Medical device formed of ultrahigh molecular weight polyolefin

Medical devices having at least a component, such as a catheter balloon, stent cover and vascular graft, formed of ultrahigh molecular weight polyolefin, such as ultrahigh molecular weight polyethylene. The device component is formed from ultrahigh molecular weight polyethylene that has been processed so that it is microporous and has an oriented node and fibril structure. The device component expands compliantly at low strains and are substantially less compliant at higher strains. The invention also comprises methods for making such medical devices, including the steps of compacting a polyethylene powder and deforming it to impart the oriented structure.