Multivalent
polymers offer a powerful opportunity to develop theranostic
materials on the size scale of proteins that can provide targeting,
imaging, and therapeutic functionality. Achieving this goal requires
the presence of multiple targeting molecules, dyes, and/or drugs on
the polymer scaffold. This critical review examines the synthetic,
analytical, and functional challenges associated with the heterogeneity
introduced by conjugation reactions as well as polymer scaffold design.
First, approaches to making multivalent polymer conjugations are discussed
followed by an analysis of materials that have shown particular promise
biologically. Challenges in characterizing the mixed ligand distributions
and the impact of these distributions on biological applications are
then discussed. Where possible, molecular-level interpretations are
provided for the structures that give rise to the functional ligand
and molecular weight distributions present in the polymer scaffolds.
Lastly, recent strategies employed for overcoming or minimizing the
presence of ligand distributions are discussed. This review focuses
on multivalent polymer scaffolds where average stoichiometry and/or
the distribution of products have been characterized by at least one
experimental technique. Key illustrative examples are provided for
scaffolds that have been carried forward to in vitro and in vivo testing with significant biological
results.