The ostracod carapace window as a biomimetic basis for development of a novel eye shield.

Lead Research Organisation: CARDIFF UNIVERSITY
Department Name: Optometry and Vision Sciences

Abstract

Myodocopid ostracods are small crustaceans varying from 1 to 32 mm. Their shrimp-like bodies are flattened from side to side and protected by a relatively thin, two-part shell or "carapace" made from the polysaccharide chitin coupled with proteins, often with the incorporation of calcium. The two valves of the carapace are connected by a hinge, and can open and close while retaining their rigidity. Most myodocopids can be distinguished from other ostracods by their well-developed compound eyes; some occupying a third of their total body size. Indeed, they use visual signals in the form of iridescence or bioluminescence for courtship. In one group - "Macrocypridina" (about 8mm long) - the carapace is heavily pigmented except for a round, clear transparent window directly covering the eye, through which the animal can see. These windows have some interesting properties; they are very thin yet rigid, and prevent crack formation and propagation, avoid scratches, allow oxygen to pass through them, and appear resistant to the buildup of surface contamination. Our proposal is to understand the biophysical and structural basis of the properties of these ostracod windows, and consequently to mimic these structures on a larger scale to develop very thin, hard contact lenses suitable for humans. These lenses will act as eye shields in military applications but will also be beneficial for the treatment of eye-related problems in the general population.

Technical Summary

Myodocopid ostracods are small, marine crustaceans varying from 1 to 32 mm in length. Their shrimp-like bodies are bilaterally flattened and enclosed within a relatively thin, bivalved carapace composed of a chitin-protein complex and low magnesium calcite. The two valves of the carapace are connected by a hinge, and can open and close while retaining their rigidity. Most myodocopids can be distinguished from other ostracods by their well-developed compound eyes; some occupying a third of their total body size. Indeed, they use visual signals in the form of iridescence or bioluminescence for courtship. In one group - "Macrocypridina" (about 8mm long) - the carapace is heavily pigmented except for a round, clear transparent window directly covering the eye, through which the animal can see. These windows are thin, tough, clear, scratch resistant, resistant to crack formation and propagation, permeable to oxygen and, presumably, biofilm resistant. To date, very little information is available, and none at high magnification, about the ultrastructure of these transparent windows. The aims of this project are: 1. To use synchrotron x-ray diffraction and transmission electron microscopy to explain the basis of carapace transparency; 2. To measure the spectral transmission through the carapace window; 3. To measure other properties of the window (wettability, biomechanical brittleness/ductility, oxygen permeability). If these properties are found to be suitable, or can be influenced by appropriate treatments, we will use the principles to biomimic the structure to produce a thin, hard contact lens shield, suitable for corneal protection in a military context.

Planned Impact

This application is for a "proof of principle" pilot study aimed at determining some important properties of the transparent carapace windows in certain ostracods, which, if successful, will lead to further work aimed at developing a biomimetically designed and optimized eye shield/contact lens.
Direct beneficiaries:
1. Military personnel who wear the shields/lenses.
o The incidence of ocular injury has increased during combat to 13%
o Non-compliance in use of traditional protective eyewear on the battlefield is reported at 85%
2. Eye care professionals (ophthalmology, optometry)
o Contact lenses are used for refractive correction and also wound healing. Soft, hydrogel contact lenses are used most frequently across the world, but have a significantly higher incidence of eye infection compared to rigid gas-permeable lenses. Whilst rigid gas permeable lenses are associated with less complications. A new contact lens type which takes the best qualities from nature would be highly desirable.
3. People with keratoconus
o In some pathological eye conditions (such as keratoconus), hard contact lenses are essential, but their thickness and rigidity can exacerbate corneal scarring with long-term wear. By providing a thin, but mechanically and optically stable lens, it may be possible to improve management of such patients.
Indirect beneficiaries:
1. The contact lens industry
o Current contact lenses fall into three groups - hydrogels, silicone hydrogels and rigid gas permeable lenses. Despite innovation in synthetic polymer technology to increase oxygen permeability, the challenge of producing a contact lens that is inherently wettable, durable and permeable, i.e. biomimetic, remains, and the higher risk of infection with contact lenses has not changed significantly in the last twenty years.
2. Fellow scientists
o Structural biologists and biophysicists interested in how the optical and biomechanical properties of the ostracod carapace are achieved. They will benefit by understanding how chitin is used to create a tough transparent tissue (this has analogies with how proteins are used in the cornea and lenses of mammals to create transparent structures)
o Our project will inform ostracod and other crustacean researchers (a large community) how the ostracod carapace can be so thin, and possess other properties, which will provide important information for studies of arthropod adaptation and evolution (remarkably, this is currently missing for myodocopid ostracods).
3. Public health
o The outcomes from this work could provide insight into contact lens materials that may safeguard the ocular health of those who desire or require refractive correction via contact lenses. Thus, the development of such a contact lens would be a major benefit to public health in the UK and elsewhere.

