Protein drugs such as insulin are almost universally delivered via glass syringes lubricated with silicone oil. It is not uncommon for prefilled syringes (PFS) to become cloudy, which may affect bioavailability or total drug dose. To examine the role, if any, of the silicone oil lubricant in this process, a systematic evaluation of the degree of insulin denaturation and aggregation as a function of silicone oils of different molecular weights was undertaken. The former was measured using fluorescence changes of aqueous insulin/silicone dispersions, while the latter examined changes in turbidity as a function of mixing and silicone oil type; the results were confirmed at two different insulin concentrations and agitation speeds. Lower molecular weight silicones led to the most rapid denaturation and aggregation, and when examined in blends of silicones at a fixed viscosity of 1000 cSt, commonly used for syringe lubrication, more rapid denaturation/aggregation was noted in blends of silicones containing the largest fractions of low molecular weight materials. As a consequence, the molecular weight profile of silicone lubricants should be established prior to the preparation of prefilled syringes.

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Understanding conformational changes are important when studying a protein such as calmodulin (CaM), which activates various target enzymes and regulates numerous physiological functions. CaM is a highly flexible protein that can transitorily adopt various conformations. A quartz crystal microbalance with dissipation (QCM-D) sensor was used to study binding-induced conformational changes of surface-immobilized CaM. Structural changes of CaM were evaluated using the Voigt's viscoelastic model with frequency (ΔF) and dissipation change (ΔD). When Apo-CaM layer was incubated in 0.1 mM Ca 2+ solution, the layer decreased by approximately 0.56 nm, due to the release of coupled water molecules and conformational change. The application of CaM itself also caused a significantly more compact layer, supporting previous findings that CaM dimerization forms a collapsed structure that exposes a hydrophobic tunnel. The binding characteristics of CaM with peptides derived from proteins in a signal transduction pathway also demonstrated diverse biophysical properties of the CaM complexes. Each peptide showed a unique ΔF/ΔD pattern indicating versatility of CaM configuration to favorably adjust to each target molecule. The study demonstrates that the QCM-D sensor is capable of simultaneously studying binding affinity and plasticity of protein configuration for target binding. The CaM data obtained on hydrated protein layer thickness is complementary to configuration measurements of a single CaM molecule.

The adhesion of Escherichia coli to copolymers of methacrylates and a trisiloxane-polyether acrylate surfactant was found to be at a minimum with copolymers containing a low (20%) fraction of the surfactant monomer. Rather than wettability, hardness, or water uptake, adhesion was found to be limited by the presence of low concentrations of bound surfactant that can interact with hydrophobic domains on the bacterium inhibiting anchoring to the polymer surface.