Doctors simply cut a small hole in the patient's neck/back and inject a hydrogel<unk>  into the bone gap much the same way they would a titanium rod. This<unk>  absorbs fluids from within the wound and grows to fill the gap. Doctors control how far the<unk>  expands in any specific direction by first inserting a "cage"—basically a pre-expanded shell that the<unk>  fills in as it spreads. Think of it as the wooden frame that keeps a freshly-poured concrete sidewalk in place until it hardens. Once the<unk>  fills in the cage, which takes 5 to 10 minutes on average, it will set and harden into a viable prosthetic. From there, surrounding bone tissue grows into and through the<unk> , reinforcing and cementing it in place.
Polymer sponge
Gauze sponge
Fibrin glue
Ligature 
Surgical staple
Surgical mesh
Surgical tape
Chemical peel