The soft fur of an animal, the pain that protects us from the burn of a hot mug, and the tender touch of a loved one, are sensations we often take for granted. Unfortunately, people with hand prostheses have only the ability to hold and move objects but they cannot “feel” the object. Providing sensation through a prosthetic device is a major unmet need. Current prostheses lack the sensory feedback mechanism to take in data from external environments and convert it into “natural” sensation for the user. The objective of this study is to find a functional solution for people with thumb amputations that restores embodiment of the prosthesis and sensation to the thumb.This thesis proposes a surgical and mechanical solution to transfer skin onto a novel implantable prosthetic thumb. Since current designs of prosthetic fingers do not allow for fixation to the bone and implantation under the skin, the first aim of this study is to design a prosthetic thumb that is implantable, allows for osseointegration with the residual phalanx, and restores grasp motion. To test the surgical solutions, the second aim of this study is to design a rat model that utilizes similar surgical techniques and allows for implantation of a prosthesis.

The UCLA Anatomical Engineering Group has developed an innovative attachment method for prosthetic sockets using an implantable ferromagnetic element and an externally controlled electromagnet to connect the socket to the limb. As part of this project, it was crucial to construct sensorized silicone limb models to effectively compare the new attachment method with conventional ones. These limb models also serve to validate various socket types, such as ischial containment sockets or quadrilateral sockets.

To design the limb models, the team used a 3D scan of an actual patient's limb, provided by the Veterans Affairs (VA) Medical Center, ensuring anatomical accuracy. The bone model within the limb was precisely sized and positioned using X-ray data, which informed the design's structural elements. The limb models were embedded with piezoelectric (PZT) crystals to measure localized tissue deformation through sonomicrometry, a technique that uses acoustic signals to determine distances between crystals.

The construction phase involved 3D printing with advanced materials to create anatomically accurate limb models. The inclusion of pressure and temperature sensors allowed for comprehensive data collection on the limb's response during movement. An important aspect of the design was to account for volume changes, as an amputee’s limb volume can vary throughout the day due to factors such as diet, weather, and comorbidities. Different mold sizes were constructed to test the same limb geometry at different volumes, ensuring the attachment method’s effectiveness under varying conditions.