WO1996039908A1

WO1996039908A1 - Custom molded cushion and methods

Info

Publication number: WO1996039908A1
Application number: PCT/US1996/005641
Authority: WO
Inventors: Kelly T. Mcgurran; Richard E. Anderson; Timothy C. Sandvig
Original assignee: Minnesota Mining And Manufacturing Company
Priority date: 1995-06-07
Filing date: 1996-04-22
Publication date: 1996-12-19
Also published as: EP0833580A1; CA2220137A1; EP0833580B1; DE69615029T2; DE69615029D1; JPH11506377A

Abstract

A custom molded cushion is provided. The custom molded cushion preferably comprises a multilayer structure comprising a first resilient layer and a second layer. The second layer comprises a foamimpregnated with a curable resin. The first and second layers areadapted to deform against a body part of a patient and to create and retain an impression of the body part. The first and second layers are selected to act in concert to distribute the pressure applied to the cushion. Methods of preparing such custom molded cushions are also provided.

Description

CUSTOM MOLDED CUSHION AND METHODS

Field The present invention relates to custom molded cushions and methods of preparing these cushions. In particular, this invention relates to cushions which utilize an open-celled foam impregnated with a water-curable resin. Such cushions and methods are particularly suited for providing seat cushions and especially for custom molded wheelchair seat cushions to achieve uniform pressure distribution and alleviate irritation to the patient.

Background

Persons con ined to wheelchairs experience several problems associated with their prolonged confinement in a sitting position. Among such problems are discomfort and skin irritation. These problems occur, in part, because the seat does not adequately distribute pressure applied to it, and because of friction between the patient and the seat. Pressure builds because the patient is not in full contact with the seat.

Skin irritation is especially troublesome because it leads to skin breakdown and the formation of ulcers. This problem is common in patients confined to wheelchairs. When an ulcer occurs, special procedures, even surgery, are required to remedy the situation and heal the ulcer. The special procedures involved in healing the ulcer are very uncomfortable for the patient and extremely expensive. These problems are exacerbated because many patients confined to wheelchairs experience significant wasting of muscle, fat, and connective tissue such that their ischeal tuberosities protrude when the patient is seated in the wheelchair. This condition can cause further ulcerative problems, and extreme pain and discomfort to the patient. One possible solution to the ulcer formation problem is to uniformly spread the pressure with a custom fit wheelchair seat. Custom fitting wheelchair seats, made by currently known methods, involve casting the patient to make a negative mold, making a positive form from the negative, and building a custom seat around the positive form. This is a time-consuming and very expensive process. A custom fit wheelchair made by this technique may cost as much as $5,000, and does not entirely solve the pressure distribution problem. Such a custom fit seat can only function to evenly distribute pressure if the patient remains in one position. If the patient leans or slumps, pressure builds because the patient is not in full contact with the custom seat.

Another possible solution to the ulcer formation and discomfort problems associated with wheelchair-confinement is to provide a gel-filled cushion or air bladder to distribute applied pressure or otherwise increase comfort. Such materials are somewhat successful in more uniformly distributing applied pressure. However, these materials do not retain the form of the patient, require re-forming with each seating, and are not custom fit to the particular patient.

In addition to wheelchair seats, there are numerous situations in which a custom fit cushion which effectively distributes pressure and otherwise provides added comfort would be beneficial. Some of these situations include: bed cushions for bedridden or convalescing patients; car seat cushions, e.g., for persons who spend a significant amount of time in their vehicles, such as taxi or truck drivers; and business furniture such as office chair cushions.

Summary The present invention provides a solution to the above-described problems associated with wheelchair seats, including problems associated with currently available custom fit wheelchair seats. This invention comprises a custom molded, supportive element which "floats" on a foam or air bladder layer. The custom molded, supportive element may be a custom molded open-celled foam containing a cured resin or a custom molded thermoplastic material. This configuration allows the patient to change position by leaning in any direction and still remain in contact with the custom molded cushion. Pressure points are reduced by keeping the custom molded cushion in full contact with the patient. In a preferred embodiment, a pressure relief area is provided in the cushion which corresponds to a focal area of high pressure exerted by the body part being cushioned.

