Membrane emulsification for the production of uniform poly-N-isopropylacrylamide-coated alginate particles using internal gelation

• Solid particles injected through membrane in membrane emulsification process.
• Median particle size controllable within range between 55 μm and 690 μm.
• Span values (D90-D10)/D50 as low as 0.2 measured.
• Functionalisation using pNIPAM to form temperature responsive particles.
• Biological cell attachment, growth and detachment successfully demonstrated.

Alginate particles, crosslinked by calcium ions, have a number of potential biopharmaceutical industry applications due to the biocompatibility of the materials used and formed. One such use is as microcarriers for cell attachment, growth and then detachment without the use of proteolytic enzymes. A straightforward and reproducible method for producing uniform calcium alginate particles with controllable median diameters which employs membrane emulsification and internal gelation (solid particles contained in the dispersed phase) is demonstrated, as well as functionalisation of the resulting beads with amine terminated poly N-isopropylacrylamide (pNIPAM) to form temperature responsive particles, by taking advantage of the electrostatic interaction between the carboxyl groups of the alginate and amino groups of the modified pNIPAM. Cell attachment, growth and detachment capabilities of these core–shell structures were assessed and successfully demonstrated by using phase contrast microscopy and fluorescent staining with calcein-AM and ethidium homodimer-1.The formulation used for the alginate particles avoided non-GRAS chemicals by only using food grade and pharmaceutical grade reagents. The median particle size was controllable within the range between 55 μm and 690 μm and the size distributions produced were very narrow: ‘span’ values as low as 0.2. When using a membrane pore size of 20 μm no membrane blockage by the suspended calcium carbonate necessary for internal gelation of the alginate particles was observed. Membrane pore openings with diameters of 5 and 10 μm were also tested, but blocked with the 2.3 μm median diameter calcium carbonate solids.