PolyHIPE Microspheres for Injectable Bone Tissue Engineering Applications

Injectable microsphere-based delivery systems have great potential in tissue engineering, since they remove the need for open surgery. Current bone filler systems for non-load bearing applications do not fully resorb and only allow regrowth of bone at the implant interface. Within this thesis, a tissue engineered injectable bone filler was developed and optimised. This was in the form of polymeric microspheres that support human embryonic stem cell-derived mesenchymal progenitor (hES-MP) cells for implantation. A polymer high internal phase emulsion (polyHIPE) microsphere fabrication system was selected over a range of other fabrication techniques including 2-photon direct write, projection based stereolithography and microfluidic particle manufacture. A combination of the microfluidic technique and the double emulsion method were selected for further study due to their rapid production rate and inclusion of customisable internal microfeatures (porosity). Using a EHA/IBOA copolymer system the manufacturing conditions were explored to allow independent control over the microspheres external diameter (70 - 1000 µm) and interconnected internal pore size (2 – 60 µm). Static culture of hES-MP cells over 30 and 60 days on EHA/IBOA microspheres were conducted and increased cell activity was observed. Cell enabled microsphere aggregate formation was observed and the steady ingrowth of cells was observed up to day 30. The detection of calcium and collagen deposits confirmed the presence of osteoblasts within the pores of the microspheres. Osteocyte like cell morphology was observed within the pores of the microspheres after 60 days in culture. A biodegradable PCL polyHIPE system was used to repeat the key experiments performed with the non-degradable EHA/IBOA system and similar results were observed. Injection studies found superior cell survival on porous PCL microsphere compare to non-porous microspheres. A Chorioallantoic membrane assay was used to determine angiogenic potential of both seeded and unseeded microspheres. An increased angiogenic response was observed for pre-seeded microspheres. This research began with initial selection of micro-particles for a tissue engineering injectable scaffold and successfully progressed to the pre-in-vivo stage, having investigated manufacturing conditions, biocompatibility, degradability, injectability and angiogenic potential.