Tribo-Mechanical Stability of Mucous Boundary Layers in Biofidelic Contacts
Shari Gamaniel is a PhD student in the department Skin Tribology. (Co)Promotors are prof.dr.ir. E. van der Heide and dr. D.T.A. Matthews from the faculty Engineering Technology (ET), University of Twente.
In everyday life, stable mucous boundary layers on wet epithelial tissues play a vital role in providing lubrication, reducing friction and preventing tissue damage. Understanding the stability of these layers under tribo-mechanical and tribo-chemical stresses, as well as the extent of damage to the exposed surfaces following mucous film rupture, is crucial for informing the development of food ingredients, consumer products and biomedical devices. In this thesis, biofidelic experimental platforms were employed to systematically evaluate the stability and functionality of mucous boundary layers under controlled conditions. The main aim of the current work is to investigate and understand the mechanisms governing friction, lubrication and the protective function of mucous layers by assessing their stability during tribological interactions of biological tissues.
Following a systematic approach, lab-scale systems that replicate the bio-tribological and tribo-mechanical behaviour of wet epithelial tissues were used to simulate the contact of biological tissues. A novel methodology was introduced to evaluate the mechanical stability of mucous protein films adsorbed on PDMS surfaces, distinguishing between stable and unstable mucous boundary layers. This enabled the study of molecular mechanisms driving lubrication loss and film rupture, particularly during tribological interactions in the presence of mucins and plant-derived compounds. Studies explored the effects of fava bean protein isolate (FBPI), tannic acid (TA), and microcrystalline cellulose (MCC) particles on bovine submaxillary mucin (BSM) layers.
To link experimental observations with theoretical modelling, a mechanical contact framework was developed for a sphere-on-flat geometry. The model incorporated the boundary lubrication model of Bowden and Tabor using a binary and Gaussian-smoothed boundary layer coverage fraction (BLCF) approach, coupled with the JKR contact model, to predict contact pressures, and shear stresses. Comparison with experimental data confirmed the capability of the BLCF model to capture lubrication behaviour under varying surface coverage conditions.
Building on this foundation, a biofidelic platform consisting of protein boundary layers on epithelial cell monolayers adhered to PDMS substrates was introduced to study the influence of mucous layers on stresses transmitted to the underlying surfaces. This system enabled simultaneous evaluation of friction and tissue damage, revealing mechanisms by which mucous layers protect underlying cells. Further investigations into the interactions between the interfacial layer and the cell monolayer examined particle-mediated (de)lubrication and stress-induced cell responses. The study revealed a clear distinction in the friction levels and the amount of damage to the cell monolayer resulting from the absence of mucous coverage, strong adhesive interactions and the presence of particles within the contact.
The findings from this work highlight the mechanical stability of mucous layers during tribological interactions, revealing the role of stable mucous layers in providing lubrication and protective coverage that prevents damage to underlying tissues. The methodology and test platforms introduced in the current work offer practical applications in biomedical testing, development of sustainable food formulations, and biomedical device–tissue interaction studies.
