Manipulating the chemistry and nanotopography of cultured diatoms for the application in tissue regeneration technologies

The overall objectives of this PhD are to investigate the ability of diatoms (microalgae) to uptake and incorporate a selection of metal ions into their silica cell walls (known as frustules). This is intended to be achieved via a simple "in-vivo culturing" method, in which the salts of the desired metals are dissolved into the diatoms' culture medium. Once we confirm successful uptake, we will then shift the focus to optimise the conditions for maximum metal ion uptake, through altering the culturing conditions. After the diatoms have incorporated the metal ions they will then be characterised, with particular attention to any chemical or physical changes that occur post metal uptake.

As stated above we will culture our own diatoms, provided by our collaborators (Dr Matthew Julius, St Cloud State University), and vary multiple conditions and parameters, such as concentrations of metals and nutrients, to available lighting etc. Once the diatoms have been successfully grown their metal uptake will be measured through a range of analytical techniques. The metal ions that are incorporated into the frustule may change the nanotopography (mainly pore distribution and size), and any ions that are incorporated into the organic phase may change the composition of fatty acids. To analyse the physical/structural features, methods such as AFM, EDX, SEM and TGA will be used. For the chemical/fatty acid analysis, methods used will include GCMS & ICP.

We will use these techniques to monitor metal incorporation and try to optimise conditions to allow for maximum uptake. After this stage dissolution studies may be carried out to try and determine the metal ion release kinetics.

This research is of particular interest for two key reasons:
Firstly, this research should shed light on the process by which diatoms take up and incorporate metals into their frustules - prior work has shown that Ca and Ti are incorporated into frustules, however not a great amount of detail is known about the process. Therefore, we wish to extend the database of metals known to be utilised by diatoms, and further understand what effects these metal ions have on the biochemistry and frustule structure.

The other core reason for this research being of interest is the potential applications in biomaterial technology that may be derived and further developed from the understanding this research will provide. Diatoms themselves produce very intricate porous nanostructures that are perfectly replicated each generation, and with precision that would be hard to replicate from current nanofabrication processes (which are extremely costly and utilise hazardous materials). If we can harness these biological nanofabricating "factories" and begin doping these frustules with substitute metal ions we may have a more environmentally friendly & inexpensive pathway to nanomaterials. We can then tune these structures with the ions being incorporated - within our research we have chosen particular metal ions that have been shown within the current literature to have beneficial effects on bone cells to inspire bone regeneration and increase bone density (therefore, may be the preliminary research to inspire new drugs/therapies for bone deterioration diseases like osteoporosis).
To now there are not many hassle free implantable materials that do not cause an immune response, and other porous nanomaterials are difficult and expensive to manufacture, typically requiring hazardous chemicals, It has already been shown that "diatom biosilica is non-toxic and does not invoke a pro-inflammatory response", therefore offering a relatively benign and inexpensive pathway to highly porous implantable nanostructures, and hopefully they will be shown to incorporate metal ions that in one way or another help bone healing / regeneration.