Assembly-Controlled Permeability of Layer-by-Layer Polymeric Microcapsules Using a Tapered Fluidized Bed

Nano- and microcapsules engineered through layer-by-layer (LbL) assembly are finding an increasingly large number of applications as catalysts, electrochemical biosensors, bioreactors, artificial cells and drug delivery vehicles. While centrifugation-based LbL assembly is the most common method for coating template particles and preparing capsules, it is a batch process and requires frequent intervention that renders the system challenging to automate and scale up. Here, we report the use of a tapered fluidized bed (TFB) for the preparation of multilayered polymer capsules. This is a significant improvement over our recent approach of fluidizing particles in cylindrical fluidized beds (CFB) for LbL assembly. We demonstrate that TFB is compatible with particles <3 mu m in diameter (an order-of-magnitude improvement compared with CFB), which can be fluidized with minimal entrainment. Additionally, layering materials were expanded to include both electrostatic and hydrogen-bonding polymer pairs (e.g., poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate) (PSS), and thiol-modified poly(methacrylic acid) (PMA(SH)). and poly(N-vinylpyrrolidone) (PVPON), respectively). Finally, difference's between capsules prepared via centrifugation-based and TFB LbL assembly were investigated. The obtained TFB micro capsules demonstrate increased film thickness and roughness compared with those prepared using centrifugation-based LbL assembly. Furthermore, PMA(SH) microcapsules exhibit lower swelling and permeability when prepared via TFB LbL assembly compared with centrifugation-based LbL assembly due to enhanced multilayer deposition, entanglement, and cross-linking. Therefore, polymeric capsules fabricated via TFB LbL assembly may be useful for encapsulation and retention of relatively low molecular weight (similar to 20 kDa) hydrophilic biomacromolecules to passively or responsively release the payload for drug delivery applications.