The present invention also provides a method of making a custom molded cushion in which the custom molded element is molded directly to the patient while the patient is positioned on the cushion. This method provides an extremely accurate custom fit and a cushion which is ready for use in a matter of hours instead of weeks. The present invention provides a custom molded cushion which is far less costly and time consuming than custom fit cushions currently available.

In accordance with the present invention, a custom molded cushion is provided which comprises a first resilient layer and a second layer. In preferred embodiments, the first resilient layer is a foam material, and may be a flat sheet of foam material or a sculpted foam having a back portion, opposing side portions, and a base portion comprising a pommel. In other embodiments, the first resilient layer may comprise an air bladder, or any resilient material on which the second layer may float.

The second layer of the cushion preferably comprises a foam, preferably an open-celled foam, impregnated with a curable resin. The curable resin preferably comprises a moisture curable prepolymer resin formed by reacting a polyisocyanate with a polyol. Preferably, the ratio of NCO groups in said polyisocyanate to OH groups in said polyol is between about 2 to 1 and 5 to 1, and the prepolymer resin has an NCO equivalent weight of from about 275 to 1000 grams of prepolymer resin per NCO group. More preferably, the ratio of NCO groups in the polyisocyanate to OH groups in the polyol is between about 2.5 to 1 and 4 to 1, and the prepolymer resin has an NCO equivalent weight of from about 350 to 700 grams of prepolymer resin per NCO group. The prepolymer resin preferably is formed by reacting the polyisocyanate with the polyol while the polyisocyanate and the polyol are inside the open-celled foam material.

The open-celled foam material used in the second layer of the cushion of the present invention preferably has from about 12 to about 48 pores/cm and a density of from about 77.5 to about 349 kg/m³. The prepolymer resin preferably comprises from about 70% to about 95% by weight of the open-celled foam material.

In another embodiment of the present invention, the first resilient layer is as described above, but the second layer of the cushion comprises a sheet of thermoplastic material. The thermoplastic material may be heated to a softening temperature and deformed against a body part to create and, upon cooling retain, an impression of the body part.

A third layer, which may be a resilient material, and preferably comprises a foam, may be provided in the cushion prior to or following deformation of the cushion against the body part, to provide added padding and pressure distribution. The third layer is positioned in the cushion such that the second layer is between the first and third layers.

If the preferred foam containing a moisture curable prepolymer resin system is utilized, the resin is activated with water. The first resilient layer and second layer may then be placed together and the cushion is deformed against a body part of a patient while the resin cures to create an impression of the body part. Where a thermoplastic material is used as the second layer, the thermoplastic material is heated to a softening temperature, and placed together with the first resilient layer. The cushion is deformed against the body part, and the thermoplastic material cools to create and retain an impression of the body part.

The custom molded cushion conforms very accurately to the body part, and the conformed second layer "floats" on the first resilient layer, allowing the patient to change position by leaning or slumping in any direction and still remain in contact with the custom molded cushion. In another embodiment, the present invention provides an article suitable for forming a custom molded cushion. The article comprises a unitary blank of open-celled foam wherein a first portion of the blank is impregnated with a curable resin and a second portion is not impregnated with the curable resin. The unitary blank is adapted to deform against a body part to create and retain an impression of the body part and to distribute the pressure applied to the cushion.

The invention also relates to methods of preparing custom molded cushions. One preferred method comprises the steps of: providing a multi-layer cushion which comprises a first resilient layer and a second layer of foam impregnated with a curable resin wherein the first and second layers are selected to act in concert to distribute pressure applied to the cushion; activating the curable resin; and deforming the cushion by positioning a body part on the cushion until curing is substantially complete, to create and retain an impression of the body part in the cushion. The method may further comprise providing a third layer, preferably of a resilient material, and more preferably of a foam material, positioned such that the second layer is between the first and third layers. The second layer of foam preferably is an open-celled foam material and is impregnated with a resin system as described above.

