US 3689948 A
A polyvinyl alcohol gel pad. The gel pad has properties which make it useful as a support pad in the prevention and treatment of decubitus ulcers (also known as pressure sores) and for other purposes. The polyvinyl alcohol gel is made by cross-linking high molecular weight polyvinyl alcohol using a cross-linking agent, such as formaldehyde, in the presence of an acid catalyst, such as hydrochloric acid, and by incorporating at least one internal plasticizer, such as propylene glycol, in the gel. The support pad is completed by putting a thin-film envelope around the gel.
Description (OCR text may contain errors)
United States Patent Graves et al.
[ 1 Sept. 12, 1972 3,308,491 3/1967 Spence ..5/348 3,518,242 6/1970 Chrisp.; ..260/91.3
Primary ExaminerBobby R. Gay
Assistant Examiner-Andrew M. Calvert Att0rney-Charles K. Wright, J r., William G. Gapcynski and Lawrence A. Neureither  ABSTRACT A polyvinyl alcohol gel pad. The gel pad has properties which make it useful as a support pad in the prevention and treatment of decubitus ulcers (also known as pressure sores) and for other purposes. The polyvinyl alcohol gelis made by cross-linking high molecular weight polyvinyl alcohol using a cross-linking agent, such as formaldehyde, in the presence of an acid catalyst, such as hydrochloric acid, and by incorporating at least one internal plasticizer, such as propylene glycol, in the gel. The support pad is completed by putting a thin-film envelope around the gel.
4 Claims, 3 Drawing Figures DISPLAOEMENT- INCHES PAIENTEIJSEP I2 I972 FIG.I
o 5 STRESS -STRAIN BEHAVIOR UNDER RAPID LOADING I I I I I I l A ,4 (D r" u f I I O o 0.5 -"Q -O E A a" I y In I 2 l g 0.2 f l O n. I A Q O o O/ I,
0 PRIOR ART ORGANOSILOXANE GEL PAD A POLYVINYL ALCOHOL GEL SUPPORT PAD O O l l l I I I I I00 zoo :00 400 500 e00 100 800 LOAD- enms/ mcnss VISCOUS CREEP AND ELASTICITY OF GEL PADS I l I I l I I (LOADS GIVEN IN cams/mau "nus zERo: 1.0m DECREASE!) FROM 758 T0 as POINT A: LOAD INCREASED FROM 38 TO 519 W POINT a: LOAD DEGREASED FROM 319 To a FIG.3
A A B A l N 'ro answer-15s AT I046 MINUTES a PRIOR ART onsnuosmoxme GEL PAD A POLYVINYL ALCOHOL GEL SUPPORT PAD I I l l I I 0 I00 200 300 TIME-MINUTES INVENTORS DAVID J. GRAVES CHARLES R. RITCHEY A T TORNE) BACKGROUND OF THE INVENTION 1. Field of thelnvention This invention relates to the field of support padsfor bedridden patients. More particularly, this invention relates to a polyvinyl alcohol gel support pad useful for preventing and treating decubitus ulcers.
2. Description of the Prior Art The problem of preventing and treating decubitus ulcers has long vexed the medical art. The average cost of a single decubitus ulcer (pressure sore) in terms of prolonged hospitalization, medical and nursing care, has been estimated at $2,000 to $10,000. See W. Spence, Clinical Medicine, Nov. 1967, p. 25. Decubitus ulcers are a frequent complication in the case of burn patients where the ulcerations delay final recovery. They are particularly prevalent in tall, thin patients at pressure points such as the heel, base of the spine, and elbow.
The prior art reveals several methods designed to ameliorate the problem. One of the early devices employed was a water bed patented by C. Ewald on Jan. 16, I934 (U.S. Pat. No. 1,943,888). More recently there have been polyurethane foam pads (U.S. Pat. No. 3,451,071), gas-filled cushions (U.S. Pat. No. 3,340,551), and combinations of elastomeric pads, liquid-filled bladders, and air bladders (U.S. Pat. No. 3,456,270).
