Biomedical Engineering Reference
In-Depth Information
delivery of paracetamol from gels formed
in situ
in the stomach is similar to com-
mercially available suspension. Also, gellan-based ophthalmic solutions are
reported to have longer residence time in tear fl uid than saline solution. In both
applications, the solution of gellan mixed with drugs
in situ
forms a gel at acidic
pH in the stomach or in the presence of ions in the lachrymal fl uid [122] .
In a fi rst study to evaluate gellan as scaffold material for tissue engineering,
gellan could be ionically crosslinked on mixing with
- modifi ed minimum essen-
tial medium resulting in the formation of a self-supporting hydrogel. By adding a
suspension of rat bone marrow cells in
α
- modifi ed minimum essential medium
to 1% gellan solution, it is possible to immobilize cells within the three- dimensional
gellan matrix that remain viable for up to 21 days in culture. This simple approach
to cell immobilization within three-dimensional constructs poses a low risk to a
cell population immobilized within a gellan matrix and thus indicates the potential
of gellan for use as a tissue engineering scaffold [123].
α
7.9
Guar Gum
Guar gum belongs to the group of galactomannans and is a neutral polysaccharide
with a main chain composed of
β
- (1
→
4)-linked mannose units and a molecular
weight of approximately 1
×
1 0
6
Da. On average, every second mannose is substi-
tuted at position 6 with a
- d-galactopyranose. Analysis of the products obtained
by enzymatic digestion indicates that in guar galactomannan, the d - galactosyl
groups are arranged mainly in pairs and triplets [124] (Scheme 7.9).
Guar gum is isolated from the seed of
Cyamopsis tetragonoloba
, which belongs
to the Luguminosoe family. Guar gum forms crosslinked hydrogels on treatment
with borax or calcium ions. However, its aqueous solution is nonionic and hydro-
colloidal and is not affected by ionic strength or pH. In order to yield a monodis-
perse guar gum fraction, a purifi cation procedure modifi ed by Wientjes
et al.
can
α
Scheme 7.9
Chemical structure of guar gum.
