Civil Engineering Reference
In-Depth Information
cellulose membranes [89]. It has been proven that microbial cellulose nanoi bers can
mimic collagen nanoi bers for
calciu-:phosphorus
minerals (Ca-P minerals) deposition
via biomineralization. h e resultant Ca-P minerals are platelet-like calcium-dei cient
hydroxyapatite (Hap), similar to the hydroxyapatite found in natural bone [90]. Other
authors [91,92] have induced a negative charge on microbial cellulose by the adsorp-
tion of polyvinylpyrrolidone (PVP) to initiate the nucleation of Hap via dynamic simu-
lated body l uid (SBF) treatment. Shi
et al.
[93] introduced an alkaline treatment before
the biomimetic mineralization process in order to improve the mineralization ei -
ciency. Zhang
et al.
[94] have used a phosphorylation reaction to introduce phosphate
groups to the hydroxyl groups of microbial cellulose and promote the growth of cal-
cium phosphate. Wan
et al.
[92] have also shown that phosphorylation ef ectively trig-
gers Hap formation on microbial cellulose. Microbial cellulose-Hap composites with a
third phase can also be produced. In order to improve the biocompatibility and osteo-
conductivity of microbial cellulose in bone-related biomedical applications, Grande
et
al.
[81] have produced microbial cellulose-hydroxyapatite nanocomposites by adding
hydroxyapatite and carboxymethylcellulose (CMC) to the culture medium. As CMC
can change the viscosity of media, it was used to retard the settlement of Hap particles
in the microbial cellulose culture medium.
16.11.2
Cardiovascular Clinical Applications
Cardiovascular disease is a major health problem resulting in suf ering for the individual
and a high economic burden for society. It is still the major cause of death or invalidity
in the Western world today. Cardiovascular diseases alone account for approximately
30% of all global deaths, and annually about 18 million people die from cardiovascular
diseases. h e World Health Organization (WHO) estimates, that if current trends are
allowed to continue, 20 million people will die from these diseases by 2015 [95]. h e
search for arterial vascular grat s began in 1952, when Voorhees discovered the i rst
fabric grat , Vinyon N (nylon) [96]. A few years later, DeBakey discovered the poly-
ethylene terephtalate i ber Dacron® in 1958 [97]. Today synthetic blood vessels such as
Dacron and expanded polytetral uoroethylene are in use in clinics as prosthetic grat s
for reconstructive vascular surgery and are available at large diameters (6-10 mm).
In small diameter vessels (> 6 mm) like coronary, carotid and femoral arteries, their
performance is dismal, resulting in early thrombosis and intimal hyperplasia, and are
still under investigation [98]. h ey only function satisfactorily in large-diameter, high-
l ow vessels. Approximately 10% of patients with coronary artery disease are therefore
let untreated [99]. Sophisticated techniques have been evaluated to enhance patency,
including chemical modii cations as well as coatings and seeding of the surface with
dif erent cells. Synthetic materials, in contrast to natural materials, ot en lack adhesion
sites. Although sui cient physiological mechanical strength can be reproduced with
passive materials, proper metabolic function and cellular signaling require intact cel-
lular machinery. Tissue-engineered blood vessels could be a solution to this problem.
Microbial cellulose is an interesting material for biomedical applications. Materials
intended as vascular grat s must satisfy many important features such as blood com-
patibility, cell interactions and mechanical properties. Microbial cellulose has unique
properties that make it an exciting candidate as a cardiovascular grat material: strength,
