Presented below is the design and fabrication of prosthetic components consisting of an attachment, tactile sensing, and actuator systems with Fused Filament Fabrication (FFF) technique. The attachment system is a thermoplastic osseointegrated upper limb prosthesis for average adult trans-humeral amputation with mechanical properties greater than upper limb skeletal bone. The prosthetic designed has: a one-step surgical process, large cavities for bone tissue ingrowth, uses a material that has an elastic modulus less than skeletal bone, and can be fabricated on one system.

FFF osseointegration screw is an improvement upon the current two-part osseointegrated prosthetics that are composed of a fixture and abutment. The current prosthetic design requires two invasive surgeries for implantation and are made of titanium, which has an elastic modulus greater than bone. An elastic modulus greater than bone causes stress shielding and overtime can cause loosening of the prosthetic.

The tactile sensor is a thermoplastic piezo-resistive sensor for daily activities for a prosthetic’s feedback system. The tactile sensor is manufactured from a low elastic modulus composite comprising of a compressible thermoplastic elastomer and conductive carbon. Carbon is in graphite form and added in high filler ratios. The printed sensors were compared to sensors that were fabricated in a gravity mold to highlight the difference in FFF sensors to molded sensors. The 3D printed tactile sensor has a thickness and feel similar to human skin, has a simple fabrication technique, can detect forces needed for daily activities, and can be manufactured in to user specific geometries.

Lastly, a biomimicking skeletal muscle actuator for prosthetics was developed. The actuator developed is manufactured with Fuse Filament Fabrication using a shape memory polymer composite that has non-linear contractile and passive forces, contractile forces and strains comparable to mammalian skeletal muscle, reaction time under one second, low operating temperature, and has a low mass, volume, and material costs. The actuator improves upon current prosthetic actuators that provide rigid, linear force with high weight, cost, and noise.

This paper proposes a new socket design to complement Project Fishbone, a design project focused on creating a lightweight transradial prosthetic device. The socket has a simple concept of introducing perforations on the surface of the socket using cost effective, and rapid manufacturing methods such as vacuum thermoforming and drilling. The perforations on the socket allows for greater air ventilation to the prosthetic user's residual skin thus reducing the temperature within the socket. There were nine primary design iterations that were tested: 0.125, 0,187, 0.25-inch-thick designs, and 3/16, 15/64, 17/64-inch perforation sizes, and 12, 18 and 24 count of perforations. Initial test was done using the sockets of different thickness without any perforations to check for uniformity in design and manufacturing method using a regression test. It was found that an increase in thickness directly related to an increase in temperature cooling time. The temperature cooling test was run using a three-factor DOE method and no clear interaction between the factors was observed, thus the Kruskal-Wallis statistical test along with the post hoc Mann-Whitney test to check for significance among the factors as well as significance of groups within the factors. Statistical significance (p<0.05) was found in the socket thickness and size of perforations. Additionally, significance (p<0.02) was found in the 0.125 and 0.187-inch thickness and the 3/16-inch size perforations. Based on the significance between each group, the best combination for increased cooling time reduction was thus found to be with the 0.125-inch thick HDPE sheet and 3/16-inch sized perforation while the number of perforations did not make much difference. These results proved the concept of this new socket design that could be implemented into existing upper limb prosthetic systems.

This paper proposes a new framework design for the lightweight transradial prosthesis. This device was designed to be light-weight, easily manufactured, inexpensive, and to have a high interstitial free space volume for electrical components and customization. Press-fit junctions between fins allow for little or no adhesives, allowing for easily replaceable parts. Designs were constructed out of chipboard and run through an assortment of tests to see if each design iterations met structural design specifications. There were four main design iterations tested: 4, 8, 12 fin designs, and a 4 fin design with additional angled fins for torsional support (4T). Compression, torsion, and 3-point bending tests were all performed on each cylindrical iteration. Basic tensile and material testing was done on chipboard to support results. The force applied to a human arm during a fall is approximately 500 lbf [13]. Compression tests yielded a strength of approximately 300 lbf for the cylindrical designs. ANOVAs and T-tests were performed to find significance in compressive strength between the design iterations with the varied number of fins (p<<0.05). The torsional strength of the human arm, without causing great strain or discomfort has a max value of approximately 15 Nm [14]. This matched the torsional values of the 4T. design [14]. The 4, 8, and 12 designs' torsional strengths were linear with values of approximately 4, 7, and 12 Nm respectively. The 3-point bending test yielded the flexural stress and strain values to find compressive strength in the convex direction as well as the displacement and deformation in each sample. The material chipboard was found to be variable with elastic modulus, Poisson's ratio, and tensile strength. Each experimental procedure was done as a proof of concept for future prosthesis design.

This study regarding a proposed variable stiffness structure will focus on structure geometry as a proof of concept attempt to develop a new design for energy dispersion. The structure was designed such that as a greater force is experienced, more of the structure comes into contact with itself making the structure stiffer, hence the name variable stiffness structure. This variable stiffness will provide softer structure properties under small loads and stiffer properties under larger loads. This allows an impact to be absorbed by the structure under low loads without compromising structure stiffness that provides protection at higher loads. Intended function of this structure is an intermediate layer in protective gear such as helmets for military and athletic applications, athletic padding, or everyday applications such as the soles of shoes or medical crutches. Proof of concept for the variable stiffness structures was successful as validated by the observance of three distinct slopes in the load vs. compression data reflecting the desired three contact regions on four different structures tested. Structures that performed as intended were also more successful at dispersing energy as calculated by the integral of the load vs. compression curves. Observed trends include desirable increased contact spacing and geometry thickness for a 2:1 height to width structure ratio. Since these results are on the limits of the optimization conditions, additional testing will be required to determine true optimal design. Energy dispersion trends would suggest that structure 135 was the most successful structure at dissipating energy. While this structure was successful, (1.42 J of energy dissipated in the variable stiffness region) structure 313 outperformed it by nearly 1 J (2.25 J average). Upon examination of testing footage, structure 313 displayed the unique quality of engaging multiple contact points in each contact region. This suggests that the number of contact points may be the unobserved variable that will further the variable stiffness structure design for improved energy dispersion in future iterations. With further development, the variable stiffness structures could be an influential means of energy dispersion for utilization in a wide variety of applications.