Properties Of Skin Tissue Research Articles

Numerical simulation of heat transfer properties of skin tissue acted on repetitive laser irradiation

Pulsed laser has been widely used in the clinical treatment of various diseases and injuries due to its unique advantages in the process of interaction with skin tissue. In order to ensure the therapeutic effect and patient safety, it is necessary to accurately monitor the time-space response of the whole-field temperature of the target tissue irradiated by pulsed laser. A research strategy to explore the thermal response and incidental thermal damage of skin tissue induced by repeated pulses laser has been proposed in present work. A theoretical model involved variable physical properties was first proposed, in which the dual-phase lag (DPL) equation and Henrique burn equation were employed to evaluate the tissue temperature and thermal damage induced by repeated pulse laser irradiation. With the help of finite difference method, the governing equation with variable physical properties was then numerical solved to obtain the time-space distribution of tissue temperature, and the evolution process of the thermal damage was further calculated. The effects of laser input parameters and variable physical parameters on the laser penetration depth, temperature distribution and burn degree of the irradiated tissue were analyzed.

A new method for determining the ogden parameters of soft materials using indentation experiments

A full understanding of the material properties of skin tissue is crucial for exploring its tribo-mechanical behaviour. It has been widely accepted that the mechanical behaviour of skin tissue for both small and large deformations can be accurately described using a hyperelastic model, such as the one developed by Ogden. However, obtaining these Ogden parameters for in-vivo skin by in-vivo experiments no matter the indentation or suction tests is a significant challenge. The mathematical model used to describe the material behaviour during the test should consider not only the material nonlinearity but also the geometrical confinement of the tissue, the large deformations induced, and the fact that the specimens are relatively thin.A range of contact models is available to describe the contact behaviour during the indentation test. However, none of them can be used for hyperelastic materials with small thickness under large deformations. Simultaneously explaining material nonlinearity and geometric nonlinearity, either through theoretical equations or numerical calculations, poses a significant challenge.In this research, we propose a pragmatic method to obtain Ogden parameters for in-vivo skin tissue by combining experimental indentation results and numerical simulations. The indentation tests were used to obtain the force-indentation depth curves, while the numerical simulations were used to obtain the strain fields. The method assumes the material behaviour of specimens can be linearized in each small deformation increment, and the contact model developed by Hayes can be applied to accommodate each increment. Then, the linear elastic behaviour in each increment can be described by the elastic modulus E which were obtained using Hayes model, and the principal stresses in each increment were subsequently obtained using Hooke's law. By combining all stress fields, overall stress-strain curves can be constructed, from which the hyperelastic Ogden parameters can be obtained. A second numerical simulation of the hyperelastic indentation was then performed using the obtained Ogden parameters, allowing a comparison of the experimental and simulated relationships between force and indentation.

Experimental study on the effect of scanning path on skin tissue properties of femtosecond laser welding.

To study the influence pattern of femtosecond laser scanning path on the welding effect of skin tissue, this experiment analyzed the influence of scanning path on the surface morphology, degree of thermal damage, tensile strength, and microstructure of skin samples after skin attachment by designing nine scanning paths to weld skin tissue. The results showed that the skin samples connected by interrupted parallel mattress eversion sewing method with d = 0.2 mm showed no obvious color changes in morphology, the skin samples were connected on both front and back sides, the tensile strength was the highest, reaching 12.80 N/cm2 , the thermal damage parameter was low at 1.08 × 10-2 , the microstructure had obvious directionality, and the texture was clear and uniformly distributed.

Living-skin Detection using Multi-layer Skin Property Perceived by the Structured Light.

