Additive manufacturing technology is a special processing technology that has developed rapidly in the past 30 years. The materials used are divided into powder and wire. Additive manufacturing technology using wire as the material has the advantages of high deposition rate, uniform composition, and high density. It has received increasingly more attention, especially for the high efficiency and rapid prototyping of large-size and complex-shaped components. Wire arc additive manufacturing has its unique advantages. The concept, connotation, and development history of arc additive manufacturing technology in foreign countries are reviewed, and the current research status of arc-based metal additive manufacturing technology is reviewed from the principles, development history, process, and practical application of arc additive manufacturing technology. It focuses on the forming system, forming material, residual stress and pores, and other defect controls of the technology, as well as the current methods of mechanical properties and process quality improvement, and the development prospects of arc additive manufacturing technology are prospected. The results show that the related research work of wire arc additive manufacturing technology is still mainly focused on the experimental research stage and has yet not gone deep into the exploration of the forming mechanism. The research work in this field should be more in-depth and systematic from the physical process of forming the molten pool system from the perspectives of stability, the organization evolution law, and performance optimization. We strive to carry out wire arc additive forming technology and theoretical research to promote the application of this technology in modern manufacturing. Additive manufacturing (AM) technology is based on the discrete-stacking principle, which uses the method of stacking materials layer by layer to manufacture the required parts. Compared with traditional equivalent material manufacturing  technology and subtractive manufacturing  technology, additive manufacturing technology focuses on computer control of the manufacturing process and refines the manufacturing process to any part. Any point in the location is a revolutionary breakthrough in manufacturing. Additive manufacturing technology can effectively reduce processes and shorten the production cycle of products. For products with complex shapes and high raw material value, the fast and efficient production and processing characteristics of additive manufacturing technology are particularly obvious. In the fields of biomedicine and aerospace, additive manufacturing technology has shown very broad prospects.Wire arc additive manufacturing (WAAM) technology uses electric arcs as a heat source to melt the welding wire, adopts the principle of layer-by-layer cladding under program control, and is an advanced digital manufacturing technology that gradually forms a line-surface-body based on a three-dimensional digital model. The advantages of low technical cost, high production efficiency, and simple equipment have become an important means to realize economic and rapid prototyping of metal parts. The formed parts are composed of full welds, with flexible forming and uniform chemical composition. However, because the WAAM process is carried out in a high-temperature liquid metal transition-forming method, there are problems such as the accumulation of heat input and difficulty in controlling the shape and boundary. These problems seriously restrict the surface quality, dimensional accuracy, and mechanical properties of WAAM parts.This article expounds the domestic and foreign research and application status of WAAM technology from several major perspectives such as the control of defects such as the forming system, forming material, residual stress and pores, as well as mechanical properties and process quality improvement. Finally, research on WAAM technology is carried out. Looking forward, an overview of the current domestic and foreign WAAM technology research is shown in WAAM adopts the heat source of gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), or plasma arc welding (PAW). It uses the principle of layer-by-layer deposition, and through the addition of wire, the welding wire is melted layer by layer. The 3D products produced by the upper surfacing welding process is shown in The gas metal arc welding (GMAW) additive manufacturing technology uses metal welding wire as the melting electrode under shielding gas, and generates an arc between the welding wire and the weldment to melt the welding wire into the molten pool for rapid forming. GMAW additive manufacturing is shown in Xiong et al. proposed a laser vision-based system to observe the surface morphology of one side of a multi-layer single-channel thin-walled low-carbon-steel workpiece formed by GMAW additive manufacturing technology, and established a corresponding evaluation method to quantify the surface roughness, which is used to study the influence of process parameters on the side surface roughness of thin-walled parts .In order to prove the feasibility of using fusion welding for rapid prototyping, Ribeiro and others combined CAD software and GMAW technology to “print” an all-metal vase, proposed the welding parameters needed for rapid prototyping using a welding robot, and designed a set robot rapid prototyping system ,12.Zhang et al. addressed the problem that the height difference between the arc starting end and the arc extinguishing end gradually increased with the increase in the number of stacked layers during GMAW additive forming, and proposed the arc starting end, the arc extinguishing end, and the droplet transition. The method control measures and the comparison before and after technical improvement are shown in Gas tungsten arc welding (GTAW) additive manufacturing technology is similar to GMAW technology. The difference is that the electrodes of GTAW technology are made of tungsten with a high melting point, so it is also called tungsten inert gas protection (TIG) welding. Compared with GMAW, GTAW technology has a lower energy input, is not easy to splash, and has a more stable structure and better forming effect. Therefore, this technology has been widely used in precision manufacturing fields such as aerospace. The principle of typical GTAW surfacing welding is shown in Ouyang et al. manufactured 5356 aluminum alloy parts through variable-polarity GTAW additive manufacturing technology. The study found that the key to improving the forming quality of parts is to control the arc length and substrate preheating temperature: Preheat the substrate to 118 °C, adjust the arc current during the deposition process, and monitor the arc length, which effectively improves the wettability and deformation tendency of the deposited layer . SubsequMa et al. used a combination of the GTAW process and in-situ alloying method for additive manufacturing of titanium aluminide alloys, and studied the effect of interlayer temperature on forming parts. The test results showed that with the change in interlayer temperature, there was no obvious change in microstructure and tissue composition .Plasma arc welding (PAW) is a fusion welding method that uses a plasma arc high-energy-density beam as a welding heat source. Compared with TIG welding, PAW welding has the advantages of concentrated arc energy, good arc stiffness, and high arc stability, but the equipment is more complicated and consumes a lot of gas. According to the mode of operation and the speed of plasma gas flow, PAW welding can be divided into: Micro-beam plasma arc welding, plasma arc welding, and pierce-through-plasma arc welding. Micro-plasma arc welding has high energy density, low heat input, and high weld forming accuracy, so it is especially suitable for precision repair of titanium alloy products.Zhen established an additive manufacturing system based on micro-plasma arc surfacing and studied the additive manufacturing process of Ti-6Al-4V titanium alloy. After surfacing ten layers, it was found that the internal grains of the micro-plasma arc surfacing layer were the coarse columnar crystal morphology, its growth direction was perpendicular to the welding direction, the inside of the crystal grain was a mesh basket structure, and the obvious layered morphology could be observed between each layer .Jhavar, S. used the micro-beam plasma arc fuse process to replace the laser additive manufacturing process to produce small parts, and obtained a more regular and smooth weld bead shape. The wall thickness could reach 2.45 mm when processing straight walls, and the maximum deposition rate was 42 g/h. There were no cracks, pores, or inclusions between the deposited layers; the comparison found that the micro-plasma arc process had a smaller heat input and could deposit smaller columnar crystals per unit length. Therefore, he pointed out that the production structure is simple for small parts, and the micro-plasma arc fuse additive technology is suitable .Pulse plasma arc welding has high energy density and high stiffness. The pulse technology further improves the controllability of the heat source. Kaibo used the orthogonal test method to study the peak current, pulse frequency, duty cycle, welding speed, and wire feeding speed. The influence law of weld bead size, and the establishment of a calculation model for the height between layers of thin-walled remanufactured parts, can further improve the dimensional accuracy of formed parts .Welding robots are one of the most commonly used industrial robots, widely used in the fields of automobiles, electronics, and manufacturing. The use of welding robots can achieve precise control of motion parameters and motion trajectories, and solve the complex problem of arc additive structure trajectory control. Therefore, welding robots have been attracting increasingly more attention by researchers. The robot WAAM platform is mainly composed of welding robots, welding machines, collaborative control systems, control cabinets, and welding workbenches, as shown in Many research institutions are currently conducting research on robotic WAAM technology. The main types of robotic welding platforms are shown in It can be seen from According to the different heat sources used, additive manufacturing technology is mainly divided into laser additive manufacturing technology, electron beam additive manufacturing technology, arc additive manufacturing technology, and metal solid phase additive technology. Among them, the arc additive manufacturing technology is a new technology first proposed by German scientists. The technology uses metal welding wire as the raw material, adopts the method of submerged arc welding, stacks the melted materials layer by layer according to the pre-designed path, and finally solidifies molding to form large-size parts.As early as 1925, the American Baker et al. used the arc as the heat source to produce “3D-printed” metal decorative objects through the layer-by-layer deposition of metal droplets. In the 1970s, German scholars first proposed the concept of using metal welding wire as raw material to manufacture large-size metal parts by submerged arc welding. Ujiie et al. used SAW, TIG, etc. as heat sources and used different kinds of welding wires to form a pressure vessel whose outer wall was a gradient material. In 1983, German Kussmaul et al. used submerged arc welding to pile up layer by layer to manufacture large-size cylindrical thick-walled stainless steel metal containers with a total weight of 79 ton and a deposition rate of 80 kg/h, and the formed material had a high tensile strength, yield strength, and toughness. In the 1990s, the UK launched two major studies that accelerated the development of WAAM technology. One was where Ribeiro et al. described in detail the process of “rapid prototyping technology based on metal materials”; the other was where Spencer et al. fixed the GMAW welding torch to a six-axis robot, and then proceeded with the rapid manufacturing of parts. In addition, Zhang et al. also published similar work and provided a