Segmented polyurethanes hard segment chemistry

Hergenrother, R.W., H.D. Wabers, and S.L. Cooper, Effect of hard segment chemistry and strain on the stability of polyurethanes in vivo biostability. Biomaterials, 1993, 14, 449 58. 

Y.W. Tang, R.S. Labow, J.P. Santerre, Enzyme-induced biodegradation of polycarbonate-polyurethanes dependence on hard-segment chemistry, J. Biomed. Mater. Res. 57 (2001) 597-611. 

Several studies have been conducted on biostable polyurethanes to elucidate the effects of hard segment chemistry on polyurethane degradation rate. Tang et al. [104,105] observed the effects of hard segment chemistry and hard segment content... 

Labow RS, Sa D, Matheson LA, Dinnes DLM, Santerre JP. The human macrophage response during differentiation and biodegradation on polycarbonate-based polyurethanes dependence on hard segment chemistry. Biomaterials 2005 26(35) 7357-66. 

Tang, Y. W., Labow, R. S., and Santerre, J. P., Enzyme-induced biodegradation of polycarbonate-polyurethanes Dependence on hard-segment chemistry, Journal of Biomedical Materials Research 57, 597-611 (2001). 

Braatz et al.- studied the adsorption of proteins on polyurethane surfaces. They coated silica and silicone tubing with a variety of chemistries. Although they found differences, the polyuretlianes demonstrated minimal protein adsorption given sufficient coating thickness. Correlations between the relative number of hard (isocyanate) and soft (glycol) segments were drawn. More soft segments resulted in less adsorption. 

Atomic force microscopy has been used to evaluate the nature and size of the polyurethane structure at the surface of a sample. In this method, the surface of the sample is coated with a layer of gold and a probe scans over the surface. As the nature of the chemistry below the probe changes, the force field acting on the probe changes. The hard segment clusters can be visualized. 

In spite of polyurethane is a hazardous polymer, it can be modified through the basic chemistry of polyurethanes, which can modify a wide variety of soft and hard segments, morphological features, thermic and mechanical properties of structures, just by changing several conditions, such as the ratio NCO/OH, the aliphatic or aromatic isocyanate, the molecular weight, and the ester or ether form of the polyol, but especially the nature of the monomer, whether synthetic or natural. Among the natural options than can be used for synthesis are oil, polysaccharides, and amino acids. 

Diisocyanate is often used in the chain extension reactions of biopolymers such as PEA, PCL, and their copolymers [97-101]. The combination of hard segment and soft segment may confer the resulting polyurethanes with shape-memory property [100,101]. Polyurethane is an important type of elastomeric polymer for biomedical applications [1,9,11]. Chain extension or cross-linking by diisocyanate can be adapted to many -OH-terminated or H-containing polymers or prepolymers [102]. The convenience of the urethane chemistry has made it into a very popular way of polymer chain extension method in biomaterial designs. 

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