Biomedical Engineering Reference
In-Depth Information
very much the material of choice for those working with microfluidic channel-
based devices.
In a comprehensive study, Whitesides and co-workers
24
examined the
behavior of a number of mammalian cells on various forms of the polymer.
Although polymer samples were studied with respect to composition, experi-
mentally, surface adsorbed fibronectin was employed to aid cell 'adhesion'.
Accordingly, there is the caveat attached to this work in that the results are not
necessarily governed entirely by chemistry conducted at a 'bare' surface. Four
different types of cells were investigated—primary human umbilical artery
endothelial cells (HUAECs), transformed 3T3 fibroblasts (3T3s), transformed
osteoblast-like MC3T3-E1 cells and HeLa (transformed epithelial) cells.
Several polymer slab substrates were prepared for exposure to the cells with an
emphasis on the ratio of base-to-curing agent employed. Polymer samples
where the surface was treated with extracting solvents and subjection to plasma
treatment were also examined. The growth of cells was detected via fixing and
fluorescence spectroscopy, following surface characterization. In overall terms
an attempt was made to correlate the growth of cells on the various substrates
with surface chemistry, as influenced by polymer fabrication and stiffness via
Young's modulus assessment. There was some dependence on cell type but
stiffness appeared to have a marginal effect. The role of the supposed
underlying layer of fibronectin in this study remains unclear, at least in terms of
the surface chemistry component. In other words, does the behavior of cells on
the different polymer surfaces simply reflect the nature of the specific fibro-
nectin interaction?
With regard to metals there has been particular interest in medical-grade
stainless steel surfaces and how this material interacts with cells. The research
has been largely spawned by the introduction of stent technology for the
treatment of coronary disease.
25
(In the last section of this chapter we revisit
this area with regard to the medical consequences of implantation of foreign
substrates.) There are numerous examples of this sort of work involving the use
of electrochemical pretreatment of stainless steel in order to enhance biocom-
patibility. These are reviewed in ref. 26. In one example, stainless steel (316LS)
was subjected to passivation by an electrochemical process with the goal of
examining responses of fibrinogen, platelets, endothelial and smooth muscle
cells.
27
Interestingly the electrochemical treatment reduces the accumulation of
platelets on the steel surface (by around 30-50% depending on exposure time).
Also there was evidence of less activation of platelets by the modified surface
compared with the bare substrate.
The effect of cells on steel, as distinct from what the metal surface does to
cells, has also been studied. An example is the investigation of the corrosion of
steel by osteoblasts.
28
(These cells originate from marrow-derived monocyte
precursors and are multinuclear in character.) The study found that the cells
could be cultured successfully on bare surgical grade stainless steel. After
several days of exposure to the cells, corrosion-instigated pits were observed on
the steel wafers by scanning electron microscopy (SEM). Analysis of the culture
supernatant liquid revealed the presence of expected metal ions derived from
d
n
4
t
3
n
g
|
0
n
3
.
