KR20210127013A - Insole for preventing fallen arches - Google Patents

Abstract

The present invention provides an insole for preventing flat shoes having an inclined functional structure capable of providing different functions depending on the high-pressure region and the low-pressure region.

Description

Insole for preventing fallen arches

The technical idea of the present invention relates to a medical device, and more particularly, to a shoe insole for preventing flat shoes.

The modern society is equipped with material affluence and a professional medical system more than ever, and a major change is taking place in the global population structure. The change is explained by the keyword of aging. In particular, despite global changes, Korea maintains a proportion of the elderly population that far exceeds the global average due to the aging of the baby boom generation immediately after the Korean War and the low birth rate of the current generation. Furthermore, the aging rate is expected to increase significantly. . Therefore, in the future, it is expected that the elderly population will have a greater influence on the market and will also gradually increase in importance.

As humans age, the probability of appearing various diseases increases, and among them, flatfoot disease is one of the most commonly observed diseases. This flat-footed disease is a disease that 1 out of 4 adult population has, and is a disease experienced by more people than expected. The flatfoot disease does not have a significant effect on the body in a short period of time, but if left unattended for a long period of time, it causes various complex problems in the muscles and skeleton of the lower body. In particular, elderly people whose physical functions are deteriorated due to abrasion of ligaments or cartilage, etc., can lead to more fatal results if such flatfoot disease is left unattended for a long period of time. The cause of flatfoot disease is anatomically related to the structure of the foot. When viewed from the side, a typical human foot has an arcuate structure in the center. Ligaments are located within these arched structures to absorb shock when landing on the floor and help balance when moving or standing. However, as the ligaments that maintain the arch structure increase with age and lose elasticity, flatfoot disease occurs in which the arch structure collapses. A foot with a collapsed arch structure does not function properly, causing unbalanced shock distribution and abnormal upright posture, and complex problems such as overpronation of the foot.

In order to prevent and supplement such flatfoot disease, an insole for preventing or correcting flatfoot shoes may be used. The shoe insole supports the arch structure of the foot in the shoe to help maintain the original shape of the foot, and thus serves to help the lower body find balance.

The conventional shoe insole for preventing flat shoes has a structure in which pressure is redistributed by maximizing the contact area between the foot and the insole. After obtaining by scanning the shape of the wearer's sole, the pressure is uniformly induced on the sole of the foot as the contact area is increased by forming an insole curved surface that can maximize the contact area.

Korean Patent Publication No. 10-2016-0145350A

However, since the conventional shoe insole simply performs a function of evenly distributing pressure, there is a limitation in not satisfying individual functions required in the high-pressure region and the low-pressure region formed according to the formation of the foot.

The technical problem to be achieved by the technical idea of the present invention is to provide an insole for preventing flat shoes having an inclined functional structure that can provide different functions depending on the high-pressure region and the low-pressure region.

However, these tasks are exemplary, and the technical spirit of the present invention is not limited thereto.

According to one aspect of the present invention, there is provided a shoe insole for preventing flat shoes having an inclined functional structure.

According to an embodiment of the present invention, the shoe insole for preventing flat shoes may include: a plurality of first units disposed in a first area to which a first pressure is applied; and a plurality of second units disposed in a second region to which a second pressure lower than the first pressure is applied.

According to an embodiment of the present invention, the second units may have higher rigidity than the first units.

According to an embodiment of the present invention, each of the first units and the second units may have a hollow structure.

According to an embodiment of the present invention, each of the first units and the second units may have a hollow cylindrical structure, a honeycomb structure, or a triple periodic minimum curved structure.

According to an embodiment of the present invention, the first units may have a greater height than the second units.

According to an embodiment of the present invention, the first units may have a smaller thickness than the second units.

According to an embodiment of the present invention, the first units and the second units may be made of the same material.

According to an embodiment of the present invention, at least one of the first units and the second units may have a Young's modulus in the range of 0.01 GPa to 0.04 GPa.

According to an embodiment of the present invention, at least one of the first units and the second units may include thermoplastic polyurethane or ethylene vinyl acetate.

According to an embodiment of the present invention, the first units and the second units may be simultaneously formed using a 3-D printer.

According to an embodiment of the present invention, the shoe insole for preventing flat shoes may have an inclined functional structure that provides different stiffness depending on the region by changing the microstructure.

