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Recent years have witnessed a rapid development in the field of structural coloration, colors generated from the interaction of nanostructures with light. Compared to conventional color generation based on pigments and dyes, structural color generation exhibits unique advantages in terms of spatial resolution, operational stability, environmental friendliness, and multiple functionality. Here, we discuss recent development in structural coloration based on layered thin films and optical metasurfaces. This review first presents fundamentals of color science and introduces a few popular color spaces used for color evaluation. Then, it elaborates on representative physical mechanisms for structural color generation, including Fabry–Pérot resonance, photonic crystal resonance, guided mode resonance, plasmon resonance, and Mie resonance. Optimization methods for efficient structure parameter searching, fabrication techniques for large-scale and low-cost manufacturing, as well as device designs for dynamic displaying are discussed subsequently. In the end, the review surveys diverse applications of structural colors in various areas such as printing, sensing, and advanced photovoltaics.

Wound healing of skin defects is complex. For the treatment of large and deep wounds, it is a good alternative to accept artificial dermis grafting at the first stage surgery, and autologous split-thickness skin grafting 2–3 weeks later at the second stage surgery. In addition, the effectiveness of numerous cytokines such as fibroblast growth factor (FGF) on wounds healing has been widely researched. The traditional view is that direct external application or in vivo injection of exogenous FGFs may not achieve the desired therapeutic effect as the effective concentration cannot be maintained for a long time. Therefore, some researchers have tried to integrate various cytokines into skin substitutes for combined application. However, we believe that considering the current situation, it is still difficult to achieve mass production of these types of artificial dermis. Here, we manufactured a collagen-chondroitin sulfate scaffold material by imitating the marketed artificial dermis materials. Then, we combined it with recombinant human acidic FGF in a single full dose during the first-stage artificial dermis transplantation, which is simple and completely feasible but always controversial in the current clinical work, to explore whether this combinatorial therapy could serve as an efficient way wound healing in the Balb/c-nu mice full-thickness skin defect model.

Spectral responses of guided mode resonant filter (GMRF) with two-dimensional (2-D) crossed grating are comprehensively investigated in this paper. Commercially available software based on the rigorous coupled wave analysis method is used to design and optimize the device as well as to calculate the reflectance spectra. There exist two peak resonances under normal incidence and the two wavelengths generate two pairs of resonant bands as varying the incident angle from 0° to 30° (−30°) for both S- and P-polarization. The resonant positions of the split branches shift with the grating period along the x -axis; whereas the other pair of bands, which are degenerated for both normal and oblique incidences, are controlled by the grating period along the y -axis. The physical mechanism of the spectral features is also analyzed in detail by means of the wave vectors. Results and methods provided herein enable a clear understanding of the physical properties of the filter with 2-D crossed grating, which are highly beneficial for studying new features of 2-D GMRF.

We demonstrate the spectral responses of the guided mode resonant filter (GMRF) with 2D and 1D gratings, aiming to comprehensively investigate the spectral correlation between them under different incident conditions. A second-order effective-medium theory (EMT) is applied to calculate the effective refractive index of the corresponding 1D grating. Results show that the reflectance spectra of the 2D GMRF are considered to be a composition of that in two 1D GMRF structures with vertical grating bar orientation. The physical mechanism behind the spectral correlation is also analyzed in detail in terms of the wave vectors. Results and method shown in this letter provide a means to study new features of 2D GMRF, including the high angular tolerance, polarization-insensitivity under oblique incidence, and wavelength tunability.

An angular-dependent polarization-insensitive filter in the telecommunication region is demonstrated in this letter, which is based on a zero-contrast grating for incident plane between classic and full conical mountings. Particle swam optimization combined with the rigorous coupled wave analysis method is applied to design the filter and perform the reflectance spectra. Realization of the polarization-insensitive filter is based on the split feature of a 1D guided mode resonant filter, under oblique incidence in classic mounting. Results show that polarization-independent resonances occur near $1.454~\mu \text{m}$ under the oblique incidences of 4.8°, 5.3°, 6.5°, and 9.3°, with the incident plane angle being set as 15°, 30°, 45°, and 60°, respectively. During the process of varying the incident plane angle from classical mounting to full conical mounting, the mechanism of the increased angle of oblique incidence is also analyzed in detail.

