Development and Assessment of In Vitro Models of Osteogenic Microstructures

In vitro models of bone aim to use materials that encourage the fast
deposition of significant amounts of mineral and collagen. Although this
would be beneficial in tissue engineering applications, using this for in vitro
modelling oversimplifies the organised structure that is observed in mature
bone. Furthermore, cortical and trabecular bone have notably different
architectures. Within this thesis, two differential scaffolds were developed
and tested, for use in lamellar and trabecular bone models, to mimic
structural features of the two bone-type organisations that are commonly
overlooked in in vitro models.
For a model of lamellar bone, aligned and non-aligned polycaprolactone fibres
were explored, to test whether human cells at an early stage of osteogenic
differentiation would deposit collagen exhibiting a twisted plywood
deposition behaviour and provide a model system of laboratory-grown
lamellae. On aligned fibres, there was an observable spacial change in collagen
direction comparable to that seen within physiological human lamellae,
which shows a gradual change in fibril direction between 10-60° from the
initial orientation of the fibrils closest to the osteon’s centre. A method to
produce a more cortical bone-like structure may be valuable for a variety of
applications, including the development of more accurate models of lamellar
osteogenesis, or for use in high-throughput drug testing.
To produce a trabecular-like material, a novel method for producing a porous
emulsion was explored. By the combination of mechanical properties of
methacrylated polycaprolactone-triol (3PCL-MA) and the biocompatibility of
gelMA, this work aimed to develop a tuneable and mechanically robust porous
bioink for the 3D printing of trabecular bone, using a curable two-phase
emulsion system. 3PCL-MA/GelMA emulsions provide a viable route for the
fabrication of stiff, printable inks. The mechanical properties of the inks are
significantly higher than that of pure gelMA, which may make them a more
promising option for the culture of bone cells