The present invention is directed to methodology that allows a variety of compounds to be attached to self-assembling peptides using biotin/streptavidin linkages. The peptides can be used to form a biologically compatible membrane that promotes the growth and differentiation of cells. The attached therapeutic agents can be used to promote this process and the gel along with the growing cells can be implanted at a site in vivo where tissue repair is needed. Alternatively, membranes can be used for culturing cells in vitro or can be used for delivering drugs in vivo in the absence of seeded cells.