Fibre-reinforced composites (FRCs) are already well established in several industrial sectors such as aerospace, automotive, plant engineering, shipbuilding and construction. The technical advantages of FRCs over metallic materials are well researched and proven. The key factors for an even wider industrial application of FRCs are the maximisation of resource and cost efficiency in the production and processing of the textile reinforcement materials. Due to its technology, warp knitting is the most productive and therefore cost-effective textile manufacturing process. In order to produce resource-efficient textile structures with these technologies, a high degree of prefabrication is required. This reduces costs by reducing the number of ply stacks, and by reducing the number of extra operations through final path and geometric yarn orientation of the preforms. It also reduces waste in post-processing. Furthermore, a high degree of prefabrication through functionalisation offers the potential to extend the application range of textile structures as purely mechanical reinforcements by integrating additional functions. So far, there is a gap in terms of an overview of the current state-of-the-art of relevant textile processes and products, which this work aims to fill. The focus of this work is therefore to provide an overview of warp knitted 3D structures. FRCs consist on the one hand of a fibre reinforcement and on the other hand of a polymer or mineral matrix surrounding the fibre reinforcement [Achieving environmental sustainability through the use of innovative materials is a major technology driver and an effective response to resource depletion and the need to drastically reduce COmissions ,4,5. Themissions . For exaorcement . Their aorcement ,8.FRCs are key innovation drivers in the fast-growing and future-oriented market segments of renewable energy , electromobility, and aerospace. Lightweight construction is also of particular importance in mechanical and plant engineering ,14,15,16Textile semifinished products usually need to be draped to form a preform suitable for production of FRC components. In particular, the preforming results in terms of wrinkle and overlap free forming of the NCF or buckling of spacer fabrics have a major impact on the cost of the FRC part, the utilisation of the performance of the textile reinforcement structure and the saving of resources by avoiding oversizing ,18,19. EIt is concluded that a high degree of prefabrication, in the form of 3D textile structures, further enhances the economic and environmental benefits of using FRCs. Preform costs can be reduced, fibre cuttings can be saved and the utilisation of material performance can be increased ,25,26,27Warp knitting is one of the most productive and cost-effective textile manufacturing processes due to its technology of simultaneously forming stitches across the entire working width of the machine, making it particularly interesting for industrial applications. Basically, the warp knitting process either creates a textile surface with the warp threads or the warp threads are used to fix additional reinforcement yarns ,28,29.The industrial implementation of 3D warp knitted structures is an important basis for increasing the economic efficiency and further reducing the environmental footprint of FRC. Reducing the cost of preforming is therefore the key parameter for increasing the industrial attractiveness of composites ,31,32,33In this context, the use of warp-knitted FRCs with a high degree of prefabrication plays a key role in the economical and material-saving use of the limited resources available. Particularly important are multiaxial non-crimp fabrics (NCFs) produced on highly productive multiaxial warp knitting machines and warp knitted spacer fabrics produced on double bar warp knitting machines. Non-crimp fabrics are characterised by the fact that the reinforcing yarns are stretched (no crimp), allowing forces to be absorbed directly by this type of fabric in the FRC without structural stretching.Significant quantities of multiaxial fabrics are already in use today, particularly for large-scale applications , large area components  and highly stressed aerospace FRC components  ,34. WarpThe review provides an overview of the manufacturing requirements, textile production methods and process limitations for the implementation of 3D warp knitted fabrics. Possibilities for varying the 3D appearance through material, structure and process changes are discussed in detail.The paper is a guide for a wide range of readers, from fibre and textile scientists to those involved in the research and development of new generation 3D textile products, especially warp knitted structures.In order to assess the state of scientific and technical knowledge in the field of 3D textiles, with a focus on warp-knitted three-dimensional fabrics, an investigation was carried out. The state-of-the-art and research was investigated, based on the literature and patent search as well as interviews with experienced textile technologists. Accordingly, an overview of warp knitted three-dimensional fabrics, in particular 3D non-crimp fabrics and warp knitted spacer fabrics is given. The focus of the presentations is on the documentation of existing machine technologies and their current technological limitations, products already implemented and their applications.The research results provide a basis for the derivation of suitable basic technologies for future developments. The knowledge gained also enables the derivation of future research fields.There are two different approaches to the realisation of 3D warp knitted fabrics, these include non-crimp fabrics (NCFs) and spacer fabrics. Focusing on the draping process of these warp knitted fabrics, the subdivision is as follows:A: subsequent draped. Wrapping a component contour with warp knitted fabrics without wrinkles or distortion is made possible by the sliding integration of the reinforcing yarns, which can slide past each other during the draping process until the required yarn length distribution is achieved, and also in combination with the high elasticity of the warp knitting yarn.B: direct draped. This approach provides for the targeted predefinition of reinforcing yarn lengths in warp and weft directions for wrinkle- and distortion-free wrapping of or over a component contour with warp knitted fabrics in the production process, in order to save the subsequent forming process described in A.An overview about the classification of warp knitted fabrics for 3D reinforcements is given in Due to the special spacer structure of the warp knitted spacer fabric, which creates hollow chambers, there are other applications than NCF, such as medical filters for dialysis applications.The established basic process for the production of 3D NCF is the multiaxial warp knitting technique ,45,46,47The weft yarns move in a continuous, translatory motion to the knitting point. At the knitting point the 0° yarn layer is inserted. The layers of yarn are then fixed with a knitting or binding yarn by the stitch process (warp knitting process). In principle, it is possible to produce lattice-like and closed non-crimp fabrics (NCF) .The looping of the yarn plies with the warp knitting thread in the stitch formation process provides a basic structural stability to the textile structure. After the knitting process, the weft yarns of the textile surface are cut or needled out from the transporting warps and wound onto a fabric beam. Due to the straight and ondulation-free orientation of the yarn layers, structural elongation is reduced to a minimum. Therefore, in addition to the numerous applications in the automotive, aerospace and sporting equipment industries, scrim structures are particularly suitable for use in the construction industry, for reinforcing the brittle material concrete ,50. The The machine technology enables the production of two opposite arranged RL warp knitted fabrics, which form the surface layers of a warp knitted spacer fabric and that can be joined in z-direction by a third thread system, see The so-called pile yarns be inserted into both sides of the fabric sides to connect them in defined densities. The maximum spacing of warp knitted spacer fabrics depends on the maximum distance between the trick plates. Currently, machine spacing settings for the production of spacer fabrics are realised to up to 65 mm ,54.Warp knitted spacer fabrics are generally produced on double needle bar raschel machines also known as double needle bed raschel machines, as shown in The high pattern variation range of warp knitting technology allows the pressure stability and air permeability of spacer fabrics to be specifically adjusted. As a result, warp-knitted spacer fabrics are commonly used in seating, automotive, functional clothing, mattresses, medical support textiles such as bandages and orthopaedics. Their sideways open structure provides elasticity, insulation and acoustic damping properties as well as being used for filtration. Other technical applications are therefore currently in the field of filtration systems and water harvesting methods.There are also jacquard double bar raschel machines capable of producing (dendritic) tubular structures and spacer fabrics . The proNon-crimp fabrics (NCFs) are mainly made from homogeneous 2D textile structures in the form of rolls with constant yarn spacing and widths .The manipulation of a 2D NCF to create the desired shape or form is called draping for the processing of 3D fabrics. This is typically done by laying out the 2D NCF and then folding, pleating, or otherwise manipulating it to achieve the desired shape. As a basis for composites fabrication, the resulting shape is then pinned, sewn or impregnated to hold it in place .The underlying mechanism of draping is the stretching and compression of the warp knitted fabric. When the fabric is manipulated, by applying forces to the outer edges, it is stretched in some areas and compressed in others, creating a pattern of tension and compression across the material see . The effNCF can be divided into three categories according to their three-dimensional configuration and shaping. Material (a): Binding and reinforcing yarn densities are constant, draping due to lack of structural stretch in the warp knitting thread . StructuThe advantages and disadvantages of each class in terms of their applicability to complex three-dimensional composite components are discussed below. There is no known research into the use of a combination of variable binding, variable reinforcement yarn density and orientation.In this category, there are two options for the subsequent drape of the NCF. Option 1: The differences in warp knitting thread lengths required for a draping process are achieved through thread shifting during the draping process. Option 2: The differences in thread orientations required for a draping process are achieved through stretching and twisting of the warp knitting thread during the draping process from 2D to 3D.An example for draping due to lack of structural stretch of the warp knitting threads is the NCF with partial weft fringe binding “Drapetex” from the company Gerster TechTex , see Multiaxial warp knitted fabrics are basically composed of three yarn systems. 