Synthesis of Hydrogel Microparticles from Ultra‐High‐Viscosity Pre‐Gel Solution by Combining Centrifugal Force and Ultrasonic Vibration

Abstract Viscosity is a key physical parameter influencing droplet generation. Herein, the synthesis of hydrogel microparticles from an ultra‐high‐viscosity pre‐gel (UHV‐HMPs) solution using a microparticle synthesis device combining centrifugal force with ultrasonic vibration (MSDCU) is reported. The advantage of MSDCU is that it can synthesize closely spherical microparticles from ultra‐high‐viscosity pre‐gel solutions with viscosities exceeding 10 4 mPa·s in the air/water method. The ultrasonic droplet‐shooting module embedded in the MSDCU ejects an ultra‐high‐viscosity pre‐gel solution of sodium alginate through a capillary under ultrasonic vibration to overcome the viscosity limitations of using only centrifugal force. Based on an evaluation of the vibration modes of a multilayer transducer with a capillary at various resonance frequencies, a vibration mode with longitudinal and lateral vibrations of 100 kHz is selected. The combination of ultrasonic vibration at 100 kHz and a centrifugal force of 230g results in the ejection of pre‐gel solution with a maximum viscosity of 1.5 × 10 5 mPa·s. At a viscosity of 1.5 × 10 4 mPa·s, control of the distance between the capillary and crosslinking solution improves particle circularity, enabling the formation of spherical UHV‐HMPs with a diameter of ≈140 µm. With a higher viscosity solution (3.0 × 10 4 mPa·s), smaller homogeneous satellite particles with a diameter of ≈31 µm are synthesized after filtering.