Evaluation of anatomical and histological characteristics of human peripheral nerves: as an effort to develop an efficient allogeneic nerve graft.

Management of peripheral nerve defects is a complicated problem in clinical contexts. Autologous nerve grafting, a gold standard for surgical treatment, has been well known to have several limitations, such as donor site morbidity, a limited amount of available donor tissue, and size mismatches. Acellular nerve allografts (ANAs) have been developed as an alternative and have been applied clinically with favorable outcomes. However, because of the limited availability of commercialized ANAs due to supplier-related issues and high costs, efforts continue to produce alternative sources for ANAs. The present study evaluated the anatomical and histological characteristics of human peripheral nerves using 25 donated human cadavers. The length, diameter, and branching points of various peripheral nerves (median, ulnar, tibial, lateral femoral cutaneous, saphenous, and sural nerves) in both the upper and lower extremities were evaluated. The cross-sectional area (CSA), ratio of fascicular area, and numbers of fascicles were also evaluated via histologic analysis. CSA, the ratio of fascicular area, and the number of fascicles were analyzed statistically in correlation with demographic data (age, sex, height, weight, BMI). The mean length of all evaluated nerves ranged from 17.1 to 41.4 cm, and the mean diameter of all evaluated nerves ranged from 1.2 to 4.9 mm. Multiple regression analysis revealed correlations between the ratio of fascicular area and sex (p = 0.005) and BMI (p = 0.024) (R2 = 0.051). The results of the present study will be helpful in selecting necessary nerve allograft sources while considering the characteristics of each nerve in the upper and lower extremities during ANAs production.

Comparison of two different decellularization methods for processed nerve allograft.

The use of processed nerve allografts as an alternative to autologous nerve grafts, the gold standard treatment for peripheral nerve defects, is increasing. However, it is not widely used in Korea due to cost and insurance issues. Moreover, the main detergent used in the conventional Hudson method is unavailable. Therefore, a new nerve allograft decellularization process is needed. We aimed to compare the traditional Hudson method with a novel decellularization process that may remove cellular content more efficiently while preserving the extracellular matrix (ECM) structure using low concentration sodium dodecyl sulfate (SDS) and nuclease. After each decellularization process, DNA content was measured in nerve tissue. Masson's trichrome staining and scanning electron microscopy were performed to determine the state of preservation of the ECM. A significantly greater amount of DNA content was removed in the novel method, and the ECM structure was preserved in both methods. For the in vivo study, a 15-mm long sciatic nerve defect was created in two groups of Sprague-Dawley rats, and processed nerve allografts decellularized using the Hudson or novel method were transplanted. Functional and histological recovery results were measured 12 weeks post-transplantation. Ankle contracture angle, maximal isometric tetanic force of the tibialis anterior (TA), and the TA mass were compared between the groups, as well as the percent neural tissue (100 × neural area/intrafascicular area). There was no significant difference in functional and histological nerve recovery between the methods. The novel method is appropriate for developing a processed nerve allograft.

The anatomy of the saphenous and sural nerves as a source of processed nerve allografts.

As an alternative to autologous nerve donors, acellular nerve allografts (ANAs) have been studied in many experiments. There have been numerous studies on processing ANAs and various studies on the clinical applications of ANA, but there have not been many studies on sources of ANAs. The purposes of the present study were to evaluate the course of the saphenous and sural nerves in human cadavers and help harvest auto- or allografts for clinical implications. Eighteen lower extremities of 16 fresh cadavers were dissected. For the saphenous nerve and sural nerve, the distances between each branch and the diameters at the midpoint between each branch were measured. In the saphenous nerve, the mean length between each branch ranged from 7.2 to 28.6 cm, and the midpoint diameter ranged from 1.4 to 3.2 mm. In the sural nerve, the mean length between each branch ranged from 17.4 to 21 cm, and the midpoint diameter ranged from 2.3 to 2.8 mm. The present study demonstrates the length of the saphenous and sural nerve without branches with diameters larger than 1 mm. With regard for the clinical implications of allografts, the harvest of a selective nerve length with a large enough diameter could be possible based on the data presented in the present study.

