Sol-gel silica-based tissue scaffolds : freeze casting and SIMS analysis strategies
Creators: name: Wang, Daming
Publisher: name: Imperial College London
Year: 2013

description: Tissues have limited self-healing capabilities when a defect is above its critical size. Biomaterials that can act as temporary templates (scaffolds) can facilitate regeneration of damaged tissues but need to be designed to fulfill the challenging requirements for tissue regeneration. Inorganic/organic hybrids have the potential to meet these demands. Hybrids have nanoscale interpenetrating networks (IPNs) of organic and inorganic components that give them the unique potential of tailored mechanical properties and controlled biodegradation. An important factor in designing a successful hybrid is the choice of polymer. Chitosan has been widely used in the biomedical field due to its biocompatibility, biodegradability and the ability to promote cell attachment and proliferation. In this thesis, silica/chitosan hybrid scaffolds with oriented structures were fabricated through the sol-gel method, followed by a unidirectional freeze casting process. 3-glycidoxypropyl trimethoxysilane (GPTMS) was used to obtain covalent coupling between the inorganic and organic components. Various compositions were synthesized by varying the cooling rate, the GPTMS and the inorganic content, in order to investigate their effect on the hybrid chemical structures and mechanical properties. Structural characterization and dissolution tests confirmed the covalent crosslinking of the chitosan and the silica network in hybrids. The scaffolds had a directional lamellar structure along the freezing direction and a cellular morphology perpendicular to the freezing direction, respectively. Compression testing showed that the scaffolds with 60 wt % organic were flexible and elastic perpendicular to the freezing direction whilst having ~160 kPa of compressive strength parallel to the freezing direction. The freeze cast silica/chitosan hybrid scaffolds have the potential for tissue regeneration. A key to the development and optimization of sol-gel tissue scaffolds will be an understanding of the uniformity of the critical elements and compounds in the material. Therefore another part of this thesis involves application of the time-of-flight secondary ion mass spectrometry (ToF-SIMS) technique to evaluate and compare various sol-gel silica-based scaffolds. ToF-SIMS has high surface sensitivity and the ability to construct chemical maps and depth profiles for all the elements and compounds to obtain their distribution throughout the material. However, SIMS is sensitive to topography and most of the scaffolds are highly porous, thus chemical mapping of these materials using SIMS is very challenging. This work involved the development of two experimental methodologies (Soak &amp; Solid and Mark &amp; Map) to overcome this issue. Sol-gel 70S30C bioactive glass foams, electrospun 70S30C bioactive glass fibers and calcium-containing silica/gelatin hybrid scaffolds were successfully analyzed, proving the feasibility of these analytical methods, which are also applicable to many other types of porous material. In addition, different silica/γ-PGA hybrid systems with calcium incorporation were studied and the ToF-SIMS data facilitated improvements in hybrid synthesis and hybrid processing routes. ToF-SIMS was shown to be a powerful analytical technique that has the potential to play a pivotal role in the biomaterial field.