How to Unleash the Remarkable Potential of Cold Spray: A Perspective

Cold spray is a solid-state, powder-based consolidation technique for deposition of coatings, component repair and near-net-shape additive manufacturing. Its unique attributes have propelled the development and commercialization, yet cold spray has only experienced limited deployment. In fact, cold spray technology could be extended to a considerably broader range of applications and achieve a much higher level of industry adoption by focusing on innovative ways to unlock current roadblocks that prevent it from reaching its full potential. Cold spray R&D efforts have doubled during the last decade and along with new industry applications and novel demands provide both a strong body of knowledge and market pull to identify and address these roadblocks. This paper offers the authors’ perspective on what are the next steps to be taken in cold spray R&D to unleash its remarkable potential.

Introduction
In the cold spray process, micron size powder particles are accelerated to supersonic velocities by a high-pressure gas jet passing through a convergent-divergent de Laval type nozzle (Ref [1][2][3][4][5]. The solid-state particles undergo high strain rate plastic deformation upon high kinetic energy impact on a substrate at temperatures below their melting point and bond to the surface to form a layer. Due to the low heat input, the powder material does not experience undesirable phase transformation or chemical reactions and oxidation is typically minimal. In addition, the low thermal load on the substrate enables the use of this process for repair without inducing excessive thermal stresses on the part. Although the concept of consolidating powders using kinetic energy was reported over a century ago, the cold spray process as a viable technology resulted from a study, performed in a wind tunnel, on the effect of supersonic impact of particles of different nature onto objects (Ref 1). The intriguing behavior of such particles, either sticking to the surfaces or rebounding, led to a rapidly expanding research field as evidenced in Fig. 1, showing the number of peer-reviewed publications per year since the first paper published by Alkimov et al. in 1990 (Ref 6) and then later after the development of the cold spray process technology ( Ref 7). Since the introduction of the first commercial cold spray system in the 2000s, significant improvements have been made that allow application of dense deposits of a larger variety of materials by virtue of higher operating pressure and temperature capabilities, in addition to innovative nozzle materials, geometries and nozzle-injector assembly designs.
Compared to conventional additive manufacturing (AM) techniques, cold spray offers the advantage of multi-material buildup at high rates. It can be strategically used in This article is an invited paper selected to provide expert perspectives on a target subject relevant to thermal spray. The views expressed in the paper are those of the author(s). It is also part of a special issue focus in the Journal of Thermal Spray Technology celebrating the 30th anniversary of the journal. The papers and topics were curated by the Editor-in-Chief Armelle Vardelle, University of Limoges/ENSIL. combination with conventional manufacturing technologies to fabricate functional components on parts, reducing material waste and costs while increasing both material and part design flexibility. Moreover, the cold spray process operates under normal atmospheric conditions and is thereby inherently scalable to large parts as no inert gas or vacuum environment is required. These characteristics of cold spray give rise to a new degree of freedom in AM that can lead to innovation in manufacturing. Therefore, the cold spray technique is viable for a wide range of applications in diverse sectors. These applications include thermal and nuclear power plants, protective coatings, catalysts, high power line connecting switches, sputtering targets, induction heating cookware, to name a few. Currently, one of the main applications of cold spray is the dimensional restoration of damaged parts, for example corroded or worn, in particular for expensive aircraft parts. This extends to other industrial parts, such as bearings, pistons, valves and pump components. Dimensional restoration can be performed in a robotized cold spray cell but also by using portable systems with handheld operated guns. Most of these repairs have simple geometries, where the material is deposited using a raster movement over a surface or a linear movement on the part placed on a rotating table or lathe. The deposited materials generally need to meet strict dimensional requirements for the application and, therefore, machining or grinding to the final dimension is performed, post-cold spray.
The first barrier for a broader deployment of the cold spray technique is deficient properties of the as-deposited material, with cold spray deposits generally exhibiting poor strength and ductility as compared to bulk counterparts. For free-standing parts where good inter-particle interfaces and very low porosity is obtained, it is possible to perform a heat treatment to improve the deposited material to reach bulk properties. However, for deposits on a base material or substrate, heat treatment of the whole part could degrade the base material properties and, in some cases, would be impractical. Innovative ways to improve the as-deposited properties and/or to perform localized heat treatment on the deposited material could lead to a significant breakthrough for this technology. It should also be noted that most current industrial cold spray applications are using feedstock materials with a ''reasonable'' level of ductility/deformability and hence, are relatively easy to deposit. Despite demonstrations of hard material deposition are of great interest, they remain, however, anecdotal.
Another challenge is the relatively low geometrical control and precision of the final dimensions of the deposits. For coating applications using cold spray, the coating procedure is relatively well established. The cold spray gun (nozzle) is scanned over the surface using a small overlap between spray tracks, with masking sometimes employed to protect against overspray and better define the deposit outline. During path planning, the track overlap can be optimized to produce a uniform thickness by accounting for the spray track width and profile. The minimum spot size of typical commercial cold spray nozzles is *4 mm and a profile is obtained across this diameter due to variations in the gas/particle flow from the nozzle center to wall (Ref 8). However, the size and profile of spray tracks, along with the lack of robust toolpath planning tools, limit the use of cold spray for more geometrically complex AM applications. Finally, the cold spray technique consistency and reliability need to be improved for its broader adoption for mass production applications and to facilitate the development of cold spray as an AM technology.
Cost of equipment, consumables and powder as well as limitations in terms of operating gas temperature and pressure besides nozzle clogging issues are other barriers responsible for slow deployment of the cold spray technology.
This paper presents core elements that are required for the future development and industrial adoption of the cold spray technology for a broader range of applications, including (1) tailoring powders specifically for cold spray, (2) developing a hybrid cold spray approach and (3) integrating Industry 4.0 concepts (digital twin of a cold spray manufacturing cell). These core elements are the basis of the research program at the McGill-NRC cold spray facility. Topics presented in (1) and (2) are at the outmost importance for the rapid and wide acceptance of cold spray by many sectors of the industry while topic (3) aims to position the technology within the era of Industry 4.0, where the integration of cyber-manufacturing and state-of- Fig. 1 Publication on cold spray by year from search on Scopus with the following search strategy (''cold spray'' or ''cold spraying'' or ''cold sprayed'' or ''gas dynamic spray'' or ''gas dynamic spraying'' or ''gas dynamic sprayed'' or ''kinetic spray'' or ''kinetic spraying'' or ''kinetic sprayed'' or ''kinetic metallization'' or ''supersonic deposition''). Results were reviewed those irrelevant to cold spray technology were removed the-art machine learning methods is expected to greatly improve process efficiency and reliability, product quality and domain knowledge discovery.

Tailoring Powders Specifically for Cold Spray
Cold spray users mostly relied on using powder feedstocks designed or optimized for other processes, mainly conventional powder metallurgy (e.g., pressing and sintering, MIMS, HIP) or thermal spray. Concomitant with the strong adoption of laser and electron beam powder bed fusion based metal AM techniques, more spherical powders produced by gas or plasma atomization, exhibiting narrower particle size distributions and higher purity are becoming available and can be used advantageously for cold spray. With these commercially available powders, the three metrics typically used for powder specifications for cold spray are size distribution, morphology and chemistry. Beyond these three metrics, powder microstructure (and therefore mechanical properties) and surface state are paramount to maximize the cold sprayability and consistently obtain the targeted properties. Indeed, cold spray of non-optimized powders imposes limitations on the range of sprayable materials, prevents achieving optimal deposit properties and may lead to low deposition efficiencies, powder losses and additional processing costs. Clearly, in order to accelerate commercialization and industrialization of cold spray, powder feedstocks need to be specifically designed for cold spray. Powder feedstock characteristics need to be manipulated to maximize (1) cold sprayability, (2) deposit properties, and (3) manufacturing reproducibility, all while maintaining control of costs.

