A filter assembly includes a plurality of leg elements in two sets which have a generally conical form and are held together at a coupling element or hub. Disposed by the hub is a biodegradable fastener element into which proximal ends of the leg elements are embedded. The fastener element is substantially rigid and has the effect of reducing the lengths (L2, L3) of the legs of the leg elements which is able to flex, contributing to the generation of a greater radial force by the filter assembly. The fastener element will degrade over a given period, such as two to three weeks, thereby allowing flexing of the proximal ends of the leg elements embedded within the fastener element, resulting in an increase in the length of the leg elements able to flex and as a consequence a reduction in the radial force generated against the vessel wall.
