Laser confocal microscopic study of pH profiles of synthetic absorbable fibers upon in vitro hydrolytic degradation.

The objective of this study was to develop a new and non-destructive technique to measure the interior pH of synthetic absorbable biomaterials. Such a measurement would provide the required experimental evidence for validating the postulated theory that the accumulation of acidic hydrolytic degradation products within the interior of aliphatic polyesters is responsible for the observed accelerated degradation of this class of absorbable biomaterials. This new technique used a laser scanning confocal microscope coupled with pH sensitive fluorescent dyes like Texas Red sulfonyl chloride. The capability of optical thin sectioning of a laser confocal microscope would permit a non-destructive examination of the interior of biomaterials. Poly-p-dioxanone suture fibers (PDSII) of size 2/0 were used as the model compound for this new technique. The pH values of the unhydrolyzed and partially hydrolyzed PDSII fibers were found to decrease with increasing depth from the fiber surface and reached as low as about 3.5 at 70 microm depth. The largest depth that an interior pH could be measured within absorbable biomaterials was determined by the opacity of the biomaterials, i.e. a higher depth for a less opaque material. The observed interior pH profiles were correlated to the unique morphologic structure of PDSII fibers. Copyright 2001 Kluwer Academic Publishers