Photoacoustic Imaging as a Tool for Assessing Hair Follicular Organization

Hair-Reinforced Elastomer Matrix Composites: Formulation, Mechanical Testing, and Advanced Microstructural Characterization

Epoxy matrix composites reinforced with high-performance fibers, such as carbon, Kevlar, and glass, exhibit excellent specific stiffness and strength in many mechanical applications. However, these composites are disappointingly non-recyclable and are usually disposed of in landfill sites, with no realistic prospect for biodegradation in a reasonable time. In contrast, moldable composites with carbonized elastomeric matrices developed in the last decades possess attractive mechanical properties in final net-shape products and can also be incinerated or recycled. Many carbon and inorganic fillers have recently been evaluated to adjust the properties of carbonized elastomeric composites. Renewable organic fillers, such as human or animal hair, offer an attractive fibrous material with substantial potential for reinforcing composites with elastomeric matrices. Samples of unidirectional fiber composites (with hair volume fractions up to 7%) and quasi-isotropic short fiber composites (with hair volume fractions up to 20%) of human hair-reinforced nitrile butadiene rubbers (HH-NBRs) were produced in the peroxide-cured and carbonized states. The samples were characterized using scanning electron microscopy (SEM), Raman spectroscopy, and photoacoustic microscopy. Mechanical tests were performed under tension using a miniature universal testing machine. The expected effect of fiber reinforcement on the overall mechanical performance was demonstrated for both cured and carbonized composites. Considerable enhancement of the elastic modulus (up to ten times), ultimate tensile strength (up to three times), and damage tolerance was achieved. The evidence of satisfactory interfacial bonding between hair and rubber was confirmed via SEM imaging of fracture surfaces. The suitability of photoacoustic microscopy was assessed for 3D reconstructions of the fiber sub-system's spatial distribution and non-destructive testing.

Niche preclinical and clinical applications of photoacoustic imaging with endogenous contrast

In the past decade, photoacoustic (PA) imaging has attracted a great deal of popularity as an emergent diagnostic technology owing to its successful demonstration in both preclinical and clinical arenas by various academic and industrial research groups. Such steady growth of PA imaging can mainly be attributed to its salient features, including being non-ionizing, cost-effective, easily deployable, and having sufficient axial, lateral, and temporal resolutions for resolving various tissue characteristics and assessing the therapeutic efficacy. In addition, PA imaging can easily be integrated with the ultrasound imaging systems, the combination of which confers the ability to co-register and cross-reference various features in the structural, functional, and molecular imaging regimes. PA imaging relies on either an endogenous source of contrast (e.g., hemoglobin) or those of an exogenous nature such as nano-sized tunable optical absorbers or dyes that may boost imaging contrast beyond that provided by the endogenous sources. In this review, we discuss the applications of PA imaging with endogenous contrast as they pertain to clinically relevant niches, including tissue characterization, cancer diagnostics/therapies (termed as theranostics), cardiovascular applications, and surgical applications. We believe that PA imaging's role as a facile indicator of several disease-relevant states will continue to expand and evolve as it is adopted by an increasing number of research laboratories and clinics worldwide.

A fiber-coupled laser diode design for reflection mode optical resolution photoacoustic microscopy

Pulsed Laser Diodes (PLD) are compact and high pulse repetition rate laser sources that show a great potential for low-cost Optical Resolution Photoacoustic Microscopes (OR-PAM). Nevertheless, their non-uniform multimode laser beams are of low quality so that high lateral resolutions with tightly focused beams are difficult to realize at long focusing distances, as required for reflection mode OR-PAM devices of clinical application. A new strategy based on homogenizing and shaping the laser diode beam with a square-core multimode optical fiber allowed to attain competitive lateral resolutions while keeping one centimeter working distance. The theoretical expressions for the laser spot size, determining optical lateral resolution, and the depth of focus are also written for general multimode beams. An OR-PAM system was built in confocal reflection mode with a linear phased-array as the ultrasound receiver in order to test its performance, first, on a resolution test target and, afterwards, on ex vivo rabbit ears to show the system potential for subcutaneous imaging of blood vessels and hair follicles.

Photoacoustic imaging to monitor outcomes during hyperbaric oxygen therapy: validation in a small cohort and case study in a bilateral chronic ischemic wound

Hyperbaric oxygen therapy (HBO2) is a common therapeutic modality that drives oxygen into hypoxic tissue to promote healing. Here, ten patients undergoing HBO2 underwent PA oximetry of the left radial artery and forearm pre- and post-HBO2; this cohort validated the use of PA imaging in HBO2. There was a significant increase in radial artery oxygenation after HBO2 (p = 0.002) in the validation cohort. We also include a case study: a non-diabetic male in his 50s (HB 010) presenting with bilateral ischemic and gangrenous wounds. HB 010 showed higher perfusion and oxygen saturation on the right foot than the left after HBO2 which correlated with independent surgical observations. Imaging assisted with limb salvage treatment. Hence, this work shows that PA imaging can measure changes in arterial oxygen saturation due to HBO2; it can also produce 3D maps of tissue oxygenation and evaluate response to therapy during HBO2.