Powder Flowability
Powder flowability depends on various factors such as powder morphology, size, surface roughness and chemistry (Ref 9-11). Good flowablity is essential for a proper and constant powder feeding during the cold spray process and, thus, to ensure a uniform deposited thickness per pass/ layer. It is also a key factor in preventing powder feeder, injector or nozzle clogging issues that could arise by a sudden change in the feed rate. The flowability of a powder can change over time, for example, due to the presence of moisture resulting from the powder storage and handling conditions. Lack of good and constant flowability is a roadblock for full industrialization of the cold spray process for specific materials, as it is one of the factors limiting cold spray reliability as a precise AM technology.

Powder Ability to Deposit
The ability of powder to deposit depends on its acceleration by the gas jet and its subsequent deformation and adhesion upon impact to the substrate or the previously deposited particles. It is generally accepted that within the window of deposition, the ratio of particle velocity over critical velocity, the minimum velocity beyond which the particles deposit ( Ref 12,13), should be maximized to obtain, not only high deposition efficiency, but also strong inter-particle bonding, yielding optimal deposit properties ( Ref 14). For a given material and set of cold spray process parameters, powder characteristics, such as particle size, shape and surface roughness, can be optimized to maximize the particle velocity. Powder microstructure and surface chemistry profoundly impact the cold spray process characteristics and coating properties. For example, changing the surface by formation of superficial oxide scale on copper powder results in an increase in the critical velocity and therefore reduced sprayability ( Ref 15). Variability in powder characteristics such as size and surface state can also cause nozzle or powder injector clogging. Powder density also directly influences the plastic deformation behavior at impact. In other words, for a given velocity, two particles of the same material with the same size but different densities, for instance due to the presence of engineered porosities, will deform differently. Furthermore, powder microstructure depends on the powder processing route and can be controlled during production through parameter adjustment and by post heat treatments. Thus, for the same material, tailoring powder microstructure can make the difference between no deposition and the deposition of a dense deposit with good inter-particle bonding allowing the attainment of bulk-like properties (or better) after an appropriate heat treatment ( Ref 16).
Powder engineering is an approach that presents high potential in enhancing the ability of powder to deposit. For low pressure cold spray, ceramic particles additives have shown a strong effect on improving the deposition efficiency of metallic powders ( Ref 17,18). Likewise, metalalloy powder blends can provides significant improvement for both sprayability and deposit properties in high-pressure cold spray due to a combination of tampering from the hard particles and improved deformation and retention of hard particles by the softer ones forming a continuous matrix. For example, it has been shown that adding a small amount of Ti to Ti6Al4V led to a significant decrease in deposit porosity (Ref 19), addition of SS316L to Fe powder has been shown to improve the deposition efficiency (Ref 20) and addition of a low amount of Al binder has allowed for the deposition of brittle NdFeB magnetic material for the fabrication of complex-shaped permanent magnets (Ref 21). In another approach, loosely agglomerated and porous particles has been shown to accelerate more and deform more easily upon impact (pseudo-deformation), producing denser and thicker cold spray deposits ( Ref 22,23). Cladding the surface of hard powder particles with softer and more ductile materials has been shown to also improve powder cold sprayability and deposit properties, which is consistent with the cold spray bonding theory based on localized deformation at the surface of the impacting particles (

Deposit Properties
For a given material, deposit properties depend on the powder sprayability and the cold spray process parameters. For functional, non-structural materials, the as-deposited properties are often acceptable for industrial applications. For example, electrical and thermal properties of copper deposits were measured to be 60-80% (Ref 31, 32) and 55-80% (Ref 32) of bulk values, respectively, depending on the process conditions. Due to high strain hardening and the presence of inter-particle interfaces and micropores, the mechanical strength is, however, generally lower than that of bulk, while deposits exhibit typically very low ductility, although, some improvement can be obtained by optimizing the powder sprayability and by using He as propelling gas ( Ref 27). These functional and mechanical properties can be drastically improved by performing post-process treatments ( Ref 33,34). The efficacy of post-treatments depends on the quality of the inter-particle bonding and density of the as-sprayed deposit (Ref [35][36][37]. However, heat treatments could also affect the base material, which may be detrimental. As a consequence, cold spray structural repair or add-on structural fabrication using conventional alloys is still very limited. One possible approach is the development of new alloys tailored for cold spray that would provide high structural deposit properties. Indeed, current alloy compositions have been partly determined by conventional manufacturing limitations, such as the need for liquid metal flowability for casting, that are not relevant for cold spray. Cold spray preservation of powder microstructure due to solid-state deposition is a unique advantage over classic AM or powder metallurgy techniques, where the powder microstructure is significantly altered by melting or high-temperature sintering. Exploiting this advantage, powders tailored for cold spray could be developed to produce deposits that require minimal posttreatment. The success of this approach could lead to a breakthrough in AM and cold spray technology. Besides developing new alloy compositions, another method could consist of modifying the microstructure of commercially available powders, for instance via powder heat treatment. Furthermore, the development of deposits from novel materials known for their exceptional properties, such as functional and structural materials comprised of nanostructured (Ref 38), amorphous alloys (Ref 39) or advanced composites materials (Ref 40) could also benefit from tailored powders that better suit the cold spray process and that would results in enhanced properties.

Manufacturing Reproducibility and Cost Efficiency
Once the key powder characteristics are identified for a given cold spray application, appropriate powder specifications should be defined relying on practical quality control tools to ensure manufacturing reproducibility. Surface state control can be particularly challenging due to the lack of simple characterization tools as well as due to its potential alteration under storage (powder aging) as most metallic powders oxidize over time and absorb moisture, yielding major variability in flowability and sprayability. In addition to storage under inert atmosphere, which may not be always practical, mitigation strategies, such as powder additives or modification of powder surfaces, for example, by addition of protective thin films, could be considered to ensure a controlled surface state.
Powder characteristics leading to good cold sprayability may, however, differ from those yielding optimized coating properties. In that context, finding the correct balance between the process cost reductions associated with higher deposition efficiency and coating properties meeting the application requirements would be the key to the development success. Ultimately, a broad adoption of feedstocks specifically designed for cold spray will also depend on the feasibility of producing them on a large scale at reasonable costs.

