Cuticular surface structures of insects: a source of bioinspiration for novel hydrophobic designs and materials

Wettability characterizes a surface’s ability to get wet which could include an absorbent surface or a surface that does not repel water (i.e., being characterized as hydrophilic by having a contact angle lower than 90°). Wettability is influenced by surface morphology and chemistry. Two models describe the wettability of a rough surface: the Cassie-Baxter model which includes a three-phase liquid-solid-air interface, and the Wenzel model which includes a two-phase liquid-solid interface. In both models, measuring the contact angle between the droplet and the surface it is resting on allows the characterization of whether a material has hydrophilic, hydrophobic, or superhydrophobic properties. A variety of organisms have had the wettability of their surfaces characterized, most notably, plants and insects. In Chapter 1, I review insect-related hydrophobic surfaces as they are ideal models for bioinspiration due to their diverse capabilities. The cuticular surface of insects demonstrates an extensive variety of unique physical structures and surface chemicals that induce hydrophobic behavior. The cuticle, being multifunctional, is also capable of adhesion, antimicrobial activity, anti-fogging, chemical sensing and defense, color manipulation, locomotion, mechanosensation, sound production, thermoregulation, and (anti)reflectivity, making insects the perfect mentor for scientists seeking to design and fabricate novel materials. My review revealed fourteen insect orders, involving over two hundred species, have (super)hydrophobic cuticular surfaces. I organized and compiled these cuticular structures according to length scale (nano, micro, micro, and hierarchical) and by taxonomic order. Many of the current and potential human applications of insect-derived materials were also discussed. Despite decades of research, we know less than twenty percent of the world’s insect diversity and even less about the wettability of these incredible animals. The array of novel hydrophobic structures in insects will undoubtedly continue to grow along with their applications as we discover new species. This review serves as a template to further explore and design neoteric materials with highly desired characteristics and multifunctionality. Leafhoppers (Hemiptera: Cicadellidae) are unique in that they produce and excrete nanoscale granules, called brochosomes, that are spread onto the integument through grooming behaviors by the insect. These adaptations have recently captured the interest of researchers looking to draw inspiration from the natural world. The work presented in Chapter 2 explored the relationship between brochosomes and the hydrophobicity of leafhopper wings. It is the first study to explore how leafhopper body size influences brochosome size, and how brochosome size variation influences the wettability of leafhopper wings. I examined eight species from five genera that vary in body length. The mean of three body length measurements from each species group was calculated and a representative member from each species was photographed. Environmental scanning electron microscopy (ESEM) was used to investigate and photograph brochosomes from each species at three positions along the wing (proximal, medial, and distal). The diameter of nearly four thousand brochosomes was manually measured using ImageJ Fiji. Microgoniometry was used determine the wettability at each wing position from all eight species. Statistical analyses, including the two-way analysis of variance (ANOVA) test, the Tukey-Kramer HSD test, and linear regressions were used to analyze the data. I found a weak but positive correlation between leafhopper body size and brochosome diameter. Brochosome size was variable within individuals of one species, and among different species. While species was a good predictor of brochosome size, wing position was not. There was no evidence of particle-size distribution of brochosomes along the wing. Wettability also varied among individuals of the same species and among different species. Wettability varied among species but not predictably with wing position was not. Additionally, there was a weak negative correlation between brochosome size and hydrophobicity. Particle-based protective coatings are used in material science to fabricate surfaces that reduce biofilm formation and enhance general surface cleanliness. Brochosomes could be an integral source of inspiration to create optimized protective surface coatings that may have features such as being customizable, removable, and repairable. The insights revealed through this investigation along with future discoveries will undoubtedly inform the production and optimization of novel brochosome-inspired designs and materials.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Entomology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2022

Author dc:creator

• Bello, Elizabeth Ann Moore

Contributors dc:contributor

• Alleyne, Marianne
• Suarez, Andy
• Schroeder, Charles

• Insect
• Cuticle
• Hydrophobicity
• Wettability
• Bioinspiration
• Leafhopper
• Brochosome

Statement dc:rights

• Copyright 2022 Elizabeth Bello

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/115944

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F115944