1. The warp knitting yarns (threads), 2. The warp yarns and 3. The weft yarns. For all and within all three yarn systems, forces act on the yarns to induce stretching and wrinkling when the NCF is draped. Therefore, one starting point for producing NCF with a high degree of prefabrication is to determine the forces/stresses that occur prior to NCF production and to design the yarn systems accordingly so that the forces/stresses that occur during draping are minimal. In theory, this means that wrinkles, overlaps and gaps in the preform can be avoided without the need for structural over-dimensioning, e.g., through additional yarn layers, in order to compensate for these defects. Since NCF made from high-performance fibres, such as carbon or glass, have only a low material ductility, even relatively low draping forces lead to large displacements of the yarn layers. A promising approach to compensate for the different draping forces in NCF is to give each yarn a pre-defined individual length based on the final three-dimensional shape in the draped state, hereafter referred to as the yarn reserve ,42,43,61A homogeneous yarn reserve is based on the compensating for the different forces during draping by feeding yarn material from the components that were not originally in the preform area. This overlaps with the material approach.The principle of inhomogeneous yarn reserve is based on the work of Sankaran et al. , where yIn the field of technical textile production, warp reinforcement yarns are provided on bobbins. Warp beams for reinforcement yarns are not known. Since each yarn comes from its own pay-off point, there is basically the possibility of warp yarn reserve. The stitch formation process is discrete in time. The warp thread moves at a constant speed, independent of the stitch formation process, if it is wound up with a constant tension force. If the take-off speed/take-off force is changed in a warp thread-specific manner, the distances between the stitches in the formed fabric are changed in the warp direction . In this way, warp yarn reserves can be generated. The change in take-off force can be achieved, for example, by means of a single-yarn take-off or a mechanical shaping located between the take-off and the knitting point. The single yarn take-off  was developed technologically and structurally by Sankaran et al., and a schematic representation of the functioning of this principle is shown in Technical limitations are the length of the warp reserve  . HoweverFundamental research activities by Sankaran et al. led to the development of curved reinforcing grids that can be specifically adapted to geometric shapes through variable single warp yarn delivery . The appIn the case of complex component shapes, significant, undesirable deflections of the reinforcing yarn course  occur, which lead to a reduction in the load-bearing capacity in the later component. Semi-finished textile products that meet the requirements and can be precisely adapted to a given component geometry can only be produced if the lengths of both the warp and weft sections can be flexibly varied locally between the bonding points ,42.In all known methods for forming the inhomogeneous weft reserve, the yarn reserve is formed mechanically, i.e., by means of mechanical forming tools. A technological approach to forming a weft yarn reserve is shown in The limitations of mechanical forming of the yarn reserve lie in the space required for the forming elements and the forming movement. As a result, only lattice structures can effectively be produced if the high productivity of multiaxial warp knitting technology is to be maintained. Geometric design is therefore limited in this respect  ,42. The The advantage of the yarn reserve principles is that it is easier to automate than draping, e.g., Drapetex. The semi-finished textile product must be precisely positioned in the mould in two planar coordinates and one angular coordinate. There is no need to apply additional forces to move and stretch the threads. The automation technologies therefore need to be less complex than for conventional 2D textiles or material-based drapability optimisation.Investigations by Krieger et al. show approaches to influence the draping behaviour of NCF by changing the binding type of the warp knitting thread in the NCF during the production process . The so-An alternative stitch-free approach was taken by Rittner et al. by replacing the knitting yarn with a chemical binder, solidified by heat and pressure, in combination with a CAE-simulation to investigate the optimal binding in a two- or four-layer NCF, depending on the drape geometry ,42. The Inexpensive and easy to manufacture;Handling of preforms layers prevented from moving through stitching;Better impact damage tolerance;Improved delamination resistance to ballistic and blast loads;Improved interlaminar fatigue resistance;Improved joint strength under monotonic and cyclic loading.According to Hu et al., the advantages of three-dimensional warp knitted spacer fabrics are as follows :InexpensThere are several textile technological options for the production of warp knitted spacer fabrics, an overview of the basic structures is given in In order to achieve a straight yarn orientation of reinforcing yarns, they must not form a mesh by themselves. Therefore, each reinforcement yarn system must be held in place by a warp knitting thread. The following explains how the reinforcement yarn layers can be integrated into the spacer fabric in the x, y and z directions based on the double needle bar warp knitting technology.In order to achieve a straight reinforcement yarn position across the width in the X-direction, defined as the working width direction of the warp knitting machine (or 90°-direction), it is necessary to integrate weft yarns, e.g., in the form of a long weft or magazine weft. A warp knitting thread system with a pillar stitch is a suitable structure for binding these weft yarns in the spacer warp knit. It is also possible to integrate segmented straight yarn sections across the working width by means of a partial weft structure known as inlay warp knitting. The pillar stitch binding is also suitable for holding the inlay yarns in place ,65.The integration of a reinforcing layer in the Y-direction can be achieved either by a partial weft lay staggered over a needle lane and combination of elastic and inelastic yarn material. The Y-direction, or 0°-direction, is defined as the production direction. The Y-thread has to consist of low elasticity material that has to be drawn to a straight thread. The yarn supply is therefore low. The low-elasticity material yarn needs to be bound with an additional loop yarn system  consisting of an elastic yarn. Another way of integrating straight yarns in the y-direction is to use filler yarns, which are located and remain in a needle lane. They can be bound either by a weft yarn system in front of them or in combination with a loop thread system in front of them, e.g., by a pillar stitch, or the filler yarn can be integrated between two yarn systems of the outer surfaces, forming crossed wales  ,65.Pile yarns present in warp knitted spacer fabrics can also have a reinforcing function in the Z-direction (thickness direction). Basically, the shear strength, compressive strength and thickness of the spacer fabric are determined by the material used and the warp knitting integration of the pile yarn. The pile yarns can be placed in between the textile cover surfaces in a straight form. It is essential that the pile yarns are crimped in the area of the surface layers to enable fixation there. In general, the pile yarns can be fixed within the textile face layers by open or closed loops ,65.The binding of the pile yarn system defines the orientation of pile yarns in the cross section of the spacer warp knit. A possible structure for the pile yarns with a straight orientation is in a 90° I-orientation, realised with a pillar stitch lapping in pile yarn system and at least one thread system. Another option is to incorporate the pile yarns at a defined angle (V-orientation), depending on the yarn threading and machine gauge, as well as the lapping as tricot/cord/atlas. This can be implemented with one or preferably with two thread systems. Another option is the X-shaped binding of the pile yarns in the spacer fabric cross-section. This is realised by 2 pile yarn systems and a counter lapping of a tricot, cord or atlas lapping ,65. The 3D reinforcement structures made of warp-knitted spacer fabrics have been used for concrete reinforcement in recent years ,67. 3D wThe individual layers are similar to the two dimensional, lattice-like NCF described in Another application involving integration of functional materials in the z-direction is spacer-knitted thermoelectric generators (TEGs). Metal wires have been integrated as functional and reinforcing materials in different structures in z-direction, which can generate electric current from waste heat. The TEGs achieve an electrical power of 1.78 μW .In order to produce more complex spacer fabrics with additional spatial curvatures, machine modifications of the double needle bar warp knitting technology are necessary. In principle process modifications in the double needle bar warp knitting process and thus product changes can be achieved by (1) varying the trick plate spacing and position, (2) by varying the fabric take-off and yarn tension and (3) by integrating additional technologies.An overview of the known technologies for the production of modified warp knitted spacer fabrics is given below.A further embodiment of the double needle bar warp knitting process is the use of a knitted fabric take-down with frictionally engaged conical take-down rollers . This maFurther developed double bar warp knitting techniques also make it possible to produce spacer warp knits with alternating distances between the partial areas within the working width and thus contoured closed and/or lattice-like surfaces .In parallel, research by Gries et al. looked at local reinforcement using inserts, for example for shell-stringer structures. For this purpose, a multiaxial warp knitting machine was modified, with which the production of the NCF and the connection with an already prefabricated textile stringer structure are carried out in a single operation . HoweverFranz developed warp knitted spacer panels  and tubuLüling has developed a technology for lightweight building components by combining 3D spacer fabrics with 3D printed objects. Such products can be used, for example, as textile façade shells for targeted shading and insulation. A key focus in the development of such structures has been to use the same groups of materials for both the print and the textile material, making the recycling process easier ,80. An eThe use of textiles with a high degree of prefabrication, such as 3D warp knitted fabrics, reduces the effort required in the post-textile production processes for the realisation of fibre-reinforced composite structures. It also enables innovative applications for textile structures. In particular, warp knitting technology is of considerable economic importance due to its principle-based high productivity.The review shows that there are a variety of textile engineering approaches for the production of 3D warp knitted fabrics. The classification in this paper is made in terms of machine technology into multiaxial knitting for 3D non-crimp fabrics (NCF) and double-bar knitting for spacer fabrics.For 3D NCF, there are approaches at material, structure and process level to improve the pre-forming of NCF in terms of wrinkle-free drape without overlap. It should be noted here that the structural modification of NCF has the potential to enable not only wrinkle- and overlap-free draping, but also load-path-compatible filament orientation through the targeted introduction of yarn reserves in the manufacturing process. However, this has not yet been implemented, as the focus so far has been on geometry-appropriate draping and the corresponding generation of yarn reserves.In the case of warp knitted spacer fabrics, it is also possible to optimise the appearance of the spacer fabric for a specific application by varying the material, structure and process. This can reduce the number of finishing operations and therefore costs and waste. In addition, the research results researched show that application-specific performance can be increased  and that completely new textile materials open up completely new fields of application .In order to contribute to an increase in the industrial application of 3D warp knitted fabrics through targeted further development, it is necessary to have an overview of the existing technologies, to which this review contributes.


