<p>Mesenchymal stem cells (MSCs) represent a significant interest for cell therapy applications and, being primary cells, undergo gradual aging in culture. We studied the effects of low-intensity infrared laser irradiation during aging of MSCs in culture. Both young and aged MSCs respond to low irradiation doses (0.17 J / cm<sup>2</sup>) by growth activation and to middle doses (2.1 J / cm<sup>2</sup>) by growth retardation. Aged cells demonstrate a relatively higher growth response to low doses, but they are significantly more susceptible to deleterious effects of middle doses compared to young cells. Studies of MSC aging during long-term culture under hypoxia conditions demonstrate that low-dose irradiation of MSCs every 2 days in culture substantially increases the number of population doublings, compared to the control group. In addition, irradiated cells persisted in culture for two passages (4 days) longer than their control counterparts. However, irradiated cells did not proliferate more rapidly if irradiation was omitted. We conclude that growth responses of young and aged murine MSCs to infrared laser irradiation differ significantly and that regular irradiation affects MSC aging in culture but does not result in a bonafide retardation of aging process.</p>
The bleaching of polyacrylamide tattooed skin-mimicking phantoms by a series of laser pulses in a single session is studied. It is shown that compared to the single-pulse procedures tattoo removal by series of laser pulses allows not only for reducing the necessary laser fluence, but also for improving the degree of bleaching. The dynamics of formation and dissolution of microscopic gas bubbles in tattooed skin phantoms exposed to laser radiation is also studied. A laser-induced tattoo bleaching mechanism is suggested, based on the process of selective photo-thermolysis of pigmented particles in conditions where the thermal conductivity of the medium surrounding the particles is decreased because of the microbubbles formed therein.
Light field intensity distribution in three-dimensional polylactide scaffolds after irradiation with low-intensity light from one side of the samples has been determined in the visible and near-infrared regions of the spectrum. Two different types of scaffolds manufactured by the methods of supercritical fluid foaming and surface selective laser sintering have been investigated. The problem is solved by numerical calculation according to the Monte Carlo method involving experimentally obtained information about effective optical parameters of the scaffold material. Information about intensity distribution of the incident light in the matrix volume is needed to assess the radiation level for the scaffold cells after photobiostimulation. It has been shown that the formation of the light field in case of strongly scattering media, such as polylactide scaffolds, is determined by anisotropy g and the scattering coefficient μs.