METHOD OF SYNTHESIZING MULTI-LAYERED DYNAMICALLY MOULDING INTEGRATED FOOTWEAR SOLE

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit and priority of provisional specification 2107/CHE/2011 filed on 22/06/2011, the full disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present disclosure generally relates to the field of footwear, and particularly to footwear sole. The embodiments herein more particularly relate to a multi-layered integrated dynamically moulding footwear sole for a variety of applications including a sole for diabetic patients, and methods of synthesizing such a footwear sole.

DESCRIPTION OF THE RELATED ART

[0003] The prevalence of diabetes is increasing rapidly and is likely to reach epidemic proportions in the next decade. There are 246 million diabetic patients in the world today. India had about 31.7 million adult diabetic patients in the age group of 20 to 79 years in the year 2000 and the number is expected to increase to 73 million by 2025. In fact, India is likely to have the largest number of diabetic patients in the world by 2025. One of the most dreaded complications of diabetes is foot ulcer and gangrene. It is estimated that 15% of all diabetic patients get foot ulcers and 1% requires higher-level amputation; 60% of indoor admissions of diabetic patients are for foot ulcers and foot infections; 50% of non-traumatic amputations are due to diabetic foot gangrene, and 85% of these amputations are due to untreated and/or inadequately treated diabetic foot ulcers. It is therefore estimated that as the prevalence of the diabetes increases, a large number of patients in the comparatively younger age group (35 to 45) are likely to suffer from diabetic foot ulcers and many of these patients will require higher-level amputations.

This will result in loss of employment and psychological trauma for these patients.

[0004] A majority of the diabetic foot ulcers and infections observed in India are neuropathically infective as compared to developed countries. This is significant from the therapeutic and preventive perspective. These types of ulcers are easy to manage with proper cost-effective preventive strategies. Ensuring the use of proper footwear is thus an important part of a treatment programme for people with diabetes, even those in the earliest stages of the disease

[0005] An ulcer develops when an insensate foot is subjected to even a minor trauma or to an increased pressure. Ulcers are prone to develop on areas underlying the metatarsal heads and other undue bony prominences. This occurs because of the mal-distribution of pressure, especially with a Charcot foot and other foot deformities. Deformities of the foot resulting from loss of fatty tissue, hammer-toes and foot amputations must also be accommodated by the footwear. Deformities need to be stabilized to relieve pressure and avoid further destruction of tissue. Limiting the motion of certain joints in the foot can often decrease inflammation, relieve pain and result in a more stable and functional foot. Proper footwear is essential to avoid this.

[0006] Shoes must accommodate dorsal deformities and cushion areas of high plantar pressure. In particular, they should relieve excessive pressure on areas that are prominent, such as the metatarsal heads. Shoes must also reduce shock (the vertical pressure on the bottom of the foot caused by the weight of the person) and shear (horizontal movement of the foot within the shoe).

[0007] In general, footwear comprises the insole and the outsole or sole. Modified diabetic footwear have an additional mid-sole to strengthen the outsole. The insole should distribute plantar pressure equally on its surface. Previous attempts at designing special footwear for diabetics have involved removable shoe inserts (U.S. Pat. No. 4,130,948, U.S. Pat. No. 6,481,120) or multilayer insoles (U.S. Pat. Pub. No. 20040168354, McCurdy 2004, U.S. Pat. Pub. No. 20080127527). Orthotic shoe soles with gradient hardness variation have been suggested in order to address foot problems in diabetics (Phillips et al. 2003, Levine 2006). However, a separate shoe insert or insole has to be attached to the midsole or the rest of the sole, which may result in poor dynamic moulding characteristics and affects durability. These removable insoles are therefore designed to be replaceable, which, however, increases cost.

[0008] Materials presently used are microcellular rubber, microcellular polymer, polyurethane, ethyl vinyl acetate, polyethylene foam, etc. The insole should have a 'Shore-hardness' of about 10 to 15. Of these materials, only polyethylene foam and the like materials can be easily moulded in the exact shape of the foot. The outsole should be hard, rigid, lightweight and durable. This is generally made of polyvinyl chloride or high density ethyl vinyl acetate. The Shore-hardness of the outsole is about 70.

[0009] In the construction of moulded diabetic footwear, initially a plaster-of-paris mould is taken of the deformed foot of the diabetic patient. Using the plaster-of-paris mould, a 'last' or positive of the foot is made. The insole material is moulded on the 'last,' with the help of a special hot-air oven. Polyethylene foam and like materials are usually used for this purpose as only these can be moulded in an hot air oven with negative suction and will retain the moulded shape after cooling to normal air temperature. Thus the foot-wear insole has the exact configuration of the plantar surface of the foot. This technique is currently in use world-wide.