More directly related to the present invention is the prior art seen in U.S. Pat. No. 3,308,491 issued March 14, I967 to W. Spence for Cushion Structure. The
same prior art cushion structure is described and its method of use is explained in Spence, Clinical Medicine, November I967, pp. -30. Dr. Spences cushion structure is presently in commercial use and those in the art are familiar with it. Dr. Spences cushion structure is composed of a resiliently flexible and semisolid core and wall means for protecting the core from external contamination. The core is described as made of an organosiloxane gel, substantially of the type disclosed and described in U.S. Pat. No. 3,020,260, issued Feb. 6, 1962, to M. Nelson, for organosiloxane Potting Compound. The primary disadvantage of the organosiloxane gel is its very high cost, which is discussed by Dr. Spence in Clinical Medicine, November I967, at p. 27 and p. 30.
SUMMARY OF THE INVENTION A polyvinyl alcohol gel support pad comprising a polyvinyl alcohol geland a thin-film envelope inclosing the gel. More specifically, the polyvinyl alcohol gel is a cross-linked irreversible gel containing at least one inexchanging polyol molecules for the water molecules entrapped in the gel. The gel is enclosed in athin-film envelope of a strong, flexible, elastic, and tear-resistant polymeric material. The polyvinyl alcohol gel support pad is useful in the art of preventing and treating decubitus ulcers and it is an improvement over the prior art in this field of use because the polyvinyl alcohol gel exhibits the property of viscous creep which permits the gel to conform with the body contours in contact with the pad.
Accordingly, it is an object of this invention to provide a support pad for the human body in which the support pressure is uniformly distributed over a larger area so that pressure necrosis, decubitus ulcers, and skin breakdown is largely eliminated.
A further object of this invention is to provide a support pad which is easy to handle and maintain, which has long shelf life and which is nontoxic.
A further object of this invention is to provide a support pad composed of a gel which is easy to prepare from readily available commercial chemicals and which is, above-all, relatively inexpensive in total cost as compared to prior art devices.
Other objects and purposes of this invention will be apparent from the following description and the accompanying drawings.
BRIEF DESCRIPTION OF TI-IEDRAWINGS FIG. 1 is a vertical cross-sectional view through a polyvinyl alcohol gel support pad.
FIG. 2 is a graph of test data comparing the stressstrain behavior under rapid loading of a prior art organosiloxane gel pad and the polyvinyl alcohol gel support pad.
FIG. 3 is a graph of test datacomparingthe viscous creep and elasticity of a prior art organosiloxane gel pad and the polyvinyl alcohol gel support pad.
DESCRIPTION OF PREFERRED EMBODIMENTS The polyvinyl alcohol gel support pad which is the finished product comprises two components shown in cross-section in FIG. 1. The'pad 10 comprises a gel core 11 and a thin-film envelope l2 inclosing the gel. The polyvinyl alcohol gel 11 is inelosed in the envelope 12 after the gel has been prepared and the envelope is sealed in a conventional manner to make a finished pad.
EXAMPLE OF PREPARATION OF GEL The basic starting materials for the polyvinyl alcohol gel are: (I) an aqueous solution of a high molecular weight polyvinyl alcohol; (2) formaldehyde solution; and (3) concentrated I-ICI.
The polyvinyl alcohol is inexpensive and commercially available in bulk quantities as a powder. A high molecular weight polyvinyl alcohol is preferred. Du Pont Elvanol grade number 72-60 has been found satisfactory. This grade of high molecular weight polyvinyl alcohol has the following characteristics:
a. Viscosity in cp. of a 4 percent solids aqueous solution at 20 C., determined by Hoeppler falling ball method: -65
b. Percent hydrolysis (mole percent hydrolysis of acetate groups, dry basis): 99.0 99.8
c. pH: 5.0-7.0
d. Volatiles, percent max.: 5 e. Ash, percent max. (dry basis, calculated as Na O): 1.0
f. Mean Molecular Weight: approximately 180,000.
The polyvinyl alcohol gel may be prepared in the following manner: 750 grams of an aqueous percent solution of high molecular weight polyvinyl alcohol is stirred together with 240 grams of a U.S.P. solution of formaldehyde (37 percent formaldehyde) used as a cross-linking agent and 3 ml. of concentrated hydrochloric acid used as a catalyst. Other commercially available cross-linking agents may be used in lieu of the formaldehyde and other acid catalysts may be used in lieu of HCl. This quantity of starting materials is sufficient to prepare a circular pad seven inches in diameter, approximately three inches in thickness.
