Civil Engineering Reference
In-Depth Information
cellulose biosynthesis [53] . h ey successfully synthesized dif erent types of microbial
cellulose for wound dressings, including never-drying microbial cellulose. h ey suc-
cessfully employed the never-drying microbial cellulose membrane for the healing of
severe burn wounds and proved its application by clinical trials on humans. However,
due to the lack of ei cient fermentation system, commercial production of this micro-
bial cellulose is still a big question. Unlike other microbial polysaccharides that can be
synthesized economically in large stirred-tank fermenters, microbial cellulose must be
grown in static, nonagitated cultures. Sheer stresses in agitated fermenters always dam-
age the microbial cellulose during synthesis.
16.11
Use of Cellulose as Implant Material
Sutures are the largest group of medical device implanted into human or animal body.
h e primary goals of suturing are: (i) provide an adequate tension of wound closure
without dead space but loose enough to obviate tissue ischemia and necrosis, (ii)
maintain hemostasis (a process which causes bleeding to stop, meaning to keep blood
within damaged blood vessels), (iii) permit primary intention healing, (iv) reduce post-
operative pain, (v) provide support for tissue margins until they have healed and the
support is no longer needed, (vi) prevent bone exposure resulting in delayed healing
and unnecessary resorption, and (vii) permit proper l ap position. Traditionally, silk
i ber has been used as sutures in medical applications. Although it is a biodegradable,
biosorbable and biocompatible natural i ber, its prime disadvantage is its inferior ten-
sile strength and reaction with human tissues. h e strength problem of biosorbable
sutures is tackled by dif erent surface modii cation techniques. For example, Silkam®
and Virgin Silk from B. Braun Sutures are non-absorbable braided and inert wax/sili-
con-coated sutures made of natural silk i laments having high tensile strength, l exibil-
ity and outstanding smoothness. h e wax/silicon coating is employed on the silk i ber
to limit absorption, increase ductility, and minimize tissue reactivity of the stutures.
Silkam is a commercially available silk suture basically indicated for applications where
it is surgical practice to employ non-absorbable braided suture material and Virgin
Silk is a non-absorbable twisted suture indicated in ophthalmic surgery in sot tissues.
Silkam is available in black and Virgin Silk in blue color. Synthetic sutures such as
polyamide (Nylon), polypropylene (Prolene), polyethylene (Courlene) or polyester i l-
ments coated with Tel on are becoming popularized as non-absorbable sutures and are
employed even for vasuclar surgery. Sutures by the surface modii cation of cellulose i l-
ments and carbon i bers-based ones prepared by the modii cation of cellulose i lments
have also been produced [80].
Microbial cellulose derived from Acetobacter xylinum by fermentation process
has been established to be a remarkably versatile biomaterial and can be used in wide
variety of applied scientii c endeavours, especially for medical devices. Due to its ultra-
i ne network architecture, high degree of crystallinity, hydrophilicity and moldability,
microbial cellulose is a natural candidate for numerous medical and tissue-engineered
applications. h e use of direct nanomechanical measurement determined that these
i bers are very strong, and when used in combination with other biocompatible mate-
rials, produce nanocomposites particularly suitable for use in human and veterinary
