Biomaterials resistance to corrosion
Dr Mariah Hahn
For biomaterials involved in stents and joint replacements, it is critical that the material
demonstrate low cytotoxicity and high corrosion resistance under physiological loading
condition. Furthermore, stents and other blood contacting materials must demonstrate
resistance to thrombus formation. Thus, in this aspect of the proposal, we aim to
characterize the corrosion resistance, non-cytotoxicity, and non-thrombogenicity of a
series of materials as an indicator of their potential in vivo utility.
Corrosion Resistance Characterization under Physiological Loading Conditions of
Designed Materials
Designed materials will be characterized for their resistance to corrosion under both bone
and blood vessel physiological loading conditions. The materials will be exposed to
cyclic tension using a Instron 3342 equipped with an environmental chamber, which will
permit the application of cyclic loading while simultaneously allowing the immersion of
the material in Hanks Buffered Saline solution maintained at 37 ºC [1]. After the
application of 1K, 10K, and 100K loading cycles, the samples will be analyzed by for
corrosion using scanning electron microscopy (SEM) and X-ray photoelectron
spectroscopy (XPS) [2]. SEM will permit the observation of surface wear and corrosion
effects while XPS will be used to examine alterations in elemental composition of the
surface layer. Materials that display high long term corrosion resistance will be further
examined for impact on serum protein adsorption and cell behavior.
Protein Adsorption and Cell Viability in Response to Designed Material Surfaces
Contact of the artificial surface with blood results in the deposition of blood serum
proteins and cellular elements, such as platelets, on the surface [3, 4]. Following this, a
series of events, including platelet activation, may lead to thrombus formation. It is
thought that the protein molecules adsorbed onto artificial surfaces control the artificial
surface’s thrombogenicity when exposed to the blood stream [4]. Common proteins
found in blood include albumin, fibrinogen, and fibronectin. Albumin is a surfacepassivating protein. In past experiments, a marked reduction in thrombi have been
observed by SEM on surfaces coated with surface-passivating proteins such as albumin
[5]. On the other hand, fibrinogen and fibronectin are adhesive proteins. It has also been
shown experimentally that artificial surfaces preadsorbed with fibrinogen, result in higher
platelet deposition when compared to control surfaces [6]. The adsorbed albumin,
fibrinogen, and fibronectin distributions on the designed SMA will be studied by
immersing the surfaces in a phosphate buffered saline solution containing a
physiologically relevant mixture of albumin, fibrinogen, and fibronectin, each of which
has been labeled with a distinct fluorophor. After 24 h at 37 ºC [7. 8], the profile of the
proteins adsorbed onto the surfaces will be characterized using fluorescence imaging [9].
For materials that adsorb high levels of albumin relative to fibronectin and fibrinogen,
cytotoxicity assays will be conducted. The toxicity of material by-products (i.e., the
toxicity of elements within the SMA alloy) will also be investigated in separate long term
in-vitro transwell experiments [10]. In brief, various materials formulations will be
placed in individual wells of multiwell culture plates. Cell culture inserts with 8 micron
porous membranes, which permit the free intermixing of the media within the insert with
that surrounding the material, will be placed within these wells and NIH/3T3 cells will be
seeded onto the upper surface of the membranes. Thus, cells will be maintained separate
from the alloy surface, yet exposed to its leachants and by-products. Every three days,
half the media in each well will be exchanged. At 1 week, 1 month, and 3 months, cell
viability will be assessed relative to cells in control wells (no material) using a standard
metabolic activity assay. The effect of loading-induced corrosion on material toxicity will
also be evaluated using this experimental design, by placing materials exposed to various
physiological cyclic loading regimes within the wells and comparing cell response to
these material by-products relative to unloaded samples.
Fig. 1. A biomaterial on which osteoblasts are unable to spread (left). A material onto
which osteoblasts are able to adhere and spread (right).
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