Slow release fertilizer hydrogels combine fertilizer and hydrogel into one system.

In this article, the basic principles of core–shell polymers (CSPs) such as definitions, classifications and applications are critically investigated. Introduction of CSPs characterization techniques, such as Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), ¹H and ¹³C Nuclear Magnetic Resonance Spectroscopy (NMR), Small Angle Neutron Scattering (SANS), Nonradioactive Direct Energy Transfer (NRET), Photon Correlation Spectroscopy (PCS) and Dynamic Light Scattering (DLS), are highlighted. In addition, preparation techniques and recent studies of CSPs are briefly discussed. The factors that affect core-shell morphology and properties such as cross-linking radical penetration and diffusion, processing techniques and monomers polarity are considered. Core-shell polymers are structured composite particles consisting of at least two different components, one at the center as a core and surrounding by the second as a shell. Smart properties are considered to be the most desirable characteristics that allow this class of polymer to be used in various applications, particularly in biomedicine as drug delivery systems.

Herein, the basic principles, such as the definitions, classifications, and properties, of hollow polymer particles (HPPs) are critically investigated.