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Full-Text Articles in Engineering
3d Printed Microporous Collagen Constructs Using The Freeze-Fresh Methodology, Thais Sousa Senzano
3d Printed Microporous Collagen Constructs Using The Freeze-Fresh Methodology, Thais Sousa Senzano
Theses and Dissertations
Scaffold microporosity is known to play a critical role in governing cellular response including cell migration, proliferation, and tissue-specific differentiation. While fabrication approaches such as solvent leaching and freeze-casting are commonly used for the generation of microporous biomaterial scaffolds, these methods provide little control over scaffold geometry and creation of complex tissue structures. Extrusion-based 3D printing, an additive manufacturing method, is a highly versatile layer-by-layer printing approach that allows for the fabrication of easily customizable 3D scaffolds with complex architecture using a vast selection of polymeric bioinks. These 3D printed constructs are porous at the macroscale, but achieving microporosity (i.e., < 100 μm) in printed constructs is challenging due to the sub-optimal resolution of the extrusion-based printing method. A recent study using alginate inks introduced a new fabrication technique termed Freeze-FRESH(FF)that combines extrusion printing and freeze-casting approaches to generate 3D constructs with hierarchical microporosity. However, the porosity of the resultant alginate constructs was comparable despite changing the freezing temperature. In the current study, the FF method was modified to print collagen constructs with greater control of microporous architecture. Highly concentrated collagen type I ink was used to 3D print collagen constructs using the freeform reversible embedding of suspended hydrogels (FRESH)approach. Modification of the FF technique entailed melting of the FRESH bath post printing via incubation at 37 °C followed by freezing and lyophilization to allow for collagen gelation and better heat transport during the freezing process. The effect of freezing temperature on micropore size, swelling degree, degradation, and mechanical properties of printed constructs was assessed. Finite element (FE) models were generated to predict the mechanical properties of microporous scaffolds. In addition, the effect of microporosity on Saos-2 cell morphology, proliferation, infiltration, and ALP activity was evaluated. Results from the study showed that freezing temperature effectively modulated micropore size and that constructs with larger micropore size were more stable. Microporosity had no effect on swelling ratio yet caused a decrease in mechanical properties of collagen constructs; FE models confirmed experimental results. Cell metabolic activity and infiltration was enhanced in microporous constructs with larger pore size, yet there was no effect on cell morphology, and ALP activity. In conclusion, the modified FF technique can be effectively used to fabricate hierarchically porous 3D collagen constructs.
Improving Long-Term Vascular Graft Viability Using Peritoneal Pre-Implantation And Epsin-Mimetic Peptides, Mahyar Sameti
Improving Long-Term Vascular Graft Viability Using Peritoneal Pre-Implantation And Epsin-Mimetic Peptides, Mahyar Sameti
Theses and Dissertations
The primary goal of this project was to produce and develop a tissue-engineered small-diameter vascular graft which can replace the arteries and function well for long-term grafting. Implanting an electrospun tubular conduit into the peritoneal cavity to recruit autologous cells prior to grafting the conduit into the artery is a method to achieve this goal. Incorporating an epsin-mimetic peptide on the conduit prior to grafting is another proposed method to reach the goal. This will be accomplished through four complementary studies: (1) determining the effect of a pouch in peritoneal pre-implantation and reducing the potential peritoneal adhesion formation;(2) determining the …
An Experimental And Computational Mechanical Analysis Of Bone Anchors And Substrate Interface, Samantha May Schultz
An Experimental And Computational Mechanical Analysis Of Bone Anchors And Substrate Interface, Samantha May Schultz
Theses and Dissertations
Screw loosening is a common concern in orthopedic surgery. Therefore, this study is a computational and experimental evaluation of bone substrate and cortical screw interface. An axial load test was performed in an Instron with titanium alloy screws with 2.7 mm, 3.5 mm, and 4.5mm diameter orthopedic cortical screws inserted into SawBone with densities varying from 10 to 50 pounds per cubic foot (PCF), incrementing in sets of 10 PCF. SawBone was chosen in place of human bone because it has been shown to emulate the same mechanical properties (1). Twelve samples were prepared for each screw size and substrate …
Development Of A Graphical User Interface For Ecg Signals Classification Using Statistical Features Analysis, Mousa Hammad S Aldosari
Development Of A Graphical User Interface For Ecg Signals Classification Using Statistical Features Analysis, Mousa Hammad S Aldosari
Theses and Dissertations
Cardiac diseases are the most common cause of mortality in the world. The detection of cardiac arrhythmias is not a straightforward process, since minor variations in the electrocardiogram (ECG) signals cannot be easily identified manually. Therefore, automatic detection and classification of cardiac arrhythmia would shorten the diagnostic time and accelerate medical intervention resulting in reducing the mortality rate. In this thesis, I have developed a simple and low-cost computer-aided diagnostic system using MATLAB-based Graphical User Interface (GUI) to facilitate fast operation and access to the data along with the overall accuracy of the system. The acquired ECG signals are processed …
Mechanical And Material Properties Of Nitinol And Its Application To Stents, Ariana Solis Eichler
Mechanical And Material Properties Of Nitinol And Its Application To Stents, Ariana Solis Eichler
Theses and Dissertations
Nitinol is a functional material with superelastic and shape memory properties derived from its unique molecular structure. The purpose of this thesis is to explore how the material and mechanical properties of self-expanding Nitinol stents affects the forces applied to arterial walls during stent deployment compared to the traditional balloon-expanding stainless steel stents, in addition to contrasting thin and thick-walled pressure vessel mathematical models. Nitinol’s mechanical properties can be optimized for stent applications by tailoring its processing procedures. Nitinol stents demonstrated a reduced circumferential hoop stress on the vessel wall and greater factor of safety with respect to vessel rupture …