Site-specific characterization of beetle horn shell with micromechanical bending test in focused ion beam system

Hyun-Taek Lee; Ho-Jin Kim; Chung-Soo Kim; Kenji Gomi; Minoru Taya; Shûhei Nomura; Sung-Hoon Ahn

doi:10.1016/j.actbio.2017.04.026

Site-specific characterization of beetle horn shell with micromechanical bending test in focused ion beam system

Acta Biomater. 2017 Jul 15:57:395-403. doi: 10.1016/j.actbio.2017.04.026. Epub 2017 Apr 26.

Authors

Hyun-Taek Lee¹, Ho-Jin Kim¹, Chung-Soo Kim², Kenji Gomi³, Minoru Taya⁴, Shûhei Nomura⁵, Sung-Hoon Ahn⁶

Affiliations

¹ Department of Mechanical and Aerospace Engineering, Seoul National University, Seoul 08826, Republic of Korea.
² Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
³ Department of Mechanical Engineering, Tokyo Denki University, Tokyo 120-8551, Japan.
⁴ Department of Mechanical Engineering, University of Washington, Seattle, WA 98195, USA.
⁵ Department of Zoology, National Museum of Nature and Science, Tokyo 110-8718, Japan.
⁶ Department of Mechanical and Aerospace Engineering, Seoul National University, Seoul 08826, Republic of Korea; Institute of Advanced Machinery and Design, Seoul National University, Seoul 08826, Republic of Korea. Electronic address: ahnsh@snu.ac.kr.

PMID: 28455220
DOI: 10.1016/j.actbio.2017.04.026

Abstract

Biological materials are the result of years of evolution and possess a number of efficient features and structures. Researchers have investigated the possibility of designing biomedical structures that take advantage of these structural features. Insect shells, such as beetle shells, are among the most promising types of biological material for biomimetic development. However, due to their intricate geometries and small sizes, it is challenging to measure the mechanical properties of these microscale structures. In this study, we developed an in-situ testing platform for site-specific experiments in a focused ion beam (FIB) system. Multi-axis nano-manipulators and a micro-force sensor were utilized in the testing platform to allow better results in the sample preparation and data acquisition. The entire test protocol, consisting of locating sample, ion beam milling and micro-mechanical bending tests, can be carried out without sample transfer or reattachment. We used our newly devised test platform to evaluate the micromechanical properties and structural features of each separated layer of the beetle horn shell. The Young's modulus of both the exocuticle and endocuticle layers was measured. We carried out a bending test to characterize the layers mechanically. The exocuticle layer bent in a brick-like manner, while the endocuticle layer exhibited a crack blunting effect.

Statement of significance: This paper proposed an in-situ manipulation/test method in focused ion beam for characterizing micromechanical properties of beetle horn shell. The challenge in precise and accurate fabrication for the samples with complex geometry was overcome by using nano-manipulators having multi-degree of freedom and a micro-gripper. With the aid of this specially designed test platform, bending tests were carried out on cantilever-shaped samples prepared by focused ion beam milling. Structural differences between exocuticle and endocuticle layers of beetle horn shell were explored and the results provided insight into the structural advantages of each biocomposite structure.

Keywords: Biological material; Focused ion beam; Micromechanical characterization.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animal Structures / chemistry*
Animals
Coleoptera / chemistry*
Elastic Modulus*
Stress, Mechanical*