M.Sc Thesis

M.Sc StudentDozli Lilit
SubjectPectin-Thiol Hydrogels as Mucosa-Mimetic Surfaces to
Replace Animals in Mucoadhesion Testing
DepartmentDepartment of Biotechnology
Supervisor PROF. Havazelet Bianco-Peled
Full Thesis textFull thesis text - English Version


The ability of excipients to stick and retain on the surface of the mucosa layer in the human organs, referred to as mucoadhesion, attracts much attention in the development of mucoadhesive drug delivery systems, owing to benefits such as extended residence time of the drug at the site of application, a relatively rapid uptake of a drug into the systemic circulation, and enhanced bioavailability of therapeutic agents.

The evaluation of the interaction between mucoadhesive materials and the mucus layer often requires the use of 'ex vivo' mucosal tissues taken from animals. These tissues are highly heterogeneous and difficult to source, and the utilization of animals for experiments presents an ethical issue.

In this study we designed and investigated the performance of mucosal mimetic hydrogel based on thiolated-pectin (Pc-SH), aiming to replace tissues taken from animals in mucoadhesion testing, and thus to reduce the sacrifice of laboratory animals while improving the reproducibility of the results. The mucous layer is a highly hydrated gel layer composed of mucin-type glycoproteins, which possess high sugar residues content, net negative charge, and free thiol group. Pc-SH hydrogels exhibit similar qualities to that of the mucous layer and have the advantage of being from non-animal origin. Pectin (Pc) hydrogels, which differ from Pc-SH hydrogels by lacking the thiol groups, were used as control substance for evaluating the influence of thiol group’s presence on the ability of the substrate to mimic the mucosa. Both pectin-based hydrogels were crosslinked with barium ions using an in-situ gelation method in order to give homogeneous substances, stable in body stimuli liquids.

The ability of the hydrogels to mimic the mucosal tissue was tested by comparing the adhesion of chitosan derivatives with different functional groups to the hydrogels, to the adhesion of the same materials to mucosal tissues. Three common techniques of mucoadhesion assessments were employed: tensile study, rotating cylinder method, and flow-through experiments, all usually utilize 'ex vivo' tissues.

Results from tensile assay showed that both Pc and Pc-SH hydrogels were suitable mimics, as the maximum detachment force (MDF) ranking of the three different types of mucoadhesive polymers demonstrated good correlation to the ranking achieved with porcine small intestine mucosa. Further, the deformation profile of both hydrogels was similar in shape to the one obtained with mucosa. On the contrary, when using rotating cylinder and flow-through systems, for which the measurements take place in hydrated conditions, the results obtained with Pc-SH hydrogel substrate showed good agreement with the adhesion performance of the mucosa while the Pc hydrogel failed to imitate the strong adhesion of second-generation mucoadhesives to the mucosa. These results highlight the importance of presence of thiol groups on the substrate surface in order to mimic the mucoadhesion phenomena. 

Based on our findings Pc-SH hydrogel is suitable model substrate for replacing mucosal tissues in the mucoadhesion evaluation methods.