process method for manufacturing vertical wall and rotating parts. In 1993, Prinz and Weiss et al. installed welding equipment on CNC milling machines, called Shaped Metal Deposition (SMD), and applied for related patents. From 1994 to 1999, the Welding Engineering Research Centre of Cranfield University (Cranfield University) developed the forming deposition manufacturing technology (SMD) for the British aircraft engine company Rolls Royce. Instead of traditional casting technology, the performance of titanium alloys, high-temperature alloys, aluminum alloys, and other materials formed by this technology had been studied and evaluated. In 2007, Clayfield University carried out research work on WAAM technology and applied the technology to the rapid manufacturing of aircraft fuselage structures.The arc additive manufacturing technology adopts the traditional MIG welding method, which is characterized by high heat input. During the forming process, the output heat source repeatedly moves on the newly generated and formed parts, which increases the heat accumulation and makes the material during the stacking process, and a series of problems such as splashing and formation of multiple air holes will occur.High-frequency-pulse TIG welding should give full play to the characteristics of high-frequency arcs and take into account the requirements of no noise. We recommend that the current pulse frequency adopts a rectangular wave of 20 kHz . ExperimA device for generating a transverse rotating magnetic field is designed to control the rotation speed of the rotating magnetic field and the amplitude of the magnetic induction by adjusting the frequency of the low-frequency carrier wave and the duty ratio of the high-frequency amplitude modulation wave; the device is applied to TIG welding, combined with theoretical analysis. In addition, the test method reveals the movement mechanism of the TIG welding arc under the action of the transverse rotating magnetic field; the results show that the TIG welding arc regularly performs alternating rotating and offset movements under the action of the transverse rotating magnetic field, and the arc’s radius of rotation and rotation speed are always changing .Based on the GTAW (gas tungsten arc welding) power supply, the super-audio DC pulsed square wave current with di/dt ≥ 50 A/μs output pulse current is used in the 0Cr18Ni9Ti austenitic stainless steel GTAW welding process, research and analysis of welding arc characteristics, and arc force and weld penetration characteristics. The results show that the parameters of the ultra-audio DC pulse square wave current have a significant impact on the electrical characteristics, shape, and arc force. Compared with the conventional DC GTAW, the fast-changing ultra-audio DC pulse GTAW arc exhibits a significant contraction effect and weld penetration. In a certain range, the melting width decreases, the average arc force increases greatly, and the welding efficiency increases.In order to realize the precise control of the forming and formation of thin-walled metal in additive manufacturing, based on the movement of charged particles under the action of a DC magnetic field, the arc behavior under the action of an external DC magnetic field was studied, as well as the arc deflection degree, deflection direction, and additional relationship between magnetic fields. On the basis of arc deflection, the causes of weld morphology and weld grain changes are analyzed. The results show that the arc deflection occurs under the action of an external DC magnetic field, the degree of arc deflection increases with magnetic field strength within the range of the test parameters, and the direction of arc deflection is related to the direction of the external magnetic field. When a positive DC magnetic field is applied, the molten pool is backward in the welding direction offset, the weld reinforcement is relatively increased, and the weld grains are refined compared with no external magnetic field. When the reverse DC magnetic field is applied, the molten pool is located under the arc, the weld reinforcement is relatively reduced, and the weld grains are more refined than the external magnetic field refinement. The external DC magnetic field controls the shape of the weld, which has a “shape control” effect; the external DC magnetic field has an obvious grain refinement effect, which can achieve the purpose of “control.”The effect of the external magnetic field is one of the effective ways to affect the arc additive forming process and the performance of formed parts. In order to study the effect of the applied longitudinal steady-state magnetic field on the surface quality and mechanical properties of low-carbon-steel arc additive forming parts, a GMAW-based longitudinal steady-state magnetic field-assisted arc additive forming device was built, using morphology analysis, metallographic observation, and performance testing . The metTitanium alloy workpieces have low density, high specific strength, and good corrosion resistance, and have been widely used in aerospace, new energy, and other fields. However, the traditional processing methods are complex, inefficient, and costly, so the processing of titanium alloy workpieces is more suitable for use in additive manufacturing.Wang and Baufeld et al. found that the mechanical properties of WAAM titanium alloy molded parts parallel to and perpendicular to the deposition direction are anisotropic. The reason is that the primary β phase is epitaxially grown throughout the sample, resulting in the microstructure and performance in all directions. Wang et al. ,25 summaFencheng and others from Nanchang Hangkong University found in the arc deposition test of Ti-6Al-4V-molded parts that the microstructure of the molded parts was dominated by coarse columnar crystals grown epitaxially along the substrate, composed of α and β phases. The morphology of the α phase varied with the change in the forming position. In the upper part of the forming part, there was a thick needle-like Widmanstatten structure; in the middle part, there was a coarsened lamellar mesh basket; and in the lower part, there was a needle-like + Lamellar mixed structure. The hardness of the molded part was larger near the surface of the workpiece; the tensile properties showed obvious anisotropy, the tensile strength along the welding horizontal direction was higher than the strength along the deposition height direction, and the plasticity was the opposite .It can be found that the inhomogeneity of the composition of the different regions of the microstructure of the WAAM titanium alloy moldings and the resulting anisotropy of the mechanical properties are the main reasons why its application is currently limited. Research has found that optimizing the forming process parameters and heat treatment can effectively improve the overall uniformity of the formed parts, weaken the anisotropy, and improve the comprehensive mechanical properties of the formed parts.Jianjun et al. found in the preparation test of Ti-6Al-4V thin-walled parts that as the heat input of each weld pass during the deposition process decreased, the average yield strength (YS), tensile strength (UTS), elongation, and growth rate increased significantly . Ping etIn summary, it can be seen that in the process of arc surfacing welding Ti-6Al-4V molded parts, the increase in welding current and the decrease in welding speed will lead to an increase in the level of heat input, which promotes the growth of structure grains, resulting an increase in material strength. The level of mechanical properties such as plasticity and plasticity is reduced. It may also form a cluster structure and cause obvious anisotropy of molded parts. By appropriately reducing the current, increasing the welding speed, and extending the cooling time between layers, the grain size can be significantly refined, the cluster structure can be effectively eliminated, and the comprehensive mechanical properties of the material can be improved. At the same time, suitable heat treatments such as solution treatment, quenching, annealing, and other post-treatments have a certain effect on refining the grain size and reducing the anisotropy of the material. In short, follow-up research in this area includes how to suppress the formation of undesirable structures inside the molded parts in the arc additive preparation of titanium alloys, effectively control the evolution of grains and microstructures during the layer-by-layer accumulation process, reduce anisotropy, and improve the comprehensive mechanical properties of parts .Aluminum alloy-forming materials have a series of advantages such as good fracture toughness, high specific strength, low density, and good corrosion resistance. They have become the preferred materials commonly used in arc additive manufacturing. At present, the main reason that hinders the wide application of WAAM-forming aluminum alloy components is composition segregation, pore defects, and discontinuities between the deposited layer and the bonding layer structure during the forming process.Jiuyang et al. studied the 4043 aluminum alloy surfacing-forming parts and found that the slender columnar crystals in the structure continuously grew through the interlayer, the dendrite structure was obvious, there was a large amount of Al-Si eutectic structures in the dendrite gap, and the composition was seriously segregated . When stHongxuan et al. studied the effect of solution aging treatment on the mechanical properties of 6063 aluminum alloy and found that with the increase in solution treatment temperature, the dendrites in the alloy decreased, the composition distribution tended to be uniform, and the degree of supersaturation of the solid solution increased, which is beneficial to the mechanical properties. During the subsequent aging treatment, more strengthening phases were precipitated to increase the strength of the alloy. The morphology obtained by solution treatment at 525 °C for 4 h and aging treatment at 210 °C for 6 h was most ideal. While the solution treatment temperature continued to increase to 540 °C, it would cause coarse grains and even over-sintering, resulting in a decrease in the overall properties of the alloy . Gu et aIn summary, it can be seen that the size of each phase in the structure of the arc surfacing aluminum alloy-forming part shows a coarsening trend with the increase in heat input, and the mechanical properties such as material strength and plasticity decrease. Therefore, reducing the heat input level, such as increasing the welding speed, wire feeding speed, and the waiting time between layers, or appropriately reducing the welding current, can refine the grain of the molded part and improve the mechanical properties of the material. In addition, suitable post-treatment processes such as solution aging treatment and complete annealing can also improve the structure of the molded part to varying degrees to achieve the purpose of improving the mechanical properties.Stainless steel materials have high strength, good ductility, and good corrosion resistance, and the deposited layer structure and mechanical properties are relatively stable. In actual production, the forming method of multi-layer and multi-layer continuous accumulation can be adopted. Many experimental studies have found that by changing the welding current, welding speed, and other surfacing process parameters and proper post-weld heat treatment, the microstructure and mechanical properties of stainless steel arc-formed parts have a certain improvement.Fencheng et al. discovered during the surfacing welding of 316 L stainless steel samples that the liquid metal was mainly dissipated through the substrate during the cooling and solidification process, and the heat was mainly dissipated downward perpendicular to the substrate. The direction of heat flow was perpendicular to the interface, and the solidification was directional, thus causing the structure to present the form of columnar crystals growing from bottom to top . Zhixi aIt can be found that the change in welding process