Biotribology最新文献

Total joint replacement (TJR) is a successful procedure for millions of patients each year. Optimizing mechanical properties of bearing couples is important to increase implant longevity and improve patient outcomes. Softer viscoelastic materials offer a potential solution by more closely replicating the mechanical properties and lubrication regime of a native joint, but their wear properties are relatively unknown compared to the wealth of knowledge about polyethylene. In this study, the utility of an experimental set-up not widely used in wear testing was investigated through the evaluation of the mechanical characteristics of four bearing couples often used in TJR. A flat-on-flat rotational test evaluating wear through a change in height of the upper sample introduced several variables that are thought to alter the mechanical properties of compliant bearing materials. The wear properties and coefficient of friction (COF) of two polymer surfaces, ultra-high molecular weight polyethylene (UHMWPE) and polycarbonate urethane (PCU) were directly compared as they articulated against both CoCrMo and Ti-6Al-4V at contact stresses of 3.46, 2.60, and 1.73 MPa. Wear rate was influenced by both polymer surface and normal force while independent of metal counter bearing, with increased wear of couples containing PCU, and at higher forces. Increased COF was seen with PCU, but was independent of other variables. This study elucidated several factors present with this experimental set-up that may contribute to an inadequate lubrication regime and subsequently increased wear and friction of PCU. These are important considerations to maximize the mechanical properties and longevity of implants.

Hydrogels, especially double-network hydrogels, are attractive candidates as load-bearing biomaterials, e.g., tissue-engineering supports for articular cartilages and bones. In this study, we describe the modification of a double-network hydrogel by the introduction of a third monomer, N-[3-(dimethylamino)propyl]methacrylamide, to the network system, which serves as a reactive site for subsequent interfacial reactions and surface-initiated controlled radical polymerization under ambient conditions. The as-prepared poly(2-(methacryloyloxy)ethyl trimethylammonium chloride) (PMETAC) polyelectrolyte polymer brush-modified DN hydrogel exhibited an ultralow coefficient of friction (0.001–0.004) under high contact pressure—comparable to that of the synovial joint.

Lubrication in biology uses lipids, proteins, and aqueous gels to maintain hydration and provide low shear stress over a range of sliding speeds and contact pressures. The unquestionably amphiphilic nature of proteins and the complexity found in the aqueous solutions suggest that these systems operate near an optimal solvophilic condition. To explore the potential for a solvophilic transition in an amphiphilic gel, we perform tribological and swelling measurements of poly(hydroxyethyl)methacrylate, pHEMA, equilibrated over a range of water-ethanol solutions. Depending on the ethanol concentration, Gemini pHEMA gels achieve either low friction (μ < 0.02) and low adhesion or high friction (μ > 1) and high adhesion. We hypothesize that as the solution becomes increasingly ethanol-rich the alkyl regions of ethanol more fully associate with the aliphatic regions of pHEMA, effectively coating the chains with a hydroxyl presenting surface, promoting hydrogen-bonding and the influx of water and leading to maximum in swelling and mesh size, leading to a dramatic reduction in friction and adhesion. We suggest that the tribological behaviors of amphiphilic Gemini gels reflect the presentation of hydrophobic and hydrophilic domains across the interfaces during sliding. These experiments explore the lubrication and solvophilic transitions in amphiphilic Gemini gels and suggest fundamental mechanisms and solution composition through which biotribological joints leverage lipid and protein-based complex fluids to achieve lubricity.

In dentistry, clinical wear is typically measured by superimposition of plaster replica scans of the patient's actual and baseline situation. Intraoral scanning could save time and circumvent replica fabrication and associated errors. However, intraoral scanners are made for commercial use without the possibility to implement comprehensive user-specific settings. Analysis of exported stl-data is, in general, executed with commercial quality control software.

This study investigated the effect of mesh inhomogeneities on distance measurements based on target surfaces generated by different scanners and parameter settings. To quantify errors, an analytical solution for mean value and standard deviation of evenly distributed distance measurements for a spherical cap situation (resembling either a worn cusp or a wear track in a once flat surface) was derived. In vitro experiments with scans of precise spherical moulds gradually reduced in height complemented the investigation.

Due to non-weighted statistics in the quality control software, errors increased with increasing mesh inhomogeneity. Worst results were given for intraoral scans with mean relative errors of up to 13.2% and 20.5% for mean value and standard deviation of the distributed distance measurements. Homogeneous remeshing of the intraoral scan surfaces could almost eliminate these unwished effects.

Biotribology is one of the key branches in the field of artificial joint development. Wear and corrosion are among fundamental processes which cause material loss in a joint biotribological system; the characteristics of wear and corrosion debris are central to determining the in vivo bioreactivity. Much effort has been made elucidating the debris-induced tissue responses. However, due to the complexity of the biological environment of the artificial joint, as well as a lack of effective imaging tools, there is still very little understanding of the size, composition, and concentration of the particles needed to trigger adverse local tissue reactions, including periprosthetic osteolysis. Fourier transform infrared spectroscopic imaging (FTIR-I) provides fast biochemical composition analysis in the direct context of underlying physiological conditions with micron-level spatial resolution, and minimal additional sample preparation in conjunction with the standard histopathological analysis workflow. In this study, we have demonstrated that FTIR-I can be utilized to accurately identify fine polyethylene debris accumulation in macrophages that is not achievable using conventional or polarized light microscope with histological staining. Further, a major tribocorrosion product, chromium phosphate, can be characterized within its histological milieu, while simultaneously identifying the involved immune cell such as macrophages and lymphocytes. In addition, we have shown the different spectral features of particle-laden macrophages through image clustering analysis. The presence of particle composition variance inside macrophages could shed light on debris evolution after detachment from the implant surface. The success of applying FTIR-I in the characterization of prosthetic debris within their biological context may very well open a new avenue of research in the orthopedics community.