Hemisphere cone arrays (HCAs) is a popular light trapping structure in silicon solar cells. However, the light trapping mechanism research of that in solar cells is lacking. In this paper, the light trapping mechanism of the HCAs in silicon solar cells is studied by combination of numerical analysis and geometrical optics simulation. The results show that the HCAs structure can reduce surface reflectance by ∼60% compared with flat structure by multiple injections of the incident light. At the same time, the HCAs can make ∼43% unabsorbed light return to the absorbing layer of solar cells again. To verify the theoretical calculation results, a flat and a square hemispherical cone arrays PDMS thin films are prepared by a micro/nano-processing method, and the reflectivities of a silicon wafer covered the flat and the HCAs PDMS thin films were measured. The experimental measured results are basically consistent with the theoretical calculation results. The numerical calculation results also show that the total optical path length of the thin film Si solar cell covered with the HCAs structure increases from 2 ω to 4 ω .

The existing polarization-insensitive filters based on two dimensional (2-D) grating are mostly under normal incidence. However, in filtering optical devices, the normal incidence regime is usually avoided because it requires the use of beam separators which yields a loss of efficiency. Herein, we present a compact method to realize polarization-independent filter under oblique incidence, which is implemented on 2-D crossed grating in the telecommunication region. Plane of incidence is set to be in xz plane and three different polarization angles (0°, 45°, and 90°) are used to demonstrate the polarization-insensitivity. Realization of the polarization-insensitivity of the 2-D filter is based on the split feature under oblique incidence, according to the analysis of the physical mechanism. The location of the polarization-independent resonance is mainly determined by the grating period along x-axis and will right shift with increasing the period. Results show that the polarization-insensitive resonances occur at 1356.9 nm, 1372.6 nm and 1398.5 nm when the grating periods along x-axis are 830 nm, 850 nm and 870 nm, respectively. Moreover, the results and methods provided herein can be applied to search for the polarization-insensitive resonances of the 2-D grating with other planes of incidence.

To design functional vascular grafts, it is essential to explore the interactions between endothelial cells and the surface of substrate biomaterials. The present study thus aimed at evaluating the influence of micropatterned silk fibroin films on human umbilical vein endothelial cell (HUVEC) behaviors including adhesion, migration, proliferation, and protein expressions. Silk fibroin films with different grafting micropatterns (10 μm × 10 μm, 20 μm × 20 μm, 20 μm × 30 μm, 40 μm × 40 μm) were prepared by soft-lithographic technique. HUVECs were shown to attach and grow well on the silk fibroin films. The results indicated that the 10 × 10 and 40 × 40 gratings induced higher proliferation rates as compared to the 20 × 20 and 20 × 30 groups. However, the increased orientation and alignment degree and stronger protein expressions (CD31, VWF and Vinculin) were observed on the 20 × 20 and 20 × 30 groups. Overall, this study suggested that the HUVEC behaviors could be regulated in vitro by different micropattern topographies. The micropatterned silk fibroin films may offer a potential improvement for the development of functional vascular grafts.

Surface texture plays a particularly important role in surface behaviors. Herein, we report a novel hierarchical texture combining microcone arrays with nanopits for minimizing the reflection loss at the air/glass interface. Its optical properties were confirmed via spectral characterization (reflectance, transmittance and haze) and FDTD numerical simulation. The results reveal that nanopits provide a gradient index profile for improving index discontinuity and are advantageously antireflective in a shorter wavelength while microcone arrays allow multi-reflection for light scattering and prevail over a longer wavelength region. The hierarchical texture resulting from the combination of both exhibits dramatic broadband light trapping over the entire visible spectrum. Moreover, without fluorosilane modification, the hierarchical texture allows a superhydrophobic surface (contact angle of ca. 136°) due to its higher roughness. The light trapping performance of the hierarchical texture onto the front glass surface of the micromorph cell was investigated by photoelectrical current–voltage curves and external quantum efficiency spectra. The results indicate that both the number of trapped photons and their optical path length in the absorbed layer are increased, thereby achieving an overall efficiency of 11.44% out of the bare device of 10.93% efficiency, resulting in a 4.7% enhancement. Additionally, the proposed method paves a promising way for light trapping in other solar applications, owing to its advantages of large area, low cost and facile fabrication.

