The preparation and characterization of biodegradable shape-memory stent-enzyme drug formulation including L-asparaginase

L-asparaginase (L-ASNase) is the primary chemotherapeutic drug used in the treatment of Acute Lymphoblastic Leukemia (ALL). To reduce the immune response in patients, the modified form of L-ASNase with polyethylene glycol (PEG) is applied. However, usage and accessibility of this enzyme has limited due to its short plasma half-life and expensive. At this point, it is needed novel approaches to solve the problems encountered in the treatment of ALL. Biodegradable stents are promising applications for their biocompatibility and degradation over time. Within the scope of the thesis, firstly, hydrogels with CHI/GLY/PEG, CHI /GLY/PPG and CHI/GLY/PVA based on chitosan (CHI), glycerol (GLY), polyethylen glychol (PEG), polypropylene glychol (PPG) and polyvinyl alchol (PVA) were prepared and biodegradable stents with cross-linking agent (sodium tripolyphosphate) were obtained. Structural and thermal characterizations of the stents were determined by FTIR, DTA, TGA and DSC. In addition, the degree of swelling, water uptake capacity, gas permeability, in vitro biodegradability and water contact angles of the prepared stents were determined. Then, L-ASNase enzyme was immobilized on the stents as in situ and the optimal stent formulations were determined by examining enzyme concentration, immobilization time, crosslinker ratio and crosslinking times. In vitro biocompatibility of the optimal biodegradable stents was investigated on L929 cells according to ASTM standards. In addition, protein adsorption, porosity and mechanical properties were investigated in these stents. Presence of enzyme in these prepared stents (FTIR, EDX, XRD) and optimum parameters (pH, temperature, thermostability, storage stability, re-usability etc.) were studied in detail. Finally, the applicability of the stent-enzyme drug formulation in in vitro vessel flow conditions was tested in a mimetic designed bioreactor system. According to our results, CHI/GLY/PEG-3@L-ASNase, CHI/GLY/PPG-4@L-ASNase and CHI/GLY/PVA-4@L-ASNase stent formulations maintained more than half of their initial activity under vascular flow conditions. In addition, it has been found that the shape memory polymeric stent formulations containing enzyme have biocompatibility, biodegradability and sufficient mechanical character. Additonally, the pH and thermostability, reusability and long-term storage stability of the formulations were determined to be promising.