Biotribology最新文献

Retrieval analyses allow investigation of the efficacy of artificial implants to replace diseased or damaged natural joints. Implants are not always removed due to mechanical failure; a well-functioning implant may require removal due to causing pain. As an alternative treatment to fusion, total disc replacement is an evolving treatment. Recently, to eliminate the possible failure mechanisms observed in metal-on-polymer and metal-on-metal artificial discs, an all-polymer cervical artificial disc has been introduced. The NuNec cervical arthroplasty system is a self-mating, all-polymer design which utilizes a ball-in-socket configuration with each component made of polyether ether ketone. For the first time, a retrieval analysis of a NuNec cervical disc, which has been removed due to pain from a 54-year-old female patient, has been undertaken. The main reason associated with pain was the size of the implant which was found to be too big for the patient. The time in vivo of the implant was 2 years and at the time of removal, the implant was thought to be functioning well. The average surface roughness values of the socket and the ball of the explanted NuNec disc were measured as 0.067 ± 0.056 μm (Sa) and 0.037 ± 0.023 μm (Sa). Compared to an unused disc, the surface roughness significantly decreased (p = 0.00). The articulating surfaces of the explant had negative skewness and burnished appearances. Evidence for both abrasive and adhesive wear mechanisms was observed on the explant. The hydroxyapatite coatings at the backsides were completely lost.

Absorbent hygiene products like diapers, feminine hygiene, and wet wipes are life necessities. These products commonly use nonwoven fabrics as the layer that is in contact with the skin. Their performance in terms of skin health and comfort is receiving increased attention because of the existence of concerns for skin health issues such as skin irritation and dermatitis, and the large influence of skin sensation on individuals' preference. Friction is usually recognized as an important factor for skin comfort and dermatitis issues, but there is a lack of understanding of the relationship between friction and skin physiology, skin sensation, in the use of absorbent hygiene products. This study reports a measurement of friction in vivo with the evaluation of skin physiology and sensation in neutral and warm environments to explore the effects of fabric and friction on skin comfort. Friction tests between the volar forearm and nonwoven fabrics were conducted with the measurement of transepidermal water loss, skin redness, and the evaluation of subjective skin sensation. The interaction between skin and eight nonwoven fabrics with a surface roughness (arithmetic mean height) between 3 μm and 20 μm was evaluated in neutral (22 °C) and warm (35 °C) environments. Skin physiological changes after friction were able to be detected quantitatively by the transepidermal water loss and skin redness measurement. In the warm environment, there was significantly higher friction, less pleasantness, more changes in transepidermal water loss but not in skin redness. The friction can only relate to skin physiology and sensation in the neutral environment while the surface roughness of fabrics related to them in both neutral and warm environments. Both rough and smooth fabrics caused high friction in the warm environment, but the rough fabric caused a higher adverse impact on skin physiology and sensation than smooth fabrics that suggested the adhesion and deformation friction could have different effects on skin comfort. Deformation friction is more likely to have effects on skin physiology and pleasantness sensation than adhesion friction. The pleasantness sensation has a negative relationship with skin physiology. A more unpleasant sensation can indicate more impact on skin physiology. This provides a potential that the unpleasant sensation can be a precaution signal for the adverse effects on skin physiology.

The purpose of this work was to evaluate the friction and sliding wear behavior of poly-ether-ether ketone (PEEK) matrix composites containing natural amorphous silica fibers (NASF) or particulate lithium‑zirconium silicate (LZSA) glass-ceramics. PEEK and PEEK containing different weight content (10, 20, and 30 wt%) of LZSA or NASF were processed by hot pressing. Reciprocating sliding wear tests were performed on the specimens in artificial saliva solution against an alumina ball on 30 N normal force. Tests were performed at 1 Hz sliding frequency, and at 4 mm stroke length in artificial saliva solution. The worn surfaces were morphologically inspected by field emission guns scanning electron microscopy (FEGSEM) to calculate the wear volume. Coefficient of friction values recorded on PEEK or PEEK-NASF composites against alumina were lower than those on PEEK-LZSA composites. The presence of LZSA particles negatively affected the wear resistance of the PEEK composites. On sliding tests mimicking oral conditions, PEEK composites containing NASF revealed low friction and high wear resistance close to that one exhibited by PEEK. Such results can stimulate further studies on the processing and tribological characterization of PEEK composites including different percentage of natural amorphous silica fibers.

It is well known that during evolution, specific surface patterns emerged (e.g., on lotus leaves and butterfly wings) endowed with many remarkable surface properties (superhydrophobicity, vibrant structural color, delicate textures, etc.). In order to obtain these natural effects in cosmetics, we look for ways to transfer topographic patterns in coatings and treatments. Textured polymer surfaces were studied to explore their friction properties on the microscale and possible correlations with human tactile friction on the macroscale. We have chosen self-assembling block and random copolymers as model systems to prepare reliable biomimetic films with different micrometer and nanometer scale randomly patterned and randomly rough surfaces. The surface texture of the films was characterized by atomic force microscopy (AFM), and their tribological (friction) properties were studied with a surface forces apparatus (SFA) at a low sliding speed of 3 μm/s and at a speed of 10 cm/s relevant to realistic applications. The results are evaluated in terms of polymer segment mobility, interpenetration, entanglement and relaxation at interfaces, surface texture as described by roughness parameters, and interlocking of asperities. A stiction spike (static friction) was commonly found for the randomly patterned glassy polymer films. Random roughness patterns made from semi-crystalline polymers above their T_g gave high friction at low speed, but their friction coefficients were reduced at high speed due to less time for local entanglement and relaxations. The friction response of one of them was also affected differently by humidity than that of glassy polymer films. Tactile friction measurements with a human finger sliding against the polymer films revealed that the textures also provided differences at the macroscale, although the dynamic changes possibly due to lipid transfer, occlusion of moisture and/or damage of the films makes it difficult to draw robust conclusions. Finally, as an example, it is shown that these textures can be transferred to a soft elastomeric skin mimic substrate. This study introduces the concept of surface patterning by self-assembly to deliver tactile sensorial properties in coatings.

