Relationships between the material properties of silicone hydrogels: Desiccation, wettability and lubricity

Silicone hydrogels (SiHy), represent composite matrices composed of hydrophobic gas permeable silicone (Si) rich core and a surface enriched with hydrophilic polymer moieties. Their utilization in contact lens design requires number of SiHy properties (hydration, wettability, lubricity) to be optimized for the challenging conditions at the ocular surface. Typical limitations in literature are that (i) these properties are studied in isolation, monitoring only one parameter but not the rest of them, and (ii) measurements are performed with hydrated samples immediately after removal from storage solutions. Here we study the simultaneous evolution of critical material properties (evaporative loss of water, water contact angle, coefficient of friction) of different SiHy subjected to continuous blink-like desiccation/rehydration cycling. SiHy with wetting agents incorporated in their core (narafilcon A, senofilcon A) were particularly susceptible to extended desiccation. Stenfilcon A, a material with only 3% bulk Si content maintained its performance for 4 h of cycling, and delefilcon A (80% surface water content) resisted extended 8 h of desiccation/rehydration runs. Strong correlation exists between the evolution of SiHy wettability and lubricity at >= 4 h of blink-like cycling. Understanding the interplay between SiHy properties bears insights for knowledge based design of novel ophthalmic materials.

Automated summary

Silicone hydrogels (SiHy) are composite matrices designed for contact lenses, with their properties such as hydration, wettability, and lubricity needing to be optimized for use on the ocular surface. Different SiHy materials show varying performances under desiccation/rehydration cycling, with wetting agents incorporated ones being more susceptible to extended drying. There is a strong correlation between the wettability and lubricity of SiHy after at least 4 hours of blink-like cycling, providing insights for the design of novel ophthalmic materials.