Comparison of optical coherence tomography angiography features in type 1 versus type 2 choroidal neovascular membranes secondary to age-related macular degeneration

Background: Optical coherence tomography angiography (OCTA) is an advanced imaging modality that provides high resolution images at the level of different retinal layers. This study aime to evaluate choroidal neovascular membranes (CNVMs) secondary to age-related macular degeneration (AMD) quantitatively and qualitatively, according to their classification, morphological features, and flow areas, using OCTA. Methods: In this descriptive, comparative, cross-sectional study, CNVMs were divided into 2 groups according to their classification as type 1 or type 2 neovascularization. Mixed CNVMs were excluded from the study. The size (mm2) and the flow area (mm2) of the CNVMs were calculated via OCTA and the presence of the perivascular halo and loop anastomoses were analyzed. The morphological appearance of the CNVMs were classified as: medusa, sea-fan, lacy-wheel, glomerular, dead tree, and mature vascular networks. Results: Of the 85 eyes assessed for eligibility, 45 eyes of 34 individuals with CNVM were enrolled in this retrospective study. Twenty-eight eyes had type 1 and 17 eyes had type 2 CNVMs. The mean size and flow area were greater in type 1 than in type 2 CNVMs (mean ± standard deviation [SD], 6.69 ± 4.54 and 3.61 ± 3.56 mm2 versus 3.04 ± 1.98 and 1.77 ± 1.62 mm2; P = 0.044 and 0.046, respectively). Among the 22 eyes with type 1 CNVMs and the 9 eyes with type 2 CNVMs, 31 eyes had exudative membranes. Among the eyes with exudative CNVMs, 22 eyes had a perivascular halo and 22 eyes had loop anastomoses; this was significantly more than in the non-exudative eyes (P = 0.042 and 0.041, respectively). The lacy-wheel (38.7%) and dead tree (71.4%) patterns were the most frequent morphological appearance of the CNVMs in the exudative and non-exudative membranes, respectively. Conclusions: OCTA provides objective documantation about CNVMs. A perivascular dark halo around CNVMs could be a criterion to define exudative membranes activity

Lasers in the manufacturing of cardiovascular metallic stents: Subtractive and additive processes with a digital tool

Laser beams can be manipulated to achieve different types of interaction mechanisms with metals allowing them to heat, melt, vaporize, or ablate them. Today's laser sources are robust, fast-addressable optoelectronic devices, easily integrated into automation systems along with sophisticated CAD/CAM solutions. Being a photonic digital tool, the laser beam is a fundamental tool for Industry 4.0 and is already widely exploited in the manufacturing of metallic stents. The conventional manufacturing method of laser cutting employs a subtractive method to cut the stent mesh on tubular feedstock. On the other hand, laser beams can be exploited to melt metallic powders to produce stent geometries in a layer-by-layer fashion. The present work provides a short state of the art review concerning the works focusing on the two laser-based manufacturing processes underlining the evolution of the laser source types and used materials. The work provides insights into the future opportunities and challenges that should be faced by the manufacturing research communities in the light of improving the biomedical device performance by exploiting the possibilities provided by the digital tool

Densification mechanism for different types of stainless steel powders in Selective Laser Melting

Selective laser melting is a powder based additive manufacturing process where the metallic powder particles are melted by a high power laser beam. Different types of stainless steel powders made by gas and water atomization were analyzed before processing, in particular regarding their particle size distributions and morphology. Particle analysis was carried out using laser diffraction technologies and digital image analysis. A suitable designed experiment has been carried out and the specimen density has been measured and linked to the properties of the powders. Eventually the possibility to reach high density specimen by adjusting process parameters is discussed

Feasibility of using bio-mimicking fish scale textures in LPBF for water drag-reducing surfaces

In this work, bio-mimicking fish scale textures are produced by LPBF and AlSi7Mg0.6 powder to reduce drag forces on nautical components. For this purpose, a surface texture inspired by the European bass skin was modelled and parametrized. Textures were applied over the external surface of purpose-designed specimens. Additive manufacturing quality of textures was assessed using focus variation microscopy to examine surface roughness as well as geometrical errors. Once the feasibility of producing the desired bio-mimicking surfaces was confirmed, the designed surface patterns were analysed in the computation fluid dynamics modelling environment. The behaviour of the surfaces was characterized in terms of drag force generated over a fixed dimension plate model. The most promising configuration was further investigated in a sensitivity analysis where variations in main stream velocity and in surface roughness are applied. Drag reduction was related to the lowering of the viscous component and was found to be in the order of 1–2%, with respect to a smooth surface, for free stream velocity of 2.5–5 m s−1 and average roughness smaller than the as-built condition. The results confirm that the modelled surfaces can be reproduced with sufficient geometrical fidelity, showing great promise for drag-reducing metallic components produced by additive manufacturing

