Selecting Medical Polymers Based on End-Use Requirements

Medical device manufacturers constantly strive to find better, smarter and more cost-effective solutions to the problems their customers are facing. New and innovative technologies can certainly do the trick, but the foundation of any device are the materials it’s made from, not just what it can do in the hands of a surgeon or physician. So, if you want to make a better device, you must first consider using better material—or rather, the right material.

What makes a material right for the job? Depends on the nature of the job it’s asked to do. That may seem like a canned answer, but in fact it tells you one of the most important things you need to know about material selection, and about medical device design in general: consider the end use.

By having thoroughly defined application parameters from the start, device designers can select appropriate specialty polymers for healthcare that comply with regulatory requirements and meet actual end-use requirements. One such parameter is how many times the device will be used. 

 

Polymers for Single-Use Medical Devices

Single-use medical devices are typically used for one procedure and discarded. There are also instances when a single-use device can be recovered, or when only a single component of an otherwise reusable device is labeled as single-use. In any case, material considerations for single-use devices depend on two important (but dissimilar) factors: body contact and manufacturability. 

Medical devices that are brought into direct contact with a patient’s body fluids or tissues are subject to more stringent regulatory controls. In the United States, the Food and Drug Administration (FDA) evaluates material biocompatibility as part of  its evaluation of medical devices subjected to pre-market approval. Material suppliers that perform comprehensive biocompatibility testing provide their customers with greater confidence that the materials they select will meet strict regulatory requirements. 

OEMs that make single-use medical devices should also consider a material’s processing and manufacturing attributes. If injection molding will be used to manufacture the device or any associated parts, material selection should also encompass melt flow, viscosity, shear rate and other attributes related to moldability
 


CASE STUDY

Economical single-use alternative to reusable stainless-steel instruments

Single-Use Surgical Instument_Ixef PARA_Redi-Spine

Innovative Surgical Designs, a developer and manufacturer of orthopedic spinal systems, designed a new single-use surgical instrument kit for minimally invasive spinal fusion surgery. Designed to withstand the severe torsional forces and rigors of thoracolumbar spinal fixation, Innovative Surgical Designs’ Redi-Spine™ instruments received 510(k) clearance from the U.S. Food & Drug Administration (FDA) in August 2018.

It contains multiple disposable, handheld instruments including a T-ratchet handle, counter-torque tool and gearshift probe that are molded entirely or in part from Ixef® GS-1022 PARA. Innovative Surgical Designs chose Ixef® GS-1022 PARA for a few key reasons: Metal-like strength and rigidity • Gamma sterilizability • Moldability (enables metal overmolding for hybrid design) • Evaluated for ISO 10993 limited duration biocompatibility • FDA Master Access File included.


 

Polymers for Reusable Medical Devices

Material Strategy for Medical Device Recoverability

When we talk about “reuse” of a medical device, we are really talking about its “recoverability” via hygienic recovery (disinfection or sterilization). Therefore, a good material strategy considers the recoverability requirements of the device, which depends on the degree of risk of infection associated with its use. Consider the “Spaulding Scale,” which categorizes products according to “hygiene criticality,” or how important it is for biological matter to be removed after initial use:

  1. Critical devices (e.g., catheters) come in contact with blood or normally sterile tissue and must be sterile before entering sterile tissue.
  2. Semi-Critical devices (e.g., endoscopes) come in contact with mucus membranes and must undergo meticulous cleaning and disinfection with a high-level disinfectant.
  3. Non-Critical devices (e.g., stethoscopes) come in contact with unbroken skin and carry the least stringent infection control requirements. 
Medical-device-recoverability

 

Design for Disinfection

Routine cleaning brings reusable medical devices into repeated contact with a wide variety of disinfectants. Unfortunately, repeat exposure to aggressive hospital cleaners and disinfecting chemicals can deteriorate lower-grade commodity plastics. Cleaners such as isopropyl alcohol and peroxide may attach to the polymer chains of some thermoplastic resins and cause stress cracking, breakage and discoloration.

To combat environmental-stress cracking (ESC) and other plastic failure related to chemical exposure, device engineers must consider how different polymers hold up to common hospital disinfectants, including:

Aldetex®-28 / ICI Pharma Dettol® / Rechitt & Colemann Harvey's VapoSteril® / Barnstead, Thermolyne
Aseptisol® / Dr. Bode & Co Gigasept® FF / Schulke & Mayer Lysetol® FF / Schulke & Mayer
Bomix® / Dr. Bode & Co. Grotanat® / Schulke & May Neodisher® Mielclear / Dr. Weigert
Bodephen® / Dr. Bode & Co H.A.C./ ICI Pharma Neodisher ® Dental / Dr. Weigert
CIDEX® / Johnson&Johnson Habitane® / ICI Pharma  

Learn more about the chemical resistance of sulfone polymers to these and other common disinfectants, medical reagents and organic/inorganic agents. 

 

Design for Sterilization

Sterilization resistance is one of the most important performance characteristics to consider when evaluating polymers for high-value reusable critical medical devices. The three main sterilization methods are heat (both steam autoclave and dry heat), ethylene oxide (ETO) gas and irradiation with high-energy radiation (gamma or electron beam). A good starting point then is pre-selecting materials based on sterilization performance. As a general rule, higher-quality specialty polymers such as PEEK and PPSU exhibit the best resistance across a wide spectrum of sterilization procedures. 

Sterilization-compatibility-sulfones-PEI-PC

 

Use the Right Material from the Start

Pre-selecting the right material can help OEMs find materials that comply with safety standards, reduce time to market and differentiate their products in a competitive market. This requires specialized knowledge of material science and the risks inherent to specific polymers for healthcare; Solvay can help.

With over 30  years of experience as a leading materials supplier to the healthcare industry, Solvay provides the experience and innovation medical device manufacturers need from their partners. Our polymers specialists can help you select the right materials that meet compatibility  requirements for single-use and reusable medical devices.