Comparison of cytokine expression and ultrastructural alterations in fresh-frozen and dried electron beam-irradiated human amniotic membrane and chorion.

The purpose of the current study was to compare the effects of drying and fresh-freezing on human amniotic membrane (HAM) and amnion/chorion membrane (HACM) in terms of histological and structural characteristics and cytokine levels. HAM and HACM samples, obtained from six placentae, were investigated. HAM and HACM were dried, electron beam-irradiated (dehydration group; d-HAM/d-HACM), or fresh-frozen (freezing group; f-HAM/f-HACM). Luminex assay was used to assay the levels of 15 cytokines. The ultrastructural characteristics of HAM and HACM were evaluated using light and transmission electron microscopies. Total cytokine contents did not show the statistical difference between dehydration and fresh-freezing process. Significantly higher levels of total cytokines were observed in HACM than in HAM. Epidermal growth factor (EGF) level was significantly higher in d-HAM than in the other samples. The levels of most of the other growth factors were higher in HACM than in HAM, but there was no statistical difference between the dehydration process and the fresh-freezing process. The levels of the cytokines, other than the growth factors, were higher in HACM than in HAM, and higher concentrations of cytokines were observed in the freezing group than in the dehydration group. Histological examination revealed that the dehydration group had thinner tissues than the freezing group, but the structural stability, including the basement membrane, did not differ between the two groups. Microscopic structures such as microvilli and nuclei were well-preserved in the freezing group, based on the results of the transmission electron microscopy. Our dehydration process maintained the histological structure of HAM/HACM and a variety of growth factors and cytokines were identified. Especially, the HAM, processed with the dehydration method, had a higher EGF level than that processed with the fresh-freezing method. Therefore, dehydration method can be used to effectively promote wound repair.

Grating-coupled surface plasmon resonance on bulk stainless steel.

Grating-coupled surface plasmon resonance (SPR) is demonstrated with one-dimensional gratings fabricated on the surface of bulk stainless steel using imprinting combined with electrochemical etching. The extent of light coupling and the wavelengths of SPR peaks were characterized with respect to the incident angle and polarization states of the light. When the plane of incidence was orthogonal to the grating grooves, only TM polarization was absorbed at two different wavelengths. In the plane of incidence parallel to the grooves, a single resonance peak was observed only when the incident light was TE-polarized. The dependence of SPR wavelengths on the incident angle was in good agreement with theoretical consideration.

Laser Dynamic Control of the Thermal Emissivity of a Planar Cavity Structure Based on a Phase-Change Material.

Tailoring the thermal emission of a material in the long-wave infrared (IR) range of 8-13 µm is crucial for many IR-adaptive applications, including personal thermal management, IR camouflage, and radiative cooling. Although various materials and surface structures have been proposed for these purposes, space-selective and dynamic control of their emissivity is challenging. In this study, we present a planar surface cavity structure consisting of a Ge2Sb2Te5 (GST) film on top of a thin metal reflector to modulate its emissivity by using an ultraviolet laser beam. A laser-induced phase change in GST allowed for the local control of emissivity. The average emissivity in the long-wave IR range was tunable from 0.15 to 0.77 simply by changing the laser energy deposited on the GST film. This enabled the laser printing of high-contrast emissivity patterns, which were erasable by subsequent thermal annealing. Emissivity-modulated GST cavities could be fabricated on not only rigid substrates but also flexible plastic substrates such as polyimide. The GST surface cavity was highly flexible and remained stable upon repeated bending to a curvature radius of 0.5 cm. This study provides a promising route for realizing scalable and flexible thermal emitters with tunable surface emissivity.

Multispectral Imaging with a Planar Cavity-Type Metasurface for Optical Security.

