Microbicides for the Treatment of Sexually Transmitted HIV Infections

Table 5

Factors affecting the bioadhesiveness of mucoadhesive polymers.

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].