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

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.

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.

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.