Design and application of a low-temperature Peltier-cooling microscope stage

Decontamination in the Electron Probe Microanalysis with a Peltier-Cooled Cold Finger

A prototype Peltier thermoelectric cooling unit has been constructed to cool a cold finger on an electron microprobe. The Peltier unit was tested at 15 and 96 W, achieving cold finger temperatures of -10 and -27°C, respectively. The Peltier unit did not adversely affect the analytical stability of the instrument. Heat conduction between the Peltier unit mounted outside the vacuum and the cold finger was found to be very efficient. Under Peltier cooling, the vacuum improvement associated with water vapor deposition was not achieved; this has the advantage of avoiding severe degradation of the vacuum observed when warming up a cold finger from liquid nitrogen (LN2) temperatures. Carbon contamination rates were reduced as cooling commenced; by -27°C contamination rates were found to be comparable with LN2-cooled devices. Peltier cooling, therefore, provides a viable alternative to LN2-cooled cold fingers, with few of their associated disadvantages.

Whole-body Mass Spectrometry Imaging by Infrared Matrix-assisted Laser Desorption Electrospray Ionization (IR-MALDESI)

Ambient ionization sources for mass spectrometry (MS) have been the subject of much interest in the past decade. Matrix-assisted laser desorption electrospray ionization (MALDESI) is an example of such methods, where features of matrix-assisted laser desorption/ionization (MALDI) (e.g., pulsed nature of desorption) and electrospray ionization (ESI) (e.g., soft-ionization) are combined. One of the major advantages of MALDESI is its inherent versatility. In MALDESI experiments, an ultraviolet (UV) or infrared (IR) laser can be used to resonantly excite an endogenous or exogenous matrix. The choice of matrix is not analyte dependent, and depends solely on the laser wavelength used for excitation. In IR-MALDESI experiments, a thin layer of ice is deposited on the sample surface as an energy-absorbing matrix. The IR-MALDESI source geometry has been optimized using statistical design of experiments (DOE) for analysis of liquid samples as well as biological tissue specimens. Furthermore, a robust IR-MALDESI imaging source has been developed, where a tunable mid-IR laser is synchronized with a computer controlled XY translational stage and a high resolving power mass spectrometer. A custom graphical user interface (GUI) allows user selection of the repetition rate of the laser, number of shots per voxel, step-size of the sample stage, and the delay between the desorption and scan events for the source. IR-MALDESI has been used in variety of applications such as forensic analysis of fibers and dyes and MSI of biological tissue sections. Distribution of different analytes ranging from endogenous metabolites to exogenous xenobiotics within tissue sections can be measured and quantified using this technique. The protocol presented in this manuscript describes major steps necessary for IR-MALDESI MSI of whole-body tissue sections.

Physical Characterization of Pharmaceutical Formulations in Frozen and Freeze-Dried Solid States: Techniques and Applications in Freeze-Drying Development

Physical characterization of formulations in frozen and freeze-dried solid states provides indispensable information for rational development of freeze-dried pharmaceutical products. This article provides an overview of the physical characteristics of formulations in frozen and freeze-dried solid states, which are essential to both formulation and process development. Along with a brief description of techniques often used in physical characterization for freeze-drying development, applications of and recent improvements to these techniques are discussed. While most of these techniques are used conventionally in physical characterization of pharmaceuticals, some techniques were designed or modified specifically for studies in freeze-drying. These include freeze-drying microscopy, freeze-drying X-ray powder diffractometry and cryoenvironmental scanning microscopy, which can be used to characterize the physical properties of the formulation under conditions similar to the real vial lyophilization process. Novel applications of some conventional techniques, such as microcalorimetry and near infrared (NIR) spectroscopy, which facilitated freeze-drying development, receive special attention. Research and developmental needs in the area of physical characterization for freeze-drying are also addressed, particularly the need for a better understanding of the quantitative correlation between the molecular mobility and the storage stability (shelf life).

Formulation and delivery issues for monoclonal antibody therapeutics

Antibodies can have exquisite specificity of target recognition and thus generate highly selective outcomes following their systemic administration. While antibodies can have high specificity, the doses required to treat patients, particularly for a chronic condition, are typically large. Fortunately, advances in production and purification capacities have allowed for the exceptionally large amounts of highly purified monoclonal antibodies to be produced. Additionally, genetic engineering of antibodies has provided a stable of antibody-like proteins that can be easier to prepare. Together, these advances have made antibody-based therapies one of the most commonly pursued pharmaceuticals in biotechnology pipelines. With this success, however, has come a series of technical challenges in the formulation of antibody-based materials to maintain sufficient stability in a variety of configurations and sometimes at particularly high concentrations. This review focuses on issues related to identifying and verifying stable antibody-based formulations.