Multispectral imaging refers to capturing images in different wavelength ranges across the electromagnetic spectrum. Despite the potential impact of multispectral imaging, its widespread use has been limited by the poor spectral selectivity of naturally occurring materials beyond the visible range. In this study, we present a multilayered planar cavity structure to simultaneously record mutually independent visible and infrared (IR) images on solid surfaces. The structure consists of a color control unit (CCU) and an emission control unit (ECU). The visible color of the cavity is controlled by varying the thickness of the CCU, whereas its IR emission is spatially tuned by the laser-induced phase change of a Ge2Sb2Te5 layer embedded in the ECU. Because the CCU comprises only IR lossless layers, its thickness variation has negligible influence on the emission profile. This enables different color and thermal images to be printed in a single structure. The cavity structure can be fabricated on flexible substrates (plastic and paper) as well as rigid bodies. Furthermore, the printed images remain stable against bending. This study shows that the proposed multispectral metasurface is highly promising for use in the field of optical security, such as identification, authentication, and anti-counterfeiting.

Crack Evaluation of Concrete Using Mechanochromic Sensor.

In this study, the deformation of concrete materials was evaluated using a mechanochromic sensor that detects the discoloration reaction caused by deformation. This sensor was attached by applying the Loctite adhesive to both ends in the longitudinal direction. The process of applying tensile stress to the specimens was videotaped, and the deformation and discoloration were examined through image analysis. The mechanochromic sensor was not affected by the finished surface condition, and the discoloration reaction was detected for a concrete material deformation level of up to 0.01 mm. The detected level was caused by the elongation of the sensor, and the discoloration compared with the initial color was identified. In addition, the integration behavior of the mechanochromic sensor under the deterioration of concrete members in cold areas and winter environments, as well as the discoloration reaction of the sensor in a low-temperature environment, was examined. It was found that the discoloration ability of the mechanochromic sensor exposed to a low-temperature environment was restored in 2 h after the end of the freeze-thaw test, and it was judged that the deformation and discoloration levels will be properly measured when the surface temperature of the sensor is restored to a room temperature of approximately 15 °C. This appeared to be due to the room temperature recovery of the dielectric spacer of the sensor and the deformation structure of the resonance condition. The sensor was also attached when diagonal cracks occurred in the concrete beam members to evaluate the strain and discoloration rate according to the deformation and discoloration levels. Accordingly, the cracks and deformation of the concrete materials were monitored using measured values from the discoloration of the mechanochromic sensors, and the possibility of measuring the crack width was reviewed only by real-time monitoring and imaging with the naked eye.

Formation of void array inside transparent and absorptive glasses by femtosecond laser irradiation.

We demonstrate self-fabrication of void arrays in a fused silica transparent in the visible and a color-filter borosilicate glass strongly absorptive at 800 nm using tightly focused Ti-sapphire femtosecond laser pulses at 1 kHz without scanning. The period, the size, the number of voids, and the length of the aligned void structure were controlled by changing the laser pulse energy, and the position of the focal point inside two materials. The void arrays were observed by an optical microscope and also estimated by an optical diffraction experiment. The void size and period were smaller in the absorptive glass than in the transparent glass. The submicrometer-sized void was observed by a scanning electron microscope. The smaller and clearer void arrays were formed in the color filter than the fused silica glass. With increasing the laser focal depth, the void-array length increased in the fused silica and decreased in the color filter.

Laser treatment of solution-deposited carbon nanotube thin films for improved conductivity and transparency.

Solution-deposited single-walled carbon nanotube (SWCNT) films contain a surfactant material and it should be removed by a post-deposition treatment to improve the conductivity. We here report that the sodium dodecyl sulfate (SDS) surfactant in SWCNT films can be completely removed by a pulsed Nd:YAG laser (wavelength = 1064 nm, pulse width = 99 ms). SWCNT films were spray-coated onto a glass substrate and were scanned by a laser beam of 2 mm size. In this process, individual nanotubes absorb the laser energy and generate heat to vaporize the surrounding surfactant. This mechanism was supported by the fact that the required pulse energy decreased as the SWCNT density increased. An encouraging feature is that unlike typical acid treatments, the laser treatment can improve not only the conductivity but also the transmittance. This might be associated with complete surfactant removal without leaving any particulate debris. For a film, the sheet resistance decreased from 1.07 kΩ/sq to 700 Ω/sq and its visible transmittance simultaneously increased by 4%.

