The present invention relates to water soluble quaternized chitosan derivatives which form hydrogel matrix with broad antimicrobial properties for the protection and coating of medical device. Hydrogel is attractive as an antimicrobial coating since its hydrophilicity intrinsically prevents the reversible nonspecific attachment of microbes.In order to achieve hydrogel formation, quaternized chitosan can be grafted with polymerizable groups, especially photocrosslinkable groups, such as methacrylates, PEG derivatives and be converted into hydrogels through a thermal or UV polymerization process. Hydrogels are hydrated cross-linked polymeric systems that contain water in an equilibrium state forming cushion water shield. The present invention is widely used in many medical devices for example biomedical devices such as contact lenses, bio-implants such as urinary catheters, pacemaker, heart valves, artificial heart, mammary prosthesis, intraocular lenses, wound dressings, artificial organs and delivery carriers for the bioactive reagents, total joint replacement due to their high degree of biocompatibility, antimicrobial property and good wetting characteristics. This invention describes the formation of novel hydrogels based on quaternized ammonium chitosan derivatives which has been grafted with photocrosslinkable groups, hence providing hydrogels as antimicrobial water shield coating agent.