Vented implantable drug-delivery device and related methods
An implantable device has an outer shell that includes an aperture through the housing of the device and, spanning the aperture, a membrane structure permeable to gas but not to liquid. In this way, excess gas may be vented from the device. The membrane and aperture are designed to discourage or even prevent tissue ingrowth.
1. An implantable device for administering a liquid, the device comprising:
a housing including an aperture therethrough;
within the housing, a pump assembly including a reservoir, a gas-driven forcing mechanism and a cannula for conducting liquid from the reservoir to an ejection site exterior to the housing in response to pressure applied by the forcing mechanism, wherein at least a portion of gas generated by the gas-driven forcing mechanism penetrates the reservoir and accumulates in a space between the reservoir and the housing; and
external to the pumping assembly but within the housing and spanning the aperture, a membrane structure comprising a gas-permeable membrane and at least one support layer attached thereto, the membrane structure being permeable to gas but not to liquid at least within an area thereof exposed by the aperture so as to allow the gas accumulated in the space between the reservoir and the housing to vent out through the gas-permeable membrane and the aperture;
wherein the space between the reservoir and the housing is isolated from the liquid as it passes through the cannula.
2. The device of claim 1 , wherein the membrane structure, at least within the area thereof exposed by the aperture, has a pore size sufficiently small to prevent tissue ingrowth and endotheliazation.
3. The device of claim 1 , wherein the membrane structure has a pore size that allows gas to flow therethrough at a sufficient rate to substantially offset a positive pressure or vacuum pressure applied to the device.
4. The device of claim 1 , wherein the membrane structure is biocompatible.
5. The device of claim 1 , wherein at least the area of the membrane structure exposed by the aperture comprises an oleophobic coating thereover.
6. The device of claim 1 , wherein the membrane structure comprises ePTFE.
7. The device of claim 1 , wherein the at least one support layer is perforated.
8. The device of claim 7 , wherein the at least one support layer is perforated with clusters of holes each having a diameter in the range of 50-400 μm.
9. The device of claim 1 , wherein the at least one support layer is substantially rigid.
10. The device of claim 1 , wherein the membrane structure has a surface, at least a portion of which comprises an adhesive material for affixation to an interior surface of the housing.
11. The device of claim 1 , wherein a portion of the membrane structure is bonded to an interior surface of the housing with an epoxy.
12. The device of claim 1 , wherein the at least one support layer comprises at least one of polypropylene, polyethylene, polyvinylidene fluoride, poly(methyl methacrylate), or polyether ether ketone.
13. The device of claim 1 , wherein the at least one support layer comprises or consists essentially of a spunbond fabric, a woven fabric, an extruded film, a cast film, a blown film or an injection-molded film.
14. The device of claim 1 , wherein the membrane structure has a thickness less than 500 μm.
15. The device of claim 1 , further comprising a refill port, wherein the gas-permeable membrane is located at the refill port for venting the gas and thereby creating a vacuum pressure for promoting refilling.