Civil Engineering Reference
In-Depth Information
Wan mimics the mechanical behavior of cardiovascular tissues, such as aorta and heart
valve leal ets. h e stress-strain properties for porcine aorta are matched by microbial
cellulose-poly(vinyl alcohol) nanocomposite in both the circumferential and the axial
tissue directions. Relaxation properties of the nanocomposite, which are important
for cardiovascular applications, were also studied and found to relax at a faster rate
and to a lower residual stress than the tissues they might replace. h e study showed
that this nanocomposite is a promising material for cardiovascular sot tissue replace-
ment applications. h e aim of a study by Mohammadi
et al.
was to mimic not only
the nonlinear mechanical properties displayed by porcine heart valves, but also their
anisotropic behavior, by applying a controlled strain to the samples while undergoing
low-temperature thermal cycling, in order to induce oriented mechanical properties.
Hemocompatibility of surfaces that are in contact with blood should be further
studied. It is well known that blood-contacting surfaces may activate coagulation and
thrombus formation due to the interaction of such surfaces with blood proteins and
platelets. Fink
et al.
[106] evaluated the hemocompatibility of microbial cellulose-based
vascular grat tubes and compared them with commercial grat s of poly(ethylene tere-
phthalate) (PET) (Dacron®) and expanded poly(tetral uoroethylene) (ePTEE) (GORE-
TEX®). Since conventional methods are not suited for coagulation measurements on
microbial cellulose, Fink
et al.
[106] adapted the automated calibrated thrombin gen-
eration method for measurements of biomaterial-induced coagulation of microbial cel-
lulose. h rombin generation experiments revealed dramatic dif erences between the
materials tested. Both ePTFE and microbial cellulose were found to generate longer
lag times and ttpeak values than PET. h e study showed that microbial cellulose-based
grat s do not induce plasma coagulation, but induce the least and slowest coagulation
cascade. Andrade
et al.
[107] have coated microbial cellulose with the tripeptide Arg-
Gly-Asp (RGD) to favor endothelialization and improve hemocompatibility of micro-
bial cellulose. h ey cultured human microvascular endothelial cells on RGD-modii ed
microbial cellulose. Andrade
et al.
studied the adhesion of plasma protein and platelets
and blood coagulation on microbial cellulose surfaces. h e results showed that endo-
thelial cells cultured on RGD-modii ed microbial cellulose readily form a conl uent cell
layer, inhibiting the adhesion of platelets. h e studies also showed that plasma proteins
adhere on microbial cellulose in relatively high amounts, due to the high surface area
of the material. However, when albumin, c-globulin and i brinogen from pure protein
solutions adsorb to microbial cellulose they do not undergo detectable conformational
modii cations, an ef ect favorable concerning the interaction (non-activation) with
platelets. h e presence of RGD on the microbial cellulose increased platelet adhesion,
however when endothelial cells were cultured on RGD-treated microbial cellulose, a
conl uent cell layer was formed and almost no platelets adhered to the material.
Lang
et al.
[108] evaluated the biocompatibility, histopathology and immunohis-
tochemistry of microbial cellulose for closure of muscular ventricular septal defects
(mVSD). h ey investigated the
in-vivo
biocompatibility of microbial cellulose in large
animals for 90 days using microbial i ber network structures of a patch similar to col-
lagen by creating mVSDs on the beating heart. h e study found that Young´s modu-
lus and tensile strength of the microbial cellulose patch decreased signii cantly at er
blood contact, indicating increase in elasticity. Creation and closure of the mVSDs were
successful without residual shunting and no signs of thrombogenecity were observed.