Investigation of pulse shape characteristics on the laser ablation dynamics of TiN coatings in the ns regime

n this work, the ablation dynamics of TiN coating with a ns-pulsed fibre laser in a wide range of pulse durations were studied. Critical time instances within the pulse duration were assessed by reflected pulse analysis. Digital holography was employed to investigate the shock wave expansion dynamics within and beyond the pulse duration. The results depict that the absorption behaviour changes as a function of the pulse rise time. Moreover, planar expansion of the shock wave is observed, which is generally linked to higher machining quality and absence of excessive plasma. The results of the study are interpreted to depict the required characteristics of optimized pulse shapes in the ns-region for improved micromachining performance

Evaluation of Self-Mixing Interferometry Performance in the Measurement of Ablation Depth

This paper studies self-mixing interferometry (SMI) for measuring ablation depth during laser percussion drilling of TiAlN ceramic coating. The measurement performance of SMI was investigated in a large processing range producing blind microholes with depths below and beyond the average coating thickness. Signal characteristics of the measurement system were evaluated indicating sources of disturbance. The SMI measurements were compared with a conventional measurement device based on focus variation microscopy to evaluate the measurement error. The measurement error classes were defined, as well as defining the related error sources. The results depict that the measurement error was independent of the processing condition, hence the hole geometry and ablation rate. For 76% of cases, measurement error was below the intrinsic device resolution obtainable by simple fringe counting of half a wavelength (λ/2 = 0.393 μm)

Laser surface texturing of β-Ti alloy for orthopaedics:Effect of different wavelengths and pulse durations

In this work laser surface texturing of Ti-11.5Mo-6Zr-4.5Sn β-Ti alloy is investigated with different laser wavelengths and pulse durations. For benchmark purposes, three different industrial solid-state laser sources providing four different wavelength/pulse duration combinations were used. Within the experimented range pulse duration could be varied at 2.5 ps, 6 ns and 250 ns at 1064 nm, while 5 ns pulse duration was tested at 355 nm. The comparative analyses were carried within the process parameter ranges available to the laser sources in order to assess the quality and productivity aspects. In particular, surface roughness, wettability, and chemical composition were quantified as well as assessing the distinct surface morphologies obtained with different configurations. Process productivity was analysed for each configuration in terms of machining rate. The results exhibit a large variety of possible surface textures available to biomedical implant designers with nanometric to micrometric features and tailorable chemical and wetting properties. Moreover, the results help in understanding how the light/matter interaction changes between different pulse durations and wavelengths

Laser weldability of laser powder bed fused AlSi7Mg0.6

Laser Powder Bed Fusion (LPBF) allows to manufacture components with lightweight and near net shape suited to aerospace and aviation applications employing Al-alloys. The process is highly suited to one-of-a-kind or small batch production of small to medium sized parts. As the maturity of the process and its end-users increase, the demand for larger components becomes more relevant. The increase of part size by increasing the size of the LPBF machine inevitably increases the cost and the complexity of the employed system. Moreover, using multiple lasers in a large powder bed to produce larger parts may bring residual stresses, part deformation and a higher chance of process failure. In the light of these, the use of joining operations, in particular welding, appears as a suitable option for the production of large components via LPBF. Indeed, the process lends itself well to also producing dedicated joint edge preparations, thickness and section variation within the location of the welded joint. Amongst different processes, laser welding stands out as a viable option as it can provide narrower weld seam and heat affected zone, produce less deformation on the parts and be automated with cartesian or robotic manipulators. This work discusses the influence of different laser welding strategies on the LPBF produced AlSi7Mg0.6

Application of self-mixing interferometry for depth monitoring in the ablation of TiN coatings

Among possible monitoring techniques, self-mixing interferometry stands out as an appealing option for online ablation depth measurements. The method uses a simple laser diode, interference is detected inside the diode cavity and measured as the optical power fluctuation by the photodiode encased in the laser diode itself. This way, self-mixing interferometry combines the advantages of a high resolution point displacement measurement technique, with high compactness and easiness of operation. For a proper adaptation of self-mixing interferometry use in laser micromachining to monitor ablation depth, certain optical, electronical, and mechanical limitations need to be overcome. In laser surface texturing of thin ceramic coatings, the ablation depth control is critically important to avoid damage by substrate contamination. In this work, self-mixing interferometry was applied in the laser percussion drilling of TiN coatings. The ∼4 μm thick TiN coatings were drilled with a 1 ns green fiber laser, while the self-mixing monitoring was applied with a 785 nm laser diode. The limitations regarding the presence of process plasma are discussed. The design criteria for the monitoring device are explained. Finally, the self-mixing measurements were compared to a conventional optical measurement device. The concept was validated as the measurements were statistically the same