Composition for use in making bone cement

[54] COMPOSITION FOR USE IN MAKING BONE CEMENT

[75] Inventors: Michael Braden, Hertfordshire;

Laurence G. Wood, Surrey, both of
England

[73] Assignees: Bonar Cole Polymers Limited,
Surrey; The London Hospital
Medical College, London, both of
England

[21] Appl. No.: 913,311
[22] Filed: Sep. 30, 1986

[30] Foreign Application Priority Data

Oct. 1, 1985 [GB] United Kingdom 8524152

[51] Int. CL* A61K 6/08; C08K 3/10;

C08L 31/02

[52] U.S. CI 523/117; 523/116;

524/413; 524/423; 524/432; 524/560; 525/309

[58] Field of Search 523/117, 116; 524/413,

524/423, 432, 560; 525/309

[56] References Cited

U.S. PATENT DOCUMENTS

3,715,331 2/1973 Molnar 523/117

4,389,507 6/1983 Podszun et al 524/460

4,404,327 9/1983 Crugnola et al 525/228

4,456,711 6/1984 Pietsch et al 523/206

4,490,497 12/1984 Evrard et al 524/349

4,500,658 2/1985 Fox 523/117

4,547,390 10/1985 Ashman et al 523/117 X

4,617,327 10/1986 Podszun 523/116

FOREIGN PATENT DOCUMENTS

0041614 5/1981 European Pat. Off. .

1431211 4/1976 United Kingdom .

2069517 8/1981 United Kingdom .

WO82/01006 4/1982 World Int. Prop. O. .

Primary Examiner—Theodore E. Pertilla
Attorney, Agent, or Firm—Nixon & Vanderhye

[57] ABSTRACT

A composition for forming a bone cement or the like, comprising a powder component and a monomer component, the powder component comprising ethylmethacrylate polymer beads incorporating particles of opacifier therein and the monomer component comprising n-butyl methacrylate.

6 Claims, 1 Drawing Sheet

4,791,

COMPOSITION FOR USE IN MAKING BONE
CEMENT

It is necessary to attach an implant such as a hip S prosthesis to living bone by a bone cement. The cements are typically polymeric materials and the surgeon usually mixes the interactive components to make the cement at an appropriate stage during the surgical procedure. Polymers are relatively radiolucent and since 10 the surgeon will later wish to inspect the implant by x-rays it is known to add to the polymers radiopaque materials, herein called opacifiers, examples being barium salts such as barium sulphate, zirconium oxide and zinc oxide- These opacifiers are usually added to poly- 15 mer beads by the surgeon when he makes up the bone cement and while they give the necessary radiopacity, it has been observed that they tend to reduce the mechanical properties e.g. transverse strength and compressive strength of the set polymeric bone cement. U.S. Pat. 20 No. 4,500,658 points out this observation and describes a method of incorporating an opacifier in an acrylic resin by a suspension polymerisation.

It is one object of the invention to provide a composition for use in making a bone cement which incorpo- 25 rates an opacifier, will provide a cement of enhanced mechanical properties and which additionally is less likely to do damage to the patient.

According to one aspect of the invention there is provided a composition for use in making a bone ce- 30 ment or the like, the composition comprising a powder polymer component and a monomer component therefor, the components being sterile for medical use, an opacifier being incorporated within the polymer of the powder component, characterized in that the polymer 35 is ethylmethacrylate polymer and the monomer comprises n-butyl methacrylate.

With the system of the invention the ethylmethacrylate polymer dissolves almost completely in the n-butyl methacrylate monomer and when the materials are 40 reacted the exothermic heat generated is much reduced. In addition there is little release of monomer, and the formed cement has several improvements in mechanical properties such as

an elongation at fracture of about 25% 45 an improved flexural fatigue strength a reduced modulus of elasticity

When during surgery a bone cement is made up and inserted into the body a drop in the patients blood pressure can occur. The reasons for this are not clear, but it 50 is believed that monomer released from the setting cement during polymerisation is a factor. It has been observed that in the case of the composition of the invention relatively little monomer is released, and clinical data suggest that there is a noticable absence of blood 55 pressure drop and no changes in patients pulse rate were observed.

The monomer component preferably comprises the liquid monomer and an activating tertiary amine. The monomer will be n-butyl methacrylate but other mono- 60 mers may be present in minor proportions e.g. methylmethacrylate. The amine may be an aniline or toluidine, examples being N,N'-dimethyl p-toluidine, dihydroxyethyl-o-toluidine, dimethyl aniline or diethylaniline. The activator is preferably selected so that polymerisa- 65 tion takes place at or below body temperature.

The particles of the opacifier are substantially uniformly encapsulated within the polymer beads making

150

2

up the powder component and this distribution provides the necessary radiopacity coupled with the desired mechanical strength in the formed polymer bead and ultimately in the formed bone cement.

The invention further includes a method of making a powder component as defined above, the method comprising dispersing particles of the opacifier with a prepolymer by ball, high speed or similar milling, diluting the dispersion with monomer and carrying out suspension polymerisation to form polymer beads containing particles of opacifier. The beads may be recovered and used directly as the powder component without the addition of further opacifier, although an initiator such as benzoyl peroxide may be added and, as indicated below, other additions are possible.

The physical properties of the polymer and the monomer should be selected for optimum effect according to the intended use. The ethylmethacrylate polymer should have an average molecular weight should range from about 150,000 to about 1,500,000 and the particle size should be distributed in the range of about 15 to 100 micron.

The opacifier may be selected from any of those known for this purpose. Examples are barium sulphate, zinc oxide and zirconium dioxide. The proportions of opacifier may range from about 5 to 50% by weight of the polymer of the powder.

The polymer and monomer will require to be sterilised for surgical use. While different forms of sterilisation may be adopted, it is preferred to sterilise the powder by gamma irradiation and the monomer by bacteriological filtration.

The polymer beads may be made including a peroxide as catalyst and chain transfer agents such as lauryl mercaptan and trichloroethylene may be present. The aqueous phase of the suspension polymerisation may include polyvinyl alcohol and sodium or ammonium polymethacrylate and inorganic stabilisers such as talc or tricalcium phosphate. The powder component may be used directly or additions may be made. For example, extra catalyst may be added to achieve a desired curing time and cross linking agents may be present. Antibiotics may be added, colourants may also be present.

The object to be implanted may take a wide variety of forms and may be placed at for example the hip or knee. Thus for a hip replacement it may be a double cup cup type of prosthesis or the Muller prosthesis. The composition of the invention may however be used for any biomedical application e.g. devices, dentures, implants and the like.

According to other aspects of the invention there is provided for use in making a bone cement or the like,

a sterilised powder component comprising a polymethacrylate, preferably a poly (ethylmethacrylate) having a molecular weight in the range of about 150,000 to 1,500,000, the polymer being in the form of beads having a particle size distribution in the range of about 15 to 100 micron, particles of an opacifier having been incorporated within the beads by ball, high speed or similar milling; and

a sterilised monomer component comprising n-butyl methacrylate monomer in liquid form and a tertiary amine activator such as N,N'-dimethyl p-toluidine, optionally with a cross linking agent such as ethylene glycol dimethacrylate.