In vitro comparative study of deformation of 3D-printed models using different polylactic acids treated by steam sterilization.

INTRODUCTION: 3D printing, which is becoming ever more widespread in orthopedic surgery, requires specific materials. Polylactic acid (PLA) is the most widely used in general-purpose 3D printing, but its thermosensitivity can be incompatible with sterilization. Even so, it is easy to use, inexpensive, non-toxic and biodegradable. Controversy surrounds its use. 3D printing of directly sterilizable PLA parts according to surgeons' needs would be highly advantageous, but doubts remain. We therefore performed an in vitro study to determine which PLAs resist steam sterilization regarding deformation. HYPOTHESIS: The study hypothesis was that, depending on make and shape, 3D-printed PLA parts can retain their properties after steam sterilization. MATERIAL AND METHODS: We selected 4 makes of PLA and used each to print 4 simple cubes and 4 complex shapes corresponding to cuboid bones. They were subjected to steam sterilization under normal French hospital conditions. The size of the cubes was measured before and after sterilization, using a digital caliper. RESULTS: Cuboid parts in HT-PLA and PLA-WANAO showed mean deformation of -0.02mm and -0.4mm, respectively after sterilization, the differences being non-significant (p=0.679 and p=0.241, respectively). Cuboid parts in PLA-SUNLU and PLA-G3D showed significant mean deformation: respectively, -1.37mm (p=0.026) and -35.03mm (p>0.001). Cubes in all types of PLA showed significant mean deformation: HT-PLA, -0.61mm (p=0.004); PLA-SUNLU, -2.70mm (p=0.002); PLA-G3D, -28.64mm (p>0.001); and PLA-WANAO, -1.33mm (p=0.010). DISCUSSION: The study confirmed recent findings that steam sterilization is feasible with certain PLA-printed parts, with deformations less than 1mm, and that choice of PLA is crucial for success. Computer-designed objects (here, cubes) did not resist sterilization without significant deformation. Analysis of resistance to various stresses was not performed, and therefore it cannot be claimed that the process could be used other than for printing anatomic parts. Use of 3D printing in French hospitals is probably a real source of innovation and improvement in care quality; however, a legal framework needs establishing for the use of 3D-printed parts, to ensure patient safety and promote research in this field. LEVEL OF EVIDENCE: III; prospective in vitro study.

Evolutionary algorithms converge towards evolved biological photonic structures.

Nature features a plethora of extraordinary photonic architectures that have been optimized through natural evolution in order to more efficiently reflect, absorb or scatter light. While numerical optimization is increasingly and successfully used in photonics, it has yet to replicate any of these complex naturally occurring structures. Using evolutionary algorithms inspired by natural evolution and performing particular optimizations (maximize reflection for a given wavelength, for a broad range of wavelength or maximize the scattering of light), we have retrieved the most stereotypical natural photonic structures. Whether those structures are Bragg mirrors, chirped dielectric mirrors or the gratings on top of Morpho butterfly wings, our results indicate how such regular structures might have spontaneously emerged in nature and to which precise optical or fabrication constraints they respond. Comparing algorithms show that recombination between individuals, inspired by sexual reproduction, confers a clear advantage that can be linked to the fact that photonic structures are fundamentally modular: each part of the structure has a role which can be understood almost independently from the rest. Such an in silico evolution also suggests original and elegant solutions to practical problems, as illustrated by the design of counter-intuitive anti-reflective coatings for solar cells.

Interferometric control of the absorption in optical patch antennas.

Optical patch nano-antennas possess unique absorption, field enhancement and concentration capabilities - but their crosssection, as well as their response outside of normal incidence are not well understood. Here we explain the large cross-section by considering that each patch nanoantenna is a cavity excited from both sides. Such a simple physical picture allows to fully understand the influence of the angle of incidence - that odd resonances have a very high absorption cross-section which decreases when the incidence angle increases, while even resonances cannot be excited in normal incidence. A direct application would be to use these structures as an optical nanometric set-square.

A universal design to realize a tunable perfect absorber from infrared to microwaves.

We propose a design for an universal absorber, characterized by a resonance frequency that can be tuned from visible to microwave frequencies independently of the choice of the metal and the dielectrics involved. An almost perfect absorption up to 99.8% is demonstrated at resonance for all polarization states of light and for a very wide angular aperture. These properties originate from a magnetic Fabry-Perot mode that is confined in a dielectric spacer of λ/100 thickness by a metamaterial layer and a mirror. An extraordinary large funneling through nano-slits explains how light can be trapped in the structure. Simple scaling laws can be used as a recipe to design ultra-thin perfect absorbers whatever the materials and the desired resonance wavelength, making our design truly universal.

Numerical tool to take nonlocal effects into account in metallo-dielectric multilayers.