The method may further comprise selectively impregnating the second layer such that an area corresponding to a focal area of high pressure exerted by the body part is not impregnated. Alternatively, the method may comprise excising, before or after curing, a portion of the second layer corresponding to a focal area of high pressure exerted by the body part, preferably replacing the excised portion with a resilient material. In another embodiment, the invention comprises a method of preparing a custom molded cushion which comprises providing a first layer of resilient material, and a second layer of thermoplastic material. The second layer of thermoplastic layer is heated to a softening temperature and the cushion is deformed against a body part to create and retain an impression of the body part upon cooling of the second layer of thermoplastic material. The first layer preferably comprises a foam material and a third layer of material, preferably resilient material and more preferably foam material, may be provided and positioned such that the second layer of thermoplastic material is positioned between the first and third layers. Either prior to heating of the thermoplastic material or after cooling of it, a portion of the layer of thermoplastic material, corresponding to a focal area of high pressure exerted by the body part, may be excised from the second layer of thermoplastic material. The second layer of thermoplastic material may also be provided with a portion already excised. In still another embodiment, the present invention provides a kit containing materials for preparing a custom cushion. The kit contains a first resilient material to be used as the first resilient layer described above, and a second material comprising a foam impregnated with a curable resin to be used as the second layer described above. The first and second materials are adapted to receive a body part and to create and retain an impression of the body part, and are selected to act in concert to distribute pressure applied to the cushion. As with other embodiments described herein, a third material may be provided to be used as a third layer such that the second material is positioned between the first and third materials. In the kit of the present invention, the first and third materials preferably comprise foam material.

Brief Description of the Figures

FIG. 1 is an exploded view of a cushion of the present invention prior to deformation of the cushion against a body part. FIGs. 2a and 2b are partially exploded perspective views of two preferred embodiments of the custom molded cushion of the present invention. FIG. 3 is a partially exploded perspective view of another preferred embodiment of the custom molded cushion of the present invention.

FIG. 4 is a cross-section of a portion of the custom molded cushion shown in FIG. 3. Detailed Description

The present invention is directed to custom molded cushions and methods for preparing custom molded cushions. A custom molded, supportive element floats on a resilient base. This construction effectively distributes pressure applied to the cushion by the patient and allows the patient to change position and remain in contact with the custom molded cushion. The ability to remain in full contact with the patient allows for uniform distribution of pressure, greater comfort for the patient, and reduced risk of skin ulceration.

In preferred embodiments, the cushions of the present invention are multilayer structures. The first layer comprises a resilient material, such as a foam material, an air bladder, or the like. The second layer of the cushion conforms to the body part and retains an impression of the body part in the cushion. The second layer is preferably an open-celled foam material impregnated with a curable resin. Alternatively, the second layer may be a thermoplastic material which may be heated to a softening temperature, deformed against a body part, and cooled to create and retain an impression of the body part in the cushion. In preferred embodiments, a third layer is provided and is positioned such that the second layer of the cushion is between the first and third layers. The third layer is preferably a resilient material which adds padding and increased comfort, but may be any material which provides added comfort and/or enhances the distribution of pressure applied to the cushion.

Referring now to FIG. 1, there is shown an exploded view of a custom molded cushion 10 of the present invention prior to deformation of the cushion against a body part. The first resilient layer 12 may comprise any resilient material, and preferably comprises either an open-celled or a close-celled foam, for example, a urethane foam. The first resilient layer 12 may also comprise an air bladder, which may comprise a rubber or polymeric material filled to a selected level with compressed air to provide a resilient cushion-like material. The first resilient layer 12 generally may be any resilient material which is compatible with a second layer of impregnated foam or a second layer of thermoplastic material. The first resilient layer is dimensioned in length, width, and height, to receive and cushion a body part and, where appropriate, to be fitted in a receptacle, e.g., a wheelchair.

In FIG. 1, the first resilient layer 12 is shown as a sculpted layer having sides 14, back portion 16, and base portion 18 comprising pommel 20. Pommel 20 is provided for added support and comfort in the cushion. For example, pommel 20 may be provided in a custom molded wheelchair cushion to maintain the patient's legs separated from each other and to provide added support. Although first resilient layer 12 is shown as a sculpted layer in FIGs. 1-3, it will be appreciated that the first layer 12 may also comprise a flat sheet of resilient material which is preferably a foam material or an air bladder.

Second layer 22 preferably comprises an open-celled foam, e.g., a urethane foam, impregnated with a curable resin.

