Loss of an intended tissue–device or device–device barrier (hermetic or functional seal) that allows unintended passage of liquids, gases, or biological agents across an interface and impairs the device’s designed containment, pressure integrity, or infection barrier.

Principle

A breach in a seal converts a designed barrier into a conduit: fluid or gas movement and/or microbial translocation occur along new paths of least resistance, degrading device function (pressure maintenance, sterility, containment) and potentially creating new hazards.

Demonstration

Illustrative scenario: An implanted infusion port develops a crack at the septum–housing interface after repeated access. Clinically detected leakage during infusion and loss of expected pressure indicates seal failure. Actions include securing alternative access, assessing need for device removal or repair, and managing any contamination. Consequence: continuing to use a failed seal can lead to therapy loss, contamination of internal device or tissues, and device replacement.

Misapplication

Mistaken interpretation: Calling any minor wear, small scuff, or transient wetting a ‘‘seal failure’’ without evidence that the functional barrier is compromised. Semantic error: equating superficial or reversible surface changes with loss of barrier function that allows passage of fluids, gas, or pathogens.

Consequence

Consequences include loss of intended containment (drug leakage, loss of pressurization), increased risk of infection through the breached interface, impaired device performance, interruption of therapy, and often the need for device revision or replacement with associated procedural risk and cost.

Reversal

Exceptions/qualification: Not all interfaces are designed to be hermetic; some device designs intentionally permit limited permeability (e.g., fluid exchange by design). In such non-hermetic designs, detected passage across an interface may reflect intended function rather than failure. Assessment must reference the device’s design specification.

Boundary

Clearly within: breach of an intended hermetic or functional seal that permits uncontrolled passage of fluid, gas, or biological agents across the interface. Boundary case: surface abrasion that does not yet permit passage or reversible loss of sealing that can be restored by reassembly. Clearly outside: normal diffusion/permeation within expected device specifications or external circuit leaks unrelated to the interface in question.

Semantic Tension

Tension between requiring strict hermetic sealing for safety and the design constraints that favor flexibility, remote access, or tissue integration; increasing hermeticity may reduce other desirable properties (compliance, sensor access, tissue ingrowth) and vice versa.

Synthesis

Seal failure should be defined and managed by reference to the device’s intended barrier performance: the key question is whether the functional containment has been compromised in a way that allows unintended transfer of fluids, gas, or microbes, not merely whether the surface shows wear.