Biomedical Engineering Reference
In-Depth Information
geometries and type of materials can be treated, surface topography and
bulk properties are usually not affected and they exhibit high reproduci-
bility. For surface modification, plasma approaches can be classified into
different categories: plasma etching (Inoue and Kajikawa, 2003), plasma
polymerization and plasma functionalization (Chu et al., 2002) based on the
outcomes of plasma interactions. Etching, deposition or grafting of chemical
groups can dominate in modifications of the material's surface, depending
on various factors such as the gas used, the nature of the surface and the
plasma parameters.
Plasma etching occurs when the surface material removal effect, due to
ions and active neutral species as well as vacuum ultraviolet radiation, is
prominent in the modification effect. During this process, the plasma
generates volatile etched products from the chemical reactions between the
elements present on the material surface and the plasma species.
In the plasma polymerization process, the plasma interacts with organic
molecules (monomers) and involves their fragmentation and subsequent
deposition. The plasma polymer formed thus is deposited in the form of a
thin film. Notwithstanding the use of the word polymer, 'plasma polymer'
refers to a new class of material that has little in common with the
conventional polymer. In the case of the plasma polymer, the chains are
short and randomly branched and terminate with a high degree of cross-
linking, and are not constituted by regularly repeating units.
Plasma treatment using gases such as O
2
,N
2
,NH
3
or CF
4
allows reactive
chemical functionalities to be inserted onto the material's surface.
Compared with other chemical modification methods, plasma-induced
functionalization presents interesting characteristics such as being a solvent-
free and time-efficient technique. Moreover, this treatment allows the
grafting of a wide range of different functional groups depending on plasma
parameters such as power, nature of the gas used and its pressure, duration
of treatment, etc. This method also provides the possibility of scaling up to
produce large quantities necessary for commercial use. Plasma treatment is
widely used for surface activation of various materials, ranging from organic
polymers to ceramics and metals. In this field, we can cite the polymer
surface functionalization in pulsed and continuous nitrogen microwave
plasma, under admixture of hydrogen (Meyer-Plath et al., 2003). This
process makes it possible to graft nitrogen functional groups onto
polystyrene with a high selectivity in primary amine groups.
14.3.3 Plasma-based treatment of carbon nanotubes
The surface modification of carbon nanotubes can be carried out through a
wide range of plasma processes. In addition to the already cited advantages
of plasma treatments, the number of functional groups grafted on the CNT