Living-skin detection has been used to prevent the attack of face fraud in a face recognition system. In this paper, we propose a new concept that exploits the multi-layer structure property of skin for living-skin detection. We observe a significant difference in the blur of the laser spot created by the structured light on the skin and non-skin due to the characteristic properties of laser photons in skin penetration and reflection. Based on this observation, we designed a new living-skin detection algorithm to differentiate skin and non-skin based on the blur detection of laser spots. The experimental results show that the proposed setup and method have a promising performance with an averaged precision of 96.7%, averaged recall of 82.2%, and averaged F1-score of 88.6% on a dataset of 20 adult subjects. This demonstrates the effectiveness of the new concept that uses multi-layer properties of skin tissues for living-skin detection, which may lead to new solutions for face anti-spoofing.

Experimental study of the effect of temperature on collagen conformational changes in skin tissue welded by femtosecond laser

In this study, in vitro skin tissues were welded using various laser settings at four temperature ranges, 30–40 °C, 40–60 °C, 60–80 °C, and > 80 °C., Raman spectra between 500 and 2000 cm−1 were examined in order to examine the relationship between the changes of collagen and the mechanical properties of skin tissue bonding and the degree of thermal damage of tissue. How collagen in skin tissues changed into disordered and less stable structures due to the thermal damage, and how the structure of protein and amino acid-related bands changed with increasing temperature were analyzed. Analysis of the deconvolution of the amide I band (1580–1720 cm−1) and the secondary structure of collagen showed that the secondary structure of collagen changed from α-like helix-dominated to β-aggregate-dominated structures due to the thermal damage. As the temperature increased, the number of protein molecule chain dissociation and reconnection within the skin tissue increased, which contributed to the improvement of the tensile strength of the skin after welding. However, when the temperature was too high, the collagen structure presented an extremely unstable state, and the degree of protein denaturation increased, causing serious thermal damage. When the skin tissue was welded using the femtosecond laser process parameters of laser power of 18 W, scanning speed of 50 mm/s, and scanning 50 times, the tensile strength of the in vitro skin tissue incision was greater and the degree of protein denaturation was less. The degree of thermal damage characterized by the degree of protein denaturation was consistent with that characterized by the microstructure texture characteristics parameters of the skin tissue.

A statistical machine learning approach linking molecular conformational changes to altered mechanical characteristics of skin due to thermal injury

This article develops statistical machine learning models to predict the mechanical properties of skin tissue subjected to thermal injury based on the Raman spectra associated with conformational changes of the molecules in the burned tissue. Ex vivo porcine skin tissue samples were exposed to controlled burn conditions at 200 °F for five different durations: (i) 10s, (ii) 20s, (iii) 30s, (iv) 40s, and (v) 50s. For each burn condition, Raman spectra of wavenumbers 500-2000 cm−1 were measured from the tissue samples, and tensile testing on the same samples yielded their material properties, including, ultimate tensile strain, ultimate tensile stress, and toughness. Partial least squares regression models were established such that the Raman spectra, describing conformational changes in the tissue, could accurately predict ultimate tensile stress, toughness, and ultimate tensile strain of the burned skin tissues with R2 values of 0.8, 0.8, and 0.7, respectively, using leave-two-out cross validation scheme. An independent assessment of the resultant models showed that amino acids, proteins & lipids, and amide III components of skin tissue significantly influence the prediction of the properties of the burned skin tissue. In contrast, amide I has a lesser but still noticeable effect. These results are consistent with similar observations found in the literature on the mechanical characterization of burned skin tissue.

