Experimental characterization of motion resistance of the sacroiliac joint.

BACKGROUND: The human sacroiliac joint (SIJ) in vivo is exposed to compressive and shearing stress environment, given the joint lines are almost parallel to the direction of gravity. The SIJ supports efficient bipedal walking. Unexpected or unphysiological, repeated impacts are believed to cause joint misalignment and result in SIJ pain. In the anterior compartment of the SIJ being synovial, the articular surface presents fine irregularities, potentially restricting the motion of the joints. OBJECTIVE: To clarify how the SIJ articular surface affects the resistance of the motion under physiological loading. METHODS: SIJ surface models were created based on computed tomography data of three patients and subsequently 3D printed. Shear resistance was measured in four directions and three combined positions using a customized setup. In addition, repositionability of SIJs was investigated by unloading a shear force. RESULTS: Shear resistance of the SIJ was the highest in the inferior direction. It changed depending on the direction of the shear and the alignment position of the articular surface. CONCLUSION: SIJ articular surface morphology is likely designed to accommodate upright bipedal walking. Joint misalignment may in consequence increase the risk of subluxation.

FEM wear prediction of ceramic hip replacement bearings under dynamic edge loading conditions.

Hard-on-Hard hip implants, specifically ceramic tribo-pair, have produced the highest in-vivo wear resistance, biocompatibility, superior corrosion resistance, and high fracture toughness. However, this ceramic tribo-pair suffers from edge loading, sharply increasing wear and accelerating early implant failures due to micro-separation. Even though in-vitro studies have tested the occurrence of wear due to dynamic edge loading, the Finite Element Method (FEM) gives the advantage of accurately estimating the wear, minimizing the experimental time and cost. A new fundamental FEM model is developed to predict wear for ceramic hip replacement bearings under dynamic edge loading conditions for a fixed separation and fixed inclination angle. The model is directly validated with the existing hip simulator data up to 3 million cycles in terms of wear depth, wear scar and volumetric wear rate. The results from the model show that the accuracy in wear prediction was more than 98% for the wear depth and volumetric wear rate for the dynamic edge loading condition. A stripe wear scar is captured, depicting the edge loading conditions. The developed model from this study can predict wear under pure standard and dynamic edge loading conditions.

Outstanding Bio-Tribological Performance Induced by the Synergistic Effect of 2D Diamond Nanosheet Coating and Silk Fibroin.

Due to their excellent biocompatibility, outstanding mechanical properties, high strength-to-weight ratio, and good corrosion resistance, titanium (Ti) alloys are extensively used as implant materials in artificial joints. However, Ti alloys suffer from poor wear resistance, resulting in a considerably short lifetime. In this study, we demonstrate that the chemical self-assembly of novel two-dimensional (2D) diamond nanosheet coatings on Ti alloys combined with natural silk fibroin used as a novel lubricating fluid synergistically results in excellent friction and wear performance. Linear-reciprocating sliding tests verify that the coefficient of friction and the wear rate of the diamond nanosheet coating under silk fibroin lubrication are reduced by 54 and 98%, respectively, compared to those of the uncoated Ti alloy under water lubrication. The lubricating mechanism of the newly designed system was revealed by a detailed analysis of the involved microstructural and chemical changes. The outstanding tribological behavior was attributed to the establishment of artificial joint lubrication induced by the cross binding between the diamond nanosheets and silk fibroin. Additionally, excellent biocompatibility of the lubricating system was verified by cell viability, which altogether paves the way for the application of diamond coatings in artificial Ti joint implants.

Modernising Orodispersible Film Characterisation to Improve Palatability and Acceptability Using a Toolbox of Techniques.

Orodispersible films (ODFs) have been widely used in paediatric, geriatric and dysphagic patients due to ease of administration and precise and flexible dose adjustments. ODF fabrication has seen significant advancements with the move towards more technologically advanced production methods. The acceptability of ODFs is dependent upon film composition and process of formation, which affects disintegration, taste, texture and mouthfeel. There is currently a lack of testing to accurately assess ODFs for these important acceptability sensory perceptions. This study produced four ODFs formed of polyvinyl alcohol and sodium carboxymethylcellulose using 3D printing. These were assessed using three in vitro methods: Petri dish and oral cavity model (OCM) methods for disintegration and bio-tribology for disintegration and oral perception. Increasing polymer molecular weight (MW) exponentially increased disintegration time in the Petri dish and OCM methods. Higher MW films adhered to the OCM upper palate. Bio-tribology analysis showed that films of higher MW disintegrated quickest and had lower coefficient of friction, perhaps demonstrating good oral perception but also stickiness, with higher viscosity. These techniques, part of a toolbox, may enable formulators to design, test and reformulate ODFs that both disintegrate rapidly and may be better perceived when consumed, improving overall treatment acceptability.

