WO1999012582A2

WO1999012582A2 - Material for use in producing medical equipment

Info

Publication number: WO1999012582A2
Application number: PCT/GB1998/002697
Authority: WO
Inventors: Ira Norman Frost; Stephen John Wilkinson
Original assignee: Movevirgo Limited
Priority date: 1997-09-09
Filing date: 1998-09-07
Publication date: 1999-03-18
Also published as: GB9719076D0; WO1999012582A3; AU8992898A

Abstract

A composition for use in forming medical equipment intended to come into contact with a patient, comprising or including a vulcanisable silicone rubber admixed with a medicament such that, in use of a dressing incorporating the material in contact with part of a patient, at least the said medicament is subject to migration towards the surface of the dressing. A wound dressing (14) incorporating the composition of the invention in association with support means (12, 13; 20; 26) for retaining a surface of an element (23; 27) made from or including the composition in contact with the skin or other exposed tissue surface of a patient. A method of producing a wound dressing comprises the steps of: preparing a substantially rigid mould (12, 13) shaped to surround a part of the patient; fitting the mould thereto so as to form a mould cavity; introducing into the mould cavity the composition of the invention in a fluid state, including selected medicament; and causing or allowing the composition to cure or vulcanise.

Description

A MATERIAL FOR USE IN PRODUCING MEDICAL EQUIPMENT AND

MEDICAL EQUIPMENT PRODUCED USING THE MATERIAL

The present invention relates generally to a material for use in producing medical equipment, and to medical equipment produced using the material. As used in this specification, the term "equipment" will be understood to relate to any items which come into physical contact with a patient undergoing treatment and in particular (but not exclusively) to include dressings, catheters and cannulas .

Medical dressings are applied to the skin of a patient for a number of reasons but whatever the reason they primarily perform one or both of two main functions. The first of these main functions is to exclude from that area of the patient's skin covered by the dressing any contaminant (whether biological or mineral) to which it may be subject, and the second main function is ;o apply or retain in place a medicament having an active medical effect on the skin.

In use, a dressing may be placed over an area of inflammation caused by external irritants or by internal (that is organic) activity, or may be applied over burns or wounds where the skin is broken and/or damaged. It may be appropriate to place medical dressings over areas of skin suffering from allergic reactions, for example urticaria, or subject to other skin disorders, such as psoriasis and the like. Dressings for the treatment of wounds or other skin disorders are typically formed with a porous portion which can be impregnated with medicaments and which is held in place by various means including self-adhesive resilient elastomeric layers, flexible bandages and/or plastics shells (such as an epicondylyte clasp) .

Known medical dressings suffer from two major disadvantages. The first is that the amount of medicament which can be impregnated or absorbed into the porous material is limited, and its effectiveness therefore deteriorates with time as it is depleted by whatever process takes place at the interface between the patient's skin and the dressing. The second is that in many cases the medical processes taking place, especially in the case of recovery from wounds, burns or other conditions in which the skin is broken, involve the coagulation of body fluids, especially blood and blood plasma, tissue regrowth and, if the process is extended over time, even hair re-growth. These all contribute, when the dressing is removed, to cause damage to the skin's surface upon removal of the dressing, thereby creating exposed regions susceptible to contamination and, of course, pain for the patient, as well as possibly reopening the wound or wounds or creating fresh areas of damage which take time to recover. In many cases, when using prior art dressings, it is necessary to change the dressings frequently m order to renew the medicaments and to prevent the regrowth processes from proceeding so far as to cause adhesion to the dressing itself.

The present invention seeks to provide a material for use m producing a medical dressing, and a medical dressing produced using this material, m which these twin problems are alleviated to a very large extent by the properties of the material. In particular, the material of the present invention has anti-adhesion properties allied to an ability to allow migration of an incorporated material (such as a medicament) to the surface as it is depleted at the surface by whatever process takes place there.

According to one aspect of the present invention, therefore, a composition for use m forming medical equipment intended to come into contact with a patient, comprises or includes a vulcanised or vulcanisable silicone rubber admixed with a medicament such that, m use of equipment incorporating the composition at least the said medicament is subject to migration towards the surface of the equipment m contact with part of a patient .

The silicone rubber m effect acts as a slow release matrix for the exudable medicament which is continually replenished at the surface by migration from within the matrix to that surface.

As used in this specification the term, "medicament" will be understood to mean any material , compound or composition having medical, prophylactic or therapeutic properties, and to include, without limitation, antiseptics, fungicides, biocides, steroids or other compositions exhibiting a medical, prophylactic or therapeutic activity on the human or animal body.