After thorough mixing, the viscous solution is placed in a container or mold of any desired shape, such as circular or square. The solution is then heated at approximately 77 C. at atmospheric pressure for 2 2 m 3 hours. The resulting polyvinyl alcohol gel is then removed from the mold and soaked in water for 3 days in order to rid the gel of any excess unreacted formaldehyde. Any formaldehyde which remains in the gel following this soaking may be neutralized by soaking the gel in a solution prepared from 28 grams of urea in two pints of water for 3 days, changing the urea solution daily.
It should be noted that the term gel is used in a special sense in that the gel which results from this synthetic process is like a single giant molecule because the cross-linking process causes strong chemical bonds to form between the polyvinyl alcohol polymer chains. The resulting gel cannot be broken down by heat or physical manipulation short of destroying the gel completely. The gel is an aqueous polyvinyl alcohol gel because it is believed to contain water molecules trapped within the polyvinyl alcohol structure. The entrapped water molecules appear to act as an internal plasticizer. But the gel is not like the gel of gelatin food desserts where the physical structure is set up by weak intermolecular bonds after dispersal of the molecules with the aid of heat and vigorous agitation. The gel of a gelatin dessert may be thought of as a reversible gel whereas the gel in the present polyvinyl alcohol gel is formed by an irreversible chemical reaction. It should also be noted that the present polyvinyl alcohol gel is different from the hard polyvinyl alcohol plastic described in US. Pat. No. 2,083,628, issued June 15, 1937, to G. Zelger for Method of Making Vinyl Derivative Articles.
A further step in the synthetic process is considered essential. It has been found that the water trapped within the polyvinyl alcohol gel will slowly evaporate, even through a polyurethane envelope. When the water evaporates, the gel becomes hard and useless. Therefore, an improved gel may be made by partially or completely exchanging the water in the gel with a nonvolatile nontoxic liquid such as propylene glycol. This exchange may be accomplished by soaking the aqueous gel in propylene glycol before sealing the gel in the envelope 12. The step of neutralizing unreacted formaldehyde and the step of exchanging the liquid trapped in the gel may be combined in one step by soaking the aqueous gel in two pints of propylene glycol containing 28 grams of urea for three days, changing the solution each day. With propylene glycol in the gel, the pad has an almost unlimited shelf and use life. It is thought that the water molecules and the propylene glycol molecules act as internal plasticizers in the polymer structure.
Propylene glycol cannot be combined with the polyvinyl alcohol initially. Propylene glycol and urea are used in the foregoing example because they are relatively innocuous physiologically. Other polyols would function in place of propylene glycol, but propylene glycol is preferred for its nontoxic character.
The polyvinyl alcohol gel made by the above procedure is essentially colorless. If it is desired to make a colored gel, a small amount of food coloring (F D and C dyes) may be added to the original starting solution to give the gel a pleasant color.
EXAMPLE OF PREPARATION OF PAD I Once the polyvinyl alcohol gel has been prepared, the final step in preparing the finished pad is to enclose the gel in a thin-film envelope 12 which is used to prevent contamination of the gel. For example, the gel may be enclosed in a heat-sealed envelope 12 made of 0.002 gauge (2 mil thickness) polyurethane film such as type TF 1 10 made by B. F. Goodrich Company. The envelope material must be strong, flexible, elastic, and tear-resistant.
HOW TO USE THE PAD In actual use, the pad is placed under the patients pressure points where decubitus ulcers are likely to occur. Decubitus ulcers are defined as an ulceration caused by prolonged pressure in a patient confined to bed for a long period of time. Ulceration is the loss of substance on a cutaneous or mucous surface, causing gradual disintegration and necrosis of the tissue. See Dorlands Illustrated Medical Dictionary, 23rd edition 7). For purposes of this invention, the term decubitus ulcer is broad enough to include any disintegration and breakdown of the skin and tissue caused by prolonged pressure in a patient confined to a bed for a long period of time and we define the term to specifically include the breakdown of skin and tissue after skin grafting in bedridden burn patients.