[0010] It must be noted that the insole thus made is with the foot in the static position. In the dynamic state of the foot in the gait cycle, i.e., when the individual in walking or running, the configuration of the plantar surface will necessarily change according to the status of the foot in the 'stance' position. The insole made with the foot in the static position, as described above, will not adequately yield to the changing configuration of the dynamic foot (i.e. while moving). This understandably will cause increased plantar pressures when the patient is ambulant, leading to foot injuries. Over the past ten years of research, applicants have observed plantar callosities and ulcerations in a large number of patients using the existing polyethylene foam moulded footwear. These observations show that the raised plantar pressures have not been completely removed by the use of the existing footwear.

[0011] Hence there is a need to provide a better dynamically moulding integrated sole for a variety of applications including footwear for diabetic patients to uniformly distribute pressure and to reduce morbidity associated with the disease. The above mentioned shortcomings, disadvantages and problems are addressed herein, as detailed below.

[0012] The primary object of the present disclosure is to provide various embodiments of a multi-layered integrated footwear sole with dynamically moulding properties for uniformly distributing and reducing the plantar pressures and impulse loading in a diabetic foot, in both static and dynamic patterns of gait that would prevent foot injuries when used by diabetic patients.

Another object of the present disclosure is to provide methods of synthesizing a multi-layered integrated footwear sole with dynamically moulding properties for uniformly distributing and reducing the plantar pressures and impulse loading in a diabetic foot, in both static and dynamic patterns of gait.

[0013] Yet another object of the present disclosure is to provide methods of synthesizing a multi-layered integrated footwear sole such as diabetic footwear sole with gradually reduced Shore hardness that gives the required dynamic moulding effect for pressure distribution when the patient walks with the footwear.

[0014] Yet another object of the present disclosure is to provide methods of synthesizing a multi-layered integrated footwear sole such as diabetic footwear that will offer diabetic patients a customized insole which will meet their requirements for pressure distribution and support and will reduce the morbidity associated with the disease.

SUMMARY OF THE INVENTION

[0015] Described herein are a multi-layered integrated dynamically moulding footwear sole for a variety of applications including a sole for diabetic patients, and methods of synthesizing such a footwear sole. An integrated footwear sole is disclosed, comprising a plurality of layers including a bottom outsole layer, a top insole layer, and at least three layers therebetween, wherein the layers have varying hardnesses, the hardness of the layers decreasing progressively from about 70 Shore A at the bottom outsole layer to about 10 Shore A at the top insole layer. The total thickness of the footwear sole is at least 25 mm.

[0016] In one embodiment the integrated footwear sole comprises at least five layers between the bottom outsole layer and the top insole layer, wherein the thickness of each of the five layers is at least 5 mm. The three layers between the outsole and insole layers are of Shore A hardness of 60 units in the layer over the outsole layer, 40 units in the middle layer and 30 units in the layer below the insole layer. The integrated footwear sole can be made of polyurethane foam, polyethylene foam or ethyl vinyl acetate foam.

[0017] A method of producing an integrated multi-layered footwear sole is disclosed, comprising moulding a plurality of layers of a polymer into the footwear sole; moulding a bottom outsole portion to produce a base layer of Shore A hardness about 70 units; moulding a top insole portion to produce a top layer of Shore A hardness about 10 units; moulding a plurality of intermediate layers between the base layer and the top layer, wherein the Shore A hardness of the intermediate layers progressively decreases from about Shore A 70 near the base layer to Shore A 10 near the top layer, wherein the moulding of each layer comprises heating the mould to a pouring temperature, injecting a mixture of a foaming agent, a crosslinking agent and a polymer in various proportions to form a moulded layer and cooling the moulded layer to ambient temperature, and wherein the total thickness of the sole is at least 25 mm. The polymer can be a polyol and the crosslinking agent can be isocyanate.

[0018] In one embodiment of the method the plurality of layers comprises five layers, wherein the thickness of each layer is at least 5 mm, the hardness of the outsole is at least Shore A 70 and the hardness of the insole is at least Shore A 10. The method of the invention can be used to produce an integrated footwear sole made of polyurethane foam, polyethylene foam or ethyl vinyl acetate foam.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The invention has other advantages and features which will be more readily apparent from the following detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which:

Figure 1 shows one embodiment of the footwear sole with five layers of progressively reducing Shore A hardness.

Figure 2 shows one embodiment of the footwear sole with top and bottom layers of fixed thickness with the intermediate layer of gradient hardness.

Figure 3 shows pedopodogram report showing raised plantar pressures of person using a standard diabetic footwear.