The composition may include one or more of the range of known vulcanised or vulcanisable silicone rubbers. It is known that silicone rubbers can be prepared from silicone gums, highly linear high-molecular weight organo-siloxane polymers which comprise alternating atoms of silicone and oxygen as a polymeric "spine" having organic groups, generally methyl, attached to the silicone atoms of the "spine". The silicone rubber may have a low silicone content, i.e. it may contain integral or grafted silicone-free segments. Such low content silicone rubbers are commercially available and are formed from the polymerisation of compounds containing ethylenic unsaturation, epoxide groups or urethane based units.

Although vulcanisation of some organo-polysiloxanes can take place at elevated temperatures, for the purposes of the present invention organo-polysiloxanes which vulcanise at ambient temperature or close to ambient temperature should be used whenever the medicaments are likely to be detrimentally affected by elevated temperatures. This may not always be the case as some medicaments may be relatively temperature-insensitive, such as antiseptics.

As well as heat curing rubbers the present invention includes vulcanisable silicone rubbers which may be cured by radiation. Such rubbers substantially comprise polydisubstituted siloxanes, e.g. polydihydrocarbyl siloxanes, in which the majority of the hydrocarbyl units are methyl units, the remainder being vinyl and/or phenyl units.

Suitable silicone rubbers include those formed from the so-called RTV gums which contain silanol end groups. These may be vulcanised at ambient temperature. Suitable RTV gums include those in which at least the majority of the organic groups in the RTV gums are hydrocarbyl groups, especially methyl groups, whilst the remainder may be ethyl, phenyl or substituted hydrocarbyl groups such as cholorophenyl , fluoropropyl or cyanoether groups.

The vulcanisation of some RTV gums takes place utilising the assistance of a cross-linking agent such as ethyl silicate. The process for preparation of the composition from such gums preferably includes mixing the ethyl silicate with the RTV gum, preferably with the addition of a suitable catalyst such as an organic tin-salt (dibutyl-tin dilaurate is particularly suitable) in which case vulcanisation by cross linking starts immediately and continues. As well as curable RTV gums in which cross linking starts immediately after a cross-linking agent and suitable catalyst, such as an organic tin-salt or stannous octoate is admixed (together with the other desired materials) , it is also possible to utilise RTV gums which may be vulcanised after the addition of a compound of general formula RsiX₃, where : -

R is hydrocarbyl (usually methyl)

X is a hydroxyl group or a group containing a hydrolysable oxygen linkage or an amino group or a group containing a hydrolysable nitrogen linkage or another reactive site. This admixed material must be kept protected from moisture as cross linking, i.e. vulcanisation, commences when it is contacted with water. A suitable dry package may, therefore, be maintained in storage, opened, wetted and applied as a paste to a wound and held in place by a bandage or other containment .

The compositions of the present invention may additionally include one or more of the following: strengthening agents, such as fibrous materials, e.g. glass fibre; dispersing agents such as powdered polymers, e.g. polytetrafluoroethylene; fillers and lubricating (wetting) agents. A dispersing or lubricating agent which may be present in the composition to aid the dispersion of the medicament in the silicone rubber is an organic fluid. Suitable organic fluids are well known to the skilled man and include low molecular weight polyolefins, polyesters, polyisocyanates, polyurethanes and polyepoxides . The organic fluid may also or alternatively include plasticizers such as esters of carboxylic acids, esters of dicarboxylic acids and esters of fatty acids, in particular adipic acid, azeliac acid, sebacic acid, phthalic acid or esters of polyhydric alcohols. Alternatively, halogenated hydrocarbons or lubricating oils, e.g. silicone oils such as polyhydrocarbyl siloxane may be used as plastisisers . These oily substances enhance the natural anti-adhesive properties of the vulcanised silicone rubbers, and although they are not absolutely essential, their presence is preferred.

The composition may be pre-manufactured into a desired form of medical equipment, e.g. it may be provided for use with the rubber in a vulcanised state . Alternatively it may be formed in situ, e.g. the composition including vulcanisable silicone rubber, medicament and any other ingredients may be vulcanised in situ to form the desired medical equipment. As an example, a dressing formed utilising the composition of the present invention may be produced in situ on the patient's skin by applying a vulcanisable mixture after its preliminary preparation and holding this in place until it has cured. Curing may take from a matter of minutes to a matter of several tens of minutes by suitable choice of composition. The preparation of equipment, e.g. dressings, in which the curing of the composition takes an extended period of time may be enhanced by the provision of a containment mould surrounding the limb with a mould cavity defining an interspace between the skin of the patient and the mould surface to be occupied by the mixture during curing.

