Spray Drying of Uniform Silica Microencapsulates: Implications for Controlled Release

Spray drying is a scalable route for particle formation with easy product recovery. Conventional spray drying produces broad distributions of particles with various morphologies in a single batch, due to non-uniform distribution of droplets / spray trajectories and different residence times [1]. This renders any interpretation of particle behaviour in relation to their physico-chemical properties virtually impossible. Here, uniform silica microparticles encapsulating vitamin B₁₂, which was homogenously distributed within each particle, were synthesised in a single step via a micro-fluidic-jet-spray-dryer (Figure 1). The dryer utilised a micro-fluidic-aerosol-nozzle for continuous generation of monodisperse droplets from complex precursors [2]. The uniformity of the particles allowed direct correlations between their properties and the release behaviour of vitamin B₁₂ to be investigated, without the complications of wide size distribution or non-uniform shapes. The effects of additives in the forms of lactose and Na-alginate to the properties of these microparticles were demonstrated. Spherical particles with relatively smooth surface were obtained with lactose addition, while incorporation of Na-alginate resulted in noticeably increasing surface roughness with higher amount added (Figure 2). Lactose addition also accelerated the release of the encapsulated vitamin B₁₂, due to the relatively fast lactose dissolution that allowed buffer to penetrate into the matrix to facilitate diffusion and silica erosion. On the contrary, Na-alginate slowed down the release considerably by serving as an additional barrier to decelerate silica matrix erosion. Release kinetics data indicated diffusion as the main release mechanism independent of the additives. The release profiles from different compositions of the synthesized particles demonstrated good agreement with computational results, highlighting the reproducibility of particles produced with this technique and the ability to modulate the release behaviour directly from the precursor compositions.

Figure 1 – Schematic of the micro-fluidic-jet-spray-dryer

Figure 2 – Uniform silica microencapsulates with (a) 0.5%w/v Na-alginate; (b) 1.0%w/v Na-alginate

References:

1.    Woo, M.W., Rogers, S., Lin, S.X.Q., Selomulya, C., Chen, X. D., 2011, Numerical probing of a low velocity concurrent pilot scale spray drying tower for mono-disperse particle production - unusual characteristics and possible improvements, Chemical Engineering and Processing: Process Intensification, doi:10.1016/j.cep.2011.02.007

2.    Wu, W., Amelia, R., Hao, N, Selomulya, C., Zhao, D., Chiu, Y., Chen, X. D., 2010, Assembly of Uniform Photoluminescent Microcomposites Using a Novel Micro-Fluidic-Jet-Spray-Dryer, AIChE Journal, DOI 10.1002/aic.12489.