Multi-material compliant mechanisms have shown the potential to be utilized in the upper-limb prosthesis. The mechanisms consist of flexural and rigid parts, where the flexural components can serve as flexible joints between rigid bodies in the device (e.g., finger and finger segments). This configuration is feasible to be fabricated using a type of additive manufacturing called Fused Deposition Modelling (FDM) process, without the need of further assembly and extensive post-processing. Knowledge of the mechanical characteristics of such mechanisms, however, is still limited. Therefore, this study presents the strength and fatigue characteristics of bi-material compliant mechanisms to determine the feasibility of applying the mechanisms in the upper-limb prosthesis for long-term use. The basis of the mechanisms was a configuration of two rigid clamps and a flexible beam that were automatically assembled during manufacturing. Two materials selections (PLA-TPU and Tough PLA-TPU) and three geometries (rectangular, cylindrical, and tapered-shaped interface) were used to create six groups of samples. These groups were subjected to tensile testing and fatigue testing to assess their strength and fatigue behavior. The results of mechanical testing were also verified with the results of finite element simulation. It was found that four groups fulfilled the strength requirement, which were mechanisms in both material configurations with cylindrical and tapered-shaped interface. These groups, however, failed to demonstrate their durability during fatigue testing. Finally, the proposed method of fabrication and mechanical testing as well as the obtained mechanical characteristics of the mechanisms were analyzed to give insights for future development. ... Read more

In the field of prostheses, significant developments have been accomplished so far in low-cost prosthetic limbs using 3D printing technology. However, when it comes to prosthetic hands, 3D printed prosthetic hands are still limited in their grasping ability, such as the adaptability to the shape of an object and a sufficient pinch force level for practical use. The goal of this experimental study is to engineer a bio-inspired surface structure to improve the grip action of prosthetic hands. The low-cost FDM 3D printing technology in combination with the flexible material, Thermoplastic Polyurethane (TPU) 95A, was evaluated for this purpose. 3D printed surface (deformable) patterns were printed on top of a flat, rigid surface. The 3D printed patterns consisted of pillars or lines with varying thickness d, tip thickness D, wavelength λ, and curvatures α that were combined into different patterns. The frictional characteristics of the 3D printed patterns were assessed for nine different test scenarios, i.e. three different loads F_N against three different countersurfaces. Despite the small differences in the static coefficient of friction μ_s of the 3D printed patterns, some consistent trends were found. First, μ_s increases with increasing thickness d. Second, μ_s increases with increasing wavelength λ up to a point in which the decrease of number density of the 3D printed features decreases the overall friction. Third, μ_s increases for pattern curvatures with peaks in the opposite direction, such as wave or circular patterns. Lastly, μ_s decreases under increasing normal load F_N. The surface patterns were tested on the fingertips of a 3D printed prosthetic hand. The fingertips were assessed using the Box and Blocks Test (BBT), in which the pattern with the highest score displayed an ~70% increase in the number of blocks moved, compared to the original rigid fingertip of the 3D printed prosthetic hand in question. Further research and development are essential, especially for the FMD 3D print process of small dimensional printing in combination with flexible materials. Nevertheless, the proposed fingertip pattern demonstrated a first step towards future improvements of the grip action of low-budget 3D printed prosthetic hands using soft fingertip patterns.
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Background: In low- and middle-income countries there is a high demand for prosthetic devices. An automatic system, in which hand prostheses are manufactured with 3D printers can potentially offer a solution for patients having a transradial defect in these areas. As part of such a system, a detailed 3D model of the residual limbs is needed. In order to make the process of creating this 3D model more accessible to low- and middle-income countries, a new silhouette-based 3D reconstruction process is observed which can be implemented in a smartphone application.
Objective:Measure the accuracy of the observed method.
Methods: A database of artificial residual limbs and an experimental algorithm is created. This algorithm consists of two parts. The first part simulates the process of capturing pictures of a residual limb with a smartphone camera. The second part performs an automatic silhouette-based 3D reconstruction.
Results: When the reconstruction method is performed on a known residual limb shape with three silhouette images, the highest measured 3D reconstruction accuracy is 1.12 ± 0.57 mm. When the method is performed on an unknown residual limb shape with three silhouette images, the highest accuracy is 6.48 ± 2.15 mm.
Conclusion:This work presents a technique for reconstructing a residual limb by means of silhouette images. The observed method can be considered as a promising 3D reconstruction approach for prosthetic designing. The method could be improved by having access to a larger database of residual limb shapes and by analysing and finding the optimal input arguments for the optimiser.

