For the tribological properties of nanoparticle-modified PTFE, a more comprehensive study has been conducted, but there is still some room for research on tribology behavior, tribofilm formation and structure evolution of polytetrafluoroethylene (PTFE) filled with α-Al₂O₃ and SiO₂ nanoparticles during sliding against steel counterparts under different loads. At the same time, it establishes the linkage and mechanism between the maintenance of mechanical strength and the tribological application of polymers in service and provides corresponding scientific data and theoretical guidance for the long-lasting application of polymer lubrication materials. It is found that both composites exhibit good wear resistance across the pressure of 1 MPa to 10 MPa, with the α-Al₂O₃/PTFE composite demonstrating better performance stability compared to the SiO₂/PTFE composite. The high wear resistance is attributed to the formation of tribofilms at the friction interface. For the α-Al₂O₃/PTFE, an island-like tribofilm is formed with a thickness ranging from 100 to 200 nm, while the tribofilm of the SiO₂/PTFE composite is thinner, measuring approximately 50 to 100 nm, and manifests a striped pattern. The chemical composition, both at the surface and subsurface levels, as well as the morphology of the tribofilms, were studied using FTIR spectrometry, X-ray photoelectron spectroscopy (XPS), and FIB-TEM. It is found that the difference in thickness and microstructure of the tribofilms for the two composites is mainly due to the tribochemistry of the nanoparticles. The α-Al₂O₃ nanoparticle plays a “cohesion” role during the formation of the tribofilm, which facilitates the formation of a thicker, more uniform, and stronger adhered tribofilm on the metallic counterpart, making it more robust against higher shear stress.

Healthcare workers around the world are experiencing skin injury due to the extended use of personal protective equipment (PPE) during the COVID-19 pandemic. These injuries are the result of high shear stresses acting on the skin, caused by friction with the PPE. This study aims to provide a practical lubricating solution for frontline medical staff working a 4+ hours shift wearing PPE. A literature review into skin friction and skin lubrication was conducted to identify products and substances that can reduce friction. We evaluated the lubricating performance of commercially available products in vivo using a custom-built tribometer. Most lubricants provide a strong initial friction reduction, but only few products provide lubrication that lasts for four hours. The response of skin to friction is a complex interplay between the lubricating properties and durability of the film deposited on the surface and the response of skin to the lubricating substance, which include epidermal absorption, occlusion, and water retention. Talcum powder, a petrolatum-lanolin mixture, and a coconut oil-cocoa butter-beeswax mixture showed excellent long-lasting low friction. Moisturising the skin results in excessive friction, and the use of products that are aimed at ‘moisturising without leaving a non-greasy feel’ should be prevented. Most investigated dressings also demonstrate excellent performance.

Prolonged use of tight-fitting PPE, e.g., by COVID-19 healthcare workers leads to skin injuries. An important contributor is the shear exerted on the skin due to static friction at the skin-PPE interface. This study aims to develop an optimised wax-oil lubricant that reduces the friction, or shear, in the skin-PPE contact for up to four hours. Lubricants with different wax-oil combinations were prepared using beeswax, paraffin wax, olive oil, and mineral oil. In-vivo friction measurements involving seven participants were conducted by sliding a polydimethylsiloxane ball against the volar forearms to simulate the skin-PPE interface. The maximum static coefficient of friction was measured immediately and four hours after lubricant application. It was found that the coefficient of friction of wax-oil lubricants is mainly governed by the ratio of wax to oil and the thermal stability and morphology of the wax. To maintain long-term lubricity, it is crucial to consider the absorption of oil into the PPE material. The best performing lubricant is a mixture of 20 wt% beeswax, 40 wt% olive oil, and 40 wt% mineral oil, which compared to unlubricated skin, provides 87% (P = 0.0006) and 59% (P = 0.0015) reduction in instantaneous and 4-h coefficient of friction, respectively.

Human beings often explore and perceive the characteristics of objects by touching with their fingers. During this process, the contact pressure and shear stress acting on the skin also modulate the tactile sensation. The external environment is an important factor that influences tactile perception as well as the finger friction characteristics. The purpose of this study was to investigate the effects of fluid environments, such as air, deionized water (DW) and thickened water (TW), on perceived roughness and relevant friction behaviour during finger movement. Two studies were performed to analyse the effect of fluid environment as well as the influence of lubricant viscosity on finger tactile friction behaviour. Participants conducted perception and sliding friction tests with their index finger in air and submerged in DW and TW, respectively. Perception tests were performed using a pairwise comparison, scoring the perceived roughness difference between a reference sample and the test sample. The statistical analysis showed that there was no significant difference in the roughness perception between air and DW, while the sensitivity of perception reduced with increasing lubricant viscosity. An approximate calculation of the film thickness was combined with classical lubrication theory to investigate the relationship between perception and friction. In TW, the thick film formed between the finger and the polytetrafluoroethylene plate changed the contact of the asperities with the skin, thus changing the subjective judgement and friction.

The tribology behavior, tribofilm formation and structure evolution of polytetrafluoroethylene (PTFE) filled with α-Al2O3 and SiO2 nanoparticles during sliding against steel counterparts under different loads were studied. It is found that both composites exhibit good wear resistance across the pressure of 1 MPa to 10 MPa, with the α-Al2O3/PTFE composite demonstrates better performance stability compared to the SiO2/PTFE composite. The high wear resistance is attributed to the formation of tribofilms at the friction interface. For the α-Al2O3/PTFE, an island-like tribofilm is formed with a thickness ranging from 100 to 200 nm, while the tribofilm of the SiO2/PTFE composite is thinner, measuring approximately 50 to 100 nm, and manifest a striped pattern. The chemical composition, both at the surface and subsurface levels, as well as the morphology of the tribofilms were studied using FTIR spectrometry, X-Ray photoelectron spectroscopy (XPS), and FIB-TEM. It is found that the difference in thickness and microstructure of the tribofilms for the two composites is mainly due to the tribochemistry of the nanoparticles. The α-Al2O3 nanoparticle plays a "cohesion" role during the formation of the tribofilm, which facilitates the formation of a thicker, more uniform, and stronger adhered tribofilm on the metallic counterpart, making it more robust against higher shear stress.