Biomedical Engineering Reference
In-Depth Information
Several protocols are published describing the synthesis of grafted guar gum
[132] . Nayak and Singh described the ceric - ammonium - nitrate - initiated graft copo-
lymerization of polyacrylamide onto hydroxypropyl guar gum by solution polym-
erization technique. Six grades of graft copolymers have been synthesized by
varying catalyst and monomer concentrations. The percentage of grafting increases
with increasing catalyst concentration and decreases with monomer concentration
taking other parameters constant [133].
Native and modifi ed guar gum is widely used in petroleum industry as additives
in aqueous fracturing fl uids and in drilling shallow wells. These applications
utilize the properties to increase viscosity, reduce fl uid loss, and decrease fl uid
friction. Additionally, several applications were published using guar gum in the
fi eld of controlled drug release and drug delivery. Soppirnath and Aminabhavi
prepared a graft copolymer of guar gum with acrylamide, which was crosslinked
with glutaraldehyde to form the hydrogel microspheres by the water- in - oil emul-
sifi cation method. The microspheres were loaded with two antihypertensive drugs,
verapamil hydrochloride (water-soluble) and nifedipine (water-insoluble) to inves-
tigate their controlled release characteristics. The drugs could be incorporated
either during crosslinking by dissolving it in the reaction medium or after
crosslinking by the soaking technique [134]. The synthesis of acryloyl guar gum
and its hydrogel materials for use in the slow release of l - DOPA and l - tyrosine is
described by Thakur
et al.
The material obtained has good properties as release
devices for transdermal applications for the treatment of diseases like vitiligo and
Parkinson's disease. The hydrogels exhibit unique swelling behavior, and respond
well to the physiological stimuli such as pH and the ionic strength. A high loading
capacity of l - tyrosine and l - DOPA and a slow release behavior - especially at pH
7.4 - was achieved with these hydrogel materials [135] .
Tiwari
et al.
reported the synthesis of biodegradable hydrogels- based photopo-
lymerized guar gum-methacrylate macromonomers for
in situ
fabrication of tissue
engineering scaffolds. Depending on the reaction conditions, the hydrogels
exhibit equilibrium swelling ratios between 22% and 63%. The degree of
- d -
mannanases -induced biodegradation of the hydrogels decreased linearly with
increasing gel content and the degree of methacrylation of the respective mac-
romonomers [136] .
β
7.10
Hyaluronic Acid (Hyaluronan)
Hyaluronic acid (HyA) is a linear, high molecular weight polysaccharide composed
of
3) - linked
N
- acetyl - d - glucosamine (GlcNAc) and d - glucuronic
acid (GlcA) (Scheme 7.10). This polysaccharide was discovered in 1934 by Meyer
and Palmer in the vitreous humor of cattle eyes [137]. Eponymous for the polymer
was the Greek word “halos,” which stands for glass, in combination with its com-
ponent “uronic acid.” In 1986, HyA was renamed hyaluronan due to the inter-
β
- (1
→
4) - and
β
- (1
→