Accelerated Development of Tailored Cold Spray Powders
Tailoring cold spray powders is a complex and expensive task where numerous characteristics need to be taken into consideration. The ability to accelerate this R&D process while reducing costs can be drastically improved by using a comprehensive set of lab scale equipment that is the foundation of a powder development ''factory''. This includes equipment that can manipulate different powder characteristics, test rigs and cold spray equipment that require only a small amount of powder for assessing the impact/deformation/consolidation behavior, and equipment for collection of reliable data to develop a fundamental understanding of the variables involved. The collected data can be used for validating and refining numerical models that can further accelerate the powder development. Figure 2 schematically presents the proposed cold spray powder development cycle: powder tailoring or manufacturing and evaluating its cold sprayability. Powders can be acquired off the shelf and then modified, or can be produced in various compositions in a laboratory scale atomizer. These powders can then be sorted to specific size distributions in a powder classifier and their microstructures can be changed through mechanical alloying in ball milling equipment or in fluidized bed or rotational furnaces. They could be spheroidized or doped in a plasma reactor. Their surface can be changed by thermal or chemical etching, applying a thin film of a different material using a powder coater or new nanostructured or amorphous alloys can be produced through mechanical alloying.
With the evolution of high-speed imaging equipment, supersonic impact of single particle has recently been made possible and used to investigate the deposition of powder particles with size and velocity in the range used in cold spray (Ref 41). Such equipment, together with common microstructural characterization tools, could be used for evaluating the high-speed impact, deformation and bonding of single particles having various characteristics. For a set of powder characteristics, studying the impact behavior at different velocities and on different substrates could be performed with a very small amount of powder. The next step would be the use of a cold spray system with a powder feeder specifically designed to allow the injection of a few grams of powder during a very short period of time (typically 1 s). High-speed cameras can be used to image the deposition of an ensemble of particles forming a deposit at different cold spray conditions without the need for spraying kilograms of powders or meeting any flowability constraints. Powder flowability can therefore be addressed using conventional or adapted Hall or Carney flowmeter funnels still using a relatively small amount of powder for each condition (Ref 9, 11). When optimized powder characteristics and cold spray parameters are found, a larger amount of powder can be made and used in an actual cold spray system for producing coupon-scale deposits that will be tested for targeted properties.

Hybrid Cold Spray Manufacturing Cell
Although a range of cold spray equipment is available to fill various market needs, the current generation of highpressure cold spray systems faces challenges in achieving (i) the targeted deposit material properties and (ii) the geometry control demanded by additive manufacturing. This has spurred investigations into various hybrid manufacturing routes (Ref 42).

Hybrid Cold Spray-Laser Powder Consolidation
The literature clearly indicates that, for current hard-tospray materials, high-pressure cold spray in isolation is insufficient to obtain mechanical properties equivalent to conventional cast or wrought products (Ref 34). A hybrid cell, which pairs laser technology with cold spray, will have considerable potential for improving the properties of the as-consolidated material, although defining the processproperty relationships is very challenging.
The realization of clean interfaces, without cracks and entrapped grit, is likely to be critical for effective material response to post-spray processing (e.g., heat treatment) and associated improvement in material consolidation by diffusion-related mechanisms such as ''sintering'' across the interfaces ( Ref 33,43). Pulsed laser ablation has been shown to have a high potential to increase the bond strength of cold spray deposition onto a substrate surface  [44][45][46]. This non-contact, non-abrasive process also includes the important benefit of eliminating the need for chemicals or blasting media and is, of course, an excellent fit for this hybrid process. In addition to laser ablation for surface preparation, laser-assisted cold spray can be effective for improving cold sprayability (e.g., deposition efficiency) and deposit properties (e.g., bond strength, porosity) ( Ref 44,[47][48][49][50]. However, this type of laser-assisted spray processing is challenging because it is very difficult to accurately measure conditions at the target surface due to changing deposit emissivity during the process; thus, process modeling will be critical.

Combined Additive-Subtractive Manufacturing
For cold spray additive manufacturing (CSAM), building 3D structures featuring freeform geometry and low tolerances introduces a significant layer of complexity versus that required for typical cold spray coatings. For example, a tessellation concept can be used for producing vertical walls (Ref [51][52][53]. In practice, the effectiveness of such build concepts is highly dependent on the capability to accurately realize the previewed evolution of the deposit throughout the build process. This presents a few general requirements: the capability to perform precise robotic manipulation of the spray gun through the complex spray paths of a cold spray AM build strategy; management of residual stresses to minimize distortions/defects; online evaluation of the deposited tracks; a means to bring the geometry back into tolerance as needed. A hybrid cell focusing on an additive (robotic cold spray)-subtractive (robotic machining) manufacturing process, supported by lasers, combines the best attributes of CSAM (i.e., high build rate, multi-materials, solid-state) with the finishing precision and quality of advanced machining, maximizing speed, flexibility and quality, while minimizing waste.
CSAM employs a conventional AM build strategy, i.e., starting with a computer-aided design (CAD) drawing, slicing the CAD geometry into layers, and performing a layer-by-layer build (Ref 52). However, the path/trajectory planning and robot programming are challenging due to, for example, the size and profile of deposits obtained, line-ofsight and suitable nozzle access to the spray location, continuous deposition needed to maintain stable powder feeding (versus instant on/off), temperature evolution within the part/substrate. Moreover, since cold spray can be used to build features on existing parts, another complication is that the associated spray surface will not necessarily be flat; this needs to be accounted for in CSAM. The development of unique tool paths for every type of material deposit can require extensive experimentation in the absence of mass and heat transfer models.
Residual stress occurs in cold spray deposits because the process involves significant plastic deformation of powder particles. As a result, cracking within the deposit, delamination between spray layers or from the initial substrate, can occur. The hybrid cell laser (described above) can be used as a standalone tool (without simultaneous cold spray) to investigate the capacity to relieve residual stress, as well as other applicable heat treatments during the build (e.g., after a sprayed track(s), sprayed layer(s), etc.). A recent study showed the potential of the technique by stress relieving single tracks of cold sprayed copper ( Ref 54). As an alternative to localized stress relieving, an industrial infrared (IR) system can also be used to investigate managing residual stress by heating over a larger area. This can be through heating the substrate, which is akin to heating the build plate in other additive manufacturing processes, and/or heat treating the cold spray deposit itself. A recent study reported using an IR system that could reduce the hardness of single tracks of cold sprayed 6061 aluminum alloy ( Ref 55). Temperature monitoring and control can be performed using a two-color / dual-wavelength high-speed infrared camera or pyrometer, which can provide an accurate temperature measurement even when emissivity is not constant during the deposition process, for example with copper, or in the case of a multi-material component ( Ref 56).

Integrated Non Destructive Inspection (NDI) and Process Monitoring
While development of effective build strategy and toolpath is critical for cold spray to move toward delivering nearnet-shape parts, inspection and quality control of such cold sprayed complex parts becomes a challenge. New strategies have to be developed, not only for off-line, but also for online inspection. Having solutions to monitor online the geometry of added features and, furthermore, their quality, through assessment of representative properties is paramount; for this purpose, optical techniques for dimensional analysis combined with laser ultrasonics for volume probing of cold sprayed 3D structures are promising approaches (Ref 57).
Optical coherence tomography (OCT) system (Ref 57), can be used to perform online dimensional inspection at defined stages of the buildup (deposition) process and will allow rapid adjustment of the process parameters as soon as any profile discontinuities or deviations are detected. This is essential for enabling a feedback control loop in situ and dynamic adjustment of deposit thickness by adjusting robot path parameters, powder feed rate, robot machining, etc. In this way, compounded errors associated with the removal and repositioning of the substrate/workpiece between inspections will also be avoided.
As a complement to a dimensional inspection system, a laser ultrasonic system (LUT) can be used for online NDI of the integrity (e.g., adhesion, flaws, porosity) of each deposited layer (Ref 57). One particular benefit of such a capacity is in the incidence of ''catastrophic'' flaws; detection of such flaws during the build will allow corrections of the affected zone to be made using robot machining, as opposed to scrapping the part at the end of the build. The LUT also will greatly enhance the efficiency of experimental campaigns, yielding characterization and testing on an optimally fabricated part that also will allow for establishing a predictive flaws detection model based on machine learning algorithms employed with data generated by the numerous process control and industrial internet of things (IIoT) sensors, which will be discussed in the next section.
Robot-assisted AM is still in an early developmental stage with challenges to the hybrid cell such as: (i) combined control of the machining and CSAM robotic systems (lack of compatibility between robots and the slicing algorithms, CAD/CAM software, etc.) and (ii) the low accuracy and rigidity of robot systems relative to CNC machines ( Ref 58). For hybrid cold spray, an important distinction can be made in the objectives for in-process machining versus those for the finished part. A critical factor for the former is the ability to ''reset'' the geometry, e.g., bring into planned tolerances with the requirement that it can be subsequently built upon without introducing a weak interface at that machined surface. The development of process automated, laser ablation as a surface preparation method within the cell (described above for substrate surfaces) will be also investigated for robotic machined surface as more suitable technology for hybrid processing (Fig. 3).

