Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Implant or insert
Reexamination Certificate
1999-10-15
2001-05-01
Acquah, Samuel A. (Department: 1711)
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Implant or insert
C528S272000, C528S300000, C528S350000, C524S916000, C424S443000, C424S486000
Reexamination Certificate
active
06224892
ABSTRACT:
The present invention relates to hydrogels. In particular, the present invention relates to polyester hydrogels and their use as components of medical devices, for example implants and wound dressings.
Linear pyromellitic polyesters, produced by the reaction of pyromellitic anhydride and a diol have been described in U.S. Pat. No. 2,585,323.
We have now surprisingly found that novel cross-linked pyromellitic polyesters, produced by reacting pyromellitic anhydride with a polyol containing more than two hydroxy groups possess properties which make them useful as medical devices.
Thus, according to the invention we provide a polyester comprising residues of pyromellitic acid and a polyol containing more than two hydroxy groups.
The polyesters of the invention are cross-linked and are water swellable hydrogels. By the term a “water swellable hydrogel” is meant a three-dimensional network of a super absorbent polymer which interacts with water or aqueous solutions by swelling and retaining a significant proportion of water within its structure.
For the purpose of this invention a super absorbent polymer is understood to mean a polymer which, when fully hydrated, is capable of having an equilibrium water content of at least 30% w/w.
Aptly, the polyesters of the invention have a number average molecular weight (M
n
) of greater than 4500, preferably greater than 10,000, and more preferably greater than 20,000.
Any polyols, known per se, containing more than two hydroxy groups are suitable for use in the present invention. Such polyols preferably contain three or more hydroxy groups and include, for example, polyether polyols or polyhydroxyalkanes. Although such polyols are suitable for use in the present invention the invention is not to be considered as being limited to polyether polyols or the polyhydroxyalkanes.
Polyhydroxyalkanes, for use in the present invention, may have from 2 to 6 carbon atoms. Examples of such polyhydroxyalkanes include glycerol, sorbitol, mannitol, adonite, ribite, dulcitol, erythritol and xylite. Polyols such as triols which may be mentioned include trihydroxyalkanes such as glycerol. Mixtures of polyols may also be used.
Examples of polyether polyols also include those sold under the range of TP30 by Perstorp.
The polyesters of the invention may be prepared using conventional methods known per se.
Thus according to the invention we provide a method of manufacturing a polyester as hereinbefore described which comprises reacting pyromellitic anhydride and a polyol containing more than two hydroxy groups at elevated temperature.
The method of manufacturing a polyester according to the invention may optionally include the use of known catalysts.
The ratios of the pyromellitic anhydride and the polyol in the polymerisation reaction will depend upon, inter alia, the functionality of the polyol, that is, the number of free hydroxy groups, the degree of cross-linking required in the resulting polyester and the reactivity of the hydroxy groups. Defined in terms of stoichiometry the ratio of anhydride groups to hydroxy groups should be from 0.7:1 to 1:1.3, preferably 1:1. When a mixture of polyols is used the effective stoichiometry of the polyol may be a fraction.
Polyesters according to the invention may be characterised using conventional techniques known per se, such as infra red spectroscopy, nmr, rheological measurements, glass transition measurements and water uptake.
The polyesters according to the invention are particularly advantageous in that they are biodegradable.
Thus according a further embodiment of the invention there is provided a biodegradable medical device comprising a pyromellitic polyester of the present invention.
Thus the pyromellitic polyesters of the invention may be useful in preparing biodegradable implants such as medical or surgical prostheses, supports for such prostheses, supports for cell cultures such as may be used in ligament, cartilage or tendon repair, sutures, supports for cell cultures in woundcare or as woundcare agents in their own right, eg. debriding agents, pharmaceutical carriers etc. or the copolyesters of the invention may be useful in imaging during interventional procedures.
It is intended that the aforementioned uses should not be limitative and are mentioned by way of example only.
The polyesters of the invention are also advantageous in that they are sterilisable. Any conventional form of sterilisation may be used, eg. steam sterilisation, but an especial benefit of the polyesters of the invention is that they may be sterilised without detrimental effect by gamma-radiation.
Thus according to a further feature of the invention we provide a polyester as hereinbefore described in sterile form, eg. wherein the sterilisation has been carried out by gamma-radiation.
Accordingly, the polyesters of the present invention may be especially useful in wound healing, eg. as a debriding agent.
Thus according to the invention we provide the use of a polyester comprising residues of pyromellitic anhydride and a polyol in the manufacture of a wound healing agent, eg. a debriding agent.
Thus the polyesters and devices of the invention may be applied in a method of wound healing which comprises applying a pyromellitic polyester in accordance with the invention or a device incorporating such a pyromellitic polyester to the wound of a patient.
We especially provide the use of a polyester according to the invention as hereinbefore described.
The invention may now be illustrated but in no way limited by way of example only, and in which temperatures are in degrees celsius.
REFERENCES:
patent: 2585323 (1952-02-01), Elwell et al.
patent: 3975350 (1976-08-01), Hudgin et al.
patent: 5480963 (1996-01-01), Jiang et al.
patent: 5486444 (1996-01-01), Bayley et al.
patent: 5552453 (1996-09-01), Fujita et al.
patent: 956.583 (1950-02-01), None
patent: 1.162.607 (1958-09-01), None
Acquah Samuel A.
Larson & Taylor PLC
Smith & Nephew plc
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