Optical Penetration Research Articles

Commentary: Current concepts, recent updates, and future treatment options for Pythium insidiosum keratitis.

Commentary: Current concepts, recent updates, and future treatment options for Pythium insidiosum keratitis.

Synthesis of NIR‐II Fluorescent Hybrid Ag2S/ZnPc Nanoparticles for in vitro Photodynamic Therapy

AbstractFluorescence imaging‐guided photodynamic therapy (PDT), particularly near infrared II (NIR‐II) fluorescence featuring deep penetration depth, can greatly improve the treatment outcomes with precise administration. In this work, a reprecipitation‐encapsulation method was used to co‐load NIR‐II fluorescent Ag2S quantum dots (QDs) and photosensitizer zinc phthalocyanine (ZnPc) into single nanoparticles (NPs), i. e., Ag2S/ZnPc NPs. Moreover, the resultant NPs were coated by a poly‐L‐lysine (PLL) layer, which endowed the initial hydrophobic Ag2S QDs and ZnPc with good biocompatibility. Ag2S/ZnPc NPs exhibited a hydrodynamic diameter of ∼70 nm, strong NIR‐II fluorescence peaking at 1052 nm, efficient cellular uptaken, and high singlet oxygen generation. Taking advantage of Ag2S/ZnPc NPs, efficient phototherapeutic efficacy was achieved on HeLa cells upon the irradiation of 660 nm light, and a deep optical tissue penetration depth of 1.4 mm was obtained under 808 nm excitation. These results suggested that the facilely prepared Ag2S/ZnPc NPs are very promising for NIR‐II fluorescence imaging‐guided in vivo PDT.

Divinylanthracene-Containing Tetracationic Organic Cyclophane with Near-Infrared Photoluminescence

Near-infrared (NIR) light is known to have outstanding optical penetration in biological tissues and to be non-invasive to cells compared with visible light. These characteristics make NIR-specific light optimal for numerous biological applications, such as the sensing of biomolecules or in theranostics. Over the years, significant progress has been achieved in the synthesis of fluorescent cyclophanes for sensing, bioimaging, and making optoelectronic materials. The preparation of NIR-emissive porphyrin-free cyclophanes is, however, still challenging. In an attempt for fluorescence emissions to reach into the NIR spectral region, employing organic tetracationic cyclophanes, we have inserted two 9,10-divinylanthracene units between two of the pyridinium units in cyclobis(paraquat-p-phenylene). Steady-state absorption, fluorescence, and transient-absorption spectroscopies reveal the deep-red and NIR photoluminescence of this cyclophane. This tetracationic cyclophane is highly soluble in water and has been employed successfully as a probe for live-cell imaging in a breast cancer cell line (MCF-7).

Optical Properties of Human Skin Phototypes and Their Correlation with Individual Angle Typology

Objective: This study aims to correlate human skin phototypes with complete optical characterization (absorption, scattering, effective attenuation, optical penetration, and albedo coefficients) based on individual typology angle (ITA) values and colorimetric parameters. Methods: A colorimeter was used to group 12, fresh, ex vivo human skin samples according to their phototype; the CIELAB color scale and ITA values were employed. An integrating sphere system and the inverse adding-doubling algorithm were applied during optical characterization, conducted from 500 to 1300 nm. Results: On the basis of ITA values and their classification, the skin samples were separated into six groups: two intermediates, two tan, and two brown. In the visible range, for lower ITA values (darker skins), the absorption and effective attenuation coefficient parameters increased, whereas the albedo and depth penetration parameters decreased. In the infrared region, all the phototypes had similar parameters. The scattering coefficient was similar for all the samples and did not change with ITA values. Conclusions: ITA analysis, a quantitative method, showed that the human skin tissue's optical properties and pigmentation colors were highly correlated.

Photoacoustic imaging with limited sampling: a review of machine learning approaches.

