An examination of factors affecting the size, distribution and release characteristics of polymer microbeads made using electrostatics

A new technique of generating polymeric monolithic microbeads containing solid protein particles has been developed. The method involves extruding a suspension of protein particles within a polymer solution through a needle and into an electric field. The electric field force effectively pulls the forming droplet off the end of the needle, producing a series of smaller droplets. A factorial design investigation of the extrusion process using bovine serum albumin particles suspended in ethylene vinyl acetate dissolved in dichloromethane, illustrated that the size of the microbead was controlled primarily by the strength of the electric field and the gauge of the needle used. Smaller microbeads were formed by increasing the applied electric field and using a higher gauge (smaller internal diameter) needle. However, the reduction in microbead average diameter came at the expense of a much broader distribution of microbead diameters. Release studies using the microbeads illustrated the ability of the process to encapsulate and slowly release protein. From these studies, the critical volumetric loading of the microbeads was determined and found to be dependent on the size of the incorporated protein particles.