A comprehensive geometrical, metallurgical, and mechanical characteristic dynamic model of laser beam welding process

Abstract To study the influence pattern of femtosecond laser scanning path on the welding effect of skin tissue, this experiment analyzed the influence of scanning path on the surface morphology, degree of thermal damage, tensile strength, and microstructure of skin samples after skin attachment by designing nine scanning paths to weld skin tissue. The results showed that the skin samples connected by interrupted parallel mattress eversion sewing method with d = 0.2 mm showed no obvious color changes in morphology, the skin samples were connected on both front and back sides, the tensile strength was the highest, reaching 12.80 N/cm 2 , the thermal damage parameter was low at 1.08 × 10 −2 , the microstructure had obvious directionality, and the texture was clear and uniformly distributed. 

Experimental study on the effect of scanning path on skin tissue properties of femtosecond laser welding.

The influence of femtosecond laser parameters on the degree of thermal denaturation was studied experimentally. The relationship between the degree of thermal denaturation and the characteristic parameters of skin microstructure and the secondary structure of skin tissue proteins in characterizing the degree of thermal damage was analyzed. The results showed the interaction of laser power, laser power, and scanning speed had a significant effect on the degree of thermal denaturation; greater degrees of thermal denaturation were associated with larger second-order moments of the texture angle of the skin microtissue and smaller entropy values and contrast, indicating a greater degree of thermal damage; and higher peak temperature, the lower peak intensity of Raman spectra, decrease in the percentage area of α-helix fitted curves and increase in the percentage area of β-sheet and β-turn fitted curves indicate that the protein is denatured to a large extent that means thermal damage is large.

Effect of femtosecond laser process parameters on the thermal denaturation degree of skin tissue.

Laser-welding is a promising technique for welding NiTi shape memory alloys with acceptable tensile strength and comparable corrosion performance for biomedical applications. The microstructural characteristics and localized corrosion behavior of NiTi alloys in a simulated body fluid (SBF) environment are evaluated. A microstructural examination indicated the presence of fine and equiaxed grains with a B2 austenite phase in the base metal (BM), while the weld metal (WM) had a coarse dendritic microstructure with intermetallic precipitates including Ti2Ni and Ni4Ti3. The hardness decreased from the BM to the WM, and the average hardness for the BM was 352 ± 5 HV, while it ranged between 275 and 307 HV and 265 and 287 HV for the HAZ and WM, respectively. Uni-axial tensile tests revealed a substantial decrease in the tensile strength of NiTi WM (481 ± 19 MPa), with a reduced joint efficiency of 34%. The localized corrosion performance of NiTi BM was superior to the WM, with electrochemical test responses indicating a pitting potential and low corrosion rate in SBF environments. The corrosion rate of the NiTi BM and WM was 0.048 ± 0.0018 mils per year (mpy) and 0.41 ± 0.019 mpy, respectively. During welding, NiTi’s strength and biocompatibility properties changed due to the alteration in microstructure and formation of intermetallic phases as a result of Ti enrichment. The performance and safety of welded medical devices may be impacted during welding, and it is essential to preserve the biocompatibility of NiTi components for biomedical applications. 

Microstructure, Mechanical Properties and Corrosion Performance of Laser-Welded NiTi Shape Memory Alloy in Simulated Body Fluid

Laser skin tissue welding has the advantages of shallow scar and fast recovery due to the use of laser energy to suture skin tissue, and has great application potential in the field of beauty and biomedicine. However, the faster the recovery speed after surgery, the smaller the degree and scope of protein denaturation required, and the suture strength cannot be guaranteed, which makes it difficult to achieve both strength and recovery speed at the same time. Therefore, a laser targeted suture method based on energy regulation is proposed. This method can accurately control the region and extent of protein denaturation, and achieve the highest strength suture under the minimum protein denaturation. In addition, the directional fusion of collagen reticular tissue was achieved by regulating the micro morphology of denatured collagen tissue during the suturing process, and the suture samples meeting the requirements were successfully obtained. The microstructure observation and mechanical property test of the adjusted suture sample showed that the re melted collagen fiber tissue was reticular distribution, similar to the original tissue structure, with good mechanical properties, and the tensile strength reached 41.6 ± 2.5 N/cm2. This makes this method have a great potential application prospect in biological tissue welding application scenarios. 

Microstructure evolution of laser skin tissue welding under the control of energy regulation

Effect of preloading force on capability of laser welding for skin tissue

Abstract. The portable laser is indispensable for handheld laser-induced breakdown spectroscopy (LIBS) instruments. We developed a passive, Q-switched pulsed, Nd:YAG laser system with small size and low cost. The maximum pulse energy of the laser was 10 mJ and the pulse duration was <2  ns. The peak power was >5  MW. The laser exhibited very high stability without any cooling system and its relative standard deviation of the pulse energy was <0.2  %  . The laser was also used as a light source of LIBS to measure the concentrations of Cr, Cu, Mn, and Ni in alloys. The experimental results show that the determination coefficient of the calibration curves for these four elements is all better than 0.99. For its shorter pulse duration, the laser can decrease the plasma shield effect to improve the coupling of laser pulse and the target and stability of spectra intensity. The portable laser developed is a good laser source for handheld LIBS instruments.

Portable nanosecond laser for handheld laser-induced breakdown spectroscopy instruments

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Effect of preloading force on capability of laser welding for skin tissue

Portable nanosecond laser for handheld laser-induced breakdown spectroscopy instruments