Corneal microprojections in coleoid cephalopods

Reconciling the Conflict between Optical Transparency and Fouling Resistance with a Nanowrinkled Surface Inspired by Zebrafish's Cornea

Surface topography has been demonstrated as an effective nonchemical strategy for controlling the fouling resistance of a surface, but its impact on optical transparency remains a barrier to the application of this strategy in optical materials. To reconcile the conflicting effects of surface topography on optical transparency and fouling resistance, here we study the optical properties and antifouling performance of nanowrinkled surfaces inspired by the corneal surface of zebrafish (Danio rerio). Experimental and numerical analyses demonstrate that a good compromise between optical transparency and antifouling efficacy can be achieved by wavy nanowrinkles with a characteristic wavelength of 800 nm and an amplitude of 100 nm. In particular, the optimal wrinkled surface under study can reduce biofouling by up to 96% in a single-species (Pseudoalteromonas sp.) bacterial settlement assay in the laboratory and 89% in a field test while keeping the total transmittance above 0.98 and haze below 0.04 underwater. Moreover, our nanowrinkled surface also exhibits excellent resistance against contamination by inorganic particles. This work provides a nonchemical strategy for achieving the coexistence of optical transparency and fouling resistance on one single material, which implies significant application potential in various optical devices and systems, such as antibacterial contact lenses and self-cleaning solar panels.

Not As Clear As It May Appear: Challenges Associated with Transparent Camouflage in the Ocean

The "superpower" of invisibility is a reality and a necessity for many animals that live in featureless environments like the open ocean, where there is nowhere to hide. How do animals achieve invisibility? Many animals match their color patterns to their background, but this strategy is limited when the background scene is dynamic. Transparency allows organisms to match any background all the time. However, it is challenging for an organism to maintain transparency across its entire body volume. To be transparent, tissues must minimize light scattering, both at the surface and within. Until recently, it has been unclear how clear animals with complex bodies (such as many crustaceans with hard cuticles, thick muscles, and other internal organs) minimize such light scattering. This is especially challenging in an environment where light can come from many directions: reflections from downwelling sunlight and bioluminescent searchlights from predators. This review summarizes several recent discoveries of multiple unique adaptations for minimizing light scattering both on the exterior cuticle surface and throughout the body volume of transparent crustaceans, as well as the potential tradeoffs and challenges associated with transparent camouflage.

Effect of preserved and preservative-free timolol eye drops on tear film stability in healthy Africans

Background:

Preserved versus nonpreserved formulations for ophthalmic use have been well described in the literature although not specifically in the African population where beta blockers are frequently used as the first-line therapy due to economic and availability issues. This study sought to determine the effect of preserved and preservative-free Timolol eye drops on tear film stability in healthy black Africans.

Materials and Methods:

Sixty healthy nondry eye subjects aged 19–25 years were randomly assigned into four groups (n = 15) and differently treated with eye drops of phosphate buffered saline (PBS), preservative-free timolol (PFT), benzalkonium chloride (BAK) only, and BAK-preserved timolol (BPT). Noninvasive tear break-up time (NITBUT) was measured using the keratometer at baseline and 30, 60, and 90 min after drop application.

Results:

No significant decline in NITBUT was observed following treatment with PFT and PBS. However, BAK treatment showed a positive time-dependent significant decline in NITBUT (P < 0.001) while a significant decline in the BPT-treated group was only found at 90 min (−3.52 s; P < 0.001). In comparison to the PFT-treated group, treatment with BAK and BPT showed significantly lower NITBUT (P < 0.001).

Conclusion:

BPT is associated with a significant decline in tear film stability in black Africans. This finding has implications in the management of glaucoma in patients with high-risk of dry eyes in this population.

Quantification of acute vocal fold epithelial surface damage with increasing time and magnitude doses of vibration exposure

Because the vocal folds undergo repeated trauma during continuous cycles of vibration, the epithelium is routinely susceptible to damage during phonation. Excessive and prolonged vibration exposure is considered a significant predisposing factor in the development of vocal fold pathology. The purpose of the present study was to quantify the extent of epithelial surface damage following increased time and magnitude doses of vibration exposure using an in vivo rabbit phonation model. Forty-five New Zealand white breeder rabbits were randomized to nine groups and received varying phonation time-doses (30, 60, or 120 minutes) and magnitude-doses (control, modal intensity phonation, or raised intensity phonation) of vibration exposure. Scanning electron microscopy and transmission electron microscopy was used to quantify the degree of epithelial surface damage. Results revealed a significant reduction in microprojection density, microprojection height, and depth of the epithelial surface with increasing time and phonation magnitudes doses, signifying increased epithelial surface damage risk with excessive and prolonged vibration exposure. Destruction to the epithelial cell surface may provide significant insight into the disruption of cell function following prolonged vibration exposure. One important goal achieved in the present study was the quantification of epithelial surface damage using objective imaging criteria. These data provide an important foundation for future studies of long-term tissue recovery from excessive and prolonged vibration exposure.