Mechanically triggered solute uptake in soft contact lenses

Abstract

Molecular arrangement plays a role in the diffusion of water and solutes across soft contact lenses. In particular, the uptake of solutes in hydrated contact lenses can occur as long as free water is available for diffusion. In this work, we investigated the effect of mechanical vibrations of low frequency (200 Hz) on the solute uptake. Hyaluronan, a polysaccharide of ophthalmic use, was taken as example of solute of interest. For a specific water-hydrated hydrogel material, differential scanning calorimetry experiments showed that a large fraction of the hydration water accounted for loosely-bound water, both before and after one week of daily-wear of the lenses. The size (of the order of magnitude of few hundreds of nanometers) of hyaluronan in aqueous solution was found to be less than the size of the pores of the lens observed by scanning electron microscopy. However, solute uptake in already-hydrated lenses was negligible by simple immersion, while a significant increase occurred under mechanical vibrations of 200 Hz, thus providing experimental evidence of mechanically triggered enhanced solute uptake, which is attributed to the release of interfacial loosely-bound water. Also other materials were taken into consideration. However, the effectiveness of mechanical vibrations for hyaluronan uptake is restricted to lenses containing interfacial loosely-bound water. Indeed, loosely-bound water is expected to be bound to the polymer with bonding energies of the order of magnitude of 10-100 J/g, which are compatible with the energy input supplied by the vibrations.

BCLA CLEAR - Contact lens wettability, cleaning, disinfection and interactions with tears

“…It has been incorporated as an internal lubricant or used for surface modification (as discussed above). It has also been studied as a released wetting agent [56,[175][176][177]. HA interacts with the glycans of the mucous layer on the ocular surface to enhance the spreading of the tear film [178,179] and its incorporation into contact lenses improves their surface wettability [180].…”

“…HA physically incorporated into contact lens materials during synthesis can be released from conventional hydrogel materials for three weeks, while model SiHy materials showed a release for more than seven weeks [176]. Porosity and content of free and loosely-bound water affects the uptake and release of HA [177], with SiHy lenses tending to absorb HA as a thin porous top layer (typically a few micrometres thick) inside well-defined channels [181].…”

Topologically controlled hyaluronan-based gel coatings of hydrophobic grid-like scaffolds to modulate drug delivery

“…The molecular weight between crosslinks within the PEA matrix of the scaffolds here The efficiency of the crosslinking procedure was characterized by determining the amount of HA incorporated before and after its crosslinking, in the dry state ( Figure 1). In contrast to other acrylates [34], PEA permits the free diffusion of hyaluronan into the pores, because of the free water contained in the large pores and the lack of bound water on the hydrophobic surface of the PEA scaffolds. The amount of HA before crosslinking was found to increase linearly with the concentration of the starting HA solution used, its mass fraction ranging from 0.12 for the 0.5 wt.% solution to 0.40 for the 5 wt.% one.…”

<p>Effects of Aqueous-Supplementing Artificial Tears in Wearers of Biweekly Replacement Contact Lenses vs Wearers of Daily Disposable Contact Lenses</p>

“…Due to its viscosity-enhancing properties, some manufacturers also add sodium hyaluronate directly in the solutions of the CL blister to improve the comfort after CL insertion. [15][16][17][18] Lipid-supplementing ATs were introduced because a lipid deficit can cause a quicker evaporation of the tears leading to a condition of dry eye. 10 These are typically emulsions where lipid droplets are suspended, such as polar phospholipid, dimyristoyl-phosphatidyl-glycerol (DMPG), propylene glycol.…”