Patent Application
20110020168
1. Field of the Invention
The present invention relates to fabrication of implants, more particularly, to fabrication of porous metal-based biomaterial for implant dentistry and bone scaffold by microwave sintering.
2. Description of the Related Art
Over the years, a variety of metals have been used as raw materials for dental or bone implants until titanium was discovered having the inherent properties of osseointegration. As a result, titanium becomes one of the most common metals for dental implants because it displays high strength, excellent corrosion resistance and high strength-to-weight ratio. Today, titanium alloy has been widely used to create dental and orthopedic implants because of its excellent biocompatibility and mechanical properties. Most implants made of titanium alloy are fabricated via conventional powder metallurgy or melting production method.
In addition, with development of implant technology, more materials are found having chemical and biological properties that promote osseointegration, such as hydroxyapatite (HA). Hydroxyapatite is a natural and cost-effective candidate for dental implants due to its biocompatibility and its ability to support the growth of new bone tissue. Furthermore, the human bone is a composite of fibrous protein, collagen, and about 65 wt % of HA. Long-term clinical studies show that HA-coated titanium dental implants have excellent bioactivity.
Another commonly used method to improve the osseintegration of the metal-based implant to surrounding bone is through incorporation of a porous metal surface layer to the surface of the metal implants. This is done to improve the fixation of the implant to bone through in-growth of bone tissues into the porous layer. A common technique for coating a porous surface on the implant is plasma spraying technique, which is used for producing coatings and free-standing parts using a plasma jet. Then, the surface can be chemically etched or sandblasted to increase the surface area and the integration potential of the implant. However, there is a possibility that the coating surface may be loosen or detached from the metal implant.
Another shortcoming of the porous coating, as discussed in U.S. Pat. No. 7,291,012, is that porous surfaces are often a thin coating applied on a metal substrate of the implant. As such, bone surrounding the implant can only grow into the coating layer itself. The surrounding bone cannot grow through the coating and into the metal substrate. The depth of bone growth into the implant is limited to the depth of the porous coating.
While efforts have been made to produce metal-based implants with surface metal porosity, less effort has been made to create porous metal-based biomaterials for production of porous implants. It is therefore an objective of the invention to overcome the shortcomings of the conventional methods by providing a method for rapid fabrication of porous metal-based biomaterial that is lightweight, biocompatible, cost-effective and easy to produce. By taking advantage of the fast processing time of microwave sintering, the biological properties of the sintered compact can be preserved. Also, it is desirable to integrate biomaterial (e.g., HA) into the porous metal-based implant without having to provide a separate coating of a biomaterial.
According to an aspect of the present invention, a method of fabricating a porous metal-based biomaterial includes dispersing microwave susceptors with organic solvent to form a homogeneous suspension, dispersing bioactive fillers with organic solvent to form a homogeneous solution, mixing metal powder with the homogeneous solution and the homogeneous suspension to form a mixture, cold-pressing the mixture into a compact with predefined shape and size, and placing the compact in a sintering container and emitting microwave to sinter the compact.
According to another aspect of the present invention, a system for fabricating a porous metal-based biomaterial, includes a mixer adapted to mix metal powder, microwave susceptors, and bioactive fillers with organic solvent to form a compact, a molding unit adapted to mold the compact in a predetermined size and shape, and a sintering container adapted to hold the compact and sinter the compact by microwave radiation.
Further features and aspects of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
The present invention utilizes microwave energy to provide rapid fabrication of a porous metal-based biomaterial. Microwave technology has been widely used in various applications such as food processing, communication, and calcinations. Microwaves are electromagnetic waves with frequencies typically between 0.3 GHz and 300 GHz. There are some factors constraining the choice of the frequencies used in industrial or commercial microwave equipment. Hence, several frequencies are available for industrial, scientific or medical (ISM) application such as 434 MHz, 915 MHz and 2.45 GHz.
Microwave energy has been widely used in heating ceramic materials to a relatively high temperature that is suitable for sintering. In recent years, microwave sintering technology for metallic materials has been developed. For example, U.S. Pat. No. 5,227,600 discloses a method for producing articles of alumina and alumina silicon carbide using microwave radiation.
In
Then, cold pressing is performed onto the mixture of titanium powder 201, the dispersed microwave susceptors in organic solvent 130 and hydroxyapatite powder 160 using a molding unit (not shown) to create a desire shape and size. As shown in
The microwave container 300 is made of an insulation material that does not absorb microwave radiation. The compact 303 is placed on the insulation unit 300 via an opening of the microwave container. Removable plate 305 is adapted to support the compact as well as to serve as a heat insulator between the compact and the base part of microwave container 300. The removable plate 305 may be capable of rotating during the emission of microwave. Removable plate 305 should be made from a material that is transparent to microwaves so that it does not heat to a significant degree by microwave radiation. Then, microwave radiation is emitted to the compact 303 to perform microwave sintering. Removable plate 305 is made from a high temperature-resistant material with high microwave transparency. It should be capable of withstanding localized high heat emitted from sintering articles to prevent from damaging the sintering container 300.
When performing microwave sintering in the power range of 500 W-1000 W in the case of titanium powder, which has a melting point at about 1725° C., the compact is heated for 30 seconds to 5 minutes. The frequency of microwave emission is fixed at about 2.45 GHz. As discussed previously, the microwave susceptors convert the electromagnetic energy into thermal energy. During the sintering process, portions of the microwave susceptors are burned off from the heat generated. As a result, a porous metal-based biomaterial is created. By controlling the amount of concentration of the microwave susceptors and other processing parameters, the degree of porosity in the biomaterial can be controlled. In addition, since microwave sintering only take less than a few minutes to complete, the decomposition of HA will be minimized.
Next, after most of the ethanol in the mixture is evaporated, cold pressing (S504) is then performed on the mixture to create a compact by using a molding unit with a predefined shape and size. Thereafter, the compact is placed in the microwave sintering container (S505). In next step S506, microwave sintering of the compact is performed.
The invention presents a method to produce a metal-based material with porous structure. Processing duration and cost is significantly reduced by using microwave as the energy source. For instance, the present microwave sintering process only takes several minutes to complete with the aid of a carbonic substance as a susceptor agent. By properly modulating processing conditions and controlling the composition, metal-based biomaterial with various porosity can be achieved. Furthermore, the present microwave sintering technique is suitable for batch production as well as patient-specific fabrication of implant structures without investment of expensive apparatus. In addition, a special feature of the invention is the inclusion of bioactive agent in the material while bioactive agent is usually coated on the surface of the conventional biomaterials used for dental implants.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded to the broadest interpretation so as to encompass all modifications and equivalent structures and functions.
