Temperature is a central EV storage variable because membrane integrity, molecular cargo, aggregation behavior, enzymatic activity, and contaminant growth can all be temperature-dependent. Refrigeration may be suitable for short intervals for some preparations, whereas frozen storage is commonly used for longer periods. However, no single temperature can be assumed optimal for every EV product. Stability must be demonstrated using the actual formulation, container, storage duration, and quality attributes of interest. Temperature excursions during processing, shipping, thawing, or clinical handling should be evaluated rather than ignored.
Figure 1 placeholder — Temperature
Buffer composition
Buffer composition can influence pH, ionic strength, osmolarity, membrane interactions, protein stability, particle aggregation, and compatibility with downstream administration. Phosphate-buffered saline is common in research, but a research buffer is not automatically an optimized clinical formulation. Excipients such as sugars, amino acids, proteins, surfactants, or antioxidants may stabilize selected products, while other components may alter assays or biological activity. Formulation development should evaluate compatibility, purity, sterility strategy, intended route, and stability rather than selecting a buffer solely because it is conventional.
Figure 2 placeholder — Buffer composition
Freeze–thaw cycles
Freeze–thaw cycles expose EV preparations to ice formation, solute concentration, interfacial stress, membrane perturbation, and repeated temperature transitions. Depending on product and formulation, repeated cycles can alter particle concentration, size distribution, aggregation, membrane integrity, cargo measurements, or functional activity. Effects reported across studies are inconsistent because EV source, separation method, buffer, freezing rate, thawing procedure, storage temperature, and analytical methods differ. Stability studies should define allowable cycles and clinical workflows should minimize unnecessary repeated freezing and thawing.
Figure 3 placeholder — Freeze–thaw cycles
Container effects
Container effects arise from interactions between the EV preparation and vials, tubes, syringes, stoppers, filters, or other product-contact materials. EVs and associated proteins can adsorb to surfaces, particularly at low concentrations, reducing apparent recovery or changing composition. Container material, surface chemistry, headspace, fill volume, agitation, closure integrity, extractables, leachables, and compatibility with freezing can all matter. Container-closure systems for clinical products should therefore be selected and qualified as part of the product rather than treated as interchangeable laboratory hardware.
Figure 4 placeholder — Container effects
Aggregation
Aggregation occurs when EVs or other particles associate into larger structures. It can be promoted by concentration, freezing, thawing, agitation, ionic conditions, pH, surface interactions, or contaminants. Aggregation can change measured particle number and size, sedimentation, filtration behavior, biodistribution, uptake, and potentially biological activity or safety. An apparent loss of particle count can reflect aggregation rather than destruction. Stability programs should therefore monitor size distribution and aggregation with methods capable of distinguishing genuine product change from assay variability.
Figure 5 placeholder — Aggregation
Sterility
Sterility is a critical quality requirement for EV products intended for administration. Storage conditions do not create sterility; sterility must be built into source control, manufacturing, aseptic processing, container closure, and testing. Terminal sterilization methods used for conventional products may damage EVs or alter biological activity, making process design especially important. Sterility testing, endotoxin control, mycoplasma testing where appropriate, bioburden monitoring, and container-closure integrity should be integrated with the manufacturing strategy. A sterile test result does not substitute for a controlled sterile process.
Figure 6 placeholder — Sterility
Shelf life
Shelf life is the period during which a product remains within predefined specifications when stored under labeled conditions. It should be supported by a stability program that measures relevant quality attributes over time, including identity, particle characteristics, purity, potency, sterility-related attributes, and formulation or container effects. Real-time stability data are the strongest basis for assigning shelf life; accelerated or stress studies can help identify degradation pathways but do not automatically establish long-term expiration. Shelf life is product-, formulation-, container-, and condition-specific.
Figure 7 placeholder — Shelf life
Clinical takeaway
EV stability is not established by keeping a preparation cold. Temperature, formulation, freeze-thaw exposure, container interactions, aggregation, sterility assurance, and time all influence whether the product remains within specification.
Stability-indicating assays
A stability-indicating assay detects meaningful product changes during storage. Particle count alone is insufficient; a stability panel may include size distribution, aggregation, molecular markers, purity, cargo, potency, pH, appearance, and other product-specific attributes.
Real-time and accelerated studies
Real-time studies evaluate the product under intended storage conditions. Accelerated and stress studies use more challenging conditions to reveal degradation pathways and help design the stability program, but extrapolation requires scientific justification.
Shipping and handling
Shipping can introduce temperature excursions, vibration, agitation, delays, and repeated transfers between containers. Validated shipping conditions and temperature monitoring are therefore part of stability control for distributed products.
Thawing and preparation for administration
Thaw rate, mixing, dilution, hold time after thawing, syringe residence time, and filtration can alter recovery or quality. Instructions for use should define clinically relevant handling conditions supported by data.
Clinical interpretation
A claim that an EV product is stable for months or years should identify the storage temperature, formulation, container, stability-indicating tests, acceptance criteria, time points, and whether the evidence is real-time or extrapolated.
Knowledge gaps
Cross-study comparisons remain difficult because storage conditions, formulations, analytical platforms, EV sources, and stability endpoints vary substantially. Standardized stability protocols and reference materials remain limited.
Bottom-line evidence statement
EV shelf life must be demonstrated for the exact product in its final formulation and container using stability-indicating assays. Storage temperature alone cannot establish preserved identity, purity, potency, sterility, or clinical suitability.
Additional controlled terminology
A temperature excursion can challenge refrigerated storage or frozen storage. Buffer ionic strength and osmolarity may affect particles, while an excipient or cryoprotectant may improve selected stability attributes. Freezing rate and thawing rate can influence freeze-thaw stress. A container-closure system can cause adsorption and may contribute an extractable or leachable; headspace and container-closure integrity can also matter. Sterility assurance includes control of bioburden, endotoxin, and mycoplasma where relevant. A stability-indicating assay should support real-time stability, while accelerated stability provides complementary stress information. An expiration date should be supported by the demonstrated EV stability of the exact product.