Frequency-dependent skin penetration depth of terahertz radiation determined by water sorption-desorption

The role of photobiomodulation in accelerating bone repair

Bone repair is faced with obstacles such as slow repair rates and limited bone regeneration capacity. Delayed healing even nonunion could occur in bone defects, influencing the life quality of patients severely. Photobiomodulation (PBM) utilizes different light sources to derive beneficial therapeutic effects with the advantage of being non-invasive and painless, providing a promising strategy for accelerating bone repair. In this review, we summarize the parameters, mechanisms, and effects of PBM regulating bone repair, and further conclude the current clinical application of PBM devices in bone repair. The wavelength of 635-980 nm, the output power of 40-100 mW, and the energy density of less than 100 J/cm2 are the most commonly used parameters. New technologies, including needle systems and biocompatible and implantable optical fibers, offer references to realize an efficient and safe strategy for bone repair. Further research is required to establish the reliability of outcomes from in vivo and in vitro studies and to standardize clinical trial protocols.

A Comparative Study on the Viability of Normal and Cancerous Cells upon Irradiation with a Steady Beam of THz Rays

Terahertz (THz) electromagnetic radiation is commonly used in astronomy, security screening, imaging, and biomedicine, among other applications. Such approach has raised the question of the influence of THz irradiation on biological objects, especially the human body. However, the results obtained to date are quite controversial. Therefore, we performed a comparative study on the viability of normal cells and cancer cells upon irradiation with a steady beam of THz rays. We used human peripheral blood mononuclear cells and cancer cell lines. Primary human mononuclear blood cells (monocytes, and B-, and T-cells) showed an increased death rate, determined by cell counting and fluorescence microscopy, upon 0.14 THz irradiation. The effect of THz radiation was different among malignant cells of B- and T-cell origin (Ramos and Jurkat cells) and epithelial cancer cells (MCF7 and LNCaP). This was demonstrated by cell counting and by the alamarBlue assay. In conclusion, THz radiation can result in the death of human primary and malignant cells. However, the mechanism of this phenomenon is largely unknown. Hence, more work should be done to shed some light on the mechanism of action of THz irradiation in living organisms to enhance technologic developments.

Transcriptome profiling of guinea pig skin exposed to a high-power terahertz source

Terahertz (THz) radiation has a wide range of applications including use in medicine. However, effects of high‐power THz radiation have not been clearly elucidated. We used a 2.52 THz self‐made optically pumped gas THz laser, the low‐ and high‐energy group, to irradiate the backs of Hartley guinea pigs. RNA‐sequencing was done to explore global transcriptional responses in the irradiated skin. Gene Ontology analysis revealed that differentially expressed genes (DEGs) between the unexposed and low‐energy exposed groups were associated with skin development, skin barrier establishment, and multicellular organismal water homeostasis or water loss regulation via the skin. On the other hand, comparison between the unexposed and high‐energy exposed groups showed that the DEGs mediated monocarboxylic acid metabolism, blood vessel morphogenesis, establishment of skin barrier, blood vessel development, or angiogenesis. Our analyses demonstrate the potential effects of high‐power THz source on the skin and sets the basis for further studies on the safety and application of the high‐power THz in dermatology.

A New Microwave Sensor Based on the Moore Fractal Structure to Detect Water Content in Crude Oil

This paper presents a microwave sensor based on a two-ports network for liquid characterizations. The proposed sensor is constructed as a miniaturized microwave resonator based on Moore fractal geometry of the 4th iteration. The T-resonator is combined with the proposed structure to increase the sensor quality factor. The proposed sensor occupies an area of 50 × 50 × 1.6 mm³ printed on an FR4 substrate. Analytically, a theoretical study is conducted to explain the proposed sensor operation. The proposed sensor was fabricated and experimentally tested for validation. Later, two pans were printed on the sensor to hold the Sample Under Test (SUT) of crude oil. The frequency resonance of the proposed structure before loading SUT was found to be 0.8 GHz. After printing the pans, a 150 MHz frequency shift was accrued to the first resonance. The sensing part was accomplished by monitoring the S-parameters in terms of S₁₂ regarding the water concentration change in the crude oil samples. Therefore, 10 different samples with different water percentages were introduced to the proposed sensor to be tested for detecting the water content. Finally, the measurements of the proposed process were found to agree very well with their relative simulated results.

