Tetracycline Storage Stability. (A) Aliquots of tetracycline in solution and tetracycline loaded silk films stored at -20 °C, 4 °C, 25 °C, 37 °C and 60 °C, and 25 °C with ambient light exposure at 1 and 4 wks. (B) Residual bioactivity over 4 wks storage of tetracycline stored in solution or (C) in 6% (w/v) silk films at 4 °C, 25 °C, 37 °C, 60 °C, and 25 °C with ambient light exposure. Bioactivity measured using a zone of inhibition assay in S. aureus lawns. N = 4, error bars represent standard deviations (D) Comparison of tetracycline stored in silk films and as dry powder at 4 °C (refrigeration), (E) 25 °C (room temperature), (F) 37 °C (body temperature) and (G) 60 °C over 9 months. Activity measured using a zone of inhibition assay in S. aureus lawns. N = 3, error bars represent standard deviations. Data analyzed by one-tailed t-test, df = 4; significance levels of individual tests are indicated: *P < 0.05, **P < 0.01, ***P < 0.005.

Measles, Mumps, and Rubella Vaccine Stability. Vaccines prepared in 9% (w/v) silk and lyophilized films over 6 mo at 4 °C, 25 °C, 37 °C, and 45 °C. Residual potency of the (A) measles, (B) mumps, and (C) rubella components of the MMR vaccine. (⧫) lyophilized MMR-silk films, (○) MMR-silk films, (▪) MMR powder. N = 3, error bars represent standard deviations.

Kinetics of Degradation of MMR-Silk Film Systems. (A) Arrhenius plots of the degradation rates of the measles, mumps, and rubella components of the vaccine as a function of the inverse of the absolute temperature. (B) Predicted half-lives of the measles, mumps and rubella viral components as a function of temperature and the corresponding upper and lower limits of the half-life. The predicted half-lives represent the estimated time required for the viral component to degrade to 50% of the initial value. (⧫) lyophilized MMR-silk films, (○) MMR-silk films, (▪) MMR powder.

Thermal Analysis of Stabilization of MMR-Silk Films. (A) (i) Measles and mumps structures consist of single-stranded, negative-sense RNA enclosed in nucleocapsids within a lipid bilayer. The viral envelop consist of the matrix (M), haemaglutinin (H) and fusion (F) protein. (ii) By a combination of hydrophobic interaction and limited chain mobility, silk-entrapped viral particles maintain structural activity at elevated temperatures. (iii) Structurally intact F and H proteins bind and fuse to the receptors CD46 and CD150 to gain entry into the cell to initiate viral replication. (iv) Denaturation of the surface proteins can result in aggregation of the viral particles and binding and fusion cannot occur. (B) Solid-state DSC. T_g = glass transition point. (C) Nano-DSC. T_P = protein transition point. The presence of silk increases the T_P of the viral particles, indicating the effect of silk on the encapsulated viral proteins. The drop following the T_P is most likely indicative of an aggregation event as a result of the protein unfolding. (D) Comparison of dynamic light scattering of purified viral particles in water and purified viral particles in silk solution.