Catheter tubing of controlled in vivo softening

DETAILED DESCRIPTION A catheter tubing comprises a stripe or layer of a thermoplastic hydrophobic stiffening polymer encapsulated by a thermoplastic hydrophilic polyurethane base polymer.
Preferred stiffening polymers are polyesters, preferably polyester-polyether block copolymers and high hard segment polyurethanes.
Preferred base polyurethanes are polyetherurethanes.
The catheter of the invention may be fabricated by coextrusion, and may include a radiopaque agent.
The catheter of the invention retains the inherent softness and biocompatibility of polyurethane catheters, but overcomes the disadvantage of excessive pliability which may cause difficulty in repositioning conventional polyetherurethane catheters after emplacement in a blood vessel.
The degree of stiffening and degree and rate of stiffening may be controlled by the stripe or layer configuration as well as by the composition and amount of the hydrophobic stiffening polymer.
Because the stiffening polymer is completely encapsulated, the blood contacts only the hemocompatible polyurethane surface.
If desired, the catheter having a predetermined balance of stiffness for insertion and repositioning and pliability for threading through a blood vessel may include a radiopaque agent as a visualizing aid in emplacement and/or repositioning.
The thermoplastic nature of both the stiffening and base polymers retains the economy of manufacture realized by conventional catheter design and extrusion processing.