Effectiveness and Biocompatibility of Decellularized Nerve Graft Using an In Vivo Rat Sciatic Nerve Model.

BACKGROUND: Decellularized nerve allografting is one of promising treatment options for nerve defect. As an effort to develop more efficient nerve graft, recently we have developed a new decellularization method for nerve allograft. The aim of this study was to evaluate the effectiveness and biocompatibility of nerve graft decellularized by our newly developed method. METHODS: Forty-eight inbred male Lewis rats were divided into two groups, Group I (autograft group, n = 25), Group II (decellularized isograft group, n = 23). Decellularized nerve grafts were prepared with our newly developed methods using amphoteric detergent and nuclease treatment. Serum cytokine level measurements at 0, 2, and 4 weeks and histologic evaluation for inflammatory cell infiltration at 6 and 16 weeks after nerve graft. RESULTS: There was no significant difference in mean maximum isometric tetanic force and weight of tibialis anterior muscle or ankle angle at toe-off phase between two groups at 6 and 16 weeks survival time points (p > 0.05). There was no inflammatory cell infiltration in either group and histomorphometric assessments of 6- and 16-week specimens of the isograft group did not differ from those in the autograft group with regard to number of fascicle, cross sectional area, fascicle area ratio, and number of regenerated nerve cells. CONCLUSION: Based on inflammatory reaction, axonal regeneration, and functional outcomes, our newly developed decellularized nerve grafts were fairly biocompatible and had comparable effectiveness to autografts for nerve regeneration, which suggested it would be suitable for nerve reconstruction as an alternative to autograft.

Laser welding of nanoparticulate TiO2 and transparent conducting oxide electrodes for highly efficient dye-sensitized solar cell.

Poor interfacial contact is often encountered in nanoparticulate film-based devices. The dye-sensitized solar cell (DSSC) is a representative case in which a nanoporous TiO(2) electrode needs to be prepared on the transparent conducting oxide (TCO)-coated glass substrate. In this study, we demonstrate that the inter-electrode contact resistance accounts for a considerable portion of the total resistance of a DSSC and its efficiency can be greatly enhanced by welding the interface with a laser. TiO(2) films formed on the TCO-coated glass substrate were irradiated with a pulsed ultraviolet laser beam at 355 nm; this transmits through the TCO and glass but is strongly absorbed by TiO(2). Electron microscopy analysis and impedance measurements showed that a thin continuous TiO(2) layer is formed at the interface as a result of the local melting of TiO(2) nanoparticles and this layer completely bridges the gap between the two electrodes, improving the current flow with a reduced contact resistance. We were able to improve the efficiency by 35-65% with this process. DSSCs fabricated using a homemade TiO(2) paste revealed an efficiency improvement from eta = 3.3% to 5.4%, and an increase from 8.2% to 11.2% was achieved with the TiO(2) electrodes made from a commercial paste.

High-purity reflective color filters based on thin film cavities embedded with an ultrathin Ge2Sb2Te5 absorption layer.

A thin film cavity formed by stacking metal-insulator-metal (MIM) continuous layers is of significant interest as a lithography-free and scalable color-filtering structure. Such a cavity can selectively transmit a certain frequency range of incident light, thus producing vivid transmission colors. However, the generation of reflection colors with high purity and reflectivity is a challenge because a cavity in reflection mode resonantly absorbs a narrow range of wavelengths and reflects the remaining spectrum. This study shows that highly pure and reflective colors can be obtained by embedding an ultrathin Ge2Sb2Te5 layer within the cavity. Because the MIM structure exhibits a nonuniform intensity distribution across the insulator layer, the approach is to place the Ge2Sb2Te5 layer in a high-intensity region within the insulator and thereby create another absorption band in addition to the cavity resonance mode. When combined with the refractive-index engineering of the metal layer, this approach leads to red, green, and blue colors having a bandwidth of ∼100 nm and a reflection efficiency of 90%. The results of the study may be effectively utilized in numerous applications, including reflective color filters, colorimetric sensors, and surface decorations.

