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Posted: May 11, 2017

A novel concept for a synthetic articular-cartilage-like material

(Nanowerk News) Inspired by the structure of cancellous bone and the nutrition metabolism principles of articular cartilage, a research team in China has utilized friction-induced heat and pressure as a trigger to form and repair an analogue of articular cartilage. They reported their findings in ACS Applied Materials & Interfaces ("Bioinspired Smart Coating with Superior Tribological Performance").
Biologists and materials scientists have shown significant research interest in identifying the structure and understanding the mechanisms of articular cartilage and have attempted to replicate the cartilage using synthetic materials with superior friction properties.
However, previous work focused on the application of artificial articular cartilage materials in biology, and only a few applications of such materials have been examined on the industrial scale, in which lowing the coefficient of friction (COF) and reducing wear on the components is of great technological significance for improving the reliability, security, and efficiency.
For engineering applications on the industrial scale, to improve the friction and wear properties of moving components, the team developed a new artificial analogue using the common and highly effective surface engineering technology of thermal spraying.
Unlike previously reported processes that fabricated the articular-cartilage-like material before testing it, they used its working conditions to active the formation of an articular-cartilage-like layer that can be constantly repaired.
Schematic of thermal spray technology
(a) Schematic of thermal spray technology. (b) SEM images of the sprayed ceramic surface. (c) Higher-magnification image of the sprayed ceramic surface, showing the nanoscale grain, columnar structure. (d) Sketch map of a knee cap. (e) SEM image of the cancellous bone of a chicken. (f) Sketch map of the laser surface texturing process. (g) SEM image of the textured sprayed ceramic coating surface. (h) Magnified view of the morphology of the textured sprayed ceramic coating surface. (i) BSE image of the cross-sectional view of the ceramic coatings infiltrated with MPTFE (gray zones with red pointed arrows). (© American Chemical Society) (click on image to enlarge)
In this new work, the low COF of the bioinspired coatings can be maintained under ultrahigh initial Hertzian contact pressure (1411 MPa) with an extremely long lifetime (>1 106 cycles).
Moreover, the low friction properties can be maintained over a large range of sliding velocities and applied loads.
The composites also show zero-wear properties during ultralong operation and cause negligible wear damage to the surface of ceramic balls rubbing against them.
The superior tribological performance of the hybrid coatings is attributed to the spontaneously generated and constantly repaired articular-cartilage-like layer by heat and pressure generated by friction.
"Our findings represent a new area for industrial-scale engineering applications to improve the friction and wear properties of components, given that thermal spraying is a scalable, highly efficient, and economical process," conclude the researchers.
The bionic concept, utilizing the serving conditions of components as a trigger and repairing force, provides important inspiration for the development of biomimetic materials.
Source: American Chemical Society
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