Effect of preloading force on capability of laser welding for skin tissue

Laser assisted suture has become a focus in surgical suture research due to its many advantages, but the current research on the details is not deep enough. To improve the strength and quality of laser biological tissue welding and increase the success rate of penetration in the thickness direction, the effect of external restraint force on the laser tissue welding was explored, and the effect of external restraint force on the optical properties of skin tissue was analyzed. In this study, a Nd:YAG pulse laser was used to conduct welding experiments on the skin in vitro. The laser of 10 W scanned the tissue incision along a linear trajectory. The welding effects under different compression forces and stretching forces were compared. Under the effect of compression force, the skin tissue incision has improved the absorption of laser, and achieved good suture of the incision. The maximum tensile strength can reach 15.56 ± 0.61 N/cm2.The results show that the external preloading force have a significant effect on the strength of the tissue under laser welding. The optical properties of skin tissue under different forces were tested, proving that compression force changes the absorption rate of skin tissue to laser, thereby promoting the photothermal conversion efficiency and improving the welding strength. The stretching force changes the thickness of the tissue, making it easier for the laser to penetrate. At the same time, the tissue is closely attached to achieve effective contact and improve the success rate of welding. The matching combination of preloading force and laser process parameters can achieve high strength with low thermal damage.

Dielectric Characterization and Statistical Analysis of Ex-Vivo Burnt Human Skin Samples for Microwave Sensor Development

The dielectric properties of skin tissues in relation to different degrees of burn are a necessary prerequisite for designing non-invasive microwave sensing modalities. Due to the difficulties in obtaining human tissue samples, such databases are largely unavailable. To bridge the knowledge gap in this field, we attempt to create a dielectric database of various burn-degree skin samples and their statistical analysis in this work. This research is part of the European “Senseburn” project, which aims to create a non-invasive diagnostic tool that can measure the severity and depth of burns on humans in a clinical setting. In this work, several ex-vivo burnt samples were collected from the Uppsala University Hospital (Akademiska sjukhuset, Sweden). Out of that, eight samples with different degrees of burns in various human body locations were selected for the analysis. The dielectric characterization of the categorized samples was done using an Keysight N1501A dielectric open-end co-axial probe Kit. The dielectric characterization was made from 500 MHz to 10 GHz with 1001 points. The measurement was made systematically, and the clinician feedback forms were gathered and analyzed throughout the process. The measurement data followed the FASTCLUS procedure, which was initially analyzed using density plot, convergence, and cubic clustering criteria. For the statistical analysis, 11 frequency points were considered for eight samples. The results of the fundamental statistical analysis using the FASTCLUS procedure resulted in 88 data sets. Later, data sets were analyzed in sample-wise clusters. Every sample was made with two clusters, i.e., cluster 1, which consisted of healthy sectors, and cluster 2, which consisted of burnt sectors. We made the linear approximations for the sample-wise clusters and found the constant real permittivity difference. Furthermore, we found a pattern in the constant real permittivity differences of every sample that is proportional to the burn degrees. This information is needed in order to identify optimization parameters, i.e., the sensitivity with respect to dielectric difference for various burn degrees. For this purpose, extensive measurement campaigns across the microwave frequency band from 500 MHz – 10 GHz were conducted. Based on the analysis of dielectric data, each skin region of interest (ROI) has its own dielectric properties. Additionally, we developed a proof of concept non-invasive flexible microwave sensor based on the dielectric database collected from burnt ex-vivo human tissue samples. In this way, we could distinguish between phantoms with different dielectric properties in the burned human tissue sample range.

System for Non-Contact and Multispectral Examination of Blood Supply to Cutaneous Tissue

The presented system for non-contact examination of tissue perfusion is one of the tools for complex examination of human body tissues (skin, subcutaneous) and their mutual interactions, including blood flow and activity under various external stimuli. In our system, optical radiation, with wavelengths of 525 nm, 625 nm, and 940 nm, was used to investigate the perfusion and properties of skin tissue. Our work presents that it is possible to obtain comprehensive information about the cardiovascular system and skin tissue perfusion by a suitable combination of wavelengths, light intensity, and homogeneous illumination distribution with a properly chosen sensing device—a camera. The proposed system consists of an illumination device that emits light of the three wavelengths mentioned above and thus makes it possible to investigate the skin tissue structures and their interrelationships in terms of their blood supply and interactions with each other.

Isatis tinctoria L. Leaf Extract Inhibits Replicative Senescence in Dermal Fibroblasts by Regulating mTOR-NF-κB-SASP Signaling.

