17 Jul 3DMed WP4: Patient-specific 3D printed prosthetic and orthotic devices
The aim of this work package is to enable the production and validation of patient-specific prosthetic and orthotic devices with complex functionality. The current manufacturing of prosthetic and orthotic devices requires extensive specialized manual labour. Moulding of the device is done directly onto the patient, causing discomfort. After production, additional appointments are often required to further optimize the fit of the device, which can complicate or delay patient recovery after injury. In the case of children, their rapid growth may require regular replacement of the device.
Additive manufacturing (AM) is perfectly suited to produce complex patient-specific designs in a wide variety of materials. Additional advantages are high product quality, fast production speed, and minimized specialized manual labour. 3D imaging techniques, combined with 3D modelling software enable the design of patient-specific devices without the need for physical contact. Modelling software can be used to implement specific corrective functionality (orthotics) or substitutional functionality (prosthetics) to the design. In addition, 3D modelling software enables topology optimization. Further possibilities lie in weight reduction, optimisation of local stiffness, rigidity variations via metamaterial or multi-material design.
To validate these advantages, several business cases were selected. One of the cases is a transtibial socket. Transtibial socket is a prosthesis characterised by a (relatively) small contact area with the body but with a complex, substitutional functionality. The Transtibial socket provides an interface between the residual limb (stump) and the prosthesis. It is intended to preserve the appearance of the amputee and transfer loads with minimal relative movement between the stump and the socket.
We have followed several steps to produce a patient-specific transtibial socket. The first step is computed tomography (CT) scanning the residual limb of the patient to create an accurate geometry model of the residual limb and internal bones. Data from this step are converted to a reconstructed computer-aided design (CAD) model using segmentation tools. The next step is to design the socket based on the created CAD model and then all constructed 3D parts, including bone, skin, and designed socket, are imported into a finite element (FE) software. FE modelling aims to analyse the behaviour and functionality of the designed socket under different loading scenarios. The next step is to optimize the design to reduce weight and increase the comfortability of the designed socket through the uniform distribution of stress on the skin.
Currently, we are working on the validation of the results of FE simulations. For this aim, FlexiForce™A201 sensors, which are thin, flexible, and the most accurate and cost-effective commercially available sensors among the other type of FSRs sensors, are used to measure the stress distribution on the skin. After topology optimization and validation, the optimized design, which satisfies all requirements needed to design a transtibial socket, is ready for manufacturing.
Figure 1: The workflow from limb and socket scanning through FE analysis and topology optimization until production and validation of the designed device