Mechanism of poly(dioxanone-co-glycolide) (PDG) sutures in vitro degradation was studied by DSC and X-ray diffraction and the surface morphology was studied with photography for the purpose of improving properties of absorbable sutures．The model of fiber structure

Swiss-Cheese model

provides the basis for the proposed degradation mechanism of PDG in vitro hydrolysis process. It is believed that the degradation of PDG proceeds through three main stages：the first stage occurs in the amorphous region

the second in the inter-microfibrillar non-crystalline region

the third in the crystalline part．The concepts of the three stages accord with the changes of PDG sutures during hydrolysis degradation. The properties of sutures decreased greatly from three to four weeks with respect to intrinsic viscosity

knot tensile strength and weight degradation

etc．The photography results show that the breaking modes are different for polydioxanone sutures (PDG) and PDG suture．PDS was broken by cross-section cracks and PDG was degraded via falling-off of large surface layers．