Recent Advances in Polyurethane/POSS Hybrids for Biomedical Applications

Advanced organic-inorganic materials-composites, nanocomposites, and hybrids with various compositions offer unique properties required for biomedical applications. One of the most promising inorganic (nano)additives are polyhedral oligomeric silsesquioxanes (POSS); their biocompatibility, non-toxicity, and phase separation ability that modifies the material porosity are fundamental properties required in modern biomedical applications. When incorporated, chemically or physically, into polyurethane matrices, they substantially change polymer properties, including mechanical properties, surface characteristics, and bioactivity. Hence, this review is dedicated to POSS-PU composites that have recently been developed for applications in the biomedical field. First, different modes of POSS incorporation into PU structure have been presented, then recent developments of PU/POSS hybrids as bio-active composites for scaffolds, cardiovascular stents, valves, and membranes, as well as in bio-imaging and cancer treatment, have been described. Finally, characterization and methods of modification routes of polyurethane-based materials with silsesquioxanes were presented.

Effect of flame retardants on mechanical and thermal properties of bio-based polyurethane rigid foams

A soy oil-based polyol (HSBP) was synthesized from epoxidized soy oil through a ring-opening reaction with distilled water. A phosphorus-containing flame retardant (DOPO–HSBP) was synthesized through the reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and HSBP. A nitrogen-containing flame retardant (T–D) was prepared by the reaction of diethanolamine with glycol diglycidyl ether. The structures of HSBP, DOPO–HSBP, and T–D were characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (¹H NMR). The flame-retardant rigid polyurethane foam (PPUFs and NPUFs) was prepared successfully by mixing HSBP, DOPO–HSBP, and T–D. The effects of DOPO–HSBP content on the mechanical, thermal, and flame-retardant properties of PPUFs and NPUFs were investigated by tensile tests, thermogravimetric analyses (TGA), limiting oxygen index (LOI), and UL-94 vertical burning level. The morphology of PPUFs and NPUFs was studied via scanning electron microscopy (SEM). With the increase in the percentage of DOPO–HSBP added, the flame retardant property of rigid polyurethane foam (RPUF) was greatly improved. When the phosphorus-containing flame retardant DOPO–HSBP was added to 50% of the RPUF with the nitrogen-containing flame retardant T–D, the LOI value of the foam increased from 18.3 to 25.5, and the UL-94 result was classified as “V-0” with almost no effect on the mechanical properties of the RPUF. The results showed that the phosphorus and nitrogen synergistic flame retardants of DOPO–HSBP and T–D can endow excellent flame retardant properties to RPUF without affecting its mechanical properties.

A vegetable oil-based polyurethane rigid foam containing a phosphorus–nitrogen dualflame retardant system was prepared, and the foam exhibited not only excellent flame retardant properties but also good mechanical properties.

Examining the influence of functionalized POSS on the structure and bioactivity of flexible polyurethane foams

This work reports for the first time on a new class of flexible polyurethane foam hybrids (PUFs) synthesized with the use of less toxic aliphatic hexamethylene diisocyanate (HDI), which have been chemically modified by POSS moieties. The flexible polyurethane foam hybrids (PUFs) chemically modified by functionalized polyhedral oligomeric silsesquioxanes: octa(3-hydroxy-3-methylbutyldimethylsiloxy)POSS (OCTA-POSS) and 1,2-propanediolizo-butylPOSS (PHI-POSS), was obtained. The resulting foams, which contain 0 to 15 wt % POSS, were characterized in terms of their structure, morphology, density and compressive strength. The FT-IR results indicate the chemical incorporation of both OCTAPOSS and PHIPOSS into the polyurethane matrix. SEM-EDS analysis showed that both OCTAPOSS and PHIPOSS nanoparticles are distributed homogeneously in the foam structure; at 15 wt % load PHIPOSS characteristic "crosses" are formed. With the increase of PHIPOSS content in the matrix, the formation of agglomerates is observed, as revealed by WAXD spectra. The introduction of POSS compounds reduces the porosity of the polyurethane, with the number of pores increasing as the amount of modifier increases. Mechanical tests - compressive strength - show that the hardness of modified materials (5 wt % POSS) increases compared to the reference material. An incubation was carried out in a simulated physiological fluid (SBF) to pre-assess the bioactivity of the materials obtained. The obtained results confirmed the formation of a hydroxyapatite layer on the PUF-POSS surface. Cytotoxicity, cell cycle and apoptosis of osteoblast cells and fibroblasts were assessed in the presence of the PUF-POSS materials. Test materials have a cytotoxic effect on both established cell lines. PUF-PHIPOSS samples showed better biocompatibility than reference and PUF-OCTAPOSS samples, as they caused lower mortality of the examined cells.