The open-celled foam of second layer 22 can comprise any one of a number of extensible foams which are open-celled, such as polyether or polyester- based polyurethane foams. Importantly, the porosity of the foam layer 22 must be such that it can be resin-loaded sufficiently to provide a satisfactory, conformed layer. In this regard, the open-celled foam sheet preferably has from about 12 to about 48 pores/cm. As used herein, the term "pores per cm" refers to the average number of pores located along a linear centimeter of the foam sheet. The number of pores per linear centimeter may be determined, for example, by measuring the foams resistance to air flow or a pressure differential and using such information to calculate the approximate number of pores in the foam.

When the pores per cm value is decreased below 12, the foams become too course or rough, and typically do not hold enough resin to provide the necessary strength for the resulting conformed layer. Foam materials having over about 39 pores per cm are not known to be presently commercially available. It will be understood, however, that the upper limit for the pores per cm parameter is limited solely by the ability to resin-load the foam sheet to the extent needed to provide sufficient strength for a conformed foam layer, while still maintaining adequate porosity. Since foam sheets having over 39 pores per cm are not presently available, it is difficult to currently predict the performance of foams having substantially greater than 39 pores per cm as to their resin-loading characteristics and porosity. Thus, in the most presently preferred embodiment of the present invention, the open-celled foam sheet used to form second layer 22 has from about 18 to about 39 pores per cm.

The foam materials utilized in the first layer 12, the second layer 22, and the optional third layer 24, preferably have a density in the range of about 77.5 to about 349 kg/m³, and most preferably, between about 77.5 and about 232 kg/m³. The foam sheets possessing densities lower than about 77.5 kg/m³ are not known to be presently commercially available. Foam sheets having densities higher than about 349 kg/m³ tend to preclude the resin-loading which is necessary to achieve proper strength.

The foam materials utilized in the first layer 12, the second layer 22, and the optional third layer 24, preferably have an indentation force deflection (IFD) in the range of about 70 kPa to about 550 kPa, when tested as described herein. IFD is measured by compressing the center of a 40cm x 40cm x 10 cm thick foam sample (using a 10 cm diameter plunger) to a thickness of 7.5 cm (25 % of its original height). More preferred foam materials have an indentation force deflection in the range of about 170 kPa to about 475 kPa, and most preferred foam materials have an indentation force deflection in the range of about 270 kPa to about 400 kPa.

When second layer 22 is an open-celled foam impregnated with a curable resin, its thickness preferably is between about 0.64 cm and about 3.8 cm. Second layer 22 preferably is dimensioned to cover and slightly overlap the first resilient layer 12 on all sides except for the front edge of the first resilient layer 12. After cure, second layer 22 may be trimmed to remove excess material.

Second layer 22 is impregnated with a curable resin system. The presently most preferred resins for impregnating the foam sheet materials of the present invention are water curable, isocyanate functional, polyurethane prepolymers prepared by the reaction of a polyol with an excess of a polyisocyanate. The preferred resins impregnating foam second layer 22 and methods of preparing the same are fully disclosed in United States Patent 4,946,726, also assigned to 3M. The ratio of isocyanate (NCO) groups in the polyisocyanate to hydroxyl (OH) groups in the polyol is preferably between about 2 to 1 and 5 to 1, and more preferably between about 2.5 to 1 and 4 to 1. The isocyanate (NCO) equivalent weight in the resultant prepolymer preferably is between a bout 275 to about 1000 grams of prepolymer resin per NCO group, and more preferably is between about 350 to about 700 grams of prepolymer resin per NCO group. The custom molded cushion is formed by activating the polyurethane prepolymer resin and deforming the cushion (comprising the first resilient layer and the second layer) against a body part of a patient.

The strength and rigidity of the cured second layer are dependent primarily upon the rigidity of the cured prepolymer resin rather than the initially flexible open-celled foam sheet. By maintaining the NCO:OH ratio and NCO equivalent weight within the ranges disclosed herein, safe levels of heat generated during cure are maintained, while providing a cured resin having the rigidity needed. The resin system impregnated into second layer 22 is intended to produce, upon curing, a "semi-rigid" foam. By "semi-rigid" it is meant that following cure, the foam will maintain some degree of resilience. Resin systems having the NCO: OH ratios and NCO equivalent weights described herein will provide cured foams having the desired levels of rigidity. A preferred mixture for impregnation into second layer 22 comprises the following: I Ingredient Source P$a_#

