Chemistry Reference
In-Depth Information
the active, most essential components of living tissue receive numerous signals from
their environment, which are decisive for their proper function. Even basic trans-
formational procedures such as proliferation, cell differentiation, and programmed
cell death (apoptosis) are crucially influenced by them. Typically, external signals
are detected, processed, and transmitted by so-called signaling-cascades, which con-
sist of complex networks of biomacromolecules including proteins, oligopeptides,
saccharides, oligosaccharides, fatty acids, and phosphorylcholine (phospholipids).
Hereby, cells are able to respond to a large variety of environmental signals
including, e.g., mechanical, thermal, electrical, and, most importantly, chemical sig-
nals. Obviously, therefore, surface properties that allow control of attachment of
such macromolecules are decisive for the efficiency of medical devices and for
acceptance of implants. Generally, the so-called shining through of surface proper-
ties [191] is a problem for any artificial biomaterial that was selected for a certain
functional reason, e.g., mechanical strength and chemical inertness in a biological
environment. A wide variety of polymers is applied as artificial biomaterials, such as
polyethylene (PE), polypropylene (PP), polystyrene (PS), polycarbonate (PC), poly-
methyl methacrylate (PMMA), polyhydroxyethyl methacrylate (PHEMA), polyvinyl
alcohol (PVA), polydimethyl silicone (PDMS), polytetrafluorethylene (PTFE), and
polyvinylidene fluoride (PVDF). These materials establish environments very dif-
ferent from natural environments consisting of neighboring cells or extracellular
matrix components, typically. Deliberate surface modifications are needed, espe-
cially of chemical binding properties, to achieve so-called interface biocompatibility
of artificial biomaterials surfaces.
Biocompatibility is defined as
the ability of a material to perform with an appro-
priate host response, in a specific application
[192,193]. Interfacial biocompatibility
means that chemical and morphological surface properties cause a targeted or at least
tolerable physiological reaction of the biological system in the context of intended
application [194]. The essential absence of thrombogenicity and carcinogenic effects,
minimal immunological and inflammation reactions, and required interactions with
the proteins, sugars, and fatty acids to control cell adhesion are characteristics of
interface biocompatibility [191,194].
The treatment of materials surfaces with nonthermal plasmas can lead to surface
activation and functionalization, which creates unique surface properties, often not
obtainable with conventional, solvent-based chemical methods.
The term “surface activation” refers to the creation of reactive surface sites.
This type of modification can be advantageous to control biomolecule attachment
in general. The term “surface functionalization” describes an intentional generation
of certain surface functional groups (functionalities). Compared to surface activa-
tion, functionalization allows a more precise control of biomolecule attachment
by selective chemical binding strategies such as covalent bonding. Functionalities
like primary amines [195], carboxylic acids, amides [196], carbonyls [197], sul-
fonic acids [198], and amino sulfonic acids are reported to play a key role for
the adhesion of specific polypeptides (for instance, cell adhesion molecules like
fibronectin, vitronectin) and polysaccharides (like hyaluronan) [199] to polymer
surfaces.