Cold Spray 4.0: Digital Twin of a Cold Spray Manufacturing Cell
Cyber-physical integration is the core of future smart manufacturing for Industry 4.0. Two concepts are cyberphysical systems (CPS) and digital twins (DTs) (Ref 60). CPS relies on integration and collaboration of computing, communication and control known as ''3C.'' The system provides real-time sensing, information feedback, dynamic control, etc. DT integrates and supports these capabilities by incorporating high-fidelity virtual models of the physical objects in the virtual space to simulate and predict their behaviors and to perform analytics. With a complete digital footprint of the equipment and product, DT can also support product lifecycle management (PLM). DT is being explored by companies such as General Electric, Siemens and Tesla, despite several known challenges, e.g., a lack of standardization of IoT technologies (Ref 61).
For thermal spray, cyber-physical integration has been investigated in only a few studies, particularly in the form of an expert system (ES) for air plasma spray deposition. In brief, an ES emulates human expertise based on given input parameters. Kanta  To the best of our knowledge, no similar work has been reported for cold spray, nor any development of a DT in general for thermal spray. For a complex process such as a hybrid cold spray manufacturing, the complete virtual model must be realized by integrating a series of sub- ; dual robot configuration one for cold spray holding laser heads and sensors and one for manipulating the part that can be brought sequentially to a stationary spindle, to the LUT and to the OCT J Therm Spray Tech models, e.g., the powder feeding process, gas and particle flow, the laser processing, robotic machining and dimensional control, etc. In addition to these sub-models paired from every hardware asset of the physical process, the DT will be continuously interrogating the equipment operation input data and handling the component-to-component interaction. Furthermore, under the digital twin concept, human expertise can also be incorporated as a sub-model, similar to the ES. These sub-models can be formulated using either physics-based mathematical modeling or machine learning techniques.
Input parameters for the cold spray process may be of various forms, e.g., numerical and categorical values and sound signals or images (2D or 3D). Both structured (e.g., text and numeric) and unstructured (e.g., video images, sound) data need to be acquired, streamed, processed and exchanged in real time among the various physical and cyber components.
A sensor platform for hybrid CSAM processes monitoring could be upgraded to include directivity of acoustic sensors (microphones), spectral and imaging improvement of optical sensors (cameras and photodetectors), and continuous or pulsed narrowband illumination of the jet of particles, electrical impedance and gain refinement of sensors. The cold spray process environment is dusty and noisy, which is challenging for in situ sensing technologies. At the same time, ambient spray booth conditions should be recorded (e.g., temperature, humidity, ventilation) and bundled with the process and equipment records (e.g., robot acceleration, deceleration, vibrations). It will be important to identify what spray parameters can be monitored in situ and in real time to deliver useful data toward analytics and prediction of production problems before they occur.
Having an efficient framework to support the information exchange, including the communication network, protocols and/or database is essential. Due to its real-time nature, the DT may be deployed in a decentralized manner, i.e., a few sub-models may run at the ''edge'' level and a few sub-models at the server level, connected through the network. Having all the relevant information of the processes from the beginning to the end, it is evident that the DT can support the aspects of process and equipment monitoring and control and / or for instance anomaly detection. The cyber-physical infrastructure behind the ''digital twin'' facilitates and augments the logging, recording and storage of relevant information in databases that in turn may lead to advance the domain knowledge and furthermore to potentially new knowledge discovery (Fig. 4).
Several immediate benefits of sub-model development can be envisioned. For instance, one key challenge in the cold spray process is to maintain consistency in the powder feedstock delivery. This can be influenced by a number of aspects, including ambient temperature, moisture content, etc. By incorporating novel sensors for the cold spray equipment, vital process data, such as powder flow, propellant gas pressure and temperature, spray gun/robot movement, surface pressure and temperature on the part and in its vicinity, sound detected from the process operation, can be collected, streamed simultaneously and continuously (from various sources), and captured into a data storage system such as a SCADA-type industrial data management platform. After applying appropriate data preprocessing (data de-noising, feature extraction, etc.), these data become candidate features in a feature-selection/ ranking framework to identify the most relevant ones that control the powder feedstock delivery. The appropriate feature-selection approach should be determined based on the number of available training data and candidate features ( Ref 66). Techniques such as Random-Forest and Gradient-Boosting, can also highlight the relative importance of the parameters in the collected data set (Ref 67). Critical parameters may then be monitored in real time using dashboards designed via commercially available data management platform for mobile devices and/or personal computers. Ranking of the parameters also provides better direction of the next round of experiments, thus making the overall investigation more effective than the traditional design of experiment (DOE) approach.
Employing computational fluid dynamics (CFD) modeling enables the analysis of the gas flow and the particle dynamics inside the gun nozzle and even at impact with the substrate during the spray process (Ref 68). This approach can facilitate process parameter optimization through reduced DOE aimed at the optimization of the physical parameters such as particle impact velocity and temperature. Furthermore, reduced order models (e.g., using proper orthogonal decomposition (POD) methods) can be extracted from the complete CFD model for the digital twin to be used in real time. Experience gained in modeling the nozzle flow field will eventually support the investigation, for example, of another concern in cold spray that is the wear of the spray nozzle due to particle erosion. Machine learning techniques could be very effective for predicting the cold spray deposition quality and efficiency related to a specific set of factors, including the nozzle inlet, throat and exit diameter ( Ref 38). Such a machine learning framework could be built based on ANN in which the input neurons are connected to the factors and the output neuron predicts outcomes such as deposition quality and efficiency (Ref 69,70).
A key challenge in cold spray is the assessment and the design of the robotic-driven spray path for the optimization of the layer-by-layer deposition/buildup. Presently, the build strategy in cold spray employs the conventional AM strategies but has problems specific to cold spray that require the development of unique toolpaths for every type of material deposited, which becomes even more complex with the hybrid approach. Toolpath planning could be implemented using a data-driven approach (Ref 71), or in a longer term via computer vision technology and AI based on reinforced learning. Since the build strategy is a sequential operation, the optimal toolpath for a specific geometry can be obtained by employing the advanced machine learning concepts of recurrent neural networks (RNN), such as long-short-term memory (LSTM) learning techniques (Ref 72) by which, the temporal relationship across the performance/features of sub-layers can be modeled. Considering the continuous nature of the cold spray process, deep reinforcement learning techniques can effectively control the robotic-driven spray path. As previously mentioned, for such an application of dynamic control, a two-stage analysis implementation may be needed: a fast responding analysis at the ''edge'' for rapid local feedback control and a batch analysis at the central server to develop the toolpath planning model.
In summary, the development of a digital twin for a cold spray hybrid cell would provide a dynamic framework for capturing the information of the spray and machining equipment and the parts, analyzing the process data of various natures, as well as optimizing process monitoring and control strategies. The DT will support and enable the CSAM experts to use data-driven approach to advance domain knowledge. Thus, the development of a DT for a hybrid CSAM cell will have a valuable impact for both the scientific and industrial communities interested in unleashing the remarkable potential of cold spray.