Clinical Relevance:The observed method provides a low-cost and accessible approach to model a residual limb for the design of a fitting prosthetic socket that can be manufactured by a 3D printer. ... Read more

An upper limb prosthesis, i.e. a hand prosthesis, is a device to replace the function of an upper limb on upper limb amputees. In developing countries, amputees’ access to the device is scarce to unavailable. In addition to the absence of experts in those areas, currently there are no automatic measurement methods for upper limb amputees available. BME TU Delft Research Group is developing a solution for the issue by using a smartphone and 3D printing technology to provide access for the people in need.
The objective of this thesis is to automatically measure the dimensions from a digital 3D model of an upper limb stump which are required to create an upper limb prosthetic socket. The main method used in this thesis is Statistical Shape Modelling (SSM). We used Singular SSM and Multiple SSM as the approaches in this project. Geodesic distance and Intersection Line are used as measurement methods.
In order to validate the capability of the measurement algorithm to work with real human models, an experiment was conducted to test the precision of the algorithm. Nineteen participants with normal hands were 3D scanned. The manual measurement values were then compared with the values from the 3D scans by using both SSM approaches.
We propose an algorithm for automatic measurements of the human upper limb digital model for prosthetic application. The automatic measurement algorithm proved that we can measure real human upper limb for prosthetic application without human intervention. The Multiple SSM approach showed a sufficient result to be used in prosthetic application for upper limb socket. In the future, the resulting 3D-printed socket can be tested on upper limb amputees.
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As interest in additive manufacturing, or 3D printing, increases, technological improvements are making printing methods quicker and more cost efficient. Inventors and innovators are able to print low-cost and complex geometries rapidly as a result of the manufacturing time being reduced from weeks to hours. With the large amount of polymeric materials available, the design and manufacturing of products are continuously changing as more industries adopt the use of additive manufacturing. One up-and-coming application of additive manufacturing is monolithic compliant joints, which use the elastic deformation of the flexural arms as a mechanism for to complete the desired function. With additive manufacturing becoming more prevalent, it is essential that parts are able to withstand the mechanical and environmental stresses that occur during use. Understanding a material’s response to cyclic loading and unloading is important, as the majority of parts will experience fatigue behavior. Fatigue is a progressive and permanent structural change that could result in a crack or complete rupture, making a part unable to perform its desired task. Since additive manufacturing of compliant joints is a new field, it is critical to understand fatigue behavior in 3D-printed parts so that fatigue behavior can be predicted and prevented. ... Read more

Prosthetic devices remain inaccessible for many amputees in low-income countries. The lack of trained professionals and resources to fit a prosthetic (interface) are principle reasons. The low cost at which additive manufacturing technology (AM) is able to produce a custom made part could change this. As such, the aim of this study was to design an AM transradial interface specifically for low-income countries. It was decided to adopt the WILMER Open Socket design for AM. The interface was not manufactured in its final form. Instead it was decided to print the interface perfectly flat and reassemble it post-manufacturing for increased print reliability and optimal material properties. Flexible yet durable TPU 95A filament was chosen for this purpose. Reassembling the separate pieces occurred with two different locking mechanisms, which were designed specifically for this purpose. These locks were validates using tensile strength tests. The fully assembled interface was tested as well in two different orientations to validate its strength. In contrast to traditional interface fitting, the new design requires merely anthropomorphic measurements, as the actual surface of the residual limb remains mostly uncovered. This study proposes a different approach to AM prosthetic interface design. The fabrication method has been embraced fully, resulting in a comfortable, visually appealing, and durable design for low-income and challenging settings. ... Read more

Access to prosthetics is very limited to many potential
users, while the need is high. There are two main reasons
for this that both are related to the production of prosthetics: the lack of skilled people and high costs. Minimized
assembly production using 3D printing could be a solution: no training is required, assembly takes only a short
amount of time and cheap materials can be used. Besides,
3D printing is a good method for customization. Therefore, this study proposes a 3D-printed finger for a bodypowered hand prosthesis with minimized assembly. The
design approach is the following. First, the human finger
anatomy is studied. Then, a stylized version of the human
finger is made that includes only the functions required for
the prosthesis. Finally, the design principles of the stylized
finger are evaluated and structurized. Based on the design
principles, a finger for a prosthetic hand is designed and
a prototype is developed. The prototype is produced with
an Ultimaker 3 using a rigid and a flexible material in one
print. The evaluation of the prototype shows promising
results. The finger is suitable for a hand prosthesis that
can perform an adaptive power grip and a pinch grip. The
mass of the finger is 17 grams, which makes the finger
comfortable to wear. An actuation force of only 16 N is
required to fully bend the finger. Minimized assembly and
cheap production are achieved: only four assembly steps
are required and the material costs are only 1.68 euros
per finger. In conclusion, the prototype shows a promising
step in the direction of a hand prosthesis that is affordable,
functional, body-powered, and has minimized assembly ... Read more