Biological fluid absorbing pressure sensitive adhesives

Details Biological fluid absorbing pressure sensitive adhesives Biological fluid absorbing pressure sensitive adhesives

2000-02-29

2003-06-24

Mullis, Jeffrey (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S054310, C525S054320, C525S088000, C525S09200D, C525S098000, C525S099000

Reexamination Certificate

active

06583220

ABSTRACT:

This invention relates to pressure sensitive adhesive materials having particular utility in the medical field, for example for use with wound dressings and ostomy appliances.
Pressure sensitive adhesive materials are used in many medical device fields and are made into products such as tapes, bandages, surgical drapes, IV dressings and the like. Hydrocolloid pressure sensitive adhesives are medically useful adhesives that have been known for about 30 years and were originally developed as bandages for the oral cavity to aid in delivery of drugs to the gingiva. Hydrocolloid adhesives have been hitherto unique in that they are inherently adhesive and inherently absorbent. They are useful as wound dressings because they can be applied directly to open wounds and secured on the surrounding intact skin, and as skin barriers because they protect the peristomal skin of ostomy patients. Many hydrocolloid skin barriers are known and are used for these purposes. It is convenient to-divide these into “integrated” compositions and “non-integrated” compositions. In this context, “integrated” means those compositions which substantially, retain their dimensional stability and form when saturated with wound exudate and/or other body fluid. “Non-integrated” means those compositions which become soft gels and amorphous as they become saturated with fluid.
Particularly in the area of wound dressings, the known hydrocolloid adhesives have a number of limitations. First, the absorption capacity of hydrocolloid dressings is normally insufficient to handle the large amount of exudate from certain especially chronic wounds. Second, hydrocolloid compositions, by definition, contain water soluble absorbents, which provide “wet tack” to the composition, and these leach out into the wound and may be absorbed into the body. Third, hydrocolloid compositions are normally opaque, and so the healing of the treated wound cannot be assessed until the dressing is changed. Fourth, the continuous phases used in many especially non-integrated hydrocolloid adhesives contain substantial quantities of low molecular weight elastomers such as polyisobutylene. The polyisobutylene is dispersed in the soft gel from a non-integrated hydrocolloid composition which remains in the wound after dressing removal. While the polyisobutylene is chemically saturated and thus inert, it is nevertheless thought that it may be incorporated into the growing cellular structure in, for example, healing chronic wounds and the polyisobutylene has been suggested as the cause of abnormal “foam cells” observed in the histology of such dermal tissues. Although these foam cells are not thought to be permanently harmful, it is important to eliminate any leachable material from these medically useful compositions.
The first hydrocolloid compositions to be described were non-integrated. U.S. Pat. No. 3,339,546 discloses compositions which are inelastic, and which are non-integrated, i.e. which do not maintain their dimensional stability and become amorphous when imbibed with wound fluid or other body fluid. A typical formulation taught by this prior art is the composition formed from low molecular weight polyisobutylene (40% by wt.), pectin (20% by wt.), sodium carboxymethyl cellulose (20% by wt.) and gelatine (20% by wt.). This formulation was used as a dressing for the gingiva but is also believed to be the basis of commercially successful skin barrier and wound care products. Such compositions form a soft gel when in contact with an exuding wound, and the resultant gel remains in the wound when the dressing is removed. This lack of integrity is a drawback. The remaining gel must be irrigated from the wound by the nurse who is performing the change of dressing, and this is both time consuming for the nurse and painful for the patient.
Notwithstanding the drawbacks of this prior art bandage, however, the compositions taught by U.S. Pat. No. 3,339,546 are extremely gentle to the intact skin. This is thought to be due to a number of factors. First, the compositions of this patent contain a relatively small number of components. On a statistical basis therefore, a fewer number of skin reactions can be expected. Second, the ingredients are usually food components or additives, and have a long history of use. Third, polyisobutylene contains a chemically saturated aliphatic carbon-carbon backbone, and therefore needs no stabiliser to reduce the degradation often seen in rubbery materials having chemical unsaturation in the backbone. Fourth, the compositions apparently maintain the skin moisture at an optimum level, by absorbing excess perspiration and reducing the amount of skin maceration that is normally associated with the wearing of a wound dressing for several days. Skin maceration leads to a reduction in the mechanical strength of the skin, and in turn leads, on removal of the bandage, to increased skin damage to the healthy skin surrounding the margin of the wound. This is often termed “mechanical irritation”. The prior art compositions described below achieve the integration of the continuous phase for the most part at the expense of the gentle, “skin-friendly” character displayed by the compositions of U.S. Pat. No. 3,339,546.
The lack of integrity was a serious drawback in the use of dressings and barriers based on these early hydrocolloid compositions and much development was completed in efforts to overcome the deficiency. Thus, British Patent 1,576,522, corresponding to U.S. Pat. No. 4,231,369 describes improved hydrocolloid compositions that are integrated. There is provided a sealing material for ostomy use consisting of a hydrocolloid dispersed in a continuous phase of styrene-isoprene-styrene copolymer, or other thermoplastic elastomer such as an ethylene-propylene copolymer. Also present is a hydrocarbon tackifier and optionally an oil extender and an antioxidant. This material is said to have the advantage of being elastomeric and flexible, and thus bandages made from it should adhere well to the skin and be conformable. Because of the styrene-isoprene-styrene block copolymer the composition is integrated. The styrene-isoprene-styrene block copolymer forms physical cross links within the continuous phase at room temperature. This is because the polystyrene segments within the copolymer are incompatible with the polyisoprene segments, and they associate at room temperature to glassy domains which act as the physical cross links to form a three dimensional lattice. However, because of the larger number of components, and in particular the tackifying resin and stabilisers, the material does tend to experience more complaints with irritation than does the material from U.S. Pat. No. 3,339,546. Also, because the hydrocolloid absorbent components in British Patent 1,576,522 are normally at a lower concentration in the final formulation than are the hydrocolloid components in U.S. Pat. No. 3,339,546, a lower absorption level is obtained. The absorption rate is also slower, because the integrated nature of the composition makes that lower level of chemical hydrocolloid components even more slowly accessible to the body fluid.
The shortcomings of barriers and dressings based upon formulae such as are described in U.S. Pat. No. 3,339,546 are also recognised by both U.S. Pat. Nos. 4,477,325 and 4,738,257. These two later patents disclose barriers and dressings based on an integrated formulation containing a continuous phase composed of a blend of high vinyl acetate EVA copolymer (51% wt. VA and 49% wt. ethylene) and low molecular weight polyisobutylene, in which is dispersed a discontinuous phase containing a blend of a superabsorbent material, pectin and sodium carboxymethyl cellulose. The function of the EVA copolymer is to cross link in the presence of ionising radiation, such as gamma radiation at a dosage of, for example 25 KGy, which would be used to sterilise dressings formed from the compositions of the invention. The cross linked network is formed essentially from the EVA polymer by irradiation of the EVA containing elastomeric phase.

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