Conclusion
Cold spray is performed at high deposition rates in atmospheric conditions, offers multi-material AM capabilities and preserves the feedstock microstructure and phase composition while avoiding the creation of heat affected zones. Due to these unique attributes, during the past 20 years, cold spray has been receiving constantly growing attention from the research community as well as several industries, yielding significant commercial potential. Over the years, it has evolved from a coating process to a dimensional restoration tool to an additive manufacturing technique. It can now be used, for example, to produce add-on features on large parts manufactured by traditional means. This extends to the modification of parts that are manufactured out of specifications or that require a design change, or to repair damaged or worn parts, providing advantages such as shorter turnaround time, reduced material waste and lower costs. New advances in cold spray also enable deposition of a new range of materials, such as nanostructured or amorphous materials, that would be detrimentally transformed due to melting in powder bed fusion or most other direct energy AM techniques. Cold spray exhibits a unique potential for large-scale deployment addressing several industrial needs. The commercial potential of cold spray is, however, not fully exploited due to a number of technological roadblocks.
One roadblock is the relatively narrow range of materials that can be deposited due to either lack of powder sprayability or availability in the form of powder. Another roadblock is deficient properties of the as-deposited material. The low strength and ductility as compared to bulk, Fig. 4 Data information exchange overview J Therm Spray Tech alongside the difficulties relative to performing heat treatment without affecting the base material, limit using this technique for structural repair and AM applications. The relatively low geometrical control and precision of the final dimensions of the deposits along with the lack of robust toolpath planning tools are additional roadblocks to the broader deployment of cold spray for more geometrically complex AM applications. Finally, consistency and reliability issues prevent broader adoption of cold spray for mass production applications and constrain its development as an AM technique.
To unleash the remarkable potential of cold spray, powder feedstocks need to be tailored specifically for cold spray at a competitive cost. Such customized powders would allow improving cold sprayability, as-deposited properties and manufacturing reproducibility, while significantly extending the range of materials that could be effectively deposited. A hybrid approach to the cold spray technique that combines laser-assistance, NDI techniques and robot machining for improved deposit integrity and dimensional control together with IIoT sensors for in-process monitoring and control would trigger the next wave of commercial deployment for industrial applications. Construction of a digital twin of the hybrid cold spray cell will allow data-driven decisions on new equipment and powder development, further unlocking potential applications with a higher level of complexity.
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An implantable loop antenna with Hilbert curve structures

In this work, an implantable loop antenna with Hilbert curve structures is proposed. This antenna uses Hilbert curves to achieve extremely small electrical dimensions. In addition, we use magnesium instead of copper in the antenna structure, as it is healthier than copper. The proposed antenna covers a frequency band ranging from 765 to 1143 MHz (S11< -10 dB), a high efficiency (1.5%), and a maximum realized gain of -15.42 dBi. It is a promising candidate for implantable capsule antenna in medical devices.

Introduction
Powered by advanced medical wireless communication systems, implantable antennas attract increasing attention in recent years. Implantable antennas are designed for purposes: (1) monitoring information inside the body of a human or animal, such as stomach endoscopy, heartbeat monitoring, blood glucose level monitoring; (2) wireless power supply for implanted medical devices, such as cochlear implants, pacemakers; (3) locators for protecting animals or studying their behavioral patterns. The wireless transmission of data or energy, reducing the limitations of traditional equipment, has brought great convenience to today's medical treatment. As a key part of the wireless transmission system, implantable antennas become a popular area of research.
Copper is a commonly used material for metal structures in antennas due to its ductility, low cost and high electrical conductivity. However, according to the International Union for Nutritional Sciences (IUNS), the daily intake of copper for adults is 1.6 -3 mg, while the daily intake of magnesium is 315-360 mg. Excessive intake of copper can cause liver toxicity and other symptoms. Magnesium, with its high daily intake and its ability to be dissolved and absorbed in the body, is a new alternative to metal materials for implantable antennas [9]. We propose an implantable loop antenna with Hilbert curve structures. Compared to the proposed implantable antenna, this design has the following advantages.
 The antenna achieves a very small electrical size by utilizing the Hilbert curve.  The antenna achieves a large bandwidth, high gain and efficiency.  The antenna design is made of magnesium, which can be absorbed by the human body and is non-toxic and non-hazardous.

Hilbert Curve
The Hilbert curve is a fractal pattern of space-filling curves [10] as shown in Figure 1. The plane space is subdivided into 4 n squares and the center of each square is connected by a curved line, "n" is the order of the curve. A U-shaped structure of order 1 can be regarded as the smallest unit of the Hilbert curve. To get a Hilbert curve, we execute the following steps: By analogy, Hilbert curves of order 3, order 4 and even higher can be obtained. Theoretically, Hilbert curves can fill the whole space in two, three, and even higher dimensions.
Interpreting a Hilbert curve in terms of a mapping, it can be seen as a mapping of the plane region [0,1] X [0,1] to the interval [0,1]. Taking the order 1 Hilbert curve as an example, using binary, the four small squares are coded as 0.00, 0.01, 0.10, 0.11. And each subsequent increment in order is increased by 2 binary decimal places. The first square (0.00) is subdivided into four squares: 0.0000, 0.0001, 0.0010, 0.0011. By continuously subdividing and encoding each point in the two-dimensional square space, a one-to-one mapping from the plane to the interval is accomplished.
The proposed antenna structure takes advantage of the fractals of the Hilbert curve to reduce the antenna size.

Antenna configuration
The antenna consists of three order 3 Hilbert curves in series, as shown in Figure 2. The antenna is carved from a 1 mm thick magnesium board with a total length of D 1 and a width of H. The distance  3 between each order 3 Hilbert curve is D 2 and the width of the curve is D 3 . After bending, a circular antenna structure with a diameter of D is formed. Therefore, the bent antenna is placed in a ball muscle tissue ( ≈ 55, ≈ 0.948 @915 MHz) with a radius of 50 mm.
By optimizing the parameters of the antenna, the optimum dimensions are: D 1 =27.5 mm, D 2 =27.5 mm, D 3 =1 mm, D =11 mm, and H =8.5 mm.

Simulation Results and Discussions
The simulation results for the reflection coefficient (S 11 ), total efficiency, and gain of the antenna inside the muscle tissue are given in Figure 3. It can be seen that the antenna has a bandwidth of 765 -1143 MHz (S 11 < -10 dB) and can cover the ISM band (902 -928 MHz) for medical implants. 41.3% relative bandwidth ensures that the antenna can operate even when the environment changes or processing errors occur. The efficiency of the antenna in the operating band is 1-1.6%. The maximum gain of the antenna is -15.42 dBi. Figure 3(d) shows an omnidirectional pattern of this antenna.   Furthermore, the comparison between the related antennas and this design is also given, as shown in Table 1. It is obvious that the performance of this design offers considerable advantages.

