Medical Device Seals Solution: Materials, Design and Examples

Seals are among the most important small components in many medical devices.

A seal may cost little compared with the device, yet its failure can interrupt the device’s function. It might keep medication within a fluid path or maintain pressure while an instrument passes through an access port. The design must be assessed in that context.

Because of this, medical device seals should not be treated as ordinary rubber parts. A successful sealing component usually depends on 4 connected decisions:

1. The right elastomer material
2. A sealing geometry matched to the device function
3. A mold and manufacturing process that can hold critical features
4. Documentation and quality controls suitable for the intended medical application

Understanding these principles helps product teams define useful requirements and plan how the finished seal will be verified.

Why Medical Device Seals Matter

A medical seal keeps fluid or air within the intended path as the device operates. Some seals remain compressed in a housing; others flex or open repeatedly. The material and design must suit that movement and remain functional after the specified cleaning or sterilization process. Patient or drug contact adds requirements of its own.

When a medical seal is not designed correctly, the problem is rarely limited to the seal itself. Possible failures include:

• Leakage of liquid, gas, or medication
• Loss of pressure or vacuum
• Poor dose accuracy in a fluid delivery system
• Unwanted backflow
• Contamination caused by flash, particles, or handling
• Tearing at a thin wall, slit, or sealing lip
• High insertion force during assembly or use
• Compression set after storage or sterilization
• Swelling, sticking, or extractable-related concerns after fluid contact

An early manufacturing review helps identify details that are difficult to form consistently. Thin membranes and narrow sealing lips deserve particular attention before the tooling design is fixed.

Medical Seal Material

Material selection is the foundation of medical seal design.

There are many elastomers that can be used for sealing components, but not every material is appropriate for every medical device. The right material depends on the function of the seal and the environment in which it will be used.

Before choosing a material, the project team should define:

• Whether the seal contacts skin, tissue, blood, drugs, oxygen, water, cleaning fluids, or other media
• Whether contact is direct or indirect
• The expected contact duration
• Operating temperature and sterilization method
• Pressure, vacuum, and movement requirements
• Required flexibility, tear strength, rebound, and compression set
• Shelf life and aging expectations
• Color, transparency, and visual inspection needs
• Regulatory markets and customer documentation requirements

Experience matters here. A custom molding supplier and a material supplier can both provide useful input during the design stage, especially when a project requires a medical-grade silicone, EPDM, polyisoprene, or other specialty compound.

Material Names And Documentation

A material can be described in several different ways. For example, silicone rubber may be identified by its chemical family, by an ASTM rubber designation such as VMQ, PMQ, or PVMQ, and by a specific supplier grade or commercial product name.

Those descriptions are not interchangeable. The chemical family tells you the broad material type. The ASTM designation helps classify the rubber family. The supplier grade tells you the actual formulation and the documentation available for that formulation.

Specify the exact material grade. Two compounds can look alike yet respond differently to curing or release different residual substances. Review the supplier’s data for the intended contact and confirm that the material can be processed consistently.

Some formulations are offered with supporting documentation for USP Class VI, ISO 10993 testing, FDA food-contact requirements, or customer-specific medical applications. However, a material certificate alone does not automatically validate the finished device. The finished component, final manufacturing process, intended use, and device-level risk assessment still need to be considered.

The FDA’s ISO 10993-1 guidance emphasizes biological evaluation within a risk management process for devices that directly or indirectly contact the human body. For U.S. medical devices, quality system expectations also depend on the finished device and its regulatory pathway.

Silicone Rubber

Silicone rubber is widely used for medical sealing components because it can combine flexibility, thermal stability, aging resistance, clean molding, and a wide hardness range.

Liquid silicone rubber is especially useful for precision medical parts with thin walls, small features, high-volume production, and consistent dimensions. Common advantages include:

• Good elastic recovery
• Stable performance across a wide temperature range
• Options for transparent or colored grades
• Good aging and ozone resistance
• Suitability for thin-wall and complex molded shapes
• Availability of medical-grade or biocompatibility-supported grades from qualified suppliers

For applications involving drugs, long contact, implantation, or aggressive sterilization, the exact silicone grade and finished-part evaluation must be reviewed carefully.

EPDM

EPDM is often considered for seals in water-based systems, steam exposure, and certain fluid delivery applications.

EPDM can resist many aqueous fluids, but it is not compatible with every oil or drug formulation. For a fluid delivery device, assess the exact solution and temperature first. The chosen grade then needs to meet the sealing and documentation requirements of the device.

Polyisoprene

Polyisoprene can provide high elasticity, good tear resistance, and latex-like performance without using natural latex protein.

It may be selected for surgical access valves, duckbill valves, and seals that must stretch around inserted instruments and then recover quickly. As with every medical elastomer, the exact grade, additives, sterilization compatibility, and biological evaluation route should be checked.

Fluoroelastomer, TPE, And Other Materials

Fluoroelastomers may be useful when chemical resistance is the dominant requirement, but medical contact suitability must be evaluated carefully.

TPE can provide a soft overmolded surface and efficient processing. For a critical seal, however, check whether it retains compression after use and sterilization. Extractables requirements may also affect the choice.

There is no universal best material. A good seal material is the one that matches the device function, contact environment, manufacturing process, and validation plan.