According to the technical idea of the present invention, the expected effect of the shoe insole for preventing flat shoes according to the present invention can be divided into two and explained. From an economic point of view, due to an increase in the elderly population who are interested in health, the number of elderly people who invest money in these insoles for prevention of flat shoes to solve the inconvenience of walking will increase, which is expected to show marketability in the medical shoe insole market. do. On the other hand, from a technical point of view, the disadvantage that the existing shoe insole manufacturing method does not easily implement an inclined functional structure can be overcome by using a 3-D printer, so there is an effect that can be made to order. In addition, if the hollow cylindrical structure is used as a tilted functional structure using 3-D printing, it can be used not only for shoe insoles but also for manufacturing various shock-absorbing structures.

The above-described effects of the present invention have been described by way of example, and the scope of the present invention is not limited by these effects.

1 is a schematic view showing a shoe insole for preventing flat shoes according to an embodiment of the present invention.
Figure 2 is a schematic diagram showing the chemical structure of the thermoplastic polyurethane applied to the shoe insole for preventing flat shoes according to an embodiment of the present invention.
3 is a schematic diagram illustrating a first unit and a second unit included in an insole for preventing flat shoes according to an embodiment of the present invention.
4 is a graph showing the hardness change according to the internal filling rate with respect to the unit included in the shoe insole for preventing flat shoes according to an embodiment of the present invention.
5 shows a simulation model for analyzing the rigidity characteristics of an insole for preventing flat shoes according to an embodiment of the present invention.
6 shows a simulation result for a hollow cylindrical structure applied to an insole for preventing flat shoes according to an embodiment of the present invention.
7 is a graph illustrating a change in stiffness according to a hollow diameter of a hollow cylindrical structure applied to an insole for preventing flat shoes according to an embodiment of the present invention.
8 is a graph illustrating a change in stiffness according to a height of a hollow cylindrical structure applied to an insole for preventing flat shoes according to an embodiment of the present invention.
9 is a picture of a shoe insole for preventing flat shoes according to an embodiment of the present invention implemented using a 3-D printer.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments of the present invention are provided to more completely explain the technical idea of the present invention to those of ordinary skill in the art, and the following examples may be modified in various other forms, The scope of the technical idea is not limited to the following examples. Rather, these embodiments are provided so as to more fully and complete the present disclosure, and to fully convey the technical spirit of the present invention to those skilled in the art. In the present specification, the same reference numerals refer to the same elements throughout. Furthermore, various elements and regions in the drawings are schematically drawn. Accordingly, the technical spirit of the present invention is not limited by the relative size or spacing drawn in the accompanying drawings.

The human foot, who walks upright, gradually stretches the ligaments between the bones of the foot over time and the arch collapses and becomes flat. Flat feet do not effectively dissipate the shock that occurs when we walk, so the shock is transmitted to the knee joint and spinal organs. In addition, it can cause abnormal movement of the joint, which can put strain on the knee joint or the Achilles tendon. Globally, flat feet account for 20% to 30% of the average population, and there is a need to correct them.

In order to prevent or correct flatfoot disease while supporting the arch structure of the foot, it is necessary to appropriately implement redistribution of pressure applied to the foot by the body weight. In particular, in walking or running, a large pressure is applied to the metatarsal and heel of the foot, so it is necessary to reduce the pressure applied to these two areas to reduce the impact applied to the ligament of the arcuate structure. In addition, a support structure having high strength is required to support the arcuate structure. Correction of flat feet forcibly changes the walking posture, and custom shoe insoles made for each individual are used. The conventional shoe insole for preventing flat shoes realizes pressure redistribution by maximizing the degree of contact between the foot and the insole, that is, conformity. However, since the conventional shoe insole is formed as the same material or structure in the high-pressure part to which high pressure is applied and the low-pressure part to which low pressure is applied, it is difficult to perform the conflicting functions of reducing pressure and supporting the structure.

3-D printing technology has great advantages in making these custom shoe insoles and is expected to provide a suitable solution for people suffering from walking disabilities. 3-D printers have many advantages that go beyond the limitations of conventional manufacturing techniques. Among them, the biggest advantage of 3-D printer is that it can apply a unique design to each product. These features are easy to cover the human body structure. For example, a shoe insole increases stability and fit as the surface area in contact with the sole is wider, and if a 3-D printer is used, it is possible to maximize its utility by making a personalized shoe insole.

1 is a schematic view showing a shoe insole 1 for preventing flat shoes according to an embodiment of the present invention.

