Springy Polypropylene: A Novel Elastomeric Biomaterial

Abstract

Abstract Polypropylene has been fabricated into a different molecular morphology which shows the usual stiffness and high strength indigenous to this polymer, but which also exhibits surprising elastic behavior. Fibers and films in this form are extensible to several hundred percent without rupture and yet show nearly complete recovery to their original length when the force is removed. No other biomaterial which is in present use has such a unique set of mechanical properties. This study has identified the nature and extent of the unusual springy behaviour; the stress-strain, recovery, and cyclic loading properties are now well documented. A stress-softening occurs as the result of the amount of the initial deformation: this means the fibers may be conditioned in order to produce a surprisingly wide spectrum of stiffnesses. Once exercised, the deformation is quite reproducible. Initial fatigue behavior is commendable, on a par with nylon tire yarn fibers. No change in properties has resulted from either long-term conditioning in physiological saline solution or sterilization by autoclaving. Since polypropylene is already an approved biomaterial, it is not surprising that the new and different arrangement of molecules has not elicited an undesirable response in either tissue culture studies or rabbit intramuscular implantation evaluations. Because of the variation possible in the unusual properties of springy polypropylene in the fiber form, a unique opportunity is at hand to design new prostheses to match more perfectly the replaced components.