Our recently developed ensilication approach can physically stabilize
proteins in
silica without use of a pre-formed particle matrix. Stabilisation is done by tailor fitting individual
proteins with a
silica coat using a modified
sol-gel process.
Biopharmaceuticals, e.g. liquid-formulated
vaccines with adjuvants, frequently have poor thermal stability; heating and/or freezing impairs their potency. As a result, there is an increase in the prevalence of
vaccine-preventable diseases in low-income countries even when there are means to combat them. One of the root causes lies in the problematic
vaccine 'cold chain' distribution. We believe that ensilication can improve
vaccine availability by enabling transportation without refrigeration. Here, we show that ensilication stabilizes
tetanus toxin C fragment (TTCF), a component of the
tetanus toxoid present in the
diphtheria,
tetanus and
pertussis (
DTP) vaccine. Experimental in vivo immunization data show that the ensilicated material can be stored, transported at ambient temperatures, and even heat-treated without compromising the immunogenic properties of TTCF. To further our understanding of the ensilication process and its protective effect on
proteins, we have also studied the formation of TTCF-
silica nanoparticles via time-resolved Small Angle X-ray Scattering (SAXS). Our results reveal ensilication to be a staged diffusion-limited cluster aggregation (DLCA) type reaction. An early stage (
tens of seconds) in which individual
proteins are coated with
silica is followed by a subsequent stage (several minutes) in which the
protein-containing
silica nanoparticles aggregate into larger clusters. Our results suggest that we could utilize this technology for
vaccines,
therapeutics or other
biopharmaceuticals that are not compatible with lyophilization.