We propose an angular-dependent polarization-insensitive filter in the terahertz (THz) region, based on the guided-mode resonance of one-dimensional zero-contrast grating architectural design. Particle swarm optimization combined with the rigorous coupled-wave analysis method is used to design the filter and investigate the influences of the planes of incidence on the characteristics of the proposed all-dielectric THz filter. With the planes of incidence set at 0°, 30°, 45°, and 60°, the polarization-independent resonances occur at 0.458 THz, 0.459 THz, 0.461 THz, and 0.465 THz under oblique incidences of 9.3°, 10.8°, 13.3°, and 19.2°, respectively, which means the oblique incident angle of the polarization-independent THz filter increases with the rotation of the planes of incidence from classic mounting to fully conical mounting. In addition, for the fully conical mounting case, the resonance has high angular stability and is no longer split, compared with classic incidence; meanwhile, there is only a tiny blue shift in resonance of less than 3 GHz when changing the incident angle from 0° to 10°. The physical mechanism of the spectral characteristics is also analyzed in detail. The spectral properties proposed herein enable significant potential application in the fields of spectroscopy, image sensors, communication, etc., in the THz region.

Cardiovascular disease is the primary cause of morbidity and mortality in today's world. Due to the lack of healthy autologous vessels, more tissue-engineered blood vessels are needed to repair or replace the damaged arteries. Biomaterials play an indispensable role in creating a living neovessel with biological responses. Silk fibroin produced by silkworms possesses good cytocompatibility, tailorable biodegradability, suitable mechanical properties, and minimal inflammatory reactions. In addition, regenerated silk fibroin solutions can be processed into various forms of scaffolds such as films, fibers, tubes, and porous sponges. These features make silk fibroin a promising biomaterial for small-diameter vascular grafts. The present article focuses on the applications of silk fibroin for vascular regeneration. A brief overview of the properties of silk fibroin is provided, following which the current research status and future directions of the main types of silk fibroin scaffolds for vascular regeneration are reviewed and discussed. Microsc. Res. Tech. 80:280-290, 2017. © 2015 Wiley Periodicals, Inc.

Failure analysis (FA) is a basic and effective method to obtain the physical and failure information of electronic components and circuits. Most of these information can provide many useful evidences for prognostic and system health management (PHM) of electronic products. To obtain these information, many failure analysis techniques are used. This paper focuses on analyzing the relationship between FA techniques and PHM system. To test and verify the availability of the relationship between FA techniques and PHM system, a failure analysis case of an Intelligent Power Module (IPM) is used to study the relationship. This IPM contains six insulated gate bipolar transistors (IGBTs) and there are obvious burnout indications on most of them after failure. With the process of failure analysis, the key information, such as component's structure, sensitive parameters are identified. These results persuasively prove that FA techniques can provide much information to PHM system, including PoF and data-driven methods.

Spectral responses of the guided mode resonant filter under different planes of incidence are comprehensively investigated in this paper. Commercially available software based on the rigorous coupled wave analysis method is used to perform the reflectance spectra. For normal incidence, there exists a pair of resonance bands, whose diffraction efficiencies can be tuned from 3.5% to 100% and 3.2% to 100% without shifting the resonant location as the plane of incidence (POI) angle ranges from 0° to 90°, whereas the resonances split into two branches as the POI angle decreases from 90° to 0° for oblique incidence. There exists a crossing point between the split bands that is proved to be polarization independent. Moreover, the physical mechanism of the above spectral characteristics is analyzed in detail by means of the wave vectors. The intensity-tunable feature under normal incidence can be used in the field of bioactive fluorescent protein dyes, displays, and signal processing. And the split characteristic under oblique incidence is applied to seek the polarization-independent wavelength, which has potential applications in the field of dense wavelength division multiplexing and laser devices.

Cardiovascular disease is the primary cause of morbidity and mortality in today's world. Due to the lack of healthy autologous vessels, more tissue-engineered blood vessels are needed to repair or replace the damaged arteries. Biomaterials play an indispensable role in creating a living neovessel with biological responses. Silk fibroin produced by silkworms possesses good cytocompatibility, tailorable biodegradability, suitable mechanical properties, and minimal inflammatory reactions. In addition, regenerated silk fibroin solutions can be processed into various forms of scaffolds such as films, fibers, tubes, and porous sponges. These features make silk fibroin a promising biomaterial for small-diameter vascular grafts. The present article focuses on the applications of silk fibroin for vascular regeneration. A brief overview of the properties of silk fibroin is provided, following which the current research status and future directions of the main types of silk fibroin scaffolds for vascular regeneration are reviewed and discussed. Microsc. Res. Tech. 80:280-290, 2017. © 2015 Wiley Periodicals, Inc.