According to another aspect, therefore, the present invention provides a method of producing a wound dressing for a part of the human or animal body, comprising the steps of preparing a substantially rigid mould shaped to surround the said part of the human or animal body, fitting the said mould thereto, sealing at least a major portion of the perimeter of the mould against the escape of liquid between the mould and the said part of the human or animal body to form a mould cavity, introducing into the mould cavity a composition, including a selected medicament, as claimed in any of Claims 1 to 14 hereof in a fluid state and causing or allowing the composition to cure or vulcanise. Alternatively, dressings may be preliminarily formed with suitable medicaments and maintained in sterile conditions to be applied to the skin of the user when needed. The advantage of casting the dressings in situ includes the ability to vary the medicaments and/or the concentration of medicaments or mixture of medicaments to allow the medical attendants to make last minute variations before application. It also has the advantage of being applied in a liquid state so that the forces exerted on the patient's skin, which may be sensitive and/or damaged, are at a minimum, and the dressing mixture may be raised to skin temperature such that there is no thermal shock upon application. A further advantage of liquid- application lies in the fact that the dressing can be conformed exactly to the shape of that region of the skin in question, and if this should be a limb or a joint the dressing can be formed in such a way as to include a suitable exoskeletal shell for the purpose of retaining the limb or joint in a set position.

Alternatively, of course, dressings suitably preliminarily shaped to fit a portion of the anatomy such as a limb or a joint may be made and stored in sterile conditions .

The medicaments admixed to the vulcanisable silicone rubber, e.g. a liquid organo- siloxane, prior to curing may be of any suitable type having the necessary medical, prophylactic or therapeutic properties to combat the immediate medical problem. In the case of wound dressings such medicaments may be antiseptic, fungicidal or biocidal, whereas for other purposes the medicaments may be of any type known to the medical profession as suitable for application to the skin (or other exposed tissue) for treatment of the condition in question.

The composition of the present invention is especially suitable for use in a wound dressing where the natural regenerative activity of the body produces body fluids such as blood and blood plasma which congeal and/or coagulate and in doing so adhere to conventional dressings, and also where tissue growth, as well as hair growth, cause problems of unwanted adhesion in conventional dressings. The vulcanised silicone rubber provides a low-adhesion surface the properties of which are made even less adhesive by the introduction of additives, e.g. an oil or any other fluid organic compounds, as discussed above which are released slowly through the silicone rubber so that the adhesion of organic material during wound healing is further inhibited.

Dressings made according to the present invention also have the advantage that, because they do not adhere to the tissue or the detritus of tissue regrowth and coagulation of body fluids they remain uncontaminated even after a lengthy period m place, and after removal of such a dressing for inspection of the healing process can be replaced (perhaps after a brief wipe with a sterile cloth) to allow continued migration of the medicaments.

Various exemplary embodiments illustrating the use of wound dressings made m accordance with the principles of the present invention will now be described m relation to the accompanying drawings, m which.

Figure 1 is a view of an injured limb with a mould suitable for receiving a wound dressing material;

Figure 2 illustrates the mould m place and the application of the mixed liquids prior to curing; Figure 3 is a perspective view of a wound dressing formed as another embodiment of the invention; and

Figure 4 is a perspective view of a further wound dressing formed as another embodiment of the invention.

In the drawing a human elbow having serious lacerations is illustrated, generally indicated with the reference numeral 11 whilst, m an exploded view are shown the parts of a two-part mould which can be fitted about the elbow to form an enclosure to receive a dressing material made from the composition of the present invention. The two mould halves are indicated 12, 13 whilst the completed mould, shown m Figure 2, is indicated 14. A packing material 16, 17 for temporarily retaining the material before curing may be introduced around the periphery of the mould at each end thereof, whereupon a curable mixture can be introduced into the opening 15 until it overflows therefrom.

After curing, the mould 14 may be removed to leave the dressing in place, or may be retained as an exoskeletal support .

The embodiment of Figure 3 is formed as a thin flexible elastomeric layer or strip (shown with its thickness exaggerated for illustration purposes only) , which can be applied to the skin of a patient and retained in place with retaining means such as adhesive bands. In more detail, the wound dressing comprises a porous fabric support layer 20 which may be made of gauze or other woven fabric having connector tapes 21, 22 at the two opposite ends thereof bearing a light tack adhesive for holding the wound dressing in place. A central portion of the support layer 20 is impregnated with a medical dressing composition to form a medicament layer 23 comprising a vulcanised silicone rubber incorporating a medicament such as an antiseptic. The medical dressing composition may be built up to form a layer up to, for example, 1mm thick which is nevertheless flexible and capable of being fitted onto any part of the human or animal body with the surface of the medicament layer 23 in intimate contact therewith. On the opposite side of the support layer 20 there is an impermeable protective backing layer 24. The wound dressing illustrated in Figure 3 is suitable for general purpose use and can be produced in advance and packaged in suitable sterile packages ready for immediate use when required.

Figure 4 illustrates a special purpose preliminarily shaped wound dressing for a finger or thumb. This is in the form of a finger stall 26 of relatively rigid (but not necessarily absolutely rigid) material having a medical dressing composition layer 27 of vulcanised silicone rubber with incorporated medicament coated on the inner surface. A longitudinal slit 28 facilitates fitting onto a thumb or finger and tapes 29, 30 with adhesive pads 31, 32 allow the stall to be reduced in diameter to form a firm fit to retain it in position.

