Fluxible

Wearable electronics are increasingly shifting toward distributed, body-scale sensing surfaces. However, existing approaches struggle to simultaneously achieve mechanical conformability, scalable PCB-compatible manufacturing, and preservation of spatially organized electronic functionality under deformation.

Material-based approaches to flex PCBs, such as using a silicone substrate with liquid metal channels, can be expensive to produce at scale and unsuitable for full-body wearability. Stretch-based deformation also does not handle array-based sensing well. For applications like expandable LED arrays or haptic suits, an auxetic structure can maintain the spatial distribustion of sensors as it expands uniformly.

We propose Fluxible, a methodology for designing auxetic perforation patterns to induce customizable elasticity in a standard PCB manufacturing process. Instead of making the conductive material itself stretchable, we use the rotational movement of auxetic unit cells to induce elasticity in a polyimide flexible PCB produced with standard photolithography. We hypothesize that we can design a perforation pattern for flexibility and design circuits to route around these perforations, allowing the material to stretch and conform to complex dynamic forms while only requiring the traces to deform by local bending.

We perform mesh change analysis in Grasshopper by comparing edge length changes between corresponding mesh vertices on different poses, represented as 3D meshes. The resulting deformation values are mapped onto the body surface to generate a stretch heatmap, which indicates regions that require higher mechanical compliance. This informs our auxetic scaffold parameters and placement within our 2D fabric patterns.

We designed a custom Grasshopper script with independently variable parameters for cell size, strut width, and strut shape. We then produced a series of acrylic swatches to compare how different pattern configurations behaved under manual bending and extension tests. Struts were the hardest to balance: thinner struts allow greater elasticity, but less room to route electric traces.

User interviews noted that this methodology would best benefit applications that involve distributed sensing like a haptic suit with an array of vibration motors, rather than isolated electrical islands like a few medical monitoring sensors across a body. There is no reason to maintain a large area of an auxetic conductive surface if it only serves as a "wire" and not an actual circuit board with components.

As a result, we chose a haptic glove as the application context for our final prototype. We developed a glove fabric pattern, then designed the auxetic scaffold to fit fully within a single panel to reduce interference with seams. Six vibration motors were distributed along the length of the glove to create a spatially addressable haptic array. Designing the circuit within the auxetic scaffold introduced unique routing constraints: the perforated pattern divided the PCB into discrete regions suitable for component placement, connected only by narrow struts.

Fluxible establishes the computational foundations for designing conformable circuit boards, but many steps remain manual. Future work would integrate deformation analysis, auxetic scaffold generation, trace routing, and component placement into a single pipeline capable of producing custom wearable electronics for different bodies and applications.

Our final prototype demonstrates the feasibility of integrating auxetic geometry into standard flex PCB manufacturing. While it is comprised of a single wearable module, it sets the stage for future work to investigate interconnected auxetic circuit patches, automated body-specific layouts, and large-area routing strategies, enabling wearable systems that span much larger portions of the body.