Composite nanofibers with excellent physical and chemical properties are widely used in new energy, biomedical, environmental, electronic, and other fields. Their preparation methods have been investigated extensively by many experts. High-speed centrifugal spinning is a novel method used to fabricate composite nanofibers. The slip mechanism of polymer solution flows is an important factor affecting the morphology and quality of composite nanofibers prepared by high-speed centrifugal spinning. As the polymer solution flows, the liquid wall slip occurs inside the nozzle, followed by liquid–liquid interface slip and gas–liquid interface slip. The factors affecting polymer slip were investigated by developing a mathematical model in the nozzle. This suggests that the magnitude of the velocity is an important factor that affects polymer slip and determines fiber quality and morphology. Under the same rotational speed, the smaller the nozzle diameter, the greater the concentration of velocity distribution and the smaller the diameter of the produced composite nanofibers. Finally, PEO/PVA composite nanofibers were prepared using high-speed centrifugal spinning equipment at 900–5000 rpm and nozzle diameters of 0.2 mm, 0.4 mm, 0.6 mm, and 0.8 mm. The morphology and quality of the collected PEO/PVA composite nanofibers were analyzed using scanning electron microscopy (SEM) and TG experiments. Then, the optimal parameters for the preparation of PEO/PVA composite nanofibers by high-speed centrifugal spinning were obtained by combining the external environmental factors in the preparation process. Theoretical evaluation and experimental data were provided for the centrifugal composite spinning slip mechanism and for the preparation of composite nanofibers. Nanofibers exhibit excellent physical and chemical properties and are widely considered to be nanomaterials with great application potential . The mosCompared with several traditional methods of preparation methods, high-speed centrifugal spinning is simple and easy to use to produce nanofibers from various materials efficiently and cost-effectively . A serieA schematic illustration of the planar structure of the high-speed centrifugal spinning device is presented in In the early stages of hydrodynamic development, a few simple experimental observations were consistent with the assumption of no slip, so the slip phenomenon received little further attention. In recent years, with the rapid development of nanofabrication technologies, slip has played an important role in many industrial fields, such as electrochemical devices, polymer processing, and microfluidics ,29. The The slip problem was first introduced by Mooney , who expHatzikiriakos  investigYou et al.  analyzedRecent studies have shown that spinning parameters such as motor speed, nozzle length, nozzle diameter, nozzle structure, and solution concentration directly affect the morphological distribution of nanofibers during high-speed centrifugal spinning . Our stuIn previous studies, the no-slip boundary condition was one of the core concepts of fluid mechanics. This theory is reflected in a vast number of experimental results and utilized in many studies, which led to the neglect of the slip theory in related studies. With the significant improvement in experimental techniques, the slip phenomenon has been clearly demonstrated. The no-slip boundary condition is usually not maintained on the microscopic scale at sufficiently high shear rates. Many complex fluids exhibit inconsistencies with the no-slip boundary conditions, as most spinning solutions are non-Newtonian fluids characterized by a certain degree of viscoelasticity. Therefore, it is important to accurately determine the fluid properties of the polymer. In the case of high-speed rotational motion, the viscosity of the polymer solution of the wall-adherent layer varies with the shear rate, so both polymer solutions slip with the nozzle wall, the solution contact surface, and the air. The liquid–wall slip of polymer solutions during centrifugal composite spinning improves the extrusion and expansion of composite nanofibers and thins the average diameter of composite nanofibers. The liquid–liquid slip changes the internal structure of the composite nanofibers, resulting in composite nanofibers with different properties. Therefore, the polymer slip mechanism has a remarkably important effect on both polymer flow and deformation.b is the slip length . If b = 0, then there is no-slip boundary condition. However, if b ≠ 0, there is a slip boundary condition. su indicates the liquid wall slip velocity; The “slip length” is the most common concept used currently to quantify non-liquid slip on solid surfaces. This theoretical model was introduced into the nozzle to describe the slip on liquid and solid surfaces using the slip length:A parametric model was built in the nozzle, as shown in k and n are the rheological parameters. As the polymer solution is a non-Newtonian fluid, it does not conform to Newton’s law of internal friction. Considering it as a power-law fluid, its flow velocity distribution is determined:In Equation (2) above, r is the length of the distance between the nozzle wall and the middle partition; The shear stress also increases as the nozzle radius increases. The polymer flow rate distribution starts to decrease. Substituting Equation (3) into Equations (4) and (5), the following can be obtained:Q in the nozzle is:The flow rate Substituting Equations (2) and (3) into Equation (6) gives:The size of the nozzle diameter affects the velocity distribution and flow rate of the polymer solution in the nozzle as well as polymer jet formation. It also indicates differences in the quality of the composite nanofibers obtained via nozzles of different diameter.High-speed centrifugal spinning technology uses the centrifugal force generated by high-speed rotation as the driving force to produce nanofibers, primarily via high-speed rotation of the polymer in solution as the spinning material. At this time, the nozzle is in a high-speed rotational motion. The nozzle compound spinning solution in the multi-field exhibits a coupling effect along the nozzle outward movement. As the two different polymer solutions are continuous media, they permeate and couple with each other. However, the different kinematic properties lead to sliding of the two polymer solutions against each other, creating a two-phase flow. The flow of spinning solutions with different characteristics and concentrations generates a contact surface between the two solutions. The solution molecules continuously diffuse through the contact surface, forming a mixed layer with limited miscibility between the two phases, as shown in q phase is determined by:p phase; p phase; p phase; p to phase q. Using the mass equation, Equation (9) can be derived:The continuity equation of the The momentum conservation equation is as follows:In Equation (10) above, In the initial stage of jet injection, the power wave is generated by fluctuations between the liquid–liquid two-phase interface in the mixed layer of the polymer solutions due to flow instability, as the polymer solution has yet to be solidified. The liquid–liquid interface with fiber length dx was selected for analysis, as shown in The static force per unit width acting on the micro-element body of solution 2 is:The total force per unit volume of solution 1 minus the total force per unit volume of fluid 2 can be expressed as:The flow tends to stabilize when the slip velocity of the two solutions has the following relationship:Therefore, the slip velocity of the liquid–liquid two-phase is an important factor determining the fluctuation across the liquid–liquid two-phase interface, and the fluctuation occurring at the two-phase interface will lead to the instability of the flow of the two polymer solutions, which in turn will affect the preparation of the composite nanofibers and the quality of the fibers after forming.Centrifugal forces are generated when the nozzle is in high-speed rotational motion, which causes the polymer solution to be subjected to a high-speed airflow from the time it forms a jet until after it leaves the nozzle. When the polymer solution forms a jet leaving the nozzle, it is stretched and evaporated to form composite nanofibers that are eventually collected. A gas–liquid layer is generated between the jet formed by the polymer and the air, resulting in gas–liquid slip. The micro-element dx at the fiber–gas–liquid interface in the nozzle was selected for analysis. Gas–liquid slip has a phase interface, with interactions at the interface as well as between the gas–liquid phases. Energy transfer also occurs across the gas–liquid phase, but both the gas-phase medium and the liquid-phase medium have their own separate physical characteristics, so the basic equations of each phase should be established to investigate the gas–liquid slip. The gas–liquid interface with fiber length dx was selected for analysis, as shown in q is the heat flow entering from the wall; Because the polymer solution undergoes stretching and evaporation, the conversion of liquid to gas under thermodynamic equilibrium is expressed as:A is the flow cross-sectional area and In Equation (17) above, Also from the mass flow rate calculation equation:x:The continuity equation for the gas–liquid two-phase mixture at the time of gas–liquid slip is obtained by combining Equations (17)–(19):So, the slip model for polymers is summarized as follows: the liquid–wall slip of