Tuning protein delivery from different architectures of layer-by-layer assemblies on polymer films

In the past two decades, the fabrication of nanolayer coatings on polymeric materials has triggered considerable interest in the tissue-engineering field. Layer-by-Layer (LbL) assembly has attracted substantial attention due to being a convenient and low-cost method to coat materials with biomolecules while keeping their original biofunctionalities. This work aims to access a deeper understanding of the processes of adsorption and desorption of proteins by studying different architectures for the loading and release of model proteins on spin-coated flat surfaces of biodegradable polyesters such as poly(epsilon -caprolactone) (PCL) and poly(l-lactic acid) (PLLA) by the LbL technique. Surfaces of Si-wafers coated with PCL and PLLA were used as substrates for deposition of model proteins such as bovine serum albumin and lysozyme using heparin and chitosan as a pair of polyelectrolytes for LbL assembly. The analysis of the attributes of these protein reservoirs such as the protein layer position, layer thickness, surface morphology, protein adsorption and desorption quantification and kinetics was performed by ellipsometry, atomic force microscopy, fluorescence microscopy, and quartz-crystal microbalance with enhanced dissipation measurements. A homogenous LbL coating on the surface of the polyester films was achieved by assembling ten layer-pairs of reservoirs. The release profiles were evaluated, and the results showed an intricate dependence on the protein volume charge density and its relation to coacervation/complexation processes with both polyelectrolytes. Our results clearly suggest that the protein delivery kinetics can be fully controlled by precisely positioning the protein within the assembly (bottom vs. top position). They also suggest that the size and total charge of the protein are key factors for controlling its total load in the assembly.