Additive manufacturing techniques for smart prosthetic liners

Elastomeric liners are commonly worn between socket and limb by prosthetic wearers. This is due to their superior skin adhesion, load distribution and their ability to form a seal. Laboratory tests suggest that elastomeric liners allow reduced shear stress on the skin and give a higher cushioning effect on bony prominences, since they are soft in compression, and similar to biological tissues [1]. However, they also increase perspiration reducing hygiene and increasing skin irritations. Prosthetic users in general face a myriad of dermatological problems associated with lower limb prosthesis such as ulcers, cysts, and contact dermatitis, which are exacerbated by the closed environment of a fitted socket where perspiration is trapped and bacteria can proliferate [2].

Elastomeric liners are commonly worn between the prosthetic socket and the limb. A number of improvements to the state of the art of liner technology are required to address outstanding problems. A liner that conforms to the residuum more accurately, may improve the skin health at the stump-socket interface. Previous work has shown that for effective thermal management of the socket environment, an active heat removal system is required, yet this is not available. Volume tracking of the stump could be used as a diagnostic tool for looking at the changes that occur across the day for all users, which depend on activity level, position, and the interaction forces of the prosthetic socket with the limb. We believe that it would be advantageous to embed these devices into a smart liner, which could be replaced and repaired more easily than the highly costly and labour-intensive custom-made socket. This paper presents the work to develop these capabilities in soft material technology, with: the development of a printable nanocomposite stretch sensor system; a low-cost digital method for casting bespoke prosthetic liners; a liner with an embedded stretch sensor for growth / volume tracking; a model liner with an embedded active cooling system.