Bioabsorbable self-expanding endolumenal devices

Abstract

The present invention is directed to bioabsorbable self-expanding medical devices for use inside or outside body conduits that self-expand at, or below, normal human body temperature without requisite for a polymeric thermal transition

Description

FIELD OF THE INVENTION [0001] The present invention is directed to implantable medical devices. In particular, the invention is directed to self-expanding bioabsorbable endolumenal devices. BACKGROUND OF THE INVENTION [0002] A variety of implantable medical devices have been developed to treat diseased, injured, or deformed body conduits. In cases where malfunctioning body conduits have reduced inner diameters, there is usually reduced flow of vital fluid or gas through the conduits. In extreme cases, the malfunctioning conduits are occluded. Implantable medical devices used to open and / or expand, or to otherwise treat obstructed or constricted body conduits often reside in the conduits for a period of time following deployment of the devices. The devices serve primarily as mechanical supports inside the malfunctioning conduits to help maintain the conduits in more open, or patent, conditions. [0003] These types of implantable medical devices are usually threaded through a healthy b...

AI Technical Summary

Benefits of technology

[0028] Devices of the present invention are preferentially made of non-blended hydrolyzable co-polymeric materials. These polymers have a combination of an α-hydroxy ester and a soft non-crystallizing segment that imparts added resilience to the device. Possession of an α-hydroxy ester component bestows the device with a predictable hydrolytic rate that accompanies ester functionality. As a result, the hydrolytically controlled degradation is minimally affected by enzymatic activity and is thereby consistent across implant hosts.

[0033] Though sufficiently strong to resist radially compressive forces from tissue in which devices of the present invention are implanted, the devices have a Young's modulus equal to or less than the tissue in which the devices are implanted. Accordingly, tubular devices of the present invention have integral non-elongating frameworks with a Young's tensile modulus of approximately than 2.1×106 Pascals when evaluated longitudinally in an open, uncompressed, and unrestrained (i.e. fully deployed) configuration. Devices of the present invention are very compliant with implanted tissue as a consequence. A multiplicity of fenestrations is provided in the integral framework to further enhance tissue compliance of the devices and permit tissue ingrowth. Tissue ingrowth can further anchor the devices.

[0034] An object of the present invention is to provide a self-expanding, non-elongating, bio-absorbable support for a body conduit that is made of non-blended hydrolyzable polymeric compounds of known composition, mechanical properties, and bio-absorption rates that allow the device to be reliably deployed with conventional delivery means under aqueous conditions at, or below, normal human body temperature without undergoing a thermal transition. The device can be constructed so it is completely absorbed by the implant recipient within one (1) year following implantation.

Problems solved by technology

Of particular concern in leaving a metallic implant in a patient is the negative impact a subsequent procedure may have on the patient as a result of the implanted device.

For example, the strong magnetic field produced by a magnetic resonance imaging (MRI) machine can adversely interact with the metallic implant.

Also, the presence of a chronically implanted device can cause abrasions or erosions to tissue in which the device is implanted.

Additionally, a subsequent endoluminal procedure can also result in an adverse encounter, or interaction, with a previously implanted device.

Unfortunately, when the polymeric material used to make the stent is placed inside a body conduit and raised above its melt temperature to undergo a re-modeling process, any inconsistency or inadequacy in thermal transfer from the heated balloon to the device as it is deployed can cause irregular and potentially unpredictable device deformations.

Consequently, implantable medical devices intended for use as degradable stents or other temporary scaffoldings for a body conduit made of poly(ε-caprolactone), or similar homopolymers that require a thermal softening or melting transition above normal human body temperature in order to expand, are likely to lack sufficient reliable mechanical strength to be practical devices.

The stent is described as expandable using a “thermally-assisted mechanical expansion process at a temperature between about 38 degrees centigrade and 55 degrees centigrade.” Hence, the Healy et al. stent does not expand at normal human body temperature of 37 degrees centigrade and is also described as risking a “potentially hazardous” fracture if expansion is attempted in the brittle and glassy state found below the Tg of the stent.

Devices requiring in situ application of heat above normal human body temperature are problematical at best.

In addition to the possibility of causing patient discomfort in the form of pain with such a procedure, local trauma to same tissue intended to be medically treated with the device is also a possibility.

Furthermore, it is unknown whether such trauma to “lumenal tissue” will stimulate undesirable tissue processes to begin at the implant site, such as a hyperplasia.

While this may be the case, shortening of the stent may not be acceptable in some applications, such as cardiovascular applications.

Excessive shortening (e.g., greater than about ten percent (10%) during deployment can result in deployment inaccuracy and cause intragenic trauma to wall tissue of the body conduit.

While these monomeric components provide a predictable resorption rate by virtue of their hydrolyzable bonds, the monomers contribute only limited amounts of freely rotating aliphatic component into the polymer chain.

In addition to the inherent mechanical weakness conferred on the above-summarized devices by the polymers and processes from which they are formed and deployed, as discussed above, there are dangers inherent in applying heat to implantable devices, particularly endoluminal devices, at the implantation site.

None of the above-summarized stents meet the needs of an implantable medical device for use in a body conduit that is constructed from a non-blended hydrolyzable polymeric material as an integral flexible fenestrated framework that does not substantially change axial length with radial compression and expansion of the stent and is self-expanding at, or below, normal human body temperature without the polymeric material undergoing a thermal transition.

Nor do the devices provide for variable bioabsorption rates in different parts, segments, or portions of the devices.

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