Several soft tissues residing in the living body have excellent hydration lubrication properties and can provide effective protection during relative motion. In order to apply this advantage of soft matters in practical applications and try to avoid its disadvantage, such as swelling and weakening in water, a design strategy of a soft/hard double network (DN) hydrogel microsphere modified ultrahigh molecular weight polyethylene (UHMWPE) composite is proposed in this study. A series of microspheres of urea-formaldehyde (UF), polyacrylamide (PAAm) hydrogel, UF/PAAm double network, and their composites were prepared. The mechanical properties, swelling, wettability, friction properties, and the lubrication mechanisms of the composites were investigated. The results show that DN microspheres can have an excellent stability and provide hydration lubrication. The performance of 75 DN-1 composite was superior to others. This finding will provide a novel strategy for the development of water-lubricated materials and have wide application in engineering fields.

Natural materials tend to exhibit excellent performance in the engineering field because of their structure and special functions. A natural red willow, called natural porous wood material (NPWM), was found, and wear tests were conducted to determine its potential as an oil-impregnated material by utilizing its special porous structure. Fluorination treatment was adopted to improve the NPWM properties for absorbing and storing lubricating oil. The different contributions of soaking and fluorination-soaking treatments on the tribological properties of NPWMs and their respective mechanism of effect were revealed. The results showed that the fluorination-soaking treatment helped absorb and store sufficient lubricating oil in the NPWM porous structure; therefore, more lubricating oil would be squeezed out and function as a tribol-film between contacting surfaces during the friction process, thus ultimately contributing to stable and smooth wear responses even under prolong friction. However, the formation of an oil-in-water emulsion, caused by the buoyancy effect, destroyed the oil films on the worn NPWM surface in a water environment, resulting in higher coefficients of friction (COFs) under water conditions than under dry friction, even after the fluorination-soaking treatment. The knowledge gained herein could not only verify the potential of NPWM as an excellent oil-impregnated material in the engineering field but also provide a new methodology for the design of artificial porous materials with stable and smooth friction processes.