Chemistry Reference
In-Depth Information
Essentially, there are three basic advantages of plasma activation and function-
alization which suggest their use for such modifications of the afore mentioned
materials:
1. The superior chemical reactivity of plasmas allows surface activation of
inert materials, including creation of covalently bound functional groups.
2. Properly operated plasma activation and functionalization processes do
neither affect bulk material characteristics nor produce toxic substances.
Especially, the number of newly introduced chemical bonds or molecular
substances can be limited to the absolutely necessary minimum, i.e., only a
few of the topmost molecular surface layers are modified. Hence, an evo-
cation of potentially adverse effects by the introduction of large amounts of
foreign substances will be limited a priori. This is a significant advantage
compared to alternative procedures, including plasma-assisted deposition of
biocompatible plasma polymer films.
3. Properly operated nonthermal plasmas cause only minor thermal load to
substrates. This is a significant advantage if heat sensitive polymeric bio-
materials are treated. Many fine biomedical device structures do not tolerate
substantial heating too.
Both, nonthermal plasmas at normal pressure (particularly at ambient atmosphere)
andlow-pressureplasmascanbeapplied. Whilenormalpressureplasmasofferadvan-
tagesintermsofinvestmentcostandprocessintegrability,low-pressureplasmasexcel
by their superior chemical selectivity.
The interested reader is referred to numerous reviews with direct relevance to
this chapter [200-207], and reviews focusing on related applications, for instance,
on plasma polymerization [208], grafting processes [209], resorbable biomaterials
[210], blood compatibility [211], and the challenges to analysis [212].
Here, we will focus on examples for the application of plasma-functionalized
polymer surfaces. In particular, this section will deal with chemically different
surfaces applicable to control cell behavior.
8.2.3.4.2 Treatment of Polymers in Oxygen-Containing Plasmas
Surface modifications using oxygen-containing gases are easily performed by many
discharge configurations. Typically, low pressure radio frequency or microwave dis-
charges are used, but corona discharges or barrier discharges at atmospheric pressure
are also often applied. At atmospheric pressure, air is the preferred working gas.
Air, oxygen, or oxygen in argon carrier gas are used at low pressure. In most cases,
the gases are chosen for technical reasons. Regarding chemical functionalization, the
effects of all these discharges are dominated by the presence of oxygen since the
atomic oxygen produced by the discharges is extremely reactive to hydrocarbons.
It easily abstracts hydrogen from C-H bonds, thus producing hydrocarbon radi-
cal sites. Additional radical sites are produced by mechanisms such as UV photon
absorption and ion bombardment. The radical sites in turn have a very high affinity
to atomic oxygen, molecular oxygen, and OH radicals, which are often available
in relevant quantities by the mere presence of residual water vapor (e.g., humidity