Bio-Tribology and Corrosion Behaviors of a Si- and N-Incorporated Diamond-like Carbon Film: A New Class of Protective Film for Ti6Al4V Artificial Implants.

Ti6Al4V artificial implants are increasingly demanded for addressing human dysfunction caused by an aging population and major diseases. However, they are restricted due to the release of vanadium and aluminum ions in the process of corrosion and wear. This work is aimed to provide a protective film for Ti6Al4V artificial implants, and then, a Si-incorporated diamond-like carbon (Si-DLC) film and Si- and N-incorporated DLC (SiN-DLC) film were deposited on the surface of Ti6Al4V by plasma-enhanced chemical vapor deposition. Results suggest that the thickness of the as-deposited DLC film is approximately 2 µm, and the SiN-DLC film shows the lowest surface roughness (53.0 ± 3.6 nm) compared with the Ti6Al4V and DLC films. The above DLC film possesses high mechanical properties compared with Ti6Al4V, and the SiN-DLC film shows the best resistance to plastic deformation. In addition, the DLC film exhibits high adhesive strength (>13 N) with Ti6Al4V, which is a prerequisite for service in liquid environments. Whether in SBF solution or SBF + BSA solution, the friction coefficient and wear rate of the above DLC film are much lower than those of Ti6Al4V, and the SiN-DLC film displays the optimal tribological properties (0.072 and 1.82 × 10-7 mm3·N-1·m-1, respectively). Moreover, Si-DLC and SiN-DLC films possess similar corrosion resistance but are far better than Ti6Al4V. Cytotoxicity test results show that the SiN-DLC film can significantly improve cell viability and promote cell proliferation to a certain extent. Consequently, the SiN-DLC film is a protective film with more potential for artificial implants.

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.

Surface Texturing of Prosthetic Hip Implant Bearing Surfaces: A Review.

More than 300,000 total hip replacement surgeries are performed in the United States each year to treat degenerative joint diseases that cause pain and disability. The statistical survivorship of these implants declines significantly after 15-25 years of use because wear debris causes inflammation, osteolysis, and mechanical instability of the implant. This limited longevity has unacceptable consequences, such as revision surgery to replace a worn implant, or surgery postponement, which leaves the patient in pain. Innovations such as highly cross-linked polyethylene and new materials and coatings for the femoral head have reduced wear significantly, but longevity remains an imminent problem. Another method to reduce wear is to add a patterned microtexture composed of micro-sized texture features to the smooth bearing surfaces. We critically review the literature on textured orthopedic biomaterial surfaces in the context of prosthetic hip implants. We discuss the different functions of texture features by highlighting experimental and simulated results documented by research groups active in this area. We also discuss and compare different manufacturing techniques to create texture features on orthopedic biomaterial surfaces and emphasize the key difficulties that must be overcome to produce textured prosthetic hip implants.

Structural and tribological characteristics of ultra-low-wear polyethylene as artificial joint materials.

Ultra-low-wear polyethylene (ULWPE) is a new metallocene catalyzed high density polyethylene (HDPE)material. Previous studies have demonstrated that it has excellent biocompatibility and wear resistance, whereupon indicating great potential in the applications to artificial joints. However, as a newly developed material, its tribological behavior and wear resistance mechanism has not been well understood. In the current study, we experimentally evaluated the tribological behavior of ULWPE, and investigated its high wear resistance mechanism in terms of microstructure, crystallization properties, mechanical, physical, and chemical properties. ULWPE manifested the best tribological performance on pin-on-disc (POD) wear tests compared with the most widely used artificial joints materials, with a wear volume of 0.720 ± 0.032 mm3/million cycles (Mc) and 0.600 ± 0.027 mm3/Mc against cobalt-chromium (CoCr) alloy disc and zirconia toughened alumina (ZTA) ceramic disc, respectively. The results of the wear morphology analysis showed that the surface of ULWPE was the slightest, with no obvious surface damage, debris shedding and wear pits. We reveal that three major factors mainly contributed to its high wear resistance. First, ULWPE demonstrated a high crystallinity and a compact crystalline morphology comprised of long linear molecular chains, which contributed to its good mechanical performance. As confirmed by the mechanical test, ULWPE had a very high density, hardness, and tensile elongation at break. The high hardness and strength laid a solid foundation to a low wear volume, and its high ductility and hardness helped to endure abrasive and adhesive wear, resulting in excellent wear resistance. Second, the results of wettability analysis showed that the contact angle formed on the surface of ULWPE was the lowest and the surface energy was the highest. The hydrophilicity of ULWPE provided good lubrication conditions in body fluid. Third, it also had a lower oxidation index. The high hardness, high strength, high ductility and good wetting of ULWPE materials reduced the damage of the material to adhesion and abrasive wear, resulting in excellent wear resistance.

