(J-388) Self-adjustable and Breathable Lower Limb Prosthetic Liner

Prosthetic liners are the intermediary layer between a residual limb and a prosthesis, specifically designed to provide comfort. Traditionally, standard liners made of urethane and silicone result in poor breathability and increased perspiration. Thermal discomfort of these liners may reduce the quality of life for an amputee. Residual limbs change in size over time due to weight changes, swelling, and muscle growth. Consequently, this may lead to a poorly fitting prosthesis, potentially leading to numerous issues.

A woven liner could mitigate these effects, as air could circulate more effectively through the gaps in the weave. Certain weaves may also allow added adjustability for residual limbs while keeping a well-fitted prosthetic. An accommodating weave for this purpose is the Chinese finger traps. 

The Chinese finger trap is a self-tightening mechanism that relies on an interwoven pattern to create tension and increased friction on a digit when pulled. Our team intends to apply this interwoven pattern to improve current prosthetic liners. Such methods have already been employed in the medical field to elevate limbs during surgeries, as shown in Figure 1. 

Using a Chinese trap weave could create a self-tightening fit for amputees while allowing for breathability and heavy loading. We seek to utilize modeling software and 3D printing to develop this prosthetic liner.

We evaluated the methods of production available to us. Our initial research and preliminary sketches led us to conclude that either 3D printing or 3D knitting would be the optimal way to produce the initial prototype. Initially, the prototype was generated in Blender, an open-source 3D computer graphics software. Blender has unique capabilities to manipulate woven patterns onto complex bodies, unique from other modeling software suites.

We also had to choose between using single or double-woven Chinese trap weaves. The double-woven pattern is significantly stronger than the single. Initially, the single weave pattern was utilized for our prototype as it is considerably simpler to craft, particularly when using Blender.

Our initial prototype, shown in Figure 2, aimed to simulate the medical finger trap design. Overall, the methods we used were successful in wrapping a weave into a prosthetic liner shape. The next ideation was an increase in the weave size to improve printing feasibility. After completion, we chose to use the double weave for the next prototype.

Some iterations later, we obtained our current prototype, shown in Figure 3, which has a thicker weave, resulting in greater durability and ease of printing. We also implemented the double-woven pattern, which increases the weight-bearing capacity. The model includes a cap that allows for testing post-production. 

Our progress suggests that we have a realistic approach to improving current liner designs, focusing on comfortability, breathability, and adjustability. Utilizing CAD and other 3D creation suites, along with expert advice, we have successfully developed various prototypes to achieve our goals. Actively, the focus has shifted from virtual development to converting our digital model to a tangible prototype. Moving to a physical prototype has been inhibited by fabrication techniques and limited materials. At present, there are three avenues of manufacturing we are considering. 

The first avenue is to use 3D printers. However, standard printers cannot handle the complexity of our design’s weave pattern nor the shape and scale of the model. We would need to turn to more advanced 3D printing options, which are challenging to access. Standard 3D printing also has limited materials compatible with our design.

3D knitting is the next manufacturing technique implemented. 3D knitting can turn our digital designs into tangible models and also provides the advantage of offering materials, such as various fabrics, that closely mirror those used in existing liners.

The last technique currently being investigated employs production methods developed for creating medical finger traps and wire sheaths. This process incorporates a mechanical system to fabricate double-woven patterns into elongated tube-like forms. We would need to adapt this technique so that the diameter of our liner would increase to align more closely with typical residual limbs. 

These last two manufacturing techniques are under consideration for relevance to our research. Once we obtain a physical prototype, we will be testing the models to see what prototype may work best for this project. Some of the future tests include stress and strain testing, as well as testing the liner with commercially available sockets to see if they are compatible. Our team is optimistic and confident that our efforts will greatly improve the quality of life for amputees and spur meaningful advancements in the prosthetics industry.