parameters has an obvious influence on the microstructure and mechanical properties of stainless steel arc-forming parts. To a certain extent, the reduction in welding current and the increase in welding speed will lead to the refinement of the structure of the formed part, the reduction in dendrite length and spacing, and the increase in ferrite content. Therefore, the mechanical properties show a tendency to decrease in hardness and increase in strength and plasticity. In addition, proper heat treatment and other post-treatment methods can also improve the structure and performance of stainless steel-molded parts.Yadollahi et al. found that the homogenization heat treatment at 1150 °C for 2 h caused the 316 L stainless steel-molded parts to coarsen the grains, increase the large-angle grain boundaries, and reduce the delta ferrite. The structure after heat treatment was almost all austenite, and the anisotropy was eliminated, the yield strength of the molded parts decreased by 17%, the tensile strength decreased by 5%, the elongation after fracture increased by 26%, and the plasticity was significantly enhanced . Wang etNumerous studies have shown that the heat input and the resulting accumulation of repeated thermal cycles have the most obvious impact on the structure and performance of the stainless steel-deposited layer. Generally, the lower part of the molded part has undergone repeated thermal cycles to present an equiaxed morphology, and the upper part has not undergone repeated heating. It is cycle and present typical weld structure. As a result, the microstructures of the upper, middle, and lower parts of the molded part show a large difference, resulting in a gradient distribution of the overall structure and properties.Based on relevant research results at home and abroad, the research team analyzed the solidification mechanism of 309 L austenitic stainless steel and 5356 aluminum alloy using TIG welding (TIG) as the heat source, and discussed the relationship between the structure formation characteristics and mechanical properties of different parts. The layer-by-layer cladding forming characteristics of arc additive lead to the characteristics of alternate layers of bonding and deposition in the microstructure of the molded parts, which is often related to the evolution of the mechanical properties of the molded parts. Based on TIG surfacing welding of 309 L austenitic stainless steel-forming parts, the research team analyzed the evolution of the microstructure and mechanical properties of 309L stainless steel during arc additive forming. The test results showed that the matrix of the surfacing sample was austenite, and there are residual dendrites of ferrite.2, and in good shape. The range of technical parameters and organizational characteristics were unique, and qualified neck flange parts were manufactured by arc additive. Almeida et al. conducted an arc additive manufacturing test of a single wall structure of Ti-6Al-4V material.Bin et al. studied the shielding gas suitable for 316 L wire arc additive and the formability of 316 L welding wire under different welding parameters, and determined that the shielding gas suitable for 316 L arc additive was 98%Ar + 2%OOguzhan used pulse-current GTAW additive manufacturing to manufacture stainless steel parts, using AISI 308 L Si stainless steel welding wire. In the study, the influence of pulse frequency and other deposition process parameters on the morphology and microstructure characteristics of additive manufacturing components was compared.Dan et al. studied the 5A06 aluminum alloy GTA-AM process, and chose φ 1.2 mm 5A06 aluminum alloy welding wire as the forming material, using the TIG AC mode welding machine as the power source, and the four-axis linkage numerical control mechanism as the motion actuator. It is single-layer single-pass substrate preheating temperature and arc peak current process specification criteria.Martin used ER4043 welding wire as the raw material and used the arc additive method to develop a large cone-shaped cylinder with a height of about 380 mm. Bombardier used arc additive technology to directly manufacture large aircraft ribs on large flat plates. They were about 2.5 m long and about 1.2 m wide.Although there are many advantages of WAAM, there are still some defects in WAAM manufacturing that need attention and resolution.In the WAAM process, the heat input is large, the temperature field distribution of the workpiece is complex, and the residual stress generated during the additive process seriously restricts the quality of the formed part. At present, the residual stress of additive components is mainly reduced by changing the additive method, optimizing the additive path, and performing pre-weld preheating, interlayer cooling, and post-weld heat treatment.Longwei et al. summarized the causes of residual stress in the WAAM process. One is due to the uneven temperature field distribution and inconsistent cooling and solidification, and the other is due to the local phase transformation of the metal to produce phase transformation residual stress . Szost eStomatal defects are one of the main defects of metal additive manufacturing, seriously affecting the quality of manufactured parts. Effective control or even elimination of stomatal defects is the key technology to improve additive manufacturing parts.Cold metal transfer (CMT) is one of the most attractive additive methods in the manufacturing of metal electrode arc additives. It combines droplet transfer with wire drawing technology. During droplet transfer, the arc is extinguished and the welding current is almost zero, which greatly reduces the welding heat input and improves the deposition rate. Cong et al. first studied and found that increasing the flow of pure argon shielding gas can effectively reduce the generation of pores in aluminum alloy additive manufacturing, and then statistically classified the pore diameters under four different CMT  processes. The results showed that most of the pore diameters were 10–50 μm. Compared with the other three modes, the traditional CMT mode produced the most pores, with some pores exceeding 100 μm in diameter. The CMT + P process significantly reduced the number of pores and the size of the pores, the CMT + ADV process further reduced the number of pores, and the CMT + PADV process almost eliminated the stomata. Lei used the double pulse arc as the heat source to explore the effects of low frequency and arc characteristics on the pore defects and mechanical properties of high-strength Al-Mg aluminum alloy additive manufacturing. The results showed that careful removal of impurities such as oil on the surface of the base metal and wire could reduce the pore nucleation rate from the source. The use of strong and weak pulse period changes to reduce the crystallization rate was beneficial to the escape of hydrogen during the additive process .These defects include high porosity, high residual stress and deformation, cracking, and anisotropic mechanical properties. These are the challenges faced by the wide application of WAAM. Some common defects will be briefly introduced below.The cracks in WAAM are mainly divided into solidification cracks and liquefaction cracks. The former mainly depends on the material properties, usually because the deposited layer is hindered during the solidification process or caused by high strain in the molten pool. The latter is mainly distributed in the mushy zone or partly melted zone, and part of it during the solidification of the component. The melting zone will be affected by the shrinking force due to the shrinkage of the deposited layer, which may cause liquefaction cracks. Especially in WAAM’s dissimilar metal manufacturing, cracks are more likely to occur due to different material properties.The heat input of the arc is higher, and the size of the molten pool and heat-affected zone during the WAAM-forming process is larger. As the surfacing process proceeds, the thermal history of each layer is different. Therefore, studying the crystallographic characteristics and periodicity of formed parts is the basis for controlling WAAM-formed parts.The Wang Kehong team of Nanjing University of Science and Technology used the HVS1000-Z microhardness tester to measure the hardness value along the center line of the weld along the center line of the weld with the increase in the cladding height and the hardness value at different width positions at the same height when the load was 0.3 kg. As shown in The Xue Jiaxiang team of South China University of Technology compared the two WAAM processes of high-speed arc welding and high-speed cold pressure welding. The two types of microstructures are shown in Xianghui et al. studied the microstructure of additive parts by changing the wire feeding speed, as shown in The Feng Yuehai team from Nanjing University of Science and Technology used single-wire and double-wire TIG welding processes to manufacture straight-wall specimens, as shown in The research team of Dalian University of Technology analyzed the influence of laser power on the tensile properties of aluminum alloy additive parts. The result is shown in The Wang Kehong team of Nanjing University of Science and Technology studied the mechanical properties of the specimens by increasing the composition of helium in the protective gas. The tensile strength results of the specimens under different protective gas compositions are shown in The Feng Yuehai team from Nanjing University of Science and Technology used single-wire and double-wire TIG welding processes to manufacture straight-wall specimens, as shown in The research team of Dalian University of Technology analyzed the influence of laser power on the tensile properties of aluminum alloy additive parts. The result is shown in The Wang Kehong team of Nanjing University of Science and Technology studied the mechanical properties of the specimen by increasing the composition of helium in the protective gas. The results of sample elongation under different protective gas compositions are shown in It can be seen from the above research that currently focusing on the properties of WAAM specimens, researchers have studied the microstructure, hardness, and tensile fracture morphology, and explored the influence of different processes on the mechanical properties of arc additive components. In view of the complexity of WAAM technology and materials, this direction still needs more in-depth research.Heat treatment is another strengthening method widely used in WAAM. Heat treatment can effectively reduce residual stress and enhance the mechanical properties of components. However, there are different heat treatment processes for different materials or additive processes, and different heat treatment processes will greatly change the internal structure characteristics and precipitate phases, thereby significantly affecting the structure and performance. Gu  exploredIn 2012, German scholar Brandl  used a lIn 2014, domestic scholars Liu et al.  exploredIn 2013, domestic scholars Xu et al.  studied Cold rolling, as a plastic processing technology, applies large pressure on the metal surface by rollers to cause large plastic deformation of the material. The rolling deformation can break the coarse columnar crystal structure, significantly increasing the hardness and strength of the deposited layer, and accumulating a large amount of deformation in the material. During the arc deposition of the next layer, when the heat of the arc deposition reaches the recrystallization temperature of the material, it will induce the recrystallization process of the material and refine the crystal grains, thereby improving the mechanical properties of the material and improving the anisotropy. As rolling deformation can produce a greater deformation force than ultrasonic impact, Cranfield University researchers introduced cold rolling deformation into the arc additive process to achieve arc deposition and cold rolling. The rolling composite manufacturing principle is as follows, shown in The cold rolling process adopted by Cranfield University