Biomedical Engineering Reference
In-Depth Information
electron microscopy.
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The following years have seen literally hundreds of
publications where PLL is employed for cell attachment to surfaces of ceramics,
hydrogels, plastics, metals, etc. An excellent example in this area was the study
of human K562 erythroleukemic cells grown in PLL-coated culture
containers.
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Interestingly, the authors of this work established that changes in
both membrane conductivity and permittivity were apparently altered by the
cell-PLL interaction. Redistribution of cellular species after exposure to PLL
was investigated using flow cytometry and immunofluorescence microscopy.
The results seem to indicate that such redistribution may, in part, be
responsible for cellular adaptation to the new growth environment of K562
cells and for the variations in membrane electrical properties observed.
More recent rimes have seen attempts to adhere cells to substrates in a three-
dimensional fashion. In this work, thermoformable polymer films were
fabricated to produce micro-structured scaffolds, e.g. curved and m-patterned
substrates, rather than the more conventional planar system. The surface of a
poly-lactic acid membrane was coated with a photopatterned layer of PLL and
hyaluronic acid (VAHyal) to attempt spatial control over cell adhesion. Human
hepatoma cells (HepG2) and mouse fibroblasts (L929) were used to demon-
strate so-called guided cell adhesion.
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Closer to home with regard to this text, PLL has also been used recently in
conjunction with polyethylene glycol (PEG) based hydrogel to fabricate a
superior neuro-electrode interface.
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The thrust of this work was the fabrication
of neural prostheses, which is an extremely active area of research connected to
the treatment of lost neural function (discussed in more detail later in the text).
In order to mimic natural neural tissue it is important that the prosthetic device
exhibits appropriate properties, i.e. biocompatibility with respect to mechanical
and surface chemical behavior; as alluded to previously, hydrogels possess ideal
characteristics from both perspectives. In particular, the use of polyethylene
glycol is extremely popular in view of its well-established biocompatibility
properties. The polymer is known to be resistant to cell and biochemical
macromolecule non-specific adsorption, conferring reduced biological damage
at the biospecies-substrate interface. (The reason for this effect remains
obscure, although the role of trapped water has very often been ascribed to
contribute to the mechanism.) Accordingly, a technique was reported which
described enhancement of the interface between polymeric brain mimetic
coatings and neural tissue using PLL. Polymer-modified PEG-based hydrogels
were synthesized, characterized and shown to promote neural adhesion using a
PC12 cell line. In addition, it was observed that the polymeric materials
adhered to electrodes for at least four weeks. These results suggest that
PLL-PEG hydrogel biomaterials are biocompatible and can enhance stability
of chronic neural interfaces.
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2.5.4 Extracellular Matrix Proteins and Derived Peptides
Given the role played by the ECM proteins and other macromolecules with
respect to cellular adherence, progenitor development, communication and
