Efficient and high-throughput ablation of platinum using high-repetition rate radially and azimuthally polarized sub-picosecond laser pulses.

A highly productive ablation process of 100 nm thick platinum films with a processed area rate of up to 378 cm2/min is presented using radially and azimuthally polarized laser beams. This was achieved by developing a laser amplifier generating 757 fs long laser pulses at a maximum average power of 390 W and a repetition rate of 10.6 MHz with adjustable polarization states, i.e., linear, radial, and azimuthal polarization on the work piece. The pulse train emitted from the laser was synchronized to a custom-designed polygon scanner and directed into an application machine.

The Impact of Ultrashort Pulse Laser Structuring of Metals on In-Vitro Cell Adhesion of Keratinocytes.

Besides the need for biomaterial surface modification to improve cellular attachment, laser-structuring is favorable for designing a new surface topography for external bone fixator pins or implants. The principle of this study was to observe how bioinspired (deer antler) laser-induced nano-microstructures influenced the adhesion and growth of skin cells. The goal was to create pins that allow the skin to attach to the biomaterial surface in a bacteria-proof manner. Therefore, typical fixator metals, steel, and titanium alloy were structured using ultrashort laser pulses, which resulted in periodical nano- and microstructures. Surface characteristics were investigated using a laser scanning microscope and static water contact angle measurements. In vitro studies with human HaCaT keratinocytes focused on cell adhesion, morphology, actin formation, and growth within 7 days. The study showed that surface functionalization influenced cell attachment, spreading, and proliferation. Micro-dimple clusters on polished bulk metals (DC20) will not hinder viability. Still, they will not promote the initial adhesion and spreading of HaCaTs. In contrast, additional nanostructuring with laser-induced periodic surface structures (LIPSS) promotes cell behavior. DC20 + LIPSS induced enhanced cell attachment with well-spread cell morphology. Thus, the bioinspired structures exhibited a benefit in initial cell adhesion. Laser surface functionalization opens up new possibilities for structuring, and is relevant to developing bioactive implants in regenerative medicine.

Study of the tribological properties of surface structures using ultrashort laser pulses to reduce wear in endoprosthetics.

BACKGROUND: Loosening of prostheses and functional disorders represent a far-reaching problem in the clinic, and the long-term outcomes are essentially determined by wear. Despite all advances, up to 10% of prostheses still fail after 10 years. In particular, more active patients show increased revision rates. METHODS: The objective of this thesis is to examine whether the applied microstructures of the articulating surfaces can lead to a reduction in abrasion. Three different structural geometries (dimples, offset lines, grid lines) were defined. In an experimental test setup according to DIN ISO 6474 (Deutsches Institut für Normung, International Organization for Standardization), a tribological test of metal and ceramic pairings was performed using two-dimensional ring-on-disc (RoD) tests. RESULTS: In both material groups, the structuring had a positive effect on the wear behaviour. In the ceramic group, an abrasion reduction of 22.6% was achieved. However, it is important to take into account the limited informative value due to the hardness of the material. Two of the three Cobalt-Chrome-Molybdenum (CoCrMo) structure geometries (grids, offset lines) also showed a significant reduction in abrasion compared to the reference group, with a maximum wear reduction of 55.5%. CONCLUSION: By reducing abrasion, surface structuring could be used to extend the life of prostheses and minimise the number of revisions.