Responsive polysaccharide-grafted surfaces for biotribological applications

Abstract

The elucidation of biolubrication mechanisms and the design of artificial biotribological contacts requires the development of model surfaces that can help to tease out the cues that govern friction in biological systems. Polysaccharides provide an interesting option as a biotribological mimic due to their similarity with the glycosylated molecules present at biointerfaces. Here, pectin was successfully covalently grafted at its reducing end to a polydimethylsiloxane (PDMS) surface via a reductive amination reaction. This method enabled the formation of a wear resistant pectin layer that provided enhanced boundary lubrication compared to adsorbed pectin. Pectins with different degrees of methylesterification and blockiness were exposed to salt solutions of varying ionic strength and displayed responsiveness to solvent conditions. Exposure of the grafted pectin layers to solutions of between 1 and 200 mM NaCl resulted in a decrease in boundary friction and an increase in the hydration and swelling of the pectin layer to varying degrees depending on the charge density of the pectin, showing the potential to tune the conformation and friction of the layer using the pectin architecture and environmental cues. The robust and responsive nature of these new pectin grafted surfaces makes them an effective mimic of biotribological interfaces and provides a powerful tool to study the intricate mechanisms involved in the biolubrication phenomenon.

Oral tribology: Providing insight into oral processing of food colloids

“…The shear elastic modulus of the pectin layers decreased abruptly after a certain concentration of the salt was added. This suggested that the polymer chain extension, as a result of osmotic pressure, contributes to the increase in the thickness of the layer (Pradal, et al, 2019). In this study, charge distribution of the pectin layer was postulated to be an influencing factor which limits the capability to elucidate the friction results wholly by QCM.…”

“…The interplay between the properties of adsorbed film at the interface and lubrication behaviour has been of paramount importance in tribo-contacts influencing friction, wear, and corrosion performance of the tribo-pairs. In the last decade, QCM-D has been employed extensively in bio-relevant research works (Glumac, Ritzoulis, & Chen, 2019;Hu, et al, 2020;Macakova, et al, 2010;Marczynski, et al, 2020;Song, Winkeljann, & Lieleg, 2019; especially in skin (Farias, Hsiao, & Khan, 2020), articulating joints (Majd, et al, 2014;Morgese, Cavalli, Müller, Zenobi-Wong, & Benetti, 2017;Parkes, Myant, Cann, & Wong, 2015) and food science (Pradal, Yakubov, Williams, McGuckin, & Stokes, 2019;Stokes, et al, 2011;Wan, et al, 2020b;Wang, et al, 2020;Zembyla, et al, 2021). In many studies, where the relevant tissues are hydrophobic in nature, the microbalance sensors have been coated by PDMS (Farias, et al, 2020;Pradal, et al, 2019;Song, et al, 2019;Stokes, et al, 2011;Zembyla, et al, 2021) usually using spin coater instruments.…”

“…QCM-D has been used to examine the influence of the ionic strength on swelling (mass gain) and viscoelastic properties of a pectin layer covalently grafted onto PDMS surfaces through silanisation (Pradal, et al, 2019). The increase in NaCl concentration (from 1 to 100 mM) was shown to induce a thicker pectin layer and the extent of the change in thickness of the layer was shown to partially correlate with the decrease in the boundary friction depending on the degree of methyl-esterification.…”

“…Details derived by SE measurements assist in understanding tribological results. For example, SE has been used to estimate the grafting density of pectin layers grafted onto PDMS surfaces suggesting its brush-link conformation (Pradal, et al, 2019). The brush-like conformation of the grafted pectin layer was postulated to bring about lower friction coefficients as compared to adsorbed flatter pectin layers (Pradal, et al, 2019).…”

“…In biotribology, XPS has been used to confirm the grafting of lubricous layers. For examples, pectin bonding onto elastomer surfaces (Pradal, et al, 2019) was evidenced through appearance of two additional peaks corresponding to acetal and carbonyl/estercarboxylic groups. In another work, chemical bonding and stability of poly(vinylphosphonic acid) onto Ti6Al4V alloy, manifested in XPS spectra, was shown to bring about super-low friction characteristics (Zhang, et al, 2014) (see Figure 5h).…”