polymers is related to the size of the nozzle diameter; the liquid–liquid slip velocity affects the stability of the polymer flow; the gas–liquid slip velocity influences the motion of the polymer.There is a wide range of materials that can be applied to the preparation of composite nanofibers by high-speed centrifugal spinning, and polyethylene oxide (PEO) and polyvinyl alcohol (PVA) were selected as the centrifugal spinning composite fibers in this experiment. The PEO exhibits excellent properties such as low solution rheology, the combined action with organic solvents, low ash content, and thermo-plasticity. It can be used as a detergent, flocculant, thickener, lubricant, dispersant, aqueous phase reducer, textile slurry, and water-soluble film. PVA is a non-toxic, tasteless, harmless water-soluble polymer, characterized by good density, high crystallinity, and strong adhesion. It is made of flexible and smooth film. It exhibits resistance to oil and abrasion, good gas permeability, as well as water resistance. It has a wide range of uses. It is a natural non-polluting resource. However, at low concentrations, the concentration of the prepared PVA solution viscosity is not adequate to meet the requirements of centrifugal spinning out of the fiber. It exhibits worse performance. However, when the concentration of the prepared PVA solution is large, the solution viscosity is increased. Due to its strong hydrophilicity, the solvent is not easy to volatilize, seriously affecting the structure and performance of centrifugal spinning PVA fiber. The prepared PEO solution exhibits large viscosity at small concentrations. Together with PVA, it can effectively improve the material spinnability for the preparation of composite nanofibers by centrifugal spinning.In this experiment, specific amounts of PEO and PVA powder were added to water as solutes. PVA was fully dissolved at 90 °C to 100 °C with a magnetic stirrer at 200 rpm for about 5 h. PEO was fully dissolved at room temperature with a magnetic stirrer at 260 rpm for about 10 h. PVA solution with a mass fraction of 9% and PEO solution with a mass fraction of 4% were prepared.The high-speed centrifugal spinning equipment used in the experiments of this paper is shown in The centrifugal force is generated by high-speed rotation. The difference in the cooling rate of the spinning solution, and the change in concentration, viscous force, and surface tension during the solidification of the jet affect the steady-state motion of the composite jet, which eventually has an important effect on the final morphology of the composite nanofibers. Therefore, the experimental setup parameters of high-speed centrifugal spinning, the selected polymer solution parameters, and the experimental environment are important factors for the preparation and collection of composite nanofibers. In this paper, comparative experiments were performed at different nozzle diameters, different concentrations, and different motor speeds. Finally, the diameter and morphology of the collected composite nanofibers were characterized using scanning electron microscopy (SEM) and TG experiments.In the tank, 9 wt.% PVA solution and 4 wt.% PEO solution were added. The motor was connected and started after adjusting the device.Spinning experiments indicated that when the rotational speed was below 900 rpm, significant droplets were ejected and no fibers were collected. Because the rotational speed was too small, the polymer solution was not stretched enough and the jet was less stable when rotating in air. Continuing to increase the speed, the PEO/PVA composite nanofibers were prepared and successfully collected in the range of 1200~2100 rpm. Based on the morphology of PEO/PVA composite nanofibers at 1200 rpm and 1500 rpm by SEM, as shown in When the motor speed was in the range of 1200–3000 rpm, the SEM images at 1500 rpm, 2100 rpm, and 2700 rpm were selected, as shown in The initial diameter of the rotating jet is limited by the nozzle diameter as it leaves the nozzle, which in turn affects the diameter of the fibers. In order to investigate the morphological effect of nozzle diameter, PEO/PVA nanofibers were prepared using nozzles of different diameters. The SEM images of PEO/PVA nanofibers prepared with different nozzle diameters are shown in The thermal decomposition of PEO/PVA films was analyzed at a temperature increase rate of 10 °C/min and a range of 30–800 °C. As shown in According to the TG curves, the initial decomposition temperature of PEO/PVA composite film was 38.9 °C at 1500 rpm. The initial decomposition temperature of PEO/PVA composite film was 78.9 °C when the speed was increased to 2100 rpm. The thermal decomposition rate of PEO/PVA composite film fabricated at 2100 rpm was lower at 250~440 °C. Thus, the increase in the rotational speed enhanced the mixing of PEO and PVA and improved the thermal stability of the composite nanofibers of PEO/PVA. In addition, the improved spinning condition led to a gradual increase in the decomposition temperature, which enhanced the thermal stability.The external environment in centrifugal spinning experiments is also one of the most important factors affecting the final morphology and quality of composite nanofibers. In this regard, temperature and humidity are important factors of the external environment affecting the preparation of composite nanofibers. Temperature affects the solidification rate of the spinning jet, and the ability of the spinning jet to solidify quickly and be sufficiently stretched is the key to the preparation and collection of nanofibers. If the spinning jet is incompletely solidified by the time it reaches the collection device, a large number of droplets will appear on the surface of the collected composite nanofibers and stick together, which will lead to a poor morphology and quality of the prepared composite nanofibers. The effect of humidity on the water-soluble spinning solution is attributed to the solidification of PEO upon exposure to water. Therefore, excessive humidity during spinning can lead to solidification of the solution, resulting in nozzle clogging. Therefore, the temperature and humidity of spinning indirectly affected the experimental success of preparing PEO/PVA composite nanofibers. Appropriate adjustment of the environment temperature and humidity based on the physical properties of the spinning material and the device parameters is necessary to ensure a suitable experimental environment for the preparation of composite nanofibers.In this paper, the slip mechanism of the polymer in centrifugal composite spinning is analyzed and three slip models are developed. The slip distribution of the polymer is influenced by the rotational speed. As the rotational speed increases, slip occurs first between the nozzle wall and the polymer solution, then between the interfaces of the two different polymer solutions, and finally at the gas–liquid interface. At the same polymer solution concentration, fluctuations at the interface of the two phases can lead to an unstable flow of the two polymer solutions, and the slip velocity is an important factor affecting the fluctuations between the liquid–liquid interface. After the concentration of the solution is determined, a slow motor speed prevents fiber formation. As the the motor speed gradually increases, the polymer solution flow is gradually stabilized and the collected fiber morphology and quality are significantly improved; when the speed exceeds a certain range, the composite nanofibers break on the collection device. Therefore, it is necessary to control the speed within a certain range to make the polymer solution flow more stable, and the morphology and quality of the prepared composite fibers can improve. Moreover, when the speed is too large, the airflow near the nozzle is enhanced, which affects the process of gas–liquid slip and the fiber is easily broken. Meanwhile, when the velocity is the same, the smaller the nozzle diameter, the more concentrated the polymer flow velocity distribution, and the fiber diameter also decreases with decreasing nozzle diameter. Therefore, repeated controlled experiments are needed to find the optimal parameters for the preparation of composite nanofibers. The morphology, diameter distribution, and thermal decomposition process of the PEO/PVA composite nanofibers are analyzed and compared by SEM experiments and TG experiments. The effects of motor speed and nozzle diameter on the surface morphology and internal structure of the composite nanofibers during fiber preparation are obtained. It is confirmed that the motor speed and nozzle diameter are important factors affecting the polymer slip and the morphology of the composite nanofibers. However, the influence of the slip mechanism of polymer solutions on the structure and performance of composite nanofibers still needs further investigation and refinement. For example, the roughness of the wall surface during the liquid–wall interface slip and the high-speed airflow around the gas–liquid slip affect the preparation and collection of composite nanofibers significantly. Therefore, the selection of suitable experimental parameters is important to ensure composite nanofibers with good morphology for widespread application. Centrifugal spinning for the preparation of composite nanofibers has great potential for improvement. As further research and improvements are made to centrifugal spinning technology, the technology will continue to develop and be more extensively used in various fields.


