Localization of composite prosthetic feet: manufacturing ...

Each year, numerous individuals globally face complications from diseases such as diabetes, vascular disorders, trauma, and cancer that may necessitate limb amputations. The loss of a limb, particularly the lower limb, greatly impacts the quality of life (QOL) as it hinders mobility. In the United States, lower limb amputations account for nearly 97% of all amputations among a population of 1.7 million amputees, highlighting the urgent need to address this issue. Though comprehensive data for Egypt is lacking, it's expected that the trend follows a similar pattern given the high prevalence of diabetes in the country, where about 0.5% of the diabetic population suffer from lower limb extremities. With diabetes leading to vascular diseases, over 90% of lower limb extremities in Egypt occur due to this reason.

According to the Trade Map website, Egypt's import bill for Prosthetics and Orthotics (P&O) was at least 600 million L.E. in 2020, and government figures suggest it might be as high as 1 billion L.E. However, a significant portion of the P&O import bill is undocumented due to direct purchases made abroad, leading to unreliable databases about amputation levels and P&O parts.

To tackle this issue, Egypt initiated a comprehensive plan during the "Different, We Are Able" conference held in Cairo in 2018. This agenda aims to consolidate efforts from various local authorities and experts into a single consortium. Their activities include establishing high medical service standards, integrating amputees into society, creating a comprehensive database for people with physical disabilities, and advancing an industrial complex for the local manufacture and technology transfer of prosthetic limbs. This move focuses on building well-trained manpower, accredited education programs, and robust research and development (R&D) capacities to support the localization of the P&O industry. These initiatives are backed by state-funded scientific and applied projects.

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Figure 1

Amputation levels in upper and lower limbs.

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Improving the quality of life for lower limb amputees involves designing prosthetic limbs that mimic natural movements and substitute missing functions. Temporary lower limb prosthetics are used during rehabilitation to help amputees walk and perform daily activities safely. These prosthetics focus on shock absorption, weight-bearing stability, and progression.

Special attention is given to the manufacturing of ankle-foot prosthetics, given the high statistics for below-knee amputations. Ankle-foot prosthetics are a crucial part of below-knee prosthetics, affecting posture, walking correctness, and joint loading. Therefore, these prosthetics are designed and made using various materials to suit the degree of disability and required functionality.

In summary, the localization potential of lower limb prosthetic feet is examined concerning the available technologies in Egypt. Several factors influencing Egypt's manufacturing capabilities are discussed, including the target number of amputees, amputation levels, design concepts, material selection, and the technology readiness level (TRL) for different manufacturing alternatives. Consequently, a value chain for controlling the industry within Egypt is proposed.

Lower Limb Prosthesis: Material and Design Classification

The appropriate prosthetic foot design is selected based on the amputee's mobility and ability to use the prosthesis, assigned a K-level from K0 to K4 by a physician. K0 represents amputees unable to walk without assistance, while K4 signifies those capable of dynamic activities. For low K-level amputees, the solid-ankle-cushion-heel (SACH) foot—essentially a solid foot-shaped block—is the most suitable. This type offers basic support and mobility through simple hinge designs to simulate ankle joint motion.

Despite its advantages, the SACH foot loses significant energy during the gait cycle, making it unsuitable for higher K-level amputees. This led to the development of the Energy-Storage-and-Return (ESR) foot, which provides better mobility by using elastic materials that store and release energy during the gait cycle.

ESR foot prosthetics often use composites reinforced with carbon or glass fibers, offering superior strength-to-weight ratios and excellent biocompatibility. These composites enhance gait efficiency by storing and releasing energy during walking cycles.

Prosthetic foot design has both traditional and modern approaches. Traditional methods, dating back to the 1980s, classified feet based on the number of axes—single-axis SACH, multi-axis, and dynamic response feet, known collectively as conventional feet (CF). Modern classification divides prosthetics based on the energy timeline into CF, ESR, and bionic feet. Bionic feet, developed by Hansen, are advanced designs capable of adapting to various walking surfaces and mimic natural human foot dynamics.

The following section will discuss the technology readiness level for prosthetic manufacturing concerning Egypt's technological and economic landscape.

Technology Readiness Level for Prosthetic Manufacturing

Technology readiness level (TRL) is a metric for assessing the maturity of a technology, ranging from level 1 (basic principles) to level 9 (practical proof in an operational environment). This article aims to evaluate Egypt's current technologies for localizing lower limb prosthetic manufacturing, focusing on TRL for various prosthetic feet types.

According to previous literature, the four types of feet—conventional, ESR, bionic—have different TRLs. The conventional foot, with a TRL of 7, uses non-advanced technology, making it suitable for low-income countries due to its affordability and ease of maintenance. However, it suits only up to K2 level amputees. ESR feet, although meeting some dynamic needs, are expensive, costing over $5,000 per unit. Bionic feet, costing over $100,000 in Western countries, remain economically unfeasible for low-income countries. Thus, while conventional feet meet cost limitations, they negatively impact QOL and community efficiency, making ESR or higher technology beneficial despite higher costs.

Egypt's import bill for prosthetic feet is mainly due to advanced technology feet, reflecting a growing market in the Middle East for high-end prosthetics. ESR foot manufacturing technologies are promising; except for carbon fiber parts, other technologies are mature in Egypt. The carbon fiber part involves manual processes like fabric cutting, orientation, and resin infusion. Advanced techniques like resin transfer molding (RTM) or pre-impregnated fabric (PREPREG) automation could enhance manufacturing flexibility and quality.

Table 2 Technologies of manufacturing lower limb prosthesis.

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Table 3 Components breakdown of the manufacturing technologies for lower limb prosthesis.

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Methodology for ESR Foot Manufacturing

A modular design approach simplifies P&O part industrialization and defines required TRL levels. Figure 4 illustrates the common size of the selected prosthesis foot. Modular parts like the pyramid metallic adaptor and bolts help in mass production and maintenance. The socket, connecting the pyramid to the amputee's leg, is a non-modular component.

The proposed methodology for localizing prosthetic foot manufacturing in Egypt involves:

• Designing prosthetic foot components as modular parts facilitates mass production, maintenance, and interchangeability. The design is modeled and checked for endurance against expected stresses.

• Selecting manufacturing methods aligned with available TRL and product complexity.

• Testing the ESR foot for performance and durability.

• Developing a value chain based on results and discussion.

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