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IFM's Gayathri Devi Rajmohan has won the People's Prize in Deakin's Three Minute Thesis competition for 2013.
Meet the team at Deakin making it happen.
Dr Xiujuan Jane Dai
+61 3 522 72427
The challenge in the field is to to be able to reliably produce surfaces and interfaces with the desired characteristics, and understand the mechanism of plasma in liquid.
We have achieved a controllable and selectable surface functionalization using an improved gas/vapour plasma system. Now we are developing liquid plasma technology using a nanosecond pulsed generator at atmospheric pressure for specific biomedical applications and fabrication of micro / nano-devices.
Immobilisation of receptor molecules of the target analyte is necessary in order to achieve high specificity in biosensors. Surface immobilisation affects the binding affinity, sensitivity and specificity of the sensing device. Therefore, during immobilisation, it is crucial to ensure that there is a good linkage between the sensor substrate surface and immobilised receptor molecules so that they are not easily displaced by biological medium. Compared to the conventional wet chemical method used for surface modification or functionalization, gas plasma treatment offers the benefits of ease of implementation and it is a one-step process performed in a dry environment. Oxygen gas was used during the plasma treatment to produce functional groups on the SU-8 surface. A combination of continuous plasma and pulsed plasma mode was employed during gas plasma treatment. It produced a surface layer with the advantages of the higher stability obtained from continuous wave plasma and higher density of functional groups obtained via pulsed plasma. Argon plasma was used for surface cleaning and activation prior to oxygen plasma treatment. The successful immobilisation of aptamers on the sensor surface was verified using AFM.
Plasma, generated in liquid at atmospheric pressure by a nanosecond pulsed voltage, was used to fabricate hybrid structures from boron nitride nanotubes and gold nanoparticles in deionized water. The pH was greatly reduced, conductivity was significantly increased and concentrations of reactive oxygen and nitrogen species in the water were increased by the plasma treatment. The treatment reduced the length of the nanotubes, giving more individual cuplike structures, and introduced functional groups onto the surface. Gold nanoparticles were successively assembled onto the functionalized surfaces. The reactive species from the liquid plasma along with the nanosecond pulsed electric field seem to play a role in the shortening and functionalization of the nanotubes and the assembly of gold nanoparticles. The potential for targeted drug delivery was tested in a preliminary investigation using doxorubicin-loaded plasma-treated nanotubes which were effective at killing ~99% of prostate cancer cells.
The pulsed plasma functionalization approach can give nanostructured coatings or introduce various chemical functional groups (-NH₂, -COOH, -SH, etc.) onto metals, semiconductors, ceramics, polymers, fibres, CNTs and nanoparticles. The functional groups can be well controlled to match the requirements of the new surface, especially for improved biocompatibility of implants.
The second paper in the series was the first report of the novel approach of combining continuous wave (CW) and pulsed plasma modes. This has enabled the generation of stable interfaces with a higher density of -NH₂ on metals, ceramics and semiconductors. The thin CW plasma polymerized heptylamine layer provides strong cross-linking and attachment to the metal or semiconductor surface and a good foundation for better bonding of a pulsed PPHA layer. This top layer has higher levels of functional groups because it retains more of the monomer structure. The combined mode provides the pulsed mode advantage of a 3-fold higher density of -NH₂ while retaining much of the markedly higher stability in aqueous solutions, or during sterilization, of the continuous mode.
This is the third in the series of papers and demonstrated that the bio-compatibility of titanium implants can be greatly improved by appropriate plasma treatment. A novel bio-interface, produced by a combined plasma polymerization mode on a titanium (Ti) surface, was shown to enhance osteoblast growth and reduce fibroblast cell growth. This new method can securely attach a tailored interface to difficult materials such as Ti or ceramics. Here a more stable and higher density of -NH₂ functional groups is able to withstand sterilization in ethanol. The biocompatibility, in terms of cell attachment and actin cytoskeleton development, was markedly improved in vitro, compared with untreated Ti surfaces and samples treated by other plasma modes. It gave a boosted (~ 6 times higher) cellular response of osteoblasts in their initial adhesion stage. These factors should increase the formation of new bone around implants (reducing healing time), promoting osseointegration and thereby increasing implantation success rates.
Fluorescence image of the treated and untreated Ti (left) and diagram comparing different plasma treatments (right)
A new fabric with potential in medical textiles was developed by application of a surface coating on wool using pulsed plasma polymerization of HMDSO. This coating enabled a controllable MVTR and surface adhesion. MVTR in the range recommended for optimum wound healing was obtained by varying frequency, monomer pressure and deposition time. Lower surface adhesion was achieved. Peeling tests, contact angle measurements, SPM force curves and ATR FT-IR were used to characterize the surfaces for both wool and a polyethylene model substrate. All the results were consistent with a decrease in surface energy after PP-HMDSO treatment. ATR FT-IR results showed a siloxane film with less organic Si-(CH₃)n groups and more Si-O-Si cross-links.
Multi-walled carbon nanotube (MWCNT) reinforced PLLA composites were investigated as a potential new-generation implant material. The surface of the composite was functionalized with -NH₂ groups by plasma polymerization of heptylamine. A -NH₂ density of about 6% was achieved giving remarkably improved hydrophilicity. Biocompatibility was significantly improved, shown by cell growth, due to the changes in roughness and surface chemistry.
SEM images of cell growth on different surfaces
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