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 techni que to measure the interior pH of synthetic absorbable biomaterials. Such a measurement would provide the required experimental evidence for validatin g the postulated theory that the accumulation of acidic hydrolytic degradat ion products within the interior of aliphatic polyesters is responsible for the observed accelerated degradation of this class of absorbable biomateri als. This new technique used a laser scanning confocal microscope coupled w ith pH sensitive fluorescent dyes like Texas Red sulfonyl chloride. The cap ability of optical thin sectioning of a laser confocal microscope would per mit a non-destructive examination of the interior of biomaterials. Poly-p-d ioxanone 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 hyd rolyzed PDSII fibers were found to decrease with increasing depth from the fiber surface and reached as low as about 3.5 at 70 mum 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 t o the unique morphologic structure of PDSII fibers. (C) 2001 Kluwer Academi c Publishers.