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Mechanical Reinforcement of Bioglass®-Based Scaffolds

Mechanical Reinforcement of Bioglass®-Based Scaffolds

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Author
Bertolla, Luca
Advisor
Dlouhý, Ivo
Referee
Prof. Dr.-Ing. habil. Aldo R. Boccaccini
Kotoul, Michal
Pabst, Willi
Grade
P
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Abstract
Bioactive glasses exhibit unique characteristics as a material for bone tissue engineering. Unfortunately, their extensive application for the repair of load-bearing bone defects is still limited by low mechanical strength and fracture toughness. The main aim of this work was two-fold: the reinforcement of brittle Bioglass®-based porous scaffolds and the production of bulk Bioglass® samples exhibiting enhanced mechanical properties. For the first task, scaffolds were coated by composite coating constituted by polyvinyl alcohol (PVA) and microfibrillated cellulose (MFC). The addition of PVA/MFC coating led to a 10 fold increase of compressive strength and a 20 fold increase of tensile strength in comparison with non-coated scaffolds. SEM observations of broken struts surfaces proved the reinforcing and toughening mechanism of the composite coating which was ascribed to crack bridging and fracture of cellulose fibrils. The mechanical properties of the coating material were investigated by tensile testing of PVA/MFC stand–alone specimens. The stirring time of the PVA/MFC solution came out as a crucial parameter in order to achieve a more homogeneous dispersion of the fibres and consequently enhanced strength and stiffness. Numerical simulation of a PVA coated Bioglass® strut revealed the infiltration depth of the coating until the crack tip as the most effective criterion for the struts strengthening. Contact angle and linear viscosity measurements of PVA/MFC solutions showed that MFC causes a reduction in contact angle and a drastic increase in viscosity, indicating that a balance between these opposing effects must be achieved. Concerning the production of bulk samples, conventional furnace and spark plasma sintering technique was used. Spark plasma sintering performed without the assistance of mechanical pressure and at heating rates ranging from 100 to 300°C /min led to a material having density close to theoretical one and fracture toughness nearly 4 times higher in comparison with conventional sintering. Fractographic analysis revealed the crack deflection as the main toughening mechanisms acting in the bulk Bioglass®. Time–dependent crack healing process was also observed. The further investigation on the non-equilibrium phases crystallized is required. All obtained results are discussed in detail and general recommendations for scaffolds with enhanced mechanical resistance are served.
 
Bioactive glasses exhibit unique characteristics as a material for bone tissue engineering. Unfortunately, their extensive application for the repair of load-bearing bone defects is still limited by low mechanical strength and fracture toughness. The main aim of this work was two-fold: the reinforcement of brittle Bioglass®-based porous scaffolds and the production of bulk Bioglass® samples exhibiting enhanced mechanical properties. For the first task, scaffolds were coated by composite coating constituted by polyvinyl alcohol (PVA) and microfibrillated cellulose (MFC). The addition of PVA/MFC coating led to a 10 fold increase of compressive strength and a 20 fold increase of tensile strength in comparison with non-coated scaffolds. SEM observations of broken struts surfaces proved the reinforcing and toughening mechanism of the composite coating which was ascribed to crack bridging and fracture of cellulose fibrils. The mechanical properties of the coating material were investigated by tensile testing of PVA/MFC stand–alone specimens. The stirring time of the PVA/MFC solution came out as a crucial parameter in order to achieve a more homogeneous dispersion of the fibres and consequently enhanced strength and stiffness. Numerical simulation of a PVA coated Bioglass® strut revealed the infiltration depth of the coating until the crack tip as the most effective criterion for the struts strengthening. Contact angle and linear viscosity measurements of PVA/MFC solutions showed that MFC causes a reduction in contact angle and a drastic increase in viscosity, indicating that a balance between these opposing effects must be achieved. Concerning the production of bulk samples, conventional furnace and spark plasma sintering technique was used. Spark plasma sintering performed without the assistance of mechanical pressure and at heating rates ranging from 100 to 300°C /min led to a material having density close to theoretical one and fracture toughness nearly 4 times higher in comparison with conventional sintering. Fractographic analysis revealed the crack deflection as the main toughening mechanisms acting in the bulk Bioglass®. Time–dependent crack healing process was also observed. The further investigation on the non-equilibrium phases crystallized is required. All obtained results are discussed in detail and general recommendations for scaffolds with enhanced mechanical resistance are served.
 
Keywords
bioactive glass, scaffolds, composite material, mechanical properties, tensile test, SPS, bioactive glass, scaffolds, composite material, mechanical properties, tensile test, SPS
Language
angličtina (English)
Study brunch
Fyzikální a materiálové inženýrství
Composition of Committee
prof. Ing. Jiří Švejcar, CSc. (předseda) Prof. Dr.-Ing. habil. Aldo R. Boccaccini (člen) prof. RNDr. Michal Kotoul, DrSc. (člen) doc. Dr.Dip.Min. Willi Pabst (člen) prof. RNDr. Jan Kohout, CSc. (člen) prof. Ing. Martin Trunec, Dr. (člen) Ing. Zdeněk Chlup, Ph.D. (člen)
Date of defence
2015-12-10
Process of defence
Dosažené výsledky, jejich prezentace, reakce na připomínky oponentů i obecná diskuse jednoznačně prokázaly připravenost doktoranda pro tvůrčí práci. Práce je vysoce inovativní a přinesla řadu originálních výsledků a poznatků, např. použití mikrofibril celulózy na zpevnění polymerních povlaků, objasnění experimentálního i teoretického vlivu polymerního a kompozitního povlaku na zpevnění struktury a lomové chování keramické pěny, změny ve struktuře bioskla, ke kterým dochází v průběhu SPS. Práce přinesla řadu námětů k využití poznatků a dalšímu pokračování.
Result of the defence
práce byla úspěšně obhájena
Persistent identifier
http://hdl.handle.net/11012/51852
Source
BERTOLLA, L. Mechanical Reinforcement of Bioglass®-Based Scaffolds [online]. Brno: Vysoké učení technické v Brně. Fakulta strojního inženýrství. 2015.
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  • 2015 [51]
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