Degradation of Polyurethanes for Cardiovascular Applications - Advances in Biomaterials Science and Biomedical Applications - page 66

Figure 4. Molecular weight reduction in polyurethanes based on butanediamine (PUBDA), arginine (PUR), glycine
(PUG) and aspartic acid (PUD).
4.4. Enzymatic degradation
Huang et al. (Huang et al., 1979) reported that a low molecular weight poly(ester-urea),
poly(L-phenyl alanine/ethylene glycol/1,6-hexane diisocyanate), and a model diesterdiurea,
dimethyl diphenyl alanine hexamethylene urea, were hydrolyzed by chymotrypsin at pH 8.
They also observed degradation with papain latex (pH 6.5, PBS) of the model diesterdiurea.
Takahara et al. (Takahara et al., 1992) degraded SPU´s based on MDI, BD and various poly‐
ols using papain (80 U/mL) and papain activating solution (0.05 M cysteine, 0.02 EDTA,
pH=6.5 ) in sodium acetate buffer solution. In this study it was found that PEO based poly‐
urethanes exhibited the larger mass loss from all the SPU´s studied in addition to a reduc‐
tion in Young´s modulus and tensile strength due to a reduction in molecular weight.
Labow et al. (Labow et al., 1996) degraded in elastase (from human neutrophils or pancreat‐
ic porcine) a poly(ester-urea-urethane) containing [ 14 C]toluene diisocyanate (TDI), poly(cap‐
rolactone) and ethylenediamine as well as a poly(ether-urea-urethane) containing [ 14 C]TDI,
poly(tetramethylene oxide) and ethylenediamine (ED). They used neutrophils, which con‐
tain elastolytic activity, as they are present during the inflammatory response. Ten-fold
more radioactive carbon was released when porcine pancreatic elastase was incubated with
[ 14 C]TDI/PCL/ED than when human neutrophil elastase was used. Ten-fold less radioactive
carbon was released when [ 14 C]TDI/PTMO/ED was incubated with porcine pancreatic elas‐
tase (PPE) as compared to [ 14 C]TDI/PCL/ED. Radioactive carbon release data for
[ 14 C]TDI/PCL/ED polymer incubated with trypsin, a possible contaminant in pancreatic por‐