is to apply cold rolling deformation to the deposited layer after the arc deposits a layer and when the temperature of the deposited layer drops to room temperature. The rolling force is controlled by a hydraulic pressing device to achieve different pressures. Colegrove et al. and Donoghue et al. studied the influence of the cold rolling process and different rolling forces on β grain refinement and the texture of TC4 titanium alloy. As the rolling pressure increases, the grain refinement effect increases and the texture heterogeneity decreases ,75. MartIn 2012, German scholar Brandl  used theIn 2010, domestic scholar Wang et al.  studied In 2016, Australian scholar Ma et al.  used arcUltrasonic impact is a plastic forming and strengthening process. In ultrasonic impact, the ultrasonic transducer and horn transmit the high-frequency vibration of the ultrasonic generator to the surface of the workpiece through the impact tool head, forming a plastic deformation layer on the surface of the workpiece. The plastic deformation caused by high-frequency impact can effectively break the coarse columnar crystals formed during the arc additive process to form fine equiaxed crystal structures, thereby improving the mechanical properties and uniformity of materials. In addition, the impact will form a residual compressive stress layer on the surface of the material, which can significantly reduce the harmful residual tensile stress introduced by the arc additive process, and at the same time reduce the warpage and deformation of the parts after the arc additive manufacturing and the internal microscopic void defects.Zhi et al. studied the influence of ultrasonic shock on the mechanical properties of arc-added titanium alloy parts. As shown in Donoghue et al. studied the effect of ultrasonic shock on the microstructure of arc-added TC4 titanium alloy, and found that ultrasonic shock can break coarse columnar crystals and form fine equiaxed crystal structures. However, even in each layer of arc increase, after applying ultrasonic shock to the material, there were still some unbroken columnar crystal structures. From the above analysis, different impact energies and impact times have a significant impact on the microstructure of the metal.(1)WAAM complex component manufacturing based on offline programming;(2)Monitoring and forming control of WAAM process;(3)The influence of different process methods and process parameters on the macroscopic and microstructure properties of additive parts and the optimization of process parameters.Although WAAM technology is widely used, it has problems such as a difficult-to-control precision of the formed parts and poor organization performance. In recent years, domestic and foreign scholars’ research on WAAM technology has mainly focused on the following directions:Compared with traditional additive processing technology, WAAM technology has more prominent technical advantages and application prospects, and will be applied in more fields. WAAM trajectory planning and optimization, arc additive composition monitoring, WAAM process optimization and forming control, and other issues will be the focus of attention in the future.This paper analyzes and summarizes the current research status of arc additive manufacturing technology, and has a comprehensive and systematic understanding of the current research and development status of this technology field. This summary can provide a guiding direction for the subsequent research on arc additive manufacturing technology. Moreover, at this stage, my country’s manufacturing industry is developing rapidly, and the requirements for manufacturing efficiency and product quality are getting higher and higher. In this context of development, the exploration and use of emerging manufacturing technologies are particularly important. It is believed that arc additive manufacturing technology will be fully promoted and applied in the future manufacturing industry by virtue of its high efficiency and automation advantages.


This study aims to explore the relationship between race/ethnicity and length of stay in hospice care among adults over 65 years of age in the United States. This topic is understudied within a population-representative sample, particularly among non-White decedents.Secondary analysis of data from the 2007 NHHCS . Race/ethnicity included Hispanics/Latinos, Non-Hispanic Whites, African Americans, and other races. Length of hospice stay was measured by the number of days that patients received hospice care from hospice agencies.The study found that African Americans have a longer length of stay in hospice agencies than Whites, even after controlling for all other factors in the model. Female gender, older age, and several diseases are covariates that significantly impact length of hospice stay.Compared to other races/ethnicities, the long length of stay in hospice among African Americans may negatively impact the quality of end-of-life care and quantity of skilled staff visits. Future research is recommended to further explore potential consequences of longer hospice stays, especially within African American communities. Studies with larger samples of minorities that integrate socioeconomic factors need to be done to better study the relationship between length of hospice stay and race/ethnicity.


Periodontal disease (PD) is one of the most common oral conditions affecting both youths and adults. There are some research works suggesting a high incidence of PD in pregnant women. As an inflammatory disease of bacterial origin, PD may result in the activation of the pathways affecting the course and the pregnancy outcome. The authors, based on the literature review, try to answer the PICO question: Does maternal periodontitis (exposure) influence the incidence of complications rates in pregnancy and the development of systemic diseases in childhood and adult offspring (outcome) in the humans of any race (population) compared to the offspring of mothers with healthy periodontium (comparison)? The authors try to describe the molecular pathways and mechanisms of these interdependencies. There is some evidence that maternal periodontitis may affect the pregnancy course and outcome, resulting in preeclampsia, preterm delivery, vulvovaginitis and low birth weight. It can be suggested that maternal periodontitis may affect offspring epigenome and result in some health consequences in their adult life. The findings show that oral conditions remain a substantial population health challenge affecting 3.9 billion people at the beginning of the second decade of 21st century. The global burden of oral conditions has been shifting from severe tooth loss in recent decades toward severe periodontitis and untreated caries. Severe periodontitis and untreated caries in deciduous teeth were the 6th and 10th most prevalent oral conditions, affecting, respectively, 11% and 9% of the global population . Another investigated the level of interleukins during 2/3 trimester, and after delivery [NCT03449186]. The NCT01812083 study analyzed the polymorphism of the IL-1, receptor antagonist gene and adverse pregnancy outcomes in the Turkish population. It is known that active PD may stimulate the production of proinflammatory cytokines (mediated by T and B cells) and the activation of osteolytic pathways, which influence many systemic diseases ,160,161.Moreover, another clinical trial tried to assess the impact of periodontal condition on low birth delivery incidence  or preeclampsia . The NCT00893802, NCT01549587, and NCT00097656 studies prospectively investigated the impact of PD treatment on pregnant adverse events, whereas in the NCT00490165 study, a retrospective analysis was conducted. Currently, the correlation of PD with the incidence of adverse pregnancy events seems to be certain. However, the published meta-analyses faced the problem of important confounders and biased results ,164. NewThe NCT04315532 trial evaluated the impact of periodontal treatment on estrogen and dehydroepiandrosterone (DHEA) levels, whereas the NCT01422122 study assessed the role of vitamin D supplementation. It was shown that DHEA levels correlated with PD severity . Non-surAlthough we presented many pieces of evidence supporting the role of epigenetics in PD and pregnancy outcomes, there is a lack of clinical trials analyzing both conditions and epigenetic changes in the one model. Studies like this should be conducted in the future. As Kajiya et al. declared, future research should lead to the development of new preventive and therapeutic strategies, in order to make the outcome of patients with PD better .The literature review presented above indicated the existence of significant relationships between the occurrence of PD in mothers, and the appearance of epigenetically programmed general diseases in their offspring. These processes are schematically shown in Periodontitis is a complex disease. Previous epidemiologic and experimental studies have shown that it may also impact several systemic diseases, whereas periodontal treatment leads to an improvement of glycaemic control in patients with type 2 diabetes , and met


Zhou and Zhao), nutritional sciences to maternal and infant health . Various modern analytical techniques, including mass spectrometry (MS), nuclear magnetic resonance (NMR) spectroscopy, and high-throughput 16S rRNA gene sequencing, have been applied to these studies, along with comprehensive data analysis and multi-omics integration. With a mix of review article and original research papers, we expect this special issue can provide evidence-based discoveries to many readers who are working in or plan to enter this area of research.It is now well recognized that the gut microbial communities living in or on the human body are key determinants of human health and diseases . The higSillner et al. first investigated the time-dependent feeding effects on the fecal metabolome of 42 healthy infants who were either exclusively breastfed, or received infant formula with/without supplement of Bifidobacterial mix, then compared the feeding type-dependent metabolic changes over a period of 24 months . They reported that despite various metabolites such as short chain fatty acids (SCFAs), amino acids and their catabolites, human milk oligosaccharides, monosaccharides, purine degradation products and plant-based metabolites from soy-based formula can be sensitively detected, the variations of fecal metabolome overtime could be attributed to many factors from amount of food, maternal diet of breastfed children, digestion status and sampling time. However, it is clear that increased fatty acids in breastfed children reflected fatty acid composition of breast milk, and human milk oligosaccharides (HMOs) were very characteristic for the fecal metabolome of breastfed infants; while the stool metabolome of formula-fed infants was dominated by Maillard reaction products such as N-deoxyfructosylleucylisoleucine. Furthermore, microbial metabolites 4-hydroxyphenyllactic and indolelactic acid were significantly increased in fecal samples of breastfed infants compared to the formula-fed infants in the first year. Meanwhile, several secondary bile acids  were detected with significantly higher concentrations in formula-fed children. Overall, this study revealed the feeding-type dependent differences of microbial metabolism, while time and individual variabilities also play major roles in shaping the gut microbial metabolome in the studied infants. Similarly, Conta et al. and coworkers performed another time-course study that focused on the interactions between diet and gut microbes . Their study also reported that from breastfeeding to weaning to the introduction of solid food, the gut microbial community and microbial metabolites responded accordingly. In agreement with Sillner et al., their story supported that SCFAs and HMOs again served as metabolite biomarkers that reflecting the dietary transitions while shift of Firmicutes phylum occurred. Their story supported that the variations in the fecal metabolome reflected the infant’s diet transition, while the