Mass vaccination of the global population against the novel COVID-19 outbreak posed multiple challenges, including effectively administering millions of doses in a short period of time while ensuring public safety and accessibility. The government of Dubai launched a mass campaign in December 2020 to vaccinate all its citizens and residents, targeting the population aged >18 years against COVID-19. The vaccination campaign involved a transformation of multiple commercial spaces into mass vaccination centers across the city of Dubai, the largest of which was the Dubai One Central (DOC) vaccination center. It was operational between January 17, 2021, and 27 January 27, 2022.The multiphase research study aims to empirically explore the opinions of multiple health care stakeholders, elicit the key success factors that can influence the effective delivery of emergency health care services such as a COVID-19 mass vaccination center, and explore how these factors relate to one another.To understand more about the operations of the DOC vaccination center, the study follows a multiphase design divided into 2 phases. The study is being conducted by the Institute for Excellence in Health Professions Education at Mohammed Bin Rashid University of Medicine and Health Sciences between December 2021 and January 2023. To elicit the key success factors that contributed to the vaccination campaign administered at DOC, the research team conducted 30 semistructured interviews (SSIs) with a sample of staff and volunteers who worked at the DOC vaccination center. Stratified random sampling was used to select the participants, and the interview cohort included representatives from the management team, team leaders, the administration and registration team, vaccinators, and volunteers. A total of 103 people were invited to take part in the research study, and 30 agreed to participate in the SSIs. To validate the participation of various stakeholders, phase 2 will analytically investigate one’s subjectivity through Q-methodology and empirically investigate the opinions obtained from the research participants during phase 1.As of July 2022, 30 SSIs were conducted with the research participants.The study will provide a comprehensive 2-phase approach to obtaining the key success factors that can influence the delivery of high-quality health care services such as emergency services launched during a global pandemic. The study’s findings will be translated into key factors that could support designing future health care services utilizing evidence-based practice. In line with future plans, a study will use data, collected through the DOC vaccination center, to develop a simulation model outlining the process of the customer journey and center workflow.DERR1-10.2196/42278 Health care providers are continuously looking to innovate the design and delivery of health care services as it is essential to provide the highest level of patient and public health care . In geneGaining insight into the nature of the stakeholder’s interactions and individual perspectives is valuable to consistently enhance the quality of care, ensuring that these 5 topics are also incorporated within health care design ,3. TheseAnother aspect of improving health care services is applying service-oriented architecture (SOA), which was found to reduce costs, improve patient care quality, and incorporate the organization’s legacy system with updated IT infrastructure to be better aligned with the organization’s principles and targets . In addiResearch surrounding the implementation of SOA in health care has identified critical success factors (CSFs) that can influence this process and are considered valuable for its success. Koumaditis et al  developeDuring the COVID-19 pandemic, one of the health care services that needed to be immediately deployed was the creation of emergency vaccination centers to support the vaccination strategy ,6. When The typical method to improve the effectiveness of mass vaccination during health emergencies or a global pandemic is the development of emergency points, also known as points of dispensing (PODs) . PODs arThe novel COVID-19 outbreak was first declared a global pandemic by the World Health Organization on March 11, 2020 . The UniThe government of Dubai, for example, launched a mass campaign to vaccinate all its citizens and residents who met the criteria in December 2020, also targeting the population aged >18 years. The collaborating authorities managing the launch of this campaign involved the Dubai Health Authority and Dubai’s COVID-19 Command and Control Center. The expertise throughout the collective teams complemented each other; the Dubai Health Authority placed a medical guideline for the administration of the vaccines and shared updated protocols, whereas Dubai’s COVID-19 Command and Control Center developed a strategy to open and manage multiple vaccination centers across the city. The implementation of this program stretched the resources of various governmental agencies to swiftly achieve and create accessible public vaccination PODs. It included transforming commercial spaces into dedicated vaccination centers, the largest of which was the Dubai One Central (DOC) vaccination center. This was the first vaccination center opened in Dubai and was operational between January 17, 2021, and January 27, 2022.The empty commercial spaces at DOC were swiftly transformed and equipped to become a fully functioning vaccination center in just 72 hours. As a result, the team at the center administered 1,476,776 Pfizer-BioNTech vaccine doses (complete appointments) against the infection of COVID-19 in one year . They are considered as complete appointments once the customer completes the entire process of registering for and receiving a COVID-19 vaccine dose, whether it is the first, second, or third dose. The DOC vaccination center received between 147,836 and 211,859 customers per month during the peak operational times (May 2021 to September 2021), vaccinating between an average of 5280 and 7062 customers per day. Notably, the original capacity of the center was designed to hold a total of 4000 customers per day; however, through various operational improvements, the center was able to receive and vaccinate over 10,000 people per day.Our review of the literature identified multiple studies that discussed the importance of exploring the patient’s perspective when designing an optimized model to deliver a more efficient health care service ,13,14. TThrough a comprehensive research design, the following 3 research questions will be addressed:What key success factors can influence the delivery of a health care service during a public health emergency, such as a vaccination center?How do these CSFs relate to one another?To what extent do these CSFs impact the delivery of health care services?The study is being conducted by the Institute for Excellence in Health Professions Education at Mohammed Bin Rashid University of Medicine and Health Sciences, located in Dubai, UAE, between December 2021 and January 2023. To better understand the CSFs of the DOC vaccination campaign, this study follows a multiphase design divided into 2 phases, as illustrated in A qualitative design was applied to fulfill the study’s aim and answer the first research question. Individual semistructured interviews (SSIs) were conducted via Microsoft Teams with a sample of staff and volunteers (n=30) working at the DOC vaccination center. The staff and volunteers of DOC were considered key contributors to the design and execution of the vaccination program. A total of 103 people were invited to participate in the research study, and 30 people agreed to participate in the SSIs.Stratified random sampling was used to select the participants. The interview cohort included representatives from team leaders, the management team, the administration and registration team, vaccinators, and volunteers. The composition of the participants’ roles is included in The study’s cohort was recruited via email or phone invitation. Before the start of any interview, the research participants were asked to sign a consent form that outlined their rights as a research participant and complete a questionnaire that collected general sociodemographic data before the start of the interview, which can be found in The interview protocol was developed to capture the study’s objectives and included 2 main elements: the opening statement by the interviewer and the interview script, including a set of questions acting as a guide during the discussion . The opeFinally, the interviews were recorded through Microsoft Teams for documentation purposes, which later assisted with the transcription process. The SSIs conducted in English (n=16) were outsourced to be transcribed using the verbatim method and then revised by a researcher on the project. The Arabic interviews were also transcribed verbatim, translated to English, and then independently revised by a researcher. Finally, the content is currently in the process of being thematically analyzed using MAXQDA 2020 (VERBI Software) . The thoCombining qualitative and quantitative techniques, the Q-methodology aims to investigate one’s subjectivity  analyticTo answer the second research question, a topic will be identified for the Q-methodology to examine how the identified success factors from phase 1 relate to one another. The “Q-set” will be developed based on the most common and impactful answers selected from the thematic analysis of the SSIs. This “Q-set” will be shared with a smaller sample group (n=10), and they will be asked to rank each of the statements based on purposefully defined criteria such as perceived importance [The next step is data collection and will include “Q-sorting,” where each research participant ranks the statements in the “Q-set,” following the same scale set in the pilot phase. After purpose sampling, a collection of the ranked statement by an individual, known as the “Q-sort,” will be statistically analyzed using the inverted factor analysis methods . During Finally, the CSFs that may impact the delivery of health care services will be identified after discovering the relation between the factors. These CSFs will be mapped and categorized following the proposed model by Koumaditis et al .The Dubai Scientific Research Ethics Committee approved the study in November 2021 (DSREC-11/2021_04).The research population included members directly involved in developing and implementing the COVID-19 vaccination campaign in Dubai and at the DOC vaccination center. All participants signed a consent form before the interview and were notified of the study’s