Welcome to our 'All About Prosthetic Liners' series, where we break down the characteristics and uses of one of the most popular prosthetic components. In this article, we discuss the different materials used in manufacturing prosthetic liners. If you want to know about the various liner suspension systems, head to part 1. Meanwhile, the third installment of this prosthetic series will outline essential care tips to help extend the life of your prosthetic liner.
Different silicone and gel types
Prosthetic liners come in different shapes and materials to cater to the unique shapes, sizes, and needs of those that wear them. Prosthetic brands commonly use four materials when designing prosthetic liners.
1. Silicone, which is known for its firmness and durability. The material is used in the Össur Iceross.
2. Thermoplastic elastomer (TPE) gel, which is known for its high-level cushioning capabilities. TPE is used in Willowwood Alpha Liners and Össur Iceform.
3. Polyurethane gel is used for its ability to adapt to changes in residual limb size and movement without sacrificing stability. The Ottobock PUR Liner uses this material.
4. Mineral oil gel is used for its exceptional skin-friendly qualities. This material is used in the Silipos Duragel Liner.
These four materials solve real-world prosthetic issues ranging from skin preservation and cushioning to prosthetic suspension. The materials also share two common characteristics: they adhere to your skin and absorb friction within your prosthesis.
Differences between materials
Prosthetic users may prefer one material over another, depending on what they demand from their prosthetic liners.
Silicone liners are typically preferred by active amputees, as well as those who have softer redundant tissues. Silicone-based prosthetic liners provide extra stability resulting from their firmness. Some active amputees may prefer the sensation of firmness vs. cushioning or softness during high-impact sports. Anecdotally speaking, there is less wasted energy when transferring forces through a firm silicone liner vs. one that is designed to be soft.
If you have a softer residual limb or redundant tissue along the bottom, wearing a silicone liner makes it easier for your prosthetist to fabricate your socket and for you to lock into your prosthetic socket. Without this additional stability, a locking pin may not engage with the lock because your residual limb can change shape or bend when you apply your prosthesis.
Silicone does have its disadvantages; in particular, the material is notorious for its inability to provide cushioning for prosthetic users with sensitive limbs. However, as the technology matures, prosthetic brands like Össur are introducing new, softer silicone formulas to offer prosthetic users ample cushioning.
Thermoplastic elastomer (TPE)
Meanwhile, those who want high-level cushioning from their prosthetic liners will be served well by TPE gel liners. Liners made from this material are soft enough to protect any bony or scarred areas of the residual limb. Some even have viscoelastic properties which enable them to become more customized through wear and eventually take the shape of the residual limb. This is possible because the gel can move from high pressure to low-pressure areas within the prosthetic socket.
However, people with redundant soft tissue may find the stability of TPE liners wanting. This is due to the material’s inability to provide constant gentle compression—when the gel is loaded, the material gently compresses, and when the load is removed, it immediately returns to its original shape.
Prosthetic liners made from polyurethane gel, similar to TPE liners, possess the ability to flow from the loaded to the unloaded regions while walking. When the gel is loaded, the liner gradually compresses but—unlike TPE gel—does not return to its original shape immediately. The material smartly uses the pressure created from the bony parts to create relief areas in the gel.
Mineral oil gel
Low-activity individuals will be served well by liners made from mineral oil gel, which is considered the softest and most forgiving out of all the four materials. It can provide skin-nourishing vitamins to the wearer as well as a close, contoured fit. Mineral oil gel liners work great for those with a bony residual limb or hypersensitive areas. The only drawback is that it's the least durable.
Prosthetic liner shapes and thicknesses
Prosthetic liners typically come in two shapes: cylindrical (uniform) and conical. But for those with residual limbs that don’t fit the predetermined shapes, tailor-made or custom prosthetic liners are available through your prosthetist.
Prosthetic liners also feature varied thicknesses; from bottom to top and front to back. This design provides ample protection (thickness) for the user’s prominent bones, which are often found at the bottom front or side of the limb. Prosthetic liners with a varied thickness also feature thin areas which are located in specific areas to facilitate ease of movement, such as thinner behind the knee when sitting.
Prosthetic liner innovations
Prosthetic liner technology is continuously developing. Recently, researchers at the University of Bath developed a personalized solution that would minimize visits to the prosthetist every time your residual limb changes. This latest innovation uses a 3D scanner to design an intimately fitting prosthetic liner without the time-consuming and laborious process of creating a mold each time a liner is manufactured.
Today, a few prosthetic liners come with various features that include embedded aloe vera to condition the skin and silver to create an anti-bacterial effect.
However, if your most pressing concern is excessive sweat, you may want to read our article on breathable prosthetic liners. These are designed to allow sweat to pass through your liner and prosthetic socket wall.What about you? Which material do you prefer for your prosthetic liner? Also, do you wear a prosthetic liner patch? Please share your thoughts with us in the comments section below.