title: Morphology of protein particles produced by spray freezing of concentrated solutions.
abstract: The mechanisms for the formation of high surface area lysozyme particles in spray freezing processes are described as a function of spray geometry and atomization, solute concentration and the calculated cooling rate. In the spray freeze-drying (SFD) process, droplets are atomized into a gas and then freeze upon contact with a liquid cryogen. In the spray freezing into liquid (SFL) process, a solution is sprayed directly into the liquid cryogen below the gas-liquid meniscus. A wide range of feed concentrations is examined for two cryogens, liquid nitrogen (LN2) and isopentane (i-C5). The particle morphologies are characterized by SEM micrographs and BET measurements of specific surface area. As a result of boiling of the cryogen (Leidenfrost effect), the cooling rate for SFL into LN2 is several orders of magnitude slower than for SFL into i-C5 and for SFD in the case of either LN2 or i-C5. For 50 mg/mL concentrated feed solutions, the slower cooling of SFL into LN2 leads to a surface area of 34 m(2)/g. For the other three cases with more rapid cooling rates, surface areas were greater than 100 m(2)/g. The ability to adjust the cooling rate to vary the final particle surface area is beneficial for designing particles for controlled release applications.
authors.affiliation: Department of Chemical Engineering, The University of Texas at Austin, Austin, TX 78712, USA.
authors.forename: Josh D
authors.initials: JD
authors.lastname: Engstrom
authors.forename: Dale T
authors.initials: DT
authors.lastname: Simpson
authors.forename: Edwina S
authors.initials: ES
authors.lastname: Lai
authors.forename: Robert O
authors.initials: RO
authors.lastname: Williams
authors.forename: Keith P
authors.initials: KP
authors.lastname: Johnston
mesh_terms: D000465:Algorithms; D005615:Freezing; D006813:Humidity; D008855:Microscopy, Electron, Scanning; D009113:Muramidase / Q000737:chemistry; D009584:Nitrogen; D010316:Particle Size; D010420:Pentanes; D011208:Powders; D011506:Proteins / Q000737:chemistry*; D012996:Solutions; D014199:Trehalose; D014783:Viscosity
chemical_list: D010420:Pentanes; D011208:Powders; D011506:Proteins; D012996:Solutions; D014199:Trehalose; D009113:Muramidase; D009584:Nitrogen; C067038:isopentane