3D Printing - Evaluating Particle Emissions of a 3D Printing Pen.

Three-dimensional (3D) printing as a type of additive manufacturing shows continuing increase in application and consumer popularity. The fused filament fabrication (FFF) is an inexpensive method used most frequently by consumers. Studies with 3D printers have shown that during the printing process particulate and volatile substances are released. Handheld 3D printing pens also use the FFF method but the consumer's proximity to the 3D pens gives reason to higher exposure compared to a 3D printer. At the same time, 3D printing pens are often marketed for children who could be more sensitive to the printing emission. The aim of this study was to implement a low cost method to analyze the emissions of 3D printing pens. Polylactide (PLA) and acrylonitrile butadiene styrene (ABS) filaments of different colors were tested. In addition, filaments containing metal and carbon nanotubes (CNTs) were analyzed. An 18.5 L chamber and sampling close to the emission source was used to characterize emissions and concentrations near the breathing zone of the user. Particle emissions and particle size distributions were measured and the potential release of metal particles and CNTs investigated. Particle number concentrations were found in a range of 105 - 106 particles/cm3, which is comparable to previous reports from 3D printers. Transmission electron microscopy (TEM) analysis showed nanoparticles of the different thermoplastic materials as well as of metal particles and CNTs. High contents of metal were observed by inductively coupled plasma mass spectrometry (ICP-MS). These results call for a cautious use of 3D pens due to potential risk to the consumers.

Squeeze flow rheometry as a novel tool for the characterization of highly concentrated protein solutions.

This study aims at defining rheological parameters for the characterization of highly concentrated protein solutions. As a basis for comparing rheological behavior with protein solution characteristics the protein phase behavior of Lysozyme from chicken egg white with concentrations up to 225 mg/mL, changing pH values and additive concentrations was studied in a microbatch scale format. The prepared phase diagrams, scored after 40 days (t40) give insights into the kind and kinetics of the phase transitions that occur. Oscillatory frequency sweep measurements of samples with exactly the same conditions were conducted immediately after preparation (t0). The protein solutions behave viscoelastic and show a characteristic curve shape of the storage modulus (G') and the loss modulus (G″). The graphs provide information about the cross-linking degree of the respective sample. The measured rheological parameters were sensitive concerning solution composition, protein concentration and solution inner structure. The rheological moduli G' and G″ and especially the ratio of these parameters over a frequency range from 100 to 40000 rad/sec give information about the aggregation tendency of the protein under tested conditions. We succeeded to correlate protein phase behavior with the defined rheological key parameter ωCO. This point represents the frequency value of the intersection point from G' and G″. In our study Lysozyme expressed a ωCO threshold value of 20000 rad/sec as a lower limit for stable protein solutions. The predictability of lysozyme aggregation tendency and crystallization by means of squeeze flow rheometry is shown.

Determination of protein phase diagrams by microbatch experiments: exploring the influence of precipitants and pH.

Knowledge of protein phase behavior is essential for downstream process design in the biopharmaceutical industry. Proteins can either be soluble, crystalline or precipitated. Additionally liquid-liquid phase separation, gelation and skin formation can occur. A method to generate phase diagrams in high throughput on an automated liquid handling station in microbatch scale was developed. For lysozyme from chicken egg white, human lysozyme, glucose oxidase and glucose isomerase phase diagrams were generated at four different pH values ­ pH 3, 5, 7 and 9. Sodium chloride, ammonium sulfate, polyethylene glycol 300 and polyethylene glycol 1000 were used as precipitants. Crystallizing conditions could be found for lysozyme from chicken egg white using sodium chloride, for human lysozyme using sodium chloride or ammonium sulfate and glucose isomerase using ammonium sulfate. PEG caused destabilization of human lysozyme and glucose oxidase solutions or a balance of stabilizing and destabilizing effects for glucose isomerase near the isoelectric point. This work presents a systematic generation and extensive study of phase diagrams of proteins. Thus, it adds to the general understanding of protein behavior in liquid formulation and presents a convenient methodology applicable to any protein solution.