The objective of this research is to study the feasibility using nanomaterials to prevent and/or repair wear of teeth. Canine teeth have thin enamel prone to dental wear, causing pain, tooth loss, and infection. This research developed a new teeth repair agent based on the tribochemically active nanoparticles. The presence and properties of synthesized repair agents were evaluated after applying the repair agents by rubbing (simulated chewing) between extracted dog teeth. Polyether modified alpha‑zirconium phosphate (α-ZrP) nanoparticles form a strong and durable protective layer on a canine tooth's enamel surface through chewing. The effectiveness of this protective film generation was enhanced by adding hydroxyapatite (HAp) nanoparticles into the repair agent. This protective film is up to 2 μm thick and has a hardness comparable to the enamel substrate. These results show that by chewing with the repair agent, the teeth are protected. The tomography result shows this repair agent also has the potential to mend cracks on the enamel surface. This research reports a novel approach to protect the wear of teeth. Nanoparticles promoted the generation of a protective film in situ during the chewing process. This nanomaterial can be the base of novel dental protective devices such as chewing toys or gums that preventing or reversing tooth wear and reducing the stress and cost of dental restoration operations.

Human-made adhesives lose their tack rapidly after first use, while animals such as geckos can reuse their adhesive feet for a lifetime. Nature's use of fibrillar structures as strong, renewable and self-cleaning adhesives has inspired the development of synthetic adhesives with similarly structured surfaces. More than a decade of research and engineering has culminated in ‘gecko tape’: a re-useable adhesive that has a structured surface similar to that of geckos and that outperforms the usual sticky tape. We report experiments that show that, despite its name, a commercial gecko tape shares few adhesive principles with its eponym. In particular, we find no evidence that the micrometric features that are present on the surface of the gecko tape play a role in its adhesive strength. In addition, we find that contrary to the gecko, the tape leaves behind a layer of adhesive after removal from the surface. The fact that the gecko tape outperforms a conventional adhesive tape is due to the fact that the softness of the backing of the gecko tape allows to create a much larger contact area for a given normal force. The conclusion is that surface features are not necessary to create a superb adhesive; tuning the backing layer elasticity may be enough.

Biology largely manages tribological challenges either by eliminating sliding altogether or by protecting sliding interfaces with soft aqueous gels. In the body, aqueous gels are often thin (thickness, t < 100 μm), soft (elastic modulus, E < 10 kPa), lubricious (friction coefficients, μ < 0.01), and cover compliant surfaces, including cell membranes, pleura, cartilage, and the eye. These characteristics provide a natural defense against wide ranges of applied loads. In this work, hydrogel samples (7.5 wt% polyacrylamide, 0.3 wt% N,N′-methylenebisacrylamide) were prepared with spherically-capped shell probe geometries, which have been previously determined to provide constant contact pressures during indentation measurements against flat hydrogel disks. In a self-mated (“Gemini”) sliding configuration, this geometry is capable of load-independent friction over a range of low normal loads spanning 0.5 to 2.0 mN. This friction behavior is consistent with da Vinci-Amontons' friction law (F_f = μF_n) due to the large compliance of the spherically-capped shell probe geometry enabling the area of contact to increase in proportion with the applied load and due to low shear stresses reacted across the sliding interface for high water content aqueous gels. Future bio-inspired lubrication strategies involving aqueous gels may benefit from leveraging contact geometry for constant, load-independent friction.

Currently, the artificial hip joint is the best option for total hip arthroplasty, and the demand for this procedure is increasing annually. However, a major deficiency of artificial hip joints is the performance limitation in a wide range of movements, such as those in Muslim prayer (salat), a major religious practice that consists of seven positions representing extreme movements. In this work, a numerical examination is conducted to investigate the performance of artificial hip joints with three texture configurations and with two different ball materials subjected to seven loading conditions of Muslim prayer (salat). Transient non-Newtonian elastohydrodynamic lubrication analyses are solved using the two-way Fluid–Structure Interaction (FSI) method. It is found that the femoral head and the inner liner with a pattern applied to the whole of their contacted surface show a substantial increase in load support when compared with the smooth one; the improvement is approximately 11% and 13%, respectively, for the movement of sitting between two prostrations for left leg, and the bowing position. Furthermore, slight increase in fluid pressure and load support is highlighted compared with the models in which only the liner or head are textured. In addition, the simulation solution shows that for other loading positions, the textured model reveals a reduction in performance. The amount of load support in prostration, sitting between two prostrations (right leg), and sitting (right leg) positions is insufficient, which may lead to direct contact. The simulation results also indicate that the alumina femoral head gives better result compared to the stainless steel one.