Referring to FIG. 1 , the shoe insole 1 for preventing flat shoes includes a first area 10 and a second area 20 . The first region 10 is a region to which a relatively high first pressure is applied, and may be, for example, a region in which the forefoot of the foot contacts or a region in which the heel of the foot contacts. The second region 10 is a region to which a second pressure, which is relatively lower than the second pressure, is applied, and may be, for example, a region in which the long core of the foot is in contact.

A plurality of first unit bodies 110 may be disposed in the first region 10 . A plurality of second unit bodies 120 may be disposed in the second region 20 . The second units 120 may have higher stiffness than the first units 110 . Here, stiffness is a value obtained by dividing stress by strain, and the higher the stiffness, the harder the characteristic. Due to this arrangement, the heel of the foot or the heel of the foot comes into contact with the relatively flexible first units 110 , so that pressure distribution can be effectively implemented. In addition, the long core of the foot comes into contact with the relatively hard second unit body 120 , so that the foot can be more firmly supported.

The first unit bodies 110 and the second unit bodies 120 may have various shapes. For example, each of the first units 110 and the second units 120 may have a hollow structure. In addition, each of the first unit bodies 110 and the second unit bodies 120 may have a hollow cylindrical structure with an empty central part. However, such a structure is exemplary, and the technical spirit of the present invention is not limited thereto. For example, the first units 110 and the second units 120 may each have a honeycomb structure or a triple periodic minimal surface structure (TPMS).

While satisfying the above-described rigidity condition, the first unit body 110 and the second unit body 120 may have various dimensions. The first unit bodies 110 may have a greater height than the second unit bodies 120 . In addition, the first unit bodies 110 may have a smaller thickness than the second unit bodies 120 , and in this case, the diameter of the hollow of the first unit body 110 is the hollow diameter of the second unit body 120 . may be larger than the diameter of

The first unit body 110 and the second unit body 120 may be formed of various materials while satisfying the above-described rigidity condition. For example, the first units 110 and the second units 120 may be formed of the same material or may be formed of different materials. The first units 110 and the second units 120 may have a Young's modulus in the range of 0.01 GPa to 0.04 GPa. In addition, at least one of the first units 110 and the second units 120 may include thermoplastic polyurethane (TPU) or ethylene-vinyl acetate (EVA). However, this is an example, and a case made of other materials is also included in the technical spirit of the present invention.

The shoe insole 1 for preventing flat shoes may be formed using various methods, for example, it may be formed using a 3-D printer. Specifically, the first unit bodies 110 and the second unit bodies 120 may be simultaneously formed using the 3-D printer.

Hereinafter, an experimental example of the shoe insole 1 for preventing flat shoes according to the technical idea of the present invention will be described. The following experimental examples are presented to help understanding of the invention, and are not limited to the following experimental examples of the present invention.

In this experimental example, a shoe insole for preventing flat shoes was manufactured using a 3-D (three dimensional) printer. In addition, a simulation method was used to analyze the stiffness characteristics of the first and second units. In this experimental example, the insole for preventing flat shoes was made of the same material and had a different structure to implement the inclined functional structure. The case of implementing is also included in the technical spirit of the present invention.

When the shoe insole for preventing flat shoes is manufactured using a 3-D printer, a functionally graded structure that not only provides conformity but also implements different physical properties depending on the part of the shoe insole can have The inclined functional structure is a structure that provides different rigidity depending on the area by changing the microstructure of the shoe insole.

The 3-D printing method using the 3-D printer is a manufacturing method with a high degree of freedom that can implement a shape without a manufacturing device such as a separate mold with only CAD drawings, so it is difficult to implement the inclined functional structure. Suitable. Therefore, while maximizing the contact area between the sole and the shoe insole, the area in contact with the forefoot and heel has weak rigidity and the region in contact with the long core has strong rigidity. it is effective Manufacturing a shoe insole for preventing flat shoes by using the 3-D printing method may be useful for people suffering from increasing flat foot disease, and may also be competitive in the foot orthodontic device market.

The shoe insole for preventing flat shoes may include a polymer. Since the polymer has various properties and can be used in various types of printing methods, it is a material widely used in 3-D printing methods. Among the polymers, ABS (Acrylonitrile-butadiene-styrene copolymer) and PLA (Polyacetic Acid) are widely used, but the ABS has a high Young's Modulus (Young's Modulus) in the range of 1.1 GPa to 2.9 GPa, and the PLA is 3.7 GPa to 4.1 GPa. It is a hard material, and therefore has a high rigidity limit to be used as a shoe insole. On the other hand, since ethylene vinyl acetate (EVA) has a low Young's modulus in the range of 0.01 GPa to 0.04 GPa, it can perform a function of absorbing shock well. Therefore, the shoe insole for preventing flat shoes according to the technical idea of the present invention may be configured to include the ethylene vinyl acetate.

