Architected cellular ceramics with tailored stiffness via direct foam writing.

Hierarchical cellular structures are ubiquitous in nature because of their low-density, high-specific properties, and multifunctionality. Inspired by these systems, we created lightweight ceramic architectures composed of closed-cell porous struts patterned in the form of hexagonal and triangular honeycombs by direct foam writing. The foam ink contains bubbles stabilized by attractive colloidal particles suspended in an aqueous solution. The printed and sintered ceramic foam honeycombs possess low relative density (∼6%). By tailoring their microstructure and geometry, we created honeycombs with different modes of deformation, exceptional specific stiffness, and stiffness values that span over an order of magnitude. This capability represents an important step toward the scalable fabrication of hierarchical porous materials for applications, including lightweight structures, thermal insulation, tissue scaffolds, catalyst supports, and electrodes.

Microstructure and Elastic Properties of Colloidal Gel Foams.

Colloidal gel foams are composed of a continuous, attractive particle network that surrounds and interconnects dispersed bubbles. Here, we investigate their stability, morphology, and elasticity as a function of foaming intensity, surfactant concentration and hydrophobicity, pH, and colloid volume fraction. Upon optimizing these parameters, highly stable colloidal gel foams are created. Within this stability region, the specific interfacial area between the continuous (colloidal gel) and dispersed (bubble) phase can be varied over 2 orders of magnitude leading to a concomitant increase in storage modulus, which scales nearly linearly with specific interfacial area. Our observations provide design guidelines for attractive-particle stabilized foams that enable the programmable assembly of architected porous materials.

Hierarchically Porous Ceramics via Direct Writing of Binary Colloidal Gel Foams.

Hierarchically porous ceramics with a high specific surface area and interconnected porosity may find potential application as particulate filters, catalyst supports, and battery electrodes. We report the design and programmable assembly of cellular ceramic architectures with controlled pore size, volume, and interconnectivity across multiple length scales via direct foam writing. Specifically, binary colloidal gel foams are created that contain entrained bubbles stabilized by the irreversible adsorption of attractive alumina and carbon (porogen) particles at their air-water interfaces. Composition effects on foam ink rheology and printing behavior are investigated. Sintered ceramic foams exhibited specific permeabilities that increased from 2 × 10-13 to 1 × 10-12 m2 and compressive strengths that decreased from 40 to 1 MPa, respectively, with increasing specific interfacial area. Using direct foam writing, 3D ceramic lattices composed of open-cell foam struts were fabricated with tailored mechanical properties and interconnected porosity across multiple length scales.

Capacitive soft strain sensors via multicore-shell fiber printing.

A new method for fabricating textile integrable capacitive soft strain sensors is reported, based on multicore-shell fiber printing. The fiber sensors consist of four concentric, alternating layers of conductor and dielectric, respectively. These wearable sensors provide accurate and hysteresis-free strain measurements under both static and dynamic conditions.

Embedded 3D printing of strain sensors within highly stretchable elastomers.

A new method, embedded-3D printing (e-3DP), is reported for fabricating strain sensors within highly conformal and extensible elastomeric matrices. e-3DP allows soft sensors to be created in nearly arbitrary planar and 3D motifs in a highly programmable and seamless manner. Several embodiments are demonstrated and sensor performance is characterized.