Soft Material 3D Printing Toward Patient-Specific Wearable Medical Devices

Additive manufacturing (AM) is gaining widespread adoption in aerospace, automotive and biomedical industries, for example, to develop-patient-specific devices. In AM, material is directly deposited layer by layer until a product is successively built in three-dimensions (3D), also a process that is referred to as 3D printing. This build is automated and based on a computer-aided design (CAD) model, which simplifies iterative design, low-cost customization, and single-step production of complex parts. Freeform Reversible Embedding (FRE) is a novel AM technique that expands the materials for 3D printing to liquids and soft matter that in air deform upon extrusion. This is possible by 3D printing in a sacrificial bath that serves as temporary support and from which the object is removed after curing. However, finding the optimal combination of print parameters, support bath type and concentration among the millions of possibilities is difficult without trials of prints failures. A strategy is needed to align these parameters and to use soft material 3D prints in application. Here, we developed the Expert-guided optimization (EGO) strategy that interfaces the systematicity of a search algorithm with expert intervention to optimize emergent processes with minimal prior data. When applied to 3D printing of a silicone elastomer using the FRE technique, the EGO optimum produced prints with mechanical integrity comparable to cast counterparts. The prints are soft and flexible with low modulus (1.2 ± 0.1 MPa) comparable to human skin, and candidates for wearable devices. Accordingly, patient-specific finger and toe cuffs of different sizes were 3D printed and integrated with optoelectronics to develop a proof-of-concept wearable pulse oximeter. The cuff size affected the device’s signal output and diagnostic performance, showing the importance of customization. The wearable oximeter is promising for continuous monitoring of heart rate and blood oxygen content of patients at risk of peripheral arterial disease and deteriorating health. Finally, we leveraged the FRE technique to create dual silicone prints in a range of materials, shapes, sizes, and ratios and assessed the feasibility of multi-material 3D printing of soft matter. Taken together, this work is a step toward the systematic development of patient-matched, multi-component, medical devices from soft matter.