Laser-Deposited Coating Imparts Bone-Like Attributes to Implants

Purdue mechanical engineering doctoral student Shaoyi Wen (left) and technician Andrew Hecht review data using a laser deposition system. The system works by depositing layers of a powdered mixture of metal and ceramic materials, melting the powder with a laser and then immediately solidifying each layer to form parts.

Laser-based technologies under development will dramatically accelerate the manufacture of arterial stents and long-life medical implants while reducing their cost, according to Yung Shin, a Professor of Mechanical Engineering and Director of the Center for Laser-Based Manufacturing at Purdue University in the United States.

One technique involves depositing layers of a powdered mixture of metal and ceramic materials, melting the powder with a laser and then immediately solidifying each layer to form parts. The technique is suited for coating titanium implants with ceramic materials that mimic the characteristics of natural bone, says Shin. “Titanium and other metals do not match either the stiffness or the nature of bones, so you have to coat them with something that does. However, if you deposit ceramic on metal, you don’t want there to be an abrupt change of materials, because that causes differences in thermal expansion and chemical composition, which results in cracks,” explains Shin. One way to correct this is to change the composition gradually, creating a functionally gradient coating, so you don’t have a sharp boundary.

Researchers used laser deposition processes to create a porous titanium-based surface as well as a calcium phosphate outer surface. Both were designed to better match the stiffness of bone than conventional implants.

The laser deposition process also enables the fabrication of patient-specific parts with complex shapes. ”Medical imaging scans could just be sent to the laboratory, where the laser deposition would create the part from the images,” Shin says. “Instead of taking 30 days like it does now, we could do it in three days.” The laser deposition technique creates a strong bond between the material being deposited and the underlying titanium, steel or chromium. Tests show that the bond is at least seven times as strong as industry standards require, he notes.

The researchers use computational modeling to simulate, study and optimise the processes. Additional research is needed before the techniques are ready for commercialisation. Future work will involve studying shape-memory materials that are similar to bone and also have a self-healing capability for longer-lasting implants.

The researchers also are developing a technique that uses an ultrashort-pulse laser to create arterial stents. Because the pulses are so fleeting, the laser does not cause heat damage to the foil-thin stainless steel and titanium material used to make the stents. The laser removes material in precise patterns by means of cold ablation, which turns solids into a plasma. The patterns enable the stents to expand properly after being inserted into a blood vessel.

The work is funded by the National Science Foundation.

Tags: implant coating, laser deposition, Purdue, stent