Investigation of mechanical properties of soft hydrogel microcapsules in relation to protein delivery using a MEMS force sensor.

This article reports the investigation of mechanical properties of alginate-chitosan microcapsules and the relation to protein delivery. For microscale compression testing, a system based on a microelectromechanical systems (MEMS) capacitive force sensor was developed. The bulk microfabricated capacitive force sensors are capable of resolving forces up to 110 microN with a resolution of 33.2 nN along two independent axes. The monolithic force sensors were directly applied to characterizing mechanical properties of soft hydrogel microparticles without assembling additional end-effectors. Protein-loaded alginate-chitosan microcapsules of approximately 20 mum in diameter were prepared by an emulsion-internal gelation-polyelectrolyte coating method. Young's modulus values of individual microcapsules with 1, 2, and 3% chitosan coating were determined through microscale compression testing in both distilled deionized (DDI) water and pH 7.4 phosphate-buffered saline (PBS). Protein release rates were also determined in DDI water and PBS. Finally, protein release rates were correlated with mechanical properties of the microcapsules.