Lewis, JenniferBusbee, Travis Alexander2026-07-0720252025-09-032025Busbee, Travis Alexander. 2025. MULTI-MATERIAL 3D PRINTING OF STRETCHABLE ELECTRONICS VIA FILAMENTARY AND DROPLET-BASED DEPOSITION OF VISCOELASTIC INKS. Doctoral Dissertation, Harvard University Graduate School of Arts and Sciences.32240083https://dash.harvard.edu/handle/1/42743999As the boundary between digital and biological systems continues to blur, the seamless integration of electronic devices with living tissue has emerged as a technological imperative. Yet most electronic devices contain materials with elastic moduli exceeding 100 GPa, while biological tissues are inherently soft with moduli ranging from 0.1 to 1000 kPa. This pronounced mechanical mismatch fundamentally impedes electronics-human tissue integration. Current soft electronics fabrication strategies deploy rigid materials that are geometrically patterned to facilitate stretchability, or soft materials that are intrinsically stretchable. Both strategies fail to robustly integrate rigid electronic components within stretchable matrices, as stress concentrations at rigid-soft interfaces inevitably cause delamination and electrical failure under cyclic loading. This challenge is particularly critical given that high performance rigid components lack soft analogues with comparable functionality and cost. My PhD dissertation establishes multi-material 3D printing via filamentary and droplet-based approaches, as transformative manufacturing platforms for robust electromechanical integration of rigid components within soft matrices with programmable mechanics. First, a hybrid direct ink writing (DIW) platform is developed, combining printable thermoplastic polyurethane (TPU) elastomers and conductive silver-TPU inks achieving conductivities up to 3×10⁶ S/m with robotic pick-and-place assembly. This approach enables fabrication of soft electronic devices including wearable strain sensors and microcontroller systems. Systematic characterization reveals that selective TPU reinforcement around rigid components extends their composite electromechanical strain tolerance sevenfold, from 17% to 120%. Building upon these insights, a novel droplet-based viscoelastic ink printing (DVIP) method is introduced, capable of spatially patterning multiple photocurable thiol-ene elastomers, with moduli spanning three orders of magnitude, through raster image processing. Integration of robotic assembly and printable liquid metal inks enables scalable fabrication of personalized stretchable devices with spatially programmable mechanical gradients surrounding embedded components. Devices incorporating zonally graded strain relief demonstrate 100-fold improvement in electrical fatigue life compared to uniform matrices, surviving 5000 strain cycles versus 50. The versatility of DVIP is further demonstrated through multi-layer architectures incorporating printed variable capacitance sensors, vertical interconnects, and selectively encapsulated circuit modules, establishing a scalable pathway for the digital printing of next-generation biointegrated electronics.application/pdfen3D PrintingAdditive ManufacturingDirect ink writingElastomersInkjetStretchable ElectronicsMaterials ScienceMechanical engineeringThesis or Dissertation2026-07-070009-0002-9623-4356