Isonate 2143L Dow Chemical U.S.A., Midland, 58.38 MI

1 Benzoyl Chloride Velsicol Chemical Corp., 0.08 Rosemont, IL

[ Pluronic F-38 BASF Corp. 5.20

Polyol PPG-1025 Union Carbide 63.00

CAB-O-SIL TS720 Cabot Corp., Tuscola, IL 1.30

MEMPE (4-[2-{l- 3M Company, St. Paul, MN 1.30 methyl-2-(4- (described in U.S. Patent No. morpholinyl)ethoxy]- 4,705,840) | ethyl]-morpholine)

1 ANTIFOAM 1400 (Dow Corning, Midland, MI) 0.26

IONOL (Butylated Sherex Chemical Co. 0.43 hydroxy toluene)

REACTINT GREEN Milliken Chemical, Inman, SC) 0.05 1 960

The NCO equivalent weight of the above mixture is about 469. The NCO/OH ratio of the above mixture is about 3.18.

The polyisocyanate and polyol preferably are not pre-reacted, but are rather reacted while within the foam sheet to form the polyurethane prepolymer resin.

The resin system may be incorporated into the open-celled foam by layering a desired amount of resin onto or slightly beneath the surface of the foam by mechanical means, followed by rolling the coated foam piece at a pre¬ determined roller gap which allows for complete uniform resin penetration throughout the foam.

The polyurethane prepolymer resin can be loaded into the foam material of second layer 22 so as to comprise from about 70% to 95% by weight of the total article. Such a high degree of resin loading imparts to the cured layer 22 necessary strength to function as a semi-rigid conformed layer. After loading such large percentages of resin into the foam, the resultant layer 22 has quite good water vapor permeability and porosity thereby substantially avoiding skin maceration.

The resin impregnated foam layer of the present invention is preferably prepared in a relatively low humidity chamber and sealed within a water vapor impermeable package. This package is opened just prior to use. So packaged, the resin impregnated foam layer is relatively storage stable. Second layer 22 may alternatively comprise a thermoplastic material.

A suitable thermoplastic material will soften at a sufficiently low temperature to permit contact with a body part. Thermoplastic materials have been used as orthopedic splints. U.S. Patents 2,759,475 and 2,800,129 disclose such materials. Second layer 22 may comprise a similar material. In this embodiment, second layer 22 preferably is a sheet of thermoplastic material dimensioned to cover and slightly overlap the first resilient layer. To prepare a custom-molded cushion, second layer 22 is heated to a softening temperature, layered with first resilient layer 12 and deformed against a body part of a patient. The cushion is allowed to cool while being deformed so as to create and retain an impression of the body part in the cushion. After cooling the thermoplastic material may be trimmed to remove excess material.

Referring still to FIG. 1, in preferred embodiments of the present invention, third layer 24 is provided. Third layer 24 is positioned such that second layer 22 is between first layer 12 and third layer 24. Third layer 24 preferably is a resilient material, and more preferably is a foam material. Third layer 24 preferably is dimensioned to cover and overlap the second layer 22 on all sides except the front edge. Third layer 24 preferably is of a sufficient thickness to provide added comfort to the patient. After cure of the resin (where second layer 22 is a resin-impregnated open-celled foam), areas of overlap of the third layer 24 preferably are trimmed and glued to the first layer 12. Where second layer 22 comprises thermoplastic material, third layer 24 is applied to the second layer 22 preferably with an adhesive, and trimmed and glued as previously described.

To prepare a cushion of the present invention, the curable resin impregnated into second layer 22 is activated. In preferred embodiments where the curable resin is a moisture curable polyisocyanate-polyol system, the curable resin is activated with water. Where second layer 22 is a thermoplastic material, the material is heated to a softening temperature. The first layer 12, second layer 22 (and, preferably, third layer 24), are layered together. In embodiments where the first layer 12, second layer 22, and third layer 24, are comprised of foam material, the resin in second layer 22 as it cures, will cause adhesion of first layer 12 and third layer 24 to opposing sides of second layer 22. In other embodiments, where any of first resilient layer 12, second layer 22, or third layer 24 does not comprise a foam material, adhesive materials may be used to ensure that first layer 12, second layer 22, and third layer 24 (if present) adhere together. Following activation of the curable resin in second layer 22, or heating of the thermoplastic material to a softening temperature (where second layer 22 is a thermoplastic material), the multi-layer cushion is immediately deformed against a body part of a patient. Where appropriate, the positioning is performed by a qualified health care professional, such as an occupational therapist or an orthotist. The resin is allowed to cure, or the thermoplastic material allowed to cool, such that second layer 22, and the cushion as a whole, will create and retain an impression of the body part.

