They are safe and non-infectious for biomedical applications. The coat proteins that assemble into VLPs can be derived from the coat protein units of mammalian viruses, bacteriophages, and plant viruses. VLPs are generally robust structures, allowing chemical conjugation of various molecules (e.g., targeting molecules, antigenic compounds) and/or encapsidation of diverse compounds (e.g., drug molecules, fluorescent molecules, and metal nanoparticles). Their precise size, shape, and surface chemistry of protein nanocages make them ideal building blocks for designing advanced functional materials. For instance, rod-like phages, such as fd or M13 bacteriophages, were used to form hexagonally packed structures or star-like assemblies. Isotropic nanocages such as P22 VLP, cowpea chlorotic mottle virus, and ferritin have been arranged in cubic or hexagonal lattices. Structurally anisotropic phages have been researched as delivery vehicles in tumor targeting because they can traverse biological barriers more easily. However, their self-assembly into programmable, responsive structures has not been widely studied.