Figure 4 shows pedopodogram report showing plantar pressures normalised, when using the integrated dynamically moulding sole, by the same person.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Although the detailed description contains many specifics, these should not be construed as limiting the scope of the invention but merely as illustrating different examples and aspects of the invention. It should be appreciated that the scope of the invention includes other embodiments not discussed herein. Various other modifications, changes and variations which will be apparent to those skilled in the art may be made in the arrangement, operation and details of the device and method of the present invention disclosed herein without departing from the spirit and scope of the invention as described here.

[0021] Embodiments of the present invention relate generally to multi- layered, integrated footwear sole and a method for synthesizing such a sole for a variety of applications, including for diabetic patients.

[0022] In one embodiment the invention is a multi-layered integrated footwear sole as shown in Fig. 1. Footwear sole 100 comprises an outsole 110 at the bottom and a top insole layer 120, with layers 130,140, and 150 located therebetween. The layers are configured to have progressively decreasing levels of Shore hardness (Shore A), starting with 70 Shore A for the outsole 110, through 60 Shore A in layer 130, 40 Shore A in layer 140, 30 Shore A in layer 150 and ending with a Shore A hardness of 10 for the insole layer 120 to be in contact with the plantar skin of a patient's foot.

[0023] In one embodiment and as shown in Fig. 1, the total thickness t of the integrated sole is configured to be at least 25 mm. In one embodiment the thickness of each of the layers 110,120,130,140 and 150 is configured to be at least 5 mm.

[0024] In another embodiment and as shown in Fig. 2, the integrated footwear sole 200 comprises an outsole layer 210, an insole layer 220 and a midsole layer 230. The outsole layer 210 is of hardness Shore A 70 and the insole layer 220 is of hardness Shore A 10, while the midsole layer 230 is of progressively decreasing or gradient hardness from a Shore A value of 70 adjacent to the outsole layer 210 down to a Shore A value of 10 just below the insole layer 220. In one embodiment, the total thickness t of the integrated sole is at least 25 mm. In one embodiment the thickness of the outsole layer 210 and the insole layer 220 are each at least 5 mm, while the midsole gradient layer 230 is at least 15 mm.

[0025] Present disclosure further contemplates methods of producing an integrated multi-layered footwear sole. In one embodiment, the method comprising the steps of moulding in succession, a series of layers with hardness varying from about Shore A 70 at the outsole to about Shore A 10 on the insole, to produce a total thickness of 25 mm. In one embodiment, each layer of the integrated footwear sole is formed by injecting the precursors, including a polymer precursor, a crosslinking agent and/or a foaming agent into a mould in a specific quantity, proportion, and/or combination to form a first foamed layer of appropriate thickness. The molecular weight of the polymer precursor and proportion of foaming and crosslinking agents are adjusted to obtain appropriate hardness in the foamed layer. The foamed polymer layer is then allowed to cool to room temperature. A successive layer is then moulded over the first layer, with precursors injected into the mould in appropriate quantity, proportion and/or combination to obtain the necessary foaming and hardness characteristics.

[0026] While embodiments of the novel footwear sole and method of producing an integrated multi-layered footwear sole have been illustrated in the following example using polyurethane foam as material of construction, it is contemplated that any suitable material that is amenable to obtain the necessary range of hardness and durability for the application can be used, such as polyethylene foam or ethyl vinyl acetate foam.

Example 1

[0027] Polyurethane (PU) was used as the material for the manufacture of integral footwear, which has an out-sole of 70 Shore A hardness and gradually reducing to 10 Shore A at insole. The equipment consisted of two gear pumps driven independently by two variable speeds AC motors. The speed was controlled or regulated by a programmable logic control unit specifically designed for this purpose. The whole process was computer controlled.

[0028] Each of the gear pumps delivered a predetermined quantity of polyol and isocyanate to a common discharge manifold, from where the chemical mixture was delivered into the sole mould with the help of a specially designed nozzle. The isocynate also contained a foaming agent for making the PU into a micro cellular structure. This gave the desired properties of light weight and softness to the integral sole.

[0029] The polyol and isocyanate were heated separately to 42°C and were pumped into the mould in specific quantity to form a layer of appropriate thickness. The input materials were then injected into the mould, which was already heated to 42°C. The foamed polymer layer was then allowed to cool to room temperature, in about 5 to 7 minutes.

[0030] By varying the quantities of the foaming and crosslinking agents fed in each layer, foamed polyurethane layers with gradually reducing Shore hardness were obtained. Subsequent layers were automatically bonded onto the previous layers when poured over the previous layer. Before forming the next layer, the mould was again heated to 42°C.

[0031] The ratio of polyol and isocyanate determines the hardness of the PU sole, which was controlled so that the initial outsole layer had a hardness of 70 Shore A, which was reduced progressively, layer by layer to 10 Shore A, at the insole level. The rate of delivery, the ratio of the two chemicals and the periodicity of injection were controlled by the computer to achieve the desired results.

