Metal injection moulding for the production of medical implants

Abstract

An improved method for manufacturing medical implants, and particularly spinal implants, utilizing a metal injection moulding technique (MIM) is provided. The invention is generally directed to the manufacture of implants for complete insertion within the body of a patient. A special set of mechanical, physiological and legal requirements are associated with such medical implants. For example, in contrast with dental implants, such medical implants are not readily observable or removable meaning that they must be significantly more physically resilient. In addition, physiologically, such medical implants must be capable of full integration with the body. Finally, regulatory requirements provide for significantly stricter controls over such fully implanted medical devices.

Description

FIELD OF THE INVENTION [0001] The present invention is concerned with a method of manufacture medical implants. It is especially concerned with a method and material suited for some spinal implants. BACKGROUND OF THE INVENTION [0002] The traditional process for producing metal objects is to make a casting or machine the piece from a solid block of material. There are three methods: the sand casting method, the lost wax method, and machining. The sand casting method dates back to antiquity and is done by making a model, imprinting the model on two blocks of sand, removing the model, and then pouring the molten metal in between the two sand shapes. When the model has cooled, it is taken from the mould and it is then deburred, polished, and finished. The lost-wax method uses a wax replica of the item to be constructed, and into which the molten metal is poured. This method is more accurate because when the molten metal is introduced into the wax replica, the wax liquefies and is pushed...

AI Technical Summary

Problems solved by technology

Moreover, both methods inherently lead to inaccuracies.

In the sand mould method, the very fact that sand is used leads to many rough features that require a lot of extensive secondary steps to correct.

Meanwhile, in the lost-wax method the differential cooling of the poured metal model leads to shrinking and deformity of the product.

Finally, both the sand mould and lost-wax methods are inherently expensive because of the large number of individual machining steps necessary and the lack of uniformity in the case pieces.

However, implantation parts must withstand high strains over a very long life, without the benefit of regular inspection or the hope of easy replacement, and parts made from these casting methods are subject to breakage during use due to defective casting, especially due to the formation of casting pockets or metallurgical impurities, such as sulfide residues in stainless steel casting.

In addition, the creation of complicated shapes is difficult in casting due to the problem of running liquid.

For example, the shape of a screw or cage component for an implant, is too complicated to be produced exactly as designed.

On the other hand, the additional mechanical processing required by these casting methods, such as cutting and deburring, cause difficulties in processing materials with a high level of hardness, especially titanium materials that have poor machine processability, resulting in products with poor precision.

For example, the screw component of an implant must usually be mechanically fabricated because it cannot be produced satisfactorily by casting.

Poor precision in the screw component can allow cause a number of mechanical deficiencies and subsequent medical problems.

However, there are some technical limitations in the metal injection moulding field.

The technology is very applicable to shapes of high complexity, but the complex shapes are limited in weight to approximately 30 to 35 g, and in wall thickness of up to 10 mm, limiting its adoption in a number of specific fields.

Images