Synthesis of High‐Molecular‐Weight and Strength Polyisobutylene‐Based Polyurethane and Its Use for the Development of a Synthetic Heart Valve

Abstract

Under optimized synthesis conditions, for the first time, polyisobutylene‐based polyurethane (PIB–PU) is prepared with 70% PIB soft segment (i.e., a bioinert and calcification‐resistant PU) with Mn > 100 000 Da, 32 MPa ultimate strength, and 630% elongation. The key parameters for this achievement are a) the precise stoichiometry of the polyurethane forming reaction, specifically the use of highly purified di‐isocyanate (4,4′‐methylene‐bis (phenyl isocyanate), MDI), and b) the increased solid content of the synthesis solution to the limit beyond which increased viscosity prevents stirring. The shape of the stress–strain trace of PIB–PU indicates a two‐step failure starting with a reversible elastic (Hookean) region up to ≈50% yield, followed by a slower linearly increasing high‐modulus‐deformation region suggesting the strengthening of PIB soft segments by entanglement/catenation, and the hard segments by progressively ordering urethane domains. This PIB–PU is a candidate for a fully synthetic bioprosthetic heart valve since preliminary studies show that PIB–PU has impressive fatigue life.

Prosthetic heart valves for transcatheter aortic valve replacement

“… [116,117] Deodhar et al. prepared a high molecular weight and high strength polyisobutylene polyurethane (PIB‐PU) containing 70% polyisobutylene (PIB) soft segments [134] . The PIB‐PU shows a long fatigue life without failure after 1 million cycles of stretching at 50% strain (the maximum strain of polymer valves in real use is 10%).…”

“…[116,117] Deodhar et al prepared a high molecular weight and high strength polyisobutylene polyurethane (PIB-PU) containing 70% polyisobutylene (PIB) soft segments. [134] The PIB-PU shows a long fatigue life without failure after 1 million cycles of stretching at 50% strain (the maximum strain of polymer valves in real use is 10%). While the excellent fatigue life is essential for polymeric valve application, the biocompatibility and durability of longterm implantation in vivo also need to be evaluated.…”

Polyisobutylenes with Controlled Molecular Weight and Chain-End Structure: Synthesis and Actual Applications

“…Highly reactive ‘Cl-allyl-PIB-allyl-Cl’ copolymers (see Scheme 7 ) were hydrolyzed to the corresponding diols using aqueous tetrabutylammonium hydroxide in THF (reflux, 22 h, and 98.2% conversion); these diols in a mixture with butane-1,4-diol were further used for polyuerthane preparation through the reaction with 4,4′-methylenebis(phenyl isocyanate) in the presence of Sn(Oct) 2 [ 68 ]. In subsequent studies [ 168 ], the synthesis of a copolymer was optimized to achieve mechanical characteristics and biocompatibility suitable for a fully synthetic heart valve. With the use of freshly distilled 4,4′-methylenebis(phenyl isocyanate) and increasing the PIB diol concentration in the reaction mixture, a copolymer with an increased MW (>100 kDa), a tensile strength of ≈32 MPa, an elongation of ≈630%, and a toughness of >4.0 J was achieved.…”

Double Cross‐Linked Polyisobutylene‐Based Polyurethane (xPIB‐PU) I: Synthesis, Processing, and Properties

“…Reduced creep would be particularly important for heart valve prostheses. [15] While cross-linking the PIB domains could have been accomplished by many methods, [21,22] they yielded unacceptable side products and rendered the product of little medical use. [23] Thus, our challenge was to produce processible (i.e., compression or injection moldable, miscible, etc.)…”