Phosphonated polyurethanes that resist calcification.

Abstract

Cardiovascular implant mineralization involving bioprosthetic materials, such as glutaraldehyde cross linked porcine aortic valves or synthetic materials such as polyurethanes, is an important problem that frequently leads to clinical failure of bioprosthetic heart valves, and complicates long-term experimental artificial heart device implants. Novel, proprietary, calcification resistant polyetherurethanes (PEU) as an alternative to bioprosthetic materials were the subject of these investigations. A series of PEU was derivatized through a proprietary reaction mechanism to achieve covalent binding of 100 to 500 nM/mg of bisphosphonate (2-hydroxyethane bisphosphonic acid, HEBP). The stability of HEBP (physically dispersed or covalently bound) verified by studying the release kinetics in physiological buffer (pH 7.4) at 37 degrees C, demonstrated the covalent binding reaction to be stable, efficient, and permanent. Surface (FTIR-ATR, ESCA, SEM/EDX) and bulk (solubility, GPC) properties demonstrated that the covalent binding of HEBP occurs in the soft segment of the PEU, reduces surface degradation, and does not affect the original material properties of the PEU (prior to derivatization). In vitro calcium diffusion of the derivatized PEU showed a decrease in calcium permeation as the concentration of HEBP covalent binding was increased. In vivo properties of underivatized and derivatized PEU (containing 100 nM of covalently bound HEBP) were studied with rat subdermal implants for 60 days. Explants demonstrated calcification resistance due to the covalently bound HEBP without any side effects. It is concluded that a PEU containing HEBP might serve as a calcification resistant candidate material for the fabrication of a heart valve prosthesis and other implantable devices.