Printed Soft Optical Waveguides of PLA Copolymers for Guiding Light into Tissue.

The application of optical technologies in treating pathologies and monitoring disease states requires the development of soft, minimal invasive and implantable devices to deliver light to tissues inside the body. Here, we present soft and degradable optical waveguides from poly(d,l-lactide) and derived copolymers fabricated by extrusion printing in the desired dimensions and shapes. The obtained optical waveguides propagate VIS to NIR light in air and in tissue at penetration depths of tens of centimeters. Besides, the printed waveguides have elastomeric properties at body temperature and show softness and flexibility in the range relevant for implantable devices in soft organs. Printed waveguides were able to guide light across 8 cm tissue and activate photocleavage chemical reactions in a photoresponsive hydrogel (in vitro). The simplicity and flexibility of the fiber processing method and the optical and mechanical performance of the obtained waveguides exemplify how rational study of medically approved biomaterials can lead to useful inks for printing cost-effective and flexible optical components for potential use in medical contexts.

Nanopillar Diffraction Gratings by Two-Photon Lithography.

Two-dimensional photonic structures such as nanostructured pillar gratings are useful for various applications including wave coupling, diffractive optics, and security features. Two-photon lithography facilitates the generation of such nanostructured surfaces with high precision and reproducibility. In this work, we report on nanopillar diffraction gratings fabricated by two-photon lithography with various laser powers close to the polymerization threshold of the photoresist. As a result, defect-free arrays of pillars with diameters down to 184 nm were fabricated. The structure sizes were analyzed by scanning electron microscopy and compared to theoretical predictions obtained from Monte Carlo simulations. The optical reflectivities of the nanopillar gratings were analyzed by optical microscopy and verified by rigorous coupled-wave simulations.

Light Emission Intensities of Luminescent Y2O3:Eu and Gd2O3:Eu Particles of Various Sizes.

There is great technological interest in elucidating the effect of particle size on the luminescence efficiency of doped rare earth oxides. This study demonstrates unambiguously that there is a size effect and that it is not dependent on the calcination temperature. The Y2O3:Eu and Gd2O3:Eu particles used in this study were synthesized using wet chemistry to produce particles ranging in size between 7 nm and 326 nm and a commercially available phosphor. These particles were characterized using three excitation methods: UV light at 250 nm wavelength, electron beam at 10 kV, and X-rays generated at 100 kV. Regardless of the excitation source, it was found that with increasing particle diameter there is an increase in emitted light. Furthermore, dense particles emit more light than porous particles. These results can be explained by considering the larger surface area to volume ratio of the smallest particles and increased internal surface area of the pores found in the large particles. For the small particles, the additional surface area hosts adsorbates that lead to non-radiative recombination, and in the porous particles, the pore walls can quench fluorescence. This trend is valid across calcination temperatures and is evident when comparing particles from the same calcination temperature.