SUPPORTED CELL MIMETIC MONOLAYERS AND THEIR COMPATIBILITY - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 656

behavior of the pure as well as the lipid combinations was studied in detail to
know the incorporation of the anchors into the monolayer and its stability during
compression, with the help of LB trough. A bilayer of the lipid compositions were
immobilized into functionalized polymer (PMMA) substrates with the help of LB
trough and cross-linked by peptide bonds using carbodiimide chemistry. The
surface morphology of the supported lipid systems was studied by using atomic
force microscope (AFM). The fundamental interactions that regulate the blood
compatibility of these stabilized surfaces have been studied by in vitro blood cell
adhesion from washed cells, protein adsorption, and calcifi cation studies. The
surface pressure area (

-A) isotherm of the pure lipids as well as the different
lipid/macromolecular combinations were studied at the air/water interface at
ambient temperature.

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20.3.3 Air/Water Interfacial Properties of TSF
Figure 20.3A shows the pressure-area isotherm of the lipids using deionized water
as the subphase at ambient temperature. The liquid expanded (LE) and liquid
condensed (LC) phases of the

-A isotherm of the PTC and GalC as well as the
different lipid combinations are coexisting together at the air/water interface. The
collapse pressure of the isotherms of the lipid combinations are being regulated
by the parent lipid PTC, at 42 mN/m. The

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-A isotherm of the cholesterol mono-
layer (Figure 20.3A (II)) shows a sharp entry from gaseous (G) to LC phase
during compression, and is similar to that of long chain fatty acids. This is due to
the strong interaction between the hydrophobic cyclo pentano perhydro phenan-
threne ring of the cholesterol, when they are in close proximity. The collapse pres-
sure of the GalC is increased (Figure 20.3A (III)) may be due to the stabilization
effect of the galactose residues. Furthermore, the incorporation of the GalC into
the lipid monolayer under reduced cholesterol concentrations has increased the
lateral stability of the monolayer 16 .

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20.3.4 Macromolecule Incorporation into Lipid Thin Solid Films
Protein incorporation into the lipid monolayer depends on the structure, and the
transmembrane proteins with hydrophobic exterior are well incorporated.
However, this is not true in the case of hydrophilic soluble globular proteins.
The authors have attempted to change the conformation of a model globular
protein (albumin) and incorporated into the monolayer. The interaction studies
were done at air/water interface with the help of LB apparatus. Incorporation
of albumin into the monolayer, OCMC-A (Figure 20.3A (V)), evidenced by
the increase in mean molecular area and decrease in collapse pressure of

- A
isotherm. This is due to the interaction between the hydrophobic core of the
monolayer and hydrophobic core of the conformationally-changed protein 17
molecule. Further incorporation of heparin along with albumin into the mono-
layer improved the collapse pressure from 38-42 mN/m along with increase in the
mean molecular area. Further incorporation of heparin and PEG along with

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