Conclusion
This paper proposes a broadband, high gain, high efficiency implantable loop antenna with Hilbert curves. The antenna design uses magnesium that is harmless and can be dissolved in the body, making it suitable for implantable medical applications.
Simulation results show that the antenna can work in the ISM band with a bandwidth of 765 -1143 MHz and cope with the environmental changes that may occur during the implantation process. The antenna gain in the operating band is -15.42 dBi and the efficiency is greater than 1.2 %. Simulation results of the antenna in the muscle tissue model indicate that the design is suitable for implantable antenna applications.


Ecosystem of tourist business in the context of regional tourism and hospitality industry development

The evolution and problems of the definition of such notions as “business ecosystem”, “business ecosystem model” and “business platform” in the scientific environment are overviewed and analyzed in this paper. Different strategies of the management of business ecosystem models are considered and conclusions about their efficiency at different development stages are formulated. In the paper, the particular attention is paid to digital platforms as a tool of management and development of business ecosystems in modern realities, the key cases of ecosystem business models in Russian economy are analyzed. The authors consider the digital platform creation as a perspective approach to the transition to the concept “Tourism 4.0” in the Republic of Bashkortostan. However, there are different opinions regarding the practicability of the realization of regional tourist platforms in comparison with the federal ones. The paper presents the overview of the main arguments of the parties of this discussion. As a result of the conducted research, the author formulated

ecosystem model" and "business platform" in the scientific environment are overviewed and analyzed in this paper. Different strategies of the management of business ecosystem models are considered and conclusions about their efficiency at different development stages are formulated. In the paper, the particular attention is paid to digital platforms as a tool of management and development of business ecosystems in modern realities, the key cases of ecosystem business models in Russian economy are analyzed. The authors consider the digital platform creation as a perspective approach to the transition to the concept "Tourism 4.0" in the Republic of Bashkortostan. However, there are different opinions regarding the practicability of the realization of regional tourist platforms in comparison with the federal ones. The paper presents the overview of the main arguments of the parties of this discussion. As a result of the conducted research, the author formulated the conclusions on the perspective of creating crossfunctional and multi-platform solutions for the realization of federal and regional platforms. That is, the construction of platforms based on the principle of mutual integration and realization of different but supporting functions, which would serve the whole chain of creation, promotion and realization of tourist product and realization of accompanying touristic services, will allow implementing not the competitive development environment but the ecosystem cooperation environment. Such principle is Аннотация В данной статье рассматриваются и анализируются эволюция и проблемы определения таких понятий, как "бизнесэкосистема", "модель бизнес-экосистемы" и "бизнес-платформа" в научной среде. Рассмотрены различные стратегии управления моделями бизнес-экосистемы и сформулированы выводы об их эффективности на разных этапах развития. В статье особое внимание уделяется цифровым платформам как инструменту управления и развития бизнес-экосистем в современных реалиях, анализируются ключевые кейсы экосистемных бизнес-моделей в российской экономике. Авторы рассматривают создание цифровой платформы как перспективный подход к переходу к концепции "Туризм 4.0" в Республике Башкортостан. Однако существуют разные мнения относительно целесообразности реализации региональных туристических платформ по сравнению с федеральными. В статье представлен обзор основных аргументов сторон этой дискуссии. В результате проведенного исследования автором сформулированы выводы о перспективности создания кроссфункциональных и мультиплатформенных решений для реализации федеральных и региональных платформ. То есть построение платформ, основанных на принципе взаимной интеграции и реализации различных, но поддерживающих функций, которые обслуживали бы всю цепочку создания, продвижения и реализации туристского продукта и реализации сопутствующих

Introduction
Today, the tourism and hospitality industry in Russia reaches the new heights of development, which was influenced by a number of factors from the beginning of COVID-19 pandemic. It is known that Russians felt how their favorable international format is suffering. The internal tourist format does not always meet the needs of demanding tourists but it is much more predictable. Under current conditions, it is reasonable to take measures for the rest in Russia to become more attractive and comfortable for tourists with different interests, needs, preferences and financial possibilities. It is easy to see that the topic of Russian tourism is on everyone's lips. Great creative efforts are required from regions, especially from those, which have been satisfied with a little for decades not making a claim for large tourist flows but, at the same time, possessing rich tourist resources. The Republic of Bashkortostan is one of them.
The project team of the Department of Tourism, Hotel and Restaurant Services of Ufa State Petroleum Technological University considers the issue of the practicability of creating one of the tools of regional tourism development under current conditionstourist business ecosystem in Bashkiria. The investigation is carried out in the frameworks of research project "Touristinformation ecosystem of user services "Yal" in strategic project "New life environment" of the strategic development program of Ufa State Petroleum Technological University.
Business press comments periodically that such initiatives are futureless because regional digital resources will not be able to compete with acting and developing federal digital resources (Korolev, 2020). But the final conclusion can be made after analyzing the nature of the concept "business ecosystem" or business ecological system. This is one of the most discussable terms in the theory of modeling business processes.
There are a lot of opinions about the essence of this phenomenon, therefore, it is reasonable to discuss it from the basic principles.
In this regard, the objective of the present research is to analyze such notions as "business ecosystem" and "platform", as well as the development perspectives of these phenomena in Russian tourist industry. The following issues were analyzed during the research to reach the stated objective: origin of the terms and evolution of interpreting the notions, development of digital platforms in Russian business, specifics of development and expansion of platform services in Russian and regional tourism. The paper begins with the section devoted to the fundamentals of applying ecosystem approach in economy. After that the research methodology is described followed by the description of the analysis results of the current state of ecosystem approach and digital platform development in Russian entrepreneurship, including the tourism and hospitality industry, taking into account the existing barriers and drivers. As a result of the analysis carried out, the author answered the question whether it is necessary to apply ecosystem approach to develop the tourist industry in the Republic of Bashkortostan.

