(a) Molecular Weight:
The bioadhesion property depends on the molecular
weight of selected bioadhesive polymer. Bioadhesion is successful if molecular
weight is 100,000 and more. It is generally understood that the threshold
required for successful bioadhesion is at least 100,000 molecular weight.
Concentration of active polymers:
There is an optimum concentration of a bioadhesive
polymer is required for maximum bioadhesion. In highly concentrated systems,
beyond the optimum level the adhesive strength decreases significantly.
(c) Flexibility of polymer chains:
As water-soluble polymers become cross linked, it is
difficult for interpenetration and entanglement mobility of individual polymer
chains decrease and thus the effective length of the chain that can penetrate
into the mucus layer decreases, which reduces bioadhesive strength.
(d) Spatial conformation:
The spatial conformation of a molecule is also
important for bioadhesiveness. Despite a high molecular weight of dextran, they
have similar adhesive strength to the polyethylene glycol with a molecular
weight. The helical conformation of dextran shield many adhesively active
groups, primarily responsible for adhesion, unlike PEG polymers which have a
Environment Related Factors
(a) Applied strength:
The adhesion strength increases with the applied
strength or with the duration of its application. It is necessary to apply a
defined strength. If high pressure is applied for a sufficiently long period of
time, polymers become mucoadhesive even though they do not have attractive
interaction with mucin.
Bioadhesion can be influenced by the charges present
on the surface of mucus as well as certain ionisable bioadhesive polymers.
Mucus will have a different charge density depending on pH due to difference in
dissociation of functional groups on the carbohydrate moiety and the amino acids
of the polypeptide backbone. pH of the medium is important for the degree of
(c) Initial contact time:
between the bioadhesive polymer and mucus layer determines the extent of
swelling and interpenetration of the bioadhesive polymer chains. Bioadhesive
strength is directly proportional to the initial contact time.
It depends on the polymer concentration, ionic
concentration, as well as the presence of water. More hydration leads to the
formation of slippery mucilage without proper adhesion 11.