purpose in written and verbal communication. The identity of all participants will remain anonymous during the submission of the results for phases 1 and 2 of the study. All study data will be kept on a secure, password-protected computer accessible only to the research team .To fulfill the first research question, as of July 2022, 30 SSIs were conducted with the research participants outlined in The results from the project’s first phase are expected to elicit the critical success factors, enablers, and barriers of the design and operation of the COVID-19 vaccination center at DOC.Results from the project’s second phase will highlight how the success factors identified in phase 1 will relate to each other, answering the study’s second research question. Additionally, the expected results from the analysis will feature patterns of similarities and differences from the Q-sets. Finally, and to answer the third research question, we will identify the extent of these success factors’ impact on the delivery of health care services.The SSIs were conducted to explore people’s perceptions about the DOC vaccination center and elicit the key success factors surrounding its design and implementation. Another strength of the research study is the number and quality of interviews completed. The researchers organized 30 interviews—the recommended number of SSIs that need to be completed to provide meaningful results for a research study . The groIn addition to completing the SSIs, the Q-methodology will focus on allowing participants to express their opinions about the subject while reducing former expectations and possible biases introduced by the researcher. It is also known as a people-centric approach that can provide a deeper view on the matter and is beneficial when studying complex health care topics . This meThe result of our research can help bridge a noted gap in the literature  as we exIt is noted that there is limited information in the medical literature on the systematic process of creating MVCs. Although mass vaccination campaigns have been mentioned as a general component for managing communicable diseases since the 1970s during the spread of H1N1 influenza, there is a lack of clear criteria to defining an MVC, such as pertaining to the number of doses and/or number of people served in a day . For exaStudies surrounding the development of MVCs specific to the COVID-19 pandemic are still considerably low ,21. TheySince MVCs for COVID-19 are believed to be the first mass vaccination effort in the present era , it is cKnowledge generated from this study conducted in the Gulf Cooperation Council and the Middle East region will contribute to a more accurate global representation of the success factors, as we aim to empirically explore the opinion of multiple health care stakeholders and elicit the key success factors influencing the delivery of a health care service during a public health emergency, such as a vaccination center.Due to restrictions imposed because of the COVID-19 pandemic, the SSIs were completed remotely, via the videoconferencing platform Microsoft Teams. This was often considered a challenge as there were technical difficulties while the interviews were taking place such as unreliable internet connection. Utilizing an online platform to collect data may have impacted the quality of recordings, which in turn may have affected the quality of the transcriptions. Additionally, attempting to schedule at least 30 interviews in a short time frame before the center’s closure proved difficult to plan around the employee’s schedules, and the interview schedule was continuously delayed. The SSIs were conducted with a sample of DOC vaccination center’s staff and volunteers before the closure of the center by 2 months and were completed shortly afterward. Therefore, the time between data collection and the closure of the DOC vaccination center may have contributed to recall bias as the interviewees were asked to recollect events from the past. Finally, due to the workload of the front-line workers at the DOC vaccination center, pandemic fatigue may have also been a factor that could have influenced their responses in the interviews.Future research will leverage the data collected to contribute to the medical informatics field, specifically with the aims to explore approaches that can effectively analyze big data, include predictive analytics, and optimize decision-making . In lineThe simulation model will focus on capturing the data at 3 significant milestones, including when the center reached a daily capacity of administering 1000 doses, 4000 doses, and 10,000 doses to customers. This will showcase the center during various operational phases and the improvements that took place during each stage and identify areas that needed more enhancements to increase operational efficiency. Simulation modeling has been identified as a smart tool that offers the prospect of testing various scenarios using a cost-effective approach, obtaining solutions for obstacles during certain health care service phases, comprehensively visualizing the process .This analytical phase of the study will focus on the operational aspect of designing a health care service and how it can assist with the decision-making process through an optimized health care service model . In a waThe study provides a comprehensive 2-phase approach to eliciting the CSFs that can influence the delivery of high-quality health care services such as emergency services launched during a global pandemic. The findings from the study will be translated into key factors that could be optimized and applied when designing future health care services, utilizing evidence-based practice. Additionally, the results from the study conducted in the Middle East region will contribute to a more globally accurate representation of CSFs. Finally, the future work from this research study will explore methods to analyze data collected from the DOC vaccination center, include predictive analytics, and optimize decision-making.


There is a grooving body of evidence emphasising the need to support and enhance effective mentorship practices for nursing students in nursing home placements, including strengthening of the pedagogical competence of registered nurse mentors. Owing to the necessity for multifaceted mentoring competence and the challenges of workload registered nurses are facing, the use of flexible digital educational resources has been suggested. However, current knowledge on the effectiveness of digital educational resources in enhancing mentorship practices in nursing homes is scarce. This study aimed to explore the perception of registered nurse mentors regarding the effectiveness of a digital educational resource, particular its usability and value-in-use in supporting and enhancing mentorship practices in nursing homes.The study applied an exploratory descriptive qualitative design. Pre- and post-mentoring semi-structured focus group interviews were conducted among a total of 23 registered nurse mentors across three Norwegian nursing homes. The transcribed interviews were thematically analysed. Standards for reporting qualitative research were followed.The analysis yielded one pre-mentoring theme: (1) predominant enthusiasm and satisfaction and three post-mentoring themes: (2) enhanced confidence and motivation, (3) enhanced mentoring competence in supporting the nursing students’ learning process, and (4) factors influencing the value-in-use of the digital educational resource.Digital educational resources support effective mentorship practices by enhancing the confidence and motivation in the mentor role and by enabling more goal-oriented supervision and assessment tailored to the learning goals of students. The implementation of digital educational resources to support and enhance effective mentorship practices is an important avenue for further research towards achieving high-quality learning environments in clinical nursing education in general and nursing homes. Based on the study findings, nursing educational institutions should consider offering digital educational resources to develop, support, and advance mentorship training, which may more effectively impact and improve the quality of clinical nursing education.The online version contains supplementary material available at 10.1186/s12912-023-01570-9. There is a grooving body of evidence emphasising the need for educational methods to support and enhance the pedagogical and supervisory competence of registered nurse (RN) mentors  to promote effective mentorship practices –3. DigitMentorship in nursing homes somewhat differs from that in specialist health care settings  , as nursIn their recent integrative literature review, Splitgerber and colleagues  identifiDespite an emerging body of research into educational interventions to support effective mentorship practices that promote enriched learning and positive placement experience in clinical education in nursing homes, more research is required . ConsideOur study strives to address this knowledge gap by aiming to explore the perception of RN mentors regarding the effectiveness of a DER, particular its usability and value-in-use in supporting and enhancing mentorship practices for first-year nursing students during clinical education in nursing homes. Usability has been considered during the developmental process of DERs ; however(1) What characterises the first impressions of RN mentors concerning the usability of a DER designed to enhance their mentorship practices?