Lyophilization of polyethylene glycol mixtures

Lyophilization of cosolvent systems may be a beneficial way of enhancing both physical and chemical stability of a drug product. The objective of this research is to establish whether cosolvent systems commonly used in the formulation of poorly water-soluble drugs can be successfully lyophilized. Polyethylene glycol (PEG) 400 was selected because it is widely used and can be easily frozen. The addition of PEG 400 to commonly used bulking agents, such as mannitol, sucrose, or polyvinylpyrrolidone, caused a significant change in the thermal properties of the bulking agents as observed by modulated differential scanning calorimetry. In addition, PEG 8000 was evaluated as a bulking agent because it also can function as a cosolvent in solution and forms an acceptable cake after lyophilization. Addition of PEG 400 to PEG 8000 caused negligible changes in the thermogram of this bulking agent. Surprisingly, the combination of PEG 8000 and PEG 400 forms a solid lyophilized cake. The current system can be best described as the lyophilization of a miscible solution of PEG 8000 and PEG 400 resulting in a lyophile that has a crystalline structure of PEG 8000 which is able to support PEG 400.

Lyophilization and development of solid protein pharmaceuticals

Developing recombinant protein pharmaceuticals has proved to be very challenging because of both the complexity of protein production and purification, and the limited physical and chemical stability of proteins. To overcome the instability barrier, proteins often have to be made into solid forms to achieve an acceptable shelf life as pharmaceutical products. The most commonly used method for preparing solid protein pharmaceuticals is lyophilization (freeze-drying). Unfortunately, the lyophilization process generates both freezing and drying stresses, which can denature proteins to various degrees. Even after successful lyophilization with a protein stabilizer(s), proteins in solid state may still have limited long-term storage stability. In the past two decades, numerous studies have been conducted in the area of protein lyophilization technology, and instability/stabilization during lyophilization and long-term storage. Many critical issues have been identified. To have an up-to-date perspective of the lyophilization process and more importantly, its application in formulating solid protein pharmaceuticals, this article reviews the recent investigations and achievements in these exciting areas, especially in the past 10 years. Four interrelated topics are discussed: lyophilization and its denaturation stresses, cryo- and lyo-protection of proteins by excipients, design of a robust lyophilization cycle, and with emphasis, instability, stabilization, and formulation of solid protein pharmaceuticals.

Lyophilization of protein formulations in vials: investigation of the relationship between resistance to vapor flow during primary drying and small-scale product collapse

During the lyophilization process, formulations containing protein, bulking agent, or lyoprotectant form a dry product layer that can affect the transport of sublimed water vapor. We carried out an investigation of the primary drying segment of lyophilization to evaluate the relationship between the resistance to water vapor flow through the dried layer and the microstructure of the dried cake. Recombinant humanized antibody HER2 (rhuMAb HER2) formulated in trehalose was studied, as were protein-free formulations containing trehalose and sucrose. Sublimation rate and product temperature data were used to compute the resistance to mass transfer. Dried cake structure was examined by scanning electron microscopy and a novel fluorescence microscopy method. Collapse temperatures were determined by freeze-drying microscopy. Mass transfer resistance was found to decrease with increases in temperature for each material. Resistance also depended on composition, decreasing in the formulation series, rhuMAb HER2, trehalose, sucrose. The lyophilized material consisted of porous cakes, with a distinct denser region at the top. Formulation and temperature affected the microstructure of the dried cakes. The formulated trehalose and sucrose were seen, by both microscopy techniques, to possess small (2-20 microm) holes in their platelike structures after lyophilization. The quantity of holes was higher for material dried at higher temperature. The collapse temperature (Tc) of a material appeared to play a role in the process, as lower Tc was correlated with lower resistance and a greater extent of holes. Our results are consistent with the theory that lower resistance to water vapor flow in the primary drying stage of lyophilization may be due to small-scale product collapse.

Preparation of excipient-free recombinant human tissue-type plasminogen activator by lyophilization from ammonium bicarbonate solution: an investigation of the two-stage sublimation phenomenon

Dry, excipient-free recombinant human tissue-type plasminogen activator (tPA) powder was prepared by lyophilization from ammonium bicarbonate solution. Ammonium bicarbonate sublimes into ammonia, water, and carbon dioxide upon lyophilization, without causing measurable harm to the protein. There were approximately 4 mol of residual ammonium ion per mole of lyophilized tPA. Under certain lyophilization conditions, a large pressure increase in the lyophilizer chamber occurred, presenting a pressure control problem. Microscopy and sublimation rate measurements on the frozen matrix revealed that ice sublimation occurred first, followed by the sublimation of ammonium bicarbonate. Analysis of the sectioned frozen matrix indicated that the bicarbonate salt was evenly distributed throughout the vial, suggesting that the delay of ammonium bicarbonate sublimation was not due to hindrance by ice. In the two-stage process, ice sublimation proceeded according to zero-order kinetics, whereas ammonium bicarbonate sublimation followed a grain-burning (2/ 3-order) model and was governed by a higher activation enthalpy. In most cases, the sublimation rate of ammonium bicarbonate in the presence of tPA was lower than that in the absence of the protein. Sublimation activation enthalpy for ammonium bicarbonate in the presence of tPA was 26.1 +/- 3.8 kcal/mol, which was approximately 10 kcal/mol greater than that for the tPA-free system. Consistent with a prediction from our kinetic modeling, a 6-h extension of primary drying enabled us to conduct lyophilization while maintaining pressure control.