composition of the microbiota followed a more complex and still unstable behavior. This observation leads to the conclusion that during the infancy, it appears that the fecal metabolome is more representative of the diet changes than gut microbiota.As the colonization of human gut by microbes is a dynamic process that initiated from birth, studies of diet-gut microbe-microbial metabolism in infants can provide us a golden opportunity to elucidate the impacts of infant diet on the early-stage gut microbes, and eventually to human health during this important developmental phase. In this special issue, Marangoni et al. utilized quantitative 1H-NMR spectroscopy to investigate the dynamic changes that occur in the vaginal metabolome of Caucasian pregnant women at different gestational ages  . Throughout pregnancy, the vaginal microbiome becomes less diverse and converges to a lactobacilli-dominated status, characterized by a progressive reduction of biogenic amines and alcohols content, and a corresponding increase of lactate and branched amino acids level. In such study, high levels of leucine and isoleucine have been confirmed as hallmarks of a vaginal healthy condition. In addition, microbial and metabolic profiles of vaginal samples from women suffering a first-trimester miscarriage were analyzed, enabling to correlate high levels of selected metabolites  to the spontaneous abortion. The same spectroscopic technique was employed by Dall’Asta et al. to investigate vaginal metabolomic profiles of Caucasian pregnant women in the first trimester, in order to correlate metabolites content  to pre-pregnancy diet and body mass index (BMI) . The study underlined the strict inverse correlation between BMI and vaginal health status, with high levels of vaginal dysbiosis-related metabolites  related to high pre-pregnancy BMI. For the first time, it has been demonstrated that a pre-pregnancy high intake of animal-sourced proteins correlates with an increased risk of vaginal dysbiosis, which is characterized by high content of biogenic amines and selected organic acids; on the other hand, high intake of carbohydrates favors a Lactobacillus-dominated vaginal environment and high levels of selected amino acids.Closely related to the infant health, maternal health of pregnant women is also an important research topic of microbial metabolomics studies. Among these maternal women, vaginal status (eubiosis vs. dysbiosis) profoundly impacts on women’s quality of life and reproductive health. Therefore, another field of application of metabolomics studies covered in this special issue is represented by the study of the vaginal environment and its peculiarities during gestation. Indeed, the instauration of a pregnancy reflects into modifications in the microbiome composition and, in turn, in the metabolome; the depiction and comprehension of such shaping can provide new insights into the pathophysiology of pregnancy and its outcome. The study from Zhou and Zhao, reviewed the health effects of pesticides exposure based on the measurements of gut microbiome and metabolomics (Zhou and Zhao). In the past few decades, a large number of pesticides have been widely used for plant protection. Pesticides may enter non-target organisms through multiple ways and bring potential health risks (Additionally, th risks . GeneralAfter getting into the articles included in this collection, it is evidential that the microbial metabolomics studies can tap into many biomedical questions, and we are only scratching the surface of this exciting area of research. Therefore, we foresee many more research progress to be reported in near future to further assist the scientific community, and to unveil the effects of environmental and dietary factors on human health mediated by human microbes and microbial metabolites. We also want to take this opportunity to thank all the contributors to this research topic, and the reviewers for their insightful comments and suggestions.


Dear Editor,Pemphigus vegetans (Pveg) is a subtype of pemphigus vulgaris (PV), characterized by flaccid blisters which become erosions and vegetating plaques, typically in the intertriginous areas, face, and scalp.Trauma-induced pemphigus is rare following surgical procedures, with only a few reports occurring after Mohs micrographic surgery (MMS).Pseudomonas aeruginosa, but the patient failed to respond to systemic and topical antibiotics. Two months after MMS, the patient was noted to have erosions and hyperkeratotic vegetating plaques expanding circumferentially from the procedure sites  and dental procedures.Several mechanisms have been proposed to explain the induction of pemphigus and Koebnerization of pre-existing pemphigus by surgical trauma, and the process is likely to be multifactorial.Pveg poses a further diagnostic challenge as it has histological similarities with SCC due to the presence of PEH. Besides being associated with suprabasal acantholysis, PEH in Pveg cases is of adnexal (follicular) origin, confined to the epidermis and dermis, with minimal atypia, rare mitoses, and absent individual keratinocyte necrosis.nd intention or partial closure should be considered.In patients who have known bullous disease reconstruction of MMS wounds should be simple, and 2In patients like ours who present without previous history of bullous disease, Pveg associated to the Mohs surgery and the criotherapy must have a high suspicion on the appearance of non-healing wounds or localized inflammation occurring several weeks after the procedure.None declared.Nathan Jetter: Participation in the conception and planning of the study; obtaining, analyzing, and interpreting the data; writing; approval of its final version.Felipe Bochnia Cerci: Analyzing and interpreting the data; writing; approval of its final version.Karan Pandher: Participation in the conception and planning of the study; obtaining, analyzing, and interpreting the data; writing; approval of its final version.Aleksandar L. Krunic: Participation in the conception and planning of the study; obtaining analyzing and interpreting the data; critical review of the manuscript; approval of its final version.None declared.


With age, many physiological changes occur in the human body, leading to a decline in biological functions, and those related to the locomotor system are some of the most visible. Hence, there is a particular need to provide simple and safe exercises for the comprehensive development of physical fitness among elderly adults. The latest recommendations for the elderly suggest that the main goal of training should be to increase muscle power. The post-activation performance enhancement effect underpinning complex training might be an approach that will allow for the development of both muscle strength and velocity of movement, which will result in an increase in muscle power and improve the ability to perform daily activities and decrease injury risk. This article briefly introduces a complex training model adapted to the elderly with its potential benefits and proposes a direction for further studies. With age, many physiological changes occur in the human body, leading to a decline in biological functions, and those related to the locomotor system are some of the most visible . The conDespite the increasing amount of research, there is still an opinion in society that older adults are too weak or fragile to undertake high-velocity and high-intensity training. Moreover, the latest research shows that these exercises are not dangerous, but it is a recommended form of physical activity to improve the quality of life and a number of physiological functions ,10. TherA muscular phenomenon known under the term post-activation potentiation (PAP), which enhances muscular performances as a result of the recent voluntary contractile history ,12, has Nowadays, complex training is considered an effective method of integrating the development of muscle strength and power . The adaThe effects of complex training have been supported by extensive research assessing its acute and chronic impact on maximum strength, muscle power, sprint, and sports performance adaptations, also in comparison with other training methods ,18,19,20Appropriate selection of CA modalities as well as those performed post activation may induce less stress on the cardiovascular system and decreased perceived exertion, compared to traditional resistance and plyometric exercise performed separately . In addi2) also has been shown as an effective CA to elicit the PAPE effect [To date, evidence showing that the PAPE effect can be effectively elicited in several ways, by high-intensity resistance exercises  , moderatE effect . MoreoveE effect . n trials previously) could counteract a decrease in cognitive functions such as attention and memory. It seems interesting considering the positive relationship between physical activity and cognitive functions [The greatest improvement in performance is most often noted between 5–7 min after the CA for both lower- and upper-body exercises ,46. Consunctions . NeverthMost of the PAPE studies investigated the effects of a CA on a subsequent jump, vertical jump, sprint, throw, and upper-body plyometric and ballistic performances . PlyometMoreover, simple ballistic exercises could be considered as safe choices since the external load is projected onto the flight phase , allowing to omit repetitive cycles of hard braking required during high-velocity non-ballistic and plyometric exercises. The advantage is that ballistic exercise was found to generate greater speed and power than the non-ballistic alternative ,56. The Taking into account the above-mentioned considerations and scientific reports, it seems that the properly designed complex training can constitute a holistic approach to counteracting the ageing process . In an aThe use of an active recovery within and between the complex will ensure greater training density and the possibility of introducing low-intensity corrective, stabilising, mobilising, and breathing exercises or cognitive tasks. This approach would allow for the development of additional components of fitness and cognitive functions simultaneously to mitigate the consequences of the ageing process within the same exercise session. However, there is no evidence as to whether these exercises will not affect the PAPE effect and therefore needs to be verified by future investigations.While in the case of post-CA exercise, trampoline-based plyometric exercise (with the supporting bars or on the sledge) ,61 can bAlthough complex training has not been studied in the elderly, studies showed a beneficial effect of both high-intensity resistance and explosive training used separately. Therefore, it can be supposed that the mechanisms underlying its effectiveness in athletes could also be transferred to the elderly. The proposed model of complex training for the elderly may develop several components of fitness simultaneously to mitigate the consequences of the ageing process within the same exercise session. Nevertheless, the main limitation is that the proposed model is purely hypothetical, thus should be treated with caution. Furthermore, as, it is based on studies carried out on healthy elderly it may not be recommended for other older populations who have orthopaedic or other medical contraindications. Moreover, no study has yet investigated the effect of programming activity within the intra-complex and inter-complex recovery interval on subsequent performance improvement. Therefore, future studies have to verify the potential benefits of complex training after appropriate optimisation for the elderly to improve physical performance. Research protocols could compare the effects of complex training with traditional resistance training and other strength-oriented training methods, both in improving physical fitness and health, as well as increasing willingness and long-term adherence to physical activity. The proposed evidence-based model of complex training for the elderly may constitute a promising tool for exercise physiologists, strength and conditioning coaches, or personal trainers.