The evaluation of medical glove performance has mostly focused on analysing how good a barrier the glove materials are, as well as their durability. Very few studies aim to determine how these gloves affect the performance of the user. This could lead to a lowered ability to carry out tasks, leading to poor healthcare due to diminished sensitivity and dexterity. Furthermore, none of these studies incorporate contaminants to replicate the real-world environments in which medical gloves are used. The work carried out here aims to look at the effects of the bodily fluid mucin on medical glove user's performance. This was assessed via the use of the Purdue Pegboard and Crawford Small Parts Dexterity Test in conjunction with a tactile bump sensitivity test. These tests were carried each in five conditions; bare hand, donned natural rubber latex (NRL) and donned acrylonitrile butadiene rubber (XNBR) gloves – both with and without a 10 mg/ml concentration of porcine gastric mucin applied. The results show that donning gloves decreased dexterity and sensitivity compared to the bare hand. However, mucin was shown to increase dexterity and sensitivity in XNBR, but not with NRL. This is expected to be due to the different ways in which the materials interact with the mucin, affecting the ability to develop a muco-adhesive film and changing the frictional properties of the glove materials.

The elucidation of biolubrication mechanisms and the design of artificial biotribological contacts requires the development of model surfaces that can help to tease out the cues that govern friction in biological systems. Polysaccharides provide an interesting option as a biotribological mimic due to their similarity with the glycosylated molecules present at biointerfaces. Here, pectin was successfully covalently grafted at its reducing end to a polydimethylsiloxane (PDMS) surface via a reductive amination reaction. This method enabled the formation of a wear resistant pectin layer that provided enhanced boundary lubrication compared to adsorbed pectin. Pectins with different degrees of methylesterification and blockiness were exposed to salt solutions of varying ionic strength and displayed responsiveness to solvent conditions. Exposure of the grafted pectin layers to solutions of between 1 and 200 mM NaCl resulted in a decrease in boundary friction and an increase in the hydration and swelling of the pectin layer to varying degrees depending on the charge density of the pectin, showing the potential to tune the conformation and friction of the layer using the pectin architecture and environmental cues. The robust and responsive nature of these new pectin grafted surfaces makes them an effective mimic of biotribological interfaces and provides a powerful tool to study the intricate mechanisms involved in the biolubrication phenomenon.

Background

Fretting and corrosion at the head-stem taper junction has been cited as a potential clinical concern. Material loss measurement is a vital tool for quantifying changes due to in vitro, in vivo, and/or ex-vivo implant experience. Material loss measurement requires reconstruction of pre-implantation geometry to delineate damage. This is straightforward in principle for plain machined tapers, integrating between a fitted interpolated cone and the measured data. Mathematical filtration methods have been developed to remove this texture and facilitate measurement. The extent to which the assembly process could influence filtration accuracy is not currently known.

Methods

An engagement/ disengagement study was performed on 27 head/ stem pairs using 2, 4, and 8kN impact loads. Impact was delivered in three locations; axial, 10^o anterior, and 10^o anteroproximal. Pull-off force was measured, and stems were measured pre and post assembly using a Talyrond 365 roundness measurement machine.

Results

An increase in the plastic deformation of microgrooves and pull-off force was noted with increasing assembly loads. Off-axis impaction resulted in reduced pull-off strength and reduced uniform microgroove distortion. Volumetric change between pre and post assembly was below the noise threshold on stem and head surfaces.

Discussion

The measurement method was shown to be capable of capturing linear microgroove deformation of 1 μm peak – peak and volume loss above 0.1mm³. Lower peak load was noted when impacting a seated head when compared with engagement of discrete heads and stems, under the same assembly conditions.

Bacterial infection is one of the major complications occurs in biomedical implants. Bacterial adhesion on the implant surfaces can form a biofilm, which leads to infection and failure at an earlier phase of implantation. So the surface properties of the implant such as surface topography, surface energy, and chemistry play a crucial role in bacterial adhesion. For decades, several surface finishing techniques have been developed to alter the surface properties in turn to reduce the bacterial adhesion. Most of these implants exhibit freeform surfaces which are difficult to finish with available finishing methods to obtain the uniform surface properties. The current paper focused on the development of a unidirectional abrasive flow finishing process used to finish biomaterials- stainless steel (SS316L) and titanium alloy (Ti-6Al-4 V ELI) with two different abrasive media and a varying number of cycles. The purpose of this study is to evaluate the effect of this finishing process on enhancing the surface characteristics like surface finish, surface topography and its role on wettability and initial bacterial adhesion. Optical profilometer and a scanning electron microscope are used to examine the surface topography and surface morphology of the finished surfaces. The goniometer is used to study the wettability of the finished samples using the sessile drop technique. Further, for the bacterial adhesion study both Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) are selected because these bacterial strains were commonly found on implant-related infections. The obtained result shows that, the surface finish and topography influences on wettability and bacterial adhesion. In conclusion, these results demonstrate that the possibilities of the developed process to enhance the surface finish of the biomedical implants which in turn reduce the implant-related infections and chances of early phase implant failure.