Hydrocolloid pressure sensitive adhesives

Details Hydrocolloid pressure sensitive adhesives Hydrocolloid pressure sensitive adhesives

2000-06-05

2001-12-04

Zirker, Daniel (Department: 1771)

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

Synthetic resins

Processes of preparing a desired or intentional composition...

C524S027000, C524S045000, C524S054000, C524S055000, C524S071000, C524S274000, C524S419000, C523S111000, C523S118000, C428S3550BL, C428S356000, C604S344000

Reexamination Certificate

active

06326421

ABSTRACT:

This invention relates to a pressure sensitive adhesive material made of a weakly elastic mixture of the type comprising a continuous phase formed essentially from a physically cross-linked solid rubber such as a styrene-olefin-styrene block copolymer, for example a styrene-isoprene-styrene block copolymer, and a compatible tackifying resin, and a discontinuous phase comprising one or more hydrocolloids that are soluble and/or swellable in water. Small quantities of additives such as stabilisers and fumed silica may be present. The adhesive layer can be combined with a non-adhesive, water impervious film and can be used in wound care, ostomy care and in other medical products.
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 adhesives are a unique kind of medically useful pressure sensitive adhesive. Hydrocolloid adhesives have a duality of attributes 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 can be secured on the surrounding intact skin, and as skin barriers because they protect the peristomal skin of ostomy patients. Particularly in the area of wound dressings, the known hydrocolloid adhesives have some limitations, because the absorption capacity of hydrocolloid dressings is normally insufficient to handle the large amount of exudate from certain especially chronic wounds. Also, hydrocolloid compositions are normally not very flexible or conformable, so that adhesion to movable body parts is difficult. The present invention overcomes some of the problems of the prior art, and extends the utility of hydrocolloid adhesives.
One aspect of the present invention relates to skin barriers and wound dressings comprising a layer of hydrocolloid adhesive coated on a non-adhesive, waterproof film. The skin barrier is used in a number of ways. One of these is for bandaging purposes, especially on movable body parts such as joints or on curved surfaces of the body. Another important use is for the protection of the skin around body openings, especially around the surgically created openings known as colostomies, ileostomies and urostomies.
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 do substantially retain their dimensional stability and form which 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. Some of the relevant prior art is summarised below.
Non-integrated 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 gelatin (20% by wt.). This formulation is 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 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, fewer 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”.
Integrated Compositions
The lack of integrity was a serious drawback in the use of these dressings and barriers and much development was completed in efforts to overcome the deficiency. Thus, GB-A-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 GB-A-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.
Both U.S. Pat. No. 4,477,325 and U.S. Pat. No. 4,738,257 recognise the shortcomings of barriers and dressings based upon formulae such as described in U.S. Pat. No. 3,339,546. 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 composition of the invention. The cross-linked network is formed essentially from the EVA polymer by irradiation of the EVA containing elastomeric phase. The problem with this type of system is that the dose from such a sterilisation process is widely variable in practice. A company offering services for the sterilisation of medical devices to a nominal dose of 25 KGy would typically specify a dose within the r

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