The physical behaviour of moisture-activated mucoadhesive hydrogels in contact with a Plexiglas® plate or artificial mucin gels was investigated using an adapted tensile tester fitted with force and displacement transducers. Our study of the ‘Plexiglas®-hydrogel’ interface showed that the intrinsic mechanical response of most poly(acrylic acid) polymers is quite different from that exhibited by cellulose derivatives. The former exert an attractive interaction towards the substrate in contrast to the latter where the interaction is essentially repulsive. The interfacial forces developed by pure mucin were closely related to those of poly(acrylic acid) polymers. Similar results were observed when the Plexiglas® was replaced by artificial mucin gels. A correlation was found between the attractive force developed by poly(acrylic acid) hydrogels towards the inert substrate and their in vitro mucoadhesive joint strength. Therefore, a non-specific physical interaction occurs during the initial adhesive process, whatever the nature of the substrate. Besides the water absorption capacity and swelling properties of the candidate materials, it seems that their initial mucoadhesiveness depends more on their mechanical response to hydration and less on the extent of molecular interactions at the adhesive interface.