Tesi etd-09162021-173711 |
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Tipo di tesi
Tesi di laurea magistrale
Autore
ONORATI, SIMONE
URN
etd-09162021-173711
Titolo
Design and fabrication of a new micro-extruder for 3D printing of biopolymers
Dipartimento
INGEGNERIA DELL'INFORMAZIONE
Corso di studi
INGEGNERIA BIOMEDICA
Relatori
relatore Prof. Vozzi, Giovanni
relatore Prof. Dalgarno, Kenneth
supervisore Ing. Bonatti, Amedeo Franco
relatore Prof. Dalgarno, Kenneth
supervisore Ing. Bonatti, Amedeo Franco
Parole chiave
- biopolimeri
- biopolymers
- blend
- bone tissue engineering
- composites
- compositi
- filamenti
- filaments
- fused deposition modelling
- hot melt extrusion
- ingegneria tissutale
- micro-estrusione
- micro-extrusion
- miscela
- pellet
- scaffold
Data inizio appello
08/10/2021
Consultabilità
Non consultabile
Data di rilascio
08/10/2091
Riassunto
The goal of this thesis is providing solutions to fabricate, via Fused Deposition Modelling, scaffolds for the regeneration of long bones, based on biopolymeric blends or polymer-ceramic composites. The background of the thesis is the EU-funded GIOTTO project, which was conceived to fight the consequences of osteoporotic fractures by developing advanced tissue engineering solutions.
Both the direct and the indirect 3D printing of blends, starting from pellets of the pure components, were considered. The main part of the thesis focused on the direct strategy, with the design of a novel kind of ‘micro-extruder’, which brings to a miniaturized scale the process of Hot Melt Extrusion (HME) of thermoplastics. The device that can be installed on a Fused Deposition Modelling (FDM) 3D printer in place of the conventional filament-based hotend.
The micro-extruder design was carried out using a mathematical model of the polymer conveyance and extrusion process, with particular focus on maximizing multiple materials mixing, and minimizing their thermal degradation. The mechanical components were verified for extrusion flow rates and material viscosities commonly found in FDM printing, and for a nozzle diameter down to 0.6 mm. The heating system was designed with the help of finite elements simulations of the heat diffusion and convection. A value of fictitious filament diameter was found, so that the extrusion happens at the correct flow rate according to the model, when the device is controlled by conventional FDM slicing software. This simplifies dramatically the print control.
A prototype version of the micro-extruder was assembled, mounted on a pedestal, and successfully tested for warming up to 220-250 °C, and extrusion of a continuous filament from pellets with a diameter of 1.75 mm.
On the other hand, for the indirect strategy, it was designed a quantitative characterization method of the geometry of the feedstock filaments for subsequent conventional FDM. These are fabricated by conventional HME starting from pellets, and have stringent requirements of size and shape to allow a proper printing.
Both the direct and the indirect 3D printing of blends, starting from pellets of the pure components, were considered. The main part of the thesis focused on the direct strategy, with the design of a novel kind of ‘micro-extruder’, which brings to a miniaturized scale the process of Hot Melt Extrusion (HME) of thermoplastics. The device that can be installed on a Fused Deposition Modelling (FDM) 3D printer in place of the conventional filament-based hotend.
The micro-extruder design was carried out using a mathematical model of the polymer conveyance and extrusion process, with particular focus on maximizing multiple materials mixing, and minimizing their thermal degradation. The mechanical components were verified for extrusion flow rates and material viscosities commonly found in FDM printing, and for a nozzle diameter down to 0.6 mm. The heating system was designed with the help of finite elements simulations of the heat diffusion and convection. A value of fictitious filament diameter was found, so that the extrusion happens at the correct flow rate according to the model, when the device is controlled by conventional FDM slicing software. This simplifies dramatically the print control.
A prototype version of the micro-extruder was assembled, mounted on a pedestal, and successfully tested for warming up to 220-250 °C, and extrusion of a continuous filament from pellets with a diameter of 1.75 mm.
On the other hand, for the indirect strategy, it was designed a quantitative characterization method of the geometry of the feedstock filaments for subsequent conventional FDM. These are fabricated by conventional HME starting from pellets, and have stringent requirements of size and shape to allow a proper printing.
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