Agitating – In vacuum chamber
Reexamination Certificate
2002-08-20
2004-09-28
Cooley, Charles E. (Department: 1723)
Agitating
In vacuum chamber
Reexamination Certificate
active
06796701
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a preparation and application device for implant materials to be prepared from at least one powder or granulate component and one liquid component immediately before use. The device includes a first container which holds the powder or granulate component in a sterile, sealed manner; and a second container which holds the liquid component in a sterile, sealed manner and can be connected to the first container. Means are provided for producing an overflow connection between the two containers, for forcing the liquid component out of the second container and into the first container and for intimately, homogeneously mixing the components in the first container by moving a mixing device which is located in the first container on a mixing shaft that is guided out of the container in a sealed manner. The first container is configured in such a way that it can be connected to a source of negative pressure.
During the last years, minimal-invasive treatment methods have become more and more important for the surgical treatment of defects on the skeletal system. Certain methods are used in particular in orthopedics and accident surgery, wherein the treatment is performed partially under x-ray control and involves, for example, only a stab or percutaneous incision. These methods have obvious advantages over conservative open surgery: the surgery is significantly less stressful for the patient, the hospital stay is much shorter, which reduces the treatment cost. In addition, there is a significantly reduced risk of infections, which could otherwise lead to long-term and expensive complications.
In particular, during minimal-invasive treatment in the reconstruction of bone defects, filler components, stabilizing components, auxiliary and/or active components are brought percutaneously and directly to the site of the defect, where they are used particularly for filling the defects and for partial stabilization, as well as for triggering repair processes, for inducing and accelerating neovascularization and new bone formation, as well for preventing and/or treating infections in the defect area. Most of the employed materials or active ingredients, and/or their combinations, cannot be applied using conventional injection needles due to their special composition and associated consistence. It is therefore necessary to use special applicators that are adapted for a particular product, for delivering the therapeutics, i.e., the implant materials, easily and safely to the location where they are to be applied.
Of course, the implant materials, which mostly consists of several separate components, must be combined and mixed into a homogeneous matrix before they are applied.
It has been observed, however, that the chemical-physical properties of the implants, in particular their mechanical stability, are significantly affected by the particulars of the mixing process. These properties are important prerequisites for attaining optimum functionality.
This will be illustrated with reference to an exemplary implant material—bone cement—where these effects have been studied in detail:
It has been known since many years that the mechanical stability of bone cements is reduced by both larger and smaller air inclusions, which enter the cement matrix mainly at the time the cement components are mixed together. The resulting weakening of the cement can be easily measured and detected physically, considering that the cement matrix can contain up to 25% air, in particular when the components are improperly mixed by hand. The air bubbles enclosed in the cement produce pores which can cause the formation of fissures and gaps when the prosthesis is later stressed. This in turn can cause the cement jacket surrounding the prosthesis to shatter prematurely, causing the prosthesis to loosen, which can require removal of the prosthesis. Conversely, experimental and clinical studies have shown that cements that are almost air-free and therefore also nonporous tend to have a greater fatigue resistance and can therefore increase the useful life of endo-prostheses.
In addition to the above example from the technical field of bone cements, technical methods for production of ceramics will also be described. Nonporous (i.e., in particular air-free) matrices can be produced by conventional techniques, in particular when processing expensive plaster and molding materials, that attain the mechanical stability required of the end product.
Accordingly, the same conditions have to be met also for medical implant materials, for example for materials based on calcium phosphate, calcium sulfate or specific polymers, which are to provide both a physiological effect and a stabilizing function. Air inclusions have to be safely eliminated when these products are prepared and mixed, so as to ensure the desired mechanical stability of the end product of the implant material.
While such methods are commonly used in other technical fields, corresponding mixing and/or applications systems, for example for ceramic implant materials, do not yet exist in the medical field. Over the past years, these problems related to bone cements have been recognized which has led to intensive investigations of mixing systems, with the goal to develop methods that can to a large extent eliminate air inclusions in the cement when the cement components are mixed, and to develop mixing methods that guarantee reproducible and standardized mixing results.
This development will now be illustrated with reference to exemplary well-characterized bone cements: intensive investigations have led to the so-called “vacuum mixing technique,” which is today generally accepted and represents the state of the art. The cement components (polymer powder and monomer liquid) are hereby mixed in specially constructed mixing vessels and/or application cartridges under reduced atmospheric pressure.
To achieve a “vacuum” (a reduced or negative air pressure) which minimizes the air content in the thoroughly mixed cement matrix, a residual pressure of approximately 100 to 200 mbar has to be maintained during the mixing process.
In practice, the cement mixing vessel is hereby sealed after the cement components have been filled in, and is connected via a hose to a pump that is powered by compressed air. Depending on the source of the compressed air and the construction of the pump, the air volume contained in the mixing system is—more or less rapidly—reduced, resulting in a correspondingly smaller residual pressure. However, not every system on the market is capable of reducing the air pressure to a point where the intended goal—namely a cement that is nearly free a pores—is also achieved in practice.
A significant problem associated with this type of “vacuum mixing” of bone cements is related not only to the sometimes quite different pump efficiencies of the pumps, but also to the often quite large variations in the hospital-internal compressed air supply in the operating room, that is required for operating the pumps. The building pressure of the compressed air in different hospitals tends to vary not only over the course of the day, but the outlet pressure can generally range between approximately 5 and approximately 10 bar, which tends to significantly affect the pumping efficiency and therefore also the “vacuum” in the mixing vessels, and consequently also the quality of the cement as measured by the air inclusions. Standardizable and reproducible mixing results can hence not be realized in this manner.
Moreover, only a small number of the pumps operating today have a manometer that shows and controls the pumping efficiency during the mixing process. However, such measurement devices on the pumps themselves do not necessarily reflect the pressure in the actual mixing vessels. Adequate and reliable mixing results can only be obtained if the residual pressure in the mixing vessel is reliably controlled during the entire duration of the mixing process. None of the conventional “vacuum”-mixing systems includes suitable display or mea
Dingeldein Elvira
Sattig Christoph
Wahlig Helmut
Wüst Edgar
Cooley Charles E.
Coripharm Medizinprodukte GmbH & Co. KG
Norris McLaughlin & Marcus P.A.
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