The Bio-Tribological Effect of Poly-Gamma-Glutamic Acid in the Lysozyme-Ionic Contact Lens System.

Feeling comfortable is an important issue for contact lens wearers as contact lenses are worn for an extensive period of time. It has been shown that the in vitro friction coefficient of contact lenses is correlated to the degree of in vivo comfort, thus many studies focus on establishing friction testing methods for investigating the friction coefficient of contact lenses or contact lens care solution. We have previously demonstrated the lubricating property of poly-gamma-glutamic acid (γ-PGA)-containing care solution, and it could reduce the high friction coefficient caused by lysozyme. However, the mechanism of how γ-PGA-containing care solution reduces the lysozyme-induced friction coefficient of contact lenses is unclear. We investigated the bio-tribological effect of γ-PGA on ionic contact lenses in the presence of lysozyme by testing load and velocity variations. The ability to remove lysozyme deposition by γ-PGA and viscosity analysis of γ-PGA-containing care solutions were also investigated to understand the potential mechanism. Our results showed that the friction coefficient of γ-PGA-containing care solution with lysozyme was the lowest in both load and velocity variations, and γ-PGA functions distinctly in the lysozyme-ionic contact lens system. We proposed a model of how γ-PGA could reduce the friction coefficient in these two conditions.

Maximizing the Lubricant Film Thickness Between a Rigid Microtextured and a Smooth Deformable Surface in Relative Motion, Using a Soft Elasto-Hydrodynamic Lubrication Model.

We design a pattern of microtexture features to increase hydrodynamic pressure and lubricant film thickness in a hard-on-soft bearing. We use a soft elastohydrodynamic lubrication model to evaluate the effect of microtexture design parameters and bearing operating conditions on the resulting lubricant film thickness and find that the maximum lubricant film thickness occurs with a texture density between 10% and 40% and texture aspect ratio between 1% and 14%, depending on the bearing load and operating conditions. We show that these results are similar to those of hydrodynamic textured bearing problems because the lubricant film thickness is almost independent of the stiffness of the bearing surfaces in full-film lubrication.

Evaluation of the extent of damage to the esophageal wall caused by press-through package ingestion.

Press-through package (PTP) is the most common accidentally ingested foreign body in Japan. Accidental ingestion of PTP can result in esophageal damage. An approach for evaluating the risk of esophageal injury has not been established. Therefore, we used porcine esophageal tissue and silicone sheets to establish a method for assessing the risk of esophageal damage on accidental PTP ingestion. We pathologically evaluated porcine lower esophageal tissue using a scratch tester. Using porcine esophageal tissue, scratch tests were performed with 4 test objects and pathological damage was compared. It was assumed that each object was accidentally ingested. The objects were polyvinylidene chloride (PVDC)-coated polyvinyl chloride (PVC) PTP, soft PThPa, round PTP, and a disposable scalpel. The porcine esophagus was replaced with a silicon sheet, and an automatic friction machine was used for quantitative evaluation. The silicon sheet was scratched using HHS 2000 with 750-g load at 50 mm/min. We investigated the frictional force exerted on the surface for each of the objects. The degree of damage (depth) was the highest for the disposable scalpel, followed by PVDC-coated PVC PTP, while the degree of damage (depth) was the lowest for soft PThPa and round PTP. The mean frictional forces on the silicon sheet were 524.0 gf with PVDC-coated PTP, 323.5 gf with soft PThPa, 288.7 gf with round PTP, and 922.7 gf with the disposable scalpel. We developed approaches to qualitatively and quantitatively evaluate the risk of esophageal damage after accidental PTP ingestion. Our findings indicate that the risk of gastrointestinal damage after accidental PTP ingestion is low with soft PTP and round PTP.

Study on biocompatibility, tribological property and wear debris characterization of ultra-low-wear polyethylene as artificial joint materials.

Ultra-low-wear polyethylene (ULWPE) is a new type polyethylene made by experts who are from China petrochemical research institute, which is easy to process and implant. Preliminary test showed it was more resistant to wear than that of Ultra-high-molecular weight polyethylene (UHMWPE). The purpose of the research is to study biocompatibility, bio-tribological properties and debris characterization of ULWPE. Cytotoxicity test, hemolysis test, acute/chronic toxicity and muscular implantation test were conducted according to national standard GB/T-16886/ISO-10993 for evaluation requirements of medical surgical implants. We obtained that this novel material had good biocompatibility and biological safety. The wear performance of ULWPE and UHMWPE was evaluated in a pin-on-disc (POD) wear tester within two million cycles and a knee wear simulator within six million cycles. We found that the ULWPE was higher abrasion resistance than the UHMWPE, the wear rate of ULWPE by POD test and knee wear simulator was 0.4 mg/106cycles and (16.9 ±â€¯1.8)mg/106cycles respectively, while that of UHMWPE was 1.8 mg/106cycles and (24.6 ±â€¯2.4)mg/106cycles. The morphology of wear debris is also an important factor to evaluate artificial joint materials, this study showed that the ULWPE wear debris gotten from the simulator had various different shapes, including spherical, block, tear, etc. The morphology of worn surface and wear debris analysis showed that wear mechanisms of ULWPE were adhesion wear, abrasive wear and fatigue wear and other wear forms, which were consistent with that of UHMWPE. Thus we conclude that ULWPE is expected to be a lifetime implantation of artificial joint.

