ANFF-VIC Biointerface Engineering Hub

Plasma polymerisation is a technique for modifying the surfaces of materials by adding a thin film which possesses specific functional groups. This technique can deposit films with a variety of chemistries, such as alkanes, alcohols, acids, amines, thiols, PEO-like and fluorocarbons. These functional films can vary the chemistry, charge and wettability of surfaces in addition to how they interact with various biological molecules such as proteins, cells and bacteria.

Plasma is produced by a glow discharge through gas or vapour at reduced pressure. The molecules of the gas or vapour are fragmented using radio frequency energy. The thickness, structure and surface functionalities of the film can be controlled by varying the plasma power, flow rate and deposition time.

Swinburne has six custom made plasma reactors, each designated for particular surface chemistries or applications. One of the reactors is heated, to enable the vaporisation of monomers with low volatility. Commonly deposited films include, but are not limited to, allylamine to produce positively charge amine terminated surface, acrylic acid to produce negatively charge carboxyl terminated surface and octadiene to produce carbon rich hydrophobic films.

Spectroscopic ellipsometry is a model based, non-destructive and non-contact optical characterisation technique used to determine a number of properties of a thin film, including thickness. Polarised light is shined on the surface, reflected and received by the detector. The changes in polarisation also enable several other parameters to be determined, including roughness, crystalline nature, doping concentration and electrical conductivity. Our ellipsometer has a wavelength range of 210 to 1690 nm and can measure film thicknesses between 2nm and 3nm.

Dip coating is a process to deposit thin films from solution. The substrate is immersed and withdrawn from coating material at a constant speed. A large variety of films can be produced by using either self-assembly, sol-gel chemistry or layer-by-layer assembly.

Different properties of the film can be controlled by varying parameters such as the submersion time, withdrawal speed and number of cycles.

Quartz Crystal Microbalance (QCM) detects mass changes at the sensor surface with nanoscale resolution. Molecule-surface interactions are detected as changes in mass, as the mass will increase as molecules adsorb and decrease as molecule desorb.

The QCM sensor oscillates at its resonance frequency by alternating voltage. The frequency of the sensor decreases when mass is attached to the sensor. QCM can be used to measure the interactions of proteins, polymers, surfactants and cells with surfaces in solution.

Plasma, a highly excited gas or vapour, usually needs lower than normal atmospheric pressure to occur. A small plasma jet can however be generated at standard atmospheric pressure using a stream of gas. In this atmospheric plasma system, a stream of air is used to clean and treat surfaces. The main advantage of atmospheric plasma is the speed of treatment in comparison to traditional low-pressure plasma, as the sample does not need to be placed in a low-pressure vessel and the air evacuated. Using atmospheric plasma, a surface can be treated in only a few minutes.

The air plasma jet is rastered across the sample, which typically removed any surface contamination and makes the surface more wettable (hydrophilic). This type of cleaning is often required prior to the deposition of a coating, as a clean surface results in better adhesion of the coating which often results in a longer lifetime. This atmospheric plasma instrument can also be used to deposit hexamethyldisiloxane (HMDSO) films. HMDSO films can be used to deposit a coating with variable properties, depending on the deposition parameters.

Wettability is a surface property that is important for a number of applications. For a hydrophilic surface, the water droplet spreads across the surface whereas for a hydrophobic surface a water droplet beads on the surface. Various surface modification techniques, such as plasma polymerisation, can be used to vary the wettability of a surface.

Contact angle uses a syringe to place a droplet of water onto the surface being investigated. An image taken of the droplet using a high-resolution camera is processed to determine the angle between the droplet and the surface. A highly wettable (hydrophilic) surface has a contact angle less than 90°. A less wettable (hydrophobic) surface has a contact angle greater than 90°. Contact angle is extremely useful for determining the effect of changing surface roughness and/or surface chemistry on the wettability of a surface.

Everything on Earth, including our experiments, are influence by gravity. Microgravity, refers to the weightless conditions an object experiments when the effect of gravity are cancelled out. Microgravity can be achieved at a lab-scale, using instruments such random positioning machines (RPMs). These instruments simulate microgravity using a program of randomly generated position that over long periods of time (days or weeks) negate the effect of gravity on the experiment. Microgravity experiments can be utilised to investigate how a number of processes, such as plant/cell/bacteria growth, electrolysis, manufacturing or microfluidics would function in low gravity environments, such as those in space.

Four microgravity reactors are available to accommodate a wide variety of samples. These reactors typically accommodate standard T25 cell culture flasks and multi-well plates. However other samples and/or sample holders can be accommodated on the 150 mm x 120 mm sample stage. These reactors also have electrical feedthroughs for experiments requiring power or real-time monitoring. Both zero G and variable G programs are available on all four reactors. Two dedicated incubators (Nuiare Direct Heat In-VitroCell) can each accommodate one reactor to enable microgravity experiments to be undertake at specific temperature and oxygen concentrations.