Polyisobutylene-based polyurethanes: VII. structure/property investigations for medical applications

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

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 M_n > 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.

Designing a castor oil-based polyurethane as bioadhesive

Based on the stealth behavior of castor oil and poly(ethylene glycol), we selected a polyurethane system to obtain an ideal surgical adhesive. The polyurethane adhesives with varying concentrations of castor oil were investigated by Fourier transform infrared spectrometer, differential scanning calorimetry, scanning electron microscopy, goniometer, and universal testing machine. Curing results show that a 7-min to 25-min room temperature curing can be achieved, providing one possibility of shortening the surgery time. In vitro biodegradation test demonstrates that a certain proportion of the polyurethane film will be hydrolyzed in a foregone manner after a period of time (7 weeks). The adhesion strengths of these adhesives show a strong bonding between pieces of tissue, which makes them qualified for application in a moist environment.