A Non-Cytotoxic Replacement for Silicone in Prosthetics

Seven years ago, a client asked Crosslink Technology Inc. to come up with a non-cytotoxic replacement for silicone in prosthetics.

Silicone is the standard padding used in sleeves, sprints, braces, arch supports and other prosthetic devices. While soft and reasonably tear resistant, silicone can sometimes cause allergic reactions in skin.

Talking about the skin issues that lower-limb amputees face with prosthetics, one manufacturer points out:

On top of the frictional woes amputees face with their prosthetics, they must also concern themselves with both irritant contact dermatitis and allergic contact dermatitis. Unlike the breakdown caused by skin rubbing against a prosthetic, dermatitis is caused by the mere contact between skin and the material of the prosthetic and can result in skin aggravation, lesions, chronic inflammation, cellular damage and even cancer.

The New Solution Cannot Cause Cell death

So our new alternative to silicone would have to reduce skin irritation and rashes at the same time it offered softness, elasticity and durability in an easy-to-wash material that is readily adaptable to standard manufacturing processes, at an attractive price point.

To provide these properties and benefits, our development team starting experimenting with non-cytotoxic (i.e., not toxic to living cells) polyurethane elastomer compounds. Since the final use in prosthetics involves lengthy and immediate skin contact, this meant the cured polyurethane product could not impede human cell growth or cause cell death.

Special Testing Through NAMSA

To test the new formulation, our client went to NAMSA, the leading medical research organization providing expert regulatory, laboratory, clinical, and compliance services to medical device and healthcare product manufacturers.

The material was analyzed on a scale of Non-Toxic (N) to Toxic (T), where T is completely toxic and N is completely non-toxic. The urethane that the client had previously used for prosthetics had a score of Intermediate (I)—or only a conditional pass. Whereas, the new Crosslink non-cytotoxic polyurethane elastomer received an impressive rating of N, meaning that it does a much better job of preventing skin irritation than almost all other solutions on the market.

Soft but Durable

The other challenge was to get the softness required for skin contact in prosthetics, with enough elasticity and tensile strength to allow easy movement and good tear resistance.

"Urethanes don't usually go that soft,” explains Crosslink Chief Chemist Jimmy Kung. "Usually silicones are used when you get to this level of hardness. So we had to come up with something that reached this limit.”

Crosslink’s solid-soft elastomer does this, achieving a hardness from 20 shore 00 to 5 shore A. Not only is it soft, not-cytotoxic, elastic with good tensile strength, it is an easily poured, easy-to-use two-component system that is adaptable to most manufacturing processes.

Contact us today to find out how we can tailor our non-cytotoxic polyurethane elastomer to your prosthetic manufacturing needs.

Additional Properties:

Pot Life: 4 hours (80^oC)
Cure Schedule: 16 hours @ 80^oC
Hardness: 20-25 Shore 00

Crosslink received a non-toxic rating on the below three tier scale.

Toxicity Rating	Definition
Non-Toxic (N)	- Confluent monolayer - Slight or no vacuolization, crenation or swelling
Intermediate (I)	- 1% to 5% cell lysis - Marked vacuolization, crenation or swelling on remaining cells
Toxic (T)	- >50% cell lysis - Extensive vacuolization, crenation or swelling on remaining cells