Radical formation and fracture of highly drawn crystalline polymers

The hydrolytic degradation of polydioxanone (PDSII) sutures. Part II: Micromechanisms of deformation

An investigation of morphological changes in hydrolytically degraded polydioxanone sutures (PDSII) during in situ tensile deformation is reported. These changes were followed with the use of real-time small-angle X-ray scattering with simultaneous tensile deformation experiments. The results are correlated with separately performed wide-angle X-ray scattering, and optical microscopy experiments on the effects of tensile strain. Interlamellar and interfibrillar amorphous regions appear to control the microdeformation and the shape of the stress-strain curves of PDSII sutures. The fibers deform initially by interlamellar separation and at larger strains by fibrillar slip. Fractures appear to be caused by the catastrophic growth of cracks. The degradation of interlamellar tie chains in PDSII sutures does not appear to significantly affect the progress of deformation, because deformation through interlamellar separation is largely unchanged by degradation. Conversely, hydration and scission of interfibrillar tie chains lowers the load required to propagate interfibrillar shear. The fibers fail at progressively lower strains as degradation proceeds.

Hydrolytic degradation and morphologic study of poly-p-dioxanone

The in vitro hydrolytic degradation of 2-0 size PDS monofilament suture was studied for the purpose of revealing its morphologic structure and degradation mechanism. The sutures were immersed in phosphate buffer of pH 7.44 for up to 120 days at 37 degrees C. These hydrolyzed sutures were examined by the changes in tensile properties, weight, thermal properties, x-ray diffraction structure, surface morphology, and dye diffusion phenomena. It was found that hydrolysis had significant effects on the change of PDS fiber morphology and properties. Hydrolysis, however, had no significant effect on overall molecular orientation of the fiber until the very late stage. PDS suture fibers retained their skeleton throughout the earlier periods of hydrolysis concurrent with mass and tensile strength losses. PDS sutures exhibited an absorption delay of 120 days. Both heat of fusion and melting point exhibited a maximum function of hydrolysis time. Hydrolysis of PDS suture fibers proceeded through two stages: random scission of chain segments located in the amorphous regions of microfibrils and intermicrofibrillar space, followed by stepwise scission of chain segments located in the crystalline regions of microfibrils. Dye diffusion data showed that the passage along the longitudinal direction of the fiber was relatively easier than the lateral direction as evident in the diffusion coefficient, activation energy, and flexibility of chain segments. Swiss-cheese model of fiber structure appears to describe the observed dye diffusion phenomena and their dependence on hydrolysis time and dying temperature.