Porous hydrophilic sponges made from 2-hydroxyethyl methacrylate (HEMA) have a number of possible biomedical applications. We have investigated whether these poly(HEMA) hydrogels, when coated with collagen and infiltrated in vitro with cultured Schwann cells, can be implanted into the lesioned optic tract and act as prosthetic bridges to promote axonal regeneration. Nineteen rats (20-21 days old) were given hydrogel/Schwann cell implants. No obvious toxic effects were seen, either to the transplanted glia or in the adjacent host tissue. Schwann cells survived the implantation technique and were immunopositive for the low affinity nerve growth factor receptor, S100 and laminin. Immunohistochemical studies showed that host non-neuronal cells (astrocytes, oligodendroglia and macrophages) migrated into the implanted hydrogels. Astrocytes were the most frequently observed host cell in the polymer bridges. RT97-positive axons were seen in about two thirds of the implants. The axons were closely associated with transplanted Schwann cells and, in some cases, host glia (astrocytes). Individual axons regrowing within the implanted hydrogels could be traced for up to 900 mu m, showing that there was continuity in the network of channels within the polymer scaffold. Axons did not appear to be myelinated by either Schwann cells or by migrated host oligodendroglia. In three rats, anterograde tracing with WGA/HRP failed to demonstrate the presence of retinal axons within the hydrogels. The data indicate that poly(HEMA) hydrogels containing Schwann cells have the potential to provide a stable three-dimensional scaffold which is capable of supporting axonal regeneration in the damaged CNS.