Closure to “Discussion—Fabrication and Testing of Bioinspired Surface Designs for Friction Reduction at the Piston Ring and Liner Interface” (Maddox, S. R., Gangopadhyay, A., Ghaednia, H., Cai, J., Han, X., Meng, X., Goss, J. A., and Zou, M., 2021, ASME J. Tribol., 143(5), p. 051109)

Abstract

Abstract We thank the discussant for their interest in our manuscript and their very helpful remarks. Existing tribological studies of biomimetic surfaces were mostly focused on dry friction and biological surfaces are highly deformable. Therefore, the learnings on the effects of textures may not be directly translate to fully lubricated interfaces. Nonetheless, we agree that we can still learn much from these studies. Investigating additional orientations of the elongated hexagon could possibly improve the frictional response of the lubricated surfaces. Given that existing literature indicates that orienting the hexagons with two edges perpendicular to the sliding direction yields lower friction than in the case of edges parallel to the sliding direction [1], the experimental conditions in the manuscript could be the worst-case scenario and thus a lower bound for frictional improvement. Additionally, the hexagon was designed based not only on the design of the frog toe (and other natural hexagonal surfaces such as snakes) but also on existing industrial piston cylinder liner designs, where the crossing grooves are oriented nearly perpendicular to the sliding direction [2, 3]. Hence, our tested design is an extension of that existing technology with learning from nature. However, the suggestions to expand the experiment with additional hexagonal orientations is well received and will be considered for future work.