Theoretical aspects of ecosystem approach in economics
The notion "ecology" (Greek οικοςhome, native land and λόγοςscience) was introduced into the scholarly discourse by German biologist Ernst Haeckel in 1866 and since then this term, understood as "science about interactions of live organisms and their communities between themselves and habitat", has been steadily linked with biology.
The term "ecological system" is youngerit was for the first time used by English botanist Arthur Tansley in 1935, bringing ecology to a higher level based on the fact that system approach allows investigating the aggregate of organisms and habitat conditions in the self-regulation mode (Nazarenko, 2007;Mirkin & Naumova, 2011). At the beginning, this term was also studied only by the biological science. But with time, it also became relevant outside it.
In 1993 the representative of Harvard Business School James F. Moore published the article "Predators and Prey: A New Ecology of Competition", in which he compared the mutual evolution inside natural and social systems, bearing in mind that in both of them interconnected participants are developing in the mutual cycle. Moore used the notion "ecosystem", for the first time giving it an economic sense: "In order to extend the system approach to the strategy, I suggest considering a company not as a representative of one industry but as a part of the business ecosystem covering many industries. In the business ecosystem the companies develop opportunities around the innovation: they are working together on a competitive basis in order to support new products, satisfy needs of the clients and, eventually, introduce another round of innovations" (Moore, 1993). In other words, if the natural ecosystem unites live habitants of some habitat (for example, lake or taiga) interacting both with each other and the habitat, then in business, according to Moore's theory, "the habitants" of ecosystem are the representatives of entrepreneurial world (a top company and other companies: suppliers, commodity flow channels, etc.), interacting on a competitive basis to complete the common innovative business task, as well as consumers.
Let us point out that Moore reasoned about the system approach to the company strategy and illustrated his reasoning with the experience of real companies, which had been actually building up ecosystems long before his publication and, apparently, not using the term "business ecosystem", and, moreover, differently. Thus, Moore compared the strategies of such companies as Apple and Tandy, since 1970-s having launched the products based on microprocessors (the innovation of that time) onto the market, which were later converted into personal computers.
Obviously, Apple controlled its own basic developments, including software of the operation system, at the same time, the company stimulated cooperation with independent developers to write software for their computers.
The company also supported business relations with computer stores, educational institutions and independent magazines. Tandy, on the contrary, had the principle of concentration of all business processes inside the company. The company purchased everything for computers (from programming languages to word processors), it dealt with teaching, sold the equipment through its own store chain and did not cooperate with independent magazines.
At the beginning, judging by the volume of sales, Tandy's strategy looked more effective, but with time Apple's sales indicators raised much higher that can be considered as a result of realizing the strategy implying the access of other participants to its business and, hence, providing partners with new growth opportunities and bringing talents to light.
Moore considered that both companies built up ecosystems, only Tandy controlled the ecosystem more tightly (Moore,1993).
Another interesting model of the late 1970-s is mentioned in the publication. First, Digital Research developed the operation system CP/M compatible with any hardware, which gave the impulse to the development of the variety of small manufacturers of personal computers, and then Micropro developed a powerful word processor for any computers with the operation system CP/M, thus, still more stimulating the demand for these computers produced by small manufacturers. It would seem that it was the time of boom for the latter but they found themselves involved in the competitive struggle with each other, which resulted in price control, low profitability and lack of the possibility to thoroughly deal with the implementation of promotion programs. Having analyzed this experience, Moore stated that at the stage of forming the business ecosystem the correct assessment of the consumers' needs is a necessary but insufficient step: "The leader of the business ecosystem must appear who is able to initiate the process of fast, continuous improvement, which attracts the whole business community" (Moore,1993). This is the quality initially possessed by Apple and Tandy and which the ecosystem being formed, whose launch was conditioned by Digital Research's development, was lacking.
Thus, in 1990-s James F. Moore formed the initial vision of the concept "business ecosystem". But only the initial one, since in Moore's theory, with all its consistency and harmony, the effect of incompleteness was objectively observed, first of all, due to the fact that economic processes at different times rely on different technological capabilities, at the managerial level as well. We will return to this issue later but before that we will touch upon another important moment.
As pointed out by Ya.S. Matkovskaya who studied publications on the topic, the researchers have not reached the common ground regarding the nature of business ecosystems yet. The discrepancies are mainly connected with the fact that in the initial exposition the differences of ecosystems from other forms of cooperation and integration are not quite clear. Matkovskaya suggested her own approach to understanding the problem. First of all, she underlined that business models with ecosystematicity features are based on the system properties and should have the appropriate qualities. The participants' composition is important in the system. The author referred the initiator ("core"), orchestrator, partners and consumers to such, as applicable to business ecosystem model (Matkovskaya, 2021). Remembering the unregulated experience of companies placing the bet on the operation system CP/M, as described by Moore, we can agree that the lack of regulation is impossible in a system. We can also remind that A. Tansley revealed the selfregulation mode in a natural ecosystem, and the nature itself is the regulator. In an economic ecosystem the processes are organized artificially. Consequently, the mechanism imitating the self-regulation mode should be created artificially. The element called the orchestrator takes on this role.
Here we return to the issue about technological capabilities of business organization. Ya.S. Matkovskaya designated "the platform owner" as the orchestrator (Matkovskaya, 2021). A platform is a polysemic word. It is obvious that, in this case, we are talking about a digital platform. It should be indicated that this notion is understood differently. In numerous definitions, the authors call the software environment, information system, business model, enterprise, set of interconnected software and hardware, etc. as the determinative component. On the other hand, the explanations regarding the designation of platforms, as a rule, do not contradict each other. In different definitions the designation is explained as follows: provision of either "mutually beneficial interactions between third party manufacturers and consumers", or "direct interaction and execution of transactions between several groups of third party users", or "execution of interrelation functions between market participants", or "facilitating exchanges between two or more interdependent groups of participants", etc. (Niyazova, Garin & Zlydnev, 2021). Here is an example of extensive definition of a digital program: this is "a digital form of organizing interactions between suppliers and consumers to minimize transaction expenditures when seeking partners, goods, services, executing payments, signing contracts, controlling fulfilled arrangements, evaluating reputation of sectorial participants, etc." (Styrin, Dmitrieva & Sinyatullina, 2019). In the frameworks of the investigation topic it is important to single out the relevant feature of the digital platform as applicable to ecosystem concept, therefore, having summarized the abovementioned, we will claim that a digital platform is, first of all, the tool for establishing the interaction between users interested in each other.

Research methods
The present research is an overview in the frameworks of the selected topic and is based on objectiveness and systematicity principles. The objectiveness principle conditioned the use of only reliable facts and data presented in professional sources and scientific literature. The principle of consistency is based on taking into consideration in the context of the study of the socio-political and economic situation in the country and the region, technological trends in the development of the service sector and creative industries.
The indicated principles were realized with the help of general scientific empirical research methods: data collection from scientific and professional sources, analysis, synthesis and comparison of the information obtained. The use of these methods allowed conducting complex research of the factors under the influence of which the ecosystem approach in tourist industry is currently being developed in Russia and Republic of Bashkortostan. To answer the research question about the origin of the terms and evolution of interpreting the notices, scientific papers were studied and analyzed, which are the theoretical basis of the ecosystem approach in economics and the interpretation of key provisions under the conditions of the Russian market. In the analysis of the development of digital platforms in Russia, scientific works of Russian scientists on the trends in the development of digital platforms and professional thematic digests from industry leaders in Russia were used. The study and analysis of the specifics of development and expansion of platform services in Russian and regional tourism was carried out on the basis of scientific articles by Russian scientists on the prospects of digitalization and ecosystem development in the tourism and hospitality industry, as well as thematic articles from periodicals with comments from industry experts to form an idea of the diversity of opinions and the availability of professional discussion about the immediate prospects.

