Swelling fluids provide an effective, efficient and environmentally friendly way to connect silicone, polyurethane or other thermoelastic tubing to fittings and molded parts.

Today's cutting-edge medical equipment uses advanced and sophisticated materials. This includes venous access devices, drainage catheters, dialysis machines, and any other tubing used to transport fluids, drugs, gases, guide wires, or other materials.

Lighter and more flexible pipes make handling, storage, and use of equipment easier. Some next-generation devices now use multi-lumen tube structures, running multiple channels in a single tube. This simplifies the equipment by reducing the number of tubes required. In addition, the smaller diameter and thinner-walled tube reduces the overall weight of the device, making it easier to lift and carry.

However, these newer piping designs have a drawback. Small, complex equipment is often more challenging to manufacture—especially the assembly process of connecting thin tubes or hoses to rigid plastic barbed fittings is labor-intensive and slow.

Many medical device manufacturers prefer to use silicone elastomers as tubes. Medical-grade silicone tubing is durable, flexible and versatile. It also resists the growth of bacteria and is easy to disinfect. But it can be difficult to connect complex silicone tubing to parts made of harder materials. First, although silicone is flexible, it usually does not swell or stretch without assistance. Secondly, silicone has a high coefficient of friction or a sticky surface, which makes it difficult for the silicone tube to slide onto the accessory.

Many plumbing fixtures are assembled by hand. Manually pushing or twisting the tube into place is difficult for assemblers, and can sometimes cause carpal tunnel syndrome, wrist problems, and other workplace-related injuries. In addition, forcing a small silicone tube onto a barbed joint can sometimes lead to stress cracking of the tube and material scrap.

Fortunately, there are some fluids that make it faster and easier to connect fittings to pipes. There are three common fluid types: silicone oil, isopropanol and swelling liquid:

Hexane is very effective for swelling, but it must be used with care. It is very aggressive. It may remove ink marks or surface coatings, damage plastic parts, or permanently change the physical characteristics of the pipe. The smell of hexane is very heavy, so proper ventilation or personal protective equipment is essential. It is also classified as a Hazardous Air Pollutant (HAP), which may cause air quality problems.

A better choice is engineering silicon swelling liquid. One end of the silicone tube is soaked in the expansion liquid to make the tube wall expand evenly. The soaking time determines the degree of expansion of the pipe. For example, pipes that require 1%–2% expansion during assembly are usually soaked in less than one minute.

The expansion fluid does not change the physical properties of the pipeline. After the tube is installed on the connector, the expanding liquid will evaporate quickly and completely. The pipe is restored to its original size, color, shape, hardness, compression and strength. No matter how complicated the geometric shape is, it can form a tight, leak-proof and firm grip on the accessories. It does not glue or weld the pipe and joint together, so they can be separated later if necessary.

Unlike hexane, silicone swelling fluid is an environmentally sustainable choice. They have a low global warming potential (GWP) and comply with air quality regulations in most regions. The GWP of a fluid is the amount of greenhouse gases it emits and is trapped in the upper atmosphere. The trapped gas absorbs infrared radiation. The more they absorb over a long period of time, the greater their contribution to global warming. Many manufacturers choose low GWP expansion fluids to help reduce greenhouse gas emissions.

Since the active ingredient of the swelling fluid is methyl siloxane, it is a member of the silicone family, it will not affect other polymers such as polycarbonate or polyurethane, and has excellent compatibility with metal components.

There are other expansion fluids that can be used in many pipes, including polyethylene, polyimide, polyurethane, and other molded thermo-elastomer pipes and hoses.

Since the silicone swelling fluid does not require heating, glue or other adhesives that will affect the integrity of the pipe, fittings or equipment, it is easier to obtain qualification and verification during the assembly process. In addition, the expansion fluid does not produce residues that may negatively affect the integrity of the clean room or the quality of the manufacturing process.

When choosing a swelling fluid, it is best to consult a company specializing in medical lubrication and coating technology. They have extensive experience and expertise to help select the best swelling fluid for each individual application.

Jay Tourigny is the senior vice president of MicroCare Medical. With more than 25 years of experience in the medical technology industry, he holds a number of U.S. patents related to cleaning-related products used in daily medical and precision cleaning applications.

The views expressed in this blog post are only those of the author and do not necessarily reflect the views of Medical Design and Outsourcing or its employees.

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