Individual Manufacturing from digital PRocesses : human - orthopaedic device INTerface – IMPRINT

The entire design and manufacturing chain for these interface devices will be studied, modified and optimized to achieve the desired objective: digital design and additive manufacturing of prosthetic sockets.

The research will focus on sensors for acquiring geometry and measuring interface pressures; the development of software dedicated to orthopedic technicians for designing the socket, incorporating the entire traditional customization process; and testing materials and processes that meet mechanical and environmental constraints.

Specific test pieces were developed to evaluate the scanning tools. Software was programmed to geometrically design the transtibial and transfemoral sockets. Connection components with the rest of the prosthesis were designed, mechanically validated by finite element (FE) modeling and then on a test bench.

On the biomechanical modeling side, a transtibial residual limb (RL) FE model was created, its customized geometry based on EOS radiographs, tissue properties extracted from indentation tests, and loading conditions based on motion analysis results. Interface pressure measurement was made possible by integrating strain gage sensors directly into the socket wall.

A dedicated software has been developed that replicates the traditional manufacturing steps. Using a scan and clinical data, it allows orthopedic technicians to design the socket: position of the adjustment areas, definition of volume modifications, alignments, cutting lines, and choice of connection components. At the end of the design process, the manufacturing process is selected; the “3D printing” option is offered, where the design is optimized for manufacturing using this process.

A new printer meets our manufacturing process requirements: it can print a 100% recyclable material, with satisfactory mechanical characteristics for the intended use, and with great freedom to customize parameters.

Initial experiments were carried out on a test bench with a mock limb, then in a walking situation with a subject.

Finite element models of the residual limb, validated for both levels of amputation, will be integrated into the socket design software. The impact of muscle contractions will be studied. Next generation of 3D-printed sockets could use recycled material. Other printing process, quicker, will be explored. Finally, the same process can be replicated on other types of medical device interfaces.

Martinot, P.; Algourdin, P.; Naniche, T.; Rohan, Py.; Bonnet, X.; Pillet, H. Peut-on estimer la géométrie du bassin à partir de marqueurs externes palpés combinée à une déformation d’un modèle générique moyen ? Etude rétrospective sur 58 sujets. Communication orale au congrès national ISPO France. 2022.

Colobert, B.; Carre, V.; Gesbert, J.C.; Trahin, G. Technical assessment of scan solutions. Communication orale au congrès international OT World, Allemagne. 2024.

Matray, M.; Bonnet, X.; Rohan, Py.; Calistri, L.; Pillet, H. Residual limb-socket interface pressure measurement on a roll over simulator using low-cost load cells. Communication orale au congrès international ESB, Ecosse. 2024.

Prostheses and orthoses enable people with physical impairments or functional limitations to live healthy, productive, independent, dignified lives and to participate in education, the labour market and social life. The current design and manufacture of Prosthetic and Orthotic device interfaces is dominated by hand-forming of thermoplastic materials on the plaster obtained via subtraction manufacturing techniques to allow for adaptation of the geometry to every user. This manual and iterative process is necessary to target optimal load transfer and ensure a good socket fit. At the same time, the process is highly dependent on the skill and experience of the prosthetist, as well as patient feedback with no quantitative prediction of fit prior to the manufacture of the socket. The current approach also hinders the automatization of the manufacturing chain and the use of mechanically based model for the optimization of shape and material properties.

Additive Manufacturing processes are now mature enough to be used to create Orthopaedic/medical devices which are functional and in their end-use state. However, challenges remain to integrate it in a fully digitalized procedure that can take into account personalized and user-oriented design. Biomechanical modelling has been identified as a potential tool to assist the prosthetist in their design process, by providing a prediction of fit prior to manufacture. Integrating such modeling in the manufacturing process would therefore be a major innovation. However, model validation is difficult due to the large inter- and intra-individual loading and anatomic variability including accurate description of the material properties, geometrical data, loading characteristics, and boundary and interface interaction conditions.

The IMPRINT project will be a timely contribution to the scientific and technological breakthroughs required for disrupting the Orthotics and Prosthetics market with digital processes and AM. To achieve this ambitious goal, IMPRINT will pursue four research objectives: 1/ Develop and evaluate an efficient modelling-simulation framework combining Gait Analysis, MusculoSKeletal simulations and Finite Element Analysis to investigate stump-socket interaction and quantify the impact of rectifications on biomechanical metrics used as surrogates for the goodness-of-fit of the prosthetic socket 2/ Collect experimental data on the inter- and intra-individual variability including accurate description of the material properties, geometrical data, loading characteristics, and boundary and interface interaction conditions 3/ Perform a mixed experimental-numerical parametric analysis to determine what model input parameters account for variability in the model output (interface pressure) 4/ Develop and integrate a 100% digitalized and waste-free manufacturing of all the orthoses and prostheses manufactured by PROTEOR. This includes all tasks required for an effective implementation of digital manufacturing cycle within 3D printing clusters and the development of a computer framework allowing to assist the prosthetist/orthotist in their design process, by providing a prediction of fit prior to manufacture.

Beyond the very positive ecological impact, this will also have a social and economic impact: improving the comfort and function of the prosthetic limb interface are substantial to improve quality of life of the Orthopaedic device user. This will pave the way for human-centered and flexible Digital Processes to meet the demand for innovative, personalized and optimized products in waste-free processes. From a more general scope, the underlying challenge addressed by the IMPRINT project extends to all the man-machine mechanical interfaces.