Radwanul Siddique1 Vinayak Narasimhan1 Jeong-Oen Lee1 Shailabh Kumar1 David Sretavan2 Hyuck Choo1 3

1, California Institute of Technology, Pasadena, California, United States
2, University of California, San Francisco, San Francisco, California, United States
3, Samsung Institute of Advanced Technology, Suwon, , Korea (the Republic of)

While numerous multifunctional antifouling nanostructures on insect wings have been previously studied and replicated, their potential incorporation into implantable medical devices remains unexplored. We have demonstrated the use of multifunctional bioinspired nanostructured membrane inspired by transparent butterfly wings for intraocular pressure (IOP) sensing in vivo. [1].

We investigated the multifunctional properties of the biophotonic nanostructures found on the wings of the longtail glasswing (C. faunus) butterfly. The AFM, SEM, optical, and biological characterizations have revealed that two groups of dome-shaped nanostructures with different periodicity co-exist on the transparent wings of the C. faunus: (1) angle-independent anti-reflective nanostructures with periods of 140-180 nm in the postdiscal areas; (2) angle-independent transmissive light-scattering nanostructures with periods of 200-300 nm in the basal areas. In vitro testing has revealed both regions displayed antifouling properties based on physically-induced cell lysis. We have (1) adapted the coherence-preserving angle-independent transmissive light-scattering property of the basal nanostructures that could make optical sensors such as Fabry Perot (FP) resonators more angle-independent; and (2) by further engineering the basal nanostructures, created bioinspired nanostructures (BINS) that would prevent biofouling without inducing cell lysis and suppress inflammation. To produce BINS with periods of 385-505 nm on a Si3N4-membrane, we used a polymer-phase-separation process following the nature’s way of forming nanostructures [2,3]. Angle-resolved transmission spectroscopy showed that the light transmission of the BINS-integrated membrane was twice more angle-independent than a flat Si3N4-membrane. In a series of in vitro studies, the BINS-integrated Si3N4 surface displayed remarkable anti-biofouling properties against proteins (albumin and streptavidin, ***P ≤ 0.001), prokaryotes (E. coli, **P ≤ 0.01), and
eukaryotes (HeLa cells, ***P ≤ 0.001) when compared to flat Si3N4 and control (glass) surfaces.

Finally, we integrated BINS onto the FP-resonator-based IOP sensor that was recently developed in our lab [4]. However, its practical applications were limited by its narrow readout angle inherent to FP-resonators and infrequent but severe biofouling observed after long-term implantation. The BINS integration onto the IOP sensor led to a 2.5-fold improvement in readout angle allowing easy handheld monitoring and in a one-month in vivo study conducted in rabbits, showed a 3-fold reduction in IOP error and 12-fold reduction in tissue encapsulation and inflammation, compared to an IOP sensor without BINS.

[1] V. Narasimhan, R. H. Siddique, et al. Nature Nanotechnology 13, 512–519 (2018)
[2] V. Saranathan et al. Nano Letters 15(6), 3735-3742 (2015)
[3] R. H. Siddique, et al. Science Advances 3 (10), e1700232 (2017)
[4] J. O.Lee at al. Microsystems & Nanoengineering 3, 17057 (2017)