Photoacoustic imaging combines high optical absorption contrast and deep acoustic penetration, and can reveal structural, molecular, and functional information about biological tissue non-invasively. Due to practical restrictions, photoacoustic imaging systems often face various challenges, such as complex system configuration, long imaging time, and/or less-than-ideal image quality, which collectively hinder their clinical application. Machine learning has been applied to improve photoacoustic imaging and mitigate the otherwise strict requirements in system setup and data acquisition. In contrast to the previous reviews of learned methods in photoacoustic computed tomography (PACT), this review focuses on the application of machine learning approaches to address the limited spatial sampling problems in photoacoustic imaging, specifically the limited view and undersampling issues. We summarize the relevant PACT works based on their training data, workflow, and model architecture. Notably, we also introduce the recent limited sampling works on the other major implementation of photoacoustic imaging, i.e., photoacoustic microscopy (PAM). With machine learning-based processing, photoacoustic imaging can achieve improved image quality with modest spatial sampling, presenting great potential for low-cost and user-friendly clinical applications.

Non-destructive evaluation of soluble solid content in fruits with various skin thicknesses using visible–shortwave near-infrared spectroscopy

Abstract Visible–shortwave near-infrared spectroscopy has been used for internal quality measurement, but the optical penetration to the thickness of fruit skin becomes a challenge. This research aimed to develop partial least square regression model for the soluble solid content (SSC) measurement of fruits having various skin thicknesses, namely dragon fruit, tomato, guava, sapodilla, and banana. The spectra of each fruit were taken in a reflectance mode over a wavelength range of 400–1,000 nm. The best models obtained from banana and sapodilla yielded determination coefficient of prediction (R 2 p) of 0.88 and 0.90 and root mean square error of prediction (RMSEP) 0.39 and 0.38°Brix, respectively. The banana and sapodilla SSC prediction models should be able to be used carefully in a variety of applications. Tomato and guava had moderately thinner skin but had the lower R 2 p of 0.64 and 0.76 and the RMSEP of 0.17 and 0.26°Brix, respectively. The poorest model was yielded by dragon fruit, which had the thickest skin with the R 2 p of 0.59 and the RMSEP of 0.40°Brix. The model for guava, although having low R 2 p, can still be utilized as a screening criterion and in some other ‘approximate’ applications. However, the SSC prediction model for tomatoes and dragon fruit is not recommended to use and requires additional research. In addition to the effect of skin thickness, other fruit morphological influences the result of this study. Internal structure and seed number influence the reflection optical geometry, which also affects the SSC prediction model.

Understanding and Controlling Photothermal Responses in MXenes.

MXenes have the potential for efficient light-to-heat conversion in photothermal applications. To effectively utilize MXenes in such applications, it is important to understand the underlying nonequilibrium processes, including electron-phonon and phonon-phonon couplings. Here, we use transient electron and X-ray diffraction to investigate the heating and cooling of photoexcited MXenes at femtosecond to nanosecond time scales. Our results show extremely strong electron-phonon coupling in Ti3C2-based MXenes, resulting in lattice heating within a few hundred femtoseconds. We also systematically study heat dissipation in MXenes with varying film thicknesses, chemical surface terminations, flake sizes, and annealing conditions. We find that the thermal boundary conductance (TBC) governs the thermal relaxation in films thinner than the optical penetration depth. We achieve a 2-fold enhancement of the TBC, reaching 20 MW m-2 K-1, by controlling the flake size or chemical surface termination, which is promising for engineering heat dissipation in photothermal and thermoelectric applications of the MXenes.

Optical Penetration of Shape-Controlled Metallic Nanosensors across Membrane Barriers

Precise nanostructure geometry that enables the optical biomolecular delivery of nanosensors to the living intracellular environment is highly desirable for precision biological and clinical therapies. However, the optical delivery through membrane barriers utilizing nanosensors remains difficult due to a lack of design guidelines to avoid inherent conflict between optical force and photothermal heat generation in metallic nanosensors during the process. Here, we present a numerical study reporting significantly enhanced optical penetration of nanosensors by engineering nanostructure geometry with minimized photothermal heating generation for penetrating across membrane barriers. We show that by varying the nanosensor geometry, penetration depths can be maximized while heat generated during the penetration process can be minimized. We demonstrate the effect of lateral stress induced by an angularly rotating nanosensor on a membrane barrier by theoretical analysis. Furthermore, we show that by varying the nanosensor geometry, maximized local stress fields at the nanoparticle-membrane interface enhanced the optical penetration process by four-fold. Owing to the high efficiency and stability, we anticipate that precise optical penetration of nanosensors to specific intracellular locations will be beneficial for biological and therapeutic applications.

