Microfabrication of polymer microneedle arrays using two-photon polymerization.

Three dimensional (3D) printing technology has pushed state-of-the-art manufacturing towards more advanced processing methods through its ability to produce complex computer-designed 3D structures in a wide range of materials. Two-photon polymerization applied to the fabrication of ultraprecise 3D microstructures is one of the various innovative approaches to cutting-edge 3D printing. The integration of an ultrashort pulsed laser source and an appropriate photoresist has made it an attractive candidate for advanced photonics and biomedical applications. This paper presents the development of 3D solid microneedle arrays as a novel transdermal drug delivery system via two-photon polymerization in a single manufacturing step. Through a series of experiments, the best fabrication parameters are identified. Finite element simulations are then performed to investigate the interaction between a single microneedle and human skin. The results of this study highlight the influence of fabrication parameters such as laser power, scanning speed, hatch distance and layer height on the structural resolution and fabrication time of microneedles, as well as human skin deformation caused through application of force to a single polymer microneedle.

Nanosecond pulsed fiber laser irradiation for enhanced zirconia crown adhesion: Morphological, chemical, thermal and mechanical analysis.

The increasing demand for aesthetics, together with advancements in technology, have contributed to the rise in popularity of all-ceramic restorations. In the last two decades, the continuous progression in ceramic materials science for dental applications has permitted the fabrication of high-strength materials. Amongst these, zirconia-based ceramics have improved in terms of fracture resistance and long-term viability in comparison with other silica-based materials. Unfortunately, while bonding of resin cement-silica ceramics can be strengthened through creation of a porous surface by applying hydrofluoric acid (5%-9.5%) and a subsequent silane coupling agent, the glass-free polycrystalline microstructure of zirconia ceramics does not allow such a reaction. The aim of the present in vitro study was to observe the effect of 1070 nm fiber nanosecond pulse laser irradiation on zirconia samples through morphological analysis (profilometry, SEM), thermal recording with Fiber Bragg Gratings (FBGs), elemental composition analysis (EDX) and bond strength testing (mechanical tests) in order to evaluate the possible advantages of this kind of treatment on zirconia surfaces, as well as to show the potential side effects and changes in chemical composition. Despite laser irradiation with a 1070 nm wavelength fiber laser and correct process parameters demonstrating suitable outcomes in terms of improved surface roughness and minimal thermal damage, comparison between irradiated and unirradiated samples did not exhibit statistically significant differences in terms of bonding strength.

Towards Laser-Textured Antibacterial Surfaces.

Escherichia coli and Staphylococcus aureus bacterial retention on mirror-polished and ultrashort pulse laser-textured surfaces is quantified with a new approach based on ISO standards for measurement of antibacterial performance. It is shown that both wettability and surface morphology influence antibacterial behavior, with neither superhydrophobicity nor low surface roughness alone sufficient for reducing initial retention of either tested cell type. Surface structures comprising spikes, laser-induced periodic surface structures (LIPSS) and nano-pillars are produced with 1030 nm wavelength 350 fs laser pulses of energy 19.1 µJ, 1.01 µJ and 1.46 µJ, respectively. SEM analysis, optical profilometry, shear force microscopy and wettability analysis reveal surface structures with peak separations of 20-40 µm, 0.5-0.9 µm and 0.8-1.3 µm, average areal surface roughness of 8.6 µm, 90 nm and 60 nm and static water contact angles of 160°, 119° and 140°, respectively. E. coli retention is highest for mirror-polished specimens and spikes whose characteristic dimensions are much larger than the cell size. S. aureus retention is instead found to be inhibited under the same conditions due to low surface roughness for mirror-polished samples (Sa: 30 nm) and low wettability for spikes. LIPSS and nano-pillars are found to reduce E. coli retention by 99.8% and 99.2%, respectively, and S. aureus retention by 84.7% and 79.9% in terms of viable colony forming units after two hours of immersion in bacterial broth due to both low wettability and fine surface features that limit the number of available attachment points. The ability to tailor both wettability and surface morphology via ultrashort pulsed laser processing confirms this approach as an important tool for producing the next generation of antibacterial surfaces.