Preparation, Characterization And Application Of Biodegrable Medical Devices Manufactured By A New Mini-deposition Fabrication System

Melt-deposition modeling has drawn more and more attentionbecause of its better ability to manufacture biomedical devices with greatprocessing flexibility. Hence, in this study, a new mini-deposition system(MDS) was developed which can adopt biodegradable materials directlyto fabricate biomedical devices. Then, biodegradable scaffold for bonerepair and a novel biodegradable stent for the treatment of vessel stenosiswere successfully fabricated by MDS and their mechanical properties andperformances both in vitro and in vivo were investigated. The main workand conclusions of this research were as follows:(1) A linear stepper motor was adopted by MDS to deposit materialslayer by layer with a xyz position system, which is beneficial forcontrolling the scaffold fabrication accurately and stably. The materialdeposition process was studied by both experimental and theoreticalmethods. Theoretical model was obtained to depict the relationship ofapplied pressure, deposition rate and rheological properties of polymer melt for MDS. By adjusting the design and fabrication parameters, Poly(ε-caprolactone)(PCL) scaffolds were successfully fabricated by MDSwith the fiber diameter from359μm to220μm, the pore size from50μmto180μm in the z direction and from380μm to980μm in the x-y plane.The pore structures of these scaffolds are very regular and completelyinterconnected. The average porosity of these scaffolds can be variedfrom about30%to73%and the compressive modulus decreased from79.3to11.6MPa with increasing porosity. Ashby and Gibson formula canbe used to depict the relationship of porosity and mechanical properties ofpolymer scaffolds manufactured by MDS effectively.(2) Natural bone powder (BP) was blended with PCL to fabricatebiocomposite due to its good osteoconductive and osteoinductiveproperties. Then PCL/BP composite scaffolds were manufactured byMDS with controllable pore structure for bone repair. The mechanicalproperties, wettability and biocompatibility both in vitro and in vivo ofPCL/BP scaffolds were investigated. The results show that BP fillers canenhance the mechanical properties of PCL scaffold significantly. PB-40composite (with the BP content of40%) scaffold has increasedcompressive modulus of49.8MPa, while the compressive modulus ofpure PCL scaffold with similar pore structure and porosity is only about26.5MPa. Moreover, BP fillers can also improve the water intakecapability of PCL scaffold because the static contact angles of PCL/BP composites decrease from101°±3to67°±5when the BP content isincreased from zero to40%, which can facilitate cell seeding,proliferation and nutrients transportation into the pores of scaffold. APB-40composites scaffold with customized shape for mandible bonerepair was successfully fabricated to prove the good process flexibility ofMDS. The biocompatibility and biological safety of PCL/BP compositescaffolds were also studied and the results show that all the scaffolds havefine compatibility with cell, blood and tissue, and are safe for clinical use,which can provide the theoretical evidence for the further applications ofPCL/BP composites scaffold in bone repair(3) A novel bioabsorbable poly p-dioxanone (PPDO) stent withsliding-lock structure was designed and successfully fabricated by MDSfor the treatment of peripheral vascular stenosis. The sliding-lock PPDOstent had improved radial strength of about107kPa, while PPDO stentwith conventional net-tube structure had low radial strength of only about32kPa. The radial strength of sliding-lock PPDO stents decreased withthe increase of diameter. Sliding-lock PPDO stents (n=40) wereimplanted into peripheral vessels of pigs through percutaneousintervention method to investigate their technical feasibility andperformance in vivo. The results showed that the success rate ofdeployment of sliding-lock PPDO stents was about87.5%whichindicated that the rationality of sliding-lock stent was preliminarily proved. Further studies showed that sliding-lock PPDO stents could dilatevessels effectively within one month after intervention, though thediameter of the stented vessles lost a little after three months due to stentbiodegradation and intimal hyperplasia. PPDO stents can be fully coveredby endothelial cells after one month and be mostly absorbed after sixmonths. Based on the studies above, it is concluded that sliding-lockPPDO stent is promising for the treatment of peripheral vascular stenosisin the future.