In addition, since the thermoplastic polyurethane (TPU) has a Young's modulus of about 0.025 GPa, the shoe insole for preventing flat shoes according to the technical idea of the present invention may include the thermoplastic polyurethane. The thermoplastic polyurethane is used as a material for 3-D printing filaments because it is easy to 3-D printing due to excellent interfacial adhesion.

Figure 2 is a schematic diagram showing the chemical structure of the thermoplastic polyurethane applied to the shoe insole for preventing flat shoes according to an embodiment of the present invention.

2, since the thermoplastic polyurethane has a microstructure in which a soft matrix copolymer and a hard matrix copolymer cross-link at room temperature, their composition is controlled This has the advantage of being able to control the mechanical properties. In addition, the thermoplastic polyurethane has high thermal stability and excellent abrasion resistance compared to the ethylene vinyl acetate, so that it can be operated in a wide temperature range and has a long lifespan.

The shoe insole 1 for preventing flat shoes may have a lattice structure in which the first unit body 110 and the second unit body 120 are respectively repeatedly arranged. Since such a grid structure is repeatedly arranged in a simple structure, it is also easy to design and can easily absorb shock due to friction or buckling occurring in the connection part. To form the lattice structure, the first units 110 and the second units 120 may have a hollow cylindrical structure, a honeycomb structure, or a triple periodic minimum curved structure.

The honeycomb structure is a structure based on a hexagonal core, and when an impact is applied, the core can absorb the impact through the cyclic plastic deformation. The degree of absorbing the shock can be controlled by adjusting various parameters such as the thickness of the unit, the shape of the core, and the thickness of the bar. The triple periodic minimum curved structure (TPMS) is a more complex structure, and has an advantage that stress concentration can be minimized without discontinuous portions. The above-described honeycomb structure or triple periodic minimum curved structure may be difficult to implement in a 3-D printing method using fused deposition modeling (FDM) in which filaments are basically melted and stacked. In particular, when the angle formed by the upper layer with respect to the lower layer in the interlayer structure is 45 degrees or more, a support structure to support the structure is additionally required to prevent collapse, so the amount of material used increases, it takes longer, and it takes longer to support the structure later. The structure needs to be removed. In particular, in a lattice structure in which small structures are repeated, it becomes more difficult to remove the support structure. Therefore, it may be relatively easy to apply the hollow cylindrical structure to the shoe insole for preventing flat shoes.

3 is a schematic diagram illustrating a first unit 110 and a second unit 120 included in an insole for preventing flat shoes according to an embodiment of the present invention.

Referring to FIG. 3 , each of the first unit body 110 and the second unit body 120 may have a hollow cylindrical structure. The hollow cylindrical structure may have dimensions such as an overall diameter (D), a hollow diameter (G), a thickness (H), and a height (H). The hollow cylindrical structure is a relatively simple structure, and mechanical properties can be controlled by changing the above-described dimensions. In addition, there is an advantage of having a shock absorbing property and abrasion resistance at the same time.

In the shoe insole for preventing flat shoes according to the technical idea of the present invention, based on the plantar pressure distribution of each part of the sole of the wearer, units having different mechanical properties are arranged, resulting in an arcuate structure of the foot It is necessary to acquire information about the optimal strain distribution and pressure distribution that can be maintained. To this end, it is necessary to analyze the stiffness change according to the dimensional change of the unit body. Among the dimensions of the unit, the change in stiffness according to the change of the hollow diameter (G) and the height (H) will be simulated using numerical analysis.

The reason for choosing the hollow diameter (G) and height (H) as variables is as follows. All other things being equal, the larger the hollow diameter, the smaller the area subjected to the force, resulting in an increase in pressure. However, since the stress-strain curve of a viscoelastic material such as TPU is not a perfect straight line even in the elastic region, it can be expected that the stiffness represented by the ratio of the applied stress and the measured strain will change. Similarly, the height of the unit may also be a variable, that is, the rigidity may be changed according to the height, and the height is required as a variable element for consistency.

