An orthopedic implant comprises:a bone interface member comprising a metal having a bone contact surface anda water swellable IPN or semi-IPN member having a bearing surface and an attachment zone, the attachment zone being attached by a chemical linkage to the bone interface member, the water swellable IPN or semi-IPN member comprising a hydrophobic thermoset or thermoplastic polymer first network comprising a polyurethane and an ionic polymer second network comprising sulfonic acid functional groups configured to exhibit a compositional gradient between the bearing surface and the attachment zone.
