Characteristics of crosslinked blends of Pellethene® and multiblock polyurethanes containing phospholipid

Cell membrane-mimicking coating for blood-contacting polyurethanes

The aim of the present work was to develop simple modification technique for polyurethanes (PUs) intended for use in blood-contacting implants (vascular grafts, heart prosthesis, ventricular assist devices). PU surface was modified with soybean-derived phosphatidylcholine (PC) via one-step dip coating technique. In order to evaluate blood compatibility of the obtained materials, samples were contacted with human blood under static and arterial flow-simulated conditions. The PC-modified surfaces were thoroughly characterized and tested for fibrinogen resistance, the ability to resist platelet adhesion and activation, hemolysis percentage and plasma recalcification time. Results demonstrated significant, more than three-fold reduction in the amount of fibrinogen adsorbed to PC-modified materials as compared to non-modified PU. Analysis of the samples’ surface after incubation with blood showed high reduction in platelet adhesion. The results were confirmed by analysis of blood samples collected after shear-stress tests – the percentage of free (non-aggregated) platelets remaining in blood samples contacted with PC-coated materials exceeded 70%. The same parameter measured for non-modified PU was significantly lower and equaled 28%.

Optimization of the structure of polyurethanes for bone tissue engineering applications

Polyurethanes containing 22-70 wt.% hard segments were developed and evaluated for bone tissue engineering applications. Aliphatic poly(ester-urethanes) were synthesised from poly(epsilon-caprolactone) diol with different molecular masses (M= approximately 530, 1250 and 2000 Da), cycloaliphatic diisocyanate 4,4'-methylenebis(cyclohexyl isocyanate) and ethylene glycol as a chain extender. Changes in macromolecule order with increasing hard segment content were observed via modulated differential scanning calorimetry. Depending on the hard segment content, a gradual variation in polyurethane surface properties was revealed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and static contact angle measurements. As the hard segments content increased the polyurethane surface exhibited more phase separation, a higher content of urethane moieties and higher hydrophilicity. The biocompatibility results indicated that proliferation of human bone-derived cells (HBDC) cultured in vitro improved with increasing hard segment content while the osteogenic potential of HBDC decreased with increasing hard segment content.

Segmented biopolyurethanes for medical applications

Polyurethanes are one of the most popular groups of biomaterials applied for medical devices. Their segmented block copolymeric character endows them a wide range of versatility in terms of tailoring their physical properties, blood and tissue compatibility. Polyester- and polyether-urethanes have been modified with hydroxypropyl cellulose aiming the change of their surface and bulk characteristics to confer them biomaterial qualities. In this respect, dynamic contact angle measurements, dynamic mechanical analyses accompanied by mechanical testing have been done. Platelet adhesion test has been carried out in vitro and the use of hydroxypropyl cellulose in the polyurethane matrix reduces the platelet adhesion and therefore recommends them as candidates for biocompatible materials.

Isopropyl Myristate-Modified Polyether-Urethane Coatings as Protective Barriers for Implantable Medical Devices

Polyurethane films have potential applications in medicine, especially for packaging implantable medical devices. Although polyether-urethanes have superior mechanical properties and are biocompatible, achieving water resistance is still a challenge. Polyether based polyurethanes with two different molecular weights (PTMO1000, PTMO2000) were prepared from 4,4’-diphenylmethane diisocyanate and poly(tetra-methylene oxide). Polymer films were introduced using different concentrations (0.5-10 wt %) of isopropyl myristate lipid (IPM) as a non-toxic modifying agent. The physical and mechanical properties of these polymers were characterised using physical and spectroscopy techniques (FTIR, Raman, DSC, DMA, tensile testing). Water contact angle and water uptake of the membranes as a function of IPM concentration was also determined accordingly. The FTIR and Raman data indicate that IPM is dispersed in polyurethane at ≤ 2wt% and thermal analysis confirmed this miscibility to be dependent on soft segment length. Modified polymers showed increased tensile strength and failure strain as well as reduced water uptake by up to 24% at 1-2 wt% IPM.