Senescent fibroblasts progressively deteriorate the functional properties of skin tissue. Senescent cells secrete senescence-associated secretory phenotype (SASP) factor, which causes the aging of surrounding non-senescent cells and accelerates aging in the individuals. Recent findings suggested the senomorphic targeting of the SASP regulation as a new generation of effective therapeutics. We investigated whether Isatis tinctoria L. leaf extract (ITE) inhibited senescence biomarkers p53, p21CDKN1A, and p16INK4A gene expression, and SASP secretions by inhibiting cellular senescence in the replicative senescent human dermal fibroblast (RS-HDF). ITE has been demonstrated to inhibit the secretion of SASP factors in several senomorphic types by regulating the MAPK/NF-κB pathway via its inhibitory effect on mTOR. ITE suppressed the inflammatory response by inhibiting mTOR, MAPK, and IκBα phosphorylation, and blocking the nuclear translocation of NF-κB. In addition, we observed that autophagy pathway was related to inhibitory effect of ITE on cellular senescence. From these results, we concluded that ITE can prevent and restore senescence by blocking the activation and secretion of senescence-related factors generated from RS-HDFs through mTOR-NF-κB regulation.

A New Nonlinear Photothermal Iterative Theory for Port-Wine Stain Detection.

The development of appropriate photothermal detection of skin diseases to meet complex clinical demands is an urgent challenge for the prevention and therapy of skin cancer. An extensive body of literature has ignored all high-order harmonics above the second order and their influences on low-order harmonics. In this paper, a new iterative numerical method is developed for solving the nonlinear thermal diffusion equation to improve nonlinear photothermal detection for the noninvasive assessment of the thickness of port-wine stain (PWS). First, based on the anatomical and structural properties of skin tissue of PWS, a nonlinear theoretical model for photothermal detection is established. Second, a corresponding nonlinear thermal diffusion equation is solved by using the new iterative numerical method and taking into account harmonics above the second-order and their effects on lower-order harmonics. Finally, the thickness and excitation light intensity of PWS samples are numerically simulated. The simulation results show that the numerical solution converges fasterand the physical meaning of the solution is clearerwith the new method than with the traditional perturbation method. The rate of change in each harmonic with the sample thickness for the new method is higher than that for the conventional perturbation method, suggesting that the proposed numerical method may provide greater detection sensitivity. The results of the study provide a theoretical basis for the clinical treatment of PWS.

Bio-thermo-viscoelastic behavior in multilayer skin tissue

A theoretical model for skin thermo-viscoelastic behavior is proposed based on the non-Fourier bioheat transfer theory in this article. Skin tissue is regarded as a multilayer structure composed of epidermis, dermis, and subcutis, the properties of each layer is assumed to be homogeneous and thermoviscoelasticity. Analytical solutions of temperature profile and stress distribution in skin tissue are obtained, and the influence of non-Fourier effect, viscoelastic properties of skin, blood perfusion, and time-dependent thermal boundary conditions at skin surface is considered. Numerical results show that the peak stress occurred at skin surface induced by thermal injury is much larger than mechanical threshold of pain perception. The temperature profile in skin tissue may be overestimated for the long-time hyperthermia treatment when the heat convection of blood perfusion in dermis and subcutis is neglected. The thermal stress calculated based on thermoviscoelastic model is significantly lower than that based on classical thermoelastic model due to the inherent rheological properties of skin tissue. This article may be helpful in improving the fundamental understanding of complicated thermomechanical behavior of human skin and designing of biomedical devices for hyperthermia treatment.

Robustness of diffuse reflectance spectra analysis by inverse adding doubling algorithm.

