introduced. The direction of sliding, velocity, acceleration, and load varied randomly within certain, biomechanically justified limits. The measurement of the coefficient of friction was based on a three-axial load cell. In order to increase the testing capacity, the number of test stations was now increased to 4 using similar load cells. One-week tests were performed with pins made of UHMWPE and VEXLPE against CoCr in calf serum lubrication at 4 °C, 20 °C and 37 °C. The lower temperatures were included to prevent or retard protein denaturation. The lowest friction and wear were observed at 37 °C. At this temperature, the mean of the coefficient of friction of VEXLPE was 55% lower than that of UHMWPE. The wear of VEXLPE was always lower than that of UHMWPE.

Biotribological performance of medical-grade UHMW polyethylene-based hybrid composite for joint replacement

Ultra high molecular weight polyethylene (UHMWPE) is widely used for articulating surfaces in total hip and knee replacements. In the present work, the tribological properties of UHMWPE-based nano composites were studied in order to meet the demands of current bearing applications. UHMWPE matrix reinforced with 0.5, 1, and 2 weight percentage of alumina nano powder were fabricated by hot pressing. The dispersion and microstructure of composite material was established by X-ray diffraction (XRD) and scanning electron microscope (SEM) micrograph. The tests were carried out on a reciprocating sliding pin-on-disc tribometer at human body temperature (37±1°C) under dry and human serum lubricating environments for a normal load of 46 N and 52 N, a constant sliding speed of 4 mm. Under these testing conditions, it has been observed that the wear behavior of the developed composites improved with increase in weight percentage of alumina nano powder. The results show that at 52 N load, the maximum value of wear rate was 7.9x10−7 mm3/Nm and the minimum value 1.6x10−7 mm3/Nm was obtained. SEM was used to examine the worn surface and it was observed that human serum adheres to the surface of the composite pins upon sliding, resulting in the formation of a film which results in better wear resistance of the composite pins under human serum lubrication than dry sliding. This study implies that the use of nano alumina power will reduce the wear of UHMWPE based composite under human serum lubrication.

Lubricant Biochemistry Affects Polyethylene Wear in Knee Simulator Testing

Lubricant composition has been shown to influence knee simulator wear. In the present study, three types of lubricants each having different biochemistries were used in knee simulator wear tests. Alpha-calf serum was diluted with either low-ion distilled water, phosphate-buffered saline solution (PBS), or PBS with hyaluronic acid (HA), all of which affected the polyethylene wear rate. Adding HA to the PBS lubricant increased the polyethylene wear rate 2-fold. Diluting alpha-calf serum with low-ion distilled water instead of PBS increased the polyethylene wear rate 2.3-fold. Since a boundary lubrication regime was considered likely to account for these differences, the degradation to the lubricants was also monitored. Changes to the lubricant composition affected the polypeptide degradation, constituent degradation, low-molecular weight polypeptide concentration, and consequently the polyethylene wear rate. A speculative colloid-mediated boundary lubrication model was suggested, and further support was obtained by performing additional tests with osteoarthritic human synovial fluid that indicated that polypeptide constituent fractions were affected by the wear test. Diluting the alpha-calf serum lubricants with PBS, using an antibiotic-antimycotic additive to inhibit bacterial growth, and including HA created a lubricant that was similar in biochemical characteristics to human osteoarthritic synovial fluid and produced linear penetration rates and surface pitting that were comparable to those seen clinically for the same type of total knee replacements. This lubricant was recommended for producing more clinically relevant knee wear simulator testing.

Effect of deep rolling on subsurface conditions of CoCr28Mo6 wrought alloy to improve the wear resistance of endoprostheses

Wear of orthopaedic endoprostheses is associated with adverse local and systemic reactions and can lead to early implant failure. Manufacturing determines the initial subsurface microstructure of an alloy that influences the implant's wear behaviour. Therefore, this study aims at generating enhanced wear resistances by a modification of the surface and subsurface microstructure of a CoCr28Mo6 wrought alloy by applying deep rolling.The state of the art was investigated by means of eleven retrieved CoCr28Mo6 hip implant components from different manufacturers with respect to their subsurface microstructure and micro hardness profiles. CoCr28Mo6 wrought alloy samples (DIN EN ISO 5832–12) were aged at 750 °C for 24 h and/or plastically deformed by deep rolling with varying axial forces (170 N, 230 N and 250 N). The samples were metallographically prepared and investigated using optical and scanning electron microscopy with EDS and EBSD, micro hardness testing, XRD and tribological testing.The retrieved implant components revealed that, independent of the manufacturer, neither the head nor the stem trunnion exhibited a defined subsurface condition. The dominant phase within the implants was face-centered cubic (fcc). Some implants exhibited single hexagonal close-packed (hcp) grains due to a stress-induced phase transformation. The initial CoCr28Mo6 wrought alloy had a fcc crystal structure. After isothermal aging, the matrix entirely transformed to a hcp structure. In the initial fcc-condition, deep rolling generated a plastically deformed surface layer within the first 100 μm and stress-induced phase transformation to hcp was observed. Micro hardness gradients were present in the subsurface of up to 600 μm depth and exhibited a maximum increase of 34% by deep rolling in comparison to the initial fcc-matrix. This trend was confirmed by a correlated increase in residual compressive stresses. In tribological tests under serum lubrication, the modified samples generated lower wear in comparison to the contemporarily used fcc-matrix samples. This study demonstrates that deep rolling is an effective processing to modify the subsurface of a biomedical CoCr28Mo6 wrought alloy in order to increase the wear resistance. The intentional transformation from the fcc to the hcp phase induced by deformation offers great potential for implant application.

