Cytotoxicity Study of UV-Laser-Irradiated PLLA Surfaces Subjected to Bio-Ceramisation: A New Way towards Implant Surface Modification

In this research we subjected samples of poly(L-lactide) (PLLA) extruded film to ultraviolet (193 nm ArF excimer laser) radiation below the ablation threshold. The modified film was immersed in Simulated Body Fluid (SBF) at 37 °C for 1 day or 7 days to obtain a layer of apatite ceramic (CaP) coating on the modified PLLA surface. The samples were characterized by means of optical profilometry, which indicated an increase in average roughness (Ra) from 25 nm for the unmodified PLLA to over 580 nm for irradiated PLLA incubated in SBF for 1 day. At the same time, the water contact angle decreased from 78° for neat PLLA to 35° for irradiated PLLA incubated in SBF, which suggests its higher hydrophilicity. The obtained materials were investigated by means of cell response fibroblasts (3T3) and macrophage-like cells (RAW 264.7). Properties of the obtained composites were compared to the unmodified PLLA film as well as to the UV-laser irradiated PLLA. The activation of the PLLA surface by laser irradiation led to a distinct increase in cytotoxicity, while the treatment with SBF and the deposition of apatite ceramic had only a limited preventive effect on this harmful impact and depended on the cell type. Fibroblasts were found to have good tolerance for the irradiated and ceramic-covered PLLA, but macrophages seem to interact with the substrate leading to the release of cytotoxic products.

Investigations on Integrated Optical Interference Couplers in PMMA for Visible and Infrared Range Fabricated by “Direct Writing” Excimer Laser Radiation

Optical waveguides were generated in Polymethylmethacrylate using “direct” laser and contact mask structuring. Excimer laser radiation (248 nm) produced a local refractive index increase thereby achieving light guiding in waveguides with widths from 2 to 15 $\mu$m. The near field output images were analyzed using visible and infrared laser light. The mode fields of single mode structures were evaluated to elaborate numerically the parameters of the index profile. An index increase up to 0.01 could be achieved using laser pulses at fluences below $0.15$ ${\textrm{J/cm}^{2}}$. Thus it was possible to design interference couplers of 5 $\mu$m waveguides width for the visible (635 nm to 670 nm) as well as for the infrared range at 1550 nm. The coupling properties as a function of the waveguide separation and the wavelength is investigated and found compatible with numerical simulations for the structure design. The presented approach allows for designing and fabricating single mode couplers in an efficient and simple manner.