Biomedical Engineering Reference
In-Depth Information
In this study, the biomaterials used for fibroblasts adhesion are made of polyelectrolytes us‐
ing the layer-by-layer technique based on alternating oppositely charged polyelectrolytes on
glass probes (more details are shown in paragraph III.2).
2.2. Polyelectrolytes
Polyelectrolytes are highly charged nanoscopic objects or macromolecules. Their electric
charge density appears as more or less continuous, when it is seen from distances to the
macromolecule equal to several times to the intercharge distance, giving them the polyelec‐
trolytic character. Obviously, their properties will be extremely different according to their
geometry. Massive spherical objects will behave like colloids, whereas linear flexible objects
will keep some of the macromolecular polymeric character [5]. They are defined as materials
for which the solution's properties in dissolvent presenting a high permittivity are governed
by electrostatic interactions for distances superior to the molecular dimensions [6]. Polyelec‐
trolytes are by no way a mere superposition of electrolytes and polymers properties. New
and rather unexpected behaviours are observed:
•
Whereas polymers exhibit only excluded volume effects, the long ranged coulomb inter‐
actions, which are present in polyelectrolytes, give rise to new critical exponents.
•
The main difference with electrolytes is that one kind of ions, the counterions are stuck
together along a chain, and the collective contribution of the charged monomers causes a
strong field in the vicinity of the chain, even at very low dilution.
These materials are widely used in industries as dispersive substances in aqueous medium,
flocculants to aggregate sludge and industrial waste. Recently, they were used to make films
by alternating thin layers of polymers of medical use such as dental prosthesis, fabrication
of transplantable organs etc…
Polymers differ by their structure, their surface composition and their biological properties:
2.2.1. Biological properties
The biological properties reflect the origin of polymers. Indeed, one can distinguish three
different origins for polymers [7]:
•
Natural polymers coming from animal, vegetal and mineral origins
•
Artificial polymers with natural basic components and chemically transformed functions
in their units (monomers)
•
Synthetic polymers presenting synthetic basic components which are often very similar to
those of natural polymers
2.2.2. Physico-chemical properties
According to Oudet [7], polymers have different physical properties. The most important
are their thermal conductivity reflecting polymers' behaviour under temperature changes.
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