The patent's assignee is
News editors obtained the following quote from the background information supplied by the inventors: "Prosthetic heart valves with flexible leaflets, including those supported by a stent structure, are well known in the art. A variety of such prostheses are known for correcting problems associated with the cardiovascular system and in particular the heart. Therefore, the ability to replace or repair diseased heart valves with prosthetic devices has become a well-used method for treating heart valve deficiencies due to disease and congenital defects.
"Prosthetic heart valve leaflets thus perform the function of opening and closing to regulate blood flow through the valve. These heart valve leaflets must therefore typically either pivot or flex with each cycle of the heart to open and close. The prostheses themselves have been constructed from natural materials such as tissues, synthetic materials, or combinations thereof. Prostheses formed from purely synthetic materials can, for example, be manufactured from biocompatible metals, ceramics, carbon materials, and polymers. In these cases, the leaflets can be either rigid or flexible in various embodiments.
"Those heart valve prostheses which include flexible leaflets can be made from tissue leaflets or polymer leaflets. The use of polymer leaflets has become more desirable, particularly in accordance with the search for durable and stable leaflet performance over a number of years of use.
"According to U.S. Pat. No. 6,953,332 ('the '332 Patent') and U.S. Pat. No. 7,682,389 ('the '389 Patent'), dip coating methods and mandrels are used to form these polymer leaflets and valve prostheses. Such a mandrel is shown, for example FIG. 1 hereof, which corresponds to FIG. 8 of the '332 Patent, including an upper surface 314 and a number of contours 310 which correspond to the number of valve leaflets desired. The dip coating process disclosed in the '332 and '389 Patents is one in which the mandrel itself defines the leaflet profile or shape, and after the dipping process takes place, it is generally necessary to then conduct a trimming step in order to cut the extra polymer off along the free edge of the leaflet on the mandrel (see FIG. 7). This step, in turn, requires a precisely controlled apparatus with a cutting instrument applied to the leaflet and the mandrel. This, in turn, can cause defects on the leaflet at that cutting edge and on the mandrel as well, requiring precisely machined and polished mandrel surfaces which therefore must be abandoned after the trimming step. Indeed, this also restricts the type of materials which can be used for the mandrel itself, since mandrels made of certain materials such as stainless steel would not be suitable to be applied to particular cutting instruments used thereon.
"These leaflets can also be dip-coated inside an associated collapsible stent, such as those in use in connection with trans-catheter aortic valve implantation (see FIG. 6). In this case, the trimming process becomes even more difficult, particularly where the leaflet is inside the cage-like stent, as shown in FIG. 6. Since in the currently used process the leaflet cannot be trimmed inside the strut-surrounded stent, the leaflet must be preformed, trimmed, and then removed from the mandrel, and then bonded to the stent with an additional step before both the polymer of the leaflet and the polymer coated on the stent are fully cured. This therefore results in a weaker bonding force between the leaflet and the stent which cannot satisfy the functional requirements of the valve and which provide for a much more complicated manufacturing process.
"The search has therefore continued for a better manufacturing process for polymer stents, particularly in connection with the mandrel dipping process, and for potential trimming processes within the stent."
As a supplement to the background information on this patent application, NewsRx correspondents also obtained the inventor's summary information for this patent application: "In accordance with the present invention, this and other objects have not been realized by the discovery of a method for providing at least one polymer valve leaflet for a prosthesis comprising providing a mandrel including an outer surface having a plurality of ridges and at least one contoured surface between the plurality of ridges, whereby the at least one contoured surface corresponds to at least one leaflet for the prosthesis, the at least one contoured surface including an upper edge portion corresponding to the upper free edge of the at least one leaflet, the mandrel further including a mandrel extension portion above the upper edge portion including a top surface, and a circumferential gap extending around the mandrel between the upper edge portion of the at least one contoured surface and the mandrel extension portion, dipping the mandrel into a preselected polymer solution for providing the at least one leaflet, removing the mandrel from the predetermined polymer solution, removing the predetermined polymer solution from the area of the circumferential gap, curing the polymer to provide the at least one polymer valve leaflet, and removing the at least one polymer valve leaflet from the mandrel. In a preferred embodiment, the removing of the predetermined polymer solution comprises providing suction or a partial vacuum to the area of the circumferential gap, or in another embodiment applying a stream of gas to the area of the gap. Preferably, the gas comprises nitrogen or air.
"In accordance with one embodiment of the method of the present invention, the at least one contoured surface comprises three contoured surfaces, and the at least one leaflet comprises three leaflets for the prosthesis.
"In accordance with another embodiment of the method of the present invention, the step of removing the predetermined polymer solution from the area of the circumferential gap comprises moving a vacuum tip or a gas pressure tip circumferentially around the gap.
"In accordance with another embodiment of the method of the present invention, the predetermined polymer solution comprises a synthetic polymer or a purified biological polymer. Preferably the synthetic polymer is a flexible polymer material such as polyurethane, polyurethane-silicone copolymer, poly(styrene-b-isobutylene-b-styrene), polydimethyl siloxanes, polytetrafluroethylene, and derivatives and mixtures thereof.
"In accordance with another embodiment of the method of the present invention, the polymer solution includes a solvent, and the polymer solution is solidified by evaporating the solvent. Preferably, dipping of the mandrel into the preselected polymer solution comprises a plurality of dipping steps.
"In accordance with the present invention, a mandrel has been discovered for the molding of a polymer valve leaflet for a prosthesis, the mandrel comprising a body portion including an upper surface having a plurality of ridges, and at least one contoured surface between the plurality of ridges, whereby the at least one contoured surface corresponds to at least one leaflet for the prosthesis, the at least one contoured surface including an upper edge portion corresponding to the upper free edge of the at least one leaflet, the mandrel further comprising a mandrel extension portion disposed above the body portion, and an intermediate circumferential gap extending around the mandrel between the upper edge portion of the at least one contoured surface and the mandrel extension portion. In a preferred embodiment, the circumferential gap includes a gap having a depth of between about 1 and 5 mm, and preferably between about 1 and 2 mm.
"In accordance with another embodiment of the mandrel of the present invention, the at least one contoured surface comprises three contoured surfaces, and the corresponding at least one leaflet comprises three leaflets.
"In accordance with another embodiment of the mandrel of the present invention, the body portion comprises a cylindrical body portion.
BRIEF DESCRIPTION OF THE DRAWINGS
"The present invention can be more fully appreciated with reference to the following detailed description which, in turn, refers to the drawings in which:
"FIG. 1 is a side, elevational view of a dipping mandrel in accordance with the prior art;
"FIG. 2 is a side, perspective view of a heart valve prosthesis with the leaflets in a relaxed state, in which the valve is approximately fully open, as in the prior art;
"FIG. 3 is a side, perspective view of a dipping mandrel in accordance with the present invention;
"FIG. 4 is a front, elevational view of the dipping mandrel shown in FIG. 3;
"FIG. 5 is a top, elevational view of the dipping mandrel shown in FIG. 3;
"FIG. 6 is a side, perspective view of an aortic valve prosthesis with a collapsible stent, as in the prior art; and
"FIG. 7 is a side, perspective view of a valve prosthesis with leaflets in accordance with the prior art, in which extra polymer needs to be trimmed off."
For additional information on this patent application, see: Li, XueMei. Dipping Mandrel with a Gap. Filed
Keywords for this news article include: Aortic Valve, Heart Valves, Legal Issues,
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