(2) What characterises the value-in-use of a DER in mentorship practices as perceived by RN mentors?The following research questions guided the study:Based on the study aim, an exploratory descriptive qualitative design was applied  to exploThe DER was offered to RN mentors across three publicly funded nursing homes situated within a city-based municipality in western Norway in 2021. In this study, mentorship in the nursing homes referred to an 8-week  clinical placement period for first-year nursing students. A RN mentor from the nursing homes provided daily supervision and follow-up for one or two students . MoreoveThe DER used by the RN mentors in this study was co-created with mentors from nursing homes and other key stakeholders (e.g. nursing students and nurse educators) to ensure a resource in better alignment with the needs and perspectives of RN mentors . The co-Each module is organised with a main topic: Module 1: introduction on mentorship and pedagogical supervisory approaches ; Module 2: supervision and assessment strategies ; and Module 3: formal and formative assessments. The modules consist of various components such as informative text , illustrations, different digital supplies (e.g. ‘Tool for supervision and assessment’), podcast, video lectures, reflective activities, and an interactive case assignment. The Tool for supervision and assessment is a resource form stating the competencies nursing students are required to achieve and guides the supervisory approach of RN mentors. Based on observations of nursing students in a specific learning situation, RN mentors can assess the level of competence, professional development, and areas for further growth in conjunction with different areas of nursing competence of students. All modules end with a list of appropriate advice tailored to RN mentors, summarising key module contents. Moreover, the DER contains all practical information from the nursing faculty, which RN mentors usually receive as paper files. The DER could be employed from all kinds of digital devices . In this study, tablets were also distributed to the enrolled participants prior to the pre-mentoring focus group interviews. An overview of the DER content is illustrated in Fig. A total of 29 RN mentors across three nursing homes consented to use the DER during the clinical placement of first-year nursing students in the nursing homes. Of these RN mentors, 23 consented to participate in the semi-structured focus group interviews exploring the usability and perceived value-in-use of the DER. Twenty-three RN mentors participated in the pre- mentoring focus group interviews (interviews 1–3) conducted prior to the placement period and 18 RN mentors in the post-mentoring focus group interviews (interviews 4–6) conducted after the placement period. The reasons for drop out and non-participation of five mentors in the post-mentoring interviews were not registered. In line with the research design, the participants were recruited via purposive sampling , consideData were collected in February and April 2021 during one pre- and one post-mentoring focus group interview at each of the three nursing homes enrolled. All focus group interviews were audio-recorded and had an average duration of 60 min. Owing to the COVID-19 pandemic; it was not feasible to conduct face-to-face interviews at two of the three study sites. Instead, a digital platform (Teams) was applied. The pre-mentoring interviews were conducted by the first, second, and fifth authors and the post-mentoring interviews by the first, second, third, and fifth authors, all holding a nursing and education background. Semi-structured interview guides informed by the literature and previous research guided the interviews.The participants gained access to the DER 1 week before the placement and mentorship periods (i.e. week 5). In the following week (week 6), the pre-mentoring interviews (interviews 1–3) were conducted to explore the experiences of the participants regarding the usability of the DER. After the 8-week placement period (weeks 7–15), the post-mentoring interviews (interviews 4–6) were conducted in the following week (week 16) to explore the perceived value-in-use of the DER of the participants . An overThe framework for thematic analyses described by Braun and Clarke , 38 and The framework of quality criteria by Lincoln and Guba  was applDerived from the analysis of the pre-mentoring interviews, one theme reflected the first impressions of the RN mentors regarding the usability of the DER: (1) predominant enthusiasm and satisfaction. The analysis of the post-mentoring interviews yielded three themes illustrating the value-in-use of the DER as perceived by the RN mentors: (2) enhanced confidence and motivation, 3) enhanced mentoring competence in supporting the nursing students’ learning process, and (4) factors influencing the value-in-use of the DER. The themes are presented in Fig.  enhanced“It was nice to find answers right away. If we didn’t have the programme [the DER], we would have to wait until the nurse educator arrived to explain or go through everything.” The participants were predominantly enthusiastic and satisfied with the DER usability. In the pre-mentoring focus group discussions, the DER design and layout were described as appealing with the clear and appropriate structure of the modules and content components. An adequate resource functionality was highlighted by several participants, as it was easy for them to navigate searching for specific subjects. Avoiding seeking through the usual paper files from the nursing faculty was considered a great advantage. In addition to the design, layout, and ease of use, the participants related usability to the DER content and relevance for mentorship. A clear resource structure and comprehensive content added to satisfaction in pre-mentorship practices, such as being more prepared. A participant said:“I have never supervised nursing students before. The resource [the DER] will be very helpful for me, and I so delighted to have access to it. I don’t quite know how to help the students. And it is important to know what to say to them, what to show them, and what they are supposed to learn during this placement period”. The findings showed that many participants emphasised the relevance of specific components of the DER. Module 1 was described as instructive for planning the placement period, as it helped the participants to understand the mentor role and responsibility, educational context and level of competence to expect from nursing students. In Module 2, descriptions of students’ areas of competence combined with suggestions on supervision and assessment strategies were particularly engaging for many participants. The RN mentors with no or minimal mentoring experience appreciated how the DER provided them with knowledge and necessary functionalities to support the learning and development of first-year nursing students.“Being a RN mentor in Norway is completely different from my home country. What I struggle with the most is assessment… It will be good for me to go through the descriptions [areas of nursing competence described in the DER] to find out what to look for when assessing a student. Reflective dialogues are also new for me. Here [in Norway], you spend a lot of time ‘reflecting on’… I am not that used to that”. Satisfaction with the DER usability was particularly stressed by the inexperienced RN mentors with a diverse cultural and linguistic background. A participant explained:Finally, the DER could also promote a more fair and equal treatment in the supervision and assessment of nursing students. A couple of the participants explained that dissimilarities in mentorship practices and expectations of students’ competence level might affect their learning experiences negatively.“I studied the programme [DER], and it worked very well, both at the computer, smartphone, and the tablets. You can download components from the programme, print it – it works fine. I think it is fantastic”. The choice of digital devices used to access the DER differed among the participants: distributed tablets, desktop computers at the nursing home wards, private laptops at home, or mobile phones. Many participants were enthusiastic about combining devices.Although most RN mentors reacted with satisfaction on ease of use, a minor proportion of the participants across the age groups reported some difficulties accessing the resource as well as in downloading, saving and printing documents or specific design solutions within the DER.The second theme suggested that using the DER during the 8-week placement period enhanced the RNs’ mentoring competence. Thus, post-mentoring, the participants expressed values as gaining independence, confidence, and motivation in the mentor role from using the resource.“This was the first time I supervised students. I supervised two students, but they were on two different levels of competences… I knew I was going to struggle with that, so I think the resource helped me. How can I put it – it supervised me in how to supervise the students”. The participants holding no, or minimal mentoring experience emphasised various mentoring knowledge and skills gained from the DER. One of the mentors talked about a greater insight and knowledge on mentorship in general and thus gained independence when performing the mentor role. Another participant described how the DER contributed to enhancing both pedagogical competence and mentor capacity. Moreover, as a novel mentor supervising two nursing students simultaneously for the first time, one of the participants reported that the DER provided her with a better understanding of mentorship and the confidence to manage a dual mentor role.Regardless of mentoring experience, several participants stressed how the DER enhanced their capability in performing core mentoring responsibilities, such as creating a supportive learning environment. Moreover, the DER enabled the participants to align personal mentorship practices from previous periods and better prepare for the mentor role.“I think that it [the DER] recognises the nurse mentors’ role. And for my part, that I have become more aware of that. You get a little more professional input on what the mentor role is. It is very good for us who have supervised for a long time”. “It has been more enjoyable to supervise students. Obvious because I have years of experience, but when the DER came, it got even better. I have heard about other nurses disliking mentoring students because they have not attended any mentor courses. But when this [the DER] came, I know the feedback has been very good”. Some participants with more than 10 years of mentoring experience related the value-in-use of the DER to recognition of the mentor role and renewed motivation in mentorship.“I have used it [the DER] both before the students started and very actively throughout the placement period – and together with the students… The student’s professional background is important, and then it [the DER] helped me to find out what she had learnt at the nursing school and what experience she had with patients. In that way, the programme [the DER] helped me to find out where the student was [level of competence and experience], so I could tailor my supervision accordingly”. The analysis of the post-mentoring focus group interviews indicated that the participants gained knowledge from the DER on how to support the learning process of students. This included the use of a more learning goal-orientation approach as well as reflection and assessment strategies in mentorship practices. One of the participants said:Several participants appreciated the DER presenting multiple ways of combining various learning situations and students’ areas of competence . One of the mentors described how this was particularly useful in her ward , as they usually did not have first-year nursing students. The DER enabled the mentor to identify learning situations and assign appropriate tasks corresponding to the learning goals of students.Applying specific supervision strategies to support nursing students’ learning process was likewise discussed among the participants. One of the mentors used the DER before supervising students to gain mentorship inspiration and knowledge on how to promote reflection in supervision. Another participant used a specific situation from the nursing home ward during supervision to optimise the learning situations and encourage students in bridging theory and practice in reflective discussions.