Diffusion is one of the key nature processes which plays an important role in respiration, digestion, and nutrient transport in cells. In this regard, the present article aims to review various diffusion approaches used to fabricate different functional materials based on hydrogels, unique examples of materials that control diffusion. They have found applications in fields such as drug encapsulation and delivery, nutrient delivery in agriculture, developing materials for regenerative medicine, and creating stimuli-responsive materials in soft robotics and microrobotics. In addition, mechanisms of release and drug diffusion kinetics as key tools for material design are discussed.

Drug delivery systems based on the zeolitic imidazolate framework ZIF-8 have recently attracted viable research interest owing to their capability of decomposing in acidic media and thus performing targeted drug delivery. In vivo realization of this mechanism faces a challenge of relatively slow decomposition rates, even at elevated acidic conditions that are barely achievable in diseased tissues. In this study we propose to combine drug delivery nanocomposites with a semiconductor photocatalytic agent that would be capable of inducing a local pH gradient in response to external electromagnetic radiation. In order to test this principle, a model drug-releasing nanocomposite comprising photocatalytic titania nanotubes, ZIF-8, and the antitumor drug doxorubicin has been investigated. This system was demonstrated to release the drug in a quantity sufficient for effectively suppressing IMR-32 neuroblastoma cells that were used as a model diseased tissue. With locally applied UV irradiation, this result was achieved within 40 minutes, which is a relatively short time compared to the release duration in systems without photocatalyst, typically taking from several hours to several days.

K₂[TiO(C₂O₄)₂] is decomposed by micro-arcs on the anode producing TiO₂ while hydroxyapatite particles are incorporated into TiO₂ coating during electrophoretic deposition.

A novel method of 3D self‐organization of patterns made of biomimetic hydroxyapatite (HA) in agar matrix is reported. The model system involves gradual ion diffusion and phase transitions of calcium phosphates. Herein, HA is precipitated for the first time in the agar gel matrix via single‐diffusion gel growth technique to aggregate the inorganic Liesegang rings (LRs). These patterns are formed as periodic structures through precipitation reaction and arise during the reagent diffusion in a polymer matrix. The concentrations of these inner and outer electrolytes, as well as pH and temperature effects on the morphologies, periodicity, stability, and number of LRs, are studied. In this study, the periodic HA Liesegang ring structures (HA LRs) are fabricated via a diffusion‐limited aggregation process. These patterns influence the C2C12 cell growth and allow to obtain the patterns formed by the cell tissue. This method can be prospective for the generation of 3D gradients in materials/3D gradient materials generation for studying the interface tissue engineering, systematic cell–biomaterial interaction, as well as for the fabrication of the stimuli‐responsive gradients to control/mimic migration of cells during the wound healing.