In this study, we developed a microfluidics method, using a so-called H-cell microfluidics device, for the determination of protein diffusion coefficients at different concentrations, pHs, ionic strengths, and solvent viscosities. Protein transfer takes place in the H-cell channels between two laminarly flowing streams with each containing a different initial protein concentration. The protein diffusion coefficients are calculated based on the measured protein mass transfer, the channel dimensions, and the contact time between the two streams. The diffusion rates of lysozyme, cytochrome c, myoglobin, ovalbumin, bovine serum albumin, and etanercept were investigated. The accuracy of the presented methodology was demonstrated by comparing the measured diffusion coefficients with literature values measured under similar solvent conditions using other techniques. At low pH and ionic strength, the measured lysozyme diffusion coefficient increased with the protein concentration gradient, suggesting stronger and more frequent intermolecular interactions. At comparable concentration gradients, the measured lysozyme diffusion coefficient decreased drastically as a function of increasing ionic strength (from zero onwards) and increasing medium viscosity. Additionally, a particle tracing numerical simulation was performed to achieve a better understanding of the macromolecular displacement in the H-cell microchannels. It was found that particle transfer between the two channels tends to speed up at low ionic strength and high concentration gradient. This confirms the corresponding experimental observation of protein diffusion measured via the H-cell microfluidics.

The aim of this study was to develop a supercritical carbon dioxide (scCO₂) spray process to coat solid protein particles with a hydrophilic polymer. The final purpose is to manufacture drug particles exhibiting controlled release behaviour in patients. Lysozyme microparticles (about 20 μm) were suspended in a vessel into which a dextran sulphate (DS) solution was dispersed by scCO₂ via a nozzle. Upon interaction with the droplets, DS was deposited onto or mixed with suspended lysozyme particles. Particles of about 100 μm were obtained. The zeta-potential analysis and elemental analysis indicated that the top layer of the particles consisted of both lysozyme and DS. Some of the produced particulate materials showed retarded lysozyme release when exposed to water or phosphate buffered saline, holding promise for future production of controlled drug delivery systems for therapeutic proteins.