AbstractNanomaterials are defined as structures possessing one or more dimensions
below 100 nanometres in size. They display unique properties that arise as a
result of quantum behaviours, owing to their high surface area to volume
ratios. Self-assembling nanomaterials (SANs), where individual components
referred to as “building blocks” spontaneously organise into complex
structural arrangements, is a prominent field that offers technological
innovation within medicine and beyond. To effectively exploit this approach in
healthcare however, a high-level of behavioural understanding within
biological systems is required, which has yet to be ascertained.
Accordingly, work undertaken in this thesis aimed to investigate how gold
nanoparticles self-assemble and interact within a biological environment.
Molecular recognition and electrostatic attraction, two different underpinning
mechanisms of self-assembly were studied. Based on findings within this
thesis, the latter approach was chosen for further development.
Corresponding functional gold nanoparticles were incorporated into
PEGylated liposomes using a novel method and extensively characterised.
Comparative cytotoxicity evaluation was carried out in vitro on a male
Chinese hamster lung fibroblast cell line (V79), employing MTT and LDH
assays. Investigations focused on identifying any differences in biological
response after treatment with individually dispersed gold nanoparticles and
as they underwent in situ self-assembly. Cellular uptake and any ensuing
self-assembly was investigated using a combination of electron microscopy
and elemental analysis on thin-sectioned specimens.
Results presented in this thesis reveal that both electrostatic interactions and
molecular recognition facilitate self-assembly under aqueous conditions.
Within a biologically relevant medium however, considerable nanoparticlebiomolecule
complex formation occurs and only particles exploiting
electrostatic interactions persist to self-assemble. Gold nanoparticles were
capable of being encapsulated within liposomes by exploiting electrostatic attractions between oppositely charged lipids and ligands on particle
surfaces. The novel method resulted in variable internalised gold to lipid
ratios, hypothesised to result from differing magnitudes of electrostatic
attraction during preparation. At clinically relevant concentrations, gold
nanoparticles functionalised with cationic or anionic ligands did not display
significant cytotoxicity. A significant difference in cytotoxicity was displayed
as they underwent in situ assembly however. Cellular internalisation of gold
was evidenced, with nanoparticles seen to accumulate and reside within
cellular vacuoles, but no confirmation of self-assembly was obtained.
In conclusion, the current work provides further knowledge regarding the
feasibility, risk and current limitations associated with utilising and evaluating
nanomaterials for in-situ self-assembly within biological environments.
Extensive interactions shown to occur between initial building blocks and
biological components can hinder self-assembly activity, highlighting the
importance of rational design when manufacturing SANs. Individual
nanoparticles were encapsulated within surface-modified liposomes,
demonstrating a possible strategy towards implementing further control over
SANs. Cellular studies identified a difference in toxicity between individual
building blocks and their assembled suprastructures, demonstrating that
unique biological responses could arise from the self-assembly of SANs.
Evaluation of intracellular self-assembly and the ability to differentiate
between individual building blocks, assembled suprastructures and cellular
components is inherently difficult. Current techniques and approaches
require further development to enable routine and reliable assessment of
analogous in situ self-assembling nanosystems.
|Date of Award
|Dipak Sarker (Supervisor)