Stimuli‐Responsive Organic Near‐Infrared Photoacoustic Probes

AbstractPhotoacoustic (PA) imaging is an emerging biomedical imaging technique with the features of non‐invasiveness and non‐ionization. It takes advantage of the photothermal effect of PA probes to convert absorbed photon energy into heat and subsequent transient thermoelastic tissue expansion for ultrasonic waves for PA images. Thus, PA imaging exhibits the combined superiority of high‐contrast optical imaging and deep tissue penetration of acoustic imaging, which furnishes high‐resolution and high‐contrast tissue images. Stimuli‐responsive organic PA agents in the near‐infrared (NIR) biological window have attracted increasing attention because of their low biological toxicity and response characteristics. This review focuses on the recent research progress of stimuli‐responsive organic NIR probes for PA imaging, including the temperature response, pH response, redox response, metal ion response, and enzyme response. And the stimuli‐responsive mechanisms are highlighted in detail. Moreover, their perspectives and challenges are discussed. It will be of great help for the further development of organic NIR PA probes with stimuli‐response.

Influence of laser beam aberrations compensation and spot size on the transmittance in native and optically cleared skeletal muscles

Light propagation and penetration inside tissues highly affect the optical imaging of biological tissues. Two major factors influence that; the first is associated with the dense scattering properties of tissues. Consequently, optical clearing (OC) methods have been developed to reduce tissue scattering by matching the tissue layers’ refractive indices via different protocols. The second factor is related to the illuminating wavefront and the size of the incident light beam. The present work monitored the optical transmittance of skeletal muscles after applying different OC approaches (physical OC using 99%-glycerol immersion and photothermal OC using IR-laser irradiation). First, the optical transmittance of the samples before and after the two OC procedures were compared, revealing a transmittance increase of 300% and 20%. Then, the laser beam wavefront aberrations were compensated in real-time by utilizing an active-adaptive Shack-Hartmann wavefront sensor system to provide an ideal illumination wavefront. Finally, the transmittance of the samples was compared using uncompensated and compensated laser wavefronts providing a 35% increase in the transmittance after aberrations compensation. Moreover, the aberration-free incident laser beam’s transmittance with different spot diameters was investigated. The results revealed that the larger beam diameter provided higher transmittance, hence higher optical penetration within the tissue.

Near-infrared luminescence high-contrast in vivo biomedical imaging

Luminescence imaging in biomedical research has allowed new insights into the architecture of pathological tissues, signalling networks and cell interactions, and is now turning into a powerful tool for diagnostics and image-guided surgery. Luminescence in the near-infrared (NIR) window (700–1,700 nm), in particular, exhibits less interaction of scattering and absorption photons with biological tissues than imaging in the visible range, resulting in deeper optical penetration depth and reduced autofluorescence interference, and thus enabling higher imaging contrast. Despite promising preclinical results, few NIR fluorophores have been clinically approved so far. In this Review, we discuss important engineering challenges that need to be addressed to enable successful clinical translation of NIR luminescence imaging, including enhancement of imaging contrast by optimizing fluorescent probe design, reducing tissue autofluorescence and improving local accumulation of the luminescent probes in the body. Luminescence imaging in the near-infrared (NIR) region enables non-radiative, fast-feedback, low-cost and high-contrast in vivo imaging of biological tissues. This Review discusses engineering challenges that need to be addressed to enable clinical translation of NIR luminescence imaging.

