| Popis: |
Additive manufacturing has many advantages in fabricating customized orthopedic implants and scaffolds, where complex geometries can be fabricated directly. This study aimed to use additive manufacturing, particularly fused deposition modeling (FDM) to fabricate and evaluate polymeric implants scaffolds to achieve optimal functionality in orthopedic applications by investigating the effect of pore sizes on cell activities. Another aim was to evaluate the capabilities of the FDM technique to overcome challenges associated with polymeric 3D-printable biocomposites. In this study, polyetheretherketone (PEEK) and polylactic acid (PLA) were chosen to represent non-biodegradable and biodegradable polymers. Ceramic materials such as the conventional tricalcium phosphate (TCP) and novel amorphous magnesium phosphate (AMP) were used as second phases in polymer composites. The first chapter presents a brief introduction and overview of this dissertation. The second chapter is a review of additive manufacturing technologies of biomaterials and clinical applications of 3D-printed structures for orthopedic applications. In the third chapter, the effect of pore size on cell activities was investigated in which 3D-printed PEEK scaffolds were fabricated with pore sizes ranging from 800 µm to 1800 µm. PEEK scaffolds with 800 µm pores showed higher cell attachment and proliferation as compared to the other sizes. In the fourth chapter, a one-step method was developed to process a novel ceramic-polymer 3D-printable biocomposite using a single screw extruder. Specifically, the novel AMP was mixed into PLA with the help of the melt-blending technique. Magnesium phosphate (MgP) was chosen as the bioactive component as previous studies have confirmed its biocompatible and bioactive properties. The AMP-PLA biocomposite filaments were characterized for its microstructure, mechanical, thermal, and rheological properties. Scanning Electron Microscopy (SEM) results confirmed a homogenous dispersion of AMP particles in the PLA matrix and rheological studies demonstrated good printability behavior of AMP-PLA filaments. These filaments were subsequently used to fabricate scaffolds with 500 µm pore size using the FDM technique. Results revealed a faster in vitro degradation rate of AMP-PLA as compared to the PLA. The dissolution of AMP particles generated pores in the AMP-PLA composite struts. As a result, a larger surface area of AMP-PLA composite was exposed to the surrounding media. Also, the reduction of the pH caused by PLA degradation was buffered by AMP particles to 7.2. Invitro cytocompatibility results revealed higher cell attachment and proliferation on AMP-PLA scaffolds as compared to virgin PLA scaffolds. In the fifth chapter, 3D-printable TCP-PLA composite filaments were developed in-house, with high reproducibility, using a one-step single screw extruder. The effect of FDM-based nozzle temperatures of 190 0C, 200 0C, 210 0C, and 220 0C on the composites' crystallinity, rheological, and mechanical properties were invetigated. Results confirmed the successful development of constant-diameter TCP-PLA composite filaments with a homogeneous distribution of TCP particles in the PLA matrix. A higher nozzle temperature in the FDM process increased the crystallinity of the printed PLA and TCP-PLA structures. As a result, it also helped to enhance the mechanical properties of the printed structures. The rheological studies were performed in the same temperature range used in the actual FDM process, and the results showed an improvement in rheological properties at higher nozzle temperatures. The virgin polymer and polymer-ceramic composite melts exhibited lower viscosity and less rigidity at higher nozzle temperatures, which resulted in enhancing the polymer melt flowability and interlayer bonding between the printed layers. Overall, 3D-printable TCP-PLA filaments could be made in-house, and the optimization of the nozzle temperature was essential in developing 3D-printed composite parts with favorable mechanical properties. The final chapter presents a general conclusion and discusses future directions. |
