Smart invisible shield: colorless, durable and self-defending contact lens nanocoating combats keratitis on demand

Contact lens (CL) wearers are confronted with a considerable susceptibility to infectious keratitis (IK). The development of CLs that can prevent IK is challenging since it is difficult to accomplish antibacterial activity without sacrificing optical performance and wearing comfort. To overcome this challenge, a colorless and ultrasmooth polysilazane coating is constructed on CLs, which can release antibacterial ammonium ions once subjected to either an acidic or alkaline stimulus generated by bacterial growth. The released ammonium ions had significant bactericidal effects on <i>Escherichia coli</i> and <i>Staphylococcus aureus</i>, which are the main pathogens of IK. Moreover, this antibacterial coating maintains the intrinsic visible light transmittance (100%) and wearing comfort of the pristine CLs due to its colorless nature and ultrasmooth surface (surface roughness lower than 1 nm). Furthermore, this coating was covalently linked on CLs, ensuring durability after prolonged storage in a standard lens care solution. The Si-N structures and methyl groups in the coating notably augment its ability to shield against ultraviolet radiation, and the intrinsic robustness of the inorganic moieties provides strong resistance to abrasions. Therefore, this facile strategy for preparing a multifunctional coating on CLs holds immense promise for safeguarding CL wearers against the risk of IK.