Surface characterization of biopolyurethanes based on cellulose derivatives

Surface tension parameters and surface morphology of biopolyurethanes based on cellulose derivatives thin films, before and after HF cold plasma treatment has been investigated. Calculations are based on the geometric mean approach of Owens and Wendt, Rabel and Kälble, on the Lifshitz-van der Waals acid/base approach of van Oss and co-workers and on the theoretical methods involving quantitative structure-property relationship. For all the investigated samples the polar component contributes significantly to the total surface tensions, as due to the large electron donor interactions. HF cold plasma treatment modifies the surface energy of biopolyurethanes by changing their surface polarity and hydrophilicity. The hydrophilic/hydrophobic balance was studied by means of the free energy of hydration between the biomaterial film and water. The protein adsorption tests of fibrinogen were effected to evaluate the applicability of these biopolyurethanes as biomedical thromboresistant devices.

Nonfouling biomaterials based on polyethylene oxide-containing amphiphilic triblock copolymers as surface modifying additives: Solid state structure of PEO-copolymer/polyurethane blends

Three novel polyethylene oxide-containing amphiphilic triblock copolymers (PEO-PU-PEO) with PEO MWs 550, 2000, and 5000, were blended with a segmented polyurethane (PU). It was expected that the block copolymers would act as surface modifiers to produce surfaces rich in PEO. The solid state properties of the PEO-copolymer/PU blends were studied by infrared spectroscopy, differential scanning calorimetry, and tensile stress-strain measurements. Infrared analysis showed no significant hydrogen bonding between the PEO blocks of the copolymers and the PU matrix. Differential scanning calorimetry data indicated that for copolymer content up to 5 wt % the microphase structure of the blends was indistinguishable from that of the unmodified PU matrix; for copolymer content of 10% or greater, the blends showed phase separated structures. Similarly the tensile stress-strain properties of the blends were essentially the same as those of the matrix up to 5 wt % copolymer. At higher copolymer content, however, the tensile strength decreased with increasing content of the copolymers; for a given copolymer content the change in tensile properties increased with increasing PEO MW. The structures of the 20% blends were also investigated after extraction with toluene (copolymers soluble, matrix insoluble). Bulk compositional change upon extraction was determined by nuclear magnetic resonance spectroscopy. Surface compositional change was studied by X-ray photoelectron spectroscopy and water contact angles. Surface morphology was observed using scanning electron microscopy and atomic force microscopy. It was shown that the copolymers were removed from the blends by extraction and that the extent of removal increased with decreasing MW of the PEO block. After toluene extraction, the blend surfaces showed advancing water contact angle and surface elemental composition similar to those of the PU matrix. However in contrast to the relatively smooth matrix surface, the extracted blend surfaces were "decorated" with lacunae or pits. Consistent with the weight loss trends, the extent of pitting was greater for the copolymers having shorter PEO blocks, suggesting that surface enrichment of the copolymers increased with decreasing MW of the copolymers.

Improved protein-adsorption-resistant property of PES/SPC blend membrane by adjustment of coagulation bath composition

To improve surface protein-adsorption-resistant property of polyethersulfone (PES) membranes, soybean phosphatidylcholine (SPC) was added to PES casting solution. The blend membranes were prepared by a phase inversion method in a wet process. The surface of PES/SPC blend membranes was characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). XPS data revealed that the phosphorylcholine (PC) groups were concentrated at the surface by changing the composition of coagulation bath. Addition of N,N-dimethylformamide (DMF) in coagulation bath could prolong coagulation time and facilitate the migration of SPC from polymer bulk to membrane surface. The PES/SPC blend membranes dramatically reduced BSA and fibrinogen adsorption compared to PES control membrane due to effective immobilization of PC groups at the surface of PES/SPC blend membranes.