Mechanisms involved in the electrospray of biological macromolecules

Abstract

Electrospray of macro-molecules is of great interest in biomedical research for its finely controlled delivery of molecules. This thesis investigated mechanisms involved in electrospray of biological macromolecules. Hyaluronan, i.e. HA, for its biological significance, has been studied, and comparisons made to another macromolecule with similar molecular weight, dextran (DA). A mixture of ethylene glycol (EG) and deionized water with volume ratio of 1:1 is used to dissolve HA and DA molecules and reduce the surface tension of the aqueous solution. HA and DA solutions of different concentrations and molecular sizes are investigated in the study. A number of spray parameters are studied to characterise the electrospraying emission and to find the optimal control conditions. With sonication to reduce the molecular size of HA, stable cone-jet electrospray has been achieved relatively easily for HA solutions. Steady μm-sized jets are observed during spraying and the jet size has been found to increase with both the molecular size and the concentration. Experimental results demonstrate that the molecular size, rather than the molecular weight of macro-molecules is a critical factor affecting the spraying process. A hypothesis on HA partial reflection during electrospray is presented in the study. A theoretical model that describes the build up of a higher HA concentration layer near the Taylor-cone tip has been developed. 4 Based on experimental parameter values, the model predicts the concentration of HA molecules in the collected solution after the cone-jet electrospray. Good agreement between model predictions and experimental results indicates a possible mechanism in the electrospray process of biological macromolecules.