Penetrating keratoplasty following Tenon's patch graft

This report aims to describe the histopathological changes in the cornea following Tenon's patch graft. A 51-year-old male underwent Tenon's patch graft (TPG) for corneal perforation following Therapeutic penetrating keratoplasty which was performed twice for non-resolving microbial keratitis and graft infiltrate, respectively. The infection resolved following TPG resulting in formation of a vascularised scar. An Optical penetrating keratoplasty was performed six months after the TPG. Postoperative period was uneventful. Histo-pathological evaluation of the excised corneal tissue revealed excellent integration of the tenon tissue with the surrounding corneal stromal collagen. Histo-pathological evidence suggests that, tenon's tissue integrates well with surrounding corneal stromal collagen and is probably capable of regenerating new collagen and thus aid in corneal wound healing

Utility of Donor Corneas Based on Endothelial Cell Count

Aim: To assess utility of donor corneas based on analysis of endothelial cells qualitatively and quantitatively. Methods: It was a observational study of donor corneas received at eye bank in a tertiary care centre during period of January 2021 to June 2022. 94 corneoscleral buttons were excised and endothelial cell density and morphology were assessed using specular microscope. Results: With increasing age there was decrease in endothelial cell density seen. A highly significant co-relation was found between age and endothelial cell density. (p<0.001).Endothelial cell count was high in phakic compared to pseudophakic eyes. A highly significant co-relation was found between lens status and endothelial cell density (p<0.001). With increasing age there was decrease in hexagonality of endothelial cells seen. A highly significant co-relation was found between age and hexagonality of endothelial Cells (p<0.001). A highly significant correlation was found between utility of endothelial cells of mean 2018.94, hexagonality of mean 54.39 and co-efficient of variation of mean 34.50. Amongst 94 donor corneas 24.4% were used for optical penetrating keratoplasty, 22.3% for therapeutic purpose, 6.3% for DSEK, 4.2% for DALK and remaining 42.5% for research/practice purpose. Conclusion: Analysis of donor corneas demonstrated that age and pseudophakia as predictor of decrease endothelial cell density. A significant co-relation was found between endothelial cell density and utilization.

Theoretical evolution of thermal behaviour of Ti-6Al-4V subjected to selective laser melting: A powder free approach

Additive manufacturing (AM) processes are considered to be the pillar of the next industrial revolution due to their inherent qualities such as design flexibility, the ability to produce complex parts and prototypes, lower cost due to the reduced requirement of materials and curtailed lead time for manufacturing. Selective laser melting (SLM) is one of the most popular metallic AM technologies since it enables accurate control over part dimensions and fabrication of high resolution features. This research paper is aimed to develop an exact analytical model of three-dimensional thermal response captured in SLM of Ti based alloy (Ti-6Al-4V). A physical model has been proposed to predict the temperature profile during the metal additive manufacturing process with consideration of the effect of thermal history developed during moving laser heat source interaction. The corresponding mathematical solution is developed by employing an amalgamation of ‘Duhamel’s theorem’ and ‘Finite Integral Transform method’. The parametric laser-substrate interaction phenomenon is the prime deciding factor for the successful accomplishment of the manufacturing process. This research paper theoretically investigates the thermal characteristics (peak temperature, temperature distribution curvature, pulse time, optical penetration depth, time of laser exposure, laser absorption radius, and so on) by employing Fourier’s heat conduction model with a moving laser heat source. The theoretical estimation has been validated by the existing mathematical as well as experimental research outcomes. Present work might be an asset for deciding the design of process variables and protocols in terms of laser based additive manufacturing specifically the selective laser melting process.

Optical Penetration and "Fingerprinting" Analysis of Automotive Optical Liquid Silicone Components Based on Wavelet Analysis and Multiple Recognizable Performance Evaluation.