Spectroscopy of excised skin patches exposed to THz and far-IR radiation

Applications of far infrared (Far-IR) and terahertz (THz) radiation in areas such as healthcare and security are fast-growing. As a consequence, humans and the environment are becoming more exposed to mm-wave and Far-IR radiation than previously. We examined typical skin-care and sunscreen ingredients and propitiatory products with transmission FTIR, ATR-FTIR and THz-time domain spectroscopy (THz-TDS) methods using fresh and dehydrated toad and fresh human skin samples for their absorption properties in these frequency ranges. The skin hydration compounds glycerol and sorbitol have comparable absorption characteristics to physiological bulk water. Products containing these and similar hydrating compounds have significant Far-IR absorption characteristics. The sunscreen ingredients ZnO (20 micron), TiO2 (mesh 325), and graphene platelet demonstrate a generally poor Far-IR absorbance, with TiO2 displaying some frequency-specific absorption in the 3-6 THz and 12 THz regions. The Far-IR absorbance of proprietary sunscreens was, however, shown not to be significant. The absorption properties of melanin, collagen, bound water, and other constituents are significant in dehydrated skin samples but are not of the same order of importance as the hydrating agents examined.

The AC conductivity of human sweat ducts as the dominant factor in the sub-THz reflection coefficient of skin

The helical nature of human sweat ducts, combined with the morphological and dielectric properties of skin, suggests electromagnetic activity in the sub-THz frequency band. A detailed electromagnetic simulation model of the skin, with embedded sweat ducts, was created. The model includes realistic dielectric properties based on the measured water content of each layer of skin, derived from Raman Spectroscopy. The model was verified by comparing it to measurements of the reflection coefficient of the palms of 13 volunteers in the frequency band 350-410 GHz. They were subjected to a measurement protocol intended to induce mental stress, thereby also activating the sweat glands. The Galvanic Skin Response was concurrently measured. Using the simulation model the optimal ac-conductivity for each measurement was found. The range of variation for all subjects was found to be from 100 S/m to a maximum value of 6000 S/m with averages of 1000 S/m. These are one order of magnitude increase from the accepted values for water at these frequencies (~100 s/m at 100 GHz). Considering the known biochemical mechanism for inducing perspiration, we conclude that these ac-conductivity levels are probably valid, even though the real time measurements of sweat ac-conductivity levels inside the duct are inaccessible.

Continuous monitoring of deep-tissue haemodynamics with stretchable ultrasonic phased arrays

Stretchable wearable devices for the continuous monitoring of physiological signals from deep tissues are constrained by the depth of signal penetration and by difficulties in resolving signals from specific tissues. Here, we report the development and testing of a prototype skin-conformal ultrasonic phased array for the monitoring of haemodynamic signals from tissues up to 14 cm beneath the skin. The device allows for active focusing and steering of ultrasound beams over a range of incident angles so as to target regions of interest. In healthy volunteers, we show that the phased array can be used to monitor Doppler spectra from cardiac tissues, record central blood flow waveforms and estimate cerebral blood supply in real time. Stretchable and conformal skin-worn ultrasonic phased arrays may open up opportunities for wearable diagnostics.

Terahertz radiation and the skin: a review

SIGNIFICANCE

Terahertz (THz) radiation has demonstrated a great potential in biomedical applications over the past three decades, mainly due to its non-invasive and label-free nature. Among all biological specimens, skin tissue is an optimal sample for the application of THz-based methods because it allows for overcoming some intrinsic limitations of the technique, such as a small penetration depth (0.1 to 0.3 mm for the skin, on average).

AIM

We summarize the modern research results achieved when THz technology was applied to the skin, considering applications in both imaging/detection and treatment/modulation of the skin constituents.

APPROACH

We perform a review of literature and analyze the recent research achievements in THz applications for skin diagnosis and investigation.

RESULTS

The reviewed results demonstrate the possibilities of THz spectroscopy and imaging, both pulsed and continuous, for diagnosis of skin melanoma and non-melanoma cancer, dysplasia, scars, and diabetic condition, mainly based on the analysis of THz optical properties. The possibility of modulating cell activity and treatment of various diseases by THz-wave exposure is shown as well.

CONCLUSIONS

The rapid development of THz technologies and the obtained research results for skin tissue highlight the potential of THz waves as a research and therapeutic instrument. The perspectives on the use of THz radiation are related to both non-invasive diagnostics and stimulation and control of different processes in a living skin tissue for regeneration and cancer treatment.