Among the factors affecting the rigidity of the hollow cylindrical structure, the hollow diameter and height will be reviewed.

4 is a graph showing the hardness change according to the internal filling rate with respect to the unit included in the shoe insole for preventing flat shoes according to an embodiment of the present invention.

Referring to FIG. 4 , the hardness increases as the infill percentage, which is the rate at which the grating fills the space, increases. From these results, it is possible to change the hardness by adjusting the porosity similar to the internal filling rate. Therefore, if the size of the hollow in the hollow cylindrical structure is changed, the hardness may be changed, for example, if the size of the hollow is increased, the hardness may be decreased.

The reason for considering the height is that units need to have different heights in order to form a heel cup or support the long core. In addition, as the contact area between the foot and the shoe insole increases, the fit increases and the pressure acting on the heel decreases at the same time. For example, for a 7.1% larger contact area, the pressure on the heel is reduced by 26.2%.

5 shows a simulation model for analyzing the rigidity characteristics of an insole for preventing flat shoes according to an embodiment of the present invention.

Referring to FIG. 5 , a simulation model in which a hollow cylindrical structure is stacked with 5 horizontal, 5 vertical, and 3 heights is shown. To analyze the influence of the hollow diameter (G), in the hollow cylindrical structure of Fig. 3, the total diameter (D) was fixed at 5 mm and the height (H) was fixed at 5 mm, and the hollow diameter (G) was set at 0 mm (i.e., , no hollow), 1 mm, 2 mm, and 3 mm were simulated. In addition, to analyze the effect of height (H), the total diameter (D) was fixed at 5 mm and the hollow diameter (G) was set at 2 mm, and the height (H) was changed to 1 mm, 3 mm, and 5 mm. was simulated.

For reference, as for the overall diameter (D), if the size of the hollow cylinder is too small, the resolution of the 3-D printer cannot keep up with it, so it may not exhibit the expected performance when actually manufactured. Therefore, considering this, it was set to 5 mm. The size of the hollow diameter (G) and the height (H) were selected in consideration of the size of the conventional shoe insole being 0.6 mm to 2.0 mm. In addition, the thickness of the flat plate inserted between the hollow cylinders was uniformly set to 1 mm.

For the simulation, a thermoplastic polyurethane was selected as the material, and BASF Elastollan 1185A was selected as the thermoplastic polyurethane to determine the specific material properties. The thermoplastic polyurethane has a density of 1.12 g/cm ³ , an elastic modulus of 0.0250 GPa, a shear modulus of 0.0100 GPa, and a Poisson's ratio of 0.25. Then, after obtaining the stress-strain curve of the thermoplastic polyurethane through the conventional data, 168 coordinates were obtained using the 'Plot Digitizer' program and then substituted into the simulation tool to obtain the desired data of the thermoplastic polyurethane. Then, the data and the designed CAD sample were simulated using Autodesk's 'NASTRAN' structural analysis program.

6 shows a simulation result for a hollow cylindrical structure applied to an insole for preventing flat shoes according to an embodiment of the present invention.

Referring to FIG. 6 , a simulation of applying a force at regular intervals of 150 N in a range of 150 N to 1500 N to the lattice structure of the simulation model of FIG. 5 was performed, and as a result, the degree of deformation of the structure is shown. At this time, stress data can be acquired using the area to which the force is applied, and since the dimensions of the structure before deformation are known, strain data can be acquired. Accordingly, a stress-strain curve can be obtained, and assuming that Hooke's law is satisfied, the stiffness corresponding to the slope of the curve can be obtained.

7 is a graph illustrating a change in stiffness according to a hollow diameter of a hollow cylindrical structure applied to an insole for preventing flat shoes according to an embodiment of the present invention.

Referring to FIG. 7 , the stiffness change of the hollow cylindrical structure with respect to the bulk is shown. When the hollow diameter was 2 mm or less, the stiffness was reduced by about 2% or less, and when the hollow diameter was 3 mm, the stiffness decreased by about 2.8%.

8 is a graph illustrating a change in stiffness according to a height of a hollow cylindrical structure applied to an insole for preventing flat shoes according to an embodiment of the present invention.

Referring to FIG. 8 , the stiffness change of the hollow cylindrical structure with respect to the bulk is shown. When the height is 5 mm, the stiffness is reduced to about 2% or less, when the height is 3 mm, the stiffness is reduced to about 1.25% or less, whereas when the height is 1 mm, the stiffness is increased by about 1.1%. appear.