The rapid progress of the combination of medicine and engineering provides better chances for the clinical treatment and healthcare engineering. Traumatic brain injury (TBI) and its related symptoms have become a major global health problem. At present, these techniques has been widely used in the rehabilitation of TBI. In this review article, we summarizes the progress of the combination of medicine and industry in the rehabilitation of traumatic brain injury in recent years, mainly from the following aspects: artificial intelligence (AI), brain-computer interfaces (BCI), noninvasive brain stimulation (NIBS), and wearable-assisted devices. We believe the summary of this article can improve insight into the combination of medicine and industry in the rehabilitation of traumatic brain injury. With the development of the society, traumatic brain injury (TBI) is gaining more attention because of its higher rates of morbidity and mortality. It is defined as a traumatic structural or physiological disruption of brain function, mainly caused by an external physical force. Traumatic brain injury (TBI) is the mainly common cause of death and disability in those aged under 40 years in the UK . TBI stiArtificial intelligence is a broad interdisciplinary field, which is composed of logic, cognitive psychology, decision theory, neuroscience, linguistics, computer engineering, and so on . As timeCognitive dysfunction is one of the main consequences of traumatic brain injury (TBI). Cognitive impairment leads to a serious decline in the quality of life after TBI and is involved in the impact of depressive symptoms on emotional role functioning . By far,A study of 35 patients with traumatic or vascular brain injury found that compared with conventional treatment, cognitive training can effectively improve the rehabilitation effect after TBI, which brings new hope for TBI patients . In thisIn the past decades, rehabilitation robots have been rapid and vast developments. As a relatively young and rapidly developing field, rehabilitation robots are increasingly infiltrating into the clinical environment . An incrOne study presented the application of novel self-feeding robots in TBI rehabilitation, and the self-feeding robots improved the activities of daily living of patients with TBI . In anotIn the above, we can learn that robotic-assisted rehabilitation training pays more attention to the limb motor dysfunction after TBI; in my opinion, we should focus on the robot research of hand fine motion rehabilitation in the future. The advantages and disadvantages of robotic-assisted rehabilitation training are summarized in Virtual reality (VR) is a new and developing technology, which combines the characteristics of VR technology such as autonomy, interactivity, and existence with rehabilitation training. VR is described as “an advanced human-computer interaction mode that allows users to interact in a natural way with a computer-based environment for training and full immersion.” . VR is nA study of 33 TBI patients examined the usability of a virtual reality driving simulator . All patTBI can lead to severe motor, cognitive, and emotional disturbance, and the rehabilitation of TBI is a long process. Fortunately, Mobile Health  is an emerging technology, which can help to diagnose and manage patients with TBI greater.One study explored that the effectiveness of a prospective memory assists method combining smartphones with Web-based calendars in community-dwelling patients with traumatic brain injury . PatientBrain-computer interfaces (BCI) are developing into a possible method to replace the brain's normal output pathways of peripheral nerves and muscles, and allowing paralytic patients can use a new method of communication and computer control, which has developed significantly over the past several decades . Brain-cMany clinical studies confirmed the effectiveness of BCI in the rehabilitation of patients with TBI , 33. MorIn the past few years, the extensive use of noninvasive brain stimulation (NIBS) technology has led to a significant development in our understanding of brain behavioral relationships . As a poTranscranial direct current stimulation (tDCS) is one method of NIBS. It can increase or decrease cortical excitability according to different polarities (anode or cathode), regulate synaptic plasticity through long-term inhibition or enhancement, and promote long-term functional recovery . It can In 2014, Middleton et al.  conduct rTMS is another noninvasion method to stimulate the human brain. It can influence brain plasticity and cortical reorganization through stimulation-induced changes in neuronal excitability, and the treatment effects of rTMS on cortical excitability depend on the stimulation parameters applied, including the stimulus intensity, frequency, and duration of stimulation . The lowDisorders in memory and neural behavior are a common sequence of TBI. A study shows that low-field magnetic stimulation (LFMS) improved the cognitive and motor function of TBI mice significantly. The neuroprotective effect of LFMS may be achieved through the regulation of cellular prion protein (PrPc) and/or circadian rhythm-related proteins . A case Although rTMS has been widely used in the rehabilitation of TBI, there are still a lot of areas that need to improve. There is evidence that rTMS may be led to adverse events such as seizure , so we sWearable-assistive devices have been used in the rehabilitation of neurological disorder such as traumatic brain injury widely. According to the report , MikołajIn this paper, we summarized the application of interdisciplinary combination between medicine and engineering in the rehabilitation of traumatic brain injury. With the rapid development of science and technology, the interdisciplinary combination between medicine and engineering technology brings new hope to TBI patients. Artificial intelligence (AI), brain-computer interfaces (BCI), noninvasive brain stimulation (NIBS), and wearable-assistive devices have been widely used in the rehabilitation of patients with TBI; meanwhile, there are still some areas that need to improve.First, as summarized above, we can see that the application of these technologies lacks high evidence from clinical trials, so we should conduct more clinical trials to prove their effectiveness in the future. When it comes to the application of virtual reality (VR), we must consider the limitations of it. The application of virtual reality technology in clinical practice is mainly limited by two factors: accessibility and the cost of virtual tools . AdditioSecondly, clinician attitudes are important which can affect the use of any assistive technology in the training and supporting for the rehabilitation of TBI patients, so we should improve the awareness of clinician for the new rehabilitation facility. Moreover, according to report , traditi


Respiratory problems are common in horses and are often diagnosed as a cause of poor athletic performance. The basic diagnostic techniques of the equine respiratory tract examination are not always sufficient for a complete diagnosis of the disease, its exacerbation, remission, or response to treatment. Therefore, advances have been introduced in the diagnosis of equine respiratory diseases. Among them, we can distinguish the high-resolution imaging modalities like computed tomography (CT) and magnetic resonance (MR) imaging. These techniques have revolutionized the capability of visualizing detailed anatomy of the upper respiratory tract, offering the practitioners an advanced view of airway pathology and allowing for appropriate management planning. On the other hand, the pulmonary function tests (PFTs), which provide sensitive assessment of small functional changes in the lungs, are able to comprehensively characterize the mechanics of the respiratory system. Spirometry and impulse oscillation system (IOS) analyze intra-breath respiratory mechanics, while electrical impedance tomography (EIT) measures changes in lung conductivity. These methods may be successfully applied to detect airway obstruction and mechanical inhomogeneity in breathing patterns. Presented advanced diagnostic techniques comply with owners’ and trainers’ requirements for accurate and early diagnosis of respiratory tract disorders. This paper reviews advantages, disadvantages, and clinical applications of the advanced diagnostic techniques of the equine respiratory tract.The horse, as a flight animal with a survival strategy involving rapid escape from predators, is a natural-born athlete with enormous functional plasticity of the respiratory system. Any respiratory dysfunction can cause a decline in ventilation and gas exchange. Therefore, respiratory diseases often lead to exercise intolerance and poor performance. This is one of the most frequent problems encountered by equine internists. Routine techniques used to evaluate respiratory tract diseases include clinical examination, endoscopic examination, radiographic and ultrasonographic imaging, cytological evaluation, and bacterial culture of respiratory secretions. New diagnostic challenges and the growing development of equine medicine has led to the implementation of advanced diagnostic techniques successfully used in human medicine. Among them, the use of computed tomography (CT) and magnetic resonance (MR) imaging significantly broadened the possibilities of anatomical imaging, especially in the diagnosis of upper respiratory tract diseases. Moreover, the implementation of spirometry, electrical impedance tomography (EIT), and impulse oscillation system (IOS) sheds new light on functional diagnostics of respiratory tract diseases, especially those affecting the lower part. Therefore, this review aimed to familiarize the clinicians with the advantages and disadvantages of the advanced diagnostic techniques of the equine respiratory tract and introduce their recent clinical applications in equine medicine. Taking a detailed history and performing a good clinical examination is critical to the diagnostic process of equine respiratory diseases. They often provide crucial data which narrows down the diagnostic workup plan and supports the choice of the most appropriate and informative additional examinations. In the case of the equine respiratory tract, observation of the horse from a distance is important to assess the breath rate or any symptoms of respiratory distress. Attention should also be paid to environmental conditions like bedding, ventilation, or access to the pasture. Besides the basic clinical examination, a detailed assessment of the respiratory tract needs to be performed. The respiratory examination is routinely performed in a sequence of inspection, palpation, auscultation, and—when needed—percussion ,2. When Radiography (X-ray) plays an important role in diagnosing upper respiratory tract diseases affecting the fascial, nasal, and paranasal sinus regions of the horse skull . X-ray iUltrasonography (US) is another diagnostic tool that allows inexpensive, accessible, real-time, and radiation-free imaging. This technique is implemented in the diagnosis of lower respiratory tract disorders like pleural effusion, pleuropneumonia, pleuritis, pneumonia, pulmonary abscess, pneumothorax, or neoplasia . In geneRhinoscopy is of great use in the case of an ethmoid hematoma, rhinitis due to foreign body, polyps, and masses causing restricted airflow . It alsoDynamic endoscopy, in some cases, may be the only method for diagnosis of dorsal displacement of the soft palate, especially when the symptoms occur mainly during exercise. It then also provides an assessment of laryngeal hemiplegia during horse movement . Both stNew diagnostic challenges and the growing development of equine medicine has led to the implementation of advanced diagnostic techniques successfully used in human medicine. Among them, the use of computed tomography (CT) and magnetic resonance (MR) imaging significantly broadened the possibilities of anatomical imaging, especially in the diagnosis of upper respiratory tract diseases. Moreover, the implementation of spirometry, electrical