▁in ▁order ▁to ▁effectively ▁transport ▁micro - ▁or ▁n anos ized ▁drug ▁particles ▁into ▁the ▁body . ▁Bio ad hes ion ▁is ▁the ▁mechanism ▁by ▁which ▁two ▁bi ological ▁materials ▁are ▁held ▁together ▁by ▁inter fa cial ▁forces . ▁ ▁Mu co ad hes ive ▁bond ings ▁ ▁Mu co ad hes ion ▁involves ▁several ▁types ▁of ▁bond ing ▁mechan isms , ▁and ▁it ▁is ▁the ▁interaction ▁between ▁each ▁process ▁that ▁allows ▁for ▁the ▁ad hes ive ▁process . ▁The ▁major ▁categories ▁are ▁wet ting ▁theory , ▁ad s or ption ▁theory , ▁diffusion ▁theory , ▁electro static ic ▁theory , ▁and ▁f ract ure ▁theory . ▁Specific ▁processes ▁include ▁mechanical ▁inter lock ing , ▁electro static , ▁diffusion ▁inter pen etr ation , ▁ad s or ption ▁and ▁f ract ure ▁processes . ▁ ▁Bond ing ▁mechan isms ▁ ▁W et ting ▁theory : ▁W et ting ▁is ▁the ▁oldest ▁and ▁most ▁pre val ent ▁theory ▁of ▁ad hes ion . ▁The ▁ad hes ive ▁components ▁in ▁a ▁liquid ▁solution ▁anchor ▁themselves ▁in ▁irregular ities ▁on ▁the ▁substr ate ▁and ▁eventually ▁hard en , ▁providing ▁sites ▁on ▁which ▁to ▁ad here . ▁Sur face ▁t ension ▁effects ▁restrict ▁the ▁movement ▁of ▁the ▁ad hes ive ▁along ▁the ▁surface ▁of ▁the ▁substr ate , ▁and ▁is ▁related ▁to ▁the ▁therm od ynamic ▁work ▁of ▁ad hes ion ▁by ▁Dup re ' s ▁Equ ation . ▁Me as uring ▁the ▁aff inity ▁of ▁the ▁ad hes ive ▁for ▁the ▁substr ate ▁is ▁performed ▁by