We provide a numerical tool to quantitatively study the impact of nonlocality arising from free electrons in metals on the optical properties of metallo-dielectric multilayers. We found that scattering matrices are particularly well suited to take into account the electron response through the application of the hydrodynamic model. Though effects due to nonlocality are, in general, quite small, they, nevertheless, can be important for very thin (typically below 10 nm) metallic layers, as in those used in structures characterized by exotic dispersion curves. Such structures include those with a negative refractive index, hyperbolic metamaterials, and near-zero index materials. Higher wave vectors mean larger nonlocal effects, so that it is not surprising that subwavelength imaging capabilities of hyperbolic metamaterials are found to be sensitive to nonlocal effects. We find in all cases that the inclusion of nonlocal effects leads to at least a 5% higher transmission through the considered structure.

Ruptured subscapular artery aneurysm and subclavian artery occlusion in a patient with type 1 neurofibromatosis: a case report.

INTRODUCTION: Collateral muscular artery aneurysm is exceedingly rare. We report the first case of subscapular artery aneurysm in a patient with type 1 neurofibromatosis and ipsilateral chronic subclavian artery occlusion. CASE PRESENTATION: A 74-year-old Caucasian woman with a medical history of type 1 neurofibromatosis, presented a sudden left pectoral mass, later diagnosed as a ruptured aneurysm of the left subscapular artery. It was caused by a chronic occlusion of the left subclavian artery, diagnosed on angiographies prior to embolization. CONCLUSIONS: Collateral artery aneurysm in the event of a mainstream muscular artery chronic occlusion may occur in type 1 neurofibromatosis.

Controlled-reflectance surfaces with film-coupled colloidal nanoantennas.

Efficient and tunable absorption is essential for a variety of applications, such as designing controlled-emissivity surfaces for thermophotovoltaic devices, tailoring an infrared spectrum for controlled thermal dissipation and producing detector elements for imaging. Metamaterials based on metallic elements are particularly efficient as absorbing media, because both the electrical and the magnetic properties of a metamaterial can be tuned by structured design. So far, metamaterial absorbers in the infrared or visible range have been fabricated using lithographically patterned metallic structures, making them inherently difficult to produce over large areas and hence reducing their applicability. Here we demonstrate a simple method to create a metamaterial absorber by randomly adsorbing chemically synthesized silver nanocubes onto a nanoscale-thick polymer spacer layer on a gold film, making no effort to control the spatial arrangement of the cubes on the film. We show that the film-coupled nanocubes provide a reflectance spectrum that can be tailored by varying the geometry (the size of the cubes and/or the thickness of the spacer). Each nanocube is the optical analogue of a grounded patch antenna, with a nearly identical local field structure that is modified by the plasmonic response of the metal's dielectric function, and with an anomalously large absorption efficiency that can be partly attributed to an interferometric effect. The absorptivity of large surface areas can be controlled using this method, at scales out of reach of lithographic approaches (such as electron-beam lithography) that are otherwise required to manipulate matter on the nanoscale.

Lens equation for flat lenses made with hyperbolic metamaterials.

This study aims to give a general theory that enables the design of flat lenses based on hyperbolic metamaterials. We derive a lens equation that is demonstrated to involve the curvature of the dispersion relation. Guided by this theory, hyperbolic lenses of focal length ranging from zero to a few wavelength are simulated. High transmission efficiency is also obtained by reducing the amount of metal compared to the dielectric material.

Mesoscopic self-collimation and slow light in all-positive index layered photonic crystals.

We demonstrate a mesoscopic self-collimation effect in photonic crystal superlattices consisting of a periodic set of all-positive index 2D photonic crystal and homogeneous layers. We develop an electromagnetic theory showing that diffraction-free beams are observed when the curvature of the optical dispersion relation is properly compensated for. This approach allows us to combine slow-light regime together with self-collimation in photonic crystal superlattices presenting an extremely low filling ratio in air.

Large negative lateral shifts due to negative refraction.

When a thin structure in which negative refraction occurs (a metallo-dielectric structure or a photonic crystal) is illuminated by a beam, the reflected and transmitted beam can undergo a large negative lateral shift. This phenomenon can be seen as an interferential enhancement of the geometrical shift and can be considered a signature of negative refraction.

Self-collimation and focusing effects in zero-average index metamaterials.

One dimensional photonic crystals combining positive and negative index layers have shown to present a photonic band gap insensitive to the period scaling when the volume average index vanishes. Defect modes lying in this zero-n gap can in addition be obtained without locally breaking the symmetry of the crystal lattice. In this work, index dispersion is shown to broaden the resonant frequencies creating then a conduction band lying inside the zero-n gap. Self-collimation and focusing effects are in addition demonstrated in zero-average index metamaterials supporting defect modes. This beam shaping is explained in the framework of a beam propagation model by introducing an harmonic average index parameter.

Light wheel buildup using a backward surface mode.

When a guided mode is excited in a dielectric slab coupled to a backward surface wave at the interface between a dielectric and a left-handed medium, light is confined in the structure: this is a light wheel. Complex plane analysis of the dispersion relation and coupled-mode formalism give deep insight into the physics of this phenomenon (lateral confinement and the presence of a dark zone).

Goos-Hänchen effect in the gaps of photonic crystals.

We show the presence of the Goos-Hänchen effect when a monochromatic beam illuminates a photonic crystal inside a photonic bandgap.