Automated bone cement mixer

A device and related method for mixing a powdered component and a liquid component with minimal user interaction are described. A powdered component and a liquid component are separately fed into a mixing chamber. The powdered component may be released into the liquid component by removing a barrier. Alternatively, the two components are drawn into the mixing chamber from respective sources by a vacuum. The mixture is sonicated at precise vibrational frequencies to control the physical properties of the final blended content. A piston-like device is used to remove the blended content from the mixing chamber.

FIELD OF THE INVENTION

A device for and method of mixing and blending by adding one or more sources to a mixing chamber and sonicating the contents.

BACKGROUND OF THE INVENTION

Bone cement has been used in the treatment of skeletal fractures, repair of skeletal and dental cavities, and fixation of total joint replacement and other implants for over fifty years. Currently, there are a variety of bone cement products, such as, polymethylacrylate or PMMA.

There are also a variety of mixing devices for the bone cement products. Many surgeons mix cement by hand in a bowl using a spatula. However, open hand mixing entraps air bubbles. The trapped air bubbles make the cement porous and adversely affect the mechanical properties of the cement. In recent years, vacuum mixing devices have been introduced where the mixing is performed in a closed container under vacuum to reduce porosity in the bone cement. However, the actual mixing is still conducted manually. The manual mixing creates non-uniform mixing and inconsistent quality of the final product. Furthermore, mechanical stirring devices may involve manual handling in removing the stirrer. This exposes the bone cement product to non-sterile surroundings and may introduce harmful materials into the product.

Other methods for mixing bone cement products include mixing the cement by releasing two components, a liquid and a powder, such that the two components merge into each other through divided vacuum packed plastic bags. Final mixing takes place by manipulating the flexible bags. Still other devices strike a container while the liquid and powder components are brought together under a vacuum. A removable stirrer is used.

None of these devices or methods provides uniformly consistent results that can be automated or controlled. None of these devices or methods provides predictable and optimal results independent of the variability of the user.

Needs exist for new devices for mixing bone cement and methods for mixing that improve consistency between users and optimize the mechanical characteristics of the bone cement.

SUMMARY OF THE INVENTION

The present invention is a novel mixing device and method that automates the process of mixing a powdered polymer and a liquid monomer in a consistent manner independent of individual user handling. The present invention may be used for any multiple component systems that require mixing.

One embodiment of the present invention uses sonication of a mixture of powder and liquid. A mixing chamber holds a liquid component of a mixture, while a flexible compartment holds a powdered component of the mixture. The mixing chamber and flexible compartment are separated by a divider. The divider is removed to mix the powder and liquid components. The combined powder and liquid components are sonicated until a desired mixture is created. The mixing chamber may then be inverted so that the blended product may flow freely by gravity or be forced by means of a piston like device into a flexible compartment to be squeezed out manually through an opening in the flexible compartment for use. Various attachments may be connected to an exit opening on the mixing chamber depending on the application. A power source, ultrasonic or vibrating transducer, and control system, monitor and control the mixing process.

One embodiment of the present invention combines vacuum and vibration mixing with vibration frequencies optimized to create desired porosity, mechanical properties, biocompatibility, durability, viscosity, timing prior to application, and aesthetics when, for example, dentistry is involved. The high level of control allows for predetermined degrees of viscosity or porosity to suit a variety of circumstances. Furthermore, risk of infection is reduced by minimizing direct handling as well as exposure to the environment of the components and final product prior to application. The present invention is applicable to medical, orthopedic and dental application as well as other industrial or culinary applications.

The present invention is also a method of mixing using the device of the present invention. Liquid and powder components are mixed together uniformly and conveniently with minimal human technique and interaction. The liquid and powder components of bone cement, or another mixture system, can be brought together in incremental proportionate amounts from separate chambers into a blending chamber in communication with a syringe-like dispensing and mixing unit. The application of a vacuum on the system pulls the liquid and powder components from the separate chambers into the blending chamber in proportionate amounts. Sonication is applied to the system to agitate the components in the blending chamber to facilitate the blending of components without stirring. A separate stirring device that would require removal may not be needed.

The resulting blend continues to mix as the blend is drawn up into the syringe-like dispensing and mixing unit. The mixture continues sonication and vacuum mixing until a desired mixture is achieved. The syringe-like dispensing and mixing unit is free or is made free of associated parts to allow for immediate application of the mixed cement directly from the syringe-like dispensing and mixing unit without the need to transfer cement, remove stirring blades or other elements from the core of the mixed cement. In addition to causing the blending of the liquid and powder components, the applied vacuum and sonication remove bubbles that create detrimental porosity in the mixed cement.

In general, vibration mixing reduces porosity and enhances the properties of bone cement. Vibration at optimal frequencies are preset and automated with minimal user handling of the materials.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a schematic of an embodiment of a mixing device11. A mixing chamber13is vacuum sealed and sterile. Liquid monomer5is prepackaged in the sealed sterile mixing chamber13. A vacuum sealed flexible compartment10is located above and in communication with the mixing chamber13. The flexible compartment10contains a prepackaged powdered polymer15. A pinch device20separates the powdered polymer15in the flexible compartment10from the liquid monomer5in the mixing chamber13. Alternatively the liquid monomer may be stored in a sealed glass or other suitable material that forms an ampoule with a narrow region that is broken to allow the monomer to flow to the mixing chamber.

