Method for producing MPS-compatible water gradient contact lenses

A process for producing a contact lens, comprising the steps of:

• (a) obtaining a contact lens precursor which is a coated contact lens which comprises a lens bulk material completely covered with an anchor layer of a polyanionic polymer which comprises at least 60% by mole of repeating units of at least one carboxyl-containing vinylic monomer;
• and
• (b) heating, in the presence of at least one first polyaziridine which has a number average molecular weight of about 2000 Dalton or less and at least two aziridine groups, the contact lens precursor in a first aqueous solution which comprises a thermally-crosslinkable hydrophilic polymeric material which has thermally-crosslinkable groups, to and at a temperature from about 30° C. to about 140° C. for a period of time sufficient to obtain the contact lens,
• wherein the contact lens comprise (i) a crosslink anchor layer thereon and (2) an outer surface hydrogel layer which is covalently attached to the crosslinked anchor layer, wherein the crosslinked anchor layer is obtained crosslinking the polyanionic polymer in the anchor layer via crosslinkers derived from said at least one polyaziridine in coupling reaction between at least two pair of aziridine and carboxyl groups, wherein the outer surface hydrogel layer is formed by crosslinking the thermally-crosslinked hydrophilic polymeric material, wherein the contact lens has a polyquaternium-1 uptake (“PUpz”) of about 0.6 μg/lens or less.