Reactive Inkjet Printing of Novel Silk Dental Barrier Membranes

Periodontitis is a dental disease which can result in a loss of integrity of the periodontal tissues and lead to eventual tooth loss. Barrier membranes can be used in conjunction with guided bone regeneration (GBR) to help repair the damage caused by periodontitis. GBR promotes and directs the growth of new bone, whilst the barrier membrane secludes the defect site from infiltration by fast growing connective and epithelial tissues which would otherwise fill the defect space. The ideal properties for a barrier membrane are: to have a controllable degradation rate, be biocompatible, prevent surrounding tissues from collapsing into the defect space, and provide cell occlusivity. Current commercial barrier membranes are produced out of materials which are either non-resorbable, requiring a secondary surgery for their extraction, or made from resorbable materials which can have poor structural integrity or degrade into acidic by-products. Silk has had a long history of use as a biomaterial. It degrades into non-toxic components and has adaptable mechanical properties. When used in its regenerated silk fibroin form (RFS), it has recently been used for tissue engineering scaffolds. RSF has several polymorphs of which silk I and silk II are of interest. Silk I is non-crystalline and water soluble while silk II has a crystalline β-sheet structure that is non-water soluble. Silk I converts to silk II upon exposure to methanol, heat treatments and stretching. The ability to transform RSF from a water soluble structure into a non-water soluble structure makes it ideal for a variety of processing techniques. In this thesis, reactive inkjet printing has been investigated as a possible processing method of RSF for the manufacture of barrier membranes. Reactive inkjet printing has been used to control the structural conversion of silk I to silk II by printing different volumes of methanol during film fabrication. It was established that RSF crystallinity (and silk II content) was dependant on the volume of methanol printed. RSF film degradation rate was shown to be related to RSF crystallinity, and hence the volume of printed methanol. Cell studies performed on the RSF films showed that MG-63 osteosarcoma cells remained metabolically active and continued to proliferate during the duration of the study, as well as showing signs of osteogenic activity. RSF films were investigated with the inclusion of nano-hydroxyapatite (nHA) to promote osteogenic activity. nHA/RSF films were produced from a composite ink containing both nHA and RSF. It was found that the inclusion of nHA within the ink impeded the transition of silk I to silk II, and instead increased β-turn structural content, which is an intermediate structure in the transition of silk I to silk II. The inclusion of nHA within the RSF films was shown to improve the osteogenic response of the MG-63 cells. Overall, the work presented in this thesis has demonstrated for the first time that reactive inkjet printing can produce biocompatible RSF films with controllable crystallinity and degradation rate. As a result, a controllable degradation rate, the possibility of including bioactive components such as nHA, in addition to the other promising properties of RSF, make reactively inkjet printed RSF as a viable alternative for use as a barrier membrane.