The capability to image the 3D distribution of melanin in human skin in vivo with absolute quantities and microscopic details will not only enable noninvasive histopathological diagnosis of melanin-related cutaneous disorders, but also make long term treatment assessment possible. In this paper, we demonstrate clinical in vivo imaging of the melanin distribution in human skin with absolute quantities on mass density and with microscopic details by using label-free third-harmonic-generation (THG) enhancement-ratio microscopy. As the dominant absorber in skin, melanin provides the strongest THG nonlinearity in human skin due to resonance enhancement. We show that the THG-enhancement-ratio (erTHG) parameter can be calibrated in vivo and can indicate the melanin mass density. With an unprecedented clinical imaging resolution, our study revealed erTHG-microscopy's unique capability for long-term treatment assessment and direct clinical observation of melanin's micro-distribution to shed light into the unknown pathway and regulation mechanism of melanosome transfer and translocation.

The use of biomaterial carriers to improve the therapeutic efficacy of stem cells is known to augment cell delivery, retention, and viability. However, the way that carrier clearance kinetics boosts stem cell delivery and impacts stem cell function remains poorly characterized. In this study, we designed a platform to simultaneously quantify carrier clearance and stem cell retention to evaluate the impact of carrier clearance kinetics on stem cell retention. Additionally, a murine model of hindlimb ischemia was employed to investigate the effects of various cell retention profiles on mitigating peripheral arterial disease. To image the in vivo behaviors of material and cells, we used biotinylated hyaluronan with fluorescently labeled streptavidin and Discosoma sp. Red (Ds-Red)-expressing human mesenchymal stem cells. We found that the retention of transplanted stem cells was closely related to the remaining biomaterial. Furthermore, therapeutic effectiveness was also affected by stem cell retention. These results demonstrate that low-molecular-weight hyaluronan had a slow clearance and high cell retention profile, improving the therapeutic efficacy of human stem cells.

The development of solar lentigines (SLs) is related to chronic ultraviolet exposure-induced cell senescence. We have previously demonstrated that basal keratinocyte enlargement is a morphological hallmark of skin senescence correlated to the process of skin aging, while clinical studies on the long-term monitoring of the cellular morphological changes in SLs after laser treatment are lacking. In this study, we have developed the harmonic generation microscopy (HGM) for in vivo monitoring the height of basal keratinocytes (HBK) and had administered Q-switched ruby laser or picosecond 532-nm Nd:YAG laser treatment on each side of the face of 25 Asian patients with facial SLs, respectively. In vivo HGM imaging was conducted to longitudinally analyze HBK and the horizontal cell size (HCS). Before treatment, the HBK was significantly higher in the SLs lesional area than that in the adjacent normal region, whereas there was no significant difference in the HCS. After treatment, the lesional HBK remained significantly higher than normal skin regardless of the laser treatment used. Our study indicates that the basal keratinocytes remain abnormal after laser treatment and demonstrates the capability of in vivo HGM for longitudinal, quantitative monitoring of cell senescence and therapeutic effect in SLs.

Background: Nanosecond quality-switched ruby laser (QSRL) and frequencydoubled 532-nm picosecond Nd:YAG laser (532-nm picosecond Nd: YAG laser [PSNYL]) are well-documented treatments for solar lentigines (SLs). However, no studies have longitudinally tracked the microscopic findings before and after QSRL and 532-nm PSNYL treatment for SL removal.Objectives: To compare the clinical efficacy and dynamic histological changes between QSRL and 532-nm PSNYL in the treatment of SLs in Asian patients.Method: Twenty-five patients with SLs on both sides of the face were enrolled in this prospective split-face study. QSRL and 532-nm PSNYL therapy for SLs on the left and right side of the face, respectively, were performed for each subject. All subjects underwent baseline and follow-up assessment at Weeks 3 and 6. In vivo harmonic generation microscopy (HGM) imaging was adopted for the noninvasive observation of melanin mass density of basal cells (MMD basal cell ), epidermal melanocyte dendricity, and dermal melanophages before and after laser treatment.Results: At Week 6, 60% of the lesions treated with QSRL and 68% with 532-nm PSNYL had over 75% improvement. Histologically, both lasers resulted in statistically significant decrease of MMD basal cell in SLs to the level of that in the normal skin at Weeks 3 and 6. Statistically significant increase of dermal melanophages was observed 3 weeks after both laser treatments.Nevertheless, 532-nm PSNYL led to faster clearance of melanophages than QSRL at Week 6. Moreover, activated melanocytes with enhanced dendrite formation was significantly increased till 6 weeks after both laser treatments. Conclusion:Both QSRL and 532-nm PSNYL were effective treatments for SLs, and there was no statistically significant difference in clinical scoring. However,

Background and Objectives By creating microinjuries usually confined to the epidermis, a fractional picosecond 1064‐nm Nd:YAG laser that delivers an array of highly focused beamlets can be effectively used for facial rejuvenation or resurfacing. However, the mechanism of dermal remodeling underlying this nonablative treatment remains unclear. Methods Five participants having skin phototype III−IV were recruited for intervention using a fractional picosecond 1064‐nm Nd:YAG laser system equipped with a holographic diffractive beam‐splitting optic. The laser‐induced histopathological changes on human skin were examined in vivo using a harmonic generation microscopy (HGM), visualizing second harmonic generation (SHG), and third harmonic generation (THG) contrasts dichromatically. SHG refers for collagen distribution, while THG represents for epidermal components in the HGM signal. Results Histological hematoxylin and eosin staining and in vivo HGM imaging studies revealed the presence of epidermal vacuoles below the stratum granulosum along with keratinocyte degeneration or cytolysis. In addition to the epidermal vacuoles, HGM imaging exclusively demonstrated laser‐induced shock wave propagation arranged as a THG‐bright concentric pattern in the epidermis and loss of SHG signals in the papillary dermis immediately beneath the epidermal vacuoles. Conclusions Alongside generating epidermal vacuoles, the fractional picosecond 1064‐nm Nd:YAG laser induced collagen changes. These collagen changes may lead to dermal remodeling and neocollagenesis underlying the fractional picosecond laser treatment.