M. Makropoulou

Biophotonic techniques for manipulation and characterization of drug delivery nanosystems in cancer therapy.

Reactive oxygen species (ROS) are usually involved in two opposite procedures related to cancer: initiation, progression and metastasis of cancer, as well as in all non-surgical therapeutic approaches for cancer, including chemotherapy, radiotherapy and photodynamic therapy. This review is concentrated in new therapeutic strategies that take advantage of increased ROS in cancer cells to enhance therapeutic activity and selectivity. Novel biophotonic techniques for manipulation and characterization of drug delivery nanosystems in cancer therapy are discussed, including optical tweezers and atomic force microscopy. This review highlights how these techniques are playing a critical role in recent and future cancer fighting applications. We can conclude that Biophotonics and nanomedicine are the future for cancer biology and disease management, possessing unique potential for early detection, accurate diagnosis, dosimetry and personalized treatment of biomedical applications targeting cancer.

PICOSECOND LASER ABLATION OF DENTINE IN ENDODONTICS

Abstract. The interaction of picosecond laser radiation with human dental tissue was investigated in this study, in order to determine the ablation rates and the surface characteristics of the dentine by using scanning electron microscopy (SEM). Dentine ablation was performed by using tooth sections of different thicknesses (0.5–2.0 mm). Dental tissue samples were irradiated in air with the fundamental wavelength and first harmonic of a regenerative amplifier Nd:YAG laser system, at 1064 nm and 532 nm, respectively, with a pulse duration of 100 ps and a pulse repetition rate of 10 Hz. The results showed very clean craters surrounded by minimum melting of the surface of dentine when the 1064 nm pulses were used. In contrast, when the first harmonic 532 nm pulses were used, the SEM examinations revealed cracks and melting of dentine with irregular surface modification. Consequently, it seems that cleaning and shaping of the root canal walls during endodontic therapy with the picosecond Nd:YAG laser application may be possible in the future. The, as yet unexplored, field of the picosecond laser interaction with hard dental tissue is expected to be a potential alternative for powerful laser processing of biomedical structures.

Picosecond and subpicosecond visible laser ablation of optically transparent polymers

Abstract The ablation rates, as a function of the laser fluence, of the optically transparent polymers, Nylon-6,6 and PMMA, are reported using picosecond and subpicosecond laser pulses, obtained from a Regenerative Amplified Nd:YAG laser system. The laser pulses had a duration of 100 ps at 1064 and 532 nm wavelengths and 0.8 ps at 595 nm. The ablation rate results indicate a strong saturation behaviour for both polymers in the investigated irradiation conditions. The material removal is 2–3 times higher in the case of the visible (532 nm) picosecond laser ablation experiments. The surface topology of the polymers was also studied. The obtained Atomic Force Microscopy images reveal no mechanical damage in the inner ablation crater wall. The qualitative analysis of the ablation mechanism for ultrashort pulse laser irradiation reveals a combination of photochemically induced direct bond dissociation and a photothermal process due to the relaxation of the excited polymers within the vibrational levels of the ground state.

Ultra-violet and Infra-red Laser Ablation Studies of Biocompatible Polymers

Polytetrafluroethylene (PTFE) and other biocompatible polymers have been extensively used for sutures, vascular grafts and bone, and other hard tissue replacements. The use of surgical lasers for intervention on teflon-tissue interfaces has attracted a great deal of interest, as both the high intensity pulsed lasers and prosthetic biomaterials are in increasing use. The study of the ablational behaviour of PTFE films with three surgical lasers (CO2, Nd-YAG and XeCl) have been undertaken for assessing the optimal laser parameters for ablation (e.g. the absorption coefficient and the relevant threshold fluence) from ablation rate measurements.

Ablation of nylon-6,6 with UV and IR lasers

Abstract In this paper we study the basic phenomenology of nylon-6,6 ablation with XeCl, CO2 and Nd:YAG lasers and quantify on its parameters. The material degradation temperature calculated for pulsed laser heating predicts melting of the polymer surface observed by scanning electron microscopy. The results obtained assist in the elucidation of the polymer degradation mechanism at 308 nm which is important for the manufacturing of plastic optical components.

Laser-Induced Fluorescence and Reflectance Spectroscopy for the Discrimination of Basal Cell Carcinoma from the Surrounding Normal Skin Tissue

The object of this study was to investigate whether laser-induced skin autofluorescence (LIF) and/or light reflectance spectra could provide a useful contrast between basal cell carcinoma (BCC) tissues and the surrounding healthy skin. Unstained human skin samples, excised from humans undergoing biopsy examination, were irradiated with a nitrogen laser (λ = 337 nm) for excitation of autofluorescence and a tungsten halogen lamp for the reflectance measurements. The ex vivo spectroscopic results were correlated with the histopathology images to distinguish the areas of BCC from those of the surrounding health skin. A simple spectral analysis technique was also applied for better skin diagnosis. In conclusion, it seems that LIF and reflectance spectra could be used to differentiate neoplastic from normal skin tissue using an appropriate classification model analysis.

Atomic force microscopy: a tool to study the structure, dynamics and stability of liposomal drug delivery systems

Much work has been done during the past few decades to develop effective drug delivery systems (DDS), many of which are based on nanotechnology science. Liposomes are the most attractive lipid vesicles for drug delivery. The multifunctional properties of liposomes have a key role in modifying the bioavailability profile of a therapeutic agent. Different analytical techniques can be used to describe liposomes, not least applied scanning probe microscopy (SPM) techniques. Atomic force microscopy (AFM) seems to be one of the most effectively applied SPM techniques. This review article outlines the applications of AFM in evaluating the physical characteristics and stability of liposomal DDSs. Other well-known microscopy techniques used in evaluating liposome physical characteristics are also mentioned, and the contribution of AFM to evaluating liposomal stability is discussed. Among the advantages of AFM in examining the physicochemical properties of liposomal DDSs is its ability to provide morphological and metrology information on liposome properties. AFM thus appears to be a promising tool in technological characterization of liposomal DDSs.

Q-switched Versus Free-running Er:YAG Laser Efficacy on the Root Canal Walls of Human Teeth: A SEM Study

Twenty-one teeth with one root canal were prepared by the step-back technique, divided into three groups, and split longitudinally. Group A served as a control. In group B, 20 to 150 pulses of 100 micros, 30 to 70 mJ per pulse at 1 to 4 Hz from a free-running Er:YAG laser were applied to the root-canal dentin. In group C, the Q-switched Er:YAG laser, with the same energy parameters and a 190-ns pulse duration was used. Scanning electron microscopy examination revealed that control specimens had debris and smear layer obscuring the dentinal tubules at all levels in the canals without crack formation. Both groups of laser-treated dentin were clean with opened dentinal tubules except around the lased area in which there was an intact smear layer. Cracks were observed in both laser groups with higher frequency in group C. In group B, craters with different depth levels at the root canal walls were produced and the energy apparently was distributed equally, because craters were well-shaped. In contrast, the ablation efficiency in group C was questionable with the parameters used in this study. Consequently, suitable parameters of the free-running Er:YAG laser must be found before its careful use as an adjunct in endodontic therapy.

Evaluation of trapping efficiency of optical tweezers by dielectrophoresis

A relatively new method for measuring optically induced forces on microparticles and cells, different from the conventional Brownian motion and viscous drag force calibration methods widely used, is introduced. It makes use of the phenomenon of dielectrophoresis for the calibration of optical tweezers through the dielectrophoretic force calculations. A pair of microelectrodes is fabricated by photolithography on a microscope slide and it is connected to a high-frequency generator. The calibration of the optical tweezers setup is performed by the manipulation of polystyrene beads and yeast cells. Calibration diagrams of the transverse forces versus power are deduced for different cell radii and numerical apertures of the objective lenses. The optical system and the related technique provide a fast and easy method for optical tweezers calibration.

In vitro fluorescence measurements and Monte Carlo simulation of laser irradiation propagation in porcine skin tissue.

In dermatology, the in vivo spectral fluorescence measurements of human skin can serve as a valuable supplement to standard non-invasive techniques for diagnosing various skin diseases. However, quantitative analysis of the fluorescence spectra is complicated by the fact that skin is a complex multi-layered and inhomogeneous organ, with varied optical properties and biophysical characteristics. In this work, we recorded, in vitro, the laser-induced fluorescence emission signals of healthy porcine skin, one of the animals, which is considered as one of the most common models for investigations related to medical diagnostics of human cutaneous tissues. Differences were observed in the form and intensity of the fluorescence signal of the porcine skin, which can be attributed to the different concentrations of the native fluorophores and the variable physical and biological conditions of the skin tissue. As the light transport in the tissue target is directly influencing the absorption and the fluorescence emission signals, we performed Monte Carlo simulation of the light distribution in a five-layer model of human skin tissue, with a pulsed ultraviolet laser beam.