Researchers from four Italian universities have developed a digital workflow for producing patient-specific upper-limb prosthetic sockets with spatially graded lattice structures.
Combining 3D scanning, finite element analysis, elastic-plastic homogenization and Field-Driven Design, the method adjusts lattice strut diameter according to local mechanical loads. The resulting design had a reported weight of 373 g, 25.4% below the equivalent 500 g bulk model. A full-scale PA12 prototype was subsequently manufactured using Multi Jet Fusion.
Published in Materials & Design, the work brings together the Scuola Superiore Sant’Anna, the University of Trento, the University of Pisa and Sapienza University of Rome. Its central contribution is not a clinically finished prosthesis, but a workflow that connects patient anatomy and simulated stress to a manufacturable graded lattice, followed by CT inspection and mechanical testing.
Moving socket production into a digital workflow
A prosthetic socket forms the connection between an amputee’s residual limb and the rest of the artificial limb. Its inner section contacts the limb and distributes pressure, while the outer shell carries structural loads and accommodates electrodes, batteries, electronics and the wrist attachment.
The digital workflow began with a volunteer recruited through Orthopedic Panini in Milan. Ortenshape and an iPhone 15 Pro Max captured the residual limb, opposite limb and a plaster model.
Scan data then moved through Autodesk Meshmixer, Fusion and nTop. The process digitized geometry development but did not remove physical fitting. Two iterations corrected the liner’s overall alignment, followed by another two to refine its anterior surface.
These four iterations show that human-in-the-loop refinement remained necessary. The final outer socket restored the opposite arm’s approximate proportions and integrated a myoelectric hand system, including a removable combined battery compartment and wrist housing secured by a radial bolted flange.
Turning stress into lattice geometry
Weight reduction came from a single-layer lattice applied to the patient-specific outer shell. Its square-and-diagonal unit cell produced an almost isotropic in-plane response suited to the curved geometry. Rather than modelling every strut, elastic-plastic homogenization represented the lattice as an equivalent continuous material. Ten strut diameters from 0.5 mm to 5 mm were analysed to define stiffness, shear response, Poisson’s ratio and yield behaviour. A 1.5 mm minimum was then imposed to limit local flexibility and sensitivity to manufacturing defects.
Finite element analysis fixed the inner-liner interface and applied a distributed 100 N load at the wrist housing, representing weightlifting with the elbow flexed at 90 degrees.
An initial simulation using uniform lattice properties generated the stress field. MATLAB divided it into 16 intervals, linking each to a material-property set and corresponding strut diameter. High-stress regions received thicker members, while lower-stress areas used thinner ones, with the minimum diameter retained below 25% of maximum stress.
nTop then converted the resulting diameter field into the final graded lattice and blended it with the socket’s solid sections.
Lightweighting changes the structural trade-off
The optimized socket was manufactured on an HP Jet Fusion 4200 using HP 3D High Reusability PA12.
Its modelled weight was 373 g, compared with 434 g for the uniform mean-property lattice model and 500 g for the bulk model. This delivered a 25.4% reduction relative to the bulk version, but increased maximum anterior deflection from 0.7 mm to 1.6 mm and reduced the minimum predicted safety factor from 6.7 to 4.2.
The lowest safety factors occurred where the lattice met solid geometry. CT inspection showed a modal strut diameter of approximately 1.4 mm in the printed socket and 1.5 mm in the CAD model.
The slight shift toward smaller features remained within the uncertainty imposed by the CT system’s 127 μm voxel size, supporting the manufacturability of the graded lattice using MJF.
From functional lattices to stress-driven prosthetics
Recent medical 3D printing research has treated lattice geometry as more than a route to lower weight. UNSW Canberra’s biodegradable PLA and stochastic lattice structures instead of regular repeating patterns in experimental bone scaffolds. Changing the internal orientation affected impact energy absorption, fracture behaviour and fluid permeability, showing how architecture can be adapted to different mechanical and biological requirements.
A similar principle appears in Nimble, a conceptual swimming prosthesis from Essesi Design Studio. Its flexible rubber lattice compresses and stores energy during a kick before rebounding, generating thrust while distributing forces away from the attachment point.
The new socket study takes this approach in a different direction by deriving local strut dimensions from a patient-specific stress field and evaluating the result through CT inspection and full-scale mechanical testing. Its contribution is therefore not the lattice alone, but the connection between anatomical data, calculated loads, manufacturing limits and measured structural performance.
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Feature image shows a finite element model of the prosthetic socket, showing mesh discretization and boundary conditions. Image via Borracci et al.