Semiconducting Polymer Nanoparticles with Intramolecular Motion-Induced Photothermy for Tumor Phototheranostics and Tooth Root Canal Therapy

Much effort is devoted to develop agents with superior photoacoustic/photothermal properties for improved disease diagnosis and treatment. Herein, a new fused two isoindigo (DIID)-based semiconducting conjugated polymer (named PBDT-DIID) is rationally designed and synthesized with a strong near-infrared absorption band ranging from 700 to 1000 nm. Water-dispersing nanoparticles (NPs) of PBDT-DIID are prepared with good biocompatibility and a rather high photothermal conversion efficiency (70.6%), as the active excited-state intramolecular twist around the central double bonds in DIID permits most of the absorbed excitation energy flow to heat deactivation pathway through internal conversion. The photoacoustic signal can be further magnified by incorporation of polylactide (PLA) in the NP core to confine the generated heat of PBDT-DIID within NPs. The resultant doped NPs show excellent performance in photoacoustic imaging-guided photothermal therapy in an orthotopic 4T1 breast tumor-bearing mouse model. It is also found that the photothermal effect of the PBDT-DIID NPs is safe and quite efficacious to highly improve the root canal treatment outcome by heating the 1% NaClO solution inside the root canal upon 808 nm laser irradiation in a human extracted tooth root canal infection model.

Photoacoustic monitoring of angiogenesis predicts response to therapy in healing wounds

Chronic wounds are a major health problem that cause the medical infrastructure billions of dollars every year. Chronic wounds are often difficult to heal and cause significant discomfort. Although wound specialists have numerous therapeutic modalities at their disposal, tools that could three dimensional-map wound bed physiology and guide therapy do not exist. Visual cues are the current standard but are limited to surface assessment; clinicians rely on experience to predict response to therapy. Photoacoustic (PA) ultrasound (US) is a non-invasive, hybrid imaging modality that can solve these major limitations. PA relies on the contrast generated by haemoglobin in blood which allows it to map local angiogenesis, tissue perfusion and oxygen saturation-all critical parameters for wound healing. This work evaluates the use of PA-US to monitor angiogenesis and stratify patients responding versus not-responding to therapy. We imaged 19 patients with 22 wounds once a week for at least 3 weeks. Our findings suggest that PA imaging directly visualises angiogenesis. Patients responding to therapy showed clear signs of angiogenesis and an increased rate of PA increase (p = 0.002). These responders had a significant and negative correlation between PA intensity and wound size. Hypertension was correlated to impaired angiogenesis in non-responsive patients. The rate of PA increase and hence the rate of angiogenesis was able to predict healing times within 30 days from the start of monitoring (power = 88%, alpha = 0.05). This early response detection system could help inform management and treatment strategies while improving outcomes and reducing costs.

Quantitative multilayered assessment of skin lightening by photoacoustic microscopy

BACKGROUND

With the emergence of various new skin-lightening products, there is an urgent need to scientifically evaluate the efficacy and toxicology of these products, and provide scientific guidance for their use based on physiological differences between individuals. Visualized imaging methods and quantitative evaluation criteria play key roles in evaluating the efficacy of skin-lightening products. In order to quantify the changes in the multilayered morphology and endogenous components of human skin before and after the use of lightening products, high-resolution three-dimensional (3D) imaging of human skin is required.

METHODS

In this study, photoacoustic microscopy (PAM; SSPM-532, Guangdong Photoacoustic Medical Technology Co., Ltd.) was used to capture the morphological structures of human skin and reveal skin components quantitatively. The efficacy and safety of skin-lightening products were evaluated by measuring skin melanin concentration and observing skin morphology. The melanin concentration in the epidermis was obtained by examining the linear relationship between photoacoustic (PA) signals. Further, the epidermal thickness and the melanin distribution were obtained in the cross-sectional (x-z) and lateral (x-y) images. Finally, the efficacy of skin-lightening products was evaluated according to the concentration and distribution of melanin in the epidermis, and the safety of cosmetics was assessed by observing the vascular morphology in the dermis.

RESULTS

PAM noninvasively could assess the multilayered morphological structures of human skin, which allowed for quantification of epidermal thickness and melanin concentration of different skin sites. Based on this, the efficacy and safety of skin-lightening products in multilayer structures were quantitatively evaluated.

CONCLUSIONS

As a quantitative imaging method, PAM, has the potential to accurately evaluate the use of skin-lightening products. The method can also be extended to assessments within the larger field of aesthetic medicine.

Biomedical Photoacoustic Imaging and Sensing Using Affordable Resources

The photoacoustic (PA) effect, also called the optoacoustic effect, was discovered in the 1880s by Alexander Graham Bell and has been utilized for biomedical imaging and sensing applications since the early 1990s [...].