Titanium Phosphate Glass Microspheres as Microcarriers for In Vitro Bone Cell Tissue Engineering - Biointerfaces: Where Material Meets Biology - page 107

knowledge? And this question leads us to a new challenge, which is to
process the bulk glass into forms that would satisfy two seemingly disparate
requirements: (1) to be suitable in terms of size and morphology for use
either within the human body or within engineered devices that support an
active biological environment, and (2) to be reproducible using rapid, in-
expensive and easily scalable industrial techniques. Thus far, phosphate
glasses have been processed in the form of monoliths, discs, granules, cloths
and tubes in the macroscopic size range as well as powders and fibres in the
micro- and nano-sized ranges. 39 The application described in this chapter is
to use titanium phosphate glasses as a substrate material for the in vitro
expansion (or scale-up) of bone cells and ultimately the formation of viable
bone tissue for the treatment of critical sized bone defects (a few millimetres
in size). The development of such substrate materials involves the investi-
gation of the interactions between bone cells and glass systems firstly within
static systems such as culture well plates and subsequently within dynamic
systems such as spinner flasks and perfusion bioreactors.
For in vitro bone cell expansion, microspheres offer some unique advan-
tages over other surfaces. For instance, in comparison with tissue culture
plastic, they can provide a considerably larger surface area for cell prolifer-
ation. Furthermore, this surface area is easily and accurately quantifiable as
opposed to the case of microscopic glass powders. Both factors assume
significant importance in the context of industrial scale-up of the cell ex-
pansion process for providing a large quantity of cells that can be used in
cell-based therapies or for high throughput screening.
In this chapter, the main focus is centred on three topics: (1) microsphere
production, (2) microsphere degradation, and (3) cell-microsphere inter-
actions. The production of glass microspheres using a simple, rapid and
inexpensive technique is described. A novel time-lapse imaging method to
visualise the degradation of microspheres and also obtain subsequent
quantitative data is elaborated and this allows for correlation of the micro-
sphere degradation rate with the glass composition. Subsequently, guidance
on carrying out the culture of bone cells on microspheres and visualising
cell-microsphere interactions via scanning electron microscopy is given. The
experiments described in the chapter are easy to initiate and are also quite
versatile; for instance, the time-lapse imaging technique can be used for
visualising the degradation of other microscopic materials while the cell
culturing techniques can be used for different cell types.

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5.2 Production of Titanium Phosphate Glass
Microspheres by Flame Spheroidisation
The low fusion temperatures and ease of glass formation without vitrifi-
cation mean that phosphate glasses can be synthesised by simple con-
ventional melt-quench routes. However, P 2 O 5 —the main component of
these glasses—is highly hygroscopic; therefore, the inclusion of phosphorus