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Title: Graphene-based polymer nanocomposite hydrogels
Author: Piao, Yongzhe
ISNI:       0000 0004 6350 4599
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2017
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As unique soft materials, hydrogels have received remarkable attention, due to their high water content and flexibility of materials design that make them able to well mimic biological tissues. This PhD project focused on the development of strong hydrogels for potential biomedical applications. Four types of novel nanocomposite hydrogels were prepared, characterised and studied in depth, namely graphene oxide (GO)-gelatin nanocomposite hydrogels, reduced graphene oxide (RGO)-gelatin nanocomposite hydrogels, GO-polyamidoamine (PAMAM) dendrimer nanocom-posite hydrogels and double crosslinked GO-gelatin nanocomposite hydrogels. GO-gelatin nanocomposite hydrogels were synthesised by self-assembly via physical crosslinking bonds (namely, electrostatic interaction and hydrogen bonding). This technique avoided using any organic crosslinking agents, and thus would benefit a high biocompatibility. The hydrogels showed good mechanical properties, thanks to multiple crosslinking sites on GO nanosheets and gelatin chains, exhibiting a relatively high storage modulus of up to 114.5 kPa. Drug release tests showed that the drug release from the GO-gelatin nanocomposite hydrogel was pH-dependent. RGO-gelatin nanocomposite hydrogels were further prepared from physically crosslinked GO-gelatin nanocomposite hydrogels via a facile one-pot synthesis, again without using an organic crosslinker. In this synthesis, gelatin acted as a reducing agent to convert GO to RGO and consequently was chemically grafted onto the adjacent RGO surfaces. The resultant chemically crosslinked RGO-gelatin nanocomposite hydrogels showed a significant increase in the storage modulus, 50% higher than that of GO-gelatin nanocomposite hydrogels with the same original composition. Chemically crosslinked RGO-gelatin nanocomposite hydrogels demonstrated an enzyme-favourite degradation, which lost up to 29% of their original weight after degradation for 24 h, compared to 17% without enzyme. GO-PAMAM dendrimer nanocomposite hydrogels were developed using a similar method to that for physically crosslinked GO-gelatin nanocomposite hydrogels. GO-PAMAM dendrimer nanocomposite hydrogels showed a significantly improved mechanical performance and self-healing property. Both GO and PAMAM dendrimer possess abundant functional groups which can induce multiple strong crosslinking networks. The highest storage modulus was 284 kPa, that is, 2.5 times of that for GO-gelatin nanocomposite hydrogels. The storage modulus of the GO-PAMAM dendrimer nanocomposite hydrogels increased with increasing GO or polymer concentration, but GO provided a higher modulus than PAMAM dendrimers at a comparable concentration. To develop mechanically strong hydrogels, the double crosslinked GO-gelatin nanocomposite hydrogels were synthesised through a one-pot synthesis. Gelatin was crosslinked by two crosslinking agents, glutaraldehyde (GTA) and GTA modified GO sheets, at a low water content (90 wt.%) which was much lower compared to the above nanocomposite hydrogels. In contrast to the neat gelatin hydrogel, double crosslinked GO-gelatin hydrogels exhibited significant improvements in mechanical properties, for instances, by up to 288% in compressive strength and 160% in shear storage modulus. That was ascribed to the novel double crosslinked network structure in which GTA-grafted GO sheets function as multifunctional crosslinking agents. While the mechanical strength increased with increasing crosslink degree, the swelling capability of double crosslinked GO-gelatin hydrogels decreased. The results show that the graphene-based nanocomposite hydrogels could have potential in soft tissue engineering and drug delivery.
Supervisor: Chen, Biqiong ; Rehman, Ihtesham Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available