|
Factors | Effects on the bioadhesiveness of mucoadhesive polymers |
|
Concentration of polymer | (i) Optimum concentration of a bioadhesive polymer produces maximum bioadhesion. |
(ii) In highly concentrated systems, the adhesive strength drops because the coiled molecules become separated from the medium so that the chains accessible for interpenetration become limited [9]. |
|
Molecular weight of polymer | (i) The threshold required for successful bioadhesion is at least 100,000 molecular weight. |
(ii) For example, polyethylene glycol (PEG), with a molecular weight of 20,000, has little adhesive character, whereas PEG with 200,000 molecular weight has improved, and a PEG with 400,000 has superior adhesive properties [10]. |
|
Flexibility | (i) Flexibility of mucoadhesive polymer is the key for interpenetration and entanglement. |
(ii) When water-soluble polymers become cross-linked, mobility of polymer chains decreases and thus decreasing the effective penetration into the mucus layer, which finally reduces bioadhesive strength [11]. |
|
pH | (i) pH can influence the formal charge on the surface of mucus as well as certain ionizable bioadhesive polymers. |
(ii) pH of the medium is chief factor for the degree of hydration of crosslinked polymers, showing every time increased hydration from pH 4 to 7 and then a decrease as alkalinity and ionic strength increases [12]. |
|
Swelling
| (i) It mainly depends on the polymer concentration, ionic concentration, and the presence of water. |
(ii) Formation of slippery mucilage without adhesion after overhydration [13]. |
|
Contact time | (i) Contact time between the bioadhesive and mucus layer determines the extent of swelling and interpenetration of the bioadhesive polymer chains. |
(ii) Moreover, bioadhesive strength increases as the initial contact time increases [14]. |
|
Mucin turnover | (i) The mucin turnover is anticipated to limit the residence time of the mucoadhesive on the mucus layer. |
(ii) Mucoadhesive polymers are detached from the surface due to mucin turnover [15]. |
|
Disease states | The physiochemical properties of mucus are known to change during disease conditions such as bacterial and fungal infections of the female reproductive tract [16]. |
|