The powdered polymer15is released from the flexible compartment10into the mixing chamber13, which contains the liquid monomer5. To release the powdered polymer15, the pinch device20is removed. The releasing process may be performed manually or may be controlled electronically with sensors and actuators, not shown, connected to the pinch device20. In a preferred embodiment, the powdered polymer15is released into the liquid monomer5, however, in alternative embodiment, the liquid monomer5may be released into the powdered polymer15.

After releasing the powdered polymer15into the mixing chamber13containing the liquid monomer5, mixing is performed by sonicating the components in the mixing chamber13.

Power is supplied to the mixing device11by a power source40with electrical controls41and connections43. The electrical controls41monitor and control timing, sonication frequencies, vacuum, temperature, viscosity and other pertinent variables. Sonication is accomplished through the use of piezoelectric ceramics, other ultrasonic ceramic devices, or other similar devices45.

Mixing continues until the blended content achieves a desired consistency or optimal physical characteristics. After mixing is complete the mixing13and flexible10compartments are inverted as a unit to allow the blended contents to flow from the mixing chamber13to the flexible compartment10. The finished blended content is then released by gravity or by force through an opening31in the flexible compartment10. A piston device25forces the mixed contents, which do not flow out on their own by gravity when the unit is inverted, out of the mixing chamber13and into the flexible compartment10. In an alternative version the mixing chamber13is flexible as well as the flexible compartment10allowing for manual squeezing of the entire device, eliminating the need for the piston like device25.

The mixed contents are then forced out of the opening31for use. A dispensing attachment30is connected to the flexible compartment10opposite the mixing chamber13. Other additional attachments35may be connected to the dispensing attachment30or the dispensing attachment30may be used individually. Additional attachments35include, but are not limited to, long cylindrical tubes used for application of bone cement into a medullary cavity for hip replacements.

FIG. 2is a schematic of an alternative embodiment of a mixing device50. Powdered polymer is moved70from a powdered polymer source65to a powdered polymer passage60near the base of the mixing device50. Liquid monomer is moved85from a liquid monomer source80to a liquid monomer passage75near the base of the mixing device50. Small amounts of liquid monomer and powdered polymer are brought together and sonicated at a blending area55at ends of the powdered polymer passage60and liquid monomer passage75. The blending area55is preferably, but not limited to, a Y-shaped device or tube. The arms of the Y-shaped device55extend downward away from the base of the mixing device50and are both the powdered polymer passage60and liquid monomer passage75or opposite arms of the Y-shaped device55are connected to the powdered polymer passage60and liquid monomer passage75. A stem section57of the blending area55passes through a base59of the mixing device50. An opening135on the top of the stem section57opens into a mixing chamber90.

The mixing and dispensing chamber90receives the blended contents from the blending area55. Vacuum suction draws the powdered polymer from the powdered polymer source65through the powdered polymer passage60and liquid monomer from the liquid monomer source80through the liquid monomer passage75. Both the powdered polymer and liquid monomer are then drawn into the blending area55. The vacuum suction then draws the blended contents into the mixing and dispensing chamber90. The blended contents experience continued mixing until the blended contents are ready to use.

A sonicator95is in contact with the blending area55and mixing chamber90. The sonicator95is powered by a power source100connected101to the sonicator95. Sonication occurs in the blending region55and in the mixing chamber90. A control device103may be connected107to the sonicator95for sensing and automation.

A vacuum pump105is connected120to the mixing chamber90by tubing or a tube-like device110. The tubing or tube-like device has an opening125on the end furthest from the vacuum pump105, which allows vacuum pumping of the mixing chamber90and the connected powdered polymer source65and liquid monomer source80. The blended contents are held in the mixing chamber90, under vacuum, until the blended contents are ready for release and use.

To release the blended contents from the mixing chamber90, a piston-like device130is used to push the blended contents out of the mixing chamber90. The blended contents are released through the opening135in the blending region55. The powdered polymer passage60and liquid monomer passage75may be removed prior to release. Attachments140,145may be connected to the opening135before releasing the blended contents. The attachments140,145facilitate specific uses of the final product. A conical attachment140or a long cylindrical attachment145may be used. The long cylindrical attachment145may be used to facilitate dispensing bone cement into a medullary cavity in hip replacements.

The present invention is not limited to uses for bone cement or related products. Other uses in other fields are anticipated for the device and process of the present invention. The device and process of the present invention may be used for creating mixtures of many different liquid and powdered materials.

An electronic component controls one or more of the mixing parameters such as the amplitude, frequency and duration of vibration and/or sonication, duration of overall mixing, and durations and timing of mixing steps as well as the rate of flow of the components to be mixed and degree and duration of vacuum application, and other atmospheric conditions such as temperature. This produces a repeatable and consistent quality of the product and minimizes manual handling of the mixing system.