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Electrospun poly(glycolide-co-lactide) (PLA10GA90, LA/GA ratio 10/90) biodegradable nanofiber membranes possessed very high surface area to volume ratios and were completely noncrystalline with a relatively lowered glass transition temperature. These characteristics led to very different structure, morphology, and property changes during in vitro degradation, which were examined systematically. A shrinkage study showed that the electrospun crystallizable but amorphous PLA10GA90 membranes exhibited a very small shrinkage percentage when compared with the electrospun membranes of noncrystallizable poly(lactide-co-glycolide) (PLA75GA25, LA/GA 75/25) and poly(d,l-lactide). Although the weight loss of electrospun PLA10GA90 membranes exhibited a similar degradation behavior as cast thin films, detailed studies showed that the structure and morphology changes in electrospun membranes followed different pathways during the hydrolytic degradation. After 1 day of degradation in buffer solution at 37 degrees C, electrospun PLA10GA90 membranes exhibited a sudden increase in crystallinity and glass transition temperature, due to the fast thermally induced crystallization process. The continuous increase in crystallinity and apparent crystal size, as well as the decrease in long period and lamellae thickness, indicated that the thermally induced crystallization was followed by a chain cleavage induced crystallization process. The mass loss rate was accelerated after 6 days of degradation. The increase in glass transition temperature during this period further confirmed that the degradation of PLA10GA90 nanofibers was initiated from the amorphous region within the lamellar superstructures. A mechanism of structure and morphology changes during in vitro degradation of electrospun PLA10GA90 nanofibers is proposed.

On-line studies of structural and morphological changes during the heating and drawing process of isotactic polypropylene (iPP) fiber were carried out using synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) techniques. A unique image analysis method was used to deconvolute the two-dimensional (2D) WAXD patterns into quantitative fractions of crystal, mesomorphic, and amorphous phases. Results showed that the R-form crystals were quite defective in the initial iPP fibers and were converted into the mesomorphic modification by drawing at room temperature. Corresponding 2D SAXS patterns showed that there was no obvious long period (i.e., no lamellar structure) in the mesophase of the iPP fiber. We postulate that the constituents of the mesophase in iPP fibers include oriented bundles of helical chains with random helical hands and perhaps oriented chains with no helical structures; both have only partial packing ordering. The formation of the mesophase is through the destruction of the lamellar crystalline phase probably by pulling chains out from crystals. The R-form crystals were not converted into the mesophase by drawing at high temperatures. At higher temperatures, the R-form crystals became perfect and the crystallinity increased when the fiber was drawn. However, the draw ratio showed an inverse effect. The increase in draw ratio had a minimal effect on the crystallinity, but the transformation from the amorphous phase to the mesophase became dominant.

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Electrospun nonwoven bioabsorbable nanofibrous membranes of poly(lactide-co-glycolide) were effective to reduce adhesions at the site of injury using an objective rat model. The membrane acted as a physical barrier but with drug-delivery capability. The combined advantages of composition adjustment, drug-loading capability, and easy placement handling (relatively hydrophobic) make these membranes potentially successful candidates for further clinical evaluations.