The cured, or cooled, custom-molded cushion may be provided with a moisture impermeable plastic bag to protect the custom-molded cushion. This is especially advantageous where the patient is incontinent. The cushion may additionally be provided with a cloth-like cover to improve comfort and appearance.

The construction of the cushion, wherein first resilient layer and second layer which is conformed to the body part, allows for distribution of pressure applied to the cushion by the body part. In addition, the multi-layer construction of the cushion of the present invention allows second layer 22, which is a semi¬ rigid cured foam, or a rigid thermoplastic material to float in the cushion. As the patient moves the body part, the first resilient layer allows the cushion to remain in contact with the patient during a range of movement. In preparing custom molded cushions of the present invention, a protective sheath or bag may be placed over the cushion prior to deformation against the body part to protect the patient from contact with resin material and heat generated from the exothermic curing reaction, or heat from the softened thermoplastic material. Where the cushion of the present invention is a seat cushion, an adapter piece 26 may optionally be provided to fit the seat cushion into its receptacle, for example, a wheelchair. Some wheelchairs in use today have a "sling seat base". As shown in FIG. 1, the adapter piece 26 would be placed on a sling seat base of a chair to allow better fitting of the cushion into the chair. It will be appreciated that adapter piece 26 represents any of numerous possible means of improving the fit of the cushion into the wheelchair or other receptacle.

Turning now to FIGs. 2a and 2b, other embodiments of the present invention are shown.

FIG. 2a shows a custom molded cushion 30 having first resilient layer 32 and second layer 42. FIG. 2a shows first resilient layer 32 in an embodiment having opposing sides 34, a back portion 36, and a base portion 38, comprising a pommel 54, as described above. It will be appreciated, of course, that first resilient layer 32 may comprise a flat sheet or may be adapted to any desired shape. Second layer 40 is shown in its conformed state, following cure in the case of the embodiment in which second layer 42 comprises an impregnated foam, and following cooling, in the embodiment in which second layer 42 comprises a thermoplastic material. Adaptive piece 46 is shown as described with reference to FIG. 1.

FIG. 2b shows a custom molded cushion of the present invention similar to that of FIG. 2a, but with the addition of third layer 44. Third layer 44 preferably is a resilient material, and preferably is a foam material. The addition of third layer 44 provides added comfort to the patient, as well as increased distribution of pressure applied to the cushion. While a foam material is preferred for third layer 44, it will be appreciated that any material selected to provide added comfort would suffice, such as a cloth-like material, or a more rigid rubber-like material.

FIGs. 3 and 4 show another embodiment of the custom molded cushion of the present invention. There is shown in FIG. 3 custom molded cushion 70, which comprises first layer 72, second layer 82, optional third layer 84 and optional adaptor piece 86. These layers are similar to those described above with reference to FIGs. 1, 2a, and 2b, and first layer 72 is again shown with opposing sides 74, back portion 76, base portion 78, and pommel 80. Pressure relief area 90 is an area of the cushion which has been determined to be a focal area of high pressure exerted by the body part against the cushion. Pressure relief area 90 appears as a small hump in the cushion 70. The pressure relief area 90 is provided by one of two preferred methods.

In the first preferred method, second layer 82 comprises an open-celled foam material which is selectively impregnated with a curable resin such that the portion 82a of second layer 82 which corresponds to the focal area of high pressure exerted by the body part is not impregnated with the curable resin. Upon cure while the body part is in the cushion, the pressure relief area 90 which comprises the non-impregnated area which corresponds to the non-impregnated area of second layer 82, will retain its resilient character and provide added pressure relief capability to the cushion. In the second preferred method (not shown in the Figures), where second layer 82 is either an open-celled foam impregnated with the moisture curable resin or a thermoplastic material, a portion of the second layer corresponding to a focal area of high pressure exerted by the body part is excised from the second layer 82 following cure of the curable resin system or cooling of the thermoplastic material. Following excision of this area of second layer 82, a portion of the base portion 78 of first resilient layer 72 will rise through the area of excision and provide added pressure relief capability. Alternatively, the excised portion may be replaced with a resilient material, preferably a resilient foam material, again providing added pressure relief capability. The embodiment of the custom molded cushion of the present invention shown in FIG. 3 is especially advantageous in situations where a high degree of pressure is exerted by a particular area or region of the body part about which the cushion is being formed, such as the ischeal tuberosities of a patient confined to a wheelchair seat. It is advantageous to provide pressure relief area 90 in such a situation to provide added comfort and pressure distribution in the cushion.

