| The possibility of designing and building medical devices out of shape memory polymers (SMPs) has attracted several researchers. These generally biocompatible polymers lend themselves to several designs, particularly for minimally invasive surgery. The aim of this work was to improve the mechanical and thermomechanical properties of one SMP that is used in a number of investigational devices in the Polymeric Biomaterials lab at the University of Colorado at Boulder. The polymer in this study typifies many SMPs in that it has complete shape fixity when held below its glass transition temperature (T g), it has full shape recovery when heated to near or above Tg, and it is comprised of monomers that facilitate the adjustment of its Tg. This combination of properties makes it an attractive candidate material for several different endolumenal stent designs. Early prototypes made of neat polymer without any reinforcement worked well, but manufacturing was hampered by some qualities inherent to the polymer, namely low resistance to tearing, and relatively low tensile strength. For applications where the design will be required to produce significant force (e.g. radial force requirements for an endolumenal stent), the ability to adjust the rubbery storage modulus could allow thinner designs to be used.;Thus, the goals for this work were to improve the tear resistance, tensile strength, and rubbery modulus of the neat polymer while not impacting the fully functional thermomechanical properties. With improvement to these properties, this polymer would be an obvious choice for stent designs, particularly in a material that is capable of the usual benefits inherent to polymeric medical devices, i.e. ability to serve as a large reservoir for elutable drugs, low cost and ease of manufacturing.;By making a composite material out of this SMP matrix reinforced with different lengths (150 mum, 790 mum, 3175 mum) of Type E fiberglass, it was found that all of the above beneficial properties of polymers could be maintained without effecting shape memory and significantly increasing the tear resistance, tensile strength and rubbery modulus. This composite, with these enhanced properties proved advantageous in the production of a prototype SMP composite stent device that proved unmanufacturable when made of unreinforced polymer. |