In another embodiment, not shown, the vulcanised or vulcanisable silicone rubber composition is coated onto a catheter so as to maintain antiseptic properties in use by continual migration of an antiseptic material incorporated in the mixture before curing. In other embodiments (not shown) the vulcanised or vulcanisable silicone rubber may incorporate components making it sufficiently strong and rigid to be formed directly as a catheter or cannula. A further embodiment of the invention (not illustrated) comprises an anatomical component or structure suitable for use either as a prosthesis or as an extra-corporeal model for practising surgical techniques.

Claims

1. A composition for use in forming medical equipment intended to come into contact with a patient, comprising or including a vulcanised or vulcanisable silicone rubber admixed with a medicament such that, in use of equipment incorporating the composition at least the said medicament is subject to migration towards a surface of the composition in contact with part of a patient.

2. A composition as claimed in Claim 1, in which the silicone rubber is an organo-polysiloxane .

3. A composition as claimed in Claim 2, in which the organo-polysiloxane has a silanol end group.

4. A composition as claimed in Claim 3 including a cross-linking agent.

5. A composition as claimed in Claim 4, in which the cross-linking agent is ethyl silicate.

6. A composition as claimed in Claim 1 to 5 further including a catalyst .

7. A composition as claimed in Claim 6, in which the catalyst is an organic tin-salt.

8. A composition as claimed in Claim 6 or Claim 7, in which the catalyst is dibutyl-tin dilaurate.

9. A composition according to Claim 3, in which the organo-polysiloxane is admixed with a compound of the general formula RsiX₃, where:

R is a hydrocarbyl

X is a hydroxyl group or a group containing hydrolysed oxygen linkage or an amino group or a group containing hydrolysable nitrogen linkage or another reactive site.

10. A composition as claimed in any preceding claim, further including a dispersing agent to aid the dispersion of the medicament.

11. A composition as claimed in Claim 10, in which the dispersing agent is an organic fluid.

12. A composition as claimed in any preceding claim further including one or more plasticizers .

13. A composition as claimed in Claim 12 in which the or a plasticizer is chosen from the group comprising esters of carboxylic acids, esters of fatty acids, esters of dicarboxylic acids, adipic acid, azeliac acid, sebacic acid, phthalic acid, and esters of polyhydric alcohols.

14. A composition as claimed in Claim 12, in which the or a plasticizer is a halogenated hydrocarbon.

15. A wound dressing comprising a composition as claimed in any preceding claim in association with support means for retaining a surface of an element made from or including the composition in contact with the skin or other exposed surface of a human or animal body.

16. A wound dressing as claimed in Claim 15, in which the said support means comprise a woven or non-woven, natural or synthetic fabric impregnated with the said composition whilst in a liquid state.

17. A wound dressing as claimed in Claim 16, in which the said support layer has or is associated with fastening means for securing the dressing in place.

18. A wound dressing as claimed in Claim 16 or Claim 17 in which the support layer has a backing layer of impermeable material bounded or otherwise secured to a face thereof which, in use, faces away from the patient to which the dressing is applied.

19. A wound dressing as claimed in any of Claims 16 to 18, in which there are provided means for conforming at least a face of the dressing, at which the medicament is exposed, to the shape of a part of the human or animal body to which the dressing is to be applied.

20. A wound dressing as claimed in any of Claims 15 to 19 in which the said means for retaining a surface of an element made from or including the composition in contact with an exposed surface or the skin of a human or animal body comprises a substantially rigid external support member or assembly of members defining an interspace between itself and the said skin or exposed surface, in which interspace the said composition is located.

21. A method of producing a wound dressing for a part of the human or animal body, comprising the steps of preparing a substantially rigid mould shaped to surround the said part of the human or animal body, fitting the said mould thereto, sealing at least a major portion of the perimeter of the mould against the escape of liquid between the mould and the said part of the human or animal body to form a mould cavity, introducing into the mould cavity a composition, including selected medicament, as claimed in any of Claims 1 to 14 in a fluid state and causing or allowing the composition to cure or vulcanise.

22. A method as claimed in Claim 21, further comprising the steps of removing the mould and applying a protective element or layer to the cured or vulcanised composition whereby to retain it in position.

23. Medical equipment such as a catheter or cannula made from, incorporating, or coated with a composition as claimed in any of Claims 1 to 14.

24. The use of a composition comprising a vulcanised or vulcanisable silicone rubber in the manufacture of medical equipment .

24. The use of a composition comprising a vulcanised or vulcanisable silicone rubber admixed with a medicament in the manufacture of medical equipment .

26. Medical equipment made from, incorporating or coated with a composition comprising or including a vulcanised or vulcanisable silicone rubber.