Fabrication and characterisation of 3-D porous bioactive glass-ceramic/polymer composite scaffolds for tissue engineering
Creators: name: Mohamad Yunos, Darmawati
Publisher: name: Imperial College London
Year: 2010

description: Designing tissue engineering scaffolds with the required mechanical properties and favourable microstructure to promote cell attachment, growth and new tissue formation is one of the key challenges in the tissue engineering field. An important class of scaffolds for bone tissue engineering is based on bioceramics and bioactive glasses. The primary disadvantage of these materials is their low fracture resistance under load and their high brittleness. These drawbacks are exacerbated by the fact that optimal scaffolds must be highly porous (&gt;90% porosity). As a main focus of this thesis, a novel approach was investigated to enhance the structural integrity, fracture strength and toughness of partially sintered 45S5 Bioglass® based glass-ceramic scaffolds by polymer infiltration and to develop an understanding of the interaction of these two phases in the final composite structure. Commercially available synthetic poly(D,L-Lactic acid) (PDLLA) was incorporated as a coating onto the partially sintered Bioglass® based scaffolds by dipping technique. Two natural polymers synthesised from bacteria, which exhibit different properties to those of PDLLA, were also investigated: i.e. poly(3-hydroxybutryate) (P(3HB)) and poly(3- hydroxyoctanoate) (P(3HO)). The work of fracture of partially sintered 45S5 Bioglass® scaffolds was significantly improved by forming interpenetrating polymerbioceramic microstructures which mimic the composite structure of bone. It was demonstrated that coating with polymers such as PDLLA, P(3HB) and P(3HO) does not impede the bioactivity of the scaffolds but the extent of bioactivity, given by the kinetic of HA formation, was seen to depend on polymer type and on scaffold sintering conditions. Polymer coated 45S5 Bioglass® pellets sintered at the same condition as the scaffolds and immersed in SBF were investigated to better evaluate the bioactivity mechanism and interfacial properties of the materials. It was demonstrated that polymer coated 45S5 Bioglass® based glass-ceramic scaffolds can have higher bioactivity and improved fracture toughness when the basic scaffold structure is sintered at relative lower sintering temperatures leaving residual open porosity which can be efficiently infiltrated by the polymer. A bilayered scaffold structure was also designed and fabricated to develop for the first time a porous bioactive glass-ceramic scaffold coated with PDLLA nanofibers. Electrospinning was used to deposit a PDLLA fibrous layer on top of the bioactive glass scaffold. These scaffolds were developed for osteochondral tissue engineering applications. SBF studies showed that the extent of mineralisation of the PDLLA fibres depended on the fibrous mesh thickness. PDLLA fibres deposited for 2 hours did not mineralise when immersed for 7, 14 and 28 days in SBF making the structure suitable for osteochondral defect applications. Initial in vitro cell response studies showed that the bilayered scaffolds were non toxic and chondrocyte cells were able to proliferate on the PDLLA fibre layers, demonstrating the potential of the novel scaffolds for osteochondral tissue engineering.