Multi-layer cannula structure

A swelling multilayer cannula having proximal and distal end portions and a wall defining an inner lumen, comprising:

• (a) a hydrophilic layer structure having one or more hydrophilic layers having respective outer and inner surfaces and being formulated of a hydrophilic material characterized in that it increases in volume more than 1.3:1 upon contact with an aqueous medium at 37.degree. C., said hydrophilic layer structure comprising at least 1/2rds of the cross-sectional area of said wall, said inner lumen swelling such that its cross-sectional area increases more than 20% upon contact of said hydrophilic layer structure with said aqueous medium at 37.degree. C.;
• (b) a substantially non-hydrophilic layer structure having one or more substantially non-hydrophilic layers having respective outer and inner surfaces and being formulated of a substantially non-hydrophilic material, an outer or inner surface of each of said hydrophilic layers being bonded to a corresponding inner or outer surface of at least one of said substantially non-hydrophilic layers, said bonded hydrophilic and substantially non-hydrophilic layers being of a construction such that they remain bonded to one another following swelling of said lumen such that its cross-sectional area increases more than 20% upon contact of said hydrophilic layer structure with said aqueous medium at 37.degree. C.;
• and
• wherein an innermost of said hydrophilic and substantially non-hydrophilic layers is a first of said substantially hydrophilic layers and defines said lumen, wherein a first of said substantially non-hydrophilic layers has its inner surface bonded to the outer surface of said first substantially hydrophilic layer and wherein a second of said hydrophilic layers has its inner surface bonded to the outer surface of said first substantially non-hydrophilic layer.

A swelling multilayer cannula having proximal and distal end portions and a wall defining an inner lumen, comprising:

• (a) a hydrophilic layer structure having one or more hydrophilic layers having respective outer and inner surfaces and being formulated of a hydrophilic material characterized in that it increases in volume more than 1.3:1 upon contact with an aqueous medium at 37.degree. C., said hydrophilic layer structure comprising at least 2/3rds of the crosssectional area of said wall, said inner lumen swelling such that its cross-sectional area increases more than 20% upon contact of said hydrophilic layer structure with said aqueous medium at 37.degree. C.;
• (b) a substantially non-hydrophilic layer structure having one or more substantially non-hydrophilic layers having respective outer and inner surfaces and being formulated of a substantially non-hydrophilic material, an outer or inner surface of each of said hydrophilic layers being bonded to a corresponding inner or outer surface of at least one of said substantially non-hydrophilic layers, said bonded hydrophilic and substantially non-hydrophilic layers being of a construction such that they remain bonded to one another following swelling of said lumen such that its crosssectional area increases more than 20% upon contact of said hydrophilic layer structure with said aqueous medium at 37.degree. C.;
• an innermost of said hydrophilic and substantially non-hydrophilic layers being a first of said substantially non-hydrophilic layers and defining said lumen;
• a first of said hydrophilic layers having its inner surface bonded to the outer surface of said first substantially non-hydrophilic layer;
• and
• wherein said substantially non-hydrophilic layer structure includes a second substantially non-hydrophilic layer having its inner surface bonded to the outer surface of said first hydrophilic layer.