[0032] The effectiveness of the integrated footwear sole in reducing peak plantar pressures in a person wearing it is shown in Fig. 3 and Fig. 4. Fig. 3 and 4 show grayscale renderings of colour maps of plantar pressure, in which areas of normal pressure marked G are in dark gray, areas of higher pressure marked Y appear in a lighter shade within these gray areas and areas of peak pressure are within the circled areas marked R. The pedopodogram report of a person wearing standard commercially available diabetic footwear is shown in Fig. 3, where high peak plantar pressures are evident in the areas marked R. The peripheral areas where the foot does not touch the footwear are in black. Using the dynamically moulding integrated footwear of the invention, the pedopodogram of the same person is modified as shown in Fig. 4. The pedopodogram report in Fig. 4 shows that the R areas with high pressure are eliminated and the Y areas have been minimized, thereby showing significant reduction in peak plantar pressures.

[0033] It was observed that if the thickness of each layer was more than 5 mm, the entire unit was too thick or bulky for comfort, to be used by the diabetic patient. Thickness lesser than 5 mm did not give the desired result to prevent increased plantar pressures, as measured by a pedopodogram.

[0034] The present disclosure provides an integrated footwear sole that may have various advantages and/or therapeutic effects. For example, it is contemplated that the footwear sole as described herein may reduce the chances of onset of foot ulcers, gangrene and neuropathy in diabetic patients. Furthermore, the footwear as described in the present disclosure may relieve excessive pressure on prominent areas of foot, such as, metatarsal heads. The footwear as described in the present disclosure may also reduce shock and shear while walking. Additionally, the footwear as described in the present disclosure may offer diabetic patients a customized insole that meets their requirements for pressure distribution and support while reducing the morbidity associated with their disease.

[0035] While the invention has been disclosed with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. Particularly, the dynamically moulding footwear concept could be applied to several kinds of footwear such as those for orthopaedic disorders, sports shoes and the like. In addition, many modifications may be made to adapt to a particular situation or material the teachings of the invention without departing from its scope.

REFERENCES

[0036] Robert Phillips, William Olson, Doughlas Richie, Paul Scherer, Christopher E. Smith. Key insights on orthotic materials. Podiatry Today-ISSN: 1045-7860-Volumel6-issue 9-September 2003. Page: 30-36.

[0037] David Levine. How to address pronation related pathology.

Podiatry Today-issn: 1045-7860-Volume-19-issue 6-June 2006. Pages: 56-62.

[0038] Brian McCurdy. Therapeutic footwear for patients with Diabetes.

Podiatry Today-ISSN: 1045-7860-Volume 17-issue 5-May 2004-Pages: 6-16.

WHAT IS CLAIMED IS

1. An integrated footwear sole, comprising:

a plurality of layers including a bottom outsole layer, a top insole layer, and at least three layers therebetween;

wherein the layers have varying hardnesses, wherein the hardness of the layers decreases progressively from about 70 Shore A at the bottom outsole layer to about 10 Shore A at the top insole layer, and wherein the total thickness of the footwear sole is at least 25 mm.

2. An integrated footwear sole according to claim 1, further comprising at least five layers including the bottom outsole layer and the top insole layer, wherein the thickness of each of the five layers is at least 5 mm .

3. An integrated footwear sole according to claim 1, wherein the three layers between the outsole and insole layers are of Shore A hardness 60 units in the layer over the outsole layer, 40 units in the middle layer and 30 units in the layer below the insole layer.

4. An integrated footwear sole according to claim 1, wherein the sole is made of polyurethane foam, polyethylene foam or ethyl vinyl acetate foam.

5. A method of producing an integrated multi-layered footwear sole, comprising:

moulding a plurality of layers of a polymer into the footwear sole, comprising moulding a bottom outsole portion to produce a base layer of Shore A hardness about 70 units;

moulding a top insole portion to produce a top layer of Shore A hardness about 10 units;

moulding a plurality of intermediate layers between the base layer and the top layer, wherein the Shore A hardness of the intermediate layers progressively decreases from about Shore A 70 near the base layer to Shore A 10 near the top layer,

wherein the moulding of each layer comprises heating the mould to a pouring temperature, injecting a mixture of a foaming agent, a crosslinking agent and a polymer in various proportions to form a moulded layer and cooling the moulded layer to ambient temperature, and wherein the total thickness of the sole is at least 25 mm.

6. The method of claim 5, wherein the polymer is a polyol and the crosslinking agent is isocyanate.

7. The method of claim 5, wherein the plurality of layers comprises five layers, wherein the thickness of each layer is at least 5 mm.

8. The method of claim 5, wherein the hardness of the outsole is at least Shore A 70 and the hardness of the insole is at least Shore A 10.

9. The method of claim 5, wherein the sole is made of polyurethane foam, polyethylene foam or ethyl vinyl acetate foam.