Analysing diffuse reflectance spectra to extract properties of biological tissue requires modelling of light transport within the tissue, considering its absorption, scattering, and geometrical properties. Due to the layered skin structure, skin tissue models are often divided into multiple layers with their associated optical properties. Typically, in the analysis, some model parameters defining these properties are fixed to values reported in the literature to speed up the fitting process and improve its performance. In the absence of consensus, various studies use different approaches in fixing the model parameters. This study aims to assess the effect of fixing various model parameters in the skin spectra fitting process on the accuracy and robustness of a GPU-accelerated two-layer inverse adding-doubling (IAD) algorithm. Specifically, the performance of the IAD method is determined for noiseless simulated skin spectra, simulated spectra with different levels of noise applied, and in-vivo measured reflectance spectra from hyperspectral images of human hands recorded before, during, and after the arterial occlusion. Our results suggest that fixing multiple parameters to a priori known values generally improves the robustness and accuracy of the IAD algorithm for simulated spectra. However, for in-vivo measured spectra, these values are unknown in advance and fixing optical parameters to incorrect values significantly deteriorates the overall performance. Therefore, we propose a method to improve the fitting performance by pre-estimating model parameters. Our findings could be considered in all future research involving the analysis of diffuse reflectance spectra to extract optical properties of skin tissue.

Glycerol effects on optical, weight and geometrical properties of skin tissue

Complex study of glycerol effects on the skin tissue was performed. The change in optical, weight and geometrical parameters of the rat skin under the action of the glycerol solutions was studied ex vivo. Possible mechanisms of the skin optical clearing under the action of glycerol solutions of different concentrations were discussed. The results can be helpful for refinement of models developed to evaluate the effective diffusion coefficients of glycerol in tissues.

The effect of skin tension, needle diameter and insertion velocity on the fracture properties of porcine tissue

Using metal needles to penetrate skin tissue is common in medical treatments for the delivery of medication or minimally invasive surgery. In most applications the fracture properties of skin tissue is not important as the human surgeon has full control over the needle. Given that robotically controlled surgeries and self applied medical devices have become increasingly popular, a better understanding of the fracture properties and how to mathematically model the fracture process is needed. Experiments measuring the force required to fracture porcine skin tissue were done while varying the applied skin tension, needle insertion speed and needle diameter. The applied skin tension was found to have the greatest influence on the fracture properties, while the insertion speed was found to have a negligible impact. The variance in experimental results was not well explained by the three independent variables alone, suggesting that additional parameters influence the fracture process.

Numerical investigation of skin and subcutaneous tissue thermal injury during elevated heating

SummaryThis paper presents the non‐Fourier bioheat transfer prediction methodology of human skin to determine skin burn injury with non‐ideal properties of tissue, metabolism and blood perfusion. The dual‐phase lag bioheat transfer model with the inclusion of evaporation is developed for the triple‐layer skin tissues. The developed models are solved numerically using Galerkin's finite element method. Parametric studies on the effects of skin tissue properties, initial temperature, blood perfusion rate and heat transfer parameters for the thermal response and exposure time of the layers of the skin tissue are carried out. The results of the investigation are compared with experimental results in the literature. The study demonstrates that the initial tissue temperature, the thermal conductivity of the epidermis and dermis, relaxation and thermalisation time and convective heat transfer coefficient are critical parameters to examine skin burn injury threshold. The study also shows that thermal conductivity and the blood perfusion rate exhibits negligible effects on the burn injury threshold. The objective of the present study is to support the accurate quantification and assessment of skin burn injury for reliable experimentation, design and optimisation of thermal therapy delivery.

