The present invention provides a method of manufacturing a hydrogel comprising the step of crosslinking a biopolymer using a carbodiimide crosslinker of Formula I wherein at least one of R1 and R2 is a functional group that is a bulky organic functional group. R1 and R2 can each independently be an optionally substituted saturated or unsaturated functional group selected from the group consisting of an alkyl, a cycloalkyl, a heterocyclic, and an aryl. The bulky organic functional group will slow down the crosslinking reaction of carbodiimide due to the steric effects and/or electronic effects, in comparison to a crosslinking reaction using EDC. Also provided are the hydrogels and ophthalmic devices prepared using the method of the invention and uses thereof.