Plastic X-Ray Contrast Material

1. Field of the Invention

This invention relates to a plastic material which is opaque to X-rays, in particular, polyurethane having a covalently linked X-ray contrast material.

2. Description of the Prior Art

Use of plastics in industry, agriculture, medicine or other applications is often tied to the question of locating and testing the material during its use. In addition in medical applications it must not only be possible to locate the implanted or applied plastics, but also the plastics must be removable from the human or animal body after a set period of time. As a rule, removal requires a further surgical procedure. Although easily locatable plastics are known, they are chemically stable and can only be removed from the human body by a surgical procedure. On the other hand, plastics are known which degrade and are removed from the body after a certain time when their purpose has been served. However, such plastics are not easy to locate.

A polyurethane which is opaque to X-rays but which is not has been disclosed biologically degradable in Derwent Abstract 87-348546/49 of WO 8707-155 which, however, is not biologically degradable. However if it were biologically degradable, highly toxic halogen derivates of isophtalic acid would be created, as a result of which the polymer would not be biocompatible. Biocompatible and/or biodegradable polyurethanes which, however, are not X-ray contrasting, have been disclosed in J. Polym. Sci., Polym. Symp. 66, pp. 259 to 268 (1979) or J. Polym. Sci., Polym. Symp. 66, pp. 239 to 257 (1979), as well as in Houben-Weyl, Methoden der organischen Chemie [Methods of Organic Chemistry], Volume E 20, Makromol. Stoffe [Macromolecular Materials], pp. 1719 to 1721 (1987).

Accordingly, it is an object of this invention to provide a material which, can be located with a high degree of accuracy and which can also be dissolved in the human or animal body.

This object is attained by a material of polyurethane with a covalently linked X-ray contrast material in accordance with one embodiment of this invention comprising a polyurethane which is biocompatible, stable or biodegradable in an appropriate environment, and X-ray contrasting.

Polyurethanes impervious to X-rays are particularly suited for temporary or permanent use of in connection with X-ray identification. In the solid aggregate state, devices, structures, films, foils, tubes, hoses, screws, rods or other three-dimensional compact or hollow structures are made from polyurethanes in addition the polyurethane in case is also suitable for coatings of the structures, insulation, seals and as a drug carrier. In the liquid aggregate state, the polyurethane can be used for filling empty or filled biological or technical hollow spaces and/or for diagnostic, medical or technical purposes. Furthermore, the polyurethane can be used for the additional purpose of X-ray identification. The polyurethane can also be employed in the form of sprays, dispersions or as a dispersion medium. Work pieces can be coated with this polyurethane, but topical application is also not excluded. Hardening by application of external energy is used for this application.

For example blockage of the exocrinal duct system of the pancreas by injection of the dissolved plastic through a catheter is a surgical procedure which may be required during transplantation of this organ.

From a medical viewpoint, the plastic to be used for this purpose requires specific properties, including:

a. Biocompatibility

b. Solubility in solvents which are only weakly or not toxic, such as alcohol, dimethylsulfoxide, DIM or their mixtures,

c. Insolubility in an aqueous environment (water, blood, etc.)

d. Solid, resilient or visco-resilient behavior following precipitation,

e. Ability to decompose biologically, and

f. X-ray absorbency to a sufficient and variable extent.

In particular, polyurethanes are suitable in which one of their two basic compounds, in this case the diol compound, is entirely or partially replaced by the glycerine monoester of diatrizoic acid (1) or by the glycerine monoester of a triiodobenzoic acid derivative (2, 3, 4, 5) or by an iodinated pyridone-4 derivative, for example iopydol (6). ##STR1##

The following diols are used as co-condensable diol compounds:

a. Bi-valent alcohols of the type

b. Polyether diols of the type ##STR2## c. Polyester diols on the basis of I. Adipic acid/ethylene glycol-co-propylene glycol

Adipic acid/ethylene glycol

Adipic acid/propylene glycol

II. Polyglycol diol and polyglycol-co-lactide-diol

IV. Poly-3-hydroxy-butyric acid diol and poly-3-hydroxy-butyric acid-co-3-hydroxy valeric acid diol

V. Poly-3-hydroxy valeric acid diol

VI. Poly-caprolactone diol

VII. De-polymerized cellulose

VIII. De-polymerized cellulose acetate

The polyester diols on the basis of II to V are produced by transesterification of higher-molecular polyesters with ethylene glycol, diethylene glycol and triethylene glycol with simultaneous cleavage into macro-diols having mean molecular weights between M.sub.n 500 and 10000.

The following compounds can be used as diisocyanates:

1. 5-isocyanato-1-(isocyanatomethyl)-1, 3, 3-trimethylcyclohexane (isophorone diisocyanate) (IDPI)

2. 1, 3-bis(1-isocyanato-1-methyl)-benzene (TMXDI)

3. Hexamethylene diisocyanate (HDI)

4. 2, 2, 4-trimethyl-hexamethylene diisocyanate (THDI)

Condensation of the compounds occurs in solution in a mixture of dioxane/dimethylformamide having a mixing ratio between 1:1 to 20:1 at temperatures between 40.degree. and 100.degree. C., with or without a catalyst. Isolation of the polymers is accomplished by precipitation in water. Purification is accomplished by repeated dissolution of the polymer and precipitation in water.

The polymer made from the above described compounds is represented by way of example by the following formula: ##STR3## where x.gtoreq.1, y.ltoreq.1000 and 1.ltoreq.n.ltoreq.50