Parallelized laser-direct patterning of nanocrystalline metal thin films by use of a pulsed laser-induced thermo-elastic force.

Thin film patterning by the conventional lithographic technique requires a number of steps including the deposition, development, and removal of the photoresist layer. Here we demonstrate that metal thin films evaporated on glass can be directly patterned by a spatially modulated pulsed Nd-YAG laser beam (wavelength = 1064 nm, pulse width = 6 ns) incident from the backside of the substrate. This method utilizes a pulsed laser-induced thermo-elastic force exerted on the film which plays a role in detaching it from the substrate. High-fidelity patterns at the micrometer scale have been fabricated over a few square centimeters by a single pulse with pulse energy of 850 mJ. This is attributed to the fact that deposited metal films are polycrystalline with nano-sized grains, and thus localized etching of the material is possible with shearing along the weakly bonded grain boundary regions. We have also developed a nano-block model to simulate the laser-direct patterning of nanocrystalline thin films. Experimental results could be well described with this simulation model. The patterning process presented here provides a simple photoresist-free route to fabricate metal thin film patterns on transparent substrates.

Optical properties and spectroscope parameters of Sm(DBM)(3)Phen-doped poly(methyl methacrylate).

Rare-earth complex Sm(DBM)(3)Phen-doped poly(methyl methacrylate) was synthesized and its absorption and luminescence spectra were studied. The relationship between the coordinate environment of rare-earth ions and the Judd-Ofelt intensity parameter Omega(2) was analyzed and the spectroscopic quality factor, Omega(4)/Omega(6), for this material was reported. The oscillator strengths of higher energy levels of Sm(3+) were predicted, which would be useful to assign the closely spaced multiples at higher energies. The radiative properties for fluorescent levels (4)G(4)(7/2), (4)F(3)(3/2) and (4)G(4)(5/2) of Sm(3+) were evaluated. The predicted radiative parameters were compared with the observed luminescence spectrum of Sm(3+) in this system.

Structural color printing with a dielectric layer coated on a nanotextured metal substrate: simulation and experiment.

The printing of plasmonic structural colors relies on noble metal nanostructures fabricated on Si, glass, or plastic substrates. This paper presents a simple surface structure for producing vivid structural colors directly from common metal substrates. The structure is formed by texturing the surface of stainless steel (STS) via imprinting and coating it with a dielectric layer. Diverse colors are generated simply by varying the thickness of the dielectric layer. The colors arise from surface plasmon resonance and guided-mode resonance of the incident light, which are excited on the textured STS surface and inside the dielectric layer, respectively. A finite-difference time-domain simulation shows that 500 nm is the optimum texture periodicity with regard to the tunability and vividness of the colors. This is experimentally verified by printing many differently colored images on the surface of STS substrates with a texture period of 500 nm. The proposed structure/method does not require a nanofabrication technique such as electron-beam lithography or focused ion beam etching. The results of the study provide a facile route for producing vivid structural colors on metals, which may find various applications, including surface decoration, product identification, anti-counterfeiting, and perfect absorbers.

Laser-Induced Dewetting of Metal Thin Films for Template-Free Plasmonic Color Printing.

Plasmonic color laser printing has several advantages over pigment-based technology, including the absence of ink and toner and the production of nonfading colors. However, the current printing method requires a template that should be prepared via nanofabrication processes, making it impractical for large-area color images. In this study, we show that laser-induced dewetting of metal thin films by a nanosecond pulsed laser can be effectively utilized for plasmonic color printing. Ag, Au, and their complex films deposited on a glass substrate were dewetted into different surface structures such as droplets, rods, and ripples, depending on the incident laser energy. The resulting morphological evolutions could be explained by Rayleigh and capillary instabilities. For a bimetallic film comprising Ag nanowires coated on a Au layer, a few different plasmonic colors were generated from a single sample simply by changing the laser fluence. This provides a possible method for implementing plasmonic color laser printing without using a prepatterned template.