The polyvinyl alcohol gel conforms itself to the contour of the engaged surface on the supported body so that the support pressure is uniformly distributed over the entire area of engagement. In effect, the gel of cross-linked polyvinyl alcohol distributes the weight over a greater surface area and thus reduces the pressure per unit area. This pressure distribution is useful in the prevention and treatment of decubitus ulcers.
A comparison of the properties of the polyvinyl alcohol gel pad with the organosiloxane gel pad of the prior art appears in FIG. 2 and FIG. 3. The tests in each case used a cylindrical penetrator with cross-sectional loads, the polyvinyl alcohol gel support pad has the desirable characteristic of being softer or exhibiting greater displacement than the prior art organosiloxane gel pad.
FIG. 3 shows that the viscous creep and elasticity behavior is not the same in the two pads. As seen in FIG. 3, the polyvinyl alcohol gel support pad exhibits more viscous creep and its elastic rebound characteristic is slower than in the organosiloxane gel pad. These characteristics of the polyvinyl alcohol gel pad are regarded as an improvement over the prior art organosiloxane gel pad since the polyvinyl alcohol gel support pad conforms atleast partially to body contours. Thus, if the polyvinyl alcohol gel pad is placed on a ribbed surface for several hours, it will acquire a ribbed surface conformation. If removed from the ribbed surface, it will recover to substantially its original shape in several hours. The organosiloxane gel pad doesn't exhibit this behavior as may be seen by the data in FIG. 3. The organosiloxane gel pad exhibits almost complete elasticity and almost instantaneous recovery (rebound). A combination of viscosity and elasticity as exhibited by the polyvinyl alcohol gel support pad is believed to be an advantage since it permits the gel to conform to body contours.
Another physical property of interest is tensile strength. The ultimate tensile strength of the polyvinyl alcohol gel is 2.61 pounds per square inch at an ultimate elongation of 450 percent. The ultimate tensile strength of the organosiloxane gel is 0.71 pounds per square inch at an ultimate elongation of 175 percent.
RESULTS The polyvinyl alcohol gel support pad has been successfully tested at Brooke General Hospital, Fort Sam Houston, Tex. Over one-hundred patients have been successfully treated with the pads. The pads were used in providing nursing care for patients with extensive burns, and they were very useful in preventing the breakdown of skin over pressure areas, as for example, when thin and debilitated individuals must necessarily remain in one position for prolonged periods of time when skin grafting procedures are carried out. In addition to preventing skin damage, the pads also provided increased patient comfort.
OTHER USES In addition to preventing and treating decubitus ulcers in bedridden patients, other practical applications are obvious. The polyvinyl alcohol gel support pad may be used in any situation where the shock absorbing propeities of the gel are desired. In particular, the aircraft industry has unsuccessfully tried to develop a cushion to prevent coccyx fractures in aircraft pilots during high speed seat ejections. The polyvinyl alcohol gel support pad answers this need at a reasonable cost.
1. A support pad comprising:
a. a polyvinyl alcohol gel, wherein said gel is a crosslinked irreversible gel containing at least one internal plasticizer comprising a polyol compound and said gel exhibits the physical propertyof a slight amount of viscous creep when placed under a load and the physical property of slowly returning to its original conformation when said load is removed,
b. iqin-film envelope inclosing said gel.
2. The support pad as defined in claim 1 wherein the thin-film envelope is a strong, flexible, elastic and tearresistant polymeric material.
3. The support pad as defined in claim 2 wherein the polymeric material is polyurethane.
4. In the art of preventing and treating decubitus ulcers in which it is known to use an organosiloxane gel pad, the improvement comprising using a polyvinyl alcohol gel support pad wherein said pad comprises:
a. a polyvinyl alcohol gel, wherein said gel is a crosslinked irreversible gel containing at least one internal plasticizer comprising a polyol compound and said gel exhibits the physical property of a slight amount of viscous creep and thereby conforms to body contours in contact with said pad; and
b. a thin-film envelope inclosing said gel.