Report for Christophe Lecomte Össur
Materials for Prosthetic Foot Blades
Reykjavik, 26. October 2025
Thor Karason
Objective
Explore how materials science and engineering impact prosthetic blades‘ design, functionality, and user outcomes.
Introduction
A prosthetic foot is an assistive device that aids a user in walking when they don´t have a whole foot. Prosthetic feet are split into two major categories: above-knee and belowknee. These two categories are further split into different types of prosthetic feet. Prosthetic feet can range immensely in complexity, size, and purpose; however, the majority of them hold one thing in common: blades.
The main purpose of prosthetic blades is to absorb impact and return energy to the user. In other words, the user puts a force into the blade, and the blade returns a force that helps the user walk, run, or jump.
Properties
The blades are vital to the structure of a prosthetic foot and therefore must fulfil numerous properties. These include the following :
• Durable – able to resist wear, fatigue and environmental damage. Why – Prosthetics are often used over long periods of time and endure repeated use over numerous years in all sorts of environments. Durability ensures longterm performance without frequent replacement.
• Flexible – can bend or deform from the original shape without damage. Why – Allows for smoother energy transfer and can adapt better to numerous terrains/ environments.
• High Energy Return (Energy Efficient) – able to store energy when flexed and efficiently release it when needed.
Why – High Energy Return gives the user a spring effect that pushes them forward/ off the ground as well as improves the efficiency of running/ walking.
• Lightweight – low mass to volume ratio. Why – Reduces fatigue of the user, meaning longer periods of time for usage, as well as comfort of the user.
• High Strength – ability to withstand high forces without breaking/ fracturing. Why – The blades are the main components of the prosthetic that endure the highest forces, including the full weight of the user as well as the user‘s impact forces, and therefore must withstand high forces without fail.
• Moldable – ability to be shaped and formed freely. Why – prosthetics are often tailored to a user‘s needs, and therefore blades must be adjusted to certain specifications.
• Manufacturable – ability to be manufactured at a large scale. Why prosthetics must be able to be made in large quantities for larger groups of users.
Composites
Composites are engineered materials made from two or more constituents (distinct individual materials), each offering different physical properties, which can be combined synergistically (acting together in a way that creates an enhanced, combined effect).
The characteristics of composite materials make them suitable for various appliances, including prosthetics.
Carbon Fibre Reinforced Polymer
Most notable of the composites used in prosthetics is Carbon Fibre Reinforced Polymer (CFRP).
CFRP, or carbon fibre reinforced polymer, is defined as a composite material that combines carbon fibres for strength and stiffness with a polymer matrix that provides toughness, enabling a lightweight alternative to metals in various applications. Its properties can be tailored by adjusting the fibre characteristics, but it is limited by high production costs and slow manufacturing processes.
CFRP is widely used in prosthetic blades due to the matching properties of CFRP and the properties needed to make a prosthetic blade. These include :
• CFRP is durable, has high fatigue resistance and is corrosion resistant.
• CFRP can be flexible in certain directions, whilst stiffer in others.
• CFRP has high elasticity and, therefore, has energy-efficient transfer capabilities.
• CFRP has superior strength-to-weight and weight-to-volume ratios.
• CFRP is freely moldable and is easily manipulated during manufacturing stages (before curing).
• CFRP is manufacturable but relatively expensive.
Furthermore, an intriguing property of CFRP is that it is easily influenced by small tweaks to its structure, but these small tweaks make immense changes to its properties. These small tweaks include changes to: the choice of polymer; direction of carbon fibres/ weaves; layering structure.
Other Composites
CFRP has proven to be an optimal choice for prosthetic blades through years of field trials and consumer satisfaction with products that include CFRP in their blades. There are, however, other composites that have promising features.
Fibreglass Reinforced Polymer
Fibre-reinforced polymer (FRP) is defined as a composite material providing advantages such as lightweight, strength, chemical resistance, and ease of use in construction and retrofitting applications.
The main difference between FRP and CFRP is that FRP is less stiff and cheaper. This could benefit prosthetics because a cheaper prosthetic makes it more accessible for a larger population.
Thermoplastic Composites
Thermoplastic composites (TPCs) are defined as materials featuring a thermoplastic matrix that can be softened and remoulded upon heating without degrading, allowing them to harden into a final shape upon cooling. They are increasingly valued for their lightweight properties and ability to replace metals in various industries, contributing to the production of more fuel-efficient vehicles and structures.
The main difference between TPC and CFRP is that TPCs are more shock absorbent and, as a result, offer less energy return. TPCs can perhaps be used in blades of prosthetic feet for heavier users or users who have more sensitive or fragile body parts and need a more shock-absorbent prosthetic.
Graphene Reinforced Polymers
Graphene-reinforced polymer is classified as a multiphase material containing a single type of polymer, copolymer or a blend of polymers with nanofillers or nanoparticles (with dimensions of 1–50 nm) incorporated into the polymer matrix. This considerably affects the different physical, chemical and mechanical properties.
Graphene Reinforced Polymers are a relatively new technology, but show, however, promising properties to outperform CFRP in certain areas. This includes: higher energy efficiency; higher fatigue resistance; lower weight-to-volume ratio. Due to it being in the early stages of development, it does include setbacks such as price and manufacturability.
Furthermore, Graphene Reinforced Polymers offer capabilities that other materials are unable to offer. For example, Graphene Reinforced Polymers may be integrated with electrical equipment due to their high conductivity, which shows room for new opportunities to grow.
Summary
Overall, I believe that in the coming years, CFRP will continue to be the industry standard for prosthetic foot blades. There are, however, many materials that may become more popular in the coming years. For example, in developing countries, cheaper alternatives could become the norm. Moreover, materials such as graphenereinforced polymers show immense potential to replace materials like CFRPs. 25
Thor Karason
Bibliography
Scholz, M., & Blanchfield, J. P. (2011, August 30). The use of composite materials in modern orthopaedic medicine and prosthetic devices: A review. Composites Science and Technology, 71, 16. https://www.sciencedirect.com/science/article/pii/S0266353811003071 ScienceDirect
Alluhydan, K., Siddiqui, M. I. H., & Elkanani, H. (2023, September 15). Functionality and comfort design of lower-limb prosthetics: A review. Journal of Disability Research, 2, 10-23. https://www.scienceopen.com/hosted-document?doi=10.57197/JDR-2023-0031 ScienceOpen
NitPro Composites. (n.d.) How durable and reliable is CFRP? .Nitpro Composites https://www.nitprocomposites.com/blog/how-durable-and-reliable-is-cfrp nitprocomposites.com
Cleveland Clinic. (2024, August 7). Prosthetic foot: What it is, who needs it & how it’s used. Cleveland Clinic Health Library.
https://my.clevelandclinic.org/health/treatments/prosthetic-foot Cleveland Clinic
Alkbir, M.F.M., & Ishak, M.R. (2016).Fibre properties and crashworthiness parameters of natural fibre-reinforced composite structure: A literature review. ScienceDirect. https://www.sciencedirect.com/topics/engineering/fibre-reinforced-polymer ScienceDirect+1
Gamstedt, E.K., & Berglund, L.A.(2003) Fatigue of thermoplastic composites.. ScienceDirect
https://www.sciencedirect.com/topics/engineering/thermoplastic-composite
Fekete, J.R., & Hall, J.N.(2017). Design of auto body - 1.5.3 Carbon fiber reinforced polymers. ScienceDirect.
https://www.sciencedirect.com/topics/engineering/carbon-fibre-reinforced-polymer ScienceDirect