Hydrogel particles are versatile materials with applications in a wide variety of fields, ranging from photonics, optics, drug delivery and tissue engineering, to the food industry and cosmetics. These hydrophilic particles, often composed of synthetic polymers, can provide tunable control over the sequestration and delivery of materials. The favorable properties of these particles depend largely on their size, and particles ranging from nanometers to micrometers are used in different applications. Traditionally, these particles have been fabricated using a variety of advanced techniques and starting materials, and only within one size regime.

In published research in Advanced Materials, Costa and co-workers develop a simple yet powerful system for generating hydrogel particles of tunable size across multiple size scales using one single starting material. The particles are composed of an elastin-like polypeptide (ELP), a biopolymer that has been extensively utilized because of its biocompatibility and utility in a variety of tissue engineering and drug delivery applications.

The authors introduced a genetically encoded unnatural amino acid, p-azidophenylalanine, into the ELP chains to provide UV-reactive photo-crosslinking sites that helped stabilize the fabricated particles. By simply tuning the ELP composition of the particles and UV irradiation temperature, they demonstrated the ability to create precisely defined, monodisperse particles ranging from the nanoscale (50 nm in diameter) to the microscale (25 mm in diameter).

The particles retained the unique thermoresponsive behavior of the component ELP, shrinking upon heating and swelling upon cooling, providing an active mechanism for actuation and a dynamic response to the environment. According to the researchers, “[..] these particles are ideally suited as drug delivery vehicles, actuators, and biosensors. This work represents a fundamental advance in the generation of crosslinked biomaterials, especially in the form of soft matter colloids, and is the one of the first demonstrations of successful use of unnatural amino acids in generating a novel material.”