Effects of Major Components of Synovial Fluid on the Morphology and Wear Rate of Polyetheretherketone (PEEK) Particles under an Accelerated Wear Process.

Wear particle-induced biological responses are the major factors for the failure of total joint arthroplasties, but it is possible to improve the lubrication and reduce the wear of an artificial joint system. Polyetheretherketone (PEEK), with ultra-high molecular weight polyethylene, is a suitable bearing material due to its resistance to fatigue strain. However, the effects of major compositions of synovial fluid on the wear of PEEK are unclear. We characterized the effects of three major components of synovial fluid including albumin, globulin, and phospholipids on the morphology and wear rate of PEEK wear particles. Our results demonstrated that the concentrations of albumin and globulin could affect the morphology of PEEK wear particles. In addition, a higher concentration of globulin and phospholipids (12.5 mg/mL) resulted in an increase in the amount of wear particles by 2.8- and 1.7-fold, respectively. In contrast, increasing albumin caused a reduction of wear particle numbers. These results indicate increasing concentration of albumin or reducing concentration of globulin or phospholipids has a better effect on reducing the numbers of wear particles and provides a potential solution of reducing PEEK wear particles, thus it can be more effectively applied in other biomedical systems.

Comparison between PEEK and Ti6Al4V concerning micro-scale abrasion wear on dental applications.

In the oral cavity, abrasive wear is predictable at exposed tooth or restorative surfaces, during mastication and tooth brushing. Also, wear can occur at contacting surfaces between the Ti-based prosthetic structures and implants in presence of abrasive compounds from food or toothpaste. Thus, the aim of this work was to compare the abrasive wear resistance of PEEK and Ti6Al4V on three-body abrasion related to different hydrated silica content and loads. Surfaces of Ti6Al4V or PEEK cylinders (8mm diameter and 4mm height) were wet ground on SiC papers and then polished with 1µm diamond paste. After that, surfaces were ultrasonically cleaned in propyl alcohol for 15min and then in distilled water for 10min. Micro-scale abrasion tests were performed at 60rpm and on different normal loads (0.4, 0.8 or 1.2N) after 600 ball revolutions using suspensions with different weight contents of hydrated silica. After abrasive tests, wear scars on flat samples were measured to quantify the wear volume and characterized by scanning electron microscope (SEM) to identify the dominant wear mechanisms. Results showed a higher volume loss rate on PEEK than that recorded on Ti6Al4V,, when subjected to three-body abrasion tests involving hydrated silica suspensions. An increase in volume loss was noted on both tested materials when the abrasive content or load was increased. PEEK was characterized by less wear resistance than that on Ti6Al4V after micro-scale abrasion wear in contact with hydrated silica particles, as commonly found in toothpastes.

Microscopic contact area and friction between medical textiles and skin.

The mechanical contact between medical textiles and skin is relevant in the health care for patients with vulnerable skin or chronic wounds. In order to gain new insights into the skin-textile contact on the microscopic level, the 3D surface topography of a normal and a new hospital bed sheet with a regular surface structure was measured using a digital microscope. The topographic data was analysed concerning material distribution and real contact area against smooth surfaces as a function of surface deformations. For contact conditions that are relevant for the skin of patients lying in a hospital bed it was found that the order of magnitude of the ratio of real and apparent contact area between textiles and skin or a mechanical skin model lies between 0.02 and 0.1 and that surface deformations, i.e. penetration of the textile surface asperities into skin or a mechanical skin model, range from 10 to 50µm. The performed analyses of textile 3D surface topographies and comparisons with previous friction measurement results provided information on the relationship between microscopic surface properties and macroscopic friction behaviour of medical textiles. In particular, the new bed sheet was found to be characterised by a trend towards a smaller microscopic contact area (up to a factor of two) and by a larger free interfacial volume (more than a factor of two) in addition to a 1.5 times lower shear strength when in contact with counter-surfaces. The applied methods can be useful to develop improved and skin-adapted materials and surfaces for medical applications.