Can your medical device survive repeated sterilization?

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Autoclave-resistant adhesives may be the answer – by Dymax Application Engineering

High heat, humidity, chemicals and other environmental factors can cause problems for medical tools such as endoscopes, surgical instruments, dental equipment, general purpose medical devices and housing assemblies, as well as sensors and RFID tags stuck to medical tools. The materials that bond, coat, and encapsulate the components of these devices can be negatively impacted by these forces which can potentially lead to device failure, lost or misplaced instruments, or patient injury. This is why it is essential that the products used to protect and bond the parts together are able to tolerate a variety of stresses.

In addition to the rigorous types of physical testing, standards and approvals that medical device formulations are subject to, including ISO 10993, many must also be able to withstand repeated cycles of sterilization.

Two categories of sterilization used in the medical device industry are classified as physical or chemical. Physical sterilization methods include filtration, heat, radiation, and ultrasound/vibration, while chemical sterilization requires a gas or liquid process. There is a large subset of techniques that fall under these main classes, such as EtO, gamma rays, electron beams, cathode rays, and oxidizers, as well as autoclave and plasma.

There are pros and cons to using many of these processes. Positive attributes and results depending on the chosen method include high penetrating ability, very fast action against microorganisms and removal of potential residues. Some of the negative factors can include long sterilization cycles, flammability, use of hazardous materials or chemicals, yellowing of polymers, and corrosion of various metal substrates.

Considerations for the type of sterilization to use depend on the end-use product, its function, the substrate components, and the pressures and environments to which the device will be subjected. Autoclaving (steam) and vaporized hydrogen peroxide (VHP) gas plasma are two methods often used in the medical device industry.

Autoclaving uses high pressure steam to sterilize instruments from microorganisms and bacteria that can potentially contaminate substrate surfaces killing them and rendering them ineffective. However, there are critical issues to keep in mind. Many metals have the potential to corrode or rust after repeated exposure to steam. Some plastics can lose their structural integrity, be sensitive to high levels of heat, be susceptible to leaching plasticizers to the surface of the substrate, or react negatively or degrade when exposed to water.

Sterilization by autoclaving is limited to certain applications. Many medical device adhesives, for example, have difficulty withstanding autoclaving due to the high temperature, humidity and pressure involved in the process. Due to these factors, there may be a weakened bond junction which leads to failure. Alternatives to steam sterilization for instruments and devices sensitive to heat and humidity are being considered more regularly, although the autoclave remains one of the most accessible options for hospitals, laboratories, centers research, etc.

Vaporized Hydrogen Peroxide (VHP) gas plasma sterilization is an ideal method for devices sensitive to heat and humidity, as temperatures do not exceed ~50°C (140°F) during processing. VHP is a process in which hydrogen peroxide circulates through the chamber, in contact with all surfaces, before the hydrogen peroxide is split into oxygen and water vapor after the sterilization cycle is complete. This ensures that the instruments are quickly sterilized without any toxic residue.

There are many types of endoscopes and medical devices that require repeated sterilization cycles or multiple instances of autoclaving or other sterilization methods such as plasma.

Example of a list of SCOPES requiring several sterilization cycles:

  • Arthroscopes
  • Endoscopes
  • Bronchoscopes
  • Esophagoscopes
  • Colonoscopes
  • Laparoscopic instruments
  • Duodenoscopes

Example list of additional devices:

  • Dental tools/equipment
  • Ophthalmic tools/equipment
  • Endoscope biopsy accessories (usually tools, eg forceps)
  • Surgical Tools / Instruments
  • Irrigation systems (e.g. reusable irrigation cannulas)

One important application that has come to the forefront of the medical device industry is the use of identification tags, or RFID (radio frequency identification), on surgical tools, instruments and packaging such as vials. RFIDs on medical devices help maintain accurate inventory levels and help track them during procedures. Other typical areas of use and applications include:

  • Hospitals, clinics and caregivers:

– “Check in / check out” the multitude of devices and tools needed for procedures and surgeries

– Driven by cases of tools or accessories left in the body after surgery

– Validate the state of sterilization before use

– Improve inventory details and data

  • Other areas of health:

– Pharmaceutical follow-up to ensure the correct dosage is provided and proper storage conditions are followed

– Blood/biological sample tracking for storage, usage times and automatic tracking to ensure proper handling

– Goods such as surgical tools, dental and hospital equipment, patients and others

RFIDs that are affixed to often-used surgical tools and the materials used to bond them must pass multiple cases of sterilization and successfully withstand these processes for hundreds of cycles.

Although there are one-component and two-component epoxies on the market for bonding, coating and encapsulating medical devices and RFID, these products may not be the best choice. Compared to light-cured materials, epoxies have many disadvantages such as specialized mixing systems, long cure times up to 60 minutes, short pot life, use of heat-curing ovens (in some cases), lower flexibility and impact resistance, and the need for purge cycles which can result in hazardous waste. One-component light-cure adhesives offer an alternative to these solutions by providing manufacturers with fast cure times of 1 to 30 seconds, no mixing or purging, a range of qualities from rigid to flexible, and solvent-free, compliant formulations. RoHS for ease of handling and disposal. The positive benefits of light-cured materials can help improve manufacturing efficiency, reduce costs and increase throughput.

To meet the need for a product that can survive frequent sterilization sequences, a new versatile product UV/LED curable adhesive has been developed which exhibits extremely low water absorption (0.5%) and withstands over 100 cycles of autoclave and plasma processes. This material is recommended for use as a coating or encapsulant for housing assemblies, single-use or multiple-use medical instruments, and a variety of medical scopes and dental equipment. It is particularly suited for encapsulating RFID chips, sensors and other electronic components found on medical devices, tools and vials where moisture infiltration may be a concern. Bondable substrates include stainless steel, aluminum, glass, PP/PE and circuit boards.

The adhesive has been subjected to a series of performance tests including accelerated aging and sterilization, water soak evaluation, electrical property examination and water vapor transmission rate testing. Compliant with ISO 10993-5 cytotoxicity standards, it is a solvent-free material that cures in seconds when exposed to broad-spectrum UV light or 365nm LED light.

If you are a manufacturer involved in the assembly and protection of medical devices and instruments and are looking for a bonding, coating and encapsulation material that can withstand over 100 sterilization cycles, then this product may be a solution for your application.

For more information on autoclave resistant adhesives or to request a consultation with a Dymax application engineer, please Contact us.

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