impedance tomography (EIT), and impulse oscillation system (IOS) sheds new light on functional diagnostics of respiratory tract diseases, especially the lower part. Therefore, this review aimed to familiarize the clinicians with the advantages and disadvantages of the advanced diagnostic techniques of the equine respiratory tract and introduce their recent clinical applications in equine medicine.Computed tomography (CT) is an advanced technique established for the detailed imaging of the anatomical structures of the horse’s head and limbs, which nowadays is becoming more available in equine clinics. The CT refers to a computerized X-ray imaging procedure where the patient is radiographed slice by slice, using a rotating, highly collimated, X-ray beam that generates cross-sectional images throughout the area of interest. The CT image is represented by a grayscale map of the tissue’s ability to attenuate X-ray radiation . The CT The CT provides diagnostically important data in situations where X-ray or US has been unrewarding. However, because of costs and the restrictions presented below, it is usually second in line after X-ray or US. The main advantage of CT is the ability to produce high-resolution, three-dimensional, detailed cross-section images . The CT Several problems related to the CT technique that have limited the availability or usefulness in equine practice can be divided into relative and absolute groups. Within the relative group, the high cost of CT equipment and facilities necessary for this imaging is still the main limitation. The monthly maintenance costs of CT scanners are very high and equipment to move anesthetized horses is also expensive . As the Within the much more important absolute group, the size of the CT scanner is a serious limitation in the use of CT imaging in equine practices. The CT scanners were designed for people, thus in equine practice the diameter of the gantry of the CT scanner, in which the examined area must be located during imaging, ranges from 50–85 cm and allows for insertion of the head, distal limbs, and upper neck of adult full-sized horses . The entA wide range of diseases affecting the upper respiratory tract have been diagnosed successfully using CT imaging. The intravascular contrast enhancement can be used to differentiate normal soft tissue from lesions based on an alteration in vascular permeability and perfusion which significantly improves the diagnostic value of equine head CT imaging . The CT In horses, magnetic resonance (MR), similarly to CT, may support the diagnostic process by providing cross-sectional images of extremities and head. The MR imaging is based on the magnetic dipole nature of the abundant hydrogen protons within tissues and uses the magnetic field and radio waves to create the image of hydrated tissues . The MR The MR provides completely different diagnostically important data than CT, X-ray, or US. The main advantage of MR is the type of acquired data, providing not only excellent anatomic features of soft tissue structures but also functional alterations elusive in other imaging techniques. The MR does not use ionizing radiation, thus no negative biological effects in living tissues have so far been demonstrated . In the The main disadvantage of the MR technique in equine practice is similar to CT imaging limitations, and also could be divided into relative and absolute groups. Within the relative group, as it was noted for CT that the high cost is still the main limitation, it has to be realized that the costs of MR equipment and facilities are extremely high. The MR magnet, especially in the high-field MR, requires a constant high voltage power supply and continuous cooling with the use of liquid helium, even when no imaging is being performed.Therefore, the monthly maintenance costs of MR scanners are much higher than those of CT . MoreoveAs it was mentioned above, the size of the MR scanner is a serious limitation in the use of high-field MR imaging in equine practice, which should be mentioned as an important absolute disadvantage. The gantry diameter allows for the distal limb and rostral part of the head to be introduced in the center for image acquisition . MoreoveDue to the above limitations, a variety of clinical MR applications in equine practice have been reported regarding limbs ,50,51, wThe above basic and advanced imaging techniques predominantly provide data of normality or alterations of the anatomical structures of the respiratory tract. The adaptation of the pulmonary function tests (PFTs) to equine medicine significantly expands the possibilities of the functional evaluation. In contrast to static imaging techniques that allow the direct visualization of the area of interest to diagnose changes like mucus, fluid accumulation, neoplastic changes, or other anatomical abnormalities, dynamic PFTs provide information about the respiratory system in motion. Examples of dynamic measurement are pulmonary resistance and dynamic compliance, which are reliable indicators for airflow obstruction changes . RespiraAmong PFS available in human medicine , spiromeSpirometry is designed to identify and quantify functional abnormalities of the respiratory tract. In humans, the Global Initiative for Chronic Obstructive Lung Disease recommends spirometry as a diagnostic technique in earlier diagnosis and treatment monitoring in chronic obstructive diseases . In mediSpirometry begins with a full inspiration, followed by a forced expiration that rapidly empties the lungs. Expiration is continued for as long as possible or until a plateau in exhaled volume is reached. Both efforts during inspiration and expiration are recorded and graphed, demonstrating respiratory frequency, tidal volume, peak inspiratory and expiratory flows, time to peak flow, and forced vital capacity, which is an important spirometric maneuver. The forced vital capacity measurement requires the maximal inspiration followed by the rapid expiration, which should be as complete as possible . Such maIn human medicine, spirometry is the gold standard in the diagnosis of lower obstructive respiratory diseases , therefoSpirometry provides repeatable and reproducible data of the respiratory function in horses without the need of very expensive and advanced equipment, contrary to CT and MR imaging. Spirometry is a non-invasive technique that does not require the use of ionizing radiation; moreover, it is well tolerated by horses ,83. TherThe main disadvantage of the introduction of spirometry to the equine practice is the necessity of the horse’s cooperation to perform voluntary breathing maneuvers . BecauseSpirometry has been primarily used to characterize the normal equine tidal breathing flow-volume loop in healthy horses and ponies ,83. AfteRaidal et al. used spirometry for evaluation of the effect of xylazine, acepromazine, and salbutamol on lung function in horses where respiration was significantly reduced by the sedative agents in comparison to salbutamol, where no significant changes were noticed except increased peak inspiratory flow , whereasAmong the direct clinical applications of spirometry in the diagnosis of equine respiratory diseases, the spirometry-based early diagnosis of equine asthma was investigated ,67. EvanElectrical impedance tomography (EIT) is a non-invasive, radiation-free, real-time imaging modality which allows the assessment of lung ventilation and perfusion . The EITIn human medicine, EIT is frequently used for functional chest examinations, especially for monitoring regional lung ventilation in mechanically ventilated patients, and for regional PFT in people with chronic lung diseases . The EITThe EIT provides functionally unique clinical data of the lower respiratory tract ventilation which is difficult to obtain by other diagnostic techniques. The data are real-time measured and thus reflect continuous ventilation . The EITDespite many advantages, the EIT imaging modality shows several limitations. EIT is characterized by very low spatial resolution compared with other imaging techniques, such as CT or MR imaging . The EITThe first studies on the EIT application in equine practice have focused on the assessment of ventilation in healthy standing horses ,93. RegiApplication of EIT in anesthetized horses has been well described by Mosing et al. . The EITMoens et al., Wettstein et al., and Mosing et al. made an effort for a better understanding of horse ventilation by applying EIT measurements for continuous monitoring of the dynamic changes in the distribution of ventilation ,93,99. TAmong the direct clinical applications of the EIT in equine practice, recent research described the global and regional peak respiratory flows in the horses that underwent histamine challenges and drug-induced bronchodilatation ,90, as wThe impulse oscillometry system (IOS) is a non-invasive effort-independent functional modality that allows for measuring both airway resistance (R) and airway reactance (X) . The IOSThe IOS provides reliable, repeatable, and informative pulmonary functional data of the lower respiratory tract , completAlthough the IOS has many useful promising clinical applications, the examination protocol is subject to some limitations. Despite the IOS protocol being effort-independent, the horse still needs to be cooperative, especially regarding wearing a mask that sometimes might be challenging and time-consuming . MoreoveVan Erc et al. made a cornerstone in equine IOS application, providing the normal reference values for adult horses and standardizing the examination protocol concerning the effect of unfitted masks or position of the head. The horse’s gender, age, and general physical morphology determined by individual biometrics did not significantly affect the results of IOS measurements . In otheIn human medicine, specialized centers for respiratory diseases are present and the future may lead to development of similar facilities for horses, as respiratory problems highly impact the equids population. In many cases, the complexity of respiratory disorders makes the full diagnosis under field conditions inapplicable. Thus, specialized centers fully equipped to provide comprehensive diagnoses are needed. Except for the endoscopes and US machines, the remainder of the specialized equipment is not portable. Ambulatory X-ray systems are not suitable for thoracic radiography in adult horses, this area can only be achieved using high powered X-rays which are mainly stationary. Lung function tests are a very promising tool, especially regarding the worldwide occurrence of EA. Early asthmatic horses may not show recognizable signs, but their airway hyperactivity can be detected using a pulmonary function test. PFTs may be especially helpful in early diagnosis of high-performance horses where the smallest amount of respiratory disease may affect the future outcome. PFTs may be also helpful in the evaluation of response to treatment protocol and are more sensitive than BALF retake. Hopefully high demand from the owners and trainers will result in the wide implementation of those techniques in equine respiratory diseases diagnosis, as it would support effective management of affected horses, improve the outcomes, and improve the horses’ welfare.Huge improvements have been observed in the last decades and continuous technical progress is changing the capability of the diagnostic techniques, allowing for more accurate anatomical and functional studies of the equine respiratory tract. Within the advanced techniques, the sensitive diagnostic modalities like CT or MR have provided the detailed anatomical features of upper respiratory tract diseases, allowing for the exact visualization of changes and providing vital information for surgical staff in the case of a planned procedure. The further implementation of pulmonary function tests is promising as a non-invasive tool to facilitate an earlier diagnosis of equine lower respiratory tract diseases, especially in the case of equine asthma. However, more studies in the presented field are needed to create protocols that may be widely implemented by equine practitioners.