The residual stress phenomenon in the injection process of an optical lens affects the quality of optical components, and the refractive error caused by geometric errors is the most serious, followed by the degradation of the accuracy and function of optical components. It is very important to ensure that the lens geometry remains intact and the refractive index is low. Therefore, a parameter design method for an optical liquid silicon injection molding was proposed in this study. Wavelet analysis was applied to the noise reduction and feature extraction of the cavity pressure/pressure retaining curve of the injection molding machine, and multiple identifiable performance evaluation methods were used to identify and optimize the parameters of the molding process. Taking an automotive LED lens as an example, Moldex3D simulation software was used to simulate the molding of an LED lens made of LSR material, and two key injection molding factors, melt temperature and V/P switching point, were analyzed and optimized. In this paper, the transmittance and volume shrinkage of LED lenses are taken as quality indexes, and parameters are optimized by setting different V/P switching points and melt temperature schemes. The experimental results show that the residual stress is negatively correlated with transmittance, and the higher the residual stress, the lower the transmittance. Under the optimum process parameters generated by this method, the residual stress of plastic parts is significantly optimized, and the optimization rate is above 15%. In addition, when the V/P switching point is 98 and the melt temperature is 30 °C, the product quality is the best, the volume shrinkage rate is the smallest, and the size is 2.895%, which also means that the carbon emissions are the lowest.

In-depth polarisation resolved SHG microscopy in biological tissues using iterative wavefront optimisation.

Polarised nonlinear microscopy has been extensively developed to study molecular organisation in biological tissues, quantifying the response of nonlinear signals to a varying incident linear polarisation. Polarisation Second harmonic Generation (PSHG) in particular is a powerful tool to decipher sub-microscopic modifications of fibrillar collagen organisation in type I and III collagen-rich tissues. The quality of SHG imaging is however limited to about one scattering mean free path in depth (typically 100 micrometres in biological tissues), due to the loss of focus quality, induced by wavefront aberrations and scattering at even larger depths. In this work, we study how optical depth penetration in biological tissues affects the quality of polarisation control, a crucial parameter for quantitative assessment of PSHG measurements. We apply wavefront shaping to correct for SHG signal quality in two regimes, adaptive optics for smooth aberration modes corrections at shallow depth, and wavefront shaping of higher spatial frequencies for optical focus correction at larger depths. Using nonlinear SHG active nanocrystals as guide stars, we quantify the capabilities of such optimisation methods to recover a high-quality linear polarisation and investigate how this approach can be applied to in-depth PSHG imaging in tissues, namely tendon and mouse cranial bone.

Evaluating the effect of corneal tissue preservation on graft survival after penetrating keratoplasty

: To study the various tissue preparation and preservation which affect the quality of donor tissue along with the effect of recipient factors on short term graft survival. The ambi-spective study was carried out in order to know predictive value of factors like donor, tissue preservation and recipient factors and the extent of the effect on short term graft survival. A total of 26 eyes of 13 donors were studied, out of which 23 eyes had undergone penetrating keratoplasty. Out of 23 eyes, 3 eyes had undergone therapeutic penetrating keratoplasty, 16 eyes undergone optical penetrating keratoplasty and 4 eyes undergone triple procedures; penetrating keratoplasty with cataract extraction with posterior chamber intra ocular lens implantation. The results of penetrating keratoplasty were studied over a period of 3 months with follow ups at 1 week, 1 month and the final follow up at the 3rd month. The indication for penetrating keratoplasty in recipients in this study were essentially optical and therapeutic. The Statistical analysis was performed by SPSS 23.0 version. Categorical variables were described by taking percentages (analyzed using Chi Square test; Subgroup analysis was based on Adjusted Standardized Residuals). The variables with p value <0.05 was considered as statistically significant. Recipients with donor tissue from eyes retrieved within 4 hours of death and shorter preservation to utilization time have shown better graft survival. Practices including lid closure and eye drop instillation should be encouraged. Hospital cornea retrieval program should be promoted to ensure lesser death to enucleation time and preservation time for better graft outcome.

Light scattering control with the two-step focusing method based on neural networks and multi-pixel coding.