Triple-layer Tissue Prediction for Cutaneous Skin Burn Injury: Analytical Solution and Parametric Analysis

This paper demonstrates a non-Fourier prediction methodology of triple-layer human skin tissue for determining skin burn injury with non-ideal properties of tissue, metabolism and blood perfusion. The dual-phase lag (DPL) bioheat model is employed and solved using joint integral transform (JIT) through Laplace and Fourier transforms methods. Parametric studies on the effects of skin tissue properties, initial temperature, blood perfusion rate and heat transfer parameters for the thermal response and exposure time of the layers of the skin tissue are carried out. The study demonstrates that the initial tissue temperature, the thermal conductivity of the epidermis and dermis, relaxation time, thermalisation time and convective heat transfer coefficient are critical parameters to examine skin burn injury threshold. The study also shows that thermal conductivity and the blood perfusion rate exhibits negligible effects on the burn injury threshold. The objective of the present study is to support the accurate quantification and assessment of skin burn injury for reliable experimentation, design and optimisation of thermal therapy delivery.

Silver-loaded microspheres reinforced chitosan scaffolds for skin tissue engineering

In order to improve the mechanical properties and antibacterial properties of skin tissue engineering scaffolds, a microspheres-reinforced composite construct with controlled release property was designed. The silver-loaded chitosan (CS) microspheres (Ag@CMs) were prepared by emulsified crosslinking method. Ag@CMs were introduced into CS acetic acid solution and then Ag@CMs embedded porous CS scaffolds were fabricated by lyophilization method. The results show that Ag@CMs are uniformly distributed inside porous CS scaffolds and there is no significant effect on the structure of the pores. The Ag@CMs/CS composite scaffolds possess high porosity (66.03 ± 0.15) %. The compressive strength and modulus of the composite scaffold reach up to 0.47 ± 0.03 MPa and 3.95 ± 0.06 MPa, respectively, significantly higher than pure CS scaffold. The in vitro drug delivery tests and antibacterial activity tests illustrate that composite scaffolds have efficient antibacterial properties and excellent drug sustained-release performance. MTT assay indicates that Ag@CMs/CS porous scaffold can provide an interconnected porous structure and large surface area for mouse fibroblast cell (L929) adhesion and proliferation. These results suggest that Ag@CMs/CS porous scaffold is a promising candidate for skin tissue engineering.

Role of scattering and birefringence in phase retardation revealed by locus of Stokes vector on Poincaré sphere.

.Significance: Biological tissues are typically characterized by high anisotropic scattering and may also exhibit linear form birefringence. Both scattering and birefringence bias the phase shift between transverse electric field components of polarized light. These phase alterations are associated with particular structural malformations in the tissue. In fact, the majority of polarization-based techniques are unable to distinguish the nature of the phase shift induced by birefringence or scattering of light.Aim: We explore the distinct contributions of scattering and birefringence in the phase retardation of circularly polarized light propagated in turbid tissue-like scattering medium.Approach: The circularly polarized light in frame of Stokes polarimetry approach is used for the screening of biotissue phantoms and chicken skin samples. The change of optical properties in chicken skin is accomplished by optical clearing, which reduces scattering, and mechanical stretch, which induces birefringence. The change of optical properties of skin tissue is confirmed by spectrophotometric measurements and second-harmonic generation imaging.Results: The contributions of scattering and birefringence in the phase retardation of circularly polarized light propagated in biological tissues are distinguished by the locus of the Stokes vector mapped on the Poincaré sphere. The phase retardation of circularly polarized light due to scattering alterations is assessed. The value of birefringence in chicken skin is estimated as , which agrees with alternative studies. The change of birefringence of skin tissue due to mechanical stretch in the order of is detected.Conclusions: While the polarimetric parameters on their own do not allow distinguishing the contributions of scattering and birefringence, the resultant Stokes vector trajectory on the Poincaré sphere reveals the role of scattering and birefringence in the total phase retardation. The described approach, applied independently or in combination with Mueller polarimetry, can be beneficial for the advanced characterization of various types of malformations within biological tissues.

Clinical Challenge and Call for Research on Keloid Disorder: Meeting Report from The 3rd International Keloid Research Foundation Symposium, Beijing 2019

Clinical Challenge and Call for Research on Keloid Disorder: Meeting Report from The 3rd International Keloid Research Foundation Symposium, Beijing 2019