Loneliness imposes significant risks to physical, mental and brain health in older adulthood. With the social distancing regimes implemented during the COVID-19 pandemic, there is even greater urgency to understand the human health costs of social isolation. In this viewpoint we describe how the experience of loneliness may alter the structure and function of the human brain, and how these discoveries may guide public health policy to reduce the burden of loneliness in later life. In times of human crisis, personal and communal resilience depends on strength of our social connections . PerceivThe health consequences of loneliness are pervasive, affecting not only the mind, but the entire human body. The experience of loneliness is associated with physical health morbidities including hypertension and immune system dysfunction , as wellHuman and non-human animal studies have now begun to elucidate the impact of loneliness on brain structure and function . Yet uncTo directly interrogate this hypothesis, we have begun to harness large cohort data resources to identify associations between the experience of loneliness and brain structure and function. In an earlier study, we reported, in a sample of younger adults, that increased loneliness was associated with a shift in the functional connectivity patterns of the default network, towards greater functional integration with networks implicated in externally directed perceptual, attentional and cognitive control functions . We specWe have recently built on these early hints with the largest-to-date study of loneliness and brain health . DrawingWhile much work remains to be done, there is a growing urgency to understand links between age-related brain changes in the context of loneliness. According to a 2018 report from the American Association of Retired Persons, nearly one-third of individuals surveyed over age 45 reported feeling lonely. In just the last decade, the population of lonely people over age 45 has grown by more than 5 million, from 42.6 million to 47.8 million, and these data do not account for the global pandemic. Social distancing restrictions during the COVID-19 pandemic raise significant concerns about loneliness among older adults  and incr


Dehydroepiandrosterone (DHEA) and its sulfated metabolite (DHEAS) are dynamically regulated before birth and the onset of puberty. Yet, the origins and purpose of increasing DHEA[S] in postnatal development remain elusive. Here, we draw attention to this pre-pubertal surge from the adrenal gland—the adrenarche—and discuss whether this is the result of intra-adrenal gene expression specifically affecting the zona reticularis (ZR), if the ZR is influenced by the hypothalamic-pituitary axis, and the possible role of spino-sympathetic innervation in prompting increased ZR activity. We also discuss whether neural DHEA[S] synthesis is coordinately regulated with the developing adrenal gland. We propose that DHEA[S] is crucial in the brain maturation of humans prior to and during puberty, and suggest that the function of the adrenarche is to modulate, adapt and rewire the pre-adolescent brain for new and ever-changing social challenges. The etiology of DHEA[S] synthesis, neurodevelopment and recently described 11-keto and 11-oxygenated androgens are difficult to investigate in humans owing to: (i) ethical restrictions on mechanistic studies, (ii) the inability to predict which individuals will develop specific mental characteristics, and (iii) the difficulty of conducting retrospective studies based on perinatal complications. We discuss new opportunities for animal studies to overcome these important issues. The intention of this article is to discuss the possible physiological mechanisms that initiate and support the hormonal changes that characterize adrenarche in humans and some non-human primates. As such, we have not attempted a systematic review of this topic; such a review has been done expertly in recent times ,2,3,4. WAdrenarche is an early endocrine event of adrenal origin in children, but how it is brought about and its significance for the subsequent development of the child remains something of a mystery. While it is generally thought that adrenarche involves a pre-pubertal increase in the secretion of the androgen dehydroepiandrosterone (DHEA) and its sulfated conjugate DHEAS from the adrenal gland in children, from about the age of six years, increasing evidence suggests that it is a much more gradual process starting from at least infancy ,6,7, andzona reticularis (ZR) is still unclear and a matter of continuing debate. Hence, why the mechanistic understanding of adrenarche—in particular, the origin of the factors that drive the dynamic changes within a strictly defined zone of the adrenal cortex, the ZR—is still poorly defined and essentially unknown. Similarly, there has been much discussion around the impact on the brain of adrenarche and the associated increase of DHEA during human adolescence and adult life  in various aspects of neuro activity, raising the possibility that a key function of the adrenarche is to begin to modify the neural, behavioral, and psychosocial development that is so characteristic of puberty and adolescence, although exact mechanisms currently remain unclear. That is, the presence of high levels of DHEA[S] before puberty may allow for regional and/or sex-specific brain development before the commitment of the brain to the events that occur at puberty.A receptors  has long been considered in the treatment of neuropsychiatric disorders, with many studies reporting abnormal serum DHEA concentrations in patients with major neurodevelopmental and neurodegenerative pathologies, including schizophrenia, bipolar affective disorder, depression and Alzheimer’s disease ,41. In rAbnormal adrenarche, primarily premature adrenarche (PA), as measured by increased serum DHEA (>1 µmol/L) before the ages of eight and nine in girls and boys, respectively , has beeThe development of diseases in later life, including psychiatric disorders, can also be linked to the perinatal events now grouped under the developmental origins of health and disease (DOHaD) hypothesis ,68. IndeThe significance of the pre-pubertal surge of DHEA synthesis in some species, primarily humans and some other primates, and how it comes about, is yet to be fully explained. Clearly, known hormones of pituitary origin , in addition to ACTH, could be tested, and the presence of a cortical activating synthesis hormone [CASH] has long been suspected but never identified. The ready availability of adrenal glands from an animal that does secrete DHEA might provide the opportunity to provide definitive proof of the presence of a CASH hormone that specifically activates the DHEA pathway in postnatal ZR. There is the important question of what impact the adrenarche might have on brain development and function, both for normal development and following an abnormal adrenarche event. Does increased androgen production before puberty affect neuroplasticity, giving adaptability (plasticity) in behavior, learning and memory, which might differ between the sexes? The possibility that DHEA protects the adult brain against the effects of chronic stress involving glucocorticoids has been widely discussed ,86. Whil(Acomys cahirinus)—has a pre-pubertal DHEA surge underpinned by coordinated changes in the structure and functional activity of the ZR of the adrenal gland [We suggest that four goals need to be met to help resolve the enigma of the adrenarche, and to understand the impact it might have on postnatal brain development. Firstly, inquiry into the early development of animals that actually have adrenal synthesis of DHEA may provide a comparative animal model of adrenarche. We have recently discovered that a precocial rodent—the spiny mouse al gland ,27, and al gland . This gial gland .Secondly, gene expression studies could then identify changes of expression of the entire range of genes involved in cholesterol utilization by the adrenal gland, and perhaps identify the key transcriptional co-factors that regulate the growth and activity of the ZR.Thirdly, a comprehensive steroid metabolomics approach is required to track changes that occur during postnatal development in such animals, comparable to detailed analyses recently completed for humans ,89,90,91Finally, how can we settle the question of whether a circulating factor is responsible for developmental changes in the adrenal gland and the postnatal brain? One approach might be to isolate the pre-adrenarchal, undifferentiated adrenal gland from a species that has ‘adrenarche-like’ changes in early-life, maintain it in culture ex vivo and then expose it to plasma (and/or plasma extracts) obtained from progressively more mature individuals of the same species, to determine if a blood-borne factor is able to induce subsequent differentiation and maturation of the ZR. In a species such as the spiny mouse, where the adrenarche-like changes occur over a short period , maintaining the isolated adrenal gland without external stimulation would also allow the identification of maturational changes that are truly intrinsic to the adrenal gland, as suggested elsewhere ,18. AddiTo conclude, resolving the enigma of the adrenarche has proved difficult because of the absence of an experimentally tractable animal in which mechanistic studies can be performed. Closer examination of the postnatal development of some species that do synthesize androgens in both the adrenal gland and brain may be fruitful.