Biomedical Engineering Reference
In-Depth Information
calcifi cation, as well as more biodegradation resistance in triglycidylamine
fi xed tissues in comparison with GA fi xed tissues appear to offer an attrac-
tive alternative to GA fi xation for some tissues and applications (Connolly
et al.
, 2005; Sacks
et al.
, 2007; Rapoport
et al.
, 2007).
The modifi cation of GA fi xed tissues with L-arginine has demonstrated
similar improvements in device mechanical properties, calcifi cation, and
protein and platelet adsorption, likely through the binding of toxic free
aldehyde groups left after GA fi xation (Jee
et al.
, 2003). Detoxifi cation
treatments of GA fi xed tissues with homocysteic acid, L-glutamine and
others which bind free aldehyde groups also demonstrate some benefi ts
in improving EC viability (Stacchino
et al.
, 1998). Post-fi xation treated
umbilical vein grafts which were seeded with ECs and implanted in
animals demonstrated greater EC coverage after explantation with
increased EC spreading directly on the vein graft surface in comparison
with untreated umbilical vein grafts (Moritz
et al.
, 1992). The treatment
of pericardial tissue valves with L-glutamic or homocysteic acid also
inhibits post-implant calcifi cation and thrombus formation in addition to
improving endothelialization in comparison to untreated GA fi xed peri-
cardium (Grimm
et al.
, 1992b; Grabenwoger
et al.
, 1996; Valente
et al.
,
1998).
Other strategies such as precoating tissue devices with extracellular
matrix proteins such as collagens and fi bronectin in combination to post-
fi xation treatment with L-glutamic acid can signifi cantly improve EC
seeding, attachment, proliferation, and function (Eybl
et al.
, 1992; Grimm
et al.
, 1992a). A recent study demonstrated that a combination of citric acid,
aldehyde dehydrogenase, and titanium coating of bovine pericardial valves
signifi cantly reduced free aldehyde ligands and improved cell seeding via-
bility resulting in a confl uent layer of ECs on the valve with 81% viability
after exposure to 3 Pa of laminar shear stress in an
ex vivo
fl ow chamber
(Guldner
et al.
, 2009). The examination of alternative materials such as
hydroxyapatite as a potential biomaterial coating for artifi cial valves, for
example, has been considered due to its demonstrated biocompatibility and
minimum cytotoxicity to human ECs
in vitro
(Sha
et al.
, 2009). Grafting of
sulfonated polyethylene oxide (PEO-SO(3)) or heparin to GA fi xed bovine
pericardium has shown promising benefi ts in cytotoxicity, biodegradation
resistance, calcifi cation, and infl ammation compared with GA treated peri-
cardial controls (Lee
et al.
, 2001).
3.4
Strategies to improve device biocompatibility
Numerous strategies have been developed which aim to minimize host-
device interactions that limit biocompatibility while others aim to optimize
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