Our long-term aim would be to develop a very thin, biologically based semi-rigid contact lens with good optical, antibacterial, mechanical and hopefully UV protective properties, which can replace/compliment those currently used. Only one basic study exists on myodocopid carapaces (1), but from this we are confident that this is the type of laminate structure that can be made industrially (i.e. the suitable machines do exist). This would involve producing similar structures in vitro, animal and then human trials. We anticipate it would require a further 3 years funding after the pilot to carry out the work necessary to develop the lens and would take approximately 7 years to produce the first prototype for use in humans.
Reference: 1. Sohn, I.G. and Kornicker, L.S. 1988. Ultrastructure of Myodocopid Shells (Ostracoda). In: (Hanai, T., Ikeya, N. and Ishizaki, K., eds.) Evolutionary Biology of Ostracoda; Proceedings of the Ninth International Symposium on Ostracoda. Pp. 243-258. Kodansha Ltd., Tokyo, Japan.

Publications

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Parker AR (2019) Transparency in the eye region of an ostracod carapace ( Macrocypridina castanea, Myodocopida). in Philosophical transactions. Series A, Mathematical, physical, and engineering sciences

 
Description The ostracod carapace (Macrocypridina castanea) consists of a highly ordered lamellar arrangement with an as yet unidentified surface coating. Chitin fibres within the lamella are assembled into common plywood structure. However, a high number of lamellae (around 120), their thinness and uniformity are what distinguish the carapace from other cuticles. We have also found, using serial block face scanning electron microscopy, interesting channels that connect the cells on the inner to those on the outer carapace surface.

We have collected x-ray scatter pattern that revealed 7 different reflections arising from the carapace between 2.6Å and 10Å (10.0, 7.1, 5.1, 5.0, 4.7, 3.4 and 2.6). Two of those reflections correspond with so called chitin signature rings which are described to be at 3.38Å and 9.43Å.

The latter reflection showed some change between the body and the window area of the carapace. We registered a small decrease in molecular spacing in the transparent region, but it is only a preliminary result that requires a further study to be confirmed. Some of the reflections manifest the highly preferential fibre orientation.
Exploitation Route We now know that the optical and mechanical properties of the carapace are based on its multilayer microstructure. This can be mimicked using other materials to produce very thin optically transparent yet strong materials which potentially have many applications. We are currently seeking funding to develop such a material for military use Understanding the function of the carapace in the lifestyle of marine and fresh water ostracods will be of benefit to the large community of ostracodologists. Our main purpose, however, was to exploit the principles to develop a new material (see below)
Sectors Pharmaceuticals and Medical Biotechnology

Security and Diplomacy

 
Description DSTL contract
Amount £828,093 (GBP)
Organisation Defence Science & Technology Laboratory (DSTL) 
Sector Public
Country United Kingdom
Start 03/2016 
End 03/2018
 
Description Lifescaped 
Organisation Natural History Museum
Country United Kingdom 
Sector Public 
PI Contribution Characterising the ultrastructure of the ostracod carapace using a variety of imaging techniques
Collaborator Contribution Supply ostracod specimens and advice
Impact A manuscript has been written but not yet submitted due to IP issues.
Start Year 2013
 
Description (Cardiff University) Invited to speak at CITER Soc Lessons from Nature workshop 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact 120 Sixth Form Students from locals schools, as well as Cardiff University Undergraduates, Postgraduates and Staff attended the School of Optometry and Vision Sciences for a workshop. A lot of positive feedback was received.
Year(s) Of Engagement Activity 2017
 
Description DSTL Synthetic Biology Showcase (University of Birmingham) (Ben Rumney presented a poster) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact This event was to encourage the continued effective networking and awareness of the potential impacts of synthetic for good and ill across MOD, security and UK Plc. Ben's poster presentation sparked many questions and further discussions.
Year(s) Of Engagement Activity 2017
 
Description Invited to speak at SynBio Foundry Workshop (Manchester Institute of Biotechnology) (Sian Morgan presented) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact This workshop focused on the current scientific and technological challenges in defining a new paradigm for sustainable biomaterials with the aim of creating a roadmap for the new paradigm for sustainable biomaterials. The organisers were able to lay down the foundations for the delivery of the roadmap to take this area forward by the end of the event.
Year(s) Of Engagement Activity 2017