Insulin is a temperature-sensitive biologic and must be handled in accordance with manufacturer storage recommendations to preserve potency. After first opening or when carried as a spare, commonly used insulins have labelled upper temperature limits (e.g., insulin degludec [Tresiba] not above 30°C for up to 8 weeks [1]; insulin aspart [NovoRapid] during use generally stored below 30°C with a defined in-use time window [2]). Despite these instructions, many people with diabetes carry insulin for prolonged periods during daily activities, commuting, work, and travel where ambient temperatures can exceed these thresholds, especially in summer climates and during heat waves. A contemporary review highlights that real-world insulin storage conditions often deviate from recommendations and that users may face uncertainty about potency after temperature excursions [3].
At the molecular level, insulin degradation under thermal stress involves both chemical and physical pathways. Chemically, insulin undergoes hydrolytic reactions, most prominently deamidation (e.g., at AsnA21 in acidic environments and at AsnB3 in near-neutral formulations), generating desamido/isoAsp derivatives that can alter conformation and biological activity; the rate of these reactions increases with temperature and depends on formulation context [4]. In addition to hydrolysis, elevated temperatures promote intermolecular transformation reactions with formation of covalent higher–molecular-weight products, including covalent insulin dimers and, at temperatures ≥25°C, increasing amounts of oligomers and polymers, a process that may compromise potency and stability [5].
Thermal exposure also facilitates conformational destabilization and physical degradation, including aggregation, precipitation, and amyloid-like fibrillation. These processes are accelerated not only by heat but also by agitation and contact with hydrophobic interfaces—conditions that can occur during everyday carrying and (particularly) in pump systems [6]. In pump therapy, such physical instability is clinically relevant because precipitation/fibrillation can contribute to catheter occlusions and erratic delivery, while in any insulin delivery modality, partial loss of potency may manifest as unexplained hyperglycemia and increased correction requirements [7]. Clinically, heat exposure has been associated with a higher burden of diabetes-related complications and healthcare utilization; reviews emphasize that heat can affect glucose homeostasis, insulin kinetics, and insulin stability, increasing the complexity of diabetes management in hot environments [8]. In extreme cases, impaired insulin effectiveness due to heat exposure has been linked to diabetic ketoacidosis (DKA), as illustrated by a published case report of DKA following exposure of an insulin pump to heat and sunlight [9].
Device description
The thermal protection concept of VIVICap (Fig. 1) is based on a synergistic pairing of an ultra-high–performance “space-grade” vacuum insulator with a high latent-heat (phase-change) thermal buffer with a phase transition point at 30°C/98°F. The insulating element is characterized as a thin layer of ultrahigh vacuum encapsulated between thin stainless-steel layers, which markedly reduces heat transfer from the environment into the pen by suppressing conduction and convection ( and by limiting radiative heat gain through reflective metallic surfaces [10]. This “deep vacuum” approach is particularly effective for a small form factor because it provides very high thermal resistance without requiring a bulky insulation thickness.
Figure 1: VIVICap can be used with all available insulin pen devices
However, even excellent insulation does not fully prevent heat ingress-especially during prolonged exposure to hot ambient temperatures. VIVICap therefore adds a second mechanism: an internal phase-change material (PCM) placed between the insulated barrier and the pen adaptor [10]. During exposure to temperatures above the PCM’s phase-transition point, the PCM melts and absorbs a large amount of thermal energy as latent heat, keeping the internal temperature relatively stable near the melting temperature until the PCM’s phase transition progresses substantially [11]. In VIVICap-1, the PCM melting temperature was selected to be below the commonly cited “upper safe” temperature range for insulin in use, thereby creating a thermal “ceiling” effect during typical daytime carrying. The process is reversible: when ambient temperature falls below the PCM transition range, the PCM resolidifies and releases heat outward, effectively “recharging” the thermal buffer for subsequent exposures [10, 12]. The device includes a built-in temperature sensor which is positioned next to the medication section of the pen. The temperature sensor measures that internal temperature by pressing a button positioned at the bottom end of the device. The result is compared to a limit temperature of 30°c (86°F) and a GREEN/RED indicator provides the user a simple reading of the current internal temperature status.
This combination-high thermal resistance (vacuum insulation) plus high thermal capacity at a targeted temperature (PCM latent heat)-increases the system’s overall thermal time constant and extends the duration for which the protected item remains within a desired temperature range. Consistent with this principle, the VIVICap-1 report describes maintaining the insulin cartridge environment below ~29°C for at least 12 hours even under continuous 37.8°C ambient exposure, without external power [10, 12]. More broadly, the engineering literature in other harsh-environment applications likewise reports that integrating a vacuum insulation panel (VIP) with PCM can produce a measurable synergistic effect, significantly extending “safe operational time” compared with insulation or PCM alone, supporting the general rationale for combining these two passive thermal-management elements [13].
