The In Vitro Study On The Biodegradability And The Release Behavior Of A Novel Biodegradable Material Of Drug-loading Ureteral Stents

Ureteral stents and ureteral catheters have been widely used in urology. The stents areusually applied for the ureteral surgeries. The main functions of the ureteral stents arefacilitation of upper tract drainage, aligning the ureter, prevention of delayed formation ofureteral stricture and prevention of ureteral obstruction. However, two major clinicalproblems related to these medical devices have been observed, namely infection andecrustation. In addition, the commonly used materials for ureteral stents are nondegradablepolymers or metals. The reoperation is demanded to remove the nondegradable stentsinserted in the body.To overcome the problems of encrustation induced by the long-term insert and thereoperation to remove the stents, biodegradable polymers have been investigated as theureteral stents. In this paper, we investigated the polyvinyl alcohol (PVA)/starch blendsas the materials of ureteral stents. Multilayer structure of the blends was designed toimprove the performance of the blends. We investigated the biodegradability of themonolayered blends and the multilayered blends, and the influence on theirbiodegradability by the amylase was also under consideration. The weight loss, scanningelectron microscope (SEM), X-Ray Diffraction (XRD) were used to evaluate thebiodegradability of the blends. The results showed that the biodegradability of the blendswas significantly influenced by the content of starch in the blends. The higher content ofthe starch, the better biodegrability of the blends. It was also showed that thebiodegradability of the mutilayered blends was worse than the monolayerd blends.However, it was found that the additon of amylase could significantly improve thebiodegradability of the composites. The main reasons for these phenomena were thatstarch was more easily degradable than PVA, and the amylase could obviously promotethe degradation of starch so as to promote the degradation of the composites. On the other hand, eluting anti-inflammatory or therapeutic drugs on the ureteral stentscould overcome the problem of infection induced by the insertion of the ureteral stents. Inthis paper, we used gallic acid as both the anti-inflammatory drug and the therapeutic drug.Three novel drug delivery systems of gallic acid were developed, including the system ofmultilayered blends, the gallic acid loaded silica nanoparticles and the gallic acidencapsulated polymer microspheres. The release behavior of gallic acid from the systemswas investigated respectively. The Fourier Transform Infrared Spectroscopy (FTIR),X-Ray Diffraction (XRD), Thermo Gravimetric Analyzer/Differential ScanningCalorimetry (TGA/DSC), scanning electron microscope (SEM), ultraviolet visibleSpectrometry (Uv-vis) were used to characterize the products or investigate the releasebehaviors of gallic acid from the controlled release systems. The results showed that therelease of gallic acid from the multilayered blends was still very fast, and the release ofgallic acid wasn’t well controlled by the multilayer structure. Nevertheless, the release ofgallic acid from the gallic acid loaded silica nanoparticles was well controlled by thehydrolysis process in almost120hours, although a burst release of about30%of gallicacid was occurred in the former2hours. This result proved that the gallic acidencapuslated by this novel system could be used as the anti-inflammatory drug of thedrug-loading stents, which was intended to be released in dozens of hours or days.Whereas, the gallic acid from the poly-lactic-co-glycolic acid (PLGA) microspheres wasreleased by an excellent controlled manner. The release time of gallic acid wassignificantly prolonged to be almost45days by the system of PLGA microspheres. Ingeneral, the therapeutic drugs of drug-loading stents were supposed to be released inseveral months. This result indicated the use of gallic acid as the therapeutic drug ofdrug-loading stents possible.In this paper, we aimed at investigating the potential of PVA/starch blends used as thethe biodegradable materials of ureteral stents, and devoloping the controlled releasesystems of gallic acid eluted by the ureteral stents and intended to be used as both the anti-inflammatory drug and the therapeutic drug.