A. Daskalova

Ultra-short laser ablation of biological tissue

The investigation of mechanism of ultra-short laser ablation process of biological tissue represents one of the challenging subjects over the last couple of years. The femtosecond laser pulses are very well suited for high precision surgery, due to its low thermal and mechanical stress. The current research was emphasized on the examination of the interaction mechanism of high intensity ultra-short femtosecond and nanosecond laser pulses with hard biological tissue material (tooth, bones). It was established that femtosecond ablation works well for ablation of complex biological molecule systems. A more detailed view was taken by investigating the ablation dynamics at several wavelengths. The precise examination of the mass spectra of laser ablation with 193 nm and 800 nm introduces the way of altering the chemical composition of the ablated tissue. In general, it was found that ablation with ultra-short (femtosecond) pulses at 800 nm radiation yields the highest number of characteristic ions. To better understand the interaction mechanism we have performed post-ionization experiments. It was of main importance to succeed to establish efficient ionization of the organic molecules with minimal fragmentation. This work demonstrates sensitivity of the time-of-flight (TOF) technique and the great potential of the laser ablation/ultra-short laser secondary neutrals mass spectroscopy (LA/US-LSNMA) method in increasing the information content of biomolecular mass spectra.

Morphological characterization of chitosan biopolymer thin films modified via fs irradiation and its potential application as functional surfaces in regenerative medicine

The creation of microporous surface modification of chitosan thin films irradiated by ultrashort laser pulses are studied. For this purpose, chitosan substrates were treated by using an amplified Ti:sapphire laser system at 800 nm central wavelength with 30 fs and 150 fs pulse duration and repetition rate 1 kHz and 50 Hz, respectively. Formation of surface modifications for both cases (30 fs and 150 fs) after femtosecond laser irradiation were observed. The threshold values for single-pulse (N = 1) and multi-pulse (N > 1) modification were evaluated by studying the linear relationship between the squared crater diameter D2 and the logarithm of the laser fluence (F) for N = 1, 2, 5, 10, 20, 30 and 50 number of laser pulses. The coefficient of incubation ξ, a major parameter in the process of surface modification and ablation of materials also was calculated for multi - pulse fluence threshold estimation by power - law relationship Fth (N) = Fth (1) Nξ-1, where N is the number of applied laser pulses. The surface properties of chitosan based thin films before and after femtosecond laser irradiation were investigated. The aim of this work is to determine the optimal morphological characteristics of the created structures for tailoring of protein adsorption and cell behavior.

Femtosecond laser micropatterning of chitosan thin films for surface functionalization

The possibility to control surface properties of materials and to tailor behaviour of cells and biomolecules are the basic requirements in the development of a new generation biomaterials for applications in tissue engineering. Surface patterning on micro and nano-scale is critical to distinguish the effects of cell shape, focal adhesion, and ligand input for cell functions. Recently, much attention has been paid to laser-assisted micro and nanofabrication technologies to pattern surfaces with different topographies for providing valuable inside on cell-substrate junction [1]. Laser modification by pulses in the femtosecond time domain, provide a quality of modification of thin films of biopolymers that is unobtainable with longer pulses in the range of nanoseconds [2].

ESEM and AFM analysis of human dentine irradiated with femtosecond laser pulses

Different approaches for painless, fast and localized laser treatment of dental hard tissue is a subject of continuing research for the scientists. Studies of dentine ablation with Er:YAG and Ho:YAG lasers have indicated several weaknesses of the surface preparation process expressed in melting, fissuring and slow material removal rates. Some modifications of these systems (Er, Cr:YSGG) were introduced in dental practice in combination with water spray in order to enhance the surface preparation by cooling the ablated region and increasing the ablation rate [1]. Applications of Ti-sapphire laser pulses with durations ≪50fs for ablation of dental tissue, followed by examination with ESEM and AFM are seldom reported in the literature [2].