Evolution of digital platforms in Russia
Digital platforms have been blended in many spheres of activity. Social networks and messengers (VK, Tik Tok, WhatsApp, etc.) have been widely spread and have transformed the arrangement of communications. The methods and mechanisms of trade realization of E-commerce platform, i.e. electronic commerce, are actively changing (Alibaba, Wildberries, Ozon, etc.). The sharing platforms (Uber, Avito, etc.) provide users with "anywhere access to assets instead of the need to possess them" (Geliskhanov, Yudina & Babkin, 2018).
Let us return to Ya. S. Matkovskaya's publication where the differences in business ecosystem from other forms of cooperation and integration are explained. The author, having provided "platform owner" with orchestrator's functions, did not only underline the importance of development of digital technologies but also singled out one of the distinctive features of business ecosystem modelminimized bureaucracy shortening the "time-to-market" period (speed of commercialization of innovations) (Matkovskaya, 2021), and we cannot help but agree with it. As we see, the today's understanding about business ecosystems has changed from the times when James F. Moore stated his opinion. He paid attention to the system role of the control factor but could not relate it with digital platforms, which were developed several years later.
Let us also point out that the evolution of ecosystem models is going on, the understanding of ecosystem participants is also changing. In particular, in cases when the ecosystem's aim is to optimize the transaction (deal) from the point of supply and demand, the digital platform owner can function not only as the orchestrator but also as the core (Matkovskaya, 2021).
Let us point out another important moment. A business ecosystem can be built up for the sake of meeting one or several needs, to rely on one platform or set of platforms. In the evolution process, large ecosystems emerged working to satisfy multiple human needs (Bank of Russia, 2021). With such approach a human, when solving any everyday problem, gets an opportunity to use the unified access system.
In this regard, the experience of PJSC "Sberbank" is demonstrative. Using the strategy of establishing companies from scratch and merging players of financial and nonfinancial markets, Sber has built up the ecosystem where, apart from the initial financial segment, a number of segments of nonfinancial business have been developed: 1) e-commerce (marketplaces SberMarket, SberLogistika, Samokat), 2) health, including telemedicine, online medical appointment booking or calling a doctor (service Sberzdorovie), 3) entertainment (online cinema Okko and other services), 4) FoodTech&Mobility, i.e. services of ready-toeat food delivery, taxi and car sharing (Delivery Club, Citymobil, etc.), 5) B2B-services for legal entities (cloud service SberCloud to store and process information, Bi.Zone company rendering services for protecting personal and commercial data, etc.), 6) other nonfinancial services: job hunting, real estate transactions, virtual mobile operator services, etc. (Rabota dlya vas (work for you), DomClick, Sberdevices, etc.). The user gets access to the whole diversity of offers through the unified access system Sber ID (Sberbank, 2021).
But there are only a few giants like this in Russia. Apart from Sberbank, they include Yandex, Mail.ru, MTS (Serov, 2021).
There is no need to build up the ecosystem on such a large scale. It can be built up around a certain basic need, for example, need in real estate. When forming such system, it is important to wisely cover the range of required products and services, and these are not only the services for selecting and purchasing the real estate but also mortgage, design, repair works, cleaning, etc. (Bank of Russia, 2021).

Current state of development of tourist platforms in Russia
Having formed the vision of the business ecosystem essence, we move to detailing the problem in the sphere of tourism and hospitality, which is based on interterritorial interaction and, obviously, cannot ignore digital technologies opening ample opportunities both for business representatives and consumers (Morant-Martínez, 2019).
In recent years, tourists got used to services providing booking processes of travel tickets (AviaSales, Avia.tutu, etc.) and accommodation (Booking.com, AirBnB, Ostrovok.ru, etc.), search for excursion offers (Tripster.ru,Sputnik8,WeAtlas.com,etc.) and so on. At the same time, we now hear the proposals to create a national tourist and hotel ecosystem in Russia. In particular, in 2020 М.А. Morozov and N.S. Morozova gave voice for digitizing state services, i.e. to create a unified digital ecosystem of the state "instead of isolated separate information systems of federal departments, regional authorities and state services" and combine it with the national ecosystem of tourism and hospitality with different business proposals under terms of public-private partnership (Morozov & Morozova, 2020). The idea is clear as not only the services of transportation, accommodation, meals, entertainment, etc. are in demand in tourist and hotel sphere but also state services. Moreover, even then the Chairperson of the Committee on Social Policy of the Federation Council I.Yu. Svyatenko declared, "The government sees the need in unified digital tourist contour" (it was said about Russpass project). At the same time, Rostourism promoted the tourist website Russia. Travel (Korolev, 2020).
The situation became complicated in 2022 when a number of habitual foreign services left Russia (Booking.com, AirBnB, etc.). In business mass media we came across the opinion that 1) there is no point in letting them back to our market ("nobody will entrust again the data of Russian citizens to unreliable partners"), 2) there is no need to try duplicating the services, which left but it is better to create something that was created in no state of the worldown digital tourist ecosystem (this is "a difficult but quite realistic task") (Golovina, 2022). The endeavors in system tourist industry are realized. The service Russpass is being adapted to new conditions. In summer 2022 Russpass launched the project "We are opening Russia together" with SberStrakhovanie -Sber's daughter company (Vedomosti, 2022). From the information website, Russia.travel has been converted into the interactive digital platform (Interfax-Tourism, 2022). Other participants of the service market are getting more active. For instance, a part of online platform Ozon, the service Ozon Travel, which has been rendering the services of booking travel tickets for several years, has later started rendering insurance services, and in April 2022 declared about launching the hotel booking service "in the short term" (Chupanova, 2022). The services of booking travel tickets and accommodation are provided by the resource Yandex Puteshestvia. As we see, the process is going on, though there is room for improvement. Some experts affirm that digital tourism, despite the solutions for b2csegment having emerged long ago, are still "in embryonic stage", since all projects are concentrated on the limited number of one and the same functions (Solvyova, 2022).
The digitalization of regional tourist industries is an important trend. Interesting projects exist. For example, the mobile reference guide "Altai Today" with a long list of services was developed in the Republic of Altai: booking of hotels and excursions, booking of transport and tours from travel agencies, assistance in working out walking, bicycle and automobile routes linked to the map, provision of information about sights, weather, recreation facilities, prices for services, etc. (Altai Today, 2022). This is an example of individual initiative. The ideas of bigger players are implemented. Thus, several cities and regions started building up the digital ecosystem based on the information web-portal, mobile application for iOS and Android and software for interactive city panels from the company "Rusatom Infrastructural Solutions" (RIS, a part of State Corporation "Rosatom"). As it is indicated in the project presentation, the information portal is "out-of-the-box" solution, i.e. the customer specifies the brand book content and decides himself what content should be uploaded into the system (Solvyova, 2022).
The Republic of Bashkortostan participates in Russian digital tourist projects (Russpass, Russia. Travel, etc.) but there is no regional ecosystem of tourism and hospitality in the region. There can come up the question: Why do we need it, if the information about Bashkiria is accessible for millions of visitors of major digital resources? We think we need it.
First of all, the content from the region is prepared for the large system in compliance with the parameters set up in this system. In the regional system there can be own approach to forming the list of services and, consequently, to partners' business offers (Markelova & Khairetdinova, 2022).
Secondly, digital technologies allow the system owner to receive data necessary for creating a more precise vision of the regional tourist market and its players, about client preferences and correspondence of the rendered services with the expected ones, about social portrait of tourists, etc. It is important not only from the point of personifying offers and quality of targeted advertising but also for timely adaptation of the environment to changing needs of the tourists and correction of the regional strategy of tourism and hospitability development. However, in the situation of the region cooperation with a large resource, the information is concentrated not in the region but with the ecosystem leader whose vision specifies the evolutionary processes of the whole system. Therefore, we do not see contradictions in combining the already existing cooperation with the work in the frameworks of the regional ecosystem of tourism and hospitality created for the abovementioned reasons based on public-private partnership.

Conclusions
Thus, it can be affirmed that with the existing state of tourism digitalization the regional tourist ecosystem of business can be considered as a perspective phenomenon. On the one hand, the region gains certain benefit from federal digital systems, for example, in view of attracting tourists, as well as revealing demand tendencies common for the country and adapting own resources to the demand. At the same time, large systems do not cover many local issues, they are not direct data suppliers who could surgically inform the region about strengths and weaknesses of providing and rendering services, expediency of embedding new services relevant for the region into the system, trends in tourist industry development perspective for the region. Russia is a large country distinguished by natural, historical and cultural, ethnic, gastronomic diversity, and there is a reason everywhere to think what resources can be developed and provided with the necessary infrastructure. And regional digitalization can help a lot here.