Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1993-06-08
1996-11-12
Michl, Paul R.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
523117, 523118, 523218, 604 56, 604 82, 606 92, A61L 2500, C08F 2010
Patent
active
055740758
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a material as a starting material for the preparation of bone cement, a process for its preparation and a process for the preparation of bone cement.
In the surgery and orthopaedics of the locomotor system the replacement of a joint by an artificial joint has become a routine operation. The most common method here is to anchor metal prosthetic components in bone by means of a plastic mass which is also known as bone cement. The known bone cements are cold polymerizing two-component based plastics consisting of a monomer and a powdery polymer component in the form of spheres or granules. All the normal commercial bone cements are prepared with a polymethylmethacrylate (PMMA) base. Attempts to mix the two components of these bone cements have shown that homogeneity on the one hand and avoidance of bubbles on the other hand are the main problems in the mixing techniques of such two-component plastics. This is particularly the case when antibiotics are added, which is often difficult. In addition, the powder can create dust when shaken during the mixing process and contaminates the air. The powder can invade the respiratory system and indeed as far as the main bronchus, as experimental tests have shown. Furthermore, should mixing be performed under vacuum, the polymer powder is sucked up by the vacuum pump. The powder component is thus the essential obstacle for the preparation of the bone cement within a closed system which, on the other hand, would certinaly be welcomed from an industrial medicine point of view. Tests to evacuate the powder are incomplete to date in so far as it has not been possible in this way to guarantee a sufficient polymer sphere inclusion in the matrix of the bone cement. The incorporation of any filler particles, such as radiographic contrast agents or osteoinductive substances, presents even greater problems.
The object underlying the present invention is thus to overcome the above problems and to simplify the handling of the polymer powder during preparation of bone cement.
SUMMARY OF THE INVENTION
The invention is based on the idea of converting the powdery polymer component, the particles of which are usually in spherical form, into a solid in the form of a conglomerate before the mixing process. The polymer component of the bone cement is solidified similarly to cube sugar. The porosity of this conglomerate can be controllably adjusted and standardized and the polymer can be solidified such that evacuation is possible. Different porosities can be obtained by varying the size of the polymer particles, the bulk density and the nature of connection of the particles. According to the invention the polymer component of the bone cement is thus a porous pressed part of densely packed polymers connected to one another preferably at their points of contact, between which a pore system is formed.
With the present invention it is possible to create conditions which reproducibly guarantee a homogeneous mixture in the preparation of the bone cement, and indeed irrespective of the skill or ability of the person preparing the mixture. A stabilized polymer bond according to the invention is also to be safely evacuated and indeed before packing but also after the bone cement has been mixed or prepared.
The bone cement's polymer component solidified according to the present invention can be handled easily and safely like a cartridge.
Radiographs in a scanning electronic microscope show that according to the invention there is sufficient space between the polymer particles for a stable polymer/matrix bond. Thus, the conditions are created for a closed system in the preparation and possibly the application of the bone cement by orthopaedics.
The solidified polymer component can be subjected to a preevacuation in a simple manner. The mixing tests with the polymer cartridges according to the invention show that once the monomer is added it is very rapidly absorbed into the given capillary spaces between the polymer particles connected to one an
REFERENCES:
patent: 4927866 (1990-05-01), Purrmann et al.
patent: 5236971 (1993-08-01), Murray
Merriam Andrew E. C.
Michl Paul R.
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