The degradation of electrospun polydioxanone patches for rotator cuff repair

INTRODUCTION: Surgical repair of rotator cuff pathology has failure as high as 75% [1]. Biological factors such as stem cells and platelet rich plasma may improve the biological environment around the healing tendon [2]. We have investigated the use of a biocompatible and biodegradable electrospun polydioxanone (PDO) scaffold patch to restrain the spread of injected biological factors, and retain them in the desired locality. This study characterizes the degradation of PDO microfibrous patches in vitro. We have used imaging techniques, and high performance liquid chromatography to demonstrate the kinetics of PDO degradation as well as demonstrate the time scale of degradation in an in vitro representation of the physiological environment. METHODS: In-vitro weight loss: Electrospun polydioxanone patches were incubated in phosphate buffered solution (PBS) and weighed at intervals of 1 to 5 days over the course of 13 weeks. Weight loss of PDO samples was calculated as a percentage of the starting dry weight. Imaging: PDO samples were viewed in an Environmental Scanning Electron microscope (ESEM). Comparisons were made between fresh samples of PDO, and those degraded over a period of weeks in (PBS). The dimensions of the imaged fibres were measured and compared in order to characterize how they degraded. Fluorescent microscopy was used to image patches seeded with tendon-derived cells. These patches were incubated in PBS and imaged after 1, 2, and 4 weeks to demonstrate the adhesion of the cells to the electrospun fibres as the PDO degraded. High Performance Liquid Chromatography: HPLC was utilised to attempt to identify the final degradation product of polydioxanone, and to characterise the mechanisms by which it degrades. pH: PDO patches were incubated in PBS for a period of 8 weeks. At incremental time points, the pH of the solution was assessed. The Dynamic arm of the experiment involved replacing the PBS at each time point, in order to replicate the dynamic environment found in vivo. The Static arm maintained the same solution throughout the experiment. RESULTS AND DISCUSSION: The weight loss, pH, and imaging experiments provide evidence that PDO begins to significantly degrade at the 4 week time point. The ESEM images demonstrated the character of the PDO degradation, with degraded samples presenting short blocks of PDO in contrast to the long fibres of the fresh samples (Figure 3). It also provided evidence of the presence of live cells at the 4 week mark. The HPLC experiments also provided insight into the mechanisms of degradation and potential final degradation products. SIGNIFICANCE: The electrospun PDO structure maintains weight and pH well for 4 weeks which is the main window for physiological benefit from biological factors incorporated into the patch. Tenoblast cells maintain adhesion to the patch well, and the hypothesis formed from these results is that they will migrate onto the injury when exposed to physiological recruitment factors.