Irradiated stent coating

[0035]In still a further another and/or alternative feature of the present invention, the amount of biological agent that can be loaded on the polymer/copolymer is dependant on the structure of the polymer/copolymer. For biological agents that are cationic, the concentration of biological agent that can be loaded on the polymer/copolymer is a function of the concentration of anionic groups in the polymer/copolymer. Alternatively, for biological agents that are anionic, the concentration of biological agent that can be loaded on the polymer/copolymer is a function of the concentration of cationic groups (e.g. amine groups and the like) in the polymer/copolymer. For instance, when the biological agent is such as, but not limited to, Tripidil, the maximum concentration of Tripidil that can be loaded on to the polymer/copolymer is dependent on the concentration of anionic groups (i.e. carboxylate groups, phosphate groups, sulfate groups, and/or other organic anion groups) in the polymer/copolymer, and the fraction of these anionic groups that can ionically bind the cationic form of Tripidil. As a result, the concentration of biological agent bound to the polymer/copolymer can be varied by controlling the amount of hydrophobic and hydrophilic monomer in the polymer/copolymer, by controlling the efficiency of salt formation between the biological agent, and/or the anionic/cationic groups in the polymer/copolymer. Loading levels of the biological agent in the polymer/copolymer can be from zero to about 90 percent on a weight by weight basis. Therefore, the chemical properties of the biological agent typically dictates the type of polymer/copolymer to be used so as to deliver the desired levels of biological agent into a body cavity to achieve a desired biological response.

[0036]Yet a further another and/or alternative feature of the present invention is that the stent is at least partially coated and/or impregnated with one or more coating compounds that includes one or more biological agents, wherein the one or more coating compounds are cross-linked to alter the rate of release of the one or more biological agents into the body passageway or other body parts. It has been discovered that by causing the one or more coating compounds to cross-link after being at least partially coated and/or impregnated onto the stent, the rate at which the one or more biological agents disassociates from the stent and migrates into the body passageway can be controlled. As can be appreciated, the cross-linking of the encapsulated biological agents can be used to alter the rate of release of the one or more biological agents into the body passageway or other body parts. The cross-linking can be instituted by a number to techniques including, but not limited to, using catalysts, using radiation, using heat, and/or the like. In one embodiment, the coating compound is exposed to radiation to cause one or more cross-links to be formed. The radiation can include, but is not limited to, gamma radiation, beta radiation and/or e-beam radiation. When the polymer is exposed to radiation, one or more hydrogen radicals are removed from the polymer and/or copolymer chain. The removal of the hydrogen radical causes the polymer and/or copolymer chain to cross-link with another portion of the polymer and/or copolymer chain or cross-link with a different polymer and/or copolymer. The cross-linking effect results in the salt of the biological agents to become partially or fully entrapped within the cross-linked coating. The entrapped biological agent takes longer to release itself from the cross-linked coating compound and to pass into the body passageway. As

These failures typically require the procedure to be repeated.

The first generation of expandable stents did not offer a controllable radial expansion.

However, prior art stents still do not provide control over the final, expanded configuration of the stent.

Consequently, once the foregoing types of intraluminal stents were expanded at the desired location within a body passageway, the expanded size of the stent could not be increased.

However, these stents have several shortcomings which contribute to procedural failure rates.

The currently used stents are not readily visible under fluoroscopic guidance procedures.

Stent placement is hindered as a result of poor visibility.

As a result, precise positioning of the stent during the insertion procedure was difficult to achieve.

Consequently, the stent could be inadvertently positioned in the wrong or non-optimal location in the body passageway.

These stents also shorten longitudinally after radial expansion, which is not desirable for their intended use.

The shortening of the stent resulted in longitudinal movement of the stent during expansion, which sometimes resulted in the stent being fully expanded in the wrong or non-optional position.

The bending, buckling or twisting of the ribs can only be avoided if the struts are made of a very flexible or bendable material; however, the use of such material compromises the strength of the stent.

Not only does the stent not retain its longitudinal length, the complex stent design is both difficult to manufacture and uniformly expand in a body passageway.

Although the improved stent overcomes the deficiencies of prior art stents with respect to accurate stent positioning, problems can still exist with respect to tissue damage