“I have done this [supervised nursing students] many times before, and I have attended nurse mentor courses. But for me it was nice to find specific thing in resource… Particularly I didn’t know a lot about assessing the students’ clinical skills, so I could look it up in the resource [the DER] for support and guidance”. Likewise, some of the more experienced mentors spoke about enhanced mentoring competence. However, differing from the less experienced RN mentors, these participants appreciated how the DER enabled them to enhance specific pedagogical characteristics and thus reinforce their existing mentoring competence.“Me and another nurse shared a bit on the supervision since I don’t work full time. So, I used the DER on both students [my student and my colleagues’ student]. I believe that the resource can make it easier to contribute to the supervision of other nurses’ students. Because you don’t always know exactly how to handle things, but you will find it in the resource”. Supporting mentor colleagues was also related to the insights gained from the DER. One of the participants talked about how mutual reflections with a colleague helped in assessing the learning and professional development of a nursing student. Another explained how DER contributed to the utilisation of available resources in the ward.“I used the ‘Tool for supervision and assessment’ to prepare for the formal assessment discussions. It helped me to being able to follow the assessment discussions. It helped me to understand and combine the areas of competence the student should learn and write about. I thought that was useful, I can see their professional development and what they have achieved during the period. It gave me an overview, and it was much better for me, than just observing the student and nurse educator talking, and maybe not understand what they are talking about”. In preparing for the formal assessment discussions of students, some mentors shared that the DER improved their preparedness, involvement, and understanding of the formal assessment discussions. A participant explained how the use of the Tool for supervision and assessment provided her with a meta-perspective important to take a more active and informed position in the formal assessment discussion.Finally, our findings highlighted the importance of the DER content in relation to the specific nursing home context and supervision of first-year nursing students in this clinical setting. Some participants called for information on different models in supervision and challenges that can arise in mentoring nursing students. Other participants emphasised the DER content related to nursing home characteristics, such as dementia care , important to support the learning process of students.The RN mentors reported that the lack of allocated time to supervise, insufficient level of mentoring competence, and digital illiteracy limited the perceived value-in-use of the DER. Moreover, individual student- and nurse educator-related factors  played an influencing role.“Honestly, I didn’t really use it [the DER] during the placement period. It was mainly before the students arrived. I viewed all of it, and I liked the practical examples [Module 2]. For 8 weeks, I have been working overtime every time I supervise students. I had to send them [the students] home to get my own chores done”. Most participants used either all or parts of the DER but to a somewhat differing extent and mainly at the beginning of the placement period. The RN mentors with no or minimal mentoring experience used the DER on a more regular basis throughout the placement period. The participants with the longest mentoring experience reported less use of the resource. Regardless of mentoring experience, the lack of allocated time to supervise students was predominantly a negative influencing factor:“I had a lot of challenges with my student. It was about language and culture. So, it became too difficult to use the examples in the DER because I had to address so many other things first. I introduced the programme [DER] to the student but it was too challenging because of the language and cultural-related problems the student experienced… maybe if the placement period was longer, I could have use it [the DER]”. While some participants emphasised the DER as a useful tool in challenging mentoring situations , other participants experienced the opposite. Concerns of passivity and lack of interest from students or excessive introversion and reserved behaviour of students challenged the mentors’ experience of the value-in-use. Two of the participants strived to apply the DER in mentoring culturally and linguistically diverse students. Despite being an experienced RN, one of the participants faced what she experienced as a challenging situation.The other mentor was likewise aware of providing good and appropriate mentorship supporting the nursing student throughout the placement period. However, as the nursing student held a nursing degree from her native country, the participant strived in assessing the professional competence of the student and in meeting her current learning needs. The RN mentor did not find the necessary support in the DER.Nurse educator-related factors influencing the value-in-use of the DER were reported by a few of the nurse mentors. Although some participants perceived the DER as helpful for holding an active position in the formal assessment discussions, others had quite different experiences. The factors limiting the value-in-use of the DER included the lack of resource familiarity of the nurse educators. Moreover, a couple of the mentors highlighted unclear role expectations between RN mentors and nurse educators – dominance of nurse educators or peripheral role of RN mentors in the assessment discussions.The findings of this study suggest that DERs can act as an efficient mediating pedagogical tool to support and enhance effective mentorship practices for nursing students during clinical education in nursing homes. The findings emphasise two key aspects regarding the perceived value of the DER: enhanced mentoring competence in supporting the learning process of students and enhanced motivation and confidence in the mentor role. Another key aspect of the study findings relates to the interplay of multiple factors affecting the perceived usability of the DER related to mentoring of nursing students during clinical education within nursing homes. The discussion is structured around these key aspects of the findings along with other issues as they arise.Consistent with previous reports , 8, 15, In this study, the DER provided the RN mentors with more efficient and accessible knowledge, overview, and description of the level of competence, educational context, background, and learning goals of students than did traditional strategies. This insight (easily accessible in the DER) was reported by the participants as highly informative and beneficial in supporting and promoting their preparedness for the supervisory role as well as in facilitating goal orientation in their mentorship practices and encouraging the use of regular reflective discussions. A goal-oriented learning path with provision of learning possibilities tailored to the learning goals of students is stressed as essential in enabling and promoting learning and professional development of students in clinical education , 43. DesIn this study, the value of the DER was especially evident for and reported by the more inexperienced RN mentors and mentors with a diverse cultural and linguistic background. The more experienced mentors stressed the value of the DER being more related to confirmation and support of their own mentorship practices. Despite years of clinical experience, RN mentors do not necessarily achieve sufficient pedagogical teaching skills . BengtssOverall, the DER designed to support and enhance the mentorship practices of RNs was deemed satisfactory by the participants in terms of technological and instructional design aspects, such as layout, ease of use, and relevance of content. Moreover, the flexibility and accessibility offered by the DER allowed the participants to navigate the resource easily and to read and re-read at their own pace based on their own preferences and needs , 50. BotOur study contributes to the evidence base on how DERs may enhance the mentorship practices of RNs in nursing homes. The strength of the study includes the inclusion of a wide variety of participants  mirroring a Norwegian nursing home context . FurtherStrengthening the quality of mentorship is paramount to promote high-quality learning environments for nursing students in clinical education. This research provides insights into the effectiveness of a DER in supporting and enhancing mentorship practices in clinical education in nursing homes. The uniqueness of the findings is relevant for clinical nursing education, as they suggest that DERs can act as an efficient mediating pedagogical tool to supplement and support effective mentorship practices for nursing students in nursing homes. However, our findings implicate several factors that challenge and constrain the usability and value-in-use of DERs in clinical education, which must be acknowledged and addressed. These factors include digital illiteracy, a lack of allocated time for supervision, a lack of student motivation and engagement, and unfamiliarity of mentors with the DER content and use. The implementation of DERs to support mentorship training is an important avenue for further research towards achieving high-quality learning environments in nursing homes. Our findings are likewise relevant for nursing educational institutions to consider integration of DERs as a supplement to face-to-face mentorship training, which may more effectively impact and improve the quality of clinical nursing education , 15.Additional file 1.