Design For Medical Seals

Medical seal design should be based on the sealing function first, then adjusted for molding and assembly.

A seal drawing needs to define more than its outline. The cross-section determines how the part compresses, while local lip or slit geometry controls contact. Tooling features must be placed so they do not damage or distort those working surfaces.

Design factors include:

• Compression amount and gland fill
• Tolerance stack-up between the seal and mating components
• Static or dynamic sealing condition
• Fluid or gas pressure direction
• Surface finish of the mating parts
• Sealing lip geometry
• Tear risk at thin sections, corners, and slits
• Flash sensitivity on the sealing surface
• Assembly method and insertion force
• Sterilization, packaging, shelf life, and aging

A static seal mainly needs to maintain compression and contact pressure. A moving seal must also manage friction at the contact surface. Repeated motion can generate heat and wear, so lubrication and durability need separate evaluation.

Tooling And Process Control

The tool must reproduce the features that make the seal work. Plan how material will fill the cavity and how air will escape, then check that the cured part can be removed without damaging those features. For precision medical seals, important tooling and process questions include:

• Where should the parting line be placed so flash does not affect the sealing edge?
• Can the mold fill thin diaphragm areas without short shots or trapped air?
• Are vents positioned to prevent bubbles, burn marks, or incomplete filling?
• Does the gate location avoid cosmetic and functional sealing surfaces?
• Can the part be demolded without stretching, tearing, or deformation?
• Is secondary trimming, slitting, punching, bonding, or assembly required?
• Will the manufacturing environment support cleanliness and traceability requirements?

Defects To Avoid In Medical Seal Projects

Many medical seal failures are caused by small defects in critical areas. The most common risks include:

• Flash on sealing lips, valve edges and surfaces
• Voids, bubbles, or trapped air in thin sections
• Short shots in membrane or lip features
• Tearing during demolding or assembly
• Contamination from dust, oil, fibers, or trimming residue
• Compression set after storage or sterilization
• Poor rebound after repeated deformation
• Swelling or softening after fluid contact

Agree critical dimensions and acceptance criteria before finalizing the tool. This is particularly important where a small change in the seal could affect fluid delivery or access through the device.

Successful Medical Seal Applications

Medical seals appear in many different devices. The examples below show how material, geometry, and process control work together.

Case study: Duckbill Valve And Diaphragm Seal For Disposable Trocars

In minimally invasive surgery, a trocar seal may need to allow surgical instruments to pass through while maintaining insufflation pressure.

A duckbill valve seal uses a precisely formed slit that opens when an instrument passes through and closes when the instrument is removed. The slit must be centered and consistent, because misalignment can increase insertion force, reduce sealing performance, or cause premature tearing.

The material must stretch around the instrument, maintain contact, and recover after deformation. A specially selected elastomer, such as a suitable polyisoprene or silicone material, can provide the toughness and elastic memory needed for long procedures.

In this application, the seal is not only a passive gasket. It is a functional surgical interface.

Case study: Check Valve And Safety Valve Seal In Oxygen Therapy Devices

Some external oxygen therapy systems use a sealed oxygen chamber around a wound area to support oxygen delivery.

In this type of device, a check valve and safety valve may be controlled by thin silicone diaphragm seals. The check valve helps prevent oxygen from flowing backward or escaping when the system is disconnected. The safety valve helps maintain the chamber pressure within the intended range.

The seal must respond reliably to small pressure changes, open and close repeatedly, and resist permanent deformation. Silicone is often considered for this type of diaphragm because it can provide flexibility, rebound, and aging resistance.

The final material choice should still be confirmed against oxygen exposure, device pressure, cleaning or sterilization method, and customer validation requirements.

Case study: Bidirectional Seal For Reverse Pressure In IV Systems

Fluid delivery systems can experience pressure from more than one direction.

A bidirectional IV seal may use a dual-lip structure. One lip resists downward fluid pressure, while the opposite lip helps control upward pressure or negative pressure.

This design is different from a simple one-way seal. The material, lip thickness, interference, and contact area must be tuned so the seal prevents leakage without making assembly or fluid delivery difficult.

For aqueous drug delivery, saline, antibiotics, or pain-relief systems, EPDM may be considered when it matches the fluid compatibility and regulatory requirements. The goal is not only to stop leakage, but also to support controlled and accurate delivery.

Case study: Thin-Wall Diaphragm Seals For Filtration And Dispensing

Thin-wall diaphragm seals are used in dispensing systems, fluid filtration systems, purification systems, diagnostic products, and laboratory devices.

These parts often need very consistent wall thickness. If one area is too thick, the diaphragm may not respond correctly. If one area is too thin, the part may tear or deform during assembly.

LSR can be a strong option for thin-wall diaphragms because it flows well into fine features and supports stable high-volume molding. In some designs, the diaphragm must also provide long sealing life across temperature changes, good aging resistance, electrical insulation, and resistance to UV or environmental exposure.

How Fecision Supports Medical Seal Projects

Fecision supports custom medical silicone and rubber seal projects from early design review to production.

We develop the mold and production process in-house, then inspect and prepare the parts for delivery under the agreed requirements.

Fecision reviews the seal drawing against its intended function before tooling begins. We identify features that may be difficult to mold or inspect, then work with the customer to resolve them before validation and production.