Originally Published EMDM January/February 2005
Technology News
Joining Technology May Help Increase Strength of Medical ProsthesesCaitlin Cook
A recently developed joining technology could have exciting implications for manufacturers of medical implants. The Surfi-Sculpt process from UK-based TWI Ltd. (Cambridge, UK) can be used to sculpt minute shapes onto metal surfaces. The subsequent formation of strong bonds may result in less-brittle knee and hip joints.
The method uses an E-beam to grow protrusions from the molten surface of a material. Each protrusion leaves a corresponding intrusion in the bulk of the material. Software developed by the company allows the intrusions to be created in controlled arrangements. Their physical parameters can be modified with precision.
As the E-beam moves across the material’s surface, it creates a small pool of molten metal in a track, or ‘swipe.’ The E-beam heats the material rapidly at the point of interaction, which cools as the beam moves away. The surface tension of the cooling areas of the swipe is greater than that of the area most recently heated. As the molten metal vapourizes, it creates a pocket of pressurized vapour above the swipe at the point of action of the beam. The hotter, molten material is sucked back to the beginning of the swipe by the rising surface tensions behind the beam.
Such swipes may be repeated or overlapped several times. Each time, more material is displaced. After several passes of the E-beam, a protrusion begins to rise out of the swipe path.
The E-beam size and the number and pattern of passes define the height and width of each protrusion and hole. TWI has worked with Surfi-Sculpt on a range of metals, including titanium, aluminium, and stainless steel. While the physical limits of the process are still under investigation, protrusions approximately 2 mm high and 200 µm wide have been successfully produced.
Medical prostheses, such as hip and knee joints, stand to benefit from this process because it has the potential to create tougher, less-brittle joints than those formed by other methods. The Surfi-Sculpt protrusions and intrusions are arranged such that bone can grow into the surface of the metal joint. Thus, a bond of greater strength and permanency can be achieved than by means of an adhesive alone.
Copyright ©2005 European Medical Device Manufacturer
