Fibrin is a natural biomaterial that has found uses in surgery and tissue engineering as a tissue sealant and matrix for cellular ingrowth. An important feature is its ability to be remodeled and replaced by the protease activities associated with cells during their migration and invasion. In this issue, Hubbell and coworkers (p. 415) confer additional morphoregulatory signals into fibrin by incorporating exogenous bioactive peptides into the matrix during its coagulation in vitro. Using the enzymatic activity of Factor XIIIa, they incorporated peptides from laminin and N-cadherin and showed that the modified matrices enhanced neurite extension and axon regeneration in a rat model of nerve regeneration.