Note: This is the second article of a three-part series covering medical plastics (1) trends, (2) material/process advances and (3) applications.


Plastic products designed for applications in medical technology have to meet a number of special criteria. Typically, excellent mechanical properties are required, even in components with small dimensions and wall thicknesses.

In many instances, the medical devices must be germ-free and the materials they are made of must correspondingly be capable of being sterilized. Depending upon the sterilization procedures employed, the plastics used must be able to withstand hot steam or hot air, disinfectants, gamma radiation or ethylene oxide exposure.

Prostheses and implants that are subject to loads on a daily basis, as well as instruments that may injure a patient if defective, must be immune to mechanical accidents caused by material breaking, buckling or fraying. Aside from withstanding sterilization procedures, in many applications it is important for materials to be unaffected when in contact with organic substances or other chemicals in the laboratory.

Let's take a look at some innovative medical plastic material and process developments.

We'll begin with an advance in nonleaching antimicrobial material technology. The global market for healthcare antimicrobial plastics is forecast to reach 220,000 metric tons by the year 2017, fueled by rising demand from healthcare, industrial and consumer end-use sectors.

Stringent government legislation and potential liabilities for service/product related infections are prompting the use of biocidal plastics in healthcare environs. The need to prevent hospital-acquired infection (HAI) and related complications is a major impetus for the development of novel biocides, antimicrobial polymer technologies and innovative applications deploying these solutions.

New and growing medical applications include devices that break through the skin or are inserted into the body including various catheters and needleless connectors. In one study, the incorporation of antimicrobials in venous TPU (thermoplastic polyurethane) catheters used during kidney transplants was shown to significantly reduce infection risk compared to untreated TPU catheters.

NIMBUS, developed by Quick-Med Technologies Inc., is an FDA-cleared, cutting-edge antimicrobial technology custom designed for wound care and medical device applications. The technology encompasses the chemistry of antimicrobials that comprise a high charge density polycation built into the backbone of various polymers.

The nontoxic, long-chain polymers (polycations) with high charge density provide superior efficacy via a physical action on microbes. The advanced cationic, high-molecular-weight antimicrobial polymers attract bacterial cells and bind rapidly to displace calcium ions, thus physically disrupting the cell wall. The cell membrane then collapses, and the cell dies as the cytoplasm leaks out.

High charge density ensures maximum efficacy in the presence of body fluids. As the active agent is permanently bonded to the surface, there is no leaching and no depletion of the antimicrobial reservoir. Additionally, bacteria cannot develop resistance to an agent that they cannot internalize, thus the large size of NIMBUS polymers and their permanent attachment to a surface eliminates the ability of microbes to develop resistance.

Quick-Med Technologies
Three-stage physical method of antimicrobial action.


The company has been granted a range of patents for their NIMBUS technology, covering incorporation of a NIMBUS polycation into the main chain of the polyurethane polymer and the process of attaching NIMBUS antimicrobials to a range of substrates. The new polyurethane polycation is well suited for a wide range of applications including plastic films and coatings, adhesives, catheters and other types of extruded tubing.

The substrates are, in whole or in part, cellulosic or any of a list of other substrates, including polyurethane, polyester, nylon and acrylics, as well as silk, linen, rubber, alginates and collagen. These materials are commonly used in textile and medical products, filters, absorbent products and packaging.

While NIMBUS antimicrobials remain at full strength, the active agent in most other antimicrobial technologies is depleted gradually while in use. These other antimicrobials carry the risk of irritation or interference with healing in products such as wound dressings and textile applications when the treated material is next to or used on the skin.

Finally, let's review an advance in the use of fiber lasers in transparent medical plastics welding. As demand for ever-smaller medical devices grows, innovative manufacturing technologies are being adopted to allow for the production of ultraprecise designs.

Joining and assembly by a myriad of techniques including adhesives, hot plate welding, ultrasonic welding and friction welding, each with its own design demand/requirements and advantages/disadvantages, are critical steps in the manufacture of medical plastics devices. Cleanliness, precision, hermetic sealing and quality control are significant advantages of laser welding for the medical industry.

Bonding completed by ultrasonic or friction-welding processes will leave the joint with a scaling effect that is caused by what essentially is rubbing two parts together at high speeds. The scales from the joint break away and become loose, generating dust-like particulates that can contaminate the medical device. Glues and adhesives also have the potential for contamination.

On the other hand, laser welding produces tight, clean joints that are particulate-free. Hermetic sealing of a plastic joint is frequently required for medical devices, whether fluids are to be kept in or out. The excellent fusion of plastics in laser plastics welding ensures strong joints with the weld seam entirely sealed to ensure hermetic sealing.

IPG Photonics
Clean laser weld (left), scaled friction weld (center) and balloon catheter hermetic high strength seal (right).


Traditional laser welding of clear plastics required special expensive, difficult-to-apply infrared absorbers, such as Clearweld infrared inks or Lumogen or Lazenflair dyes, which may be extractable and thus unacceptable for many medical device applications.

Higher-wavelength thulium fiber lasers pioneered by IPG Photonics can be used to laser weld transparent plastics without the need for IR absorber additives, dyes or coatings. Operating in the spectral range of 1800 to 2100 nanometers (nm), these fiber lasers interact differently with plastic than typical 808 or 980 nm IR lasers used in through-transmission welding.

In this wavelength range, you get more absorption in almost all clear polymers because the wavelength is closer to some vibration frequencies of the carbon-hydrogen bond in the given transparent plastic. The technology also allows welding of thermoplastics regardless of polarity, a limitation in some plastics welding systems.

Conventional, nonproprietary radio-frequency welding of films has been limited to polar resins with high dielectric loss factors, particularly flexible PVC and thermoplastic polyurethane (TPU).

IPG Photonics
Melt zone in 20 layers of 0.1-millimeter-thick LDPE welded with 1940 nanometer fiber laser.