FIG. 4 shows, in cross-section, the pressure relief area 90 of the embodiment of the cushion shown in FIG. 3. The first resilient layer 72, second layer 82, and third layer 84 are shown in cross-section and pressure relief area 90 is shown as a small hump in the cushion. It will be appreciated that pressure relief area 90 may be provided in embodiments of the cushion of the present invention wherein only first resilient layer and second layer are provided, or where a third layer is also provided.

The present invention also provides a kit containing materials for preparing a custom cushion. Such a kit preferably contains a first resilient material to be utilized as the first resilient layer described herein and a second material to be utilized as the second layer described herein. The second material preferably is either a resin impregnated foam packaged as described herein or a thermoplastic material. The first and second materials are adapted to form a cushion as described herein to receive a body part and create and retain an impression of the body part when layered together and to act in concert to distribute pressure applied to the cushion.

In the kit of the present invention, a third material may be provided to be utilized as the third layer described herein. In a preferred embodiment, the first, second, and third layers each comprise a foam material. The present invention further provides an article suitable for forming a custom molded cushion for a body part. The article comprises a unitary blank of open-celled foam wherein a first portion of the blank is impregnated with a curable resin and a second portion is not impregnated with the curable resin. The unitary blank is adapted to deform against a body part to create and retain an impression of the body part and to distribute pressure applied to the cushion. For example, in a unitary blank of resilient open-celled foam, a top portion may be impregnated with a curable resin as described herein while a bottom portion remains unimpregnated. Upon deformation and curing, the blank creates and retains an impression of the body part, and the top, cured portion "floats" on the bottom, unimpregnated portion which remains resilient. The advantages of uniform pressure distribution and constant contact with the patient are thus obtained.

The present invention is especially useful for providing custom molded wheelchair seats and methods of making the same. It will be understood however, that it is within the scope of the appended claims to provide custom molded cushions and methods for any situation in which it is desirable to provide such a cushion for a body part which uniformly distributes pressure, allows for constant contact and provides added comfort.

While description of the preferred embodiments and parameters of the present invention is provided herein, it will be appreciated that the scope of the invention is not limited thereto and that other embodiments of the present invention are within the scope of the appended claims. Reference is made to the following claims for an understanding of the scope of the present invention.

Claims

What is claimed is:

1. A method of preparing a custom molded cushion, comprising the steps of: providing a multilayer cushion comprising a first resilient layer and a second layer comprising a foam impregnated with a curable resin, said first and second layers selected to act in concert to distribute pressure applied to said cushion; activating said curable resin; and deforming said cushion by positioning a body part on said cushion until curing is substantially complete to create and retain an impression of said body part in said cushion.

2. A method of preparing a custom molded cushion, comprising the steps of: providing a multilayer cushion comprising a first resilient layer, a second layer, and a third resilient layer, said second layer comprising a foam selectively impregnated with a curable resin such that a portion of said second layer corresponding to a focal area of high pressure exerted by said body part is not impregnated with said curable resin, said first, second, and third layers selected to act in concert to distribute pressure applied to said cushion; activating said curable resin; and deforming said cushion by positioning said body part on said cushion until curing is substantially complete to create and retain an impression of said body part in said cushion.

3. A custom molded cushion for a body part, comprising a first resilient layer and a second layer, said second layer comprising a foam impregnated with a curable resin, said first and second layers adapted to deform against a body part and to create and retain an impression of said body part, said first and second layers selected to act in concert to distribute pressure applied to said cushion.

4. A multilayer custom molded seat cushion, comprising a first resilient layer, and a second layer comprising a foam impregnated with a cured resin, said first and second layers retaining an impression of a body part of a person and selected to act in concert to distribute pressure applied to said cushion.

