Direct-write assembly of three-dimensional polyelectrolyte scaffolds, inorganic hybrids, and photonic crystals

Polyamine-rich complexes are developed for microscale patterning of planar and 3-D structures by direct ink writing. The complexes are formed by mixing poly(allylamine) hydrochloride and poly(acrylic acid) sodium salt in water in a non-stoichiometric ratio. Their phase behavior, rheological properties, and coagulation behavior in alcohol-water reservoirs are characterized. Direct comparisons are made between these complexes, which are based on mixtures of linear polyelectrolytes, to prior observations of complexes composed of linear and highly branched chains. The optimal polyamine-rich ink and reservoir compositions are identified for direct-write assembly of wavy, gradient, and 3-D micro-periodic architectures. The morphology of these coagulated ink filaments is revealed by oxygen plasma etching.; Silica-polymer hybrid structures that mimic natural occurring diatoms are created by combining direct-write assembly of polyamine-rich scaffolds with biomimetic silicification. The influence of ink composition, solution pH, and immersion protocol on the silica content is investigated. The reaction kinetics is studied by measuring the silica content as a function of the silicification time, which suggests that the biomimetic silicification of polyamine-rich scaffolds is a diffusion-limited process. The distribution of silica is found to be uniform throughout within the 3D scaffolds. These silicified hybrid structures exhibit improved thermal and mechanical stability by maintaining their structural integrity even upon complete removal of the polymer phase by heating to 1000°C.; Photonic crystals composed of a germanium hollow-woodpile architecture are created by replicating 3D microperiodic polymer scaffolds assembled by direct ink writing. First, polymer woodpiles with a face-centered tetragonal geometry are fabricated by direct ink writing. Chemical vapor depositions of silica and germanium are then performed under controlled conditions to produce optimal layer structures that maximize the photonic midgap/gap ratio. Next, the oxide and polymeric phases are removed to complete the fabrication of 3D hollow woodpile photonic crystals. The optical properties of the micro-periodic structures are measured after each processing step and correlated with changes in their geometry and composition. Together, the direct writing and replication schemes outlined above may offer a facile route for producing complex 3D structures, which may find potential application in composite, photonic, tissue engineering, and micro-fluidic devices.