When applied to the shoe insole 1 for preventing flat shoes shown in FIG. 1 , since the first units 110 require relatively low rigidity, compared with the second units 120 , the first units ( 110) may have a large hollow diameter (ie, a small thickness) and a large height.

As a result of experimenting with the two set variables as described above, although there is a small amount, there is a change in stiffness according to the variable, so there is a possibility to implement a sloped functional structure with different characteristics for each area by adjusting the size of the selected variable. Since the difference in stiffness obtained through the above experiment is not large, additional structural variables such as the number of layers of the hollow cylinder are investigated in order to obtain a more clear change according to the variables, and more complex methods such as adding other hollows to the side of the hollow cylinder It is necessary to add material parameters such as designing the structure or changing the composition of the material.

9 is a picture of a shoe insole for preventing flat shoes according to an embodiment of the present invention implemented using a 3-D printer.

Referring to FIG. 9 , a shoe insole for preventing flat shoes formed by using a 3-D printer by applying a hollow cylindrical structure having different strengths based on the above-described simulation results is shown.

By varying the size of the hollow of the hollow cylindrical structure and adjusting the height, a structure that can respond to pressures of different sizes for each location and at the same time ensure consistency was designed. In this way, by adjusting the size and height of the hollow, lattices with different strengths were appropriately placed at the positions where the corresponding characteristics should be, and a shoe insole having an inclined functional structure in which mechanical and structural characteristics continuously change for each part was realized.

Specifically, a g-code was made using the 3-D model, and 3-D printing was performed with a thermoplastic polyurethane using a 3-D printer (3DWOX 7X manufactured by Sindoh Corporation). The printing was performed at a temperature of the printing nozzle of 235° C. for 20 hours.

On the other hand, if the size of the hollow designed according to the 3-D printer used is too small, printing may not be realized due to the limitation of resolution, so it is necessary to set an appropriate size difference. next. Based on the simulation results, a 3-D printing shoe insole CAD design was produced, and a 3-D printer was used to form a shoe insole for preventing flat shoes using the CAD file.

Thereafter, the characteristics of the product may be identified and supplemented through the user's evaluation of the wearer. In order to evaluate the subjective satisfaction of the user, there is a method of statistically evaluating the satisfaction when stopping and walking using a questionnaire including items for evaluating the satisfaction in steps 1 to 7. In addition, it is possible to evaluate whether the shoe insole is actually functioning well by using the PedarX in-shoe pressure measurement system, which can obtain the plantar pressure distribution of each part of the sole when the product is worn.

The technical spirit of the present invention described above is not limited to the above-described embodiments and the accompanying drawings, and it is the technical spirit of the present invention that various substitutions, modifications and changes are possible without departing from the technical spirit of the present invention. It will be apparent to those of ordinary skill in the art to which this belongs.

Claims (11)

a plurality of first unit bodies disposed in a first region to which a first pressure is applied; and
A plurality of second units disposed in a second region to which a second pressure lower than that of the first pressure is applied;
Foot insoles for preventing flat shoes. The method of claim 1,
The second unit body has a higher stiffness than the first unit body, the shoe insole for preventing flat shoes. The method of claim 1,
Each of the first units and the second units has a hollow structure;
Foot insoles for preventing flat shoes. The method of claim 1,
The first units and the second units each have a hollow cylindrical structure, a honeycomb structure, or a triple periodic minimum curved structure,
Foot insoles for preventing flat shoes. The method of claim 1,
The first units have a greater height than the second units,
Foot insoles for preventing flat shoes. The method of claim 1,
The first units have a smaller thickness than the second units,
Foot insoles for preventing flat shoes. The method of claim 1,
wherein the first units and the second units are made of the same material;
Foot insoles for preventing flat shoes. The method of claim 1,
At least one of the first units and the second units has a Young's modulus in the range of 0.01 GPa to 0.04 GPa,
Foot insoles for preventing flat shoes. The method of claim 1,
At least one of the first units and the second units includes thermoplastic polyurethane (TPU) or ethylene-vinyl acetate (EVA),
Foot insoles for preventing flat shoes. The method of claim 1,
The first units and the second units are simultaneously formed using a 3-D printer,
Foot insoles for preventing flat shoes. The method of claim 1,
The shoe insole for preventing flat shoes has a sloped functional structure that provides different rigidity depending on the area by changing the microstructure,
Foot insoles for preventing flat shoes.

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