5. A kit containing materials for preparing a custom cushion, comprising a first resilient material and a second material comprising a foam impregnated with a curable resin, said first and second materials adapted to receive a body part and to create and retain an impression of said body part when layered together, said first and second materials selected to act in concert to distribute pressure applied to said cushion.

6. The method, article or kit of any preceding claim, wherein said multilayer cushion further comprises a third layer positioned such that said second layer is between said first and third layers.

7. The method, article or kit of any preceding claim, wherein said first resilient layer is an air bladder.

8. The method, article or kit of any preceding claim, wherein said first resilient layer comprises a foam material.

9. The method, article or kit of claims 2 and 6-8, wherein said third layer comprises a foam material.

10. The method, article or kit of any preceding claim, wherein said second layer comprises an open-celled foam sheet.

11. The method, article or kit of any preceding claim, wherein said curable resin comprises an isocyanate functional, prepolymer resin, said prepolymer resin being formed by reacting a polyisocyanate with a polyol wherein the ratio of NCO groups in said polyisocyanate to OH groups in said polyol is between about 2 to 1 and 5 to 1, said prepolymer resin having an NCO equivalent weight of from about 275 to 1000 grams of prepolymer resin per NCO group.

12. The method, article or kit of any preceding claim, wherein the ratio of NCO groups in said polyisocyanate to OH groups in said polyol is between about 2.5 to 1 and 4 to 1.

13. The method, article or kit of any preceding claim, wherein said prepolymer resin has an NCO equivalent weight of from about 350 to 700 grams of prepolymer resin per NCO group.

14. The method, article or kit of any preceding claim, wherein said prepolymer resin is formed by reacting said polyisocyanate with said polyol while said polyisocyanate and said polyol are inside said open-celled foam sheet.

15. The method, article or kit of claims 10-14, wherein said open-celled foam sheet has from about 12 to about 48 pores per cm.

16. The method, article or kit of claims 10-15, wherein said open-celled foam sheet has a density of from about 77.5 to about 349 kg/m³.

17. The method, article or kit of claims 10-16, wherein said prepolymer resin comprises from about 70% to about 95% by weight of said open-celled foam sheet.

18. The method of any preceding claim, further comprising the step of excising a portion of said second layer corresponding to a focal area of high pressure exerted by said body part on said cushion.

19. The method of any preceding claim, further comprising the step of replacing said excised portion with a resilient foam material.

20. The method of claim 19, wherein said resilient foam material comprises a foam impregnated with a resilient resin.

21. The method of claims 1 and 2, wherein said second layer is selectively impregnated with said curable resin such that a portion of said second layer corresponding to a focal area of high pressure exerted by said body part is not impregnated with said curable resin.

22. The method, article or kit of any preceding claim, wherein said first layer is a unitary sculpted foam comprising a back portion, opposing side portions, and a base portion comprising a pommel.

23. An article suitable for forming a custom molded cushion for a body part, comprising a unitary blank of open-celled foam wherein a first portion of said blank is impregnated with a curable resin and a second portion is not impregnated with said curable resin, said unitary blank adapted to deform against a body part to create and retain an impression of said body part and to distribute pressure applied to said cushion.

24. A multilayer custom molded cushion, comprising a first resilient layer, and a second layer comprising a sheet of thermoplastic material, said thermoplastic material having been deformed against a body part to create and retain an impression of said body part, said first and second layers selected to act in concert to distribute pressure applied to said cushion.

25. A method of preparing a custom molded cushion for a body part, comprising the steps of: providing a multilayer cushion comprising a first resilient layer and a second layer of thermoplastic material; heating said second layer of thermoplastic material to a softening temperature; and deforming said cushion by positioning a body part on said cushion until said thermoplastic material cools to create and retain an impression of said body part in said cushion.

26. The method of claim 25, wherein said second layer of thermoplastic material comprises an aperture therethrough corresponding to a focal area of high pressure exerted by said body part.

27. The method of claim 25, further comprising the step of excising a portion of said second layer of thermoplastic material corresponding to a focal area of high pressure exerted by said body part, after cooling of said thermoplastic material.

28. The method of claim 27, further comprising the step of replacing said excised portion with a resilient material.