BRIEF DESCRIPTION OF THE DRAWINGS
The present disclosure is explained in greater detail in the following on the basis of exemplary embodiments and the associated drawings.
FIG. 1A shows a schematic view of a detail of a stent according to a first exemplary embodiment of the present invention;
FIG. 1B shows another schematic view of a detail of the stent of FIG. 1A;
FIG. 2A shows a schematic view of a second exemplary embodiment of the present invention; and
FIG. 2B shows another schematic view of the stent of FIG. 2A.
DETAILED DESCRIPTION
FIG. 1A shows a detail of the structure of a first exemplary embodiment of a stent in the unexpanded state and FIG. 1B shows the same detail after expansion of the stent. The stent may be molded, for example, from the biocorrodible magnesium alloy WE43 (93 wt.-% magnesium, 4 wt.-% yttrium (W), and 3 wt.-% rare earth metals (E) except for yttrium). The structure of such a stent comprises multiple web sections connected to one another, which form the carrying structure and other constructive elements of the implant. The structure may, for example, comprise ring elements connected to one another via webs or helical peripheral webs. Web sections may be identified in this structure which are designed to assume a function supporting the vascular wall or preserving the mechanical integrity of the stent for a predefinable period of time after the expansion of the stent. It is assumed that FIGS. 1A and 1B show a detail of the structure which contains the web sections of this carrying structure, a first web section 10 of the carrying structure as a semicircular peripheral webs here. The structure also contains a second web section 12, in the form of a second semicircular web element, having a smaller circumference than the first web section 10.
In the unexpanded state of the stent (FIG. 1A), the electrode potentials of the first and second web sections are assumed to be identical. Upon expansion of the stent, the two web sections 10, 12 are plastically deformed to different degrees, however. Different strengths of change of the electrochemical potential result. The second web section 12 is plastically deformed more strongly and the electrode potential E2 decreases to a greater extent than the electrode potential El of the first web section 10. Accompanying this, the corrosion behavior of the two web sections 10, 12 also changes; the second web section 12 will typically corrode more rapidly, because the second web section 12 is now baser. Because the first and second web sections 10, 12 are electrically connected to one another, however, corrosion processes will also occur which result in an acceleration of the corrosion of the second web section 12 and an inhibition/slowing of the corrosion on the first web section 10 in the meaning of a sacrificial anode system. The potential difference between the two web sections 10, 12 thus causes the first web section 10 to be temporarily stabilized, specifically until the second web section 12 is completely or extensively degraded. Therefore, the first web section 10 may assume its function in the carrying structure longer.
FIGS. 2A and 2B show a second exemplary embodiment showing the first and second web sections 10, 12. The mode of operation corresponds to the first exemplary embodiment, so reference is made to the preceding statements. The first web section 10 is defined here as a part of the carrying structure which lies between the two connection points of the second web section 12. The second web section 12 is plastically deformed most strongly upon the expansion of the stent and may be used as a sacrificial anode for the first web section 10 according to the prior statements, so that the corrosion rate is temporarily inhibited.
In these two exemplary embodiments, mechanical strains of different strengths are generated in various areas of the stent structure at the instant of dilation because of the construction, namely at the first and second web sections 10, 12 shown. The second web section 12, which was subjected to a higher mechanical strain, has a lower electrode potential E2 after the dilation than the first web section 10, which is electrically connected thereto, and therefore acts as a sacrificial anode. The degradation of the first web section 10 is thus temporarily inhibited.
It is also conceivable to generate mechanical pre-tensions in the areas of the stent structure (i.e., in the second web section 12), which are less strongly strained during dilation (e.g., areas pressing relatively flat against the vascular wall), already at the time of the production by pressing the stent into a suitable shape.
All patents, patent applications and publications referred to herein are incorporated by reference in their entirety.
Patent Application
20080033535
