Mechanical behaviors of high-strength fabric composite membrane designed for cardiac valve prosthesis replacement

Thermoplastic polyurethane/POSS nanohybrids: Synthesis, morphology, and biological properties

Recent studies show good osteoinductive properties of polyurethanes modified with polyhedral oligomeric silsesquioxanes (POSS). In this work, three types of POSS; propanediolisobutyl-POSS (PHI-POSS), disilanolisobutyl-POSS (DSI-POSS), and octahydroxybutyl-POSS (OCTA-POSS) were chemically incorporated into linear polyurethane based on an aliphatic isocyanate, hexamethylene diisocyanate (HDI), to obtain new nanohybrid PU-POSS materials. The full conversion of POSS was confirmed by Fourier transform infrared spectroscopy (FTIR-ATR) spectra of the model reactions with pure HDI. The materials obtained were investigated by FTIR, SEM-EDS, and DSC. The DSC studies showed the thermoplasticity of the obtained materials and apparently good recovery. 30-day immersion in SBF (simulated body fluid) revealed an increase in the rate of deposition of hydroxyapatite (HAp) for the highest POSS loadings, resulting in thick layers of hydroxyapatite (~60-40 μm), and the Ca/P ratio 1.67 (even 1.785). The structure and properties of the inorganic layer depend on the type of POSS, the number of hard segments, and those containing POSS, which can be tailored by changing the HDI/poly(tetramethylene glycol) (PTMG) ratio. Furthermore, the obtained composites revealed good biocompatibility, as confirmed by cytotoxicity tests conducted on two cell lines; normal human dermal fibroblasts (NHDF) and primary human osteoblasts (HOB). Adherent cells seeded on the tested materials showed viability even after a 48-h incubation. After this time, the population of viable, and proliferating cells exceeded 90%. Bioimaging studies have shown the fibroblast and osteoblast cells were well attached to the surface of the tested materials.

In vitro hemodynamics of fabric composite membrane for cardiac valve prosthesis replacement

This study aimed to investigate the hemodynamics of a novel fabric composite that can be used as a substitute for bovine pericardium. The structure is composed of ultrahigh molecular weight polyethylene (UHMWPE) fabric coated with thermoplastic polyurethane (TPU) membranes on both sides. In vitro experiments were carried out on two composite valve samples with different specifications and a bovine pericardial one with the same dimension and structure. Hemodynamic properties including the effective orifice area (EOA) and regurgitant fraction (RF) were obtained and compared through pulsatile-flow testing in a pulse duplicator. Using the particle image velocimetry (PIV) technique, frames of the downstream velocity field in the aortic valve chamber were captured during cardiac cycles. Then, the field of Reynolds shear stress (RSS), viscous shear stress (VSS), and turbulent kinetic energy (TKE) at peak systole were calculated. A fluid-structure interaction (FSI) model has also been used to verify the pulsatile-flow testing. Compared with the bovine pericardial valve, composite valves have nosuperiority regarding EOA and RF due to their slightly higher rigidity. However, shear stresses of composite valves were lower than those of the bovine pericardial valve indicating more stable blood flows, which means that composite leaflets have the potential to reduce the risks of thrombosis and hemolysis induced by the mechanical contact between the blood flow and leaflets of valve prostheses.