a, The CS adhesive is applied to the cartilage surface with a swab (Step 1). A macromer (pregel) solution is added to the tissue surface modified with the CS adhesive and photopolymerized (Step 2). The resulting hydrogel biomaterial is covalently bound to the cartilage surface via the CS-adhesive bridge. Cells surgically stimulated from the marrow (blue) or exogenously added to the liquid pregel (red) can be incorporated into the hydrogel layer. b, Gross picture of a hydrogel bound to cartilage with the CS adhesive. The cartilage tissue is the white, opalescent layer adjacent to the transparent hydrogel layer. Chondrocytes were encapsulated in the hydrogel layer to test the cytocompatibility of the modified CS. c, Cells in the hydrogel, adjacent to the CS adhesive, and within the cartilage were viable after 5 weeks of culture, as determined by live–dead fluorescent staining where calcein dye (green) stains only viable cells.