text: Block copolymers are a well-studied and versatile class of self-assembling materials characterized by
  chemically distinct polymer blocks that are covalently bonded. This molecular architecture of the
  covalent bond enhancement is what causes block copolymers to spontaneously form nanoscale
  patterns. In block copolymers, covalent bonds frustrate the natural tendency of each individual polymer to remain separate (in general, different polymers, do not like to mix), so the material assembles into a nano-pattern instead. These copolymers offer the ability to self-assemble into uniform, nanosized micelles and accumulate in tumors via the enhanced permeability and retention effect. Polymer composition can be chosen to control the micelle size and compatibility with the drug of choice. The challenges of this application are the difficulty of reproducing or controlling the size of self-assembly nano micelle, preparing predictable size-distribution, and the stability of the micelle with high drug load content.