Focusing light through scattering media is essential for high-resolution optical imaging and deep penetration. Here, a two-step focusing method based on neural networks (NNs) and multi-pixel coding is proposed to achieve high-quality focusing with theoretical maximum enhancement. In the first step, a single-layer neural network (SLNN) is used to obtain the initial mask, which can be used to focus with a moderate enhancement. In the second step, we use multi-pixel coding to encode the initial mask. The coded masks and their corresponding speckle patterns are used to train another SLNN to get the final mask and achieve high-quality focusing. In this experiment, for a mask of 16 × 16 modulation units, in the case of using 8 pixels in a modulation unit, focus with the enhancement of 40.3 (only 0.44 less than the theoretical value) has been achieved with 3000 pictures (1000 pictures in the first step and 2000 pictures in the second step). Compared with the case of employing only the initial mask and the direct multi-pixel encoded mask, the enhancement is increased by 220% and 24%. The proposed method provides a new idea for improving the focusing effect through the scattering media using NNs.

Ballistic Thermal Transport at Sub-10nm Laser-Induced Hot Spots in GaN Crystal.

Ballistic thermal transport at nanoscale hotspots will greatly reduce the performance of a Gallium nitride (GaN) device when its characteristic length reaches the nanometer scale. In this work, the authors develop a tip-enhanced Raman thermometry approach to study ballistic thermal transport within the range of 10nm in GaN, simultaneously achieving laser heating and measuring the local temperature. The Raman results show that the temperature increase from an Au-coated tip-focused hotspot up to two times higher (40 K) than that in a bare tip-focused region (20 K). To further investigate the possible mechanisms behind this temperature difference, the authors perform electromagnetic simulations to generate a highly focused heating field, and observe a highly localized optical penetration, within a range of 10nm. The phonon mean free path (MFP) of the GaN substrate can thus be determined by comparing the numerical simulation results with the experimentally measured temperature increase which is in good agreement with the average MFP weighted by the mode-specific thermal conductivity, as calculated from first-principles simulations. The results demonstrate that the phonon MFP of a material can be rapidly predicted through a combination of experiments and simulations, which can find wide application in the thermal management of GaN-based electronics.

Mini-Conjunctival Limbal Autograft (Mini-CLAU) Using Platelet-Rich Plasma Eye Drops (E-PRP): A Case Series.

The purpose of this study was to introduce a new method of limbal stem cell transplantation using autologous platelet-rich plasma (E-PRP) eye drops for unilateral total limbal stem cell deficiency. Patients with total unilateral limbal stem cell deficiency due to chemical burn underwent mini-conjunctival limbal autograft using autologous E-PRP drops. One small limbal block, measuring 2 × 2 mm, was harvested from the patients' contralateral healthy eye and transplanted to the diseased eye. All patients received E-PRP drops until achieving complete corneal epithelialization. Subsequent corneal transplantation was performed in eyes with significant stromal opacification. Corneal buttons obtained during corneal transplantation underwent immunohistochemistry for the evaluation of limbal stem cell markers (ABCG2 and P63). Visual acuity, epithelial healing, corneal clarity, and regression of corneal conjunctivalization/vascularization were evaluated after surgery. Ten patients with acid (n = 7) or alkali (n = 3) burn were included. The mean follow-up period was 21.7 ± 5.8 months (range, 12-32 months). Corneas were completely reepithelialized within 14.9 ± 3.5 days (range, 11-21 days). Corneal conjunctivalization/vascularization dramatically regressed 1 to 2 months after surgery in all cases, and corneal clarity considerably improved in 7 patients. In the 3 eyes with significant stromal opacification, subsequent optical penetrating keratoplasty was performed. The ocular surface was stable throughout the follow-up period in all eyes. BSCVA improved to 0.60 ± 0.0.32 and 0.46 ± 0.0.25 logMAR in eyes with and without corneal transplantation, respectively, at the final follow-up visit. ABCG2 and P63 markers were detected on corneal buttons after keratoplasty. Based on our clinical and laboratory findings, mini-conjunctival limbal autograft using E-PRP can be considered as a promising alternative to ocular surface reconstruction.