A comparative bio-tribological study of self-mated PEEK and its composites under bovine serum lubrication

In this study, the bio-tribological performances of polyether-ether-ketone (PEEK) 450G and its composites (carbon fiber reinforced PEEK-CA30, carbon fiber/graphene/polytetrafluoroethylene reinforced PEEK-FC30, and glass fiber reinforced PEEK-GL30) were systematically investigated under self-mating combination.During 2 million cycle tribo-tests, PEEK bearings all exhibited two-stage wear. The total mass losses were 9.03 ± 1.87, 9.59 ± 0.22, 11.29 ± 1.30 and 23.01 ± 0.77 mg for 450G, CA30, FC30 and GL30, respectively. It was obvious that, glass fiber reinforcement was not favorable and had the highest wear loss among the four PEEK bearings (P ≤ 0.001). In respect to PEEK 450G, CA30 was superior in wear performance, with a 62% of reduction in steady state wear factor. While FC30 was comparable to that of 450G.Plowing grooves, scale-like wear scars, and wear debris attachment were observed within the wear zone of 450G bearing. These kinds of wear morphologies were associated with abrasion and adhesion wear. In terms of PEEK composites, surface pit and fiber breakage were common wear features. Scale-like wear scars were only observed on the CA30 and FC30 bearings. Apart from fiber detachment induced material loss, adhesion wear was dominated in CA30 and FC30, while abrasive wear was more pronounced in GL30.Under bovine serum lubrication, no solid lubrication film was found. Moreover, wear process did not induce obvious change in surface layer crystallinity. The work conducted in this study provide the basic tribological knowledge of PEEK and its composites under physiologically relevant lubrication condition, which is helpful for the design and development of artificial prosthesis.

Tribological performance of biomedical grade UHMWPE/nano-Al2O3/Vitamin-C hybrid composite for cartilage replacements

This paper presents the fabrication of UHMWPE/nano-Al2O3/Vitamin-C hybrid composites suitable for use as artificial cartilages in total joint prosthesis. Three composite variations were fabricated using the hot press technique, keeping the Vitamin C weight percentage constant at 2% and varying Al2O3 weight percentage by 0.5%, 1% and 2% respectively. Al2O3 was used as an anti-wear additive in UHMWPE and Vitamin C was used as an anti-oxidant. The fabricated composite pins were subjected to wear tests against Ti6Al4V alloy under dry sliding and human serum lubrication. It was observed that the 2 wt% Al2O3 filled UHMWPE showed better wear performance than the other composites and that human serum adheres to the surface of the composite pins upon sliding. This leads to the formation of a film which results in better wear resistance of the composite pins under human serum lubrication than dry sliding.

Effect of type and temperature of serum lubricant on VEXLPE wear and friction

Multidirectional tests were carried out to study the influence of the type and temperature of serum lubricant on the wear and friction of vitamin E stabilized, extensively crosslinked ultrahigh molecular weight polyethylene (VEXLPE) against polished CoCr. To minimize the rates of protein denaturation and microbial growth, cold wear tests were performed for the first time so that the serum lubricant was at a refrigerator temperature of 4 °C. The highest wear factors and coefficients of friction were observed at the refrigerator temperature and the lowest at body temperature where the rates of protein denaturation and microbial growth were expected to be at their maximum. The VEXLPE mean wear factor in alpha calf serum (ACS) decreased by two orders of magnitude as the lubricant bulk temperature increased from 4 °C to 37 °C. Thermal analysis indicated that the contact temperature in the pin-on-disk test was less than 2 °C above the lubricant bulk temperature. It appears that a wide range of polyethylene wear rates and coefficients of friction can be obtained depending on the temperature. The type of serum also strongly affected the obtained wear rate at and above 20 °C.

Effects of fretting wear on porous Ti materials by using rice husk as hold space

A comparative analysis of the friction coefficient of pure and porous titanium was carried out through wear tests conducted both in dry friction conditions and using a bovine serum lubricant friction conditions. The microstructure, wear mechanism and three-dimensional topography of the two specimens were studied. In pure and porous titanium, the results show that the friction coefficient, wear volume and roughness were higher in dry friction than in the presence of lubrication for both pure and porous titanium. However, in dry friction and bovine serum lubricant tested, the resistance of pure titanium was higher than that of porous titanium.