Insects use lubricants to minimize friction and wear in leg joints

Abstract

A protein-based lubricating substance is discovered in the femoro-tibial joint of the darkling beetle Zophobas morio (Insecta). The substance extrudes to the contacting areas within the joint and appears in a form of filiform flows and short cylindrical fragments. The extruded lubricating substance effectively reduces the coefficient of sliding friction to the value of 0.13 in the tribosystem glass/lubricant/glass . This value is significantly lower than 0.35 in the control tribosystem glass/glass and comparable to the value of 0.14 for the tribosystem glass/dry PTFE (polytetrafluoroethylene or Teflon). The study shows for the first time that the friction-reducing mechanism found in Z. morio femoro-tibial joints is based on the lubricant spreading over the contacting surfaces rolling or moving at low loads and deforming at higher loads, preventing direct contact of joint counterparts. Besides Z. morio , the lubricant has been found in the leg joints of the Argentinian wood roach Blaptica dubia .

Smart joints: auto-cleaning mechanism in the legs of beetles

“…For the comparison, the experiments with contamination were performed for darkling beetle Zophobas morio having simple walking leg without evident structures that can be attributed to cleaning mechanism 21 , 22 . As follows from the experimental results the leg joint of Zophobas morio can easily be contaminated by metallic particles of 2–5 μm (Supplementary Fig.…”

“…SEM images of the outflow canal show the presence of microparticles trapped in the lubricant. This could presumably be evidence of one more function of the lubricant being involved in the entrapment of contaminants particles that facilitates their removal 21 , 22 .…”

“…It may be supposed that leg joint structures involved in the cleaning mechanism in Pachnoda marginata are the result of specialized adaptation for digging. Thus, the legs of beetles not adapted to burrowing may not have such adaptive structures, as seen by the example of the simple walking legs of darkling beetle Zophobas morio 21 , 22 whose joints can easily be contaminated (Supplementary Fig. S 9 ).…”

Jumping mechanism in the marsh beetles (Coleoptera: Scirtidae)

“…8 The femoro-tibial joint of the hind jumping legs of the marsh beetles morphologically strongly differs from that of other jumping beetles. Despite of some lack of broad comparative morphological studies on this topic, one may discuss the generalized structure of the femoro-tibial joint 47,48 as that having such specific elements as a pair of symmetric femoral condyles (convex, circular structure of the toroid shape) and a pair of tibial concavities with the corresponding complementary shape. The femoral condyle inserts into the tibial concavity and is bent Table 2.…”

A review of advances in tribology in 2020–2021

“…The effective tribological mechanisms of animals and consequent bionics designs were investigated. A protein-based lubricating substance was found in reducing friction and wear in the femoro-tibial joint of an insect [773]. The normal and tangential peeling behaviour of gecko spatulae was investigated with a coupled adhesion-friction model [774].…”