Liposomes are the most attractive lipid vesicles for targeted drug delivery in nanomedicine, behaving also as cell models in biophotonics research. The characterization of the micro-mechanical properties of drug carriers is an important issue and many analytical techniques are employed, as, for example, optical tweezers and atomic force microscopy. In this work, polyol hyperbranched polymers (HBPs) have been employed along with liposomes for the preparation of new chimeric advanced drug delivery nanosystems (Chi-aDDnSs). Aliphatic polyester HBPs with three different pseudogenerations G2, G3 and G4 with 16, 32, and 64 peripheral hydroxyl groups, respectively, have been incorporated in liposomal formulation. The atomic force microscopy (AFM) technique was used for the comparative study of the morphology and the mechanical properties of Chi-aDDnSs and conventional DDnS. The effects of both the HBPs architecture and the polyesters pseudogeneration number in the stability and the stiffness of chi-aDDnSs were examined. From the force-distance curves of AFM spectroscopy, the Young’s modulus was calculated.
Commercially available intraocular lenses (IOLs) are manufactured from silicone and acrylic, both rigid (e.g. PMMA) and foldable (hydrophobic or hydrophilic acrylic biomaterials), behaving different mechanical and optical properties. Recently, the use of apodizing technology to design new diffractive–refractive multifocals improved the refractive outcome of these intraocular lenses, providing good distant and near vision. There is also a major ongoing effort to refine laser refractive surgery to correct other defects besides conventional refractive errors. Using phakic IOLs to treat high myopia potentially provides better predictability and optical quality than corneal-based refractive surgery. The aim of this work was to investigate the effect of laser ablation on IOL surface shaping, by drilling circular arrays of holes, with a homemade motorized rotation stage, and scattered holes on the polymer surface. In material science, the most popular lasers used for polymer machining are the UV lasers, and, therefore, we tried in this work the 3<sup>rd</sup> and the 5<sup>th</sup> harmonic of a Q-switched Nd:YAG laser (λ=355 nm and λ=213 nm respectively). The morphology of the ablated IOL surface was examined with a scanning electron microscope (SEM, Fei - Innova Nanoscope) at various laser parameters. Quantitative measurements were performed with a contact profilometer (Dektak-150), in which a mechanical stylus scanned across the surface of gold-coated IOLs (after SEM imaging) to measure variations in surface height and, finally, the ablation rates were also mathematically simulated for depicting the possible laser ablation mechanism(s). The experimental results and the theoretical modelling of UV laser interaction with polymeric IOLs are discussed in relation with the physical (optical, mechanical and thermal) properties of the material, in addition to laser radiation parameters (laser energy fluence, number of pulses). The qualitative aspects of laser ablation at λ=213 nm reveal a smooth optical surface on the intraocular lens with no irregularities, observed with other wavelengths.
The aim of this work is to investigate the effect of UV solid state laser radiation on intraocular lens (IOL) polymer surfaces as an alternative method to conventional surface shaping techniques for IOLs customization. Laser ablation experiments were performed on PMMA plates and commercially available hydrophobic and hydrophilic acrylic IOLs with the 5<sup>th</sup> harmonic of a Q-switched Nd:YAG laser (λ=213 nm). Circular arrays of holes were drilled on the polymer surface, covering the centre and the peripheries of the IOL. The morphology of the ablated IOL surface was examined with a conventional optical microscope (Leitz GMBH Wetzlar) and with a scanning electron microscope (SEM, Fei - Innova Nanoscope) at various laser parameters. Quantitative measurements of ablation rates were performed with a contact profilometer (Dektak-150), in which a mechanical stylus scanned across the surface of gold-coated IOLs (after SEM imaging) to measure variationsF in surface height. Laser interaction with IOLs depends on optical and mechanical material properties, in addition to laser radiation parameters. The exact ablation mechanism is discussed. Some polymer materials, depending on their properties, are more susceptible to the photothermal mechanism than the photochemical one or <i>vice versa</i>. In summary, every IOL polymer exhibits specific attributes in its interaction with the 5<sup>th</sup> harmonic of Nd:YAG laser.
The mechanical properties of cells, as well as their dysfunction, have been implicated in many aspects of human physiology and patho-physiology. Hence, new biophysical techniques, as optical tweezers, are of great importance for biomechanical measurements in both cells and cell simulators (e.g. liposomes). Liposomes are used, among other applications, as drug delivery nanosystems in cancer therapy. In this work, experimental measurements of the optical forces exerted by line optical tweezers on trapped cells (erythrocytes) and liposomes, using the dielectrophoresis method for calibration, are presented. Folding and elongation of trapped red blood cells was observed, in the direction of the electric field of incident beam, while, upon removal of the optical trap, the red blood cells were observed to unfold to their original biconcave shape. By measuring the folding and unfolding times, membrane elasticity properties such as bending modulus were estimated. Shear and bending modulus of liposomes were also estimated by measuring the liposome deformations, induced by optical forces along the beam long axis. The optical force is quasi-linearly increased with the increase of liposome diameter. In the elasticity regime, when the laser was turned off, the liposome acquired gradually its initial shape without any hysteresis.
In this work optical tweezers with elliptical beam profiles have been developed in order to examine the effect of optical
force on fresh red blood cells (RBC) in isotonic, hypertonic and hypotonic buffer solutions. Considering that the optical
force depends essentially on the cell surface and the cytoplasmic refractive index, it is obvious that biochemical
modifications associated with different states of the cell will influence its behaviour in the optical trap. Line optical
tweezers were used to manipulate simultaneously more than one red blood cell.
After we have been manipulated a RBC with an elliptical laser beam profile in an isotonic or hypertonic buffer, we
noticed that it rotates by itself when gets trapped by optical tweezers and undergoes folding. Further shape deformations
can be observed attributed to the competition between alignment and rotational torque which are transferred by laser
light to the cell. In hypotonic buffer RBCs become spherical and do not rotate or fold since the resultant force due to rays
emerging from diametrically opposite points of the cell leads to zero torque. Manipulation of fresh red blood cells in
isotonic solution by line optical tweezers leads to folding and elongation of trapped RBCs. Membrane elasticity
properties such as bending modulus can be estimated by measuring RBC's folding time in function with laser power.
The use of intraocular lenses (IOL) is the most promising method for restoring excellent vision in cataract surgery. In
addition, multifocal intraocular lenses for good distant and near vision are investigated. Several new materials,
techniques and patterns are studied for the formation and etching of intraocular lenses in order to improve their optical
properties and reduce the diffractive aberrations. As pulsed laser ablation is well established as a universal tool for
surface processing of organic polymer materials, this study was focused in using laser ablation with short and ultra short
laser pulses for surface modification of PMMA and intraocular lenses, instead of using other conventional techniques.
The main advantage of using very short laser pulses, e.g. of ns, ps or fs duration, is that heat diffusion into the polymer
material is negligible. As a result high precision patterning of the sample, without thermal damage of the surroundings,
In this study, laser ablation was performed using commercially available hydrophobic acrylic IOLs, hydrophilic acrylic
IOLs, and PMMA IOLs, with various diopters. We investigated the ablation efficiency and the phenomenology of the
etched patterns by testing the ablation rate, versus laser energy fluence, at several wavelengths and the surface
modification with atomic force microscopy (AFM), or scanning electron microscopy (SEM). The irradiated polymers
have different optical properties, at the applied wavelengths, and therefore, present different ablation behaviour and
morphology of the laser ablated crater walls and surrounding surfaces. The experimental results, some theoretical
assumptions for mathematical modeling of the relevant ablation mechanisms are discussed.
Efficient cornea reshaping by laser irradiation for correcting refractive errors is still a major issue of interest and study.
Although the excimer laser wavelength of 193 nm is generally recognized as successful in ablating corneal tissue for
myopia correction, complications in excimer refractive surgery leads to alternative laser sources and methods for efficient cornea treatment. In this work, ablation experiments of human donor cornea flaps were conducted with the 4<sup>th</sup> harmonic of an Nd:YAG laser, with different laser pulses. AFM analysis was performed for examination of the ablated cornea flap morphology and surface roughness.
In this work, ablation experiments of ex vivo porcine cornea tissue were conducted with two solid state lasers (an
Er:YAG laser and the 4th harmonic of an Nd:YAG laser, both in the ns pulse width range) emitting in mid infrared and
ultraviolet part of the spectrum respectively, at moderate laser fluences. The cornea epithelium of each porcine eye was
manually removed before the ablation. Histology analysis of the specimens was performed, in order to examine the
microscopic appearance of the ablated craters and the existence of any thermal or mechanical damage caused by the midinfrared
and the UV laser irradiation. For a detailed and complete examination of the morphology of the laser ablated
corneal tissue, the surface roughness was investigated by scanning electron microscopy.
Ablation rates measurements with free-running Er:YAG laser (λ=2.94 μm) were performed in
hydrophilic acrylic intraocular lenses. We studied the role of water in the laser ablation mechanisms by
using hydrophilic lenses with different concentrations of H<sub>2</sub>0 and D<sub>2</sub>0. A mathematical model
simulated the experimental results.
Despite the fact that the laser applications in human ophthalmology are well established, further research is still required,
for better and predictable ablation dosimetry on both cornea tissue and intraocular lenses. Further studies for alternative
laser sources to the well established excimer lasers, such as UV or mid-infrared solid state lasers, have been proposed for
refractive surgery. The precise lens ablation requires the use of laser wavelengths possessing a small optical penetration
depth in the cornea and in the synthetic lenses, in order to confine the laser energy deposition to a small volume. In order
to eliminate some very well known problems concerning the reshaping of cornea and the modification of the optical
properties of the intraocular lenses, ablation experiments of <i>ex vivo</i> porcine cornea, acrylic PMMA and hydrophilic
lenses were conducted with an Er:YAG laser (2.94 &mgr;m) and the fifth harmonic of a Nd:YAG laser (213 nm). The
morphology of cornea was recorded using a cornea topography system before and immediately after the ablation.
Histology analysis of the specimens was obtained, in order to examine the microscopic appearance of the ablated craters
and the existence of any thermal damage caused by the mid-infrared and UV laser irradiation. The macroscopic
morphology of the intraocular lens craters was inspected with an optical transmission microscope. Measurements of the
ablation rates of the lenses were performed and simulated by a mathematical model.