Originally Published EMDM September 2002
INDUSTRY NEWS
Biodegradable Shape-Memory Polymers DevelopedThere are several alloys with shape-memory capabilities, but only nickel-titanium is biocompatible. Consequently, nitinol, as it is commonly known, has enjoyed a near monopoly in medical device applications where shape-memory properties are desirable. But competition may be on the way.
Recently developed shape-memory polymers, which exhibit greater deformation capabilities and easier shaping procedures at a lower cost, already show considerable promise as alternative materials. Now comes word that researchers have added biodegradability to the recipe, potentially opening up new areas of application. A paper on this topic authored by Andreas Lendlein, director of mnemoScience (Aachen, Germany), and Robert Langer, professor of chemical engineering at Massachusetts Institute of Technology (Cambridge, MA, USA) and a partner in the firm, was published on-line by Science magazine.
Programming shape-memory properties into nitinol is a delicate process. A minute change in the percentage of the nickel composition can engender a shift of several degrees in the material's transformation temperature. Moreover, its transition temperature and mechanical properties can be affected by oxygen, carbon, nitrogen, or other contaminants. Processing nitinol is a time-consuming and exacting task that, in the end, produces a material with a maximum deformation of about 8%.
By contrast, biodegradable shape-memory polymers can be programmed in seconds, according to Lendlein, and they can achieve deformations of several hundred percent, "even 1000% in some cases." The transition temperatures and mechanical properties can be altered with minor changes to the polymer's chemical structure and composition, he adds. In their paper, Lendlein and Langer cited the development of a degradable suture to illustrate the material's biomedical applications.
"When using minimally invasive techniques, it is very difficult to perform complex mechanical operations within a confined space," says Lendlein. "One of the most difficult tasks in this regard is knotting the suture. Using biodegradable shape-memory polymers, we have found a way to facilitate this process." In the paper, the authors describe the design of a smart surgical suture whose temporary shape is obtained by elongating the fibre with controlled stress. The suture can be loosely applied in its temporary shape; it reverts to its permanent shape when exposed to its transition temperature. The suture has been tested four times on two different animals.
"For these tests, the fibres were elongated by 200% during programming and were able to generate a force of 1.6 N upon actuating the shape-memory effect in vitro," write Lendlein and Langer. The feasibility study, they conclude, suggests that this material has the potential to reshape the way in which implants are designed, and could lead to new surgical procedures.
The paper is available at www.sciencexpress.org. For more information about mnemoScience, contact the company at Pauwelsstr. 19, D-52074 Aachen, Germany; phone: +49 241 9632250; fax: +49 241 9632258; e-mail: a